리튬 이차전지용 LiPF6 계 전해액 안정화를 위한 첨가제 연구

Abstract

Enhancing the performance of lithium-ion batteries (LIBs) is of paramount importance to widely leverage LIBs in a variety of industries from electronic mobile devices to grid/utility energy storage systems and electric vehicles. However, conventional LIBs exhibit rather limited long-term cycling lifetimes, which can be increased by structural and compositional tuning of the corresponding electrode materials and electrolytes. For instance, despite their high ionic conductivity and reasonably good cathodic and anodic stability, LiPF6-based electrolytes commonly used in conventional LIBs exhibit instability when exposed to moisture and high temperatures, which limits their widespread use. In particular, ion-paired LiPF6 readily undergoes autocatalytic decomposition into LiF and PF5 that react with background moisture to produce reactive species such as POF3 and various acids. In turn, the formation of these species induces the destruction of interfacial layers on electrodes, dissolution of transition metals (TMs) from the cathode, and the decomposition of electrolyte solvents. The problematic behavior of acids produced by LiPF6 decomposition is most critical for promising Li-rich and Ni-rich cathode materials used in high-energy-density batteries, where it results in challenges such as unwanted TM dissolution caused by HF attack and cathode-electrolyte interface instability caused by electrolyte decomposition. Herein, we highlight the recent advancements in the development of (i) scavengers with high selectivity and affinity toward unwanted species and (ii) promoters of ionpaired LiPF6 dissociation, showing that the utilization of the above additives can effectively mitigate the problem of electrolyte instability that commonly results in battery performance degradation and lifetime shortening. A deep mechanistic understanding of LiPF6-containing electrolyte failure and the action of currently developed additives is demonstrated to enable the rational design of effective scavenging materials and thus allow the fabrication of highly reliable batteries.