Controllable Preparation And Modification Of Na_0.67Ni_0.33Mn_0.67O₂ Cathode Materials For Na-Ion Batteries

P2-type layered metal oxides have become one of the most studied cathode materials for sodium ion batteries because of its high-capacity density,high operating voltage and simple synthesis process.However,the materials have an irreversible phase transition process during charge and discharge,which seriously hinders their development.In this paper,Na_0.67Ni_0.33Mn_0.67O₂,which has good air stability,high working voltage and high theoretical specific capacity is used as the matrix material to exploration the effects of raw material,component,synthetic process,morphology and use conditions on the structure and electrochemical properties of materials.The specific research contents are as follows:（1）In order to explore the effect of process conditions on Na_0.67Ni_0.33Mn_0.67O₂ cathode materials,research on different solid-phase reaction temperatures（750℃,800℃,850℃）and different sodium sources（Na₂CO₃,Na OH）.With Na₂CO₃ as raw material,the samples prepared by calcination at 800℃have smooth surface,more obvious polygonal layered structure,higher purity and crystallinity.In addition,under the voltage range of 2.0-4.5 V,the reversible capacity of this material reaches 165 m Ah g^-1 for the first time,but after undergoing an unfavorable phase change at 4.2 V,the capacity drops very rapidly,and the retention rate after 100 cycles is only 39.3%.Under 2.0-4.0 V,the first reversible capacity is only 97 m Ah g^-1,but the capacity retention rate after 100 cycles reaches 86.4%.（2）A series of Na_0.67Ni_0.33-xCu_xMn_0.67-yTi_yO₂（x=0,0.07,0.14,0.21;y=0,0.05,0.10,0.15,0.20）materials were synthesized,which Na_0.67Ni_0.19Cu_0.14Mn_0.52Ti_0.15O₂ cathode material exhibits a good cycling stability and rate performance at a high voltage of 4.5 V.The reversible capacity at 5 C reaches 93 m Ah g^-1.With the increase of Ti/Cu content,the modified cathode material gradually disappeared at the voltage platform of 4.2 V,indicating that the phase change of the material was suppressed to a certain extent.And the redox of Cu²⁺/Cu³⁺had a certain contribution to the capacity,its first discharge capacity up to 153.2 m Ah g^-1,and at 0.5 C its capacity retention rate increased to 76.2%after 100 cycles.（3）A series of hollow micro spherical Na_0.67Ni_0.33Mn_0.67-0.75xAl_xO₂（x=0,0.05,0.10,0.15）materials were synthesized used template method.The effect of aluminum doping on the structure and battery performance of the cathode material of Na_0.67Ni_0.33Mn_0.67O₂ were further studied.It was found that the samples doped with aluminum showed good cyclic stability.The cathode material with hollow microsphere structure has a higher capacity at 2.0-4.0 V,which the first reversible discharge capacity at 0.1 C reaches 128 m Ah g^-1,and the capacity retention rate was 86.8%after 150 cycles at 0.5 C.