Preparation And Modification Of Sodium Manganate As Cathode Material For Sodium-Ion Batteries

Sodium-ion batteries,following the same charge-discharge principle as lithium-ion batteries,are considered as a potential replacement for lithium-ion batteries because of their lower manufacturing cost.Due to the sodium manganese of layered transition metal is high theoretical specific capacity,its considered one to be the most potential cathode material for sodium-ion batteries,but the actual specific capacity is low,and cycle performance is also poor.Therefore,this thesis modified sodium manganate by the anions and cations co-doping method,discusses the influence of doping on the structure and electrochemical properties for the cathode materials,and using the surface coating strategy to improve the long cycle performance for doped cathode materials,the storage mechanism and dynamics of sodium-ion batteries were tested.This study mainly carried out the following aspects:（1）The sodium manganese of layered transition metal cathode materials was prepared by simple solid phase sintering method,studied the effect of increase temperature rate on the composition and electrochemical properties of cathode materials,and studied suitability of sodium manganate cathode material with different electrolyte was explored.When the increase temperature rate is 5℃/min,the sodium manganate cathode material is composed of NaMnO₂ and Na_0.7MnO_2.05,which shows good electrochemical properties.Using ester electrolyte to assemble NMO||Na half-cells,showing good long cycle performance.When the electrolyte is ester,showing good rate performance.（2）The increase temperature rate of 5℃/min prepared sodium manganate with ammonium acid fluoride and iron trichloride co-doping to obtain Na_0.7Mn_1-xFe_xO_2.05-yF_y new cathode materials.Through the characterization,it is known that a little amount of iron and fluorine can modify the cell,and P2 phase sodium manganate can be obtained.Co-doping of iron and fluorine help to improve the electrochemical properties.When the doping content of x=y=0.1,Na_0.7Mn_0.9Fe_0.1O_1.95F_0.1||Na half-cell reaches 193 mAh g^-1(current density is 20 mA g^-1);when the current density is 1000 mA g^-1,the reversible specific capacity is 114 mAh g^-1,indicating that the cathode material has excellent rate performance.Meanwhile,the cathode materials have excellent cycle stability.In addition,the test Na_0.7Mn_0.9Fe_0.1O_1.95F_0.1||HC full-cells found that have excellent energy density,indicating that it has a potential application value.（3）To further improve the electrochemical properties of the cathode materials,AlPO₄coating modification of Na_0.7Mn_0.9Fe_0.1O_1.95F_0.1 material,explore the influence of the coating content and the temperature of the preparation on the structure and electrochemical properties of the cathode materials,and the results show that the structure and morphology of the cathode materials are hardly affected.When the coating content is 2 wt%and the temperature of the preparation condition is 400℃,the 2 AlPO₄@Na_0.7Mn_0.9Fe_0.1O_1.95F_0.1 cathode materials have the best electrochemical properties.