Dual-ion regulation of coordination chemistry for high-voltage stabilized P2-type cathode
Jiangnan Huang, Jinqiang Gao, Ningyun Hong, Baichao Zhang, Haoji Wang, Fangjun Zhu, Lianshan Ni, Guoqiang Zou, Hongshuai Hou, Hongyi Chen, Wentao Deng, Xiaobo Ji
Abstract
P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 has shown great potential as cathode material for sodium-ion batteries with its high theoretical capacity and energy density . However, severe structural changes are induced by charging P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 above 4.2 V, resulting in rapid capacity decay and poor kinetic capability. In this study, we propose a Zn/Ti synergistic modification strategy to stabilize the P2-type cathode under high voltage. It is found that the P2-O2 phase transition with large volume change is replaced by a milder P2-Z phase transition with the noteworthy improvement in structural stability and Na + diffusion kinetics , due to the disordered Na + /vacancy and the suppressed of the sliding of transition metal layers, as disclosed by density functional theory calculations and in-situ X-ray diffraction. Concurrently, The phenomenon of Ni and O reductive coupling is inhibited by regulating local O coordination owing to the incorporation of a strong Ti−O covalence bond, leading to the more reversible charge compensation mechanism and the inhibited lattice O evolution, as clearly revealed by ex-situ X-ray absorption spectroscopy and Differential Electrochemical Mass Spectrometry . Consequently, we obtained a stable P2-Na 0.67 Zn 0.05 Ni 0.28 Mn 0.52 Ti 0.15 O 2 cathode, achieving an average discharge voltage of 3.62 V at 0.1 C and a capacity retention of 80% after 500 cycles at 2 C. This research provides valuable insights into the enhancement of sodium-ion battery cathode materials by utilizing different functional ions in synergy.