Exploration of fluorine-free electrolytes with superior functions

2022 Fiscal Year Annual Research Report

• Project/Area Number: 22F22340
• Allocation Type: Single-year Grants
• Research Institution: The University of Tokyo
• Principal Investigator: 山田 淳夫 東京大学, 大学院工学系研究科(工学部), 教授 (30359690)
• Co-Investigator(Kenkyū-buntansha): HARKS PETRUS 東京大学, 工学(系)研究科(研究院), 外国人特別研究員
• Project Period (FY): 2022-11-16 – 2025-03-31
• Keywords: Li-ion batteries / Anode-free batteries / Metallic lithium / LiPF6

Outline of Annual Research Achievements

An exploratory study was performed in which several suitable carbonate and ether solvents were identified for a LiPF6 based electrolyte compatible with a lithium metal anode. For the ethers, which are generally incompatible with LiPF6, new electrolyte preparation methods and cell configurations were developed. The electrolytes were further optimized through solvation structure regulation by increasing the salt concentration and additives, which presumably leads to an improved (i.e. thin, inorganic) solid electrolyte interphase on the lithium anode (yet to be characterized). The obtained Coulombic efficiencies and cycle lifetimes are comparable with the state-of-the-art performance for electrolytes based on expensive salts (e.g. LiFSI) that are (contrary to LiPF6) not commercially viable.

Current Status of Research Progress

2: Research has progressed on the whole more than it was originally planned.

Reason

More potential high performance electrolyte systems were found/developed than expected during the first 6-month period. As a consequence, less time will have to be spent on further exploration/optimization, which means that the characterization of the metallic anode (and interphase) and the mechanistic study of the electrolytes can start sooner than planned.

Strategy for Future Research Activity

To improve costs, viscosity and performance of the electrolytes, development of localized highly concentrated electrolytes with the use of cost effective diluents will be pursued. The solvation structure of these novel electrolytes will be studied with spectroscopy and DFT calculations. After cycling the morphology and elemental composition of electrodes will be characterized with microscopy and spectroscopy. With these studies we hope to apply the recent breakthroughs in understanding the influence of the solvation structure and lithium electrode potential on the cell performance for the development of practical electrolytes to improve high energy density batteries.