Exploration of Battery Systems Utilizing Metal Anodes for Advancements Beyond Lithium-ion Batteries

Abstract

Driven by the implementation of global carbon-neutral policies and the increasing demand for environmentally friendly energy sources, research on energy storage systems capable of storing and supplying electrical energy is experiencing significant momentum. Notably, lithium (Li)-ion batteries (LIBs), leveraging Li+ ions as charge carrier transfer carriers, have remained a steadfast choice as energy storage devices since their initial commercialization by Sony in 1991. Thanks to their stable performance and suitable energy density, LIBs have been extensively applied across various domains of energy storage. However, with the surging energy demand, the limited energy capacity provided by LIBs highlights the growing urgency for developing novel electrode materials to offer breakthrough solutions by replacing existing ones. Specifically, despite concerted development efforts, the presently available commercial cathode materials for LIBs, such as graphite or silicon-graphite blends, still fail to deliver adequate energy density. Furthermore, as the utilization and scale of energy storage systems continue to expand, apprehensions regarding safety are progressively mounting. Indeed, incidents of personal and material damages stemming from LIB explosions are consistently being reported, with their repercussions being perceived as more severe compared to conventional fire accidents due to their challenging extinguishment. Thus, the imperative to design battery systems with high energy density and enhanced safety by replacing current electrode materials and systems is paramount for realizing the next generation of battery systems. Li metal is an anode material that offers a significantly higher energy density compared to current anode active materials, based on its high theoretical capacity and lowest redox potential, driven by the conversion reaction of Li+ ions. However, the utilization of Li metal as an anode in Li metal batteries (LMBs) suffers from issues related to the irregular electrodeposition of Li and the subsequent formation of Li dendrites during repetitive charge and discharge processes. These Li dendrites have chances to induce internal short circuits, causing serious safety hazards to the battery. Moreover, even in the absence of short circuits, vertically grown Li dendrites can fracture, forming an insulating layer known as ‘dead Li’ on the electrode surface, increasing surface resistance and leading to continuous electrolyte consumption. Therefore, suppressing the dendritic growth of Li during cycling and enhancing the stability of the anode are regarded as crucial research issues for the practical application of Li metal anodes. Meanwhile, conventional LIBs operate based on organic solvent-based electrolytes, leading to various issues such as electrolyte decomposition, gas generation, and combustion during thermal runaway processes. As a result, battery fire and explosion accidents occur, highlighting the necessity of ultimately replacing the currently used flammable organic solvent-based electrolytes with non-flammable solvent-based electrolytes to enhance battery safety. Aqueous batteries, utilizing a mixture of metal salt and water as the electrolyte, are considered as a major candidate for replacing the current LIB system due to their non- flammability and intrinsic safety attributed to their water-based nature. Additionally, apart from safety concerns, aqueous batteries offer economic advantages by not requiring water- free facilities like dry rooms or glove boxes. Also, aqueous batteries are highly productive, environmentally friendly, and exhibit high ionic conductivity, making them advantageous for fast charge and high power. Among various aqueous battery systems, the aqueous zinc (Zn) metal battery (AZMB), utilizing Zn2+ ions as the charge transfer carrier and Zn metal as the anode, has attracted considerable interest from researchers due to its advantages such as high volumetric capacity and low material cost associated with Zn metal. However, similar to LMBs, AZMBs face challenges in ensuring sufficient cycle retention due to the irregular plating of the metal anode and dendrite formation during cell operation, posing obstacles to commercial application. In this thesis, I aim to discuss strategies for enhancing the durability of metal anode-based batteries. The primary issue with metal anode lies in the uncontrolled growth of metal during operation, leading to various deteriorations in electrochemical performance such as electrolyte depletion, increased internal resistance, and reduced cycle life. The unevenness of metal growth is accelerated by the tip effect, where charge accumulation occurs at specific points, making it crucial to address. Therefore, one effective approach to improving the uniformity of metal plating is to alleviate the concentration gradient of internal charge transfer cations, thereby preventing intensified electrodeposition at specific points due to the tip effect. Additionally, providing appropriate nucleation sites for metal plating on the electrode surface and promoting anode stabilization through continued metal plating over these sites is another effective approach. Furthermore, structural approaches utilizing frameworks can prevent dendrite issues caused by structural metal growth. Based on these perspectives, this thesis will cover various strategies for stabilizing metal anodes, including electrolyte modification, introducing artificial interphase layer, providing nucleation sites, and structural approaches. Moreover, I will present the underlying mechanisms and changes in electrochemical performance associated with these strategies. It is expected that the feasibility of practical applications of metal anode-based batteries, considered as next- generation battery systems, will increase based on the strategies introduced in this study.