Quantifying the Density and Mobility of Mobile Ions in Solid Electrolytes By Transient Current Measurements

Abstract

Solid electrolytes are a key component in enabling new technological advances for rechargeable batteries by mitigating many of the challenges associated with the use of liquid organic electrolytes. One of the key properties of solid electrolytes is their ability to transport ions between the anode and the cathode. This ion migration is usually characterized by measuring the ionic conductivity by means of impedance spectroscopic measurements. However, the ionic conductivity is proportional to both the density and the mobility of mobile ions. Only the mobility represents the actual velocity of the mobile ions.Using lithium phosphorus oxynitride (LiPON), we show how measuring the temperature-dependent current transients can be used to independently quantify both the mobility and the density of mobile ions in solid electrolytes. By changing the mobile ion density in Li7La3Zr2O12 (LLZO) solid electrolyte by co-sputtering LLZO and Li2O, we show how samples that seem to have the same ionic conductivity can still differ in ionic mobility. Finally, we employ this method to quantify the effects of Al and Ga doping on the ion migration in LLZO solid electrolytes. The proposed approach in quantification of mobile ions can be extended to other solid electrolytes for a better understanding of ion migration and the influence on battery performance.