Aerosol-assisted synthesis of metal compound-based anode materials for rechargeable batteries

Abstract

Lithium and sodium ion batteries have used as energy storage systems for various applications thanks to high energy densities and no memory effect. To improve battery performances, metal compounds having numerous nanoscale structures are considered promising anode materials thanks to their theoretical capacities. Nanostructures composed with nanoparticles provide excellent properties such as short diffusion distances and large reaction areas for anode materials for rechargeable batteries. In addition, nanostructures can efficiently control the problem of volume change occurring in charge and discharge processes, resulting in excellent cycle performances. This dissertation introduces the design and synthesis of various metal compound-based nanostructures prepared by spray pyrolysis processes and describes their enhanced electrochemical properties. First, metal sulfide microspheres with a yolk-shell structure were synthesized and the sodium ion storage capacities of the synthesized material was evaluated. The yolk-shell structured metal sulfide microspheres having a unique structure of material@void space@material showed high reversible capacities and stable cycle performances due to short diffusion distances and internal void spaces for volume expansion of electrode materials. Second, the carbon nanotube(CNT)-metal oxide composite powder was synthesized in a few seconds by spray pyrolysis using an aqueous solution containing polystyrene, CNT and metal salts. Inside the reactor, polystyrene formed macropores and metal salts changed to metal oxides through thermal decomposition. CNTs were uniformly distributed in the generated metal oxides, and the CNT-metal oxide composite synthesized as an anode material for lithium-ion batteries exhibited excellent electrochemical characteristics thanks to excellent conductivity of CNT and macropores in the composites. Third, lithium ion conductive glass powder composed of Li, Ge, B, and O components was rapidly synthesized in the form of a spherical powder having uniform shape and composition inside the reactor. The prepared lithium ion conductive glass was capable of effectively storing lithium ions. Finally, a metal phosphide/graphene (=reduced graphene oxide, rGO) composite powder was prepared by a spray pyrolysis and subsequent phosphorization proecesses. In order to solve the problem of volatility of phosphorus, vacuum-sealed ampoule was used. The metal nanocrystals-graphene composite powder prepared by a spray process was reacted at high temperature in an ampoule vial to form a uniform metal phosphide-graphene composite. The nanostructured metal compounds introduced in this dissertation have shown excellent electrochemical properties such as fast charge and discharge characteristics and stable cycle life. In addition, the direction of development of new materials using spray pyrolysis process is suggested and prepared functional materials can be applied to various fields including lithium and sodium secondary batteries.