Development of nanostructured alloy-based composite anode materials for lithium- and sodium-ion batteries
Lithium-ion batteries are the dominant energy storage technology in portable electronic applications due to their high energy density, long cycle life, and low self-discharge rate. Efforts to extend their implementation into rapidly growing electric vehicles and large-scale stationary energy storage devices require further improvements of performance and safety, as well as cost reduction. In this regard, the development of low-cost, advanced electrode materials for next generation lithium-ion batteries or sodium-ion batteries is increasingly being pursued to achieve these requirements. The purpose of this dissertation is to explore and develop several types of composite alloy-based anodes that can possibly lead to the enhancement of lithium- or sodium-storage performance. Alloy anodes have shown great potential for realization of high-performance lithium- or sodium-ion battery systems with enhanced safety as they offer high theoretical specific capacity and higher operating voltages than graphite. In addition, the successful employment of earth-abundant materials such as silicon and phosphorus could also result in a reduction in battery manufacturing cost. However, the major obstacles associated with the large volume change upon electrochemical reactions give rise to severe capacity fading in the first few cycles, making their implementation into commercial cells quite challenging. In order to overcome this issue, the alloy-based composite anodes are synthesized by applying the active/inactive matrix concept. The composites are capable of possessing the following advantages: (i) structural reinforcement and suppression of particle agglomeration upon cycling through a mechanically durable buffer; (ii) enhanced electrochemical reversibility and fast electrode kinetics through nanoscale active materials; (iii) high conductivity and facile electron transport through a conducting phase; (iv) high chemical and electrochemical stability through an electrochemically inert buffer. Moreover, the composites synthesized have reasonably high tap density that is beneficial for improving the volumetric capacity of lithium- or sodium-ion cells. In this dissertation, three different low-cost alloy-based composite anodes are developed by a low-cost, facile, and scalable high-energy mechanical milling: silicon-, zinc-, and phosphorus-based composites. All the composite systems studied in this work demonstrate enhancements in lithium- or sodium-ion storage performance in terms of high capacity, long cycle life, and high rate capability, while maintaining high tap density. By controlling the type and amount of an inactive matrix, the effects of each inactive matrix on the electrochemical performance of the composite anodes are investigated. In addition, the mechanism for the performance improvement is discussed.