Achieving 766.5 Wh kg-1 Electrode-Level Energy Density via Solid-State Cathode Integrating Ultrahigh Nickel Oxide and Lithium Iron Chloride.

Coupling chloride solid electrolytes (SEs) with ultrahigh-nickel oxide cathodes (LiNixCoyMn1-x-yO2, x > 0.9) exhibits higher interfacial stability and better safety than traditional sulfide SE-based cathodes. However, the inevitable ∼30 wt% addition of inactive chloride SEs for sufficient Li+ percolation sacrifices the electrode-level energy density. Herein, using ion-conductive and electrochemically active Li2FeCl4 (LFC) to pair ultrahigh-nickel cathode LiNi0.92Co0.05Mn0.03O2 (Ni92), we fabricate an all-active-cathode Ni92@LFC which unlocks an extra 22% capacity in comparison to Ni92@Li3InCl6, thus realizing a remarkable electrode energy density of 766.5 Wh kg-1. We demonstrate that the lithium-deficient LFC exhibits sufficient ionic conductivity to achieve a higher capacity of Ni92@LFC than Ni92@Li3InCl6 cathode at 3 C (114 mAh g-1 vs 86 mAh g-1). More attractively, we observe an in-situ formed LixFeOCl interphase with rapid dynamics and high stability, facilitating durable cycling with 83.4% capacity retention after 1000 cycles. Our all-active-cathode design paves the way to higher-energy-density all-solid-state cathodes.