Li₃BO₃–Li₂CO₃: Rationally Designed Buffering Phase for Sulfide All-Solid-State Li-Ion Batteries

Most inorganic solid electrolytes (SEs) suffer from narrow intrinsic electrochemical windows and incompatibility with electrode materials, which results in the below par electrochemical performances of all-solid-state Li-ion or Li batteries (ASLBs). Unfortunately, in-depth understanding on the interfacial evolution and interfacial engineering via scalable protocols for ASLBs to mitigate these issues are at an infancy stage. Herein, we report on rationally designed Li3BO3–Li2CO3 (LBO-LCO or Li3–xB1–xCxO3 (LBCO)) coatings for LiCoO2 in ASLBs employing sulfide SE of Li6PS5Cl. The new aqueous-solution-based LBO-coating protocol allows us to convert the surface impurity on LiCoO2 and Li2CO3, into highly Li+-conductive LBCO layers (6.0 × 10–7 S cm–1 at 30 °C for LBCO vs 1.4 × 10–9 S cm–1 at 100 °C for Li2CO3 or 1.4 × 10–9 S cm–1 at 30 °C for LBO), which also offer interfacial stability with sulfide SE. By applying these high-surface-coverage LBCO coatings, significantly enhanced electrochemical performances are obtained in terms of capacity, rate capability, and durability. It is elucidated that the LBCO coatings suppress the evolution of detrimental mixed conducting interphases containing Co3S4 and effectively passivate the interfaces by the formation of alternative interface phases