Protective and ion conductive: High-Rate Ni-Rich cathode with enhanced cyclic stability via One-Step bifunctional dual-layer coating

Ni-rich Li[NixCoyMn1-x-y]O-2 (NCM, x > 0.6) is a promising cathode material for lithium-ion batteries while disadvantages like rapid capacity fading and poor rate performance hinder its practical application. In this work, a dual-layer coating is designed and utilized through a solid-gas reaction between the cathode particles and gaseous P2O5, where Li3PO4 acts as a protecting layer against acid attack and LiNiPO4 as a fast ion-conducting layer. The modified sample (LL-NCM94) exhibits a much higher capacity retention of 89.6% after 100 cycles at 1C between 2.8 and 4.3 V in comparison with the capacity retention of 65.9% for pristine sample (P-NCM94). Under the high C-rate of 5C and 10C, the discharge capacity of LL-NCM94 is 20% and 45% higher than P-NCM94, respectively. The better electrochemical performance of LL-NCM94 is attributed to the dual-layer coating in which each layer functions differently and simultaneous elimination of lithium residual compounds during the solid-gas reaction. This work provides an effective method and insights into surface coating design to enhance electrochemical performance of Ni-rich cathode materials.