Cold-Water Washing Strategy Enables Stable Slightly-Lithium-Rich Nickel Oxide Cathodes for High-Energy Batteries

Ni-rich layered cathode materials often utilize water washing to reduce residual alkali after synthesis, yet the impact of this process is complex and multifaceted, involving active Li+ leaching, transition metal reduction, and surface layered structure collapse. Here we report a cold-water-washing strategy at 5 °C to mitigate these degradation mechanisms and preserve both the structural and electrochemical integrity of slightly lithium-rich nickel oxide (SLR-LNO) cathodes. Multimodal characterization reveals that cold-water washing effectively minimizes the formation of surface rock-salt phases and maintains the bulk structural ordering, whereas higher washing temperatures exacerbate these detrimental effects. The cold-water-washed SLR-LNO cathode demonstrates good electrochemical performance, delivering a high initial discharge capacity of 231.8 mAh g–1 at 0.1 C and exceptional cycle stability in practical pouch full-cells, retaining over 80% of its initial capacity after 2000 cycles. This work not only provides a deeper understanding of the effects of water washing but also offers a broadly applicable approach for various battery cathodes.