Preparation Of P2-type Manganese-based Cathodes Of Sodium Ion Battery With Microsphere Structure And Study Their Electrochemical Performance

P2 type manganese-based layered metal oxide is used as a cathode material for sodium ion batteries.It has high specific capacity,faster sodium ion deintercalation ability and good stability in the air.It has become a research hotspot of sodium ion batteries.For the P2 type Na_0.67Mn O₂,the Mn³⁺content is too high,which makes the material have a high initial capacity,but because Mn³⁺easily leads to the Jahn-Teller effect,it causes phase change and manganese dissolution during the charging and discharging process,thereby causing its capacity of the rapid decay,thus limiting its practical application.In order to improve the electrochemical performance of Na_0.67Mn O₂,structural design,metal/non-metal element doping and coating are commonly used research strategies.This paper intends to design P2 type layered manganese-based metal oxide cathode materials through metal/non-metal element doping and sacrificial template method to study the improvement of the structure and electrochemical performance of P2 type cathode material by metal/non-metal element doping.The specific research on the relationship is as follows:（1）Based on the high redox potential of Cu²⁺/Cu³⁺and the multi-electron transfer characteristics of Ni²⁺/Ni⁴⁺,using Mn CO₃ microspheres as the precursor,in order to ensure the structural stability in the high-temperature reaction,it is converted into Mn O₂,which is more thermodynamically stable.Using it as a reactant template,P2 type layered Na_0.67Mn_0.7Ni_0.15Cu_0.15O₂ microspheres co-substituted by copper and nickel bimetals were prepared by high-temperature solid-phase reaction.Low Ni²⁺and Cu²⁺doping can affect the unit cell parameters of the material,reduce the average valence of Mn,and reduce the ratio of Mn³⁺,thereby stabilizing the frame of the material and the P2 type Na_0.67Mn O₂,compared with Na0.67Mn0.7Cu0.3O2 and Na0.67Mn0.7Ni0.3O2,the P2 type layered Na0.67Mn0.7Ni0.15Cu0.15O2has better electrochemical properties,including higher average potential,better cycle stability,rate performance,and better electrochemistry kinetics.It can be observed that the material performs better regardless of rate performance or cycle performance.（2）Based on the findings in the previous study,Na_0.67Mn_0.7Ni_0.3O₂ has superior cycle performance,but the electrochemically active Mn³⁺content is low due to the doping of excessive Ni²⁺ions,which sacrifices the specific capacity.Based on this,F-ion replaces a small part of O^2-,and the electrochemical activity of Mn element can be released through charge compensation.Research has found that F^-ion doping can form a more stable F-metal bond with metal,shrink the cell volume and increase the interlayer spacing;Increase the ratio of Mn³⁺and regulate the electrochemical activity of Ni²⁺/Ni⁴⁺and Mn³⁺/Mn⁴⁺redox couples;Interfere with the orderly arrangement of cations and enhance the structural stability of the material.By comparing the specific capacity,cycle stability and rate performance,it is found that when the fluorine content is 0.05（ie F-0.05）,it is the optimal ratio.The pre-sodiumized Mo Se₂/P-C is used as the anode to be matched and assembled into a full battery,showing good specific capacity and cycle stability.The material has the best performance in both electrochemical performance and kinetic performance.