Our research lies at the frontier between solid-state chemistry for the design of redox active materials and physical chemistry of liquids. We apply these principles to understand and develop efficient electrochemical energy storage and conversion devices, including secondary batteries, water electrolyzers and the electrosynthesis of commodity chemicals.
Latest JACS Contribution
In this newest work from our group, Dr. Michael Spencer et. al. present the lithium exchange mechanisms for a new family of lithiated chloride materials, the A2MCl4 compounds. The abstract and link to the article are presented below:
Intense research efforts on transition metal chalcogenides (oxides and sulfides), pnictides (nitrides and phosphides), and fluorides have demonstrated the complex, intertwined effects of structural and chemical changes on their electrochemical response leading to intercalation, conversion, or displacement reactions when reacting with lithium. Prior efforts largely left halides unexplored due to their heightened solubility in classical liquid electrolytes. In this work, we employ superconcentrated electrolytes to demonstrate the composition- and structure-dependent electrochemical reactivity of A2MCl4 compounds (A = Li or Na and M = Cr, Mn, Fe, and Co). Comparing four lithiated compounds, we demonstrate that they all undergo conversion reactions when reacting with 2 Li+ per formula unit, associated with large polarization and limited cycling ability. Nevertheless, combining in situ XRD with post-mortem XPS and STEM/EDS analysis, we demonstrate that Li2CoCl4 first reacts with one Li+ following a displacement reaction providing a reversible capacity of 125 mAh g–1. This reaction is enabled by the formation of a Li6CoCl8 intermediate, which shares a similar anionic framework with pristine Li2CoCl4, ensuring the topotactic insertion of Li+ balanced by the Co2+/Co0 redox couple and the formation of metallic Co nanoparticles. Comparing these compounds, we propose that two criteria are necessary to trigger the displacement reaction in A2MCl4 compounds: the presence of 1D chains of edge-sharing octahedra to favor electronic delocalization and the availability of a metal-deficient intermediate. Screening numerous A2MCl4 compounds, we demonstrate the universality of these design principles, which extend to Na-ion materials by demonstrating a low-polarization, reversible displacement reaction for Na2MnCl4.
