Microwave heating enables near-carbonless liquid-phase-derived Li Argyrodites for all-solid-state batteries

The liquid-phase synthesis of sulfide solid electrolytes (SEs) is promising for the mass production of practical all-solid-state batteries (ASSBs). However, upon conventional furnace-based heat treatment of liquid-phase-derived intermediates, SEs contain deleterious carbon impurities from organic residues, negatively impacting the electrochemical performance of ASSBs and hindering their practical application. Herein, we present a novel approach utilizing ultrafast targeted heating through microwave-induced thermal shock, demonstrating the enhanced crystallization of SEs while effectively suppressing the carbonization of organic impurities during the liquid-phase synthesis of argyrodite SEs. Complementary analyses confirm the reduced sulfur loss and minimized impurity evolution achieved through microwave heating, as compared to conventional furnace heating. The microwave-derived argyrodite SEs exhibit high Li conductivities (Li5.5PS4.5Cl1.5: maximum 3.1 mS cm−1) and acceptably low electronic conductivities (Li6PS5Cl: 1.2 × 10−9 S cm−1), in stark contrast to the mixed conducting property of furnace-derived Li6PS5Cl (Li+ conductivity: 1.1 mS cm−1, electronic conductivity: 1.7 × 10−5 S cm−1). As a result, when utilized as SE layers or catholytes in LiNi0.70Co0.15Mn0.15O2||Li-In ASSB cells, the cells incorporating microwave-derived SEs significantly outperform those with furnace-derived SEs (e.g., the capacity retention after 250 cycles: 93.6% vs. 32.0%). Furthermore, a proof-of-concept for microwave self-heating of SEs is successfully demonstrated.