Electrochemical Analysis of Garnet-Type Solid Electrolytes – Effect of Dopants on Li-Conductivity and Dendrites Formation

Abstract

The development of solid state lithium-metal batteries (SSLB) is a key requirement to enable the use of energy storage systems with high energy and power densities in the automotive sector. Garnet-type solid electrolytes are considered suitable electrolytes candidates for SSLB due to their stability against lithium metal and high ionic conductivity at room temperature (10-3 S cm-1). Currently their use is limited because of their short life-time due to high interfacial resistance between electrode and electrolyte, and to the formation of lithium dendrites.1 A better understanding of the transport properties and the mechanism of dendrites formation in garnet type electrolytes is therefore required in order to develop solid electrolytes with a long enough life-time to be employed in commercial systems. In this work, alongside to an extended and systematic electrochemical characterisation of garnet-type electrolytes by Electrochemical Impedance Spectroscopy (EIS),2 we employed cubic Al- and Ga- doped Li7La3Zr2O12 (LLZO) as solid electrolytes in symmetrical cells and we investigated the formation of dendrites as a result of electrochemical cycling. We suggest that the presence of local chemical inhomogeneities promoted by the type of dopants used to stabilise the cubic phase might greatly affect the critical current density (CCD) for the dendrites formation and propagation.3 This is of fundamental importance for the development of solid state batteries based on LLZO. 1 A. Sharafi et al., J. Power Sources, 2016, 302, 135–139 2 F. M. Pesci et al., Manuscript in preparation 3 F. M. Pesci et al. , J Mater. Chem. A, 2018 , 6, 19817-19827