Boron-doped sodium layered oxide for reversible oxygen redox reaction in Na-ion battery cathodes
Yu-Jie Guo, Pengfei Wang, Yubin Niu, Xu‐Dong Zhang, Qinghao Li, Xiqian Yu, Min Fan, Wan‐Ping Chen, Yang Yu, Xiangfeng Liu, Qinghai Meng, Sen Xin, Ya‐Xia Yin, Yu‐Guo Guo
Abstract
Abstract Na-ion cathode materials operating at high voltage with a stable cycling behavior are needed to develop future high-energy Na-ion cells. However, the irreversible oxygen redox reaction at the high-voltage region in sodium layered cathode materials generates structural instability and poor capacity retention upon cycling. Here, we report a doping strategy by incorporating light-weight boron into the cathode active material lattice to decrease the irreversible oxygen oxidation at high voltages (i.e., >4.0 V vs. Na + /Na). The presence of covalent B–O bonds and the negative charges of the oxygen atoms ensures a robust ligand framework for the NaLi 1/9 Ni 2/9 Fe 2/9 Mn 4/9 O 2 cathode material while mitigating the excessive oxidation of oxygen for charge compensation and avoiding irreversible structural changes during cell operation. The B-doped cathode material promotes reversible transition metal redox reaction enabling a room-temperature capacity of 160.5 mAh g −1 at 25 mA g −1 and capacity retention of 82.8% after 200 cycles at 250 mA g −1 . A 71.28 mAh single-coated lab-scale Na-ion pouch cell comprising a pre-sodiated hard carbon-based anode and B-doped cathode material is also reported as proof of concept.