Investigation Of Electrode Materials For Lithium-ion Batteries:Li_1.20Ti_0.44Cr_0.36O₂ And MoO₂

Layered Li-Ti-Cr-O cathode has a characteristic of multi-electron transfer, which results in high specific capacity. However, its cyclic performance is not satisfied. As anode materials, metal oxide MoO₂ has high specific capacity, but cyclic stability is poor. In this thesis, layered Li_1.20Tio.44Cr_0.36O₂ cathode and nanosized MoO₂ anode have been prepared by sol-gel, solid-state reaction and hydrothermal methods. In addition, carbon-coating and nitrogen treatments have been employed. The composition, micro structure, morphology of the electrode materials have been characterized. The electrochemical performance has also been evaluated. The conclusions are as follows:1. The initial discharge/charge capacities of the layered Li_1.20Ti_0.44Cr_0.36O₂/C are 217.1/141.6 mAh g^-1 at current density of 23 mA g^-1. The reversible capacity retention can reach 94% after 100 cycles, which is higher than Li_1.20Ti_0.44Cr_0.36O₂.2. The disorder degree of the cation layers in the layered Li_1.20Ti_0.44Cr_0.36O₂ increases with discharge/charge cycling, and reaches almost full disorder state after 100 cycles.3. The Li ion diffusion coefficient of Li_1.20Ti_0.44Cro.3602/C is higher and more stable than Li_1.20Ti_0.44Cr_0.36O₂.4. The cyclic stability of nitrogen-treated MoO₂ is higher than pristine MoO₂. However, the capacity is not satisfied. The charge/discharge capacities of MoO₂/C with 30.1 wt.% carbon content are 589.8/595.5 mAh g^-1 after 50 cycles. Its charge/discharge capacities can reach 519.4/524.5 mAh g^-1 at 1 C (838 mA g^-1).5. The discharge/charge capacities of MoO₂ increase with cycling and then decrease gradually, which may caused by transition of lithiation mechanism from the initial "insetion mechanism" to "conversion mechanism". The electrochemical inert Li₂MoO₄ formed during lithiation/delithiation cycling may result in the gradual decrease of the cyclic capacity.