Search

In this work, the effect of Cr3+ partial substitution on vanadium site in monoclinic lithium vanadium(III) phosphate (LVP) structure resulting in compounds with general formula: Li3V2- xCr x(PO4)3-C ( x = 0, 0.05, 0.1, 0.15) was studied. A two-step sol-gel combustion method was employed in syntheses. The samples were characterized by X-ray powder diffraction, scanning electron microscopy, coupled plasma optical emission spectroscopy, and flash combustion. The electrochemical performance of the active materials was examined through rate capability tests and cyclic voltammetry. The unsubstituted compound LVPC delivers higher capacity compared to the Cr-containing samples due to chromium inactivity in the potential range 3.0–4.4 V vs. Li/Li+. However, the Cr-substituted materials show better overall capacity retention (97–97.6%) in contrast to Li3V2(PO4)3-C (96%) in long cycling.

We investigated the effect of different electrolyte additives such as vinyl carbonate (VC), succinic anhydride (SA), and lithium bis(oxalato)borate (LiBOB) on the chemical composition of Solid Electrolyte Interphase (SEI) layer and the electrochemical performance of Si/MC electrodes. The electrochemical behavior of the Si/MC electrodes was evaluated by galvanostatic charge/discharge and rate capability tests. It was found that various electrolyte compositions result in the formation and the resulting properties of the SEI of the electrodes with different compounds. From X-ray Photoelectron Spectroscopy (XPS) analysis, the electrodes cycled in SA- and LiBOB-containing electrolytes show a higher amount of lithium carbonates and a thicker SEI layer than those in standard and VC-containing electrolyte. The electrode with VC 5w% shows an excellent reversible capacity of ∼1100 mAh g −1 up to 100 charge-discharge cycles.

The spray roasting process is recently applied for production of catalysts and single metal oxides. In our study, it was adapted for large-scale manufacturing of a more complex mixed oxide system, in particular symmetric lithium nickel manganese cobalt oxide (LiNi1/3Co1/3Mn1/3O2—NMC), which is already used as cathode material in lithium-ion batteries. An additional lithiation step was coupled with the main process in order to obtain the desired layered structure. Thermogravimetric analysis and high-temperature X-ray diffractometry built the basis for determining suitable synthesis temperature regions for the used chloride precursors and the post-treatment step. The optimized process was proven on an industrial pilot line where a setup for minimum production capacity of 12 kg h−1 was possible. The powder obtained directly after roasting had a very striking morphology compared to the final lithiated product. Hollow aggregates (≥250 μm) with overall 10.926 m2 g−1 surface area and a pore diameter of 3.396 nm were observed. Their well-faceted primary particles were converted into nanosized spheres after lithiation, building a few micrometer big high-porous agglomerates. Actual composition was verified by inductively coupled plasma atomic emission spectroscopy analysis, and the crystal structure and corresponding unit cell parameters were identified and confirmed by Rietveld fit of the derived X-ray diffraction pattern. The initial electrochemical measurements show a 149-mAh g−1discharge capacity, as determined from cyclic voltammetry.

The electrification of mobility has a strong potential to reduce fuel consumption and CO2emissions. This alternative to combustion engines, however, is hampered by battery systems still insufficient in terms of energy, power and lifetime. Therefore it is important to investigate and understand the electrochemical processes and mechanisms that can maximize the power-to-energy ratio. The electrolyte plays an important role for the efficient operation of the battery. For example, electrolytes with low lithium-ion transport numbers and salt diffusion coefficients cause large concentration polarizations during operation of Li-ion batteries. This leads to poor high-rate performance, unwanted side reactions and ageing. It is therefore important to characterize and model the transport phenomena in electrolytes under battery operation conditions. There are numerous experimental methods that can be used to characterize the thermodynamic and transport phenomena in electro-diffusion processes (e.g. NMR, Raman spectroscopy, etc.), but the electrochemical methods are more powerful, as they can mirror the relevant working processes occurring in a battery. In the presented work, the electrolyte characteristics such as viscosity, conductivity, diffusion coefficients of lithium ions and transfer numbers are determined for various LiFP6concentrations. Conductivity was measured by alternating current technique (PEIS and test cell with Pt-electrodes); the transfer numbers were obtained from the diffusion technique (concentration cell) and the diffusion coefficient was determined by the rotary disk electrode method and also calculated from conductivity measurements. Additionally, the temperature dependence of the studied properties was taken into account. The results were further used for the modelling of the mass transport processes in the real cell. The analysis of mass transport phenomena over a range of salt concentrations will be shown and discussed. Acknowledgement The authors would like to thank the Austrian Federal Ministry for Transport, Innovation and Technology (bmvit) and the Austrian Research Promotion Agency (FFG) for their financial support.

