Advancing Sodium-ion Battery Cycle Life: Understanding Degradation in Hard Carbon Anodes

Na-ion battery (NIB) is the most promising technology among the next generation battery technologies. The main issue facing NIB is in their low cycle life. Limited cycle life of Na batteries results from degradation mechanisms occurring at both the cathode and the anode. While multiple cathode materials have been developed, the best-performing anode material remains hard carbon. Despite hard carbon's acceptable energy density, it suffers from inadequate cycle life. Significant efforts have been made to understand Na storage mechanisms in hard carbon. However, little effort has been devoted to understanding the degradation mechanisms and strategies to mitigate them. I propose research spanning multiple scales to evaluate the mechanisms causing degradation in hard carbon anodes and develop strategies to inhibit them, focusing on SEI and charge transfer mechanisms, and their influence by various operating parameters. This work will involve intensive mechanistic studies of Na-ion charge transfer and interfacial processes by conducting in-situ Electrochemical Impedance Spectroscopy (EIS) and Nuclear Magnetic Resonance Spectroscopy (NMR) measurements, which will identify and quantify the contributions of both Na-ion charge transfer and interface to hard carbon degradation. I will employ hard carbon symmetric cell configuration that allows for detailed analysis without the contribution from other electrodes. I will scale this mechanistic work with various parameters including electrolyte composition and temperature. The results will identify the primary contributors to the low cycle life of hard carbon anodes and bring strategies to extend their cycle life.