Controllable Preparation Of Hierarchical Transition Metal Oxide Architectures And Their Lithium Ion Battery Performance

Lithium ion batteries (LIBs) are widely used in many portable electronics such as laptops, mobile phones and cameras. In response to the needs of modern society, it is essential to constitute low-cost、environmentally friendly energy storage system with high energy density and power density. And the innovative electrode materials hold the key to the new generation LIBs. This dissertation focused on the controllable preparation of hierarchical structured NiCo2O4 and LiNixCoyO2 and their LIBs performances. The main results are summarized below.1. The controllable preparation and LIBs performances of hierarchical NiCo2O4 architectures. We have prepared four NiCo2O4 samples with microflower-like, urchin-like, random packed nanosheet and granular particle morphologies by adjusting the precipitators in the precursor synthesis. The microflower-like NiCo2O4 delivers a discharge capacity of 1300 mA h g-1 in the first cycle and of 376 mA h g-1 after 20 cycles at a current density of 0.1 A g-1. In contrast, the granular NiCo2O4 particle shows the discharge capacity of 1096 mA h g-1 in the first cycle and of 112 mA h g-1 after 20 cycles. The microflower-like NiCo2O4 shows superior performance to granular particle counterpart, suggesting the advantage of hierarchical structure in energy storage.2. We report the first synthesis of 3D porous sphere-shaped hierarchical LiNixCoyO2 (h-LNCO) materials synthesized by lithiating porous mesostructured nickel cobaltite precursors via a solid state reaction. It exhibits 214 mA h g-1 at current density of 0.1C, and can still deliver a capacity of 144 mA h g-1 after 300 cycles. At high rate of 15C, the h-LNCO can still deliver a capacity of 101 mA h g-1. The superior performance of the h-LNCO material to the p-LNCO counterpart is attributed to the unique porous mesostructured morphology. First, h-LNCO possesses porous structure and relatively large surface area, which is beneficial to electrolyte penetration and provide more contact areas with electrolyte. Second, h-LNCO comprises primary particles with relatively small size and abundant exposed surfaces in favor of Li+ intercalation/deintercalation, which facilitates the Li+ ion diffusion in the material. Third, the mesoporous structure of h-LNCO can endure the volume change resulting from the Li+ insertion/deinsertion, and thus retain the 3D hierarchical mesostructures after cycling, which contributes to the excellent capacity retention and cycling performance. The synergism of these merits endows the h-LNCO with much improved performance as the cathode for LIBs.