Ion Doping And Surface Coating Synergistically Modify Nickel-rich LiNi_0.6Co_0.1Mn_0.3O₂ Cathode Material

Nickel-rich layered cathodes LiNi_0.6Co_0.1Mn_0.3O₂（NCM613）are promising cathode materials because of their high energy density and low cost.However,they are facing problems such as short life and poor rate performance.In response to the above problems,this work prepared NCM613 cathode material modified by ion doping and surface coating,and studied the structural properties of the modified material and the electrochemical performance at high cut-off voltage.The main research content include:B³⁺doped and LiBO₂ coated NCM613 cathode material was prepared by solid state method.The effects of modification on the structure of NCM613 were studied by XRD,XPS,TEM and other characterization methods.The capacity retention of the optimized modified material LBO-0.4 is 94.8%after 100 cycles at 2.8-4.5 V and 1C,while the retention of the unmodified material is only 79.7%.At a high rate of 5C,LBO-0.4 can still discharge capacity of 100.5 mAh g^-1 after 1000 cycles and the retention is70.7%,which is much higher than that of the unmodified sample（less than 1%）.At the same time,B³⁺doping and LiBO₂ coating also improve the lithium ions diffusion coefficient,lower the impedance,and enhance the rate performance of the material.Sodium hypophosphite（NaH₂PO₂）is decomposed during heating to produce reducing PH₃ gas.In this work,the nickel-rich layered NCM613 material was modified by this property.The layered structure of NCM613 surface was reconstructed in situ and transformed into spinel and rock salt structure protective layer,and the lattice parameters are adjusted by phosphorus dopants.The heterogeneous structure protective layer formed in situ during the modification process is compatible with the layered structure of the material,and will not fall off during the cycle,which is beneficial to the long-term cycle stability of the material.The PO₄^3-doping and the spinel structure on the surface are beneficial to increase the lithium ions diffusion rate.Modified NCM613-0.3P and NCM613-0.6P exhibit the capacity retentions of 76.1%and 77.3%in the voltage range of 2.8-4.5 V,after 700 cycles at 1C,respectively,which are still higher than that of unmodified materials after 200 cycles,which is only 70.6%.And the NCM613-0.6P exhibits an impressive capacity retention of 98.0%after 350 cycles at5C,far superior to 25.7%of the pristine NCM613.