Colloidal Syntheses-Driven Discovery of Inorganic Solid Electrolytes Containing Unconventional Crystal Lattices and Composition to Optimize Ionic Conductivity and Mechanical Stability Parameters

Lithium-ion (Li⁺), and beyond-Li⁺ batteries power most portable electronic devices¹ and electric vehicles. Although current commercial Li⁺ batteries primarily use liquid electrolytes, all-solid-state batteries² have been increasingly explored due to their improved safety³ and energy density (500 Wh-kg, LGPS-type⁴). Solid electrolytes⁵ allow to avoid the use of volatile, flammable organic electrolytes and increase Li⁺ conductivity⁶, chemical stability, electrochemical stability, and cycle life⁷ of ion batteries. The biggest problem with solid electrolytes is the high temperatures⁸ required (&gt;353 K) for Li⁺ to move around in the electrolyte materials. Sustainable battery development will additionally require solid electrolytes manufactured from earth abundant materials. Moreover, the correlation between crystal structural aspects⁹ (such as the phase, cationic Schottky defects) and ionic mobilities remain inconclusive and material-dependent.<br/>We utilize variations of colloidal hot-injection methods to synthesize nanostructured inorganic I-VI, IV-VI, V-VI nanocrystals with excellent size dispersity. Using post-synthetic cation exchange mechanisms in both colloidal and solid states, we achieve two key objectives: (a) engineer defects and determining how local structural perturbations induced by small amounts of Li⁺, Na⁺ intercalations can facilitate the intercalation of other cations (Zn²⁺, Al³⁺) to stabilize beyond-Li⁺ solid electrolyte materials with fast ionic conductivities. (b) fully exchanging one or more cationic species at ambient conditions from these nanocrystals with alkali or other suitable elements, enabling the design of potentially unlimited compound combinations within a fast timescale of seconds or minutes.<br/>We were able to test the ionic conductivity performance of these compounds at ambient conditions reaching 1 Ω⁻¹ cm⁻¹, significantly higher than that of commercially used solid electrolytes. Further, using Argonne’s Advanced Photon Source, we demonstrated the structural stability in these nanocrystals up to several Gigapascals (GPa), making these solid electrolytes promising candidates for battery fabrication processes that range only between 100-100 MPa. Moving forward, in my independent laboratory in Chicagoland starting in Fall of 2024, my new academic research group will focus on connecting our discoveries and understanding from fundamental inorganic chemistry, condensed matter physics, electrochemistry, and nanoscale colloidal synthetic techniques to solid battery electrolyte materials innovation.<br/>(1) <i>InfoMat </i><b>2019</b>, <i>1</i> (1), 6-32. DOI: 10.1002/inf2.12000<br/>(2) <i>Nat Commun </i><b>2020</b>, <i>11</i> (1), 6279. DOI: 10.1038/s41467-020-19991-4<br/>(3) <i>eScience </i><b>2022</b>, <i>2</i> (2), 138-163. DOI: 10.1016/j.esci.2022.02.008<br/>(4) <i>Nature </i><b>2021</b>, <i>593</i> (7858), 218-222. DOI: 10.1038/s41586-021-03486-3<br/>(5) <i>Science </i><b>2023</b>, <i>381</i> (6653), 50-53. DOI: 10.1126/science.add7138<br/>(6) <i>Energy Material Advances </i><b>2023</b>, <i>4</i>, 0015. DOI: 10.34133/energymatadv.0015<br/>(7) <i>Science </i><b>2022</b>, <i>378</i> (6626), 1320-1324. DOI: 10.1126/science.abq1346<br/>(8) <i>ACS Nano </i><b>2022</b>, <i>16</i> (8), 12445-12451. DOI: 10.1021/acsnano.2c03732<br/>(9) <i>Nature Materials </i><b>2015</b>, <i>14</i> (10), 1026-1031. DOI: 10.1038/nmat4369