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 (LiNi_<i>x</i>Co_<i>y</i>Mn_1-x-yO₂, <i>x</i> > 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 LiNi_0.92Co_0.05Mn_0.03O₂ (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 <i>in-situ</i> formed Li_<i>x</i>FeOCl 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.