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Manganese hexacyanoferrate is a promising cathode material for lithium and sodium ion batteries, however, it suffers of capacity fading during the cycling process. To access the structural and functional characteristics at the nanometer scale, fresh and cycled electrodes are extracted and investigated by transmission soft X-ray microscopy, which allows chemical characterization with spatial resolution from position-dependent x-ray spectra at the Mn L-, Fe L- and N K-edges. Furthermore, soft X-rays prove to show superior sensitivity toward Fe, compare to hard X-rays. Inhomogeneities within the samples are identified, increasing in the aged electrodes, more dramatically in the Li-ion system, which explains the poorer cycle life as Li-ion cathode material. Local spectra, revealing different oxidation states over the sample with strong correlation between the Fe L-edge, Mn L-edge, and N K-edge, imply a coupling between redox centers and an electron delocalization over the host framework.

Rechargeable aqueous Zn-ion batteries (ZIBs) have obtained extensive attention owing to their high safety, low-cost, environmental friendliness and high energy density. Nevertheless, developing suitable cathode materials remains challenging due to requirements for appropriate microstructure. We present a porous N-doped carbon nanosheet/MnO2 (NCS/MnO2) derived from bacterial cellulose (BC) by a simple route. BC chunks were soaked in urea solution and then carbonized under Ar flow at 900 °C. N-doped carbon nanosheets were obtained and MnO2 was added by reaction with NaMnO4. Benefiting from both the conductivity and porosity of the NCS support, the NCS/MnO2 composite delivers a high capacity and long cycling stability (114 mA h g−1 at 2 A g−1 after 1800 cycles). The electrode reaction mechanism was further investigated and the MnO2 dissolution/deposition mechanism was confirmed, with a critical role of zinc sulfate hydroxide (ZSH) to assist the deposition of MnO2

In operando experiments aim to perform in situ measurements of an electrochemical cell on a chip using transmission electron microscopy (TEM) during operation, which is a crucial requirement for understanding the fundamental physical and electrochemical phenomena taking place in a battery. These findings can enhance the understanding of electrochemical cells' behaviour and pave the way for designing more efficient and effective electrochemical energy-storage devices. Hence, the aim of this project is manufacturing a thin-film cell suitable for in operando TEM measurements by testing different chip designs and liquid electrolytes. This kind of cells require electrodes thinner than a few hundred nanometers, but typical commercial active material powders mainly consist of micrometric particles. So, this dissertation is focused on designing a process to prepare suitable cells from commercial materials. To accomplish this, particle size selection of LiMn2O4 was performed using separation methods. Having the ability to both deintercalate and intercalate, LiMn2O4 is used as active material for all electrodes in the thin-film cell. Therefore, nanoparticles are selected by centrifugation suspended in ethanol. Dynamic Light Scattering is employed to characterize their size and concentration to study the effects of the solvent, the centrifugation speed, and the use of filters. Then, adequate particles are drop casted on the chip with Polyvinylidene Fluoride (PVDF) in N-Methyl-2-pyrrolidone (NMP) to adhere them onto the surface. This particle distribution on the chip can be observed in Scanning Electron Microscopy (SEM). It was possible to demonstrate with planar microcells on chips electrochemical features that reproduce those typically shown by macroscopic cells. For example, 5 M LiNO3 had a good CV performance with 70 nA for the oxidation peak and -55 nA for the reduction one when selected depositing LiMn2O4 particles with 500 rpm centrifugation. The cell collectors represen

This thesis is developed at the Nanostructured Interfaces for Electrochemical Energy Storage research line of the Institute of Materials Science of Barcelona (ICMAB, CSIC) and focuses on experimental investigation of activation carbon felts (CF) as vanadium redox flow battery (VRFB) electrodes by electrochemical treatments. Because of the environmental impact of the present days, the Redox Flow Battery has emerged as an energy storage system. In this work, a series of electrochemical treatments were carried out using either sulphuric or phosphoric acids to activate the carbon felts that act as electrodes in these batteries. Following treatments, these were tested using a VRFB, and characterised by SEM and XPS. The felts treated in sulphuric acid slightly improve the thermally activated felt benchmark when placed in the positive electrode. Conversely, treatments in phosphoric acid demonstrated capable of improving results provided by the benchmark at both the negative and positive electrode. Overall, the work shows that electrodes activated by electrochemical treatments with low environmental impact and proper performance can be produced.

