Collaborative Research: Tunable Control of Mixed Ionic and Electronic Conductivity through Ion Irradiation in Electroceramic Materials for Energy Storage System

NON-TECHNICAL DESCRIPTION: The goal of this foundational study is to significantly improve the performance of lithium ion batteries. These batteries are among the most promising energy storage technologies and are much needed for near-term growth of the renewable energy and electric vehicle markets. This project examines how electroceramic materials (used in batteries) can be intentionally altered by adding impurities or producing other defects. For electrode (i.e., anode and cathode) materials, conductivity is critical for high energy and high-power lithium ion batteries. Recent research demonstrates improved performance when electrode materials contain defects, with the potential to extend battery energy, power density, stability, tolerance in extreme conditions, and calendar life. This project focuses on and explores the model oxide system, titania (TiO2) to shed light on the underlying conductivity phenomena in these electroceramic materials. In addition, this project is coupled to education, diversity, and training activities that are integrated across two participating universities (Boise State and Purdue). For example, this project is implementing a cross-institutional undergraduate researcher 'exchange' program. TECHNICAL DETAILS: This study presents a unique method for tailoring ionic/electronic conductivity using irradiation, which could open new research pathways in irradiation-enhanced materials functionality and lead to an unprecedented advancement in tailoring electrochemical performance in electroceramic materials. The project investigates the hypothesis that irradiation-induced defects can provide tunable control over the mixed ionic/electronic conductivity in electroceramic materials, thus delivering enhanced electrochemical properties for lithium-ion battery applications. Electrodes containing extrinsic (e.g., doping) and intrinsic defects (e.g., vacancies, cation disorder) exhibit improved electrochemical properties. Specifically, extrinsic defects may enhance electronic conductivity, while intrinsic defects may enhance ionic conductivity. Intermediate energy ion irradiation creates intrinsic defects, while the irradiating ion species becomes implanted in the target material as extrinsic defects. Thus, it is theorized that the appropriate selection of the irradiating ion species and energy enables tuning of the ionic and electronic conductivity to produce better electrochemical properties. This project focuses on a model metal oxide, TiO2 (anatase). Specimens irradiated with niobium ions to produce both intrinsic and extrinsic defects, are compared to specimens irradiated with helium ions, which diffuse from the target material and leave behind only intrinsic defects. The hypothesis is being tested on crystalline thin films, which enables a mechanistic understanding of intermediate energy irradiation effects on metal oxides to be formed. Building on these results, research on a polycrystalline nanoarchitectured TiO2 electrode follows to elucidate the ion irradiation effect on the electrochemical properties of the electrode. This research is being incorporated into teaching and outreach modules for integration across the two participating institutions and is being made available via NanoHUB. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.