Lithium carboxylate: Effectively suppressing hydrogen evolution by self-introducing CO2 in aqueous electrolyte

Abstract

We have found that the formation of passivation film plays a major role in the negative shift of the decomposition voltage in the hydrogen-generating process. Both the hydrolysis of weak acid ions and the decarboxylation reaction of carboxylate can make the LiCO2CH3 produce a passivation film to inhibit the water decomposition to a certain extent. As for the LiCO2CF3 without hydrolysis of weak acid ion, it can be highly possible to facilitate the introduction of CO2 via its carboxylate specific decarboxylation reaction, and further produce lithium carbonate passivation film as well. However, the water decomposition voltage in the oxygen-producing process is more dependent on the properties of lithium salt anions. Those with strong electron-absorbing groups such as the trifluoromethyl are more likely to effectively endue the aqueous electrolyte with a high oxidative decomposition potential. Moreover, the concentration of LiCO2CF3 aqueous electrolyte can reach up to 28 mol kg−1, and hence the electrochemical stability window of this water-base electrolyte can be expanded to about 3.0 V. This work provides a new idea for the selection of high concentration lithium salt.