In situ lithiation modulation of LiNi0.8Co0.1Mn0.1O2 as bifunctional electrocatalysts for highly efficient overall water splitting.

LiNi0.8Co0.1Mn0.1O2 (NCM811) is a common cathode material in lithium-ion batteries (LIBs), and the ever-increasing consumption of large quantities of LIBs raises critical concerns about their recycling. Herein, we propose an in-situ lithiation route to tune the structure and electrocatalytic properties of NCM811 by Li+ intercalation and exfoliation in LIBs. In this strategy, the morphology and microstructure of the lithiated NCM811 can be controlled by a specified discharge voltage. The lithiation modulation effectively converted the large NCM811 particles into many flower-like nanosheets. The resulting nanosheets are interconnected and have a rich porous structure, which is conducive to the complete penetration and diffusion of electrolytes and accelerating the charge transfer rate. Moreover, oxygen vacancies and amorphous regions were induced in the nanosheets to provide more active sites. The novel lithiation-modulated nanosheets demonstrate high activity and bifunctional characteristics for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Specifically, the lithiated NCM811 nanosheets demonstrate a low HER overpotential of 58 mV@10 mA cm-2 and OER overpotential of 222@10 mA cm-2. The assembled electrolytic cell for overall water-splitting requires only 1.74 V to reach 100 mA cm-2 with outstanding durability. This work provides a unique strategy for structural modulation of NCM811 cathode in LIBs as high-performance electrocatalysts for water splitting, and demonstrates a high-value recycle of spent LIB electrodes.