Hydrophobic surface coating against chemical environmental instability for Ni-rich layered oxide cathode materials

Ni-rich layered oxide LiNi_0.8Co_0.1Mn_0.1O₂ (NCM) as a most promising cathode material for Li-ion batteries suffers easily from the deterioration of electrochemical performance during storage because of the chemical environmental instability. Herein, a simple and scalable strategy is reported to overcome these issues by a hydrophobic coating with dihexadecyl phosphate (DHP) on NCM particle surface, which is composed of an outer-layer hydrophobic alkyl surface and an inner-layer phosphate-based coating with O=POLi covalent bonds. The former layer can alleviate the absorption of H₂O/CO₂ on the particle surface in the humid environment, and the later can improve Li⁺ transportation coefficient during charge–discharge process. As a result, profiting from these two synergistic effects, the DHP-coated NCM shows excellent rate performance and cycling stability, particularly, after 14 days of exposure to air, the DHP-coated NCM delivers the initial capacity of 168.7 mAh g⁻¹ at 2 C rate, but only 134.7 mAh g⁻¹ for the pristine NCM. This work provides an effective approach to improve the environmental stability in Ni-rich layered oxide cathodes.