UC Santa Barbara

Conventional liquid electrolyte batteries are nearing their practical energy density limits despite the intensifying demand for greater energy and power densities. Solid-state batteries (SSBs), enabled by ion-conducting solid electrolytes (SEs), offer promise for meeting these needs while simultaneously providing improved safety, but still face challenges in high voltage cathode incorporation and economic competitiveness against liquid counterparts.

Chloride SEs, which are subject to complex structure-property relationships, show promise as catholyte candidates in dual SE high-voltage SSBs when paired with another SE. Taking a joint computational-experimental approach, we reveal the presence of a high concentration of planar and nonstoichiometric defects in mechanochemically-synthesized Li3YCl6 that facilitate Li-ion conduction and present a method of controlling its Li+ conductivity by tuning the defect concentration with synthesis and heat treatments. By carefully modulating the synthetic conditions in the Na-Y-Zr-Cl family of SEs, we demonstrate control of polymorphism and conduction properties in Na2ZrCl6 and Na3YCl6. Transition metal orderings in the Na2.25Y0.25Zr0.75Cl6 composition are shown to strongly impact Na-ion transport, providing a new way to optimize conductivity in aliovalently-doped SEs. Motivated by our improved understanding of chloride SE processing, we develop a reaction temperature-based approach to identify SE candidates chemically compatible with chlorides. We demonstrate that the Li2ZrCl6 and Li6PS5Cl pairing is a conductive, scalable, and kinetically stabilized system with high potential for implementation in dual SE SSBs.

Finally, we focus on facilitating manufacturing of air-sensitive sulfide SEs and Li-Si anodes. First, we propose a reversible 1-undecanethiol coating for sulfide SEs (LPSC), enabling handling in humid ambient air. Leveraging solid state NMR, we reveal that the thiol chain end anchors to the LPSC surface with S-S bonds while the hydrocarbon tail repels water, preserving the LPSC structure and conductivity after two days of air exposure. Next, we outline a prelithiation strategy for Si anodes designed to decrease first cycle losses, quantifying the phase fraction of Li-Si alloy formed with 7Li NMR.The guidelines for materials selection and improved processing parameters in SSBs outlined herein represent important advancements towards elevating energy storage technologies beyond the limitations of conventional Li and Na-ion batteries.