Preparation,Modification And Electrochemical Performance Of LiNi_0.6Co_0.2Mn_0.2O₂ As Cathode Material For Lithium Ion Batteries

Since the lithium-ion battery was first commercialized by Japan Sony Corporation in 1990,it will become an inevitable trend to use it as a high-energy-density power supply in electric vehicles and other fields due to its advantages of large energy density,long cycle life,and environmental friendliness.Therefore,the development of power batteries with high energy density is a key factor to promote the rapid development of hybrid electric vehicles and pure electric vehicles.However,the existing lithium ion battery system is difficult to meet the requirements of high energy density and safety performance of power batteries.According to energy=capacity?voltage,the optimal design and synthesis of high-capacity electrode materials is one of the effective ways to increase the energy density of power batteries,especially the evelopment and research of high-capacity cathode materials.The high-nickel ternary cathode material has a higher energy density advantage than lithium iron phosphate and lithium manganate.Herein,Li Ni_0.6Co_0.2Mn_0.2O₂is chosen as research object to improve its rate performance,cycle stability and heat stability is carried out from these three aspects:precursor synthesis,technology optimization,and modification:?1?With ethanol-water as the binary solvent system,the reaction kinetics of Ni,Co,Mn,and Li and their relative order of supersaturation are adjusted to promote the coprecipitation.With the optimization of the volume ratio of ethanol-water mixed solvent,reaction temperature and time,the final one-dimensional precursor for ternary cathode materials?NCM111,NCM622,NCM90505?was synthesized under the following conditions the volume ratio of ethanol to water was 4:1,the reaction temperature was ice bath,and the reaction time was 6 h.?2?The systematic research on key factors of precursor systhesis,such as sintering technology,reaction temperature and lithium salt ratio,was carried out.Combining the optimize sintering technology,reaction temperature and ratio of metal salt to lithium salt,the suitable preparation process was chosen:the ratio of metal salt to lithium salt n _TM:n _Li=1:1.15,pre-sintered at 450?for 8 h,and continued to be heated to 800?After roasting for 15 h,cooling to 500?within 240 min,then cooling to room temperature.The NCM622 cathode prepared by this process has a reversible specific capacity of 191.2 m Ah/g at a current of 0.1 C within a voltage window of 2.8?4.4 V.The first coulomb efficiency is 87.7%,and reversible specific capacities of 183.9,174.9,165.5,153.5 m Ah/g at 0.2,0.5,1 and 2 C,respectively,are achieved.After 100 cycles at 2 C current,it has a capacity retention rate of 81.0%.This NCM622 cathode has good kinetic characteristics,with a lithium ion diffusion coefficient of?10^-8 cm²/s.?3?The modification of NCM622 cathode with different boron sources?B₂O₃,H₃BO₃ and Li BO₂?was also carried out.The effect of different boron sources modification on the physical structure,cation mixing phenomenon,morphology and other physical properties of the cathode were studied.Further,the effect of boron modification on the long-cycle performance,rate performance and thermal stability at different voltages were explored.Through the addition of boron element,the capacity decay caused by the voltage drop and polarization is effectively suppressed.Besides,the cycle stability,thermal stability and rate performance are also improved.Within the voltage window of 2.8?4.5 V,H₃BO₃-modified NCM622 has a reversible specific capacity of 185.3 m Ah/g at a current of 0.1 C.It reaches the peak after 3 cycles of activation,and the specific capacity is close to 200 m Ah/g.The reversible specific capacity of197.9,188.2,179.8,170.4,154.5 m Ah/g at 0.2,0.5,1,2 and 5 C,respectively,are obtained.It has a capacity retention rate of 87.7%after 200 cycles at 1 C current.The B-modified NCM622cathode has good kinetic characteristics,with a high thermal decomposition temperature of 290.6?.