Mixed Ion-Electron Conducting LixAg Alloy Anode Enabling Stable Li Plating/Stripping in Solid-State Batteries via Enhanced Li Diffusion Kinetic

Although showing huge potential in prospering the marketplace of all-solid-state lithium metal batteries (ASSLMBs), garnet-type solid electrolytes (Li6.5La3Zr1.5Ta0.6O12, 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 LixAg 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 LixAg 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 LixAg/current collector interface rather than the LLZTO/LixAg interface. Therefore, the contact loss is avoided at the LLZTO/LixAg interface. As a result, excellent cycling stability (∼1200 h at 0.2 mA cm-2), and dendrites tolerance (critical current density of 1.2 mA cm-2) are demonstrated by using LixAg 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.