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Z litijem bogati oksidi prehodnih kovin (LMR-TMO) so skupina katodnih materialov, ki se jih lahko uporablja v litij ionskih akumulatorjih. Zaradi večjega deleža litija in odsotnosti kobalta v strukturi materiala, predstavljajo LMR-TMO cenejšo in bolj zmogljivo alternativo katodnim materialom na trgu. Z magistrskim delom smo želeli uspešno uporabiti sintezni postopek, ki se ga uporablja za pridobivanje NMC katodnih materialov, za sintezo LMR-TMO materiala. Po uspešni sintezi NMC materialov, smo sintezno tehniko uporabili za pridobitev ciljnega materiala. Vzorce smo nato analizirali s pomočjo vrstične elektronske mikroskopije in rentgenske praškovne difrakcije. Sintetizirane materiale smo uporabili kot aktivni material v katodah. Sestavili smo laboratorijske akumulatorje ter jih podvrgli ciklom polnjenja in praznjenja. Z analizami smo ugotovili, da smo uspešno pridobili želene materiale, hkrati pa smo preučili kako se je material odrezal, ko smo ga uporabili v celicah. Lithium rich transition metal oxides (LMR-TMO) are a group of cathode materials, which can be used in Lithium-ion batteries. Higher lithium percentage and the lack of cobalt in the structure of the material, makes LMR-TMO cheaper and more capable alternative for cathode materials in use. In this master’s thesis, we used a modified synthesis method, which is used to attain NMC cathode materials, to produce LMR-TMO materials. After the successful acquisition of NMC dust, we used the method for the synthesis of the desired material. Samples were analysed by scanning electron microscopy and x-ray powder diffraction. Synthesised materials were used as active material in cathodes, put in battery cells, and subjected to charging cycles. By doing before mentioned analyses, we concluded, that we successfully acquired LMR-TMOs and proved they can be used in battery cells.

Uporaba akumulatorjev v zadnjih letih vse bolj narašča. Že dolgo so najboljša izbira za komercialno uporabo Li-ionski akumulatorji, pri katerih se za anodni material še vedno večinoma uporablja grafit, katodni materiali pa so še kar v razvoju. Prvi in komercialno največkrat uporabljen katodni material je LCO (LiCoO2), ki je zaradi visoke cene Co in zmožnosti reverzibilne izmenjave 0.55 mola Li predrag za uporabo v električnih avtomobilih. Kot alternativni katodni material se vse pogosteje omenja LNO (LiNiO2). LNO ima višjo kapaciteto saj lahko reverzibilno izmenja 0.75 mola Li in ima nižjo ceno zaradi večje dostopnosti Ni v primerjavi s Co. Njegova težava je stabilnost pri višjih napetostih. Zato smo v sklopu te magistrske naloge poskušali izboljšati stabilnost LNO katod s tvorbo Al2O3 prevlek s pomočjo sol-gel metode s tremi različnimi prekurzorji: aluminijev sek-butoksid (Al(O-s-But)3), aluminijev izopropoksid Al(O-i-Pr)3 in aluminijev acetat (Al(Ac)2(OH)). Iz dobljenega materiala smo izdelali katode ter z galvanostatskimi meritvami ugotavljali, s katerim prekurzorjem, s kolikšno količino prekurzorja ter s katero temperaturo žganja dosežemo najboljšo stabilnost. Kot najboljši prekurzor se je izkazal Al(Ac)2(OH), in sicer v količini, ki rezultira v 0,25 ut.% Al2O3 glede na LNO, pri temperaturi žganja 400 °C. The use of batteries has been increasing in recent years. For a long time, the best choice for commercial use have been Li-ion batteries, where graphite is still the most used anode material, and cathode materials are still being developed. The first and commercially most successful cathode material is LCO (LiCoO2), which is impractical for use in electric cars due to the high cost of Co and the ability to reversibly exchange only 0.55 mol of Li. As an alternative to LCO cathode material, LNO (LiNiO2) material is presented. LNO has a higher capacity (0.75 mol of Li can be reversibly exchanged) and a lower price due to the greater availability of Ni. Since LNO has a problem with stability at higher voltages, the improvement of the stability of LNO cathodes was the main goal of my master's thesis. We tried to improve the stability by forming Al2O3 coatings using the sol-gel method with the use of three different precursors: aluminium sec-butoxide (Al(O-s-But)3), aluminium isopropoxide (Al(O-i-Pr)3), and aluminium acetate (Al(Ac)2(OH)). We made cathodes from the obtained material and using galvanostatic measurements determined, with which precursor, with what amount of said precursor, and with which calcination temperature the best stability is achieved. Al(Ac)2(OH) in an amount that results in 0.25 wt% of Al2O3 and calcinated at 400 °C showed the best results.

Magnezij organski akumulatorji predstavljajo napredno rešitev nove generacije akumulatorskih sistemov iz okoljsko trajnostnih materialov. Energijska gostota magnezija in organskih spojin ter razlika v njunem redoks potencialu zagotavlja atraktiven galvanski člen z zmožnostjo reverzibilnega delovanja. Težava magnezij organskih akumulatorjev je izkoriščenost kapacitete zaradi številnih kinetičnih ovir. V diplomskem delu smo sistematično preučevali vpliv katode, anode in elektrolita na kinetiko akumulatorja, s pomočjo elektrokemijskih metod. Uporabili smo pulzno metodo, kjer pri določeni stopnji praznjenja uporabimo tokovne pulze različnih velikosti in merimo spremembo napetosti v odvisnosti od časa. Magnesium organic batteries represent an advanced solution for a new generation of battery systems made from environmentally sustainable materials. The energy density of magnesium and organic compounds and the difference in their redox potential provides an attractive galvanic cell with reversible performance. The problem with magnesium-organic batteries is capacity utilisation due to several kinetic barriers. In the thesis, the influence of the cathode, anode, and electrolyte on the kinetics of the battery was systematically studied using electrochemical methods. We used the pulse method, where current pulses of different magnitudes are applied at a given discharge rate and the voltage change is measured as a function of time.

Kovinski litij se že več kot 40 let uporablja kot anoda v litijevih baterijah. Njegova stabilnost v organskih elektrolitih je povezana s spontano tvorbo pasivne površinske plasti, ki učinkovito preprečuje nadaljnjo elektronsko interakcijo z elektrolitom. Po drugi strani ta plast prevaja litijeve ione, zato je splošno znana kot trdna elektrolitska medplast (Solid Electrolyte Interphase, SEI). Podrobna sestava in morfologija spontano nastale SEI sta močno odvisni od uporabljenega elektrolita. Model delovanja SEI predvideva, da je struktura plasti vsaj dvojna. Bližje kovinski anodi nastane tanek (nekaj nm) kompakten sloj SEI, ki je elektronsko neprevoden, omogoča pa prevajanje Li+ ionov. Za tem kompaktnim slojem sledi debelejši (nekaj 100 nm) porozni sloj SEI. V porah tega dela SEI se zadržuje elektrolit, preko katerega poteka transport aktivnih zvrsti do elektrode. Ta model je osnovan na meritvah impedančnih spektrov, ki so bile opravljene v kombinaciji s sistematičnim spreminjanjem parametrov celice, kar je omogočilo bolj natančno razumevanje procesov. Trenutno v raziskovalni skupnosti še ni vzpostavljenega konsenza o prisotnosti in velikosti impedančnega prispevka za reakcijo prenosa naboja, ki poteka na fazni meji med kovinskim litijem in kompaktnim SEI, ter prispevka za desolvatacijo Li+ iona, ki poteka na meji med poroznim in kompaktnim SEI. V sklopu diplomskega dela smo z meritvami impedančne spektroskopije na simetričnih celicah z litij-kovinskimi elektrodami poskušali določiti in razločiti med prispevkom reakcije prenosa naboja in desolvatacije litijevega iona. V ta namen smo litijeve elektrode predhodno pasivirali v različnih mešanicah elektrolitov in topil. Tako pripravljene elektrode smo potem uporabili za sestavljanje simetričnih celic z različnimi koncentracijami soli v elektrolitu. Celicam smo pomerili impedančne spektre pri potencialu odprtega tokokroga. Ti spektri so bili analizirani z namenom določitve sprememb zaradi nižje koncentracije elektrolita pri enaki predhodni sestavi SEI. Sklepali smo, da spreminjanje koncentracije elektrolita znatno spremeni impedančni prispevek desolvatacije, ne pa tudi prispevek redoks reakcije prenosa naboja, saj se ta dogaja na fazni meji, do katere elektrolit nima dostopa. Lithium metal has been used as an anode in lithium batteries for more than 40 years. Its stability in organic electrolytes is linked to the spontaneous formation of a passive surface layer, which effectively prevents further electronic interaction with the electrolyte. On the other hand, this layer conducts lithium ions and is therefore commonly known as the Solid Electrolyte Interphase (SEI). The detailed composition and morphology of the spontaneously formed SEI is strongly dependent on the electrolyte used. The SEI working model assumes that the structure of the layer is at least double. Closer to the metal anode, a thin (few nm) compact SEI layer is formed, which is electron-impermeable but allows the conduction of Li+ ions. This compact layer is followed by a thicker (some 100 nm) porous SEI layer. The pores of this part of the SEI hold the electrolyte through which the active species are transported to the electrode. This model is based on measurements of impedance spectra taken in combination with a systematic variation of the cell parameters, which allowed a more accurate understanding of the processes. Currently, there is no established consensus in the research community on the presence and magnitude of the impedance contribution for the charge transfer reaction, which takes place at the phase boundary between lithium metal and compact SEI, and the contribution for Li+ ion desolvation, which takes place at the boundary between porous and compact SEI. As part of the thesis work, we have attempted to determine and distinguish between the contribution of the charge transfer reaction and the desolvation of the lithium ion by impedance spectroscopy measurements on symmetric cells with lithium-metal electrodes. For this purpose, lithium electrodes were pre-passivated in different mixtures of electrolytes and solvents. The electrodes prepared in this way were then used to assemble symmetric cells with different salt concentrations in the electrolyte. The impedance spectra of the cells were measured at open circuit potential. These spectra were analysed to determine the variation due to a lower electrolyte concentration at the same SEI pre-composition. We hypothesised that changing the electrolyte concentration significantly changes the impedance contribution of desolvation, but not the contribution of the redox charge transfer reaction, since this occurs at the phase boundary to which the electrolyte has no access.

