The Effect of Li2CO3 on Mechanical and Electrochemical Behavior of Li6.4La3Zr1.4Ta0.6O12 Solid-State Electrolyte

Abstract

Li6.4La3Zr1.4Ta0.6O12 (LLZTO) is a very promising solid-state electrolyte for all solid-state battery. Due to its high ionic conductivity and chemical and electrochemical stability that can allow to use Li metal as anode with a high energy density as well as enhanced battery safety. However, there is little research to study the intrinsic mechanical properties of LLZTO which is a key factor that will influence the capacity fading and shortened lifetime of battery. In this study, we examine the effect of different densities on the elastic modules, hardness and toughness of Ta substituted LLZO solid-state electrolyte which will result the varieties of the mechanical and electrochemical performance. After annealing, the densities of the sample varied from 85% to 96% with the grain size from 3.5μm to 5.1μm. By introduction of the Li2CO3 additive, the grains become more connected and the number of pores at the grain boundaries becomes much smaller. The grain size rages from 3 to10μm. 5%-LLZTO has more strong grain boundary. It is suggested that the mechanical fracture happened during the Li plating process. Impedance of ion diffusion and electron transfer increase as density increase. Hardness decreases with increasing porosity and increasing grain size. The young’s modulus and the hardness increased from 121.9 to 138.8 Gpa and 4.54 to 11.26 Gpa for the 85% and 96% relative density samples, respectively. The results of this study reveal that the density of LLZTO was influenced by the amount of Li2CO3, so that the mechanical performance can be optimized through the selection of the microstructure, network, and properties of the active materials.