Ethyl 2,2-difluoroacetate as Possible Additive for Hydrogen-Evolution-Suppressing SEI in Aqueous Lithium-Ion Batteries

• Main Author: Törnblom, Pontus
• Format: Others
• Language: English
• Published: Uppsala universitet, Strukturkemi 2021
• Subjects: Lithium; Lithium-ion; Aqueous; Battery; LIB; ALIB; WISE; SEI; Solid Electrolyte interphase; Solid Electrolyte interface; Ethyl difluoroacetate; Ethyl 2; 2-Difluoroacetate; Ethyldifluoroacetate; high reduction; water; additive; EDFA; Materials Chemistry; Materialkemi
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-448596

The performance and lifetime of lithium-ion batteries are strongly influenced by their composition. One category of critical components are electrolyte additives, which are included primarily to stabilize electrode/electrolyte interfaces in the battery cells by forming passivation layers. The presented study aimed to identify and study such an additive that could form a hydrogen-evolution-suppressing solid electrolyte interphase (SEI) in lithium-ion batteries based on aqueous electrolytes. A promising molecular additive, ethyl 2,2-difluoroacetate (EDFA), was found to hold the qualities required for an SEI former and was herein further analyzed electrochemically. Analysis of the battery cells were performed with linear sweep voltammetry and cyclic voltammetry with varying scan rate and EDFA concentrations. Results show that both 1 and 10 w-% EDFA in the electrolyte produced hydrogen-evolution-suppressing SEI:s, although the higher concentration provided no apparent benefit. Lithium-ion full-cells based on LiMn2O4 vs. Li4Ti5O12 active materials displayed poor, though partly reversible, dis-/charge cycling despite the operation of the electrode far outside the electrochemical stability window of the electrolyte. Inclusion of reference electrodes in the lithium-ion cells proved to be immensely challenging with unpredictable drifts in their electrode potentials during operation. To summarize, HER-suppressing electrolyte additives are demonstrated to be a promising approach to stabilize high-voltage operation of aqueous lithium-ion cells although further studies are necessary before any practical application thereof can be realized. Electrochemical evaluation of the reaction mechanism and efficiency of the electrolyte additives relies however heavily on the use of reference electrodes and further development thereof is necessary.