Na-ionski akumulatorji zadnja leta pridobivajo na priljubljenosti zaradi potencialno nizke cene in relativno visoke energijske gostote. Kot anodni material so med najbolj priljubljenimi negrafitizirani ogljiki zaradi učinkovitega shranjevanja Na v strukturi in relativno nizkih stroškov sinteze. Ena izmed ključnih komponent pri shranjevanju natrija v negrafitiziranih ogljikih je elektrolit, katerega vloga je slabo raziskana. V diplomski nalogi smo z elektrokemijskimi analizami preučevali vpliv treh soli (NaPF6, NaFSI, NaTFSI) oziroma petih elektrolitov v organskih karbonatnih topilih na mobilnost Na-ionov in stabilnost akumulatorja z anodnim materialom iz negrafitiziranega ogljika. Za delo smo uporabili tehnike galvanostatske stopenjske titracije (GITT) in galvanostatskega praznjenja in polnjenja. Glede na eksperimentalne rezultate izstopata elektrolita, ki vsebujeta sol NaFSI, saj imata najvišje difuzijske koeficiente v stopnji polnjenja akumulatorja. Elektrokemijska analiza praznjenja in polnjenja je pokazala, da dodatek 0.1 M NaFSI soli v komercialnem 1 M NaPF6 v EC : DMC (1 : 1 vol. %) elektrolitu izkazuje najvišje kapacitete (270 mAh/g) Na-ionskega akumulatorja za izbrani anodni material in relativno stabilno delovanje z nizkimi izgubami kapacitete v opravljenih sedemdesetih ciklih. Na-ion batteries have been gaining in popularity in recent years due to their potentially low cost and relatively high energy density for large-scale applications. Non-graphitized carbons are among the most popular anodes for practical use in Na-ion batteries due to efficient Na storage and relatively low production costs, but the role of electrolytes in determining Na-ion capacity and binding mechanism is poorly studied. In this work, we systematically studied the influence of three sodium salts (NaPF6, NaFSI, NaTFSI) or five electrolytes in organic carbonate solvents EC and DMC on cycling stability and charge transfer kinetics of the non-graphitized carbon anode in Na-ion battery, using galvanostatic intermittent titration technique (GITT) and galvanostatic cycling. Based on the experimental data, the most promising electrolytes for the specific anode material are containing NaFSI salt. This was determined by the fact that these two electrolytes exhibit highest values of diffusion coefficients obtained by the GITT measurements. The addition of 0.1 M NaFSI in commercial 1 M NaPF6 in EC : DMC (1 : 1 vol. %) also exhibits the highest capacity (270 mAh/g) in the electrochemical analysis of galvanostatic cycling in addition to high capacity retention during 70 cycles

Aluminij-organski akumulatorji so zaradi visoke dostopnosti komponent in posledične nizke cene, konkurenčen kandidat na področju elektrokemijskega shranjevanja energije. Aluminij odlikuje tako visoka gravimetrična, kot tudi volumetrična teoretična kapaciteta. Ozko grlo trenutnih aluminijevih akumulatorjev, predstavlja izbira elektrolitov in pozitivnih elektrodnih materialov. Med elektroliti so zaenkrat najboljše elektrokemijsko delovanje izkazale ionske tekočine na osnovi aluminijevega klorida in 1-etil-3-metilimidazolijevega klorida, med pozitivnimi elektrodnimi materiali pa organski materiali. V magistrskem delu smo se lotili študije elektrokemijskega mehanizma Al-fenantrenkinon akumulatorskega sistema. Z ex situ in operando IR-spektroskopskimi meritvami smo potrdili dvoelektronsko redukcijo fenantrenkinona, s pomočjo ex situ XPS, SEM-EDS in MAS NMR meritev, pa dokazali, da pri elektrokemijskem mehanizmu delovanja takšnega akumulatorja, večinsko sodelujejo [AlCl]2+ zvrsti iz elektrolita. Dobro razumevanje delovanja je bistvenega pomena, saj količina klorida v koordinirajočem kationu bistveno vpliva na anodno kapaciteto, število sprejetih elektronov pa na katodno. Due to the high availability of components and the consequent low price, aluminum-organic batteries are a competitive candidate in the field of electrochemical energy storage. Aluminum has both high gravimetric and volumetric theoretical capacity. The bottleneck of current aluminum batteries is the choice of electrolytes and positive electrode materials. Among electrolytes, ionic liquids based on aluminum chloride and 1-ethyl-3-methylimidazolium chloride have so far shown the best electrochemical performance, while organic materials were demonstrated as the best electrode materials. In this master's thesis we studied the electrochemical mechanism of Al-phenanthrenquinone battery system. Two-electron reduction of phenanthrenequinone was confirmed by ex situ and operando IR spectroscopic measurements and ex situ XPS, SEM-EDS and MAS NMR measurements were used to conclude that [AlCl]2+ species from the electrolyte are mostly involved in the electrochemical mechanism of this battery. A good understanding of the operation is essential, as the amount of chloride in the coordinating cation significantly affects the anode capacity and the number of electrons received affects the cathode capacity.

