IMPROVED ELETROCHEMICAL PROPERTIES OF SURFACE-COATED Li(Ni,Co,Mn)O2 CATHODE MATERIAL FOR Li SECONDARY BATTERIES

The surface of Li(Ni0.4Co0.2Mn0.4)O2 was coated with amorphous aluminum oxide using Al-isopropoxide. The effect of the surface coating on the cycling performance and high-temperature storage characteristics was investigated using coin-type cells. The surface-coated materials showed superior capacity retention at 55°C as well as at room temperature and limited impedance rise during high-temperature storage compared with the uncoated material. From the a.c. impedance measurement, it was found that the uncoated material exhibited very large increase in the cathode/electrolyte interfacial impedance during cycling whereas the surface-coated materials showed a limited increase in the interfacial impedance.