(Invited) Semi-Solid Alkali Metal Electrodes Enabling High Critical Current Densities and Accessible Areal Capacities in Solid Electrolyte Batteries

Abstract

The need for higher energy-density rechargeable batteries has generated interest in alkali metal electrodes paired with solid electrolytes [1]. However, metal penetration and electrolyte fracture at low current densities [2], as well as impedance growth at the metal-solid electrolyte interface due to void formation during cycling at practical current densities (> 0.5 mA cm-2), have emerged as fundamental barriers [3]. Here we demonstrate two semi-solid electrode architectures in which the presence of a minor liquid phase enables high current densities while it preserves the shape retention and packaging advantages of solid electrodes [4]. First, biphasic Na–K alloys selected for controlled liquid fraction between the state-of-charge limits show K+ critical current densities (with a K-β″-Al2O3 electrolyte) that exceed 15 mA cm‒2. Second, introducing a wetting interfacial film of Na–K liquid between a Li metal electrode and Li6.75La3Zr1.75Ta0.25O12 solid electrolyte doubles the critical current density and permits cycling at areal capacities that exceed 3.5 mAh cm‒2. These design approaches hold promise for overcoming electrochemomechanical stability issues that have heretofore limited the performance of solid-state metal batteries.We acknowledge support from the US Department of Energy, Office of Basic Energy Science, through award no. DE-SC0002633 (J. Vetrano, Program Manager).[1] Albertus, P., Babinec, S., Litzelman, S. & Newman, A. Nat. Energy 3, 16–21 (2018).[2] Porz, L. et al. Adv. Energy Mater. 7, 1701003 (2017).[3] Kasemchainan, J. et al. Nat. Mater. 18, 1105–1111 (2019).[4] Park, R.J-Y. et al. Nat Energy 6, 314–322 (2021). Figure 1