Preparation And Modification Of Cathode Materials For Ni Fe-based Sodium Ion Batteries

Due to the wide distribution of raw materials,low price and high specific capacity,the cathode material of nickel-iron-manganese-based sodium-ion batteries have become a research focus in recent years.This has also become a bottleneck restricting its commercial development.Doping and coating are considered to be effective means to improve the electrochemical performance of materials.As far as coating is concerned,the ideal coating material should have a certain ionic conductivity and electronic conductivity.Different from the traditional"interstitial,vacancy"ion transport mechanism,the plastic crystal rotor phase has higher ionic conductivity due to the coupling mechanism between the rotation of the anion group and the cation diffusion.As far as the coating route is concerned,the traditional coating route is usually a two-step method.From the synthesis of the material to the combination of the coating material and the matrix material,two steps heat treatments are required.The cathode electrode material will inevitably come into contact with air during the coating process,causing material failure and making the coating more than the loss.In particular,the synthesis conditions of Na_3-3xAl_xPO₄ are similar to the coprecipitation-solid reaction.Therefore,Na_3-3xAl_xPO₄ was introduced as a coating material to carry out a one-step in situ coating experiment.The results show that this method is feasible,and during the sintering process,part of the aluminum ions enter the bulk phase,and part of the sodium ions in the bulk phase are"extracted"to form a sodium-deficient transition layer.The outer layer of high ionic conductivity Na_3-3xAl_xPO₄ coating layer,the middle transition Na-deficient layer,the innermost layered structure of the unique"sandwich"interface structure.This greatly improves the interfacial properties,so that the modified material has excellent kinetic properties,and still has 88%retention rate of the original capacity at 5C.In the full battery with hard carbon negative electrode,the cycle life is improved compared to It tripled before sex,and still had a 70%capacity retention rate after 500cycles at 1C.In this work,a simple and efficient material modification idea is proposed,which significantly improves the electrochemical performance of the material.Mn³⁺will deteriorate the nickel-iron-manganese-based cathode material due to the"Jahn-Teller effect"and the possible disproportionation reaction.Al doping can stabilize the bulk lattice.The nickel-iron-aluminum-based cathode material that completely replaces Mn with Al is expected to solve this problem.Problem,the preparation experiment of NFA602515 was carried out,but its electrochemistry did not meet expectations.Its performance needs to be further optimized.