Tailoring Electronic Structure to Achieve Maximum Utilization of Transition Metal Redox for High-Entropy Na Layered Oxide Cathodes
Feixiang Ding, Haibo Wang, Qinghua Zhang, Lirong Zheng, Hao Guo, Pengfei Yu, Nian Zhang, Qiubo Guo, Fei Xie, Rongbin Dang, Xiaohui Rong, Yaxiang Lu, Ruijuan Xiao, Liquan Chen, Yong‐Sheng Hu
Abstract
Charge compensation from cationic and anionic redox couples accompanying Na + (de)intercalation in layered oxide cathodes contributes to high specific capacity. However, the engagement level of different redox couples remains unclear and their relationship with Na + content is less studied. Here we discover that it is possible to take full advantage of the high-voltage transition metal (TM) redox reaction through low-valence cation substitution to tailor the electronic structure, which involves an increased ratio of Na + content to available charge transfer number of TMs. Taking Na x Cu 0.11 Ni 0.11 Fe 0.3 Mn 0.48 O 2 as the example, the Li + substitution increases the ratio to facilitate the high-voltage TM redox activity, and further F-ion substitution decreases the covalency of the TM–O bond to relieve structural changes. As a consequence, the final high-entropy Na 0.95 Li 0.07 Cu 0.11 Ni 0.11 Fe 0.3 Mn 0.41 O 1.97 F 0.03 cathode demonstrates ∼29% capacity increase contributed by the high-voltage TMs and exhibits excellent long-term cycling stability due to the improved structural reversibility. This work provides a paradigm for the design of high-energy-density electrodes by simultaneous electronic and crystal structure modulation.