Failure mechanisms of the Li(Ni 0.6 Co 0.2 Mn 0.2 )O 2 -Li 4 Ti 5 O 12 lithium-ion batteries in long-time high-rate cycle

(LTO) batteries excel in safety and cycling performance, their full potential for long-term, high-rate cycling still yet remains unrealized. In this paper, we present an analysis of a pouch battery with an LTO anode system that was cycled for an extended period at high rates. We compared the performance changes and internal component properties between fresh and cycled batteries. Our results reveal that, after tens of thousands of high-rate cycles, microcracks emerged on the cathode electrode material (NCM622) particles of the battery, whereas the LTO remained largely unchanged. Additionally, we observed significant electrolyte reduction, characterized the separator surface, and measured its properties. Our findings indicate that the electrolyte reactions are the primary cause of battery failure, leading to capacity fading and impedance increase. This research provides valuable insights into the failure mechanisms of lithium-ion batteries at high rates, thus contributing to the improvement of high-rate lithium-ion batteries.