High Nickel LiNi_0.8Mn_0.2O₂ Cathode Material Particle Size Regulation And Its Carbon Based Conductive Agent Modification Study

High nickel cathode materials have good application prospects with high specific capacity and low cost.However,their low electrical conductivity and complex phase transition seriously affect their electrochemical performance and hinder their commercialization.In order to solve the above deficiencies of high nickel layered cathode materials,this paper prepared high nickel layered cathode materials(LiNi_0.8Mn_0.2O₂)with different particle sizes by co-precipitation-high temperature solid phase method and airflow mill treatment,and investigated the mechanism of particle size on the performance of cathode materials,and also selected graphene and carbon nanotubes for conducting modification of the target cathode materials.SEM,XRD,TEM,Raman and XPS were used to characterize the structure and morphology of the material,and the electrochemical properties were analyzed and studied by CV and EIS using lithium metal flakes as counter electrodes,and the specific results are as follows:（1）LiNi_0.8Mn_0.2O₂（NM82）with different particle sizes were prepared by mixing and sintering different excesses of lithium hydroxide with precursors,mechanical crushing and water washing to investigate the effects of NM82 particle size and morphology on the electrochemical properties of the materials.The results showed that due to the small particle size of NM82-1.23μm,the cation mixing of Li⁺/Ni²⁺was reduced.Refinement of XRD tests using GSAS software revealed that NM82-1.23μm has a more stable structure and 2.05%cation mixing than the other two types of NM82with a larger particle size,and also exhibits relatively better cycling performance at 1C with a discharge specific capacity of 170.5 m Ah·g^-1 after 200 cycles.（2）Commercial graphene and LiNi_0.8Mn_0.2O₂ materials with different particle sizes were selected for ball-mill mixing to study the effect of graphene conductive agents on their electrochemical properties.The results showed that the appropriate amount of graphene（0.5-1 wt%）could enhance the conductivity of LiNi_0.8Mn_0.2O₂materials and their electrochemical properties were significantly improved,with the increase of graphene content,graphene tends to agglomerate and NM82-1.31μm-0.5wt%G has a fast lithium ion migration and low impedance,with a discharge specific capacity of 185.99 m Ah·g^-1 at 0.5C for 100 cycles;NM82-7.80μm-1wt%G has a discharge specific capacity of 172.49 m Ah·g^-1 at 0.5C for 100 cycles.,and the lithium ion diffusion coefficient is 9.13×10^-11 cm²·s^-1,with good material diffusion performance.（3）Carbon nanotubes and carbon nanotubes/carbon black component conductive agents were used to modify LiNi_0.8Mn_0.2O₂ with different particle sizes,and graphene/carbon nanotubes/carbon black conductive agents were applied to different particle sizes of LiNi_0.8Mn_0.2O₂ materials to make composite electrodes for electrochemical performance study based on the above work.The results show that the large specific surface area of small particle size materials can increase the contact area between the active material and electrolyte and promote the migration of lithium ions and electron conduction.the discharge specific capacity of NM82-1.31μm（CNT:SP=7:3）is 189.76 m Ah·g^-1 after 100 cycles at 0.5C.In the graphene/carbon nanotubes/carbon black composite electrode,its conductive network can reduce the polarization of the cathode material and accelerate the lithium ion migration;the discharge specific capacity of NM82-1.31μm at 0.5C after 100 cycles was 200.98m Ah·g^-1.