Seminal Literature

Carbonate Electrolytes - The Most Used Solvents for Commercial Li-Ion Batteries CYCLIC CARBONATES

LINEAR CARBONATES

Propylene carbonate PC

Linear carbonates are typically used as co-solvents with their cyclic counterparts. In 1994, Tarascon and Guyomard first added DMC as a cosolvent to EC 3 4. Linear carbonates have relatively low boiling points, viscosities, and dielectric constants. Therefore, they are often used to improve ionic transport in the electrolyte. Surprisingly, when combined with cyclic carbonates, the stability window of the resulting mixture is increased 5. Other popular linear carbonates include DEC, EMC, and PMC.

Between 1950s and 1990s, typical electrolytes consisted of various lithium salts dissolved in PC 1. PC demonstrates strong solvating ability and has a high oxidative stability above 4.0 VLi. Unfortunately PC can cointercalate with lithium into graphite, leading to graphite exfoliation, which limits its practical application.

propylene carbonate PC

Ethylene carbonate EC

Initially, PC was preferred over EC because EC has a melting point of 37 °C. To overcome this high melting point, EC is often mixed with linear carbonate esters such as dimethyl carbonate and diethyl carbonate 1. Dahn et al.ʼs discovery that EC forms a stable solid electrolyte interphase SEI was key to enabling the graphite anode 2. EC-based electrolytes combined with graphite anodes increased energy density of LIBs by 3050%.

ethylene carbonate EC

dimethyl carbonate DMC

diethyl carbonate DEC

ethyl methyl carbonate EMC

“Within the various brands of lithium ion cells,... the formulas remain proprietary information; however, the overwhelming majority of these are apparently based on two indispensable components: EC as the solvent and LiPF6 as the solute. In most cases, one or more linear carbonates, selected from DMC, DEC, or EMC, are also used as cosolvents to increase the fluidity and reduce the melting point of the electrolyte.ˮ 5

Source: 1 Xu, K. Nat Energy 2021. 2 Rosamaría Fong et al J. Electrochem. Soc. 1990; 3 Guyomard, D.; Tarascon, J. M. J. Electrochem. Soc. 1993; 4 Tarascon, J. M.; Guyomard, D. Solid State Ionics 1994; 5 Xu, Kang. Chem. Rev 2004

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