Operando WAXS on in-situ wetting of thick cathode by polymer electrolyte in solid state battery

Solid-state batteries hold promise to improve energy density without sacrificing safety. An intimate contact between solid electrolyte and cathode is key to batteries' energy density, rate capability and cyclability. However, it is challenging to form such solid-solid contact, especially when using thick cathodes for energy density. We developed a new polymer electrolyte that delivers attractive electrochemical performances even when matched with thick cathodes, and the functioning mechanism is unknown. Preliminary tests at ID31 show that the polymer only reaches half of cathode thickness in the assembled cell, but impregnates into the whole depth of the cathode after the first electrochemical charge-discharge. We therefore propose to monitor the polymer impregnation process during battery operation to discover when and how it is triggered. The in situ wetting mechanism revealed by this study may be provide insights to design polymer electrolytes and solid-state batteries.