Perfluoroalkyl-substituted ethylene carbonates: Novel electrolyte additives for high-voltage lithium-ion batteries

• Published in: Journal of power sources Vol. 246; pp. 184 - 191
• Main Authors: YE ZHU, CASSELMAN, Matthew D, YAN LI, WEI, Alexander, ABRAHAM, Daniel P
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier 2014
• Subjects: Applied sciences; Cycles; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Electrochemical impedance spectroscopy; Electrodes; Electrolytes; Electrolytic cells; Ethylene; Exact sciences and technology; Graphite; Lithium-ion batteries; X-ray photoelectron spectroscopy; Lithium ion batteries; Lithium-ion battery; Solid electrolyte interface; Organic carbonate; Solid electrolyte; Electrode electrolyte interface; Secondary cell; Solid electrolyte interphase (SEI); High voltage, high capacity; Additive; High voltage; Capacitance; Polyfluoroalkyl compounds; Electrolyte additives
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2013.07.070

A new family of polyfluoroalkyl-substituted ethylene carbonates is synthesized and tested as additives in lithium-ion cells containing EC:EMC + LiPF sub(6)-based electrolyte. The influence of these compounds is investigated in Li sub(1.2)Ni sub(0.15)Mn sub(0.55)Co sub(0.1)O sub(2)//graphite cells via a combination of galvanostatic cycling and electrochemical impedance spectroscopy (EIS) tests. Among the four additives studied in this work (4-(trifluoromethyl)-1,3-dioxolan-2-one (TFM-EC), 4-(perfluorobutyl)-1,3-dioxolan-2-one (PFB-EC), 4-(per-fluorohexyl)-1,3-dioxolan-2-one (PFH-EC), and 4-(perfluorooctyl)-1,3-dioxolan-2-one (PFO-EC)), small amounts (0.5 wt%) of PFO-EC is found to be most effective in lessening cell performance degradation during extended cycling. Linear sweep voltammetry (LSV), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy are used to further characterize the effects of PFO-EC on the positive and negative electrodes. LSV data from the electrolyte, and XPS analyses of electrodes harvested after cycling, suggest that PFO-EC is oxidized on the cathode forming surface films that slow electrode/cell impedance rise. Differential capacity (dQ/dV) plots from graphite//Li cells suggest that PFO-EC is involved in solid electrolyte interphase (SEI) formation. Raman data from anodes after cycling suggest that structural disordering of graphite is reduced by the addition of PFO-EC, which may explain the improved cell capacity retention.