Surface stabilization for enhancing air/moisture resistance of layered Ni-rich oxide cathodes

Abstract

Layered Ni-rich oxides (LiNi_xCo_yMn_zO₂, with x ≥ 0.8 and x + y + z = 1) are promising cathode materials for high-energy-density lithium-ion batteries (LIBs) owing to their high specific capacity and high operating voltage. However, the Ni-rich cathode suffers from notorious deterioration when in contact with ambient air, primarily driven by nickel's multivalent (Ni²⁺/Ni³⁺/Ni⁴⁺) reactions and humidity sensitivity. In this study, we report a novel surface modification strategy for LiNi_0.83Co_0.12Mn_0.05O₂ (NCM83) via Li_xSiO_y coating, achieved through chemical grafting using the silane coupling agent, (3-aminopropyl) triethoxysilane (KH550), followed by thermal treatment. The modified NCM83 exhibits enhanced moisture resistance due to a superhydrophobic surface that suppresses detrimental reactions between residual lithium species (Li₂O, LiOH, etc.) and water. Furthermore, the Li_xSiO_y coating mitigates mechanical degradation by facilitating strain relaxation. Notably, the modified NCM83 retains high electrochemical performance after 28 days of air exposure, delivering a specific capacity of 157 mAh g⁻¹ after 100 cycles at 1C, compared to 108 mAh g⁻¹ for the uncoated counterpart. Overall, these findings present an effective strategy for improving upon the surface stability of Ni-rich cathodes, facilitating their processing and paving the way for large-scale applications in high-energy LIBs.