Silicon is a promising candidate for anodes in lithium-ion batteries (LIB) due to its high theoretical capacity. However, Si has low electrical conductivity (theoretical: 6.7 x 10-4 S cm-1). Proper conductive additive is needed in order to improve the electrical conductivity of Si-based anodes. Here we focus on applying two commercial conductive addictives: graphite and carbon black Super C65 for silicon-mesoporous carbon (Si/MC) composite anodes. The structure and morphology of the electrodes were characterized by nitrogen adsorption, scanning electron microscopy (SEM), and focus ion beam/transmission electron microscopy (FIB/TEM). Furthermore, the electrochemical performance of the electrodes was characterized by cyclic voltammetry, galvanostatic charge/discharge tests, and impedance spectroscopy. In principles, our work could be effective for the choice of conductive additives to improve the electrical performance of Si/MC anodes.

The electrolyte/electrode interactions on the anode side of a lithium-ion cell and the formation of the solid electrolyte interphase (SEI) have been investigated intensively in the past and are fairly well understood. Present knowledge about the reactions on the cathode side and the resulting cathode electrolyte interphase (CEI) is less detailed. In this study, the electrolyte/electrode interactions on the surface of the high-voltage cathode material LiNi0.5Mn1.5O4 (LNMO), both bare and FePO4-coated, were investigated. The gases evolving upon first time charging of the system were investigated using a GC/MS combination. The degradation products included THF, dimethyl peroxide, phosphor trifluoride, 1,3-dioxolane and dimethyl difluor silane, formed in the GC’s column as its coating reacts with HF from the experiments. Although these substances and their formation are in themselves interesting, the absence of many degradation products which have been mentioned in the existing literature is of equal interest. Our results clearly indicate that coating a cathode material can have a major influence on the amount and composition of the gaseous decomposition products in the formation phase.

Lithium storage metals and alloys can be suitable high-capacity anode materials for lithium-ion batteries, when the morphology is specifically designed. Here, we compare three different Sn/SnSb multiphase anode materials in powder form, which have been prepared in aqueous and organic solution by chemical precipitation using NaBH4 or Zn as reductive agents. The obtained morphologies, chemical compositions, and the electrochemical performance will be comparatively discussed. The variety of synthesis parameters which have an effect on the morphology of the obtained anode materials will be particularly highlighted.

Sn/SnSb, Sn/Bi, and Sn/SnSb/Bi multi-phase materials were synthesised via reduction of cationic precursors with NaBH4 and with Zn, and were tested for their suitability as anode materials for Li-ion batteries by galvanostatic cycling. The rapid reduction with NaBH4 yielded the finer materials with the better cycling stabilities, whereas the reduction with Zn yielded the purer materials with the lower irreversible capacities in the first cycle. Reversible capacities of ∼ 600 mAh g−1, ∼ 350 – 400 mAh g−1, and ∼ 500 mAh g−1 were obtained for Sn/SnSb, Sn/Bi, and Sn/SnSb/Bi, respectively. The cycling stability of the materials decreased in the order Sn/SnSb>Sn/SnSb/Bi>Sn/Bi, which is in part attributed to the presence / absence of intermetallic phases which undergo phase-separation during lithiation.

