Revealing Principles for Design of Lean-Electrolyte Lithium Metal Anode via In Situ Spectroscopy

Abstract

Lean electrolyte conditions are highly pursued for the practical lithium (Li) metal batteries. The previous studies on the Li metal anodes, in general, exhibited good stability with a large excess of electrolyte. However, the targeted design of Li hosts under relatively low electrolyte conditions has been rarely studied so far. Herein, we have shown that the electrolyte con-sumption severely affects the cycling stability of Li metal anode. Considering carbon hosts as typical examples, we innova-tively employed the in-situ synchrotron X-ray diffraction, in-situ Raman spectroscopy and theoretical computations to ob-tain better understanding of the Li nucleation/deposition processes. Besides, we showed the usefulness of in-situ electro-chemical impedance spectra to analyze interfacial fluctuation at the Li/electrolyte interface, and together with the nuclear magnetic resonance data to quantify electrolyte consumption. We have found that uneven Li nucleation/deposition and the crack of surface-area-derived solid-electrolyte-interface (SEI) layer both leads to a great consumption of electrolyte. Then, we suggested a design principle for Li host to overcome the electrolyte loss, that is, uneven growth of Li structure and the crack of SEI layer must be simultaneously controlled. As a proof of concept, we demonstrated the usefulness of a 3D low-surface-area defective graphene host (L-DG) to control Li nucleation/deposition and stabilize SEI layer, contributing to a highly reversible Li plating/stripping. As a result, such a Li host can achieve stable cycles (e.g., 1.0 mAh cm-2) with a low elec-trolyte loading (10 μL). This work demonstrates the necessity to design Li metal anodes under lean electrolyte conditions and brings the Li metal batteries a step closer to their practical applications.