Magnezijevi (Mg) akumulatorji so obetavni nasledniki litijevih (Li) akumulatorjev zaradi izboljšane varnosti, volumetrične kapacitete, cene in večje dostopnosti materiala. Klasični anorganski katodni materiali, kjer se kovinski ioni vgrajujejo v kristalno rešetko, se pri multivalentnih Mg ionih ne obnesejo dobro. Veliko boljša alternativa so organski katodni materiali, ki zaradi svoje odprte in prilagodljive strukture veliko lažje shranjujejo Mg ione. Glavna tema disertacije so poliimidni polimeri kot katodni materiali v Mg akumulatorjih. Na začetku smo se osredotočili na različne sintezne poti in opazovali kakšen vpliv imajo na elektrokemijsko delovanje materiala. Elektrokemijsko delovanje v bolj uveljavljenih in raziskanih Li akumulatorjih nam je služilo kot prvi pokazatelj delovanja polimera. Naslednji korak je bila sinteza novih polimerov in raziskovanje njihovega elektrokemijskega odziva v Li in Mg akumulatorjih. V zadnjem delu dizertacije smo se osredotočili na sam mehanizem elektrokemijske reakcije v Mg akumulatorjih. Delovanje poliimidov v Mg akumulatorjih smo primerjali s kinonskimi materiali in ugotavljali, ali se redoks mehanizem med različnimi skupinami polimerov razlikuje. Mehanizem shranjevanja naboja v poliimidih smo raziskovali s pomočjo in-operando infrardeče spektroskopije, ki smo jo dodatno potrdili še s pomočjo teorije gostotnih funkcionalov (DFT). Zaradi netopnosti poliimidov smo bili znatno omejeni z analiznimi tehnikami. Uporabili smo infrardečo spektroskopijo, jedrsko magnetno resonanco v trdnem, elementno analizo in vrstično elektronsko mikroskopijo. Pri karakterizaciji spojin smo se osredotočili tudi na potencialne nečistoče med polimernimi verigami. Ugotovili smo, da so poliimidi elektrokemijsko aktivni v Mg akumulatorjih, potrdili smo tudi njihov elektrokemijski mehanizem. Zaradi še večje kompleksnosti Mg sistema v primerjavi z Li, njihovega delovanja v vlogi katode nismo mogli temeljito opredeliti. Na celotno delovanje akumulatorja vpliva preveč med seboj tesno prepletenih in soodvisnih dejavnikov, še posebej elektrolit in njegovo občutljivo ravnovesje elektrokemijsko aktivnih kompleksov. Mg batteries are promising post-Li battery technology due to their improved safety, volumetric capacity, price and abundance. It has been shown that traditional inorganic intercalation cathodes are not the best fit for multivalent Mg ions, while organic cathode materials seem as favorable option on account of their flexible, open structure. This thesis is about studying polyimides as cathode materials in Mg batteries. Not much data is published about polyimides as cathodes in Mg system and our goal was to explore their general Mg electrochemistry. Initially we focused on exploring various synthetic conditions and observed how it affected the electrochemical performance in a battery. Electrochemistry in Li system served us as an early indicator how a certain polymer behaves as a cathode. Besides having a better cycling performance in terms of stability, Li-organic system is more understood. The next step was synthesis and battery cycling of some novel polymers, which were not yet published at that point. In the last part of the thesis, our focus was building better understanding of electrochemical mechanism of charge storage in Mg system. We briefly compared polyimide Mg electrochemistry to quinones to see if they share similar mechanism. More detailed study of charge storage mechanism was performed by in-operando infrared spectroscopy, which was supported by density functional theory study. Because of polyimides insolubility, we were notably limited by possible analytical techniques. We used elemental analysis, infrared spectroscopy, solid-state nuclear magnetic resonance and scanning electron microscopy. Some effort was devoted to determination of possible impurities within polymer chains. Polyimides were found to be electrochemically active in Mg system, with confirmed electrochemical mechanism of carbonyl bond reduction. Mg electrochemistry is even more complex than Li and we could not thoroughly estimate role of polyimides as a cathode since there seem to be many factors, that are tightly intertwined and co-dependent, especially electrolyte and its fine balance of electroactive species.

Sodium-ion batteries (SIBs) have been studied as one of the most promising alternatives to lithium-ion batteries (LIBs), due to the abundance of sodium in the earth’s crust and its lower cost. Hard carbons (HC) are non-graphitizable carbons and have proven to be the best anode materials for SIBs in terms of insertion chemistry and specific electrochemical capacity (300 mAh.g-1 and beyond). These carbon materials can be synthesized from very diverse precursors and depending on their synthesis route, their mechanical properties differ inducing different behaviors during the electrode formulation and electrochemical cycling. The impact of the mechanical properties (particularly hardness) of these carbon materials on their electrochemical properties is very poorly reported in the literature. This work developed an indentation in-situ in a scanning electron microscope using a micromanipulator and associated force measurement tips to determine the mechanical properties of carbon anode materials for sodium-ion batteries. The results showed that graphitizable carbons are generally softer than hard carbons. Sucrose-derived HC proved to be harder than hard carbon synthesized from pitch while also showing a better specific capacity than the latter. Upon sodiation (i.e. discharge down to 0 V vs. Na+/ Na), graphitizable carbons showed an increased hardness while the hard carbons showed a reduction in their mechanical property with a decrease of around 33% in their hardness. However, a commercially available HC showed a different result when compared to the lab-synthesized HCs, exhibiting a lower hardness while also having an increasing hardness upon sodiation. These anomalous results are not understood yet but they could be attributed to the unknown synthesis route of the commercial HC. Sodium-ion batteries (SIBs) have been studied as one of the most promising alternatives to lithium-ion batteries (LIBs), due to the abundance of sodium in the earth’s crust and its lower cost. Hard carbons (HC) are non-graphitizable carbons and have proven to be the best anode materials for SIBs in terms of insertion chemistry and specific electrochemical capacity (300 mAh.g-1 and beyond). These carbon materials can be synthesized from very diverse precursors and depending on their synthesis route, their mechanical properties differ inducing different behaviors during the electrode formulation and electrochemical cycling. The impact of the mechanical properties (particularly hardness) of these carbon materials on their electrochemical properties is very poorly reported in the literature. This work developed an indentation in-situ in a scanning electron microscope using a micromanipulator and associated force measurement tips to determine the mechanical properties of carbon anode materials for sodium-ion batteries. The results showed that graphitizable carbons are generally softer than hard carbons. Sucrose-derived HC proved to be harder than hard carbon synthesized from pitch while also showing a better specific capacity than the latter. Upon sodiation (i.e. discharge down to 0 V vs. Na+/ Na), graphitizable carbons showed an increased hardness while the hard carbons showed a reduction in their mechanical property with a decrease of around 33% in their hardness. However, a commercially available HC showed a different result when compared to the lab-synthesized HCs, exhibiting a lower hardness while also having an increasing hardness upon sodiation. These anomalous results are not understood yet but they could be attributed to the unknown synthesis route of the commercial HC.

NMC katodni materiali z visoko vsebnostjo niklja predstavljajo spojine, s katerimi lahko povečamo količine shranjene energije v litij ionskih akumulatorjih. Največji izziv pri takih materialih predstavlja spreminjanje strukture materiala in s tem povezan upad specifične kapacitete med zaporednim polnjenjem in praznjenjem akumulatorjev. S tem magistrskim delom smo želeli prikazati pozitiven vpliv polimernih prevlek na ohranjanje strukture materiala in stabilno delovanje akumulatorjev. Uporabljali smo elektronsko prevoden polimer PEDOT:PSS in ionsko prevoden polimer PAA. Iz rezultatov elektrokemije in vrstične elektronske mikroskopije sklepamo, da je optimalen delež dodanih polimerov 3 ut. %. Ugotovili smo tudi, da s povečanjem ionsko prevodne komponente dosežemo višje začetne kapacitete sistema, kot tudi boljšo stabilnost delovanja akumulatorja. Optimalno razmerje med PEDOT:PSS in PAA smo določili med 25/75 in 15/85. Z termogravimetrično analizo in infrardečo spektroskopijo smo potrdili, da nastale prevleke res vsebujejo oba polimera PEDOT:PSS in PAA v dodanih razmerjih. NMC materials, with high Ni content, represent promising cathode materials for Li-ion batteries which demonstrate higher specific capacities in comparison to traditional cathode materials. The challenge of using such materials is related to the structural changes and the associated specific capacity fading during the electrochemical cycling of batteries. With this master’s thesis, we have shown the positive influence of the polymer coating on the stability of the material structure and the electrochemical performance of such batteries. Two different types of polymers have been used for coatings on the secondary particles of NMC, an electron conductive polymer PEDOT:PSS and an ion conductive polymer PAA. The results of electrochemical cycling and scanning electron microscopy (SEM) show that the optimal percentage of added polymers is 3 wt. %. We show that by increasing the ion-conducting component, we achieve higher initial specific capacities as well as better cycling stability. The determined optional ratio between PEDOT:PSS and PAA are between 25/75 and 15/85. Using thermogravimetric analysis and infrared spectroscopy we confirmed that the synthesized coatings contain both polymers PEDOT:PSS and PAA and coating percentages are equal to percentages of added polymers.

