Origin and suppression of structural degradation in Ni-rich layered oxide cathodes at elevated temperatures

Abstract

Ni-rich layered oxide cathode materials are at the forefront of advancements in long-range electric vehicles. However, these materials confront significant challenges related to structural destabilization during cycling, especially when operated at elevated temperatures. Here we explore the intricate relationship between operating temperature, lattice resilience, and Ni content in Ni-rich cathodes. Our investigation emphasizes the crucial role of lattice thermal expansion in causing structural degradation and capacity fading of cathodes at elevated temperatures. The results reveal that higher Ni content intensifies the vulnerability of cathode structures to thermal expansion, particularly within the Li slabs, thereby expediting oxygen loss and phase transitions. To address the challenges associated with thermal-induced structural degradation, we propose introducing lattice distortion by incorporating large-radius elements, for example Na and La, to enhance the structural robustness of cathodes. The electrochemical results demonstrate that this strategy enables a Co-free ultrahigh-Ni cathode, Li_0.99Na_0.01Ni_0.98La_0.02O₂, with a high discharge capacity (227.9 mAh g⁻¹ at 0.1 C and 25 °C) and outstanding cycling stability (78.9 % capacity retention after 500 cycles at 1 C and 50 °C in pouch cells). These findings offer feasible guidance for boosting the performance of layered oxide cathodes under harsh conditions.