# Achieving Fast Charging and Superior Cycling Stability Single‐Crystal Ni‐Rich Cathodes by Ultrafast Aqueous Washing

## TL;DR

A fast washing method improves the performance of single-crystal Ni-rich cathodes in lithium-ion batteries by removing surface impurities and enhancing stability.

## Contribution

An ultrafast aqueous washing strategy that removes residual lithium compounds while preserving structural integrity in Ni-rich cathodes.

## Key findings

- The 3-min ultrafast washing removes 94.5% of surface residual lithium compounds.
- The method achieves 80% capacity retention at 5 C charging and superior cycling stability at 1 C.
- In situ XRD shows improved structural reversibility and ionic conductivity due to an ultrathin rock-salt layer.

## Abstract

Single‐crystal Ni‐rich layered oxides represent ideal cathodes for high‐energy‐density lithium‐ion batteries due to their high compaction density and volumetric capacity. However, lithium‐excess high‐temperature synthesis generates substantial residual lithium compounds (RLCs; e.g., Li2CO3/LiOH) on particle surfaces. These RLCs elevate interfacial impedance, while protracted Li⁺ diffusion pathways in micrometer‐sized crystals collectively degrade fast‐charge capability and cycling stability. To address these challenges, we develop an efficient strategy employing 3‐min ultrafast washing followed by 600°C annealing for LiNi0.85Co0.1Mn0.05O2 single crystals. This approach achieves 80% capacity retention at 5 C charging meeting extreme fast‐charging targets while maintaining superior cycling stability at 1 C. The ultrafast wash removes 94.5% of surface RLCs while confining structural deterioration to a mere 2–4 nm rock‐salt reconstruction layer. Complementarily, in situ X‐ray diffraction (XRD) reveals that this attenuated surface rock‐salt phase enables smooth bulk phase transitions during Li+ (de)intercalation, thereby enhancing structural reversibility, ionic conductivity, and long‐term stability.

Prolonged water washing severely damages the surface layered structure of single‐crystal Ni‐rich cathodes, forming a thick rock‐salt barrier. In contrast, our 3‐min ultrafast washing removes residual lithium while confining surface reconstruction to an ultrathin 2–4 nm layer, thereby unlocking excellent fast‐charging and cycling stability.