Synchrotron radiation based techniques are powerful tools for battery research and allow probing a wide range of length scales, with different depth sensitivities and spatial/temporal resolutions. Operando experiments enable characterization during functioning of the cell and are thus a precious tool to elucidate the reaction mechanisms taking place. In this perspective, the current state of the art for the most relevant techniques (scattering, spectroscopy, and imaging) is discussed together with the bottlenecks to address, either specific for application in the battery field or more generic. The former includes the improvement of cell designs, multi-modal characterization and development of protocols for automated or at least semi-automated data analysis to quickly process the huge amount of data resulting from operando experiments. Given the recent evolution in these areas, accelerated progress is expected in the years to come, which should in turn foster battery performance improvements.

A single-step electrochemical liquid-liquid-solid (ec-LLS) deposition route is developed for growing nanowire-based Ge-Sn nanostructures with tailored morphologies and compositions. Composite films, submicron fibers, nanowires, and also three-dimensional (3D) hierarchical structures are fabricated in the same electrolyte, simply by varying the electrodeposition current density. COMSOL simulations indicate that the current density is able to generate sufficient Joule heating to activate the ec-LLS growth mode. A concomitant reduction of Ge and Sn ions during Sn-doped Ge nanowire growth results in the formation of multicomponent heterostructures comprising non-equilibrium GexSn1-x, pure Sn, and Sn-rich amorphous phases. The proposed deposition technique enables the fabrication of high mass loading electrodes with enhanced Li storage properties. In particular, a 3D hierarchical structure composed of 38 wt % Ge delivers a specific capacity of 938 mA h g-1 after 400 cycles, corresponding to a high areal capacity of 4.95 mA h cm-2. We believe that the present study could be considered as a low-cost procedure for the industrial fabrication of anode materials for high-performance Li-ion battery applications.

Developing low-cost and efficient electrodes for hydrogen evolution reaction (HER) under neutral electrolytes remains an unattained milestone. We report a highly performing binder-free electrode through electroless deposition of Ni–P nanoparticles on bacterial cellulose (BC). Not needing carbonization to provide the electric conductivity, BC can maintain its excellent mechanical properties and thin fiber microstructure. The nanometric cellulose fibers facilitate the formation of small Ni–P nanoparticles, leading to more catalytic active sites. The obtained Ni–P/BC electrode presents remarkable HER activity with an overpotential of only 161 mV at 10 mA cm−2 and a low Tafel slope (141 mV dec−1) in 1 M potassium phosphate-buffered saline (pH = 7) electrolyte. Besides, Ni–P/BC also exhibits good stability for 24 h at 10 mA cm−2. This binder-free, low-cost, and easily fabricated electrode holds excellent promise for HER applications in benign neutral environments.

A simple route has been developed for the preparation of mesoporous graphitic carbons with embedded cobalt nanoparticles just using glycine as a nitrogen source, cobalt nitrate and distilled water. After heating the mixture to 300 °C under magnetic stirring, a dry solid product was obtained, which was then carbonized at 900 ºC under argon atmosphere. Changing the glycine/Co molar ratio allowed controlling the size of the cobalt particles and their dispersion in the carbon matrix, the porosity of the carbon and its graphitic character. The carbon–metal composites obtained were tested as oxygen cathodes in Li–O batteries. Cells assembled exhibited a full discharge capacity up to 2.19 mAh cm at a current of 0.05 mA cm and over 39 cycles at a cutoff capacity of 0.5 mAh cm. This work provides a green, feasible and simple way to prepare mesoporous graphitic carbons with embedded cobalt nanoparticles without involving templates. Graphical abstract: [Figure not available: see fulltext.].

