A cathode homogenization strategy for enabling long-cycle-life all-solid-state lithium batteries

Abstract

All-solid-state lithium batteries typically employ heterogeneous composite cathodes where conductive additives are introduced to improve mixed conduction. These electrochemically inactive additives are not fully compatible with layered oxide cathodes that undergo large volume change, significantly reducing battery energy density and cycle life. Here we propose a cathode homogenization strategy by cold pressing a zero-strain cathode material with efficient mixed conduction throughout the (dis)charge process. Li1.75Ti2(Ge0.25P0.75S3.8Se0.2)3 possesses considerable Li+/electronic conductivity of 0.22/242 mS cm−1 when fully charged, increasing monotonically to 0.66/412 mS cm−1 when fully discharged. It delivers a specific capacity of 250 mAh g−1 and undergoes a 1.2% volume change. Homogeneous cathodes composed of 100% Li1.75Ti2(Ge0.25P0.75S3.8Se0.2)3 enable room-temperature all-solid-state lithium batteries to achieve a cycle life of over 20,000 cycles at 2.5 C with a specific capacity retention of 70% and a high energy density of 390 Wh kg−1 at the cell level at 0.1 C. This cathode homogenization strategy contrasts to the conventional cathode heterogeneous design, potentially improving the viability of all-solid-state lithium batteries for commercial applications. Solid-state lithium batteries typically utilize heterogeneous composite cathodes with conductive additives, which limit energy density and cycle life. Here the authors present a cathode material that exhibits efficient mixed conduction and near-zero volume change during cycling, thereby improving battery performance.