Regulating Na Occupation in P2-Type Layered Oxide Cathode for All-Climate Sodium-Ion Batteries

摘要

P2-type Na_2/3Ni_(1/3)Mn_(2/3)O_2 (NNMO) has been investigated as one of thepromising cathode materials of sodium-ion batteries (SIBs) due to a low-costand wide-temperature-range adaptability. However, its application faces anumber of obstacles because of the poor cycling stability and bad rate capabilities.Herein, by accommodating more Na-ions at the e-site (Na_e) in P2-typeNNMO, which is thermodynamically more stable, P2-type layered oxides(Na_e/Na_f > 1.64) with outstanding electrochemical performance are obtained.Specifically, the Na_(0.696)Ni_(0.329)Mn_(0.671)O_2 (NM-2) exhibits a remarkable capacityretention of 71.9 after 1000 cycles at 1C and an excellent rate capability of54.33 mAh g~(?1) at 50C. In addition, NM-2 exhibits a wide temperature workingrange, even at extreme temperatures for batteries (?30 or 60 ℃), it still showsa capacity close to room temperature and good cycle stability comparedwith 25 ℃. These performances are demonstrated to be attributed to thefast kinetics of the Na ions in the Na_e site, which has a lower energy barriercompared to Naf (0.8301 eV for edge sites and 1.0664 eV for face sites). Thiswork gives a fundamental understanding of the Na-storage mechanism inNa_(2/3)Ni_(1/3)Mn_(2/3)O_2, and also provides a universal strategy to improve the rateand cycling life of P2-type layered oxide cathode materials.