Manipulating Hardness to Construct Favorable Electrode Microstructures for All‐Solid‐State Batteries

Abstract All‐solid‐state batteries hold great promise for achieving high energy densities. Fabrication of solid‐state electrodes involves cold compaction of the active material—typically an oxide—with a sulfide electrolyte, during which the softer sulfide particles deform and enwrap the harder oxide particles to afford an “active material‐in‐electrolyte” microstructure where the electrolyte forms a continuous ion‐conducting network. This mechanism however does not apply to emerging active materials that promise even higher energy densities like organic and sulfur‐based compounds. These materials are softer than sulfides and form unfavorable “electrolyte‐in‐active material” microstructures where ionic conduction is interrupted. Improvement of these electrodes is challenging in the absence of strategies to overcome the intrinsic material hardnesses. Here, it is demonstrated how the relative hardness difference can be reversed by simultaneously “softening” a sulfide electrolyte Li 6 PS 5 Cl by solvent treatment and “hardening” an organic material pyrene‐4,5,9,10‐tetraone (PTO) through partial lithiation. The lithiated PTO ends up harder than the treated Li 6 PS 5 Cl, thus forming the favorable “active material‐in‐electrolyte” microstructure. Cell performance improved as a result, including a 91% increase in material utilization compared with electrodes with unfavorable microstructures, as well as enhanced discharge−charge rates and cycling stability. Such a hardness manipulation strategy has broad applications in solid‐state devices and energy storage.