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Page 2 of 14 Wang et al. Energy Mater 2023;3:300040 https://dx.doi.org/10.20517/energymater.2023.28

voltage of 4.4 V and > 97% for 100 cycles with a charge cut-off voltage of 4.5 V, respectively. The dense and firm
solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) formed by the fluorinated ether
electrolyte on the anode and cathode, respectively, are key to excellent cell performance. These results have
significance for the subsequent application of ether electrolytes for high-voltage lithium ion batteries (up to 4.5 V)
with graphite anodes.

Keywords: Lithium ion batteries, fluorinated ether, high-voltage layered oxides, graphite, solid electrolyte
interphase, cathode electrolyte interphase

INTRODUCTION
Lithium ion batteries (LIBs) have been widely used in the field of consumer electronics due to their
advantages of high energy density and long cycle life and have shown great development prospects in the
field of electric vehicles . Graphite anodes combined with high-voltage cathode materials, such as layered
[1,2]
oxides, including LiCoO (LCO) and LiNi Co Mn O (NCM811), are currently widely used in high-
0.8
2
2
0.1
0.1
energy-density commercial LIBs . The most widely used electrolyte system is composed of lithium
[3-6]
hexafluorophosphate (LiPF ) as the lithium salt, ethylene carbonate (EC), and other linear carbonates, such
6
as diethyl carbonate (DEC), dimethyl carbonate (DMC), etc., as solvents, and with different functional
additives . However, the use of these electrolytes under some harsh conditions is limited due to high
[7,8]
viscosity of carbonates, high melting point of EC, and poor thermal stability of LiPF 6 [9,10] . Thus, a new
research direction has emerged to design an electrolyte without EC that can quickly transfer lithium ions
and is suitable for use over a wider temperature range (0-60 °C).
Ether compounds are promising electrolyte solvents and have been widely used in different battery systems,
such as those based on lithium metal anodes and silicon anodes, due to their low melting point, low
viscosity, and good reduction stability . However, reports in the literature suggested that ether electrolytes
[11]
are not compatible with graphite anodes [12-14] . It has been reported that ether electrolytes lead to solvent co-
intercalation, graphite exfoliation, and electrolyte decomposition, with which the cells show decreased
Coulombic efficiency and poor cycle stability. In recent years, due to the rapid development of
hydrofluoroethers (HFEs) used as co-solvents in other anode systems [15-18] , researchers have turned their
attention to the possibility of designing ether electrolytes that are suitable for graphite electrodes . Some
[19]
electrolytes based on fluorinated ether co-solvents have been reported to deliver stable cycling of graphite
anodes [12,20,21] . In these reports, in addition to the regulation of the solvation structure, the formation of a
stable anion-based solid electrolyte interphase (SEI) film on the graphite surface is the key to suppressing
the co-intercalation of solvent molecules with graphite. This, in turn, helps maintain their functionality and
performance over extended cycles [22-24] .

In this work, a fluorinated ether co-solvent, 1,1,1-trifluoro-2-[(2,2,2-trifluoroethoxy) methoxy] ethane
(TTME), was introduced to the conventional ether electrolyte system comprising of 1,2-dimethoxyethane
(DME) and lithium bis(fluorosulfonyl)imide (LiFSI) to form a fluorinated ether-based electrolyte. On the
one hand, the fluorinated ether electrolyte can generate a stable SEI on the surface of the anode to inhibit
the co-intercalation, protect the structure of graphite, and inhibit the decomposition of the electrolyte. On
the other hand, due to the high degree of fluorination of TTME, the overall oxidation stability of the
fluorinated ether electrolyte is improved, making it less susceptible to oxidative degradation.

The EC/DEC carbonate electrolyte containing 1 wt.% vinylene carbonate (VC) and 1 wt.% 1,3-
propanesultone (PS), which has been reported previously by our group to exhibit good performance for