Advanced materials for solid state batteries

Abstract

Lithium/sodium-ion batteries, recognized for their superior features, have emerged as predominant power sources to maintain reliable and continuous power supply. Researchers are intensifying efforts to advance wearable energy storage devices to enhance breathability and user comfort while ensuring comparable performance during dynamic physical activities. The widespread adoption of wearable devices often faces challenges due to reliance on conventional rigid batteries, limiting device functionality and user comfort. To address this, the first part of this thesis introduces a novel "holey" battery design, offering breathable and deformable power sources with high energy density and fabrication simplicity. Utilizing the Finite Element Method, this innovative design incorporates a strategic array of holes within a standard pouch cell framework, enhancing battery breathability and stretchability. The battery demonstrates robust electrochemical performance even under 10% stretching deformation and 180° folding. This scalable and commercially viable approach represents a significant advancement in integrating comfortable, high-performance batteries into wearable electronics.Simultaneously, to tackle safety risks associated with liquid electrolytes, which are explosive and prone to leakage, attention is shifting towards Solid State Electrolytes (SSEs) as a promising alternative, offering high energy density and enhanced stability. This thesis discusses two oxide-based ionic conductors: lithium-ion conductor, Lithium Lanthanum Zirconium Oxide (LLZO), and sodium-ion conductor, β″-alumina. LLZO is a compelling candidate for next-generation batteries due to its exceptional ion conductivity, stability, and compatibility with lithium metal electrodes. The thickness dependence of the solid electrolyte on the internal resistance and energy densities of All-Solid-State Lithium Batteries (ASSLBs) makes employing thin films a promising approach. Therefore, large-area LLZO thin films of thickness 120 µm and 60 µm were fabricated using cost-efficient and straightforward fabrication methods, including the solid-state reaction method and tape casting. To enhance the density of these extensive films, Ultrafast High-Temperature Sintering (UHS) was applied, and the influence of the temperature profile and its uniformity on thin film sintering was explored. The protocol for temperature and time required to sinter thin films with a surface area of 2x8 cm2 and thickness of 120 µm was optimized through repetitive feedback screening. β″-alumina garners significant interest as a sodium ion conductor in advanced battery technologies due to its crystal structure, high ionic conductivity, wide electrochemical stability window, and chemical and thermal stability. However, sintering beta'' alumina requires a high temperature of around 1600°C, which can cause significant sodium loss and lead to detrimental phase transformations. To address this issue, the third part of this thesis discusses the synthesis of β″-alumina via Ultrafast High-temperature Sintering from cheap boehmite precursor to achieve β″-alumina with a purity and relative density of 95%.