Design,Preparation And Sodium Storage Performance Of Na₄MnCr（PO₄）₃ Cathode Material

Compared with lithium-ion battery（LIBs）,sodium-ion battery（SIBs）has low cost and abundant resources,so it is considered as one of the ideal next-generation energy storage technologies,and has become the development frontier and research hotspot of energy storage equipment.Although great progress has been made in the research of phosphate poly-anionic sodium storage cathode materials,the vast majority of poly-anionic sodium storage cathode materials are 1～2 electron reaction,specific capacity is generally less than 130 mA h·g^-1,energy density is generally lower than 500 Wh·kg^-1,There is still a big gap between LiFePO₄(580 Wh·kg^-1),LiMn₂O₄(610 Wh·kg^-1)and LiCoO₂(750Wh·kg^-1).Therefore,Developing high energy cathode for sodium ions batteries（SIBs）that enables three-electron reaction is the most effective way to reduce high cost and solve range anxiety and safety hazards.A new NASICON carbon coated Na₄MnCr（PO₄）₃（NMCP@C）was synthesized as a high-energy cathode material for SIBS.For practical application,the whole battery system of NMCP@C//HC is also explored.Finally,considering the safety hazard of electrolyte leakage in traditional batteries and the problem of unstable decomposition of electrolyte under high pressure,the ceramic electrolyte plate with Na_3.3La_0.3Zr_1.7Si₂PO₁₂ and 3wt%Na₂B₄O₇ additive（NLZSP（NBO3））was selected to replace the traditional electrolyte.The electrochemical performance of NMCP@C//NLZSP（NBO3）//Na solid-state batteries was investigated.Specific research contents are as follows:（1）The sol-gel method was used to prepare nano-sized NMCP@C cathode materials successfully, ；and 700℃is the most suitable for the sintering temperature by comparing the XRD pattern and electrochemical properties of NMCP@C sintered at 650℃,700℃and 750℃.Subsequently,the influence of the internal carbon content on the electrochemical performance of NMCP@C was explored.The coating with different carbon content was achieved by controlling the ratio of citric acid to transition metal（CA:MI）.Finally,it was found that the electrochemical performance of NMCP@C was the best when CA:MI was 1.5（carbon content was 6.4wt%）.The as-prepared 6.4wt%carbon coated Na₄MnCr（PO₄）₃（NMCP@C）cathode annealed at 700℃delivers a high discharge capacity of 107.3 mA·h·g^-1 at 0.1 C,and well capacity retention of 69.3%after 500 cycles at 5 C within 1.4～4.3 V.Meanwhile,it can provide a high discharge special capacity of 164.3 mA·h·g^-1 at0.1 C within 1.4～4.6 V and an excellent energy density of 523.6 Wh·kg^-1.Besides,galvanostatic intermittent titration technique was employed to evaluate the reaction kinetics of NMCP@C cathode,high Na⁺ions diffusion coefficients(D_Na+,10^-12～10^-9 cm² s^-1)demonstrate the superior electrode process kinetics.（2）Using hard carbon as anode,the cathode and anode were matched according to the ratio of anode capacity=0.83,1,1.11,1.51,1.76.The cyclic performance and coulomb efficiency under each ratio were compared,and the optimal P/N was determined to be 1.51.Then,the anode was prenatalized by the anode formation method.The first coulomb efficiency of the whole battery after pre-natritization is increased from 40.1%to 81.3%,and the reversible specific capacity is increased from 41.8 mA·h·g^-1 to 102 mA·h·g^-1.At 0.2 C,the capacity retention rates of 1.4～4.3 V and 1.4～4.6V are 62.2%and 64.3%after 50 cycles.（3）In order to reduce the safety risks of battery applications and solve the problem of unsatisfactory NMCP@C cycle performance due to electrolyte decomposition under high voltage,Na_3.3La_0.3Zr_1.7Si₂PO₁₂with 3wt%Na₂B₄O₇ additive（NLZSP（NBO3））ceramic electrolyte was utilized to assemble NMCP@C//NLZSP（NBO3）//Na solid state sodium metal batteries（SSSMBs）for the first time,which revealed an initial discharge capacity of 99.1/121.7 mA h·g^-1 at 0.1 C and excellent cycling performance（capacity retention of 75.8/72.6%after 100 cycles at 0.2 C）with（1.4～4.3）/（1.4～4.6）V.We have successfully improved the cycle stability of NMCP@C,which also provides ideas and basis for the research and application of all-solid-state batteries.