materials Review A Review of Functional Separators for Lithium Metal Battery Applications Jooyoung Jang y, Jiwoong Oh y, Hyebin Jeong y, Woosuk Kang y and Changshin Jo * School of Chemical Engineering & Materials Science, Chung-Ang University (CAU), 84, Heukseok-ro, Dongjakgu, Seoul 06974, Korea;
[email protected] (J.J.);
[email protected] (J.O.);
[email protected] (H.J.);
[email protected] (W.K.) * Correspondence:
[email protected]; Tel.: +82-2-820-5477 These authors contributed equally to this work. y Received: 31 August 2020; Accepted: 12 October 2020; Published: 16 October 2020 Abstract: Lithium metal batteries are considered “rough diamonds” in electrochemical energy storage systems. Li-metal anodes have the versatile advantages of high theoretical capacity, low density, and low reaction potential, making them feasible candidates for next-generation battery applications. However, unsolved problems, such as dendritic growths, high reactivity of Li-metal, low Coulombic efficiency, and safety hazards, still exist and hamper the improvement of cell performance and reliability. The use of functional separators is one of the technologies that can contribute to solving these problems. Recently, functional separators have been actively studied and developed. In this paper, we summarize trends in the research on separators and predict future prospects. Keywords: lithium metal battery; separator; next-generation batteries 1. Introduction Rechargeable batteries are chemical energy storage systems that interconvert chemical energy and electrical energy through the redox reactions of cathode and anode materials. Fossil fuel-based energy cycles are being replaced by renewable energy cycles at a high pace. In this regard, energy storage devices have proven to be essential in fulfilling the global demands of sustainable energy supply and solving problems such as oil depletion and environmental pollution [1–5].