Upad kapacitete zaradi izgube litija v formacijskih ciklih delovanja je ena izmed težav litij ionskih akumulatorjev. Del litija iz katodnega materiala se porabi za pasivacijski sloj, ki se tvori na grafitni anodi. To vpliva na zmanjšanje kapacitete akumulatorja, kar poskušamo nadomestiti s predlitijacijo oziroma dodajanjem litija v celico. V sklopu diplomske naloge smo želeli eksperimentalno preveriti, če lahko z litijem bogata struktura litij manganovega oksifluorida (Li2MnO2F), pridobljenega z mehansko-kemijsko sintezo, v formacijskem ciklu delovanja akumulatorja predlitijira sistem. Za očiten prikaz predlitijacije je bil kot katodni material izbran TiO2, kjer vgradnja litija poteka v drugem potencialnem oknu kot pri spojini Li2MnO2F. Pripravili smo TiO2 elektrode in TiO2 elektrode z dodatkom Li2MnO2F ter jih galvanostatsko ciklali proti kovinskemu litiju oz. proti litiju in grafitu. Ugotovili smo, da se pri galvanostatskih meritvah z grafitno anodo ves litij iz žrtvovalne spojine Li2MnO2F porabi za nastanek pasivacijskega sloja. Zato ne pride do ciklanja katodnega materiala TiO2. To smo preverili tako, da smo h grafitni elektrodi dodali manjši kos kovinskega litija, in celoten sistem primerjali s sistemom, ki se je ciklal proti kovinskemu litiju. Tako smo pokazali, da je v primeru uporabe žrtvovalne spojine Li2MnO2F res zmanjkalo litija. Sklepamo lahko, da Li2MnO2F ne vsebuje dovolj litija za predlitijacijo celice. Z elektronskim vrstičnim mikroskopom (SEM) smo opravili analizo elektrod po končanih elektrokemijskih meritvah in pri tem ugotovili, da med galvanostatskim ciklanjem ni prišlo do degradacije katodnega materiala (Li2MnO2F). Capacity loss, which happens in formation cycles, is one of the problems of Li-ion batteries. A part of the lithium originally stored in the cathode material is used for the passivation layer, that is formed on the graphite anode. The formation of the SEI contributes to lower battery energy density. With the prelithiation or by adding lithium to the cell, capacity loss could be compensated. The aim of this bachelor’s thesis is to investigate whether the lithium rich compound lithium manganese oxyfluoride (Li2MnO2F), which is obtained by mechanochemical synthesis, has the ability to prelithiate the cell in the formation cycle. To clearly show the prelithiation process, TiO2 was selected as a cathode material. Electrodes containing TiO2 and electrodes with TiO2 / Li2MnO2F mixture were prepared and then cycled versus metal lithium, graphite electrode and versus graphite with lithium. It was found that during galvanostatic cycling versus graphite anode all the lithium from the sacrificial compound Li2MnO2F was used for passivation. Because of that, cycling of TiO2, that is part of the cathode material does not continue. This hypothesis was verified by adding a small piece of lithium to the graphite electrode. Results from cycling of the cathode material (Li2MnO2F and TiO2) versus metal lithium and versus graphite were then compared. This way, it was shown that when using the sacrificial compound Li2MnO2F, lithium is used for passivation and afterwards, no lithium is left for cycling. Thus, it can be argued that Li2MnO2F does not contain enough lithium to prelithiate the cell. After cycling, electrodes were analysed with scanning electron microscopy (SEM). It was observed that, while cycling, cathode material (Li2MnO2F) does not degrade.

Li–S akumulatorji v zadnjem času vse bolj pridobivajo na svoji veljavi. Glavni vzrok za vse večji pomen teh sistemov je v njihovi visoki energijski gostoti in specifični kapaciteti. Žveplo je tudi eden izmed elementov, ki so v naravi zelo zastopani. Njegova cena je zato nižja in posledično je privlačen za uporabo v akumulatorjih. Pri klasičnih sistemih z etri se pojavlja več problemov. Med njimi je sigurno največji migracija polisulfidnih zvrsti. Temu pojavu se lahko izognemo z uporabo ultramikroporoznega ogljikovega kompozita z velikostjo por manj kot 0,7 nm. S tem močno omejimo stik med elektrolitom in žveplom, ki predstavlja naš aktivni material znotraj por ultramikroporoznega ogljikovega kompozita. Posledično lahko v tovrstnih sistemih uporabljamo tudi karbonate, ki jih sicer ne bi morali. Z oblikovanjem zaščitnega filma na površini por kompozita v začetnih ciklih delovanja akumulatorja bi se dalo stik še dodatno zmanjšati in s tem preprečiti kontinuirno izgubo žvepla zaradi migracije polisulfidov. Sistem je mogoče optimizirati z uporabo različno debelih nanosov za katodni material, različnih elektrolitov in z uporabo različnih napetostnih oken delovanja akumulatorja. Sklepamo lahko, da je možno z elektrokemijskimi eksperimenti preko uravnavanja teh parametrov oblikovati akumulator, ki nam bo zagotavljal kar se da stabilno in efektivno delovanje preko večjega števila ciklov. Li–S batteries are experiencing a large increase in their research lately. The main reason for this efforts is their high energy density and specific capacity. Sulphur is also very abundant and thus enables a reduced cost for usage in batteries. In Li–S batteries with eter based electrolytes we can easily discover the polysulphide shuttle effect which represents the biggest problem in such systems. It can be smoothly avoided with the use of ultramicroporous carbons with pore size less than 0,7 nm. If we use such composites, we can disable the contact between our electrolyte and active sulphur material within the pores of the carbon composite. This actually means we can also use carbonate based electrolytes which are meant to be useless in combination with bigger pore sizes. With the design of a cathode electrolyte interphase at the surface of the pores, we can further decrease the contact and therefore the loss of active sulphur due to the polysulphide shuttle effect. We can perform the optimization through different parameters. The most common ones are: changing of electrode thickness, use of different electrolytes and use of different voltage cutoffs. We can conclude that through this optimization process we can create a stable and effective battery for longer cycling.

Magistrsko delo proučuje polarizacijo in elektrokemijske procese na magnezijevi anodi v ekvimolarni raztopini magnezijevih soli MgCl2 in Mg(TFSI)2 v tetraetilen glikol dimetil etru (TEGDME) in 1,3-dioksalanu (DOL). Z galvanostatskim jedkanjem in odlaganjem magnezijevih ionov, elektrokemijsko impedančno spektroskopijo (EIS) in galvanostatsko elektrokemijsko impedančno spektroskopijo (GEIS) smo preučili vpliv koncentracije elektrolita in debeline separatorja. Koncentracija Mg2+ ionov v elektrolitu ni imela bistvenega vpliva na prenapetost celice, vendar glede na obliko dinamičnih impedančnih spektrov sklepamo, da so izmerjeni prispevki odvisni od koncentracije magnezijevih zvrsti adsorbiranih na površino elektrode. Pri spreminjanju debeline separatorja nismo opazili bistvenega vpliva na prenapetost celice oziroma na izmerjene impedančne spektre, vendar smo bili pri GEIS meritvah omejeni na višjefrekvenčno območje, izbrani časovni parametri galvanostatskega jedkanja in odlaganja pa so bili prekratki, da bi lahko zaznali razliko med pripravljenimi celicami. EIS meritev je nakazovala na neenakomerno odlaganje magnezija na površino, kar smo s SEM tudi potrdili. Master degree thesis studies polarisation of electrochemical processes on magnesium metal anode in MgCl2, Mg(TFSI)2, 1,3-dioxalane (DOL) and tetraethylen glycol dimethyl ether (TEGMDE) electrolyte solution. Effects of electrolyte concentration and separator thickness were studied using galvanostatic cycling (GCPL), electrochemical impedance spectroscopy (EIS) and galvanostatic electrochemical impedance spectroscopy (GEIS). Despite Mg2+ concentration in electrolyte does not have essential effect on cell overpotential, we concluded, that dynamic impedance measurements are dependent on concentration of magnesium species, adsorbed to electrode surface. In experiments with changing separator thickness we were limited to high frequency GEIS measurements and chosen parameters of galvanostatic cycling were too short to detect difference between prepared cells. GEIS measurements also provided clues to uneven deposition of magnesium ions, which was proved with SEM imaging.

