Influence of charge rate on the cycling degradation of LiFePO4/mesocarbon microbead batteries under low temperature

The lithium-ion batteries show extremely poor cycling performance at low temperature. The main degradation mechanism is not clear. To address the fading mechanism, the cycling degradation of commercial LiFePO₄/mesocarbon microbead (MCMB) batteries under various charge rate (1/10C, 1/3C, 1/2C, and 1C) at ?10 °C is systematically investigated using nondestructive tests combining with post-mortem analysis. The low-temperature charging under high charge rates of 1/3C, 1/2C, and 1C results in severe lithium plating, which leads to extremely serious capacity loss. In contrast, no lithium plating occurred under low charge rate of 1/10C. The lithium plating on the anode surface leads to consumption of active lithium ions and electrolyte, which causes the capacity decay and increases ohmic resistance (R _b) with cycling number under high charge rates. The lithium plating on the anode surface is partially reversible, which brings about the capacity recovery of batteries after 80 cycles at 25 °C. The above results are proved by the followed post-mortem measurements. The evolution of the surface morphologies of MCMB electrodes upon cycling shows that a layer composed of rod-like lithium is formed on the anode surface.