Surface-modified composite separator for lithium-ion battery with enhanced durability and security

In the long-term repeated cycling process of lithium-ion batteries (LIBs), the seamless transmission of lithium ions through the separator is crucial for the normal operation of the batteries. However, the irregular porous structure of the commonly used polyethylene (PE) separator leads to the accumulation of chaotic lithium ions and the formation of lithium dendrites, which pose serious safety risks. To enhance the safety performance of LIBs, we propose a novel composite separator design that incorporates ultrafine Al₂O₃ particles and a multifunctional gel polymer binder, which are mixed and coated onto PE membranes. This composite separator improves the wettability and lithium-ion transference number, resulting in impressive cycling lifespan and high average Coulombic efficiencies for large-scale prismatic LiFePO₄//graphite batteries. These batteries exhibit approximately 80 ​% capacity retention over 1900 cycles with average Coulombic efficiencies of 99.95 ​%. Furthermore, even after 1000 cycles, LIBs fabricated with the composite separator pass the rigorous nail penetration test. These enhancements in safety performance offer promising prospects for achieving dendrite-free LIBs during long-term cycling processes.