Understanding Metal Deposition in Solid Electrolytes Due to Mixed Ionic-Electronic Conduction

The effect of ionic and electronic conductivity in the solid electrolytes (SE) on metal (such as Li, Na) deposition and dendrite propagation in the SE are investigated. A new framework for metal formation inside defects (such as voids, grain boundaries) in the SE due to the electronic conductivity of the SE is established. We find that for typical SE material (with ionic conductivity ~0.1mS/cm and electronic conductivity ~10^-5 mS/cm) isolated voids in the SE that are close enough to the anode side (~0.1 um) may be filled in with metal within several minutes under typical galvanostatic charging condition (with current density 0.1~1mA/cm^2). Continuous deposited metal in the voids may lead to fracture of the SE, which triggers mode II dendrite growth (isolated dendrites growth in the SE). We will propose two strategies to prevent metal deposition in the SE.