Electrolytes chloroethylene carbonate

Numerous research activities have focused on the improvement of the protective films and the suppression of solvent cointercalation. Beside ethylene carbonate, significant improvements have been achieved with other film-forming electrolyte components such as C02 [156, 169-177], N20 [170, 177], S02 [155, 169, 177-179], S/ [170, 177, 180, 181], ethyl propyl carbonate [182], ethyl methyl carbonate [183, 184], and other asymmetric alkyl methyl carbonates [185], vinylpropylene carbonate [186], ethylene sulfite [187], S,S-dialkyl dithiocarbonates [188], vinylene carbonate [189], and chloroethylene carbonate [190-194] (which evolves C02 during reduction [195]). In many cases the suppression of solvent co-intercalation is due to the fact that the electrolyte components form effective SEI films already at potential which are positive relative to the potentials of solvent co-intercalation. An excess of DMC or DEC in the electrolyte inhibits PC co-intercalation into graphite, too [183]. 

Ethylene carbonate (EC) and propylene carbonate (PC) have favorable physical and electrochemical properties such as high relative permittivity, high donicity, and relatively wide potential window. The direct fluorination of EC was successfully carried out to provide 4-fluoro-l,3-dioxolan-2-one (fluoroethylene carbonate, FEC) as shown in Scheme 2.3 [20], The fluorination of EC was strongly dependent on a choice of a reaction medium and no solvent was preferred from the viewpoint of conversion. FEC was further fluorinated to give three di-fluorinated derivatives. On the other hand, FEC was also prepared from 4-chloroethylene carbonate by exchange with KF [21], FEC was tested as an electrolyte additive for rechargeable lithium cells [21, 22] and is now practically used [23, 24],... 

Winter, M. Imhof, R. Joho, E Novak, R, FXIR and DBMS investigations on the electroreduction of chloroethylene carbonate-based electrolyte solutions for lithium-ion cells, J. Power Sources., 1999, 81-82, 818-823. 

PC is also a very useful solvent of LIBs because of its superior ionic conductivity over a wide temperature range. However, despite the close structural similarity between EC and PC, PC cannot form as effective SEI films as EC does, for LIBs that employ graphite as negative electrodes. " To enable to use PC in these batteries, there have been a lot of efforts focusing on the identification of proper additives and/or co-solvents for PC-based electrolytes, which would help to generate an efficient SEI layer. The typical liquid additives include chloroethylene carbonate (CEC), other halogen-substituted carbonates, a variety of unsaturated carbonates such as vinylpropylene carbonate and vinylene carbonate, and ethylene/propylene sulfite (ES/PS). The most common co-solvents are DMC, DEC, EMC, y-butyrolactone (y-BL), dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), dimethyl amide (DMA), 1,2-dimethoxy-ethane (DME) and 1,2-dimethoxy-methane (DMM). To explore the role of these additives and co-solvents, it is necessary to understand their structures and some properties that may affect the SEI formation on graphite anodes. 

Shu ZX, McMillan RS, Murray JJ, Davidson U (1996) Use of chloroethylene carbonate as an electrolyte solvent for a graphite anode in a lithium-ion battery. J Electrochem Soc 143 2230-2235... 

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