The reversible and irreversible cationic and anionic charge compensation mechanisms occurring along the first charge and discharge cycle of Li- and Mn-rich Li[Li0.2Ni0.16Mn0.56Co0.08]O2 cathode material at (dis)charge rates of 0.1C and 5C have been identified and quantified by X-ray absorption and emission spectroscopy. The analysis provided the oxidation states of the transition metals, the Mn local coordination, and the lattice elastic constants. Lattice softening occurs along the first charge, while a minor spinel phase forms irreversibly at the expense of the layered phase. Higher charge rate increases the spinel formation and induces an increased softening in the delithiated lattice, which is expected to correspond to a reduced reversible anionic redox. The results evidence a comparable cationic and anionic oxidation since the beginning of the charge, while only anions are contributing towards its end, equivalent to roughly 10% of structural oxygen irreversibly lost. Higher charge rates resulted in a decreased reversible anionic redox, anticipating the cationic oxidation. The reported results provide a reliable experimental approach to characterize the key parameters controlling the reversible and irreversible cationic and anionic contributions to the charge compensation mechanism.

The use of slurries of conducting particles has been considered a way to extend the electrode area in some energy storage electrochemical cells. When suspensions of conducting particles are used in electrolytes a decreased impedance is observed, even for concentrations much lower than the theoretical percolation limits. Indeed, it is known that polarization occurs when a conducting material is immersed in an electrolyte in presence of electric fields, and bipolar electrochemistry processes may occur. This work demonstrates the dramatic drop in resistance for electrochemical cells with just a few macroscopic conducting pieces immersed in the electrolyte, in the absence of any electrical contact, through bipolar induction. Furthermore, mediation of soluble redox species between adjacent induced poles of opposite charge results in an additional mechanism for charge transfer, contributing further to the decrease in impedance. Relevant parameters like size, geometry, and spatial occupation of inducible pieces within the electric field, are relevant. Remarkably, the effects observed can explain some empirical observations previously reported for carbon suspensions and slurries. Thus, no electronic percolation requiring particle contact, nor ordering, are needed to explain the good performance associated to lowered impedance These results suggest new engineering designs for electrochemical cells with enhanced currents.

Porous carbons are important cathode materials for metal-air batteries, but the most usual methods to prepare these porous structures are complex and of high cost. We have prepared porous carbons from bacterial cellulose (BC) hydrogels by a simple water-alcohol solvent exchange before carbonization. Alcohol treatment facilitates looser and more open structures than untreated BC, resulting in porous carbon structures with high surface area, appropriate for electrochemical applications. Used as cathodes in lithium-oxygen batteries, the carbon derived from 1-butanol treated BC has excellent discharge capacity (5.6 mA h cm−2) and good cycle life. This work presents a sustainable, straightforward and fast way to prepare porous carbon materials from BC.

The local structural and electronical transformations occurring along the first charge and discharge cycle of Li- and Mn-rich Li[Li0.2Ni0.16Mn0.56Co0.08]O2 cathode material have been characterized by X-ray absorption spectroscopy at several complementary edges. The irreversible spinel formation, occurring at the expenses of the cycling layered phase during the first charge, is quantified (about 10%) and spatially localized. The local strains induced by the Ni oxidation have been evaluated. They induce the formation of a low spin Mn3+ in the layered structure in parallel to the irreversible formation of the spinel phase in the particles bulk. The charge balance has been quantified for all the elements along the first charging cycle, confirming a reversible oxygen oxidation along the charge. Overall, these quantitative results provide an experimental basis for modeling aimed to control the structure and its evolution, for instance, hindering the spinel formation for the benefit of the material cycle life.

Energy-dependent full field transmission soft X-ray microscopy (TXM) is able to give a full picture at the nanometer scale of the chemical state and spatial distribution of oxygen and other elements relevant for battery materials, providing pixel-by-pixel absorption spectrum. We show different methods to localize chemical inhomogeneities in Li1.2Mn0.56Ni0.16Co0.08O2 particles with and without VOx coating extracted from electrodes at different states of charge. Considering the 3d(Mn,Ni)-2p(O) hybridization, it has been possible to discriminate the chemical state of Mn and Ni in addition to the one of O. Different oxidation states correspond to specific features in the O-K spectra. To localize sample regions with specific compositions we apply two different methods. In the first, the pixel-by-pixel ratios of images collected at different key energies clearly highlight local inhomogeneities. In the second, introduced here for the first time, we directly correlate corresponding pixels of the two images on a xy scatter plot that we call phase map, where we can visualize the distributions as function of thickness as well as absorption artifacts. We can select groups of pixels, and then map regions with similar spectral features. Core-shell distributions of composition are clearly shown in these samples. The coating appears in part to frustrate some of the usual chemical evolution. In addition, we could directly observe several further aspects, such as: distribution of conducting carbon; inhomogeneous state of charge within the electrode; molecular oxygen profiles within a particle. The latter suggests a surface loss with respect to the bulk but an accumulation layer at intermediate depth that could be assigned to retained O2.

