Abstract
Solid polymer electrolytes have been widely proposed for use in all solid-state lithium batteries. Advantages of polymer electrolytes over liquid and ceramic electrolytes include their flexibility, tunability and easy processability. An additional benefit of using some types of polymers for electrolytes is that they can be processed without the use of solvents. An example of polymers that are compatible with solvent-free processing is epoxide-containing precursors that can form films via the lithium salt-catalyzed epoxide ring opening polymerization reaction. Many polymers with epoxide functional groups are liquid under ambient conditions and can be used to directly dissolve lithium salts, allowing the reaction to be performed in a single reaction vessel under mild conditions. The existence of a variety of epoxide-containing polymers opens the possibility for significant customization of the resultant films. This review discusses several varieties of epoxide-based polymer electrolytes (polyethylene, silicone-based, amine and plasticizer-containing) and to compare them based on their thermal and electrochemical properties.
Highlights
Polymers based on ethylene oxides such as poly(ethylene oxide) (PEO) and nitrile groups such as polyacrylonitrile (PAN) have traditionally been used to prepare solid polymer electrolytes for use in all solid-state batteries [1,2]
Note 1: acetonitrile (ACN), tetrahydrofuran (THF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), succinonitrile (SN); Note 2: lithium bis(trimethanesulfonyl)imide (LiTFSI), lithium difluoroborate (LiDFOB), lithium trifluoromethanesulfonate (LiTF), 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide, 1-butyl-3-methylimidazolium bis(fluorosulfonyl)imide (BMIM-TFSI), octadecyl-triphenyl phosphonium iodide (OdTPP), N,N’-dioctadecylimidazolium iodide; Note 3: LiFePO4 (LFP), Li4 Ti5 O12 (LTO), Ni1/3 Mn1/3 Co1/3 O2 (NMC); Note 4: the symbol * denotes a Li-Li symmetric cell; Note 5: All lithium cation transference numbers reported in Table 1 were measured using the Bruce-Vincent method
These results suggest that ionic liquid-containing epoxide-based polymer electrolytes are about on par when compared to epoxide-based electrolytes that contain plasticizers
Summary
Polymers based on ethylene oxides such as poly(ethylene oxide) (PEO) and nitrile groups such as polyacrylonitrile (PAN) have traditionally been used to prepare solid polymer electrolytes for use in all solid-state batteries [1,2]. A solution to this dilemma is to investigate polymerization reactions that allow films to be produced in the absence of solvents One such reaction is the ring opening polymerization reaction of epoxides which can be catalyzed by lithium salts and/or amine-containing reagents and can yield crosslinked films that tend to have superior mechanical strength and decreased crystallinity relative to typical PEO-based solid polymer electrolytes [7]. As a wide variety of solid-state polymer electrolytes can be produced via the ring opening polymerization of epoxide-containing reagents, this review will discuss the ionic conductivities, thermal properties and electrochemical stability of various types of epoxidebased polymers (Table 1). (LTO), Ni1/3Mn1/3Co1/3O2 (NMC); Note 4: the symbol * denotes a Li-Li symmetric cell; Note 5: All lithium cation transference numbers reported in Table 1 were measured using the Bruce-Vincent method
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