Approaches toward lithium metal stabilization
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Introduction In the 1990s, commercialization of rechargeable batteries containing metallic lithium anodes was abandoned due to unexpected and dangerous failures.1 With rapid improvements in and development of Li-ion batteries, there was a good alternative that has satisfied the largest battery markets for the last two decades. Lithium metal batteries are now again being examined because of the potential to significantly improve the energy density and performance for a variety of applications. This article explores some of the promising approaches to stabilize the lithium-metal anode, such that it will maintain low resistance, full capacity, dense and compact structure, and uniform distribution along the anode for a long and safe battery cycle life. Any tendencies of the lithium to roughen or form irregular features that allow for continuous reaction with the electrolyte or impurities need to be avoided. Such processes can lead to electrochemically dead or disconnected lithium, decreasing capacity and increasing the possibility of dangerous reactions under unforeseen circumstances. Before turning to solid-state batteries, recent work to stabilize lithium metal within conventional battery architecture through interface layers and new formulations of the liquid electrolytes are noted. The references cited throughout this article are just illustrative with no attempt to capture the entire scope of interesting activities and publications in this field.
Strategy to stabilize lithium within liquid electrolyte batteries Typical liquid electrolyte lithium batteries are fabricated with extruded, rolled, or electroplated lithium as Cu/Li metal/ liquid electrolyte in separator/cathode/Al. Since Li has high electronic conductivity, the Cu current collector may be omitted. During normal battery cycling, the Li dissolves and deposits at the anode, while reversibly reacting or intercalating at the cathode. For lithium, the relative kinetics of the side reactions, electrodeposition, and diffusion combine to make it nearly impossible to maintain a smooth, dense, unreacted surface, more so than for other electroplated metals, such as copper and zinc. The interface of the Li with the organic liquid electrolyte invariably reacts to form a layer, either native or engineered, often referred to as a solid-electrolyte interphase (SEI). The transport properties of this interphase are not well understood.2 For the SEI to passivate and protect the lithium from further reaction, it must be physically and chemically stable to survive large variations in the volume of lithium during battery cycling. Because batteries are often constructed with a large excess quantity of Li, beyond that needed to balance the cathode capacity, problems at the Li metal anode often go undetected. Indeed, such batteries, referred to as half cells, are typically used to study the extended performance of battery cathode materials where loss of some lithium is inconsequential. But to develop commercial batteries with high energy density,
Nancy J. Dudney, Materials Sci
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