Chlorine-doping boosting Na+ transport kinetics of P2-type layered Na0.66Ni0.27Zn0.06Mn0.67O2 cathode for Na-ion batteries via regulating ion migration path

Sodium-ion batteries (SIBs) with high-energy-density require high-capacity and high-voltage cathode materials. Among various cathode materials, P2-type Na_0.66Ni_0.27Zn_0.06Mn_0.67O₂ (NNZMO) is attractive due to its high theoretical capacity, high working voltage, low production cost, and low toxicity. However, its cycle life and rate performance still need to be further enhanced for serving the needs of commercial applications. In this work, we demonstrate that Cl doping can effectively enhance the structural stability, working voltage, and capacity of the NNZMO-x (x = 0.03, 0.06), especially NNZMO-0.03, attributed that chlorine-doped NNZMO can provide more superior structural integrity, more favorable Na⁺ ion migration path, more electrochemical active sites. Such as, NNZMO-0.03 can provides a specific discharge capacity of 95.40 mAh g⁻¹ and a capacity retention of 86.26 % after 100 cycles at 100 mA g⁻¹, showing marked improvement compared with NNZMO (83.40 mAh g⁻¹ and 77.36 %). Besides, the rate performance of NNZMO-0.03 is also significantly improved after doping Cl⁻. Such as, specific discharge capacity of 81.5 and 76.1 mAh g⁻¹ for NNZMO-0.03 vs. that of 76.3 and 65.9 mAh g⁻¹ for NNZMO at 1000 and 2000 mA g⁻¹. Therefore, this work provides a new strategy by means of Cl doping to enhance the electrochemical performance of layered oxide cathode materials for SIBs