Synthesis And Surface Modification Of High Specific Capacity Lithium-rich Cathode Materials

Lithium-rich manganese-based cathode material is a layered material that can meet the current goal of achieving a power density of 400Wh kg^-1for power batteries.It has ultra-high specific capacity(250?300m Ah g^-1),good thermal stability and safety,can make up for the shortcomings of current power batteries,and has broad application prospects in the application of electric vehicles and hybrid electric vehicles.However,there are many difficult problems in the material itself.For example,the first electrochemical activation process has a large irreversible capacity loss,an irreversible phase change occurs in the cycling process,chemical instability under high voltage,and poor rate performance,etc.,Limiting its practical application.In view of the shortcomings of the nature of lithium-rich manganese materials,the current main solutions include various forms of surface coating,ion doping of lithium sites and transition metal sites,halogen-doped oxygen ion sites that reduce oxygen reactions,and surface Modifications such as oxygen vacancies,protective surface phase change layers,etc.The purpose of this article is to prepare submicron-level lithium-rich manganese particles with high specific surface area,improve the rate performance and capacity by shortening the lithium ion transmission path and appropriately expanding the electrolyte contact area;by activating the material in advance,the surface oxygen vacancy is constructed To alleviate the phenomenon of oxygen desorption,inhibit phase transition and severe voltage decay.Main contents of the study are as follow:?1?In this paper,the nano-scale lithium ion battery cathode material Li_1.2Mn_0.54Ni_0.13Co_0.13O₂with high specific capacity was prepared by the sol-gel method.The effects of solution p H,calcination method,et al on the material were investigated from the perspectives of structure,morphology and electrochemical performance.The research results show that the over-addition amount of lithium salt is 5%,the p H of the salt solution is adjusted to 8.0,and the material obtained by calcination at 900?for 12h in the form of tablet has the best layered structure and cation mixing arrangement.By using conventional electrolytes and charging and discharging at a voltage range of 2.0 to 4.8 V at a rate of 0.1 C under controlled gel formation parameters and calcination cathode material's best sample has a first discharge specific capacity of 261.1 m Ah g^-1,the initial coulombic efficiency of80.8%,and a capacity retention rate of 88.1%after 50 cycles?2?The lattice deoxidation during cycling causes the elemental migration and internal local shrinkage and particle breakage of the particle surface caused by the transformation of the layered-spinel-rock salt phase,resulting in deterioration of cycle life and increased voltage attenuation,which severely limits its application.In this paper,we report a high-pressure and weakly carbonated environment made with supercritical CO₂that produces oxygen vacancies on the surface of lithium-rich manganese.HAADF-STEM and synchrotron radiation XRD showed that oxygen vacancies were uniformly formed on the surface of the particles at around 10 nm,but the overall structure did not change.Electrical performance tests show that supercritical carbon dioxide modification will not affect the specific discharge capacity of lithium-rich manganese materials for the first time,but the initial coulombic efficiency of the material is greatly improved to 95.3%,and the cycle stability is better.After 100 cycles,the voltage attenuation was reduced by 0.1V.After150 cycles,the reversible capacity of 220 m Ah g^-1was still maintained.The method is simple in operation and can be scaled up,and is a promising method for realizing lithium-rich manganese modification and batch application.