Regulation Of Organic Interface And Electrochemical Performance Of Layered Cathode Materials For Lithium-Ion Batteries

Layered cathode materials are one kind of the most promising cathode materials for power batteries owing to their high energy density and high operating voltage.Nevertheless,during the charging and discharging process,both lithium-rich manganese-based layered materials and nickel-rich ternary ternary layered cathode materials suffer from the dissolution of transition metals,destabilized cathode/electrolyte interface and structural deterioration,leading to largely attenuation of capacity and voltage,and therefore hinders the commercial application of layered cathode materials.In order to modulate the cathode/electrolyte interface,Surface coating method was applied to construct a highly electronegative polymer coating layer on the surface of the layered cathodes,thus significantly improving the performance of materias.（1）A strong electronegative polymer coating layer was performed on the surface of Li_1.2Mn_0.53Ni_0.27O₂（LMNO）by in-situ solution polymerization.How the polymer layer effects on the structure and electrochemical properties of LMNO materials,and its effect mechanism on LMNO materials were detailly studied.The results show that the highly electronegative polymer coating layer is closely adhered to the surface of the cathode,which reduces the direct contact between the cathode and the electrolyte and suppresses the adverse side reactions of the cathode/electrolyte.Meanwhile,the catalytic activity of transition metal ions were weakened by the coordination of the electronegative group and the transition metal ions on the surface of LMNO cathode materials,which enhance the structural stability of cathode materials.The LMNO cathode coated with poly（acetoacetoxyethyl methacrylate）（PAAEM）exhibits excellent cycling stability with 82%capacity retention（the original selection is only 67%）.The first coulombic efficiency reaches up to 81.04%at 0.1 C rate.（2）Li Ni_0.6Mn_0.2Co_0.2O₂（NCM622）cathode modified by a strong electronegative polymer coating layer,which was constructed by isocyanoethyl methacrylate grafted polyethyleneimine（PEI-IEM）,was synthesized via in-situ solution polymerization.The results indicate that the organic coating layer and its synthesis process have no influence on the crystal structure of the material,and the thickness of the coating layer is about 12 nm.The organic coating layer with a large number of polar amino groups and ketoester groups not noly enhance lithium-ion transport,but also can coordinate with the transition metal ions of the NCM622 cathode material,which weakens the decomposition of the electrolyte catalyzed by transition metal ions,and thus enhances the interfacial stability and delays the structural degradation.Hence the material coated by PEI-IEM coating layer surface maintains the first discharge specific capacity of 173.2 m Ah g-1 and the highly coulombic efficiency of 88.1%at 0.1 C.The cathode coated with PEI-IEM coating layer has a high capacity retention rate of 81%after 300 cycles at 1 C.