Research On Preparation And Modification Of Li-rich Cathode Materials For Li-Ion Batteries

Li-and Mn-rich cathode materials have attracted more and more attention due to their high specific capacity（≥250 m Ah/g）and abundant raw materials.However,the poor structural stability and low ionic conductivity of Li-and Mn-rich cathode materials lead to discharge capacity and voltage fading,low rate performance and poor safety performance in charge and discharge cycle,which hinder the practical application of Li-and Mn-rich cathode materials.In this paper,the effects of calcination temperature and calcination time on the electrochemical properties of Li-and Mn-rich cathode materials were explored.Then,spinel phase was induced on the surface of Li-and Mn-rich cathode materials by glucose treatment,and graphene was coated on the surface of the materials after treatment.The effects of spinel phase introduction and graphene coating on the electrochemical properties of Li-and Mn-rich cathode materials were explored.（1）Calcination temperature and calcination time are one of the factors that affect the structure and morphology of the materials.Calcination temperature and time will affect the layered structure of Li-and Mn-rich cathode materials.When calcined at high temperature or for a long time,the primary particles of Li-and Mn-rich cathode materials are sintered and the secondary particles agglomerate more.Under the appropriate calcination temperature and time,the materials have better structure and appearance,and coprecipitation method is used.The spherical precursor was synthesized.In order to solve these problems,Li-and Mn-rich cathode materials were synthesized by molten salt method.Samples calcined at 800℃,900℃and 1000℃for10 h and samples calcined at 900℃for 10 h,13 h and 16 h were prepared.Through characterization and analysis of the data,the electrochemical performance of the materials calcined at 900℃for 10 h was the best.（2）The poor rate performance of Li-and Mn-rich cathode materials is related to the inactive Mn⁴⁺ions and low ionic conductivity in Li₂Mn O₃ composition.Li Mn₂O₄spinel has good structural stability and three-dimensional Li⁺diffusion channel.Glucose modification induces the formation of Li Mn₂O₄ spinel phase on the surface of Li-and Mn-rich cathode materials,which can improve the structural stability and ionic conductivity of the materials.The results show that the sample with 10%glucose to active material ratio has the best electrochemical performance,and the discharge capacities at 1 C and 2 C are 193 m Ah/g and 147.7 m Ah/g,respectively after 100 cycles,the capacity retention rate was 98.4%.（3）The conductivity of Li₂Mn O₃ component in Li-and Mn-rich cathode materials is low,and the ion transport performance of monoclinic phase is poor,which makes Li⁺diffuse slowly in the composite cathode materials,resulting in poor rate performance of Li-and Mn-rich cathode materials.After graphene coated with glucose surface treatment,the charge transfer resistance of Li-and Mn-rich cathode materials is reduced,and the performance is significantly improved at high rate.The discharge capacity of Li-and Mn-rich cathode materials coated with glucose is 200.1 m Ah/g and 172 m Ah/g at 1 C and 2 C.