Electrodeposited iridium oxide (K1.7IrO0.8 (OH)2.2 × 1.8 H2O; also called IrOx) is among the best substrates for neural growth, decreasing impedance and stimulating cell growth, when used as a connected electrode. Without direct contact, it has been proven to stimulate neurons through a bipolar mechanism related to the conducting character of the material in the presence of remote electric fields. The remote wireless electrostimulation that arises from it is of large significance in clinical applications. Ionic intercalation simultaneous with iridium oxidation state changes at the induced IrOx cathode and the formation of a redox and ionic gradient at the IrOx substrate is envisaged as the most probable explanation for the observed effects on neural cell growth. This work shows the iridium state gradient using X-ray absorption spectroscopy (XAS) with significant electrochemical features and relaxation times that allow for a persistent effect in the material even after the electric field creating the induced dipole is switched off. It also shows correlated intercalated sodium gradients observed by semiquantitative energy-dispersive X-ray (EDX) analysis data. The bipolar effect is proven and yields new evidence for the behavior of other biocompatible neural growth substrates.

A template free, single-step process is developed for fabrication two-dimensional tin nano-platelets by electrochemical deposition in the presence of Triton X100 (TX100). Electrochemical studies combined with structural characterization revealed that during electrodeposition, TX100 molecules adsorb preferentially on {022} planes of Sn and highly anisotropic growth promotes in [200] direction which results in the formation of platelet morphology. The deposited platelets exhibit a high aspect ratio of 30 (width to thickness) and thickness of 25 ± 5 nm that uniformly covered the substrate with a high platelet density of 9 × 108 cm−2. The electrochemical performance of nano-platelets for lithium storage was studied in detail and compared with other morphologies of tin. Tin nano-platelets exhibited high reversible capacity and excellent cycling performance, the capacity was maintained at 820 mA h g−1 for 100 cycles and more, far superior to the other structures. Excellent rate capability was also observed for nano-platelets up to 5 C, with the ability to be operated at 20 C without damage. The superior electrochemical performance of tin platelets is mainly attributed to its two-dimensional structure that efficiently distributes strain, allowing high mechanical stability even after 100 cycles, as confirmed by Scanning Electron Microscopy (SEM).

Lithium-rich transition-metal-oxide cathodes are among the most promising materials for next generation lithium-ion-batteries because they operate at high voltages and deliver high capacities. However, their cycle-life remains limited, and individual roles of the transition-metals are still not fully understood. Using bulk-sensitive X-ray absorption and emission spectroscopy on Li[Li0.2Ni0.16Mn0.56Co0.08]O2, we inspect the behavior of Mn, generally considered inert upon the electrochemical process. During the first charge Mn appears to be redox-active showing a partial transformation from high-spin Mn4+ to Mn3+ in both high and low spin configurations, where the latter is expected to favor reversible cycling. The Mn redox-state with cycling continues changing in opposition to the expected charge compensation and is correlated with Ni oxidation/reduction, also spatially. The findings suggest that strain induced on the Mn−O sublattice by Ni oxidation triggers Mn reduction. These results unravel the Mn role in controlling the electrochemistry of Li-rich cathodes.

