Accelerated Growth of Electrically Isolated Lithium Metal during Battery Cycling.

Severe capacity loss during cycling of lithium-metal batteries is one of the most concerning obstacles hindering their practical application. As this capacity loss is related to the variety of side reactions occurring to lithium metal, identification and quantification of these lithium-loss processes are extremely important. In this work, we systematically distinguish and quantify the different rates of lithium loss associated with galvanic corrosion, the formation of a solid-electrolyte interphase, and the formation of electrically isolated lithium metal (i.e., "dead" lithium). We show that the formation of "dead" Li is accelerated upon cycling, dominating the total lithium loss, with much slower rates of lithium loss associated with galvanic corrosion and formation of the solid-electrolyte interphase. Furthermore, photoacoustic imaging reveals that the three-dimensional spatial distribution of "dead" Li is distinctly different from that of freshly deposited lithium. This quantification is further extended to a solid-state Li/Cu cell based on a LiGePS solid-state electrolyte. The lithium loss in the solid-state cell is much severer than that of a conventional lithium-metal battery based on a liquid electrolyte. Our work highlights the importance of quantitative studies on conventional and solid-state lithium-metal batteries and provides a strong basis for the optimization of lithium-metal electrochemistry.