Unlocking Stable Multi‐Electron Cycling in NMC811 Thin‐Films between 1.5 – 4.7 V

Among cathode materials, LiNi0.8Mn0.1Co0.1O2 (NMC811) is the most discussed for high performance Li-ion batteries, thanks to its capacity of approximate to 200 mAh g(-1) and low Co content. Here, it is demonstrated that NMC811 can reversibly accommodate more than one Li-ion per formula unit when coupled with a solid-state electrolyte, thus significantly increasing its capacity. Sputtered Li-rich NMC811 cathodes are tested with lithium-phosphorus-oxynitride as a solid-state electrolyte in a thin-film architecture, which is a simplified 2D model with direct access to the cathode-electrolyte interface. The solid-state electrolyte helps to stabilize the interface and prevents capacity fading, voltage decay, and interface resistance growth, thus allowing cycling at extended voltage ranges of 1.5-4.7 V. While the liquid electrolyte cells suffer from rapid capacity decay, the Li-rich NMC811 cells with the solid-state electrolyte can cycle at a fast rate and an initial capacity of 149 mAh g(-1) from 1.5 to 4.3 V for 1000 cycles. The all-solid-state thin-film cells with a lithium metal anode yield a discharge capacity of up to 350 mAh g(-1) at C/10 because of multi-electron cycling with a coulombic efficiency of 90.1%. The results demonstrate how solid-state electrolytes that are stable against NMC811 cathodes can unlock the full potential of this Li-rich and Ni-rich cathode class.