Thermoexpandable Microsphere-Coated Al Foil Current Collector for Lithium-Ion Batteries with Improved Safety

Recently, the safety of Li-ion batteries (LIBs) has received considerable attention. In particular, LIBs experience internal short-circuit thermal runaway under abusive conditions. The most fundamental cause of internal short circuits is the direct contact between the Al foil current collector and the anode. In this study, an Al foil current collector protective layer precoated with thermoexpandable microspheres (TEMs) and conductive carbon black was prepared. The LiNi0.5Mn0.2Co0.3O2/graphite batteries fabricated with the protective layer demonstrate an internal resistance of 74 mΩ and a capacity retention of 88.8% after 500 cycles; this is consistent with the room-temperature electrochemistry performance of a normal battery. Furthermore, the battery had no internal short circuit or thermal runaway during high-temperature storage or nail penetration experiments because of the volume expansion of the TEMs, which blocked the channel for electron transport. Therefore, this cathode protective layer approach provides guidance for the development of next-generation, high-safety LIBs.