Surface modification and doping effects on the electrochemical performance of cathode materials(LiFePO4, LiMn2O4, and LiMn1.5Ni0.5O4) for large size Li-ion batteries

Abstract

The development of improved lithium-ion battery system is critical for advancements in a variety of applications ranged from consumer electronics as small-size lithium-ion batteries to electric vehicles and energy storage systems as large-size lithium-ion batteries. The improvement of battery performance depends on the development of materials for the various battery components. Especially, cyclic performance, rate capability, and energy density of lithium-ion batteries are strongly controlled by characteristics of cathode materials. Commercial lithium-ion batteries are mostly composed of a layered LiMO2 (M ≡ Co, Mn, and Ni) positive electrode, graphite negative electrode, and moderate electrolyte compatible with both electrode materials. However, the lithium-ion batteries are not appropriate for the large-size systems due primarily to the poor thermal stability and low kinetics of cathode material LiMO2. In particular, the thermal/structural instability of LiMO2 could lead to lithium-ion battery explosion at elevated temperature. For this reason, new type of positive electrode materials such as LiFePO4, LiMn2O4, and LiMn1.5Ni0.5O4 have been considered as one of the most attractive positive electrode materials for large-size lithium-ion batteries because of their remarkable thermal/structural stability in severe environments. However, the promising candidates of the positive electrode materials for large-size batteries also have disadvantages as follows: (1) low energy/power density of LiFePO4, (2) poor cyclic performance at elevated temperature resulting from the Mn2+ dissolution of LiMn2O4, and (3) formation of impurity phase and structural instability during cycling of LiMn1.5Ni0.5O4. In this study, we made an effort to solve the problems of LiFePO4, LiMn2O4, and LiMn1.5Ni0.5O4 by following strategies: (1) fabrication of graphene embedded LiFePO4 using catalyst assisted assembly method, (2) Al2O3 coating on LiMn2O4 by electrostatic attraction forces betwee...