LiMn_0.8Fe_0.2PO₄/Li₄Ti ₅O₁₂, a possible Li-ion battery system for load-leveling application

We examined a new Li-ion battery system based on the combination of a high voltage LiMn_0.8Fe_0.2PO₄ (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-LiMn _0.8Fe_0.2PO₄ 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 Li₄Ti₅O ₁₂ anodes was investigated with the anodic surface reactions arising mainly from the salt (LiPF₆).