(Invited) Designing Fault-Tolerant Interfaces Between Metal Electrodes and Solid Electrolytes

Abstract

The use of alkali metal electrodes is widely considered to be an enabler for the next generation of high energy-density rechargeable batteries [1]. In all-solid-state systems, the most critical interface appears to be that between the alkali metal and the solid electrolyte, from which metal-filled cracks can initiate and grow into single-crystal, polycrystal, and glassy electrolytes alike [2] under sufficiently high electrochemical stress. However, failure can be mitigated by softening of the metal electrode, whether through increases in temperature (including melting) or changes in composition (including changing alkali metals [3]). Here, we discuss semi-solid metal electrode design approaches in which a minor liquid phase fraction is deliberately introduced to produce a self-healing function that enables high current densities [3]. A bulk semi-solid electrode approach is demonstrated using Na–K alloys with controlled liquid fraction between the state-of-charge limits; these show potassium ion critical current densities (using the a K-β″-alumina electrolyte) that exceed 15 mA cm‒2. An interfacial wetting approach uses a thin interfacial film of Na–K liquid between a Li metal electrode and an LLZTO solid electrolyte; here the critical current density is doubled, and cyclable areal capacities exceed 3.5 mAh cm‒2. Moreover, evidence from both approaches suggest that void formation in solid metal electrodes during cycling at practical current densities (>0.5 mA/cm2) [4], manifested as impedance growth at the metal-solid electrolyte interface, can be largely mitigated through these semi-solid design strategies.Support from the US Department of Energy, Office of Basic Energy Science, through award no. DE-SC0002633 (J. Vetrano, Program Manager), is gratefully acknowledged.[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] Park, R.J-Y. et al. Nat Energy 6, 314–322 (2021).[4] Kasemchainan, J. et al. Nat. Mater. 18, 1105–1111 (2019). Figure 1