A Low-Temperature Boron-Based Composite Coating for Ni-Rich Li-Ion Battery Cathode with Enhanced Cycle Life and Safety

Due to the continuously aggravating global warming crisis, the aim of reducing CO2 emissions by replacing fossil fuels with clean energy sources has raised the demand for electric vehicles (EVs) and driven research in pursuing high-energy rechargeable lithium-ion batteries (LIBs). For the cathode component, Ni-rich cathode materials such as LiNixCoyMn1-x-yO2 (NCM) have been widely adopted in commercial EVs due to their high specific capacity (~200 mAh/g) and high operating voltage (~ 4V vs. Li/Li+). However, Ni-rich cathode materials are still confronting challenges such as poor cycle stability and safety issues. To tackle these problems, a boron-based surface modification of Ni-rich cathode material (NCM) is achieved via a low-temperature process in this work. The coated NCM shows comparable rate capability but with substantially improved cycle stability. In terms of safety issues (thermal runaway process), the onset temperature of the thermal runaway process in presence of electrolyte is delayed by 40°C while the total heat release and the maximum heat flow are both decreased by over 40%. Post mortem and in situ X-ray characterizations using synchrotron radiation further illustrate the reasons of the enhanced cycle stability and safety. Results show that the boron-based composite coating is able to decrease the extent of reaction between NCM and the electrolyte during both cycling and the thermal runaway process. Our results demonstrate the use of a low-temperature boron-based composite coating as an effective surface modification method of Ni-rich cathode materials to achieve long-life and high-safety lithium-ion batteries.