Mixed ion-electron conducting LixAg alloy anode enabling stable Li plating/stripping in solid-state batteries via enhanced Li diffusion kinetic

Abstract

Although showing huge potential in prospering the marketplace of all-solid-state lithium metal batteries (ASSLMBs), garnet-type solid electrolytes (Li_6.5La₃Zr_1.5Ta_0.6O₁₂, LLZTO) are critically plagued by interface instability with Li anode and the vulnerability to Li dendrite, which are attributed to poor Li diffusion kinetic in bulk Li metal. Herein, a Li_xAg solid solution alloy with high Li diffusion kinetic is reported as a mixed ion-electron conductor (MIEC) alloy anode. The high Li diffusion kinetic stemming from a low eutectic point and a high mutual solubility of Li_xAg could reduce the Li concentration gradient in the anode, regulate Li electrochemical potential, and change the relative local overpotential for Li stripping/plating in the anode. Notably, Li stripping/plating prefers energetically at the Li_xAg/current collector interface rather than the LLZTO/Li_xAg interface. Therefore, the contact loss is avoided at the LLZTO/Li_xAg interface. As a result, excellent cycling stability (∼1,200 ​h at 0.2 ​mA/cm²), and dendrites tolerance (critical current density of 1.2 ​mA/cm²) are demonstrated by using Li_xAg as anode. Further research has elucidated that those alloys with low eutectic temperature and high mutual solubility with lithium should be focused on, as they would provide and maintain a soft lattice and a high lithium diffusion rate during composition change. This provides a basis for the selection of alloy phases in negative electrode materials, as well as their application in garnet-based ASSLMBs.