Li-O2 batteries can offer large discharge capacities, but this depends on the morphology of the discharged Li2O2, which in turn is strongly affected by the nanostructured carbon used as support in the air cathode. However, the relation with the textural parameters is complex. To investigate the combined effect of channels of different sizes, meso-macroporous carbons with similar mesopore volume but different pore size distribution were prepared from the polymerization of resorcinol-formaldehyde (RF) in the presence of surfactants and micro-CaCO3 particles. The carbon materials were used as active materials of air cathodes flooded by ionic liquid-based electrolytes in Li-O2 cells with two different configurations, one with a static electrolyte and the other with a stirred electrolyte, which favor a film-like and large particle deposition, respectively. The presence of large pores enhances the discharge capacity with both mechanisms. Conversely, with respect to the reversible capacity, the trend depends on the cell configuration, with macroporosity favoring better performance with static, but poorer with stirred electrolytes. However, all mesoporous carbons demonstrated larger reversible capacity than a purely macroporous electrode made of carbon black. These results indicate that in addition to pore volume, a proper arrangement of large and small pores is important for discharge capacity, while an extended interface can enhance reversibility in Li–O2 battery cathodes.

A versatile method based on the matrix assisted pulsed laser evaporation (MAPLE) technique was used for the fabrication of graphene-based electrodes for application in supercapacitors. The simultaneous deposition and chemical transformation of graphene oxide (GO) and GO–NiO nanoparticles was attained by including nitrogen-containing chemically reactive compounds (ammonia, urea and melamine) in aqueous MAPLE targets. Morphological analyses reveal the formation of hundreds of nanometres to tens of micrometres thick porous films on both plastic and metallic flexible substrates. Structural and compositional studies, carried out by transmission electron microscopy, and Raman and X-ray photoelectron spectroscopies, disclose significant deoxidation and nitrogen doping of the GO material. The electrodes reveal remarkable electrochemical performance, showing a maximum volumetric capacitance of 350 F cm 3 (9 mF cm 2 areal capacitance) in aqueous electrolyte. Symmetric supercapacitors fabricated with these electrodes reveal excellent long-term stability at high specific intensities. From the obtained results, it can be asserted that the reactive inverse MAPLE method stands out as a promising technology not only for the adaptable fabrication of flexible graphene-based composite electrodes but also for a wide variety of advanced functional materials for diverse applications.

In this paper, phosphomolybdic acid H3PMo12O40 (PMo12) was anchored to four synthetic micro-mesoporous carbons and a commercial one to analyse the relationship between the porous texture of the support, the PMo12 adsorption and the performance of the resulting hybrid materials as electrodes in supercapacitors. The uptake of PMo12 on carbon supports follows a clear correlation with the micropore volume, which implies that PMo12 is mainly adsorbed in microporosity as a consequence of a greater confinement in this kind of pores instead of mesopores. Transmission electron microscopy indicates that the PMo12 adsorbed is homogeneously dispersed in the carbon texture. Finally, the addition of PMo12 to the original carbon electrodes provided capacitances up to 293 F per gram of electrode, substantially larger than the 206–240 F g−1 of the unmodified activated carbon. This result represented an increase of up to 35% in terms of gravimetric energy density and 160% in terms of volumetric energy density, after PMo12 integration into the carbon matrix.

Herein, we are presenting all-solid-state symmetric supercapacitors (ASSSCs) with an innovative double hybrid strategy, where a hybrid material based on reduced graphene oxide (rGO) anchored with phoshotungstic acid, rGO-H3PW12O40) is combined with hybrid electrolyte (hydroquinone-doped gel electrolyte). Initially, a hybrid electrode is fabricated by decorating H3PW12O40 nanodots onto the surface rGO (rGO-PW12). Next, a symmetric cell based on rGO-PW12 electrodes was assembled with PVA-H2SO4 polymer gel-electrolyte. Interestingly, rGO-PW12 symmetric cell revealed a substantial enhancement in the cell performance as compared to parent rGO systems. It featured a widened potential range of 1.6 V, thereby providing 1.05 mWh/cm3 energy density. The electrochemical performance of rGO-PW12 cell was further advanced by introducing redox-active (hydroquinone) species in to the PVA-H2SO4 gel-electrolyte. Indeed, the performance of rGO-PW12 cell was surprisingly improved with an ultra-high energy density of 2.38 mWh/cm3 (more than two-fold).

