Transition metal oxides for battery applications

• Main Author: Huang, Bicheng
• Other Authors: Xu Zhichuan, Jason
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Materials::Energy materials; Science::Chemistry::Physical chemistry::Electrochemistry
• Online Access: https://hdl.handle.net/10356/161211
• Institution: Nanyang Technological University

Li-ion batteries that are used in our daily lives cannot satisfy the gradually increasing energy device demand. Next-generation battery techniques such as Li-S and Na-ion batteries may offer higher energy density and lower cost choices as alternatives to Li-ion batteries. Li-S batteries are raised to substitute commercial Li-ion batteries for their high energy density which is 5 to 8 times of commercial Li-ion batteries. Aqueous sodium-ion batteries are developed to substitute commercial Li-ion batteries for their low cost, high safety, and environmental benignancy. These next-generation battery techniques have their respective bottleneck for wider applications. Li-S batteries face the shuttle effect that would lead to capacity decay and even decrease the lifespan of the batteries. Aqueous sodium-ion batteries have a limited working potential window and limited electrode capacity which would lead to the low energy density of the batteries although the cost is low. To solve or relieve these problems, transition metal oxides have been recently studied as additives and electrode materials for these two battery techniques. Transition metal cations with redox ability can also contribute to promoting the polysulfides redox in Li-S batteries as catalysts. The variable valences are also good for sodium-ion insertion and extraction. Thus, a series of magnesium cobalt oxides are prepared and used in S cathode for Li-S batteries. The cobalt cations in the oxides can accelerate the kinetics of the redox while magnesium cations can make up the lithium polysulfides-affinity of cobalt oxides. Balancing the catalytic activity and the lithium polysulfides-affinity can be realized by adjusting the ratios of Mg to Co. In this way, the higher-performance additive for Li-S batteries is successfully found. With this additive, the cathode delivers 513.5 mAh/g at 0.2 C over 300 cycles which is 47% more than the control cathode. Meanwhile, another series of cathode additives are prepared by concentrated HCl washing incineration ash, which serves as the resource of metal oxides. After washing and pre-treatment, SiO2/Fe2O3/Fe3O4 composites are obtained. The transition metal, Fe, in the composites helps improve the cycling performances of the batteries. One of the samples can deliver 665.5 mAh/g at 0.2 C in the 100th cycle which was 100 mAh/g higher than the blank S cathode. For aqueous sodium-ion batteries, Na0.44MnO2 nanorods are prepared as cathode active materials. This particle size is tuned by controlling the ratio of surfactant to Mn atoms. It is shown that the smaller size of the active material could contribute to the higher sodium ion diffusivity of the electrode and the higher cycling capacity. The initial discharging capacity of Na0.44MnO2 nanorods cathode attains 60 mAh/g at 1 C and it can remain at 55 mAh/g after 200 cycles which is 37.5 % higher than Na0.44MnO2 bulk cathode. At 5 C, the discharging capacity of Na0.44MnO2 nanorods cathode reaches 53 mAh/g in the first cycle and maintains 47 mAh/g after 200 cycles which is 147 % higher than that of Na0.44MnO2 bulk cathode. In summary, the transition metal cations in Mg1-xCo2+xO4 samples and SiO2/Fe2O3/Fe3O4 composites contribute to catalytic activity for polysulfides redox and polysulfides affinity of the electrodes and thus improve the electrochemical performances of Li-S batteries. The nano-sized transition metal oxides, Na0.44MnO2 nanorods enhance the Na-ion diffusivity of the electrode and improve the cycling performances of aqueous Na-ion batteries.