Electrolyte Additive Enabled Low Temperature Lithium Metal Batteries

Abstract

One of the key challenges in the development of energy storage devices is the ability to operate efficiently under extremely cold environments (i.e. below -20 °C), especially for batteries in temperature-sensitive applications such as portable electronic devices, transportation, and stationary energy storage. As reported, at low temperature, the increased internal resistance and sluggish ion diffusion in batteries lead to declined charge-delivering capability, which deteriorates cell performance and eventually terminates the power output. Although lithium (Li) metal battery (LMB) with ether electrolyte is considered promising in overcoming these issues due to the low viscosity of ether solvent and its distinctive electrode structure, the low-temperature performance of LMBs remains unsatisfactory. A series of problems are observed upon the anode-electrolyte interphase, including aggravated side reactions, abnormal Li deposition, and dramatically increased solid-electrolyte interphase (SEI) resistance. Thus, building a stable SEI layer on the Li metal anode is critical for the development of low-temperature LMBs.Here, we demonstrate a dioxolane (DOL)-based electrolyte with dimethyl sulfoxide (DMSO) as the low-temperature additive, which helps to construct a robust SEI layer that possesses uniform structure and good composition consistency even under extremely cold condition. In this electrolyte, DOL works as the primary electrolyte component that defines the basic electrochemical properties, while DMSO further tunes the SEI composition to boost the low-temperature performance. To elucidate the modified microstructure and chemical composition of the SEI film, cryogenic transmission electron microscopy, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectroscopy are conducted to make a comprehensive investigation. Moreover, a series of electrochemical tests are conducted under extremely cold environments, and results demonstrate that the adjusted SEI is resilient to the stripping and plating cycles of Li metal at temperatures as low as -80 °C. Full cells with lithium iron phosphate as the cathode material are assembled and good electrochemical performance is achieved at -40 °C at 0.2 C. The solvation structure of DMSO added electrolyte is also investigated to fundamentally understand how it affects the SEI formation. Our work establishes fundamental insights into the low-temperature electrolyte additives and paves the road to the further applications of LMBs in harsh environments.