Structure Modulation And Electrochemical Performance Of P2-phase High-rate Cathode Material For Sodium-ion Batteries

P2 phase layered Mn-based materials（Na_xMnO₂）with attractive low-cost,non toxicity and wide distribution of sodium has become a research hotspot both at home and abroad.However,the practical application of layered manganese-based cathode materials for sodium ion batteries is still limited by the following drawbacks:The continuous phase transition during charging and discharging affects the cyclic reversibility of the material and the transportation of sodium ions.We use methods of doping and surface modification are utilized to increase the charge and discharge capacity and the reversibility at high rates of the material.In this work,we prepared a series of P2-Na_0.67MnO₂ cathodes(Na_0.67Ni_0.2-xMn_0.8Mg_x O₂)with varying doping amounts of Mg and Ni to realize the maximization of the interlayer spacing within the experimental range and optimize the Na+/vacancy ordering.Consequently,the as-prepared Na_0.67Ni_0.1Mn_0.8Mg_0.1O₂ illustrates an excellent rate performance of 193 mAh g^-1 discharge capacity at 0.1 C(1C=180 mA g^-1),and even at a high rate of 8C,the battery can deliver a capacity of 70 mAh g^-1.The kinetics analysis indicates the raising of Na⁺mobility,which could be due to the reduced Na⁺/vacancy ordering and the enhanced Na interlayer spacing.The codoping of Ni and Mg also enhances the stability of the layered structure,leading to improved cycling performance of74.7%capacity retention after 100 cycles.We synthesized a novel cathode for sodium-ion batteries by doping lathanium into Na_0.67Co_0.2Mn_0.8O₂.the rate performance of the material is enhanced due to the formation of solid electrolyte on the P2-phase surface and the interface between P2-phase and lathanium-manganese phase,the battery can get 80.5 mAh g^-1 in 20C.The lathanium in P2-phase can suppress the phase change during charging/discharging process,which promote the cycle stability of the material,the capacity retention is 66%after 300 cycles.All these prove that the doping of lathanium and surface modification enhance the electrochemical performance of P2-phase.