Preparation And Performance Studies Of Layered Lithium-enriched Manganese Materials

With the huge demand for energy storage devices of electronic products and new energy vehicles,high-performance lithium-ion batteries have become a hot topic of research.Li-rich layered oxides(LRLO),with the general formula xLi2MnO3·(1-x)LiMO2(M=Ni,Co,and Mn,etc.),is a novel high-capacity high-voltage cathode material,and has a good commercial prospects in the future.However,its large-scale production and commercial applications are still hindered by its own problems:the serious losses of first cycle irreversible capacity,poor rate performance,and voltage decay issues.For improve the above problems,first,this paper studied the influence of co-precipitation process parameters on the performance of lithium-manganese cathode materials,and optimized the process conditions.Second,a new organic co-precipitation method using 8-hydroxyquinoline as precipitant was designed to prepare LRLO,with the exploration of influence of process parameters on material properties and the determination of the best synthesis scheme.Third,Sb-doping Li1.2[Mn0.54Ni0.13Co0.13]O2 was achieved by using the best organic co-precipitation process conditions,with the determine of the optimum doping amount and the exploration of the mechanism of Sb3+ doping.Precipitation pH value and complexing agent ammonia of co-precipitation process mainly affect the dispersity and agglomeration degree of the synthesized precursor,and have little effect on the particle size of the material.The calcination temperature mainly affects the particle size of the synthetic material,with the higher temperature,the larger particle size of material.In contrast,the best process conditions for producing lithium-rich manganese cathode material as follow:In the liquid phase system with complexing agent ammonia,using sodium hydroxide as a precipitant,the co-precipitation reaction was controlled at a pH of 11 with continuous stirring;After aging for 24 h,the precipitate was collected and ground with lithium hydroxide;Then,the mixture was calcined at 450? for 6 hours and calcined at 850?for 12 hours to obtain the material.The first discharge specific capacity was 282.2mAh/g at 0.1C,with the Coulomb efficiency of 79.5%.The capacities at 1C,3C,and 5C rates were 205.3mAh/g,176.6mAh/g,and 146.2mAh/g,respectively,and the capacity after 1C cycling 100 times remained There was 191.5mAh/g,and the capacity retention rate was 94.6%.The initial discharge specific capacities at 1C,3C,and 5C rates were 205.3mAh/g,176.6mAh/g,and 146.2mAh/g,respectively.After 1C cycling 100 times,the capacity was still 191.5mAh/g,with the capacity retention rate of 94.6%.A new type of organic co-precipitation method was used to synthesize lithium-manganese-rich cathode materials.The prepared precursor were identified as having 8-hydroxyquinoline corresponding functional groups by infrared spectroscopy,which confirmed that the precursor is 8-hydroxyquinoline salt.The influence of organic solvents and calcinations on the properties of the material was studied,and the optimum synthesis process was determined as follow:Using 8-hydroxyquinoline as organic precipitant and glacial acetic acid as organic solvent,the precursor was prepared by organic co-precipitation,and was directly dried and ground,then carbonized at 300?for 18 hours,then calcined at 600? for 6 hours,and finally calcined at 850? for 12 hours at a heating rate of 3?/minute.Sb3+ doping L1i.2[Mn0.54Ni0.13Co0.13]O2 was achieved by using the best organic co-precipitation process conditions.Through characterization methods such as XPS,XRF and XRD,S it was confirmed that Sb3+ was doped into the interior of the material crystal.The crystal structures and electrochemical performance of the synthesized sample are the best when the optimum amount x of Sb3+ doping was 0.01.The initial discharge specific capacity was 298.2mAh/g.the first discharge specific capacities at 1C,3C,and 5C rates were 219.1 mAh/g,180.4mAh/g and 151.1 mAh/g,respectively.The specific discharge capacity was 209mAh/g after 100 cycles at 1C,with the capacity retention rate of 95.6%.The main reason of Sb3+ doping enhanced the electrochemical performance of lithium-rich manganese materials as follow:The substitution of Sb3+ for the main elements(Ni,Co,Mn)in the lithium-rich manganese material causes lattice distortions,which increased the lattice spacing,expanded the diffusion channel for lithium ion release/intercalation,increased the charge transfer capacity and the material discharge capacity,and improves the rate performance under the premise that proper doping amount ensures the structural stability.Meanwhile,defects formed in the crystal inhibit the transition from the lamellar phase to the spinel phase during the cycle,and enhance the structural stability during the long cycle of the material.