Study On High-voltage Electrochemical Performances Of Fe-/Al-modified Lithium Cobalt Oxides

LiCoO₂ cathode material has been used widely in lithium-ion batteries,however,if being charged and discharged under high voltage(above 4.5 V),its structure is easy to be collapsed,resulting in the degradation of cycle performance.In order to improve the structural stability of LiCoO₂ under high voltage,the Fe-/Al-modified LiCoO₂composite materials were prepared using a solid-phase-grinding-calcination method,and assessed the high-voltage electrochemcial performance,together with the structural characterization.The main research results are presented below.The modified lithium cobalt oxide composite materials were prepared using different amount of iron oxide,and assessed the electrochemcial performance under the conditions of 3-4.55 V,25?and 0.1 C.The optimal sample LCO-L-Fe-0.5%showed the specific discharge capacity of 210 m Ah g^-1,exhibiting the capacity retention rate of71.9%after 100 cycles at 1 C,whereas the unmodified LCO-L showed the retention rate of 43.7%.Characterized using XRD,SEM,TEM,XPS,etc.,it is indicated that Li Fe O₂ andCoFe₂O₄coating protection layer can be formed at the interfaces through iron oxide modification,and Fe³⁺can be partially doped into the LiCoO₂crystal structure.The optimal sample LCO-L-Fe-0.5%showed the lithium ion diffusion rate of9.372×10^-14cm² s^-1,higher than that of unmodified material,1.120×10^-14 cm² s^-1(LCO-L).The modified lithium cobalt oxide composite materials were prepared using different amount of aluminum metaphosphate,and assessed the electrochemcial performance under the conditions of 3-4.55 V,25?and 0.1 C.The optimal sample LCO-L-AP3-0.75%showed the specific discharge capacity of 188.9 m Ah g^-1,exhibiting the capacity retention rate of 77.5%after 100 cycles at 1 C.Characterized using XRD,SEM,TEM,XPS,etc.,it is indicated that a coating layer including Al₂Co O₄,Li₃PO₄and Al PO₄ can be generated at the interfaces after the aluminum metaphosphate modification,and Al³⁺can be partially doped into the LiCoO₂crystal structure.The optimal sample LCO-L-AP3-0.75%showed the lithium ion diffusion rate of 1.85×10^-13 cm² s^-1cm² s^-1.