Design principles for electrolytes and interfaces for stable lithium-metal batteries (original) (raw)

A lithium-metal battery (LMB) consists of three components: a Li-metal anode, a Li-ion-conducting electrolyte separator, and a cathode 1. Recharging a LMB requires electrodeposition of lithium on to itself, a process that is fundamentally unstable. At low current densities, concentration of electric field lines and preferential transport of ions to rough regions on the electrode surface produce the morphological instability loosely termed dendrites. Meanwhile, at high current densities, depletion of anions in the electrolyte near the anode creates a space charge that drives a hydrodynamic instability termed electroconvection 2. This electroconvection draws ions away from regions surrounding a growing dendrite and focuses them on the dendrite tip, enhancing dendrite growth. Thus, for quite fundamental physical reasons, recharge of a LMB at either low or high currents produces rough and dendritic deposition of the metal. Reactivity of Li with aprotic liquid electrolytes forms a porous, ion-conducting solid electrolyte interphase (SEI) layer on the metal 3 (stage I in Fig. 1). A uniform and stable SEI can passivate the Li surface, preventing further reaction, but spontaneously formed SEIs on Li are typically inhomogeneous and mechanically fragile (stage II in Fig. 1). An inhomogeneous SEI destabilizes LMBs by providing nucleation sites for dendrite formation at any current density, while a fragile SEI may crack or delaminate during battery cycling, exposing fresh Li to the electrolyte each cycle, which ultimately depletes the electrolyte. Because the two processes (dendrite formation and electrolyte loss) occur in tandem, it is a formidable challenge to create a LMB that operates stably for an extended time. This Perspective surveys approaches for designing batteries based on Li-metal anodes that do not fail via dendrite-induced short circuits. We specifically focus on rational strategies based on regulating charge transport and Li reactivity at interfaces for stabilizing the Li-metal anode. It is shown that a universal state diagram can be created, in which knowledge of material parameters and cell operating conditions can be used to provide explicit guidance about the electrolyte separator and interface designs for stable LMB operation. The Perspective also highlights recent successes and discusses