Solid-Solid Interfacial Chemistry in Energy Storage and Conversion Systems

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The substantial growth of energy demand requires safe, large scale, and sustainable future energy conversion and storage devices, which are often made of solid materials. Poorly defined interfacial chemistries are likely the origins that hinder the performance and lifetime of these devices. This proposal addresses the fundamental processes at interfaces of the next-generation energy devices-all-solid sodium-ion batteries and perovskite solar cells. We combine electrochemistry with multi-disciplinary spectroscopic and microscopic analysis to interrogate chemistry occurring at electrode and solid-electrolyte (or Perovskite) interface, particularly during device operation. Perturbations allow for explicit interpretation of interfacial chemical identity at different stages of device operation. The long-term objective is a thorough understanding of the structure-property relationship at the solid-solid electrochemical interfaces, and ultimately combine material synthesis and processing to enable optimized interfacial design for promoted device performances. We initiate this research program by developing in-situ measurement tools to realize two short-term objectives. 1. Control the electrode/electrolyte interface for All-solid Sodium Battery (ASSB). ASSB utilize abundant resources and improve battery safety. Degradation at the solid electrolyte (SE) and electrode interface hinders the battery cycle life. The identity and transformation of the SE/electrode interface during cycling remain elusive. We will investigate the (chemical and mechanical) stabilities of sodium thiophosphate solid Na-ion conductor- a potential solid electrolyte material for ASSB-at the electrode surfaces during battery operation. This work will reveal the mechanisms of interfacial decomposition that associated with battery shorting and capacity fade. These implications will guide the molecular design of stable SEs or interfacial protection materials, and shed light on interfacial engineering protocols. 2 Understand Hysteresis of Perovskite Solar Cell (PSC). Perovskite solar cells show outstanding energy conversion efficiencies. Structural origins of device hysteresis remain unclear. Device stabilization is highly desired. We will implement our expertise in in-situ interfacial characterization and interrogate the two potential reasons for the device hysteresis: (1) interfacial charge trapping due to Perovskite/oxide interaction and built-in potentials, and (2) ion mobility in Perovskite structure under electrical potential. Results will provide insights into the material and interface design for high-performance PSCs with excellent stability. The in-situ interfacial measurement methods developed in this program will serve as a transportable platform to study other next-generation energy devices such as high energy solid state batteries (multivalent batteries), lead-free PSCs, and other emerging energy storage and conversion systems.