Low‐cost BPO4 In Situ Synthetic Li3PO4 Coating and B/P‐Doping to Boost 4.8 V Cyclability for Sulfide‐Based All‐Solid‐State Lithium Batteries

Abstract Structural damage of Ni‐rich layered oxide cathodes such as LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) and serious interfacial side reactions and physical contact failures with sulfide electrolytes (SEs) are the main obstacles restricting ≥4.6 V high‐voltage cyclability of all‐solid‐state lithium batteries (ASSLBs). To tackle this constraint, here, a modified NCM811 with Li 3 PO 4 coating and B/P co‐doping using inexpensive BPO 4 as raw materials via the one‐step in situ synthesis process is presented. Phosphates have good electrochemical stability and contain the same anion (O 2− ) and cation (P 5+ ) as in cathode and SEs, respectively, thus Li 3 PO 4 coating precludes interfacial anion exchange, lessening side reactivity. Based on the high bond energy of B─O and P─O, the lattice O and crystal texture of NCM811 can be stabilized by B 3+ /P 5+ co‐doping, thereby suppressing microcracks during high‐voltage cycling. Therefore, when tested in combination with Li─In anode and Li 6 PS 5 Cl solid electrolytes (LPSCl), the modified NCM811 exhibits extraordinary performance, with 200.36 mAh g −1 initial discharge capacity (4.6 V), cycling 2300 cycles with decay rate as low as 0.01% per cycle (1C), and 208.26 mAh g −1 initial discharge capacity (4.8 V), cycling 1986 cycles with 0.02% per cycle decay rate. Simultaneously, it also has remarkable electrochemical abilities at both −20 °C and 60 °C.