2D layer structured molybdenum disulfide (MoS2) has been considered as an alternative next generation anode material over graphite, hard carbon and metal alloys, because MoS2 is structurally analogous to graphite (0.335nm) and has the interlayer d-spacing of 0.615nm while exhibiting two or three times the specific capacity of graphite. We will show how electrochemically active molybdenum disulfide (MoS2) with extended interlayer d-spacing was successfully prepared by the solvothermal synthesis method in an ethylene glycol-based mixed solvent at 200oC for 24h under an inert gas atmosphere. Then the prepared MoS2 samples were thermally annealed at various temperatures (300oC, 500oC, 800oC) to remove ethylene glycol from between the MoS2 nanosheets and to tune the d-spacing distance. The main redox reaction is described as Li2S ↔ 2Li+ + S + 2e-, and it suggests that the electrical conductivity of the MoS2 electrode must be enhanced by impregnation with carbonaceous materials to counteract the insulating properties of the sulfur. Therefore, the as-prepared MoS2 powders were surface- modified with nano-carbons (e.g. graphite and graphene) by the substrate-induced coagulation coating process and subsequent annealing at 600oC for 5h under the argon gas environment. The surface-modified carbon-MoS2 composite had a lithium diffusion coefficient (DLi: 1.08x10-6 cm2/s) during charging and discharging as compared to the as-prepared MoS2 (DLi: 4.14x10-7 cm2/s); the cell with the modified MoS2also exhibited higher capacity with a good capacity retention. The carbon-modified MoS2 electrode showed an initial capacity of 1150mAh/g and an average specific capacity of around 900 mAh/g, comparing favorably to the as-prepared MoS2 (700mAh/g). The carbon-MoS2 composite showed a higher capacity with good capacity retention and higher rate capability. The cells were electrochemically characterized by cyclic voltammetry, rate capability measurements, electrochemical impedance spectroscopy, lithium ion diffusion coefficient (DLi) measurement, differential capacity measurements, and in-situ electrochemical XRD measurement. In particular, the volumetric dilatation of the electrode materials during repeated cycles was monitored by in-situ electrochemical dilatometry. It was observed that the dilatations occur during charging /discharging, which corresponds to lithium inter-/deintercalation reactions at redox potentials of reduction at 1.1 V and oxidation at 1.6 V, 2.2V, respectively. The improved electrochemical properties of MoS2 tuned by the enlargement of the d-spacing and by the surface modification make it possible for MoS2to be used as a promising anode material for lithium-ion batteries.

Mixed transition metal oxides are among the most promising cathode materials for lithium ion batteries. The high specific capacity, low cost and thermal stability makes Li(Ni1/3Mn1/3Co1/3)O2, so-called NMC, an excellent material for power tool applications. Therefore, main leading battery manufacturer focus on the combination of these three transition metals to combine the strengths of each of them [1]. The development and design of battery materials require deep understanding of the relations between chemistry, structure and its properties. Nowadays, the commercialized NMC can only reach around 60 % of its theoretical capacity when cycled up to 4.2 V. Higher specific capacities might be reached when the upper voltage limit is raised up to 4.5 V [2], but the lifetime of the cathode then decreases drastically. The deintercalation of more than 0.6 moles of lithium in the charge process of the battery leads to irreversible capacity losses. Lithium nickel manganese cobalt oxides with different transition metal ratios were successfully synthesized via coprecipitation route. The cathode materials were characterized physico- and electrochemically and the composition was confirmed via inductive coupled plasma atomic emission spectroscopy (ICP-AES). Structural changes of non-symmetric NMC compounds at different stages of lithiation were recorded using x-ray diffraction. The resulting patterns were analyzed and the structures refined using the Rietveld method implemented in the GSAS (General Structure Analysis System) package [3]. The same procedure of crystallographic characterization of the NMC structure was carried out for different transition metal ratios cycled up to 4.5 V. The results are presented and comparison between symmetric and non-symmetric lithium nickel manganese cobalt oxides will give better insight into structural changes at higher voltages and the relation to their compositions. Acknowledgement This work was financially supported by the Austrian Federal Ministry for Transport, Innovation and Technology (bmvit) and the Austrian Research Promotion Agency (FFG). [1] N. Yabuuchi, T. Ohzuku, Journal of Power Sources 119-121 (2003): 171-174 [2] Q. Yu, Z. Chen, L. Xing, D. Chen, H. Rong, Q. Liu,W. Li, Electrochimica Acta 176 (2015): 919-925 [3] A. C. Larson, R. B. Von Dreele, Los Alamos National Laboratory Report, No. LAUR-86-748, (1987)