Organske elektrode predstavljajo pomembno smer pri uveljavljanju akumulatorjev nove generacije. Njihove lastnosti, kot so nizka cena, prijaznost okolju, trajnostna vzdržnost, odlična strukturna večnamenskost in fleksibilnost, predstavljajo prednosti, ki jih delajo bolj zaželene in uporabne v primerjavi z ostalimi aktivnimi materiali. Eden takih materialov je tudi poli(hidrokinonil-benzokinonil sulfid)/CNT oz. PHBQS/CNT, ki je tema preučevanja te magistrske naloge. Polimerni nanokompozit PHBQS/CNT je zanimiv organski katodni material predvsem zaradi visoke teoretične kapacitete (382 mAh/g). Sestavljen je iz hidrokinonskih in benzokinonskih enot povezanih preko tioeterskih vezi žvepla. Dodatek ogljikovih nanocevk (CNT) izboljša njegovo električno prevodnost in približa kapaciteto teoretični vrednosti. V raziskavi smo optimizirali potrebno količino dodatka CNT. Prevelika količina namreč zmanjša energijsko gostoto materiala, s premajhnim dodatkom pa ne dobimo želenih lastnosti. Vgradnja CNT v polimerno matriko je potekala v fazi polimerizacije. S solvotermalno in situ polimerizacijsko tehniko smo uspešno sintetizirali sedem polimernih nanokompozitov PHBQS/CNT, pri čemer smo spreminjali količino dodanih CNT (0, 0,5, 0,75, 1, 5, 10 in 15 mas. %). Z elektrokemijsko impedančno spektroskopijo smo izmerili impedance in določili prevodnost vsakega polimernega nanokompozita. Zaznali smo perkolacijsko obnašanje, ki nam je omogočilo določitev koncentracije, pri kateri neprevoden polimerni nanokompozit postane električno prevoden. Kritična koncentracija (prag perkolacije), pri kateri je prišlo do povečanja električne prevodnosti za nekaj redov velikosti, je bila opažena pri dodatku 1 % CNT. To pomeni, da je za tvorbo prevodne mreže znotraj polimerne matrike potrebno dodati vsaj 1 % CNT. Elektrokemijsko učinkovitost nanokompozitov smo preverili pri, pod in nad pragom perkolacije z galvanostatskimi meritvami proti Li polčlenu. Pri vsebnosti 0 % CNT je maksimalna kapaciteta znašala 301 mAh/g. Pri pragu perkolacije je nanokompozit dosegel kapaciteto 320 mAh/g, nad pragom perkolacije (pri dodatku 5 % CNT) pa 342 mAh/g, kar predstavlja 89,5 % teoretične kapacitete polimera PHBQS. Za dobre elektrokemijske lastnosti je posledično potrebno dodati vsaj 1 % ogljikovih nanocevk. Za najbolj optimalne elektrokemijske zmogljivosti pa jih je potrebno dodati še nekaj odstotkov nad pragom perkolacije. Organic electrodes represent an important direction in the implementation of new generation batteries. Their properties – such as low cost, environmental friendliness, sustainability, excellent structural versatility and flexibility – represent advantages that make them more desirable and useful compared to other active materials. An example of such a material is poly(hydroquinonyl-benzoquinonyl sulfide)/CNT or PHBQS/CNT, which is also the topic of the study of this master's thesis. Polymer nanocomposite PHBQS/CNT is an interesting organic cathode material mainly due to its high theoretical capacity (382 mAh/g). It consists of hydroquinone and benzoquinone units which are linked by the thioether bonds. The addition of the carbon nanotubes (CNTs) improves the electrical conductivity of this material and brings its capacity closer to the theoretical value. In the study, we optimized the required amount of the additive. Adding too big amount of the CNTs reduces the material's energy density, whereas insufficient addition does not give us the desired properties. The incorporation of the CNTs into the polymer matrix took place in the polymerization phase. Seven PHBQS/CNT polymer nanocomposites with different amount of added CNTs (0, 0.5, 0.75, 1, 5, 10 and 15 wt%) were successfully synthesized by the solvothermal in situ polymerization technique. We used the electrochemical impedance spectroscopy method for measuring the impedances and determining the conductivity of each polymer nanocomposite. Percolation behaviour was observed, which allowed us to determine the concentration at which a non-conductive polymer nanocomposite becomes electrically conductive. The critical concentration (percolation threshold) at which there was an increase in electrical conductivity by several orders of magnitude was observed at 1% addition of CNTs. This means that at least 1% of CNTs must be added to form a conductive network within the polymer matrix. The electrochemical performance of nanocomposites was analysed at, below and above the percolation threshold by galvanostatic measurements versus Li half-cell. At 0% of CNTs content, the maximum capacity was 301 mAh/g. At the percolation threshold, the nanocomposite reached the maximum capacity of 320 mAh/g, whereas above the percolation threshold (at 5% CNTs content) the maximum capacity was 342 mAh/g, which represents 89,5% of the theoretical capacity of the PHBQS polymer. As a result, at least 1% of the carbon nanotubes needs to be added for good electrochemical properties. For the most optimal electrochemical performance, it is necessary to add them a few percent above the percolation threshold.

Potreba po pridobivanju električne energije izobnovljivih virov energije, kot sta sonce, veter in plimovanje, postaja čedalje pomembnejše. Pridobivanje energije iz obnovljivih virov energije ni konstantno, za shranjevanje električne energije so potrebni stacionarni akumulatorji, za katere so se Na-ionski akumulatorji izkazali kot dobra alternativa Li-ionskim akumulatorjem. Natrija je v zemeljski skorji veliko, kar pomeni nižjo ceno in trajnostno proizvodnjo te zvrsti akumulatorjev. S prenosom znanja o Li-ionskih akumulatorjih je bilo doseženega precej uspeha pri razvijanju katodnega materiala. Za anodni material se v Na-ionskih akumulatorjih ne more uporabljati čisti grafit, ki je standardni material za Li-ionske akumulatorje. V magistrski nalogi sem sintetizirala trdi ogljik iz kavnih usedlin in ga testirala z namenom ugotovitve ustreznosti pri uporabi v Na-ionskih akumulatorjih. Trdi ogljik sem sintetizirala pri različnih temperaturah (900°C, 1200°C, 1400°C in 1600°C). Pridobljeni material sem analizirala z XRD, Raman in SEM. Z analizo sem podala povezavo med temperaturo karbonizacije in strukturo materiala. S pridobljenim materialom sem sestavila testne laboratorijske celice za elektrokemijske meritve. Analiza je potekala po vnaprej določenem programu polnjenja in praznjenja, s katerim sem določila karakteristike shranjevanja natrija v sintetiziranih vzorcih. Glede na analizo strukture materiala in elektrokemijske teste sem ugotovila, da ima trdi ogljik sintetiziran iz kavnih usedlin potencial za uporabo kot anodni material v Na-ionskih akumulatorjih. Struktura materiala sintetiziranega pri 1200°C ima na podlagi analize in elektrokemijskih testov, med testiranimi materiali najboljše lastnosti. There is a greater need for the production of electric energy from renewable energy sources like sun, tide and wind every day. Energy from renewable energy sources is produced intermittently and therefore requires a suitable energy storage system to store it. So far, Na-ion batteries have shown potential to be used in stationary energy storage systems instead of Li-ion batteries. Due to the high content of sodium in Earth's crust Na-ion batteries have the potential for low production cost and continuous manufacturing. Transferring the knowledge gained with Li-ion batteries has lead to the development of good cathode materials. Graphite in commercial Li-ion batteries can not be used in Na-ion and this leads to the search of anode material. In this thesis hard carbon was synthesized from spent coffee grounds and was tested to determine the possibility to be used as anode material in Na-ion batteries. Hard carbon was synthesized at different temperatures (900°C, 1200°C, 1400°C and 1600°C). Material was analyzed with XRD, Raman and SEM to show the connection between the temperature of carbonization and the structure of the material. With obtained material testing half cells were assembled for electro-chemical testing, where the cells were charged and discharged repeatedly to determine the behaviour of synthesized material during cycling. Based on structure analysis and electro-chemical test results it was conducted that hard carbon synthetized from spent coffee grounds has the potential for usage in Na-ion batteries. Based on the results, material synthetized at 1200°C shows the best properties.

