Enhanced high-voltage robustness of ultra-high nickel cathodes by constructing lithium-ion conductor buffer layer for highly stable lithium-ion batteries

Abstract

Ultra-high nickel layered oxide cathode materials, of much interest due to their higher energy density and price advantages, have become one of the key development directions of cathode materials for lithium-ion batteries. However, a critical challenge for commercial applications is the rapid capacity fading and severe structural degradation, especially at the high cut-off voltage, which originates from interfacial instability and irreversible phase transition. Here we designed a protective Li3PO4 buffer layer modified ultra-high nickel cathode materials LiNi0.92Co0.04Mn0.04O2 (denoted as NCM9) to dramatically improve high-voltage robustness and structural stability through a mild synchronous lithium strategy. Our results affirmed that the Li3PO4 buffer layer plays an undeniable role in suppressing the capacity and structural degradation, and found that it effectively alleviates the irreversibility of the H2-H3 phase transition of the ultra-high nickel cathode material and enhances mechanical and interfacial stability. Additionally, the main exothermic peak temperature of the modified sample at 256.86 °C was higher than that of the pristine sample at 236.86 °C, which fully confirms the significant improvement of the thermal stability of the modified sample. This work provides additional insights into the complex mechanism of high-voltage robustness and improved structural stability of ultra-high nickel cathodes at high cut-off voltage.