Silicon exhibits the highest theoretical capacity of 4200 mAh g-1, which is 10 times more than the capacity of graphite. Therefore, Si is a promising candidate for anode in lithium-ion batteries. However, Si has low electrical conductivity (theoretical: 6.7 x 10-4 S cm-1). To reach the high performance anode, the proper conductive additives are still needed in order to improve the electrical conductivity of Si-based anode. Here we investigated the effects of conductive nano-graphite and Carbon Black (CB65) on electrochemical performance of silicon-mesoporous carbon composite anode (Si/MC). The material has been synthesized by pyrolysis of polymer aerogel with embedded Si nanoparticles. The electrode was made by 75% active material, 15% conductive additive, and 10% polyacrylic acid (PAA) binder. The electrochemical characterization using impedance spectroscopy, voltammetry, and galvanostatic charge/discharge tests were conducted for both samples. Impedance spectroscopy showed that Si/MC anode with conductive graphite exhibited lower charge-transfer resistance (Rct ≈ 150 Ω), compared to those with carbon black (Rct ≈ 380 Ω). The collected results showed that the graphite additive improved significantly the electrochemical performance of Si/MC anode. In addition, the thermal and long cycling tests will be demonstrated.

Lithium ion batteries operate beyond the thermodynamic stability of the aprotic organic electrolyte used. In 1 M LiClO(4) propylene carbonate electrolyte, with and without the addition of ethylene sulfite as a film forming electrolyte additive, we have used in situ electrochemical dilatometry and on-line electrochemical mass spectrometry to study the volume expansion/contraction of graphitic anodes and the formation of propylene gas, which both can occur during the graphite anode reduction (charge) process. The combination of both methods allows us to get insights into the respective electrolyte reduction mechanisms. The results indicate that the major failure mechanisms of graphitic anodes in pure PC electrolyte can be attributed to the intercalation of solvated lithium ions and the formation of propylene gas, which causes the graphite particles to exfoliate and crack.

In ethylene carbonate- and propylene carbonate-based electrolytes, ethylene and propylene gas evolution have been monitored by on line mass spectrometry. The gases evolve on graphite but not on the lithium storage alloy. The results point to a difference in the electrolyte decomposition mechanism and thus in the solid electrolyte interphase (SEI) formation mechanism. This is discussed in view of solvent co-intercalation reactions, which only arise when graphite anodes are used. The ultimate conclusion is that, due to the different side reactions occurring on graphite and lithium storage alloys, the SEI compositions and the requirements on the SEI performance are different.

To improve interface adhesion between anode film and Cu foil, ultrafast laser structuring was implemented to construct dot patterns with a variety of periodic spacing (25, 50, and 75 µm) on Cu foil. The microstructure and electrochemical performance of anode films coated on those structured Cu foils were characterized. It was shown that adhesive force of the electrodes increased as periodic distance between the dots on the Cu foil decreased. Comparison of XRD patterns of the wet slurries with the dried anode films showed that after drying in the case of 50 µm period dot structured Cu foils the most graphite particles were aligned with the c-axis, vertical to the Cu foil surface. EIS, CV, and rate capability measurements confirmed that the anode film on the 50 µm dot period Cu foil had the lowest impedance, strongest lithiation and de-lithiation peaks, and highest discharge capacity. The cycling test carried out under C/2 rate confirmed that the cells with the 50 µm dot interval Cu foil showed the highest capacity retention. We inferred that this was due to the relatively shorter diffusive path in the anode due to vertical orientation of more graphite particles against the laser structured Cu foil.