Zaradi visoke energijske gostote, varnosti in nizkih stroškov glede na ostale akumulatorske sisteme, je sekundarni magnezijev akumulator zanimiv kandidat za prihodnje generacije hranilnikov električne energije. Glavna izziva, pred katerimi je postavljen razvoj magnezijevega akumulatorja, sta razvoj ustreznih elektrolitov in katodnega kompozita, ki bi omogočili čim večjo učinkovitost delovanja magnezij žveplovega akumulatorja. V diplomskem delu sem preučeval vpliv borovega nitrida (BN), ki smo ga dodali v žveplovo elektrodo na izboljšanje delovanja magnezijevega akumulatorja. Preizkušen je vpliv dodatka BN v kompozitno žveplovo katodo z namenom ugotoviti ali dodatek lahko vpliva na stabilnost delovanja. Rezultati meritev kažejo, da dodatek BN v žveplovo kompozitno elektrodo deloma izboljša specifično praznilno kapaciteto in stabilnost delovanja Mg-S akumulatorja in izboljša reverzibilnost delovanja žveplove elektrode ter zmanjša prenapetost. Due to its high energy density, safety and low cost compared to other battery systems, the secondary magnesium battery is an interesting candidate for future generations of electricity storage devices. The main challenges facing the development of the magnesium accumulator are the development of suitable electrolytes and cathode composite, which would enable the highest possible efficiency of the operation of magnesium in the sulfur accumulator. In my diploma thesis I studied the effect of boron nitride (BN), which was added to the sulfur electrode on the improvement of magnesium battery performance. The effect of BN additive on the composite sulfur cathode was tested to determine if the additive could affect the stability of operation. The measurement results show that the addition of BN to the sulfur composite electrode partially improves the specific discharge capacity and stability of the Mg-S battery operation and improves the reversibility of the sulfur electrode operation and reduces overvoltage.

Kovinski litij je idealni material za anodo v akumulatorjih, saj ima najnižji elektrokemijski potencial in najvišjo teoretsko dosegljivo kapaciteto. Visoka reaktivnost kovinskega litija in dendritska rast med procesom polnjenja sta v preteklosti omejevala njegovo uporabo. Z ustrezno zaščito kovinskega litija bi lahko premostili omenjeni težavi in utrli pot komercialni rabi litij-kovinskih akumulatorjev. Eden izmed obetavnih zaščitnih materialov je celulozni kompozit, ki je sestavljen iz modificirane nano-fibrilirane celuloze in litijevega nitrata, ki zapolni praznine med celuloznimi vlakni. Z uporabo elektrokemijske impedančne spektroskopije smo določili, da mehanizem prenosa litijevih ionov preko kompozitne plasti poteka v skladu s principom elektrolita topilo v soli. Kot ustrezno topilo smo identificirali tetraetilen glikol dimetil eter (TEGDME), katerega masa je morala biti manjša od mase litijevega nitrata v celuloznem kompozitu. Metallic lithium is an ideal anode material for secondary batteries because it has the lowest electrochemical potential and the highest theoretical specific capacity. The high reactivity of metallic lithium and the formation of dendrites on repeated charging have so far prevented its use. With suitable protection it has the potential to become commercially viable in many different areas. A promising protective material is a cellulose-based composite material consisting of modified nanofibrillated cellulose and lithium nitrate that fills pores created by cellulose fibers. Using electrochemical impedance spectroscopy, we have found that lithium ion migration through the composite protective layer of cellulose follows the concept of solvent-in-salt electrolyte. We identified tetraethylene glycol dimethyl ether (TEGDME) as a suitable solvent. To show conductive properties, the mass of lithium nitrate in the cellulose protective layer had to be higher than the mass of TEGDME.

Uporaba akumulatorjev v zadnjih letih vse bolj narašča. Uporabljajo se v avtomobilski in računalniški industriji, prisotni so v večini vsakdanjih elektronskih naprav, pomembno vlogo pa imajo tudi pri shranjevanju energije, pridobljene z naravnimi energijskimi viri. Zaradi vedno večje porabe je vedno večja tudi potreba po njihovem razvoju. Zato raziskovalci iščejo nove materiale za elektrode in elektrolite, s katerimi bi presegli zmožnosti Li-ionskih akumulatorjev. Kot dobra alternativa se kažejo magnezijevi akumulatorji, katerih razvoj je sicer še precej na začetku. Eden glavnih problemov magnezijevih akumulatorjev je odtapljanje in nalaganje magnezija, saj se pri tem izgublja precejšnja količina magnezija, zaradi česar proces ni popolnoma reverzibilen. Na reverzibilnost procesa lahko pomembno vplivajo elektroliti, zato se v svoji diplomski nalogi posvečam možnim izboljšanjem določenih obstoječih elektrolitov z dodajanjem različnih dodatkov. Trem elektrolitom, APC v THF, Mg(B(hfpi)4)2 v DME in Mg(TFSI)2-2MgCl2 v DME, smo dodajali MgBr2, Bu2Mg in I2 ter s kronopotenciometričnimi meritvami ugotavljali, kako ti dodatki vplivajo na učinkovitost in prenapetost elektrokemijskih celic z magnezijevo anodo. Ugotovili smo, da različni dodatki na elektrolite različno vplivajo, saj določeni dodatki precej izboljšajo reverzibilnost odtapljanja in nagalanja magnezija ter zmanjšajo prenapetost, medtem ko drugi, zaradi reakcij z anodo ali samim elektrolitom, povzročijo ravno nasprotne rezultate. The use of batteries has increased in recent years. They are being used in the automotive and computer industry, they are present in most of portable electronic devices and also play an important role in storing energy obtained from renewable energy sources. Due to the increasing consumption, there is also a growing demand for their development. Researchers are looking for new active materials and electrolytes to exceed the capabilities of Li-ion batteries. Magnesium batteries are proving to be good alternative, but their development is still at its infancy stage. One of the main problem of magnesium batteries is deposition and stripping of magnesium, as a considerable amount of magnesium is lost, which makes the process not completely reversible. The reversibility process can be affected partially by electrolytes. For that reason, in this thesis, I focus on the possible improvements of selected electrolytes by adding various additives. MgBr2, Bu2Mg and I2 were added to three electrolytes APC in THF, Mg(B(hfpi)4)2 in DME and Mg(TFSI)2-2MgCl2 in DME, and galvanostatic measurements were used to determine how these additives affect coulombic efficiency and overpotential of electrochemical cells with magnesium anode. We found that different additives have different effects on electrolytes, as certain additives significantly improve the reversibility of magnesium stripping and deposition and decrease overpotential, while others, due to reactions with the anode or the electrolyte itself, cause the exact opposite.

Litij žveplovi akumulatorji so eden najobetavnejših kandidatov za prevzem primata litij ionskim akumulatorjem na področju shranjevanja energije,saj jih odlikujejo številne zaželene lastnosti, kot so nizka cela aktivnih materialovin majhen vpliv na okolje. Poleg tega je njihova teoretična gostota energije veliko višja od komercialnih litij ionskih akumulatorjev, ki temeljijo na interkalacijskih materialih. Kljub tem prednostim množično uporabo Li-S akumulatorjev ovirajo številni izzivi, povezanis hitro izgubo kapacitete večinoma zaradi izgube aktivnega materiala in elektrokemijsko nestabilnega pasivnega sloja med kovinski litijem in različnimi vrstami elektrolitov. Celuloza je najbolj razširjen polimer na Zemlji in zaradi svojih dobrih mehanskih lastnosti, enostavne modifikacije ter biorazgradljivosti primeren kandidat za naslovitev problemov Li-S akumulatorjev, če se uporabi kot separacijski sloj med žveplovo katodo in anodo iz kovinskega litija. Primarna vloga separatorja v akumulatorskih celicah je preprečitev kontakta med anodo in katodo, s primerno modifikacijo in izdelavo pa je z njim mogoče vplivati tudi na procese v akumulatorski celici. Primerne lastnosti celuloze in zmožnost njenega vpliva na procese v akumulatorski celici so bile glavne smernice te doktorske disertacije. V našem delu smo najprej iz nanofibrilirane celuloze (NFC) izdelali samostoječe NFC-separatorje in dokazali, da se izboljša delovanje Li-S akumulatorjev v primerjavi s komercialnimi separatorji. Z uporabo XPS-spektroskopije in SEM-FIB-mikroskopije smo pokazali, da NFC-separator še posebno dobro vpliva na kovinsko litijevo elektrodo. Za naslovitev problema difuzije in migracije topnih polisulfidnih zvrsti iz žveplaste katode smo sintetizirali dva različna celulozna materiala: fluoro NFC in s polianilinom oplaščeno NFC ter jih implementirali v Li-S akumulator. Oba materiala sta imela pozitiven učinek na migracijo topnih polisulfidnih zvrsti po Li-S akumulatorski celici, nista pa v celoti odpravila problema hitre izgube kapacitete Li-S akumulatorjev. Pozitivni vpliv NFC materialov na kovinsko litijevo elektrodo smo z izdelavo zaščitnih preverili slojev direktno na litijevi površini z uporabo trimetilsilil celuloze. Rezultati analiz so pokazali, da tanek zaščitni sloj na osnovi NFC uspešno zavre dendritsko rast litija, prepreči korozivne reakcije med kovinskim litijem in elektrolitom tertako stabilizira kovinsko litijevo elektrodo. Lithium sulphur batteries are one of the most promising candidates to take primacy of the lithium-ion batteries in the field of energy storage due to their desirable features, such as competitive cost of production and low environmental impact. In addition, their exceptional theoretical energy density is much higher than commercial Li-ion batteries based on intercalation materials. Despite of these advantages, the mass commercialization of Li-S batteries is still hampered by the many challenges associated with rapid loss of capacity, mainly due to the loss of active material and the electrochemically unstable passive layer between lithium metal and various types of electrolytes. Cellulose is the most abonded polymer material on the Earth and, due to its good mechanical properties, easy modification and biodegradability, is a suitable candidate for addressing Li-S battery problems and it can be used as separation layer between sulphur cathode and lithium metal anode. The primary role of the separator in the battery cell is to prevent contact between the anode and the cathode, with appropriate modification and fabrication it can also affect the processes in the battery cell. Appropriate cellulose properties and the ability to influence processes through separator has been the main focus of this doctoral dissertation. In presented work, we first constructed self-standing separator membranes from nano-fibrillated cellulose (NFC) and proved that they improve the performance of Li-S batteries compared to commercial separator membranes. Using XPS spectroscopy and FIB-SEM microscopy, we showed that the separator membranes from NFC has, in particular, good effect on the lithium metal electrode. To address the problem associated to the diffusion and migration of soluble polysulphides species from the sulphur cathode, two different NFC materials were synthesized: fluoro NFC and polyaniline coated NFC, and implemented in a Li-S battery. Both materials had a positive effect on the migration of soluble polysulphides species across the Li-S battery cell, but did not completely solved the problem of rapid capacity loss of Li-S batteries. Positive effect of NFC materials on the metal lithium electrode was verified with implementation of protective layers based on cellulose directly on the lithium metal surface using trimethylsilyl cellulose. The results of the analyses showed that a thin NFC based protective layer successfully inhibits dendritic growth of lithium, preventing corrosive reaction between the lithium metal and the electrolyte, thus stabilizing the lithium metal electrode.