The stabilization of the intermediates formed during oxygen reduction reaction and their efficient solubilization and diffusion is a crucial issue that needs to be improved in non-aqueous lithium oxygen batteries. By adding 0.1 M K+ (as KOTf salt) to the electrolyte we have observed remarkable improvements in the rate capability of the discharge process. The K+ cation facilitates a more homogeneous discharge product deposition in the porous cathode. Instead, as evidenced by synchrotron measurements, we find that K+ does not influence the cell chemistry, suggesting that it rather assists the superoxide solvation, thus enhancing the solution-based growth of the discharge products. In addition, if iodide (I-) is added as redox mediator we find an extended cycle life when K+ instead of Li+ is used as cation. This finding remarks the benefits of stabilizing the oxygen reduction products in the electrolyte leading to a solution-based mechanism.

Ionic liquids’ (ILs) reusability, non-volatility and non-corrosiveness, as well as their ease of isolation and a large electrochemical stability window make them an interesting choice as environment-friendly electrolyte for metal/air batteries. ILs have been described as designer solvents as their properties and behaviour can be adjusted to suit an individual reaction need. In the framework of this study we applied a conceptually similar designer approach and show that a simple parameter as the concentration of a Li+ dopant dramatically affects the reactions yields of Li/O2 based energy storage devices. We studied the effect of Li+ concentration from 0.1 to 1 M in a LiTFSI:PYR14TFSI ionic liquid electrolyte on the kinetics of the oxygen reduction reaction (ORR) and on the formation rate of different Li-O species at two different temperatures, finding that discharge capacity, rates and product distribution change in a non-linear way. At 60 °C highest rates and up to one order of magnitude larger capacities were observed at intermediate LiTFSI concentrations, implying a complete mechanism switch from surface to volume phase mediation for Li2O2 precipitation. At room temperature the same evolution was observed, even if in this case the surface mediation remained predominant at all concentrations. These results suggest the possibility to optimise the ionic liquid based Li/O2 battery performances in terms of discharge capacity and lithium use, by playing on temperature and alkali cation concentration.

Despite the considerable initial optimism behind its development and prospective commercialization, the Li/air battery chemistry has now reached a mature stage of development, which has served to highlight the main underlying technological limitations, as well as what can realistically be expected from it. One of the main challenges is the control of the discharge product morphology, that is, Li2O2, onto the positive electrode. In this article, we show how the three‐phase configuration required to ensure cell operation can be induced in a two‐phase system made of mesoporous carbon and an ionic liquid electrolyte [N‐butyl‐N‐methylpyrrolidinium bis(trifluoromethane sulfonyl)imide, Pyr14TFSI] by means of an oxygen‐bubbling device (OBD) and a peristaltic pump. The use of a non‐flammable, non‐volatile electrolyte ensures long‐term, extensive discharging (up to 4.78 mAh cm−2), as well as operation at temperatures higher than room temperature.

In pursuit of high capacitance and high energy density storage devices, hybrid materials have quickly garnered well-deserved attention based on their power to merge complementary components and properties. Here, we report the fabrication of all-solid state symmetric supercapacitors (ASSSC) based on a double hybrid approach combining a hybrid electrode (reduced graphene oxide-phoshomolybdate, rGO-PMo12) and a hybrid electrolyte (hydroquinone doped gel-electrolyte). To begin with, a high-performance hybrid electrode based on H3PMo12O40 nanodots anchored onto rGO was prepared (rGO-PMo12). Later, an all-solid state symmetric cell based on these rGO-PMo12 electrodes, and making use of a polymer gel-electrolyte was assembled. This symmetric cell showed a significant improvement in cell performance. Indeed, it allowed for an extended potential window by 0.3 V that led to an energy density of 1.07 mW h cm-3. Finally, we combined these hybrid electrodes with a hybrid electrolyte incorporating an electroactive species. This is the first proof-of-design where a redox-active solid-state gel-electrolyte is applied to rGO-PMo12 hybrid supercapacitors to accomplish a significant enhancement in the capacitance. Strikingly, a further excellent increase in the device performance (energy density of 1.7 mW h cm-3) was realized with the hybrid electrode-hybrid electrolyte combination cell as compared to that of the conventional electrolyte cell. Thus, this unique symmetric device outclasses the high-voltage asymmetric counterparts under the same power and represents a noteworthy advance towards high energy density supercapacitors.

