Synthesis Of Chain-structured Li₄Ti₅O₁₂/C And Electrochemical Performance Of LiMn₂O₄/Li₄Ti₅O₁₂ Lithium Ion Battery

Lithium ion battery was considered as a promising energy to use in electric vehicles (EV) or hybrid electric vehicles (HEV) to reduce the oil or coal consummation et al. Because of its high power, high energy, long cycle life, nontoxic, and no memory effect et al. Material is one of very important effects lihium-ion battery for EV or HEVs, therefore, the material with lower cost, higher potential, higher energy, safer and lower cost for the large scale applications. However, the commercial LiCoO2has not been satisfy the requirement for the EVs or HEVs, due to it possesses high cost and the structure always transforms during the charge/discharge process. And the commercial graphite neither satisfy the requirement, owing to the low lithium intercalating voltage of approximately0.1V (vs. Li/Li+) to form SEI film on the surface and deposit on the surface of electrode particles and react with the electrolyte to form dendritic lithium during the fast charge rate, resulting in safety issues. Therefore, LiCoO2/graphite lithium ion battery was formed the cathode LiCoO2combined the graphite anode material can not satisfy the requirement for large scale application.The materials possess higher voltage, higher energy, lower cost, non-toxic, safer attracted much attention for the large scale application. The LiMn2O4was considered as a promising cathode material for EVs or HEVs, due to it has high potential (4.0V versus Li+/Li), low cost, nontoxic, safety and prolonged life-cycle et al. and the Li4Ti5O12anode material not only exhibits excellent reversibility, structure stability, higher Li intercalation voltage (1.55V versus Li+/Li), but also possesses low cost, nontoxic, safety et al. However, the low electronic conductivity is limited the electrochemical performance. Therefore, synthesis and modification the anode Li4Ti5O12in this paper, and then Li4Ti5O12/C combined with LiMn2O4cathode material to form LiMn2O4/Li4Ti5O12/C lithium ion battery. Study the electrochemical performance of the anode material Li4Ti5O12and the LiMn2O4/Li4Ti5O12lithium ion battery, and the conclusions were obtained as follows:1. The chain-structured Li4Ti5O12/C composite was prepared by sol-gel assisted filter paper method at850℃for6hours and characterized by XRD, SEM, TEM. The results show that the chain-structured Li4Ti5O12/C material has cubic spinel crystalline structure and the morphology is smooth, and a4nm-thick carbon film is uniformly coated on the surface of Li4Ti5O12, The particles size of the composite was250nm, and the chain composed of several grains extends1-3μm. The electrochemical performances were examined by charge/discharge cycling, impedance techniques and cyclic voltammetry. The results show the initial discharge capacity of the pristine Li4Ti5O12/C can reach165.1mAh g-1at0.2C,110.3mAh g-1at12C, respectively, and the capacity can retain89%after470deep cycles at5C, demonstrates that the chain-structured Li4Ti5O12/C exhibits excellent rate capability and cyclying performance.2. The Li4Ti5O12/C was prepared by starch sol assisted rheological phase method using inexpensive raw material starch. The physically characterized of Li4Ti5O12/C power was characterized by XRD, SEM, TEM and TG. The results show that the carbon coating does not affect the crystal structure, and the space group is Fd3m, and a5nm-thick carbon film uniformly coated on the surface of the Li4Ti5O12with particle size about500nm. The electrochemical performance of Li4Ti5O12/C was tested and the results indicate that Li4Ti5O12/C presents an excellent cycling stability, high capacity and long life, compared to the pure Li4Ti5O12.The initial discharge capacity of Li4Ti5O12/C composite is171.5mAh g-1at0.2C and110mAh g-1at20C, respectively. The capacity retention was at87%(500cycles at1C) and73.0%(2000cycles at20C) of initial discharge capacity with high cycling stability, indicating promising high rate performance anode materials for lithium ion battery in EV or HEV.3. The commercial LiMn2O4was characterized by XRD, SEM, and granularity analysis, charge-discharge cycling, impedance techniques and cyclic voltammetry. The results show that the LiMn2O4material has cubic spinel crystalline structure with average particles size of275nm, the electrochemical performance indicates that the LiMn2O4not only exhibits two discharge voltage plateaus at4.0V and4.1V, but also show excellent rate performance at different rates. The initial discharge capacity of LiMn2O4composite is116mAh g-1at0.5C and68mAh g-1at20C, respectively. After500cycles at1C, the capacity remains66%of its initial value.4. The electrochemical performance of LiMn2O4/Li4Ti5O12lithium ion battery was examined by charge-discharge cycling, electrochemical impedance spectroscopy and cyclic voltammetry. The results show the cell has two voltage plateaus about at2.5V, and the initial discharge capacity is113.1mAh g-1at0.5C and67.1mAh g-1at12C, respectively. The initial discharge capacity is87.1mAh g-1at6C, and its capacity retention is97%after85charge/discharge cycles. After475cycles at higher rate12C, the capacity with a loss only0.0568%per cycle, indicating the excellent high rate capability and cycle performance. The results demonstrate that the LiMn2O4/Li4Ti5O12lithium ion battery with excellent rate capability and electrochemical performance for EVs or HEVs.