Low-cost BPO₄ In Situ Synthetic Li₃PO₄ Coating and B/P-Doping to Boost 4.8 V Cyclability for Sulfide-Based...

Structural damage of Ni-rich layered oxide cathodes such as LiNi_0.8Co_0.1Mn_0.1O₂ (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 Li₃PO₄ coating and B/P co-doping using inexpensive BPO₄ 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 (P⁵⁺) as in cathode and SEs, respectively, thus Li₃PO₄ 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 B³⁺/P⁵⁺ co-doping, thereby suppressing microcracks during high-voltage cycling. Therefore, when tested in combination with Li─In anode and Li₆PS₅Cl 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.