Preparation And Modification Of Lithium-rich Manganese-Based Cathode Materials

Lithium-ion batteries have developed rapidly due to their high energy density,no memory effect,long cycle life,and small self-discharge.After half a century of development,lithium-ion batteries have played a major role in electronics,power vehicles,and energy storage.Among the many lithium ion battery cathode materials,the ternary manganese-based cathode material consisting of x Li₂Mn O₃·?1-x??Li MO₂??0<x<1,M=Ni,Co,Mn??NCM?is become a research hotspot by high capacity,but its low cycle stability and first coulomb efficiency have become bottlenecks limiting its widespread application.Among the ternary materials composed of Ni,Co,and Mn,the ratio of Li₂Mn O₃and the composition of M are highly selective.In this paper,lithium-rich manganese-based cathode materialswithdifferentproportionsofLi_1+y[Ni_0.3Co_0.1Mn_0.6]_1-yO₂(x Li₂Mn O₃·?1-x?Li Ni_0.3Co_0.1Mn_0.6O₂)were studied.A systematic study on different lithium-rich and carbon material composites and Li₂Mn O₃composites was carried out.Firstly,the electrolytic manganese anode mud produced by the electrolytic manganese industry was used as raw material,and the Mn source was obtained by purification and disproportionation.After the calcination,the dense structure of the anode mud was destroyed,and the lead migrated from the solid phase to the liquid phase in the leaching system.The macroscopic kinetic equation for the leaching process of lead in electrolytic manganese anode mud was determined by leaching experiments.Lithium-rich manganese-based cathode materials with different lithium content y were prepared by two-step pre-firing-baking method.The effects of different lithium-rich y on SEM,XRD,AAS,particle size and electrochemical properties of cathode materials were investigated.The optimum lithium enrichment was determined to be 20%.When y=20%,the crystal form of the material is relatively complete and the size is more uniform.XRD shows that the synthesized cathode material belongs to the hexagonal system and exhibits?-Na Fe O₂layered structure.The AAS test shows that the material element content is close to the theoretical value.When y=20%,the material showed the best performance,the first discharge specific capacity reached 138.9m Ah/g,the discharge specific capacity after 50 cycles was 122.1m Ah/g,and the capacity retention rate was 87.9%.The retention ratios of discharge specific capacities at a rate of 0.5C,1C,2C,and 5C were 65%,53.2%,38.5%,and 22.7%.The effects of different carbon materials,proportions of carbon material,calcination time on material structure and electrochemical properties were investigated.The lithium-rich manganese-based cathode material was modified by three kinds of carbon sources:glucose Glu,phenolic resin PF and conductive graphite SAG.The best carbon source was phenolic resin PF,the optimum coating amount was 3%,and the best calcination was carried out.The time is 2h.Under the optimal conditions,the first charge specific capacity of the material reached 263.9m Ah/g,the discharge specific capacity reached 158.5m Ah/g,and the first coulombic efficiency was 60.1%.The capacity retention of the material after 50 cycles was 96.1%,which was significantly higher than that of the unmodified LMO cathode material of 88.1%.In addition,after 0.5C,1C,2C,5C rate,the higher capacity can be restored at 0.1C rate,and the capacity retention rates of materials at different magnifications are 72.9%,59.7%,46.4%,26.5%.Due to the coating of the carbon material,the electron and charge conductivity of the LMO material are increased,which facilitates the rapid migration of Li⁺.The effect of 1%,3%,5%coating of Li₂Ti O₃on the structure and electrochemical properties of the material was investigated by using Li₂Ti O₃coated modified cathode material?LMO?.The optimum coating amount was determined to be 3%.The structure of the material after coating modification has not changed significantly.The specific charge-discharge capacity decreases for the first time.It may be that Li₂Ti O₃has poor conductivity.With the increase of coating amount,the electrode polarization increases correspondingly,which is not conducive to the improvement of comprehensive electrical properties of the battery.Cyclic performance tests showed that the capacity retention of Li₂Ti O₃-3%material after 50 weeks of cycling was 158.8%,much higher than 94.9%of LMO materials.In terms of rate performance,the capacity retention rate of the material after Li₂Ti O₃coating is improved,but the retention rate decreases at high rate.It may be that Li₂Ti O₃is a fast ion conductor,but the conductivity is poor.