V diplomski nalogi je predstavljen dizajn ekonomičnega eksperimentalnega sistema s katerim bi lahko enostavno merili hitrost regresije različnih goriv. Na teoretičnem modelu je demonstrirana uporaba matematičnega algoritma na katerem sloni merilna metoda. This thesis presents an economical experimental setup design which could be used to effectively measure regression rates of various fuels. The mathematical algorithm used to calculate regression is demonstrated on a theoretical model

Za uspešno komercializacijo magnezijevega akumulatorja je potrebno razviti ustrezne anodne in katodne materiale ter elektrolite, ki so kompatibilni z kovinskim magnezijem in z uporabljenim katodnim materialom. Pri uporabi magnezijeve folije za anodo se srečujemo z relativno visoko upornostjo, ki je posledica pasivacije površine magnezija in relativno majhne specifične površine za elektrokemijske reakcije. V tem delu smo pripravili aktiven in fin magnezijev prah s postopkom mehanskega mletja, ki bi lahko bil zanimiv tudi za industrijsko proizvodnjo. Magnezijeve delce smo mleli skupaj z dodatkom organskih topil in magnezijevih soli. Uspešnost zmanjšanja delcev in stopnjo kontaminacije prahu smo preverjali z vrstično elektronsko mikroskopijo in emisijsko disperzijsko spektroskopijo. Elektrokemijsko aktivnost prahu smo določevali z galvanostatskimi meritvami v 0,4 M raztopini Mg(TFSI)2:MgCl2 v 1-metoksi-2-(2-metoksietoksi)etanu (DIG) in kasneje v 0,8 M raztopini Mg(TFSI)2-2MgCl2 v 1,2-dimetoksi etanu (DME). Rezultati so pokazali, da je najprimernejše topilo za mletje magnezija tetrahidrofuran (THF). Z dodatkom reduktivnih specij smo zmanjšali organsko kontaminacijo prahu. Tako dobljen prah smo nadalje uporabili za izdelavo kompozitnih elektrod iz magnezijevega prahu, saj in veziva. Te elektrode so izkazale nižjo upornost, kot magnezijeva folija. Pri elektrodah smo najprej preverili učinkovitost odtapljanja in nalaganja magnezija v anodah iz različnih pripravljenih prahov. Preverjali smo tudi njihovo elektrokemijsko stabilnost pri spreminjanju deleža veziva in saj. Najbolj stabilno delovanje kažejo elektrode, ki imajo sestavo kompozita iz Mg prahu, ki je bil mlet v THF, saj in veziva v razmerju 88:10:2. Različne prahove in kompozitne anode smo na koncu testirali še v laboratorijskih akumulatorjih, kjer smo uporabili magnezij kot anodo in redoks aktivni organski material kot katodo. Rezultati so pokazali, da bolj stabilno delovanje dosežemo z večjimi delci Mg prahu, ki imajo manjšo aktivno površino. Successful commercialization of a magnesium battery requires the development of suitable anode and cathode materials and electrolytes that are compatible with metal magnesium and with used cathode material. When using magnesium foil as an anode, we encounter a relatively high resistance resulting from the magnesium surface passivation and the relatively small specific surface area for electrochemical reactions. In this thesis, we have prepared an active magnesium powder using a mechanical milling process, which may also be of interest to industrial production. The magnesium particles were milled together with the addition of organic solvents and magnesium salts. The particle size reduction and the degree of contamination of magnesium were examined by scanning electron microscopy and emission dispersion spectroscopy. Electrochemical activity of magnesium powder was determined by galvanostatic measurements in 0.4 M solution of Mg(TFSI)2: MgCl2 in 1-methoxy-2-(2-methoxy ethoxy)ethane (DIG) and later in 0.8 M solution of Mg(TFSI)2 -2MgCl2 in 1,2-dimethoxyethane (DME). The results show that the most suitable milling solvent for magnesium is tetrahydrofuran (THF). With the addition of reductive spices, we can reduce contamination of milled powder with organic side products. Thus obtained powder was further used for preparation of composite electrodes of magnesium powder with addition of carbon black and binder. First, we checked the efficiency of stripping and deposition magnesium on composite anodes, which we prepared from different powders. These electrodes exhibited lower resistivity than magnesium foil. We also checked their electrochemical stability whit a changing amount of binder and carbon black. The best performing electrode composite had a composition of 88: 10: 2 between Mg powder, carbon black and binder. Different powders and composite anodes were eventually tested in laboratory batteries, where magnesium was used as the anode and redox-active organic material as the cathode. The results showed that more stable performance is achieved with larger magnesium particles because they are having a smaller active surface.

Diplomsko delo obravnava mehansko in keramično sintezo spojine A2MnO2F s strukturo ploskovno centrirane kocke (fcc). Pri tem A označuje Na ali Li. Sintezo smo izvajali z uporabo različnih reaktantov in jo optimizirali s procesom spreminjanja dveh parametrov: temperature in časa. Poleg sinteze smo izvedli tudi karakterizacijo sintetiziranega materiala. Karakterizacijo smo izvedli z uporabo različnih analiznih metod kot so: rentgenska praškovna difrakcija (XRD), vrstična elektronska mikroskopija z energijsko disperzijsko spektroskopijo (SEM/EDX), nuklearna magnetna resonanca (NMR), transmisijska elektronska mikroskopija (TEM) in Induktivno sklopljena plazma z masnim spektrometrom (ICP-MS).V sklopu karakterizacije smo z uporabo swagelock tipa celic preverili tudi elektrokemijsko obnašanje materiala. Rezultati so pokazali, da temperatura in čas vplivata na potek reakcije. Z višjo temperaturo in časom je reakcija bolj zaključena. Na uspešnost sinteze želenega produkta vplivajo tudi reaktanti in način sinteze. V primeru uporabe natrija, pri obeh načinih sinteze želenega produkta nismo uspeli sintetizirati, medtem ko smo v primeru litija z mehansko sintezo dobili željen produkt. Present thesis explores the mechanical and ceramic synthesis of A2MnO2F compounds with face cubic centered (fcc) structure. In which A stands for Na and Li. The synthesis was performed using different reactants and optimized by the process of changing two parameters: temperature and time. In addition to the synthesis, the characterization of the synthesized material was carried out. Characterization was carried out using various analytical methods such as: X-ray diffraction (XRD), Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX), Nuclear magnetic resonance (NMR), Transmission electron microscopy (TEM) and Inductively coupled plasma with mass spectrometry (ICP-MS). As part of the characterization, the electrochemical behavior of the material was also tested using swagelock cells. The results show that temperature and time influence the course of the reaction. With higher temperature and longer time, the reaction is more complete. Success of the synthesis, to get the desired product is also influenced by reactants and the synthesis method. In the case of sodium, in both methods of synthesis we were not able to synthesize the product, while in the case of lithium, the desired product was obtained by mechanical synthesis.

