Interfacial percolation enables high-conductivity lean-lithium oxychloride electrolytes for all-solid-state batteries.

Inorganic solid-state electrolytes (SSEs) underpin the development of all-solid-state batteries (ASSBs), but their ionic conductivity relies heavily on Li-concentrated or even Li-stuffed materials, which not only elevates Li consumption but also compromises their (electro)chemical stability. Here, we establish an interfacial percolation strategy that enables high ionic conductivity at lean-Li content, breaks the conventional dependence of ionic conductivity on high Li content and allows tuning of electrolyte properties such as high-voltage stability. With a typical percolative SSE that consists of Ta2O5 nanocrystals embedded in an amorphous matrix (Ta2O5 ·a-LTOC), we demonstrate that, contrary to common perception, insulating dispersoids can lower Li concentration while increasing ionic conductivity by forming an interfacial percolation network. Ta2O5 ·a-LTOC achieves a high ionic conductivity of 15.2 mS cm-1 at a Li content of 1.46 wt% (6.4 mol L-1), together with high-voltage stability up to 4.8 V. As a result, ASSBs using Ta2O5·a-LTOC and high-nickel cathode materials deliver a long cycle life of 5000 cycles at 2 C, stable high-rate cycling of 4000 cycles at 6 C and high-loading performance with an areal capacity >3 mAh cm-2 and 80.4% capacity retention over 800 cycles. This interfacial percolation strategy provides a universal design route to lean Li, highly conductive SSEs with tunable properties, thereby enabling high-energy and fast-charging ASSBs.