Improving the Safety of HED LIBs by Co-Coating Separators with Ceramics and Solid-State Electrolytes

Abstract

Internal short circuits because of deformation or melting down of separators have been recognized as a root cause for many thermal runaway (TR) events of high-energy-density (HED) lithium-ion batteries (LIBs). Ceramic coating of the polyolefin separators is a promising strategy but generally hinders ionic conduction. In this study, we demonstrate that co-coating the separators with boehmite ceramics and Li1.5Al0.5Ti1.5(PO4)3 (LATP) solid-state electrolytes could markedly improve the safety of LIBs while mitigating detrimental effects on electrochemical performance. We assembled HED (~350 Wh/kg) lithium-ion pouch cells with nickel-rich Li(Ni0.9CoxMn0.1-x)O2 cathodes, silicon-based/graphite blended anodes, and co-coated separators of varying thicknesses. It is found that LATP reacts with the organic liquid electrolytes and lithium to generate a robust solid-electrolyte-interface-filled LATP layer during the formation, which can prevent the thermal deformation of separators. During the thermal abusive tests, the battery's TR failure thresholds raised from 146.2 to 162.0 °C. Correspondingly, the direct failure cause of the cell TR hurdled the separator malfunction to the thermochemical reactions of the nickel-rich cathodes. Additionally, pouch cells exhibited impressive electrochemical performance, maintaining a capacity retention of 87.99% after 500 cycles at 1C.