Stretchable separator/current collector composite for superior battery safety

Abstract

Safety is the most concerning issue for high-energy-density batteries. Here we show how mechanical abuse-induced short-circuiting can be mitigated by designing a structure of highly deformable separator/current collector (SCC) composite that wraps around broken edges and electronically insulates them upon penetration. We report progress in roll-to-roll processed metalized plastic SCC, where 750 nm thick nanocrystalline aluminum deposited on 6 μm polyethylene terephthalate (PET) substrate is used to replace 14 μm Al foil as the current collector (CC) in rechargeable lithium-ion batteries (LIBs). The Al-PET SCC nanocomposite not only increases the cell-level energy density by lowering CC's thickness and weight, but also dramatically increases the battery safety in harsh mechanical penetration accidents. The improved safety is due to better mechanical ductility of PET than Al and cathode, such that in penetration, the insulating PET can extend and isolate around the broken edges and the cathode can be automatically delaminated and insulated from the external circuit, thus preventing short-circuiting induced thermal runaway.