Abstract:

Lithium cobalt oxide has a theoretical capacity of up to 274 mA·h/g and it is one of the earliest commercialized cathode materials for lithium-ion batteries.However，the instability of the layered structure of lithium cobalt oxide at high voltage makes it difficult for its actual charging voltage to exceed 4.45 V（vs.Li），thus greatly limiting its capacity.In response to the above problems，the method of co-doping with small-radius aluminum ions and large-radius zinc ions was used to improve the structural stability of lithium cobalt oxide cathode materials at high voltage.High-resolution transmission electron microscopy and X-ray diffraction proved that Al-Zn co-doping could increase the interplanar spacing of lithium cobalt oxide.The scanning electron microscopy-element distribution analysis proved the uniform doping of Al-Zn.And the electrochemical impedance spectroscopy proved the inhibitory effect of co-doping on interfacial side reactions.The results showed that the electrochemical stability of lithium cobalt oxide at high voltage could be effectively enhanced by regulating the crystal structure and interfacial side reactions.Through the assembly of soft-pack metal lithium batteries，it was found that the Al-Zn co-doped lithium cobalt oxide cathode material has a charge and discharge specific capacity of 218.8 mA·h/g at a charge cut-off voltage of 4.6 V and a rate of 0.2C.The capacity retention rate could reach 83.3% after 600 cycles，and its comprehensive electrochemical performance was much higher than that of aluminum-doped and unmodified lithium cobalt oxide cathode materials.

Key words: lithium-ion batteries, LiCoO₂, high voltage, Co-doping, cathode materials