Effects Of Tio_2 Coating On High-temperature Cycle Performance Of Lifepo_4-based Lithium-ion Batteries

摘要

LiFePO_4 particles were coated with TiO_2 (molar ratio = 3%) via a sol-gel process, and the effects of the coating on cycle performance of LiFePO_4 cathode at 55 C against either a Li or a C (mesocarbon microbead) anode were investigated. It was found that, while the coating reduces capacity fading of the LiFePO_4/Li cell, it imposes a deteriorating effect on the LiFePO_4/C cell. Analyses on cell impedance and electrode surface morphology and composition showed that the oxide coating reduced Fe dissolution from the LiFePO_4 cathode and hence alleviated the impedance increase associated with the erosion process. This leads to reduced capacity fading as observed for the LiFePO_4/Li cell. However, the oxide coating itself was eroded upon cycling, and the dissolved Ti ions were subsequently reduced at the anode surface. Ti deposit on the C anode was found to be more active than Fe in catalyzing the formation of the solid-electrolyte interphase (SEI) layer, causing accelerated capacity decay for the LiFePO_4/C cell. The results point out the importance of evaluating the effect of cathode coating material on the anode side, which has generally been overlooked in the past studies.