Optimizing Oxygen Redox Activity by Local Chemical Disorder toward Robust Co-Free Li-Rich Cathode with High Voltage...

Despite extensive investigation on the lattice oxygen redox (LOR) in Li-rich cathodes, significant challenges remain in utilizing LOR activity without compromising structural and electrochemical stability. Related breakthroughs are hindered by the lack of understanding regarding how different LOR activity influences the structural evolution and electrochemical stability, and what is the optimal LOR activity. Herein, the degree of LOR activity is successfully regulated from 22% to 92% in Co-free Li-rich cathodes (Li_1+xMn_0.62Ni_0.18O₂) by controlling local chemical disorder, and the relationship between LOR activity and cycling stability is revealed. Conventional consensus is challenged by new findings that the over-suppressive LOR activity also undermines electrochemical/structural stability, and even causes more severe voltage fading compared to cases with excessive LOR. However, their failure mechanisms related to lattice strain present different characteristics. Based on the established understanding, the appropriate LOR activation is necessary to balance the maximum reversible LOR activity and good stability, and the optimal degree is identified as 86% in Li_1.18Mn_0.62Ni_0.18O₂ (LR-78). LR-78 exhibits remarkable voltage retention of 96% after 400 cycles at 1 C, and superior high-rate cyclability without capacity decay within 600 cycles at 5 C. These findings significantly broaden the understanding of LOR mechanisms and provide critical guidance for designing durable LOR-based cathodes.