Magnezijevi akumulatorji naj bi bili tisti, ki bodo v prihodnosti predstavljali enega izmed načinov shranjevanja energije. Z uporabo magnezija v akumulatorskih aplikacijah lahko namreč dosežemo višje kapacitete pri manjši masi in precej nižji ceni v primerjavi z Li-ionsko grafitno anodo. So pa ti akumulatorji v zgodnji fazi razvoja. Ena od glavnih komponent, ki je precej nerazvita, so elektroliti. Od njih je namreč močno odvisno delovanje akumulatorja. Z dodatkom različnih soli se njihove lastnosti spremenijo. V diplomskem delu smo v eksperimentalnem delu preverili vpliv različnih anionov na delovanje akumulatorjev. Za osnovne magnezijeve elektrolite, ki smo jim nato dodajali različne litijeve soli, smo vzeli do zdaj že uveljavljen APC in pa dva nova nekorozivna elektrolita Mg(TFSI)2 in Mg(B(hfip)4)2. Delovanje akumulatorjev smo ocenjevali preko reverzibilnega odlaganja Mg na delovno elektrodo. Pripravljene elektrolite smo ocenjevali glede na coulombsko učinkovitost odlaganja in prenapetost pri odlaganju. Magnesium batteries are often seen as the future of energy storage. The use of magnesium metal anode inside a battery cell allows greater capacity at lesser mass and lower price when compared to Li-ion graphite anode. However, these batteries are in the early stages of development. One of the main components, that is currently underdeveloped, are electrolytes, as the performance and even research testing of batteries and potential battery materials depends on them. With the addition of different salts, their properties change. In the experimental part of diploma, we tested the influence of different anions on the performance of batteries. The basic magnesium electrolytes, to which different lithium salts were added, were previously established APC and two new non-corrosive electrolytes Mg(TFSI)2 and Mg(B(hfip)4)2. The performance of batteries was evaluated by reversible Mg deposition on the working electrode. The prepared electrolytes were evaluated for Coulombic efficiency and deposition overvoltage during Mg deposition process.

Magnezij-žveplovi akumulatorji predstavljajo novo tehnologijo shranjevanja energije. Pri tem akumulatorskem sistemu se trenutno soočamo s številnimi izzivi, tako na katodni (redoks prenos naboj preko polisulfidov, samopraznjenje akumulatorja, …) in anodni (tvorba ionsko neprevodnega filma) strani celice. V eksperimentalnem delu diplomske naloge smo preverili vpliv različnih dodatkov v magnezijevo anodo na delovanje celice s katodo iz ogljik-žveplovega kompozita in elektrolitom na osnovi etra. Rezultati so pokazali, da dodatek soli MgBr2 in MgCl2 izboljša delovanje sistema v začetnih ciklih. V drugem delu testiranj smo preizkusili tudi, kako učinkuje povečanje koncentracije elektrolita v sistemu. Ugotovili smo, da se s povečanjem koncentracije močno izboljša stabilnost kapacitete, obenem pa koncentracija elektrolita vpliva tudi na obliko krivulje praznjenja in redoks prenosa naboja preko polisulfidov. Preverili pa smo tudi kako na delovanje akumulatorja vpliva koncentracija žvepla v ogljik-žveplo kompozitu. Iz testiranj je razvidno, da povečanje koncentracije žvepla močno zniža tako začetne kot tudi končne kapacitete sistema. Magnesium-sulfur batteries present a new developing technology of energy storage. While working with Mg-S cells we are faced with many challenges at the anode (passive film formation) and cathode (polysulfide shuttle effect, self-discharge) side. In this thesis we examined the influence of various additives into magnesium anode on the operation of the cell. The results show that the addition of salts MgBr2 and MgCl2 improve the system performance in the initial cycles. We also tested how concentration of the electrolyte effect the battery performance. We found that, by increasing the concentration of the electrolyte, stable capacities are greatly improved and at the same time the concentration also affects the shape of the discharge curve and the polysulfide shuttle effect. We also checked how the concentration of sulfur in the carbon-sulfur composite influences the operation of the battery. The test show that the increase in sulfur concentration greatly reduces both initial and established capacity of the system.

V diplomskem delu smo prikazali vpliv različnih sestav elektrolita iz 1-etil-3-metilimidazolijevega klorida (EMIMCl) in aluminijevega klorida (AlCl3) na delovanje aluminij-organskega akumulatorja. In this thesis we have shown the influence of different compositions of 1-ethyl-3-methylimidazolium chloride (EMIMCl) and aluminium chloride (AlCl3) electrolytes on the performance of aluminium-organic secondary battery.

Namen magistrskega dela je bil izdelati delujoče tiskane litij-žveplove baterije, ki bodo imele za vezivo v katodah uporabljene različne materiale. V teoretičnem delu naloge so predstavljene osnove elektrokemije, lastnosti in delovanje baterij, njihova zgodovina ter osnove delovanja litij-žveplovih baterij. Opisane so tudi osnove o površinski prosti energiji, ki je pri tisku zelo pomembna. V tem poglavju je nekaj besed namenjenih tudi plazmi in obdelavi površin z njo. Predstavljene so osnove reologije, saj ima viskoznost velik vpliv na tiskanje v tehniki sitotiska. Prav tako je v teoretičnem delu predstavljena tehnika sitotiska in pregled dotedanjih raziskav tiskanih baterij. V eksperimentalnem delu je najprej predstavljena izdelava aktivnega materiala za katode v litij-žveplovih baterijah, nato še postopek impregnacije elementarnega žvepla v ogljik. Največji del pa je namenjen raziskavi o vezivih. Predstavljena so veziva karboksimetil celuloza, poliviniliden fluorid in polimerne ionske tekočine. Opisani so tudi postopki priprave suspenzij za tiskanje za vsa tri različna veziva in njihove reološke lastnosti. Predstavljen je tudi postopek uporabe atmosferske plazme za zviševanje površinske proste energije tokovnega nosilca. Opisan je postopek tiskanja in kasnejša izdelava litij-žveplovih baterij. V poglavju Rezultati in razprava so predstavljeni rezultati obdelave površine aluminijeve folije z atmosfersko plazmo, s katero je zvišana površinska prosta energija. Predstavljeni so rezultati tiskanja, SEM posnetki površin in prečnih prerezov, s katerimi so prikazane tudi debeline nanosov in kvaliteta adhezije nanosa na tiskovni material. Sledijo še rezultati reoloških meritev suspenzij za katode in elektrokemijski rezultati, predstavljeni z grafi, ki kažejo delovanje baterij ter krivulje polnjenja in praznjenja. Purpose of master thesis is to make functioning printed lithium-sulfur batteries in which we will use three different binders. In the theoretical part of the master's thesis basics of electrochemistry, principle of battery functioning, their history and basics about lithium-sulfur batteries are explained. Some basics of surface free energy are also described. In this section atmospheric plasma is presented as tool for treating surface free energy of substrate – aluminum foil. Theoretical part also presents rheology which is important in screen printing. Screen printing technique is explained as well. The last theoretical part is review of research on printed batteries. Focus of the experimental part is on different binders (carboxymethylcellulose, polyvinylidene fluoride and polymer ionic liquids). The aim was to prepare effective mixtures of cathode materials for lithium-sulfur batteries with those binders. We also present preparation of impregnated sulfur into carbon black as active material for cathodes. Preparation of suspensions and their rheology properties are presented too. Particular importance for the cathode material is contact between active material and aluminum foil since it provides pathway for electrons and therefore influence electrochemistry of the battery. Improved contacts between cathode particles and aluminum foil were achieved by increasing of surface free energy of the aluminum foil with atmospheric plasma. Process of printing cathodes is also presented. As the last part we present procedure of preparation of “coffee bag” batteries. In result section we present our results of increasing surface free energy of current collector with atmospheric plasma. We show the results of printing with SEM photos of surface and cross-sections of printed suspensions. With those photos we can define thickens and adhesion of printed layer. We also present results of rheological measurements of suspensions and in the end there are electrochemical results of batteries performance.