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We examined a new Li-ion battery system based on the combination of a high voltage LiMn0.8Fe0.2PO4 (LMFP) cathode with a Li4Ti5O12 (LTO) anode. Due to the relatively high red-ox voltage of LTO (1.5 V vs. Li) and the excellent stability of its spinel structure, as well as the fact that the red-ox potential of a Li[MnFe]PO4 cathode, up to 4.1 V, does not endanger the anodic stability of a standard electrolyte solutions, it is assumed that such cells can be safe, stable, highly reversible, and suitable for load-leveling applications. The LMFP/LTO cells exhibited excellent rate capability and cycle life at 30°C, delivering discharge capacity of 153, 152, 146, and 118 mAhg-1 (cathode) at 0.1 C, C, 2 C, and 5 C rates. These cells demonstrated excellent high temperature performance when the LTO anodes were pre-passivated before cell operation. By XRD and ICP analyzes of C-LiMn0.8Fe0.2PO4 electrodes before and after charge/discharge cycles, the capacity fading of these systems at high temperatures was attributed to depletion of active Li from the electrodes, due to side reactions on the anode side. These were avoided by pre-passivation of the LTO electrodes. The surface chemistry of Li4Ti5O12 anodes was investigated with the anodic surface reactions arising mainly from the salt (LiPF6). [ABSTRACT FROM AUTHOR]

Si electrodes are the most important high capacity substitutes of Li metal and carbon anodes in high energy density Li ion batteries, including those based on sulfur or air cathodes. In this study we examined amorphous columnar structure silicon film anodes prepared by sputtering in rechargeable Li ion battery prototypes based on TiS2 cathodes. The choice of this cathode material enabled focusing on the examination of pre-lithiated Si films as anode candidates in alkyl carbonate electrolyte solutions. The effectiveness of fluoro-ethylene carbonate (FEC) as a co-solvent in alkyl carbonates/LiPF6 solutions for good performance of silicon anodes was exhibited. Hundreds of cycles were demonstrated in full Li ion cells containing these components. The columnar morphology of these anodes is retained after 1000 cycles. Their surface chemistry, measured by EDS and XPS is discussed. The results of this work encourage further R&D efforts toward the use of amorphous silicon films as anodes in advanced rechargeable Li batteries. [ABSTRACT FROM AUTHOR]

The thermal behavior and structural changes of representative types of lithiated graphitic materials were investigated in solutions comprising ethylene carbonate (EC), ethylmethyl carbonate (EMC), dimethyl carbonate (DMC) and LiPF6. We show that the protective films formed on intercalated graphite electrodes upon cathodic polarization are stable in these electrolyte solutions up to ∼80°C, in DSC experiments. Upon increasing the temperature, between 80 and 120°C, reactions of the surface films with solution species take place and the level of the graphite lithiation is reduced. After destruction of the surface films on lithiated graphite at higher temperatures >120°C, solvent molecules diffuse into the graphite particles and interact with Li ions therein thus forming reduction products. The later decompose upon further heating at temperatures >200°C, with the formation of gaseous products. This results in an internal pressure within the graphite particles that causes their partial exfoliation in an endothermic process. While the protective surface films on the lithiated graphite are removed from the particles in the course of the thermal reactions, we have indications that surface films on fully delithiated graphite do not react with the electrolyte solution at least up to 200°C. [ABSTRACT FROM AUTHOR]