Growth mechanisms of Li dendrite and the suppression strategies

Abstract

<p indent="0mm">Lithium metal battery (LMB) is widely acknowledged as one of the most promising battery technologies for nextgeneration energy storage systems due to its ultra-high energy density. Unfortunately, the practical application of LMB has been plagued by the uncontrollable growth of Li dendrites during electrochemical cycling, which would not only consume the electrolyte irreversibly and reduce its cycling lifespan, but also cause the internal short-circuit and result in severe safety issues. Aiming to effectively suppress or even eliminate the growth of Li dendrites, a great deal of strategies such as adding electrolyte additives, employing superconcentrated electrolytes, forming artificial solid electrolyte interphase (SEI) layers, physical modification of Li anodes and/or designing advanced structured Li anodes have been proposed. Although the cycling performance of LMBs has been significantly improved by above-mentioned approaches, yet their overall performance is still inferior to that of the commercialized lithium ion batteries (LIBs) counterpart. To further enhance the performance of LMBs so as to accelerate their research and development process, an in-depth and comprehensive understanding of the fundamental growing mechanisms of Li dendrites is highly desirable. To shed lights on designing novel strategies to suppress or eliminate the growth of Li dendrites, a comprehensive overview of the current understanding of the growth mechanisms of Li dendrites during electrochemical cycling is provided in the current article. Herein, several models proposed from both theoretical derivation and experimental observation are reviewed to fundamentally illustrate the formation and growth behaviors of Li dendrites. The space-charge model that is proposed to describe Li dendrite nucleation is firstly introduced. In this model, the dendritic Li is formed because of a very large space charge near the electrode surface that is created by the anion depletion during Li ion deposition. The SEI-induced growing model, which illustrates that the cracking/pinholes at the defects of SEI films could cause electrochemical hot spots and triggers the dendritic Li growth, is then presented. In addition, the heterogeneous nucleation and growth model, which considers both the thermodynamic and kinetic conditions to rationalize the nucleation and growth of Li dendrites, is also explained. After that, the surface nucleating and diffusion model, which indicates that lower surface energy and higher migration energy are two important factors for Li dendrite growth on the surface of Li metal, is briefly presented. The following is the tip-induced nucleation model, which states that the Li ion deposition occurs easily on the protrusions of metal tips due to the enhanced electric and ionic fields therein. Finally, the film growth model, which is inspired by the plasma enhanced chemical vapor deposition (PECVD) process, is introduced to explain the underlying growing behaviors of Li dendrites. In addition to these models proposed to illustrate the growing mechanisms of Li dendrites, the corresponding strategies, which are derived from these models and aimed to suppress the growth of Li dendrites, are also concisely presented. This review article ends with an insightful discussion together with some suggestions for future research directions of the Li dendrites. In brief, the current article tends to not only summarize the fundamental understandings regarding the growth mechanisms of Li dendrites but also provide a few instructive suggestions for future research activities of the LMBs.