Li4Ti5O12 spinel (LTO) is a potential candidate for anode materials in power LIBs due to the high Li-ion mobility and cyclability. At 1.56V Li4Ti5O12 inserts 3 lithium ions with a theoretical capacity of 175 mAh/g. Li4Ti5O12 spinel consists of lithium and titanium atoms randomly distributed on one-half of the octahedral sites and lithium atoms filling one-eighth of the tetrahedral sites within the oxygen close packed lattice. As current is applied and lithium is passed, Ti4+ is reduced to Ti3+ within the octahedrally coordinated framework, allowing a topotactic transition between Li4Ti5O12 ¿current ¿Li7Ti5O12. The inserted lithium ions and the tetrahedrally coordinated lithium move to occupy adjacent octahedral sites. A variety of preparation methods, including sol-gel, hydrothermal and template synthesis, have been developed in order to obtain structures with large surface area and open pores as the three dimensionally ordered macroporous (3DOM) spinels. The synthesis of pure phases of 3DOM-LTO structures presents difficulties; some samples results in different amounts of Li2TiO3, rutile, and anatase as side products and the high temperatures destruct the porous structure. As calcination time increases, grains of lithium titanate grow larger and, consequently, the 3DOM structure breaks down. 3DOM architecture, however, comes at the expense of phase purity. In spite of the interest for this material, to the best of our knowledge reports on its preparation as 3DOM material are scarce. Since we found the result critically depended on the salt used and the thermal treatment, particular emphasis was given to the understanding of the formation process. This study aims to achieve the best synthesis conditions to prepare nanostructured 3DOM-LTO. Samples have been synthesized by a colloidal templating process with and without hydrothermal conditions. It is also studied the effect of a pre-forming step and subsequent incorporation of lithium or directly addressing the chemic

We analyze in detail the relationship between pore size distribution and discharge capacity for cathodes in ionic liquid-based Li/O2 batteries at room temperature (RT) and 60 °C. We used several porous carbons with similar composition and apparent surface area but with pore distribution peaks in different points of the meso/macroporous region. The porous structure of carbons caused a significant influence on the discharge specific capacity. However, no obvious correlations between specific capacity and surface area or total pore volumes were observed. Carbons with high mesopore volumes and a predominant pore size of 20-40 nm exhibited the highest specific capacities. When temperature rises from room temperature to 60 °C, discharge capacity increases by a factor higher than two, with the smallest pores providing the highest increases. A model is introduced to empirically correlate capacity with pore size distribution. This model assumes that during electrochemical discharge the pore walls are uniformly coated in their thickness but that pores below a threshold size value do not participate at all to the capacity. Our model can account for the effects of pore size distribution using a discharge layer thickness of a few nanometers and with threshold values of excluded pore sizes, of 12 nm at RT and 10 nm at 60 °C. The model also allowed the estimation of the penetration depth of the discharge reaction on the electrode thickness and indicates that its increase is the main factor justifying the increase of capacity when temperature is increased.

Lithium extraction from the Li-excess Li1.10Mn 1.90O4 spinel has been performed by chemical and electrochemical methods in aqueous and in organic media, respectively. De-lithiated samples have been investigated by XRD, SEM, TG, 7Li and 1H MAS-NMR techniques. The comparative study has allowed demonstrating that the intermediate de-intercalated samples prepared during the chemical extraction by acid titration are similar to those prepared by the electrochemical way in a non-aqueous electrolyte. LiMn2O4 based spinel with a tailored de-lithiation degree can be prepared as a single phase by controlling the pH used in chemical extraction. 7Li MAS-NMR spectroscopy has been used to follow the influence of the manganese oxidation state on tetra and octahedral Li-signals detected in Li-extracted samples. The oxidation of Mn(iii) ions goes parallel to the partial dissolution of the spinel, following Hunter's mechanism. Based on this mechanism, a generalized chemical reaction has been proposed to explain the formation of intermediate Li+ de-intercalated samples during acid treatment in aqueous media. By the 1H MAS NMR study, no evidence of Li-H topotactic exchange in the bulk of the acid treated material was found. This journal is © the Owner Societies 2014.