Lithium Borate Polycarbonates for High‐Capacity Solid‐State Composite Cathodes

Abstract

Improving composite cathode function is key to the success of the solid‐state battery. Maximizing attainable cathode capacity and retention requires integrating suitable polymeric binders that retain a sufficiently high ionic conductivity and long‐term chemo‐mechanical stability of the cathode active material‐solid‐electrolyte‐carbon mixture. Herein, we report block copolymer networks composed of lithium borate polycarbonates and poly(ethylene oxide) that improved the capacity (200 mA h g‐1 at 1.75 mA cm‐2) and capacity retention (94% over 300 cycles) of all‐solid‐state composite cathodes with nickel‐rich LiNi0.8Co0.1Mn0.1O2 cathode active material, Li6PS5Cl solid electrolyte, and carbon. Tetrahedral B(OR)2(OH)2‐ anions immobilized on the polycarbonate segments provide hydrogen‐bonding chain crosslinking and selective Li‐counterion conductivity, parameterized by Li‐ion transference numbers close to unity (tLi+ ~ 0.94). With 90 wt% polycarbonate content and a flexible low glass transition temperature backbone, the single‐ion conductors achieved high Li‐ion conductivities of 0.2 mS cm‐1 at 30°C. The work should inform future binder design for improving the processability of cathode composites towards commercialising solid‐state batteries, and allow use in other cell configurations, such as lithium‐sulphur cathode designs.