Effect of formamide and DMSO additives on the electrolyte properties of a lithium-ion battery: Experimental and theoretical study

Electrolytes play a vital role in the performance of lithium-ion batteries by enabling efficient ion transport and energy storage. To improve battery efficiency, additives are often incorporated into electrolytes. This study investigates the impact of formamide and dimethyl sulfoxide (DMSO) as additives in a typical lithium-ion battery electrolyte, ethylene carbonate/diethyl carbonate (EC/DEC). Formamide and DMSO were individually added to EC/DEC, and the electrochemical properties of the resulting electrolytes EC/DEC, EC/DEC in formamide, and EC/DEC in DMSO were assessed using linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The EC/DEC typical electrolyte and EC/DEC in DMSO were further analyzed using cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) testing. Density functional theory (DFT) calculations were also performed to theoretically assess the electrolyte behavior and lithium-ion (Li⁺) solvation in the studied electrolytes. The findings exhibit enhanced conductivity and ion transference numbers of the electrolytes with formamide and DMSO compared to the typical EC/DEC electrolyte. The EC/DEC in formamide and DMSO electrolytes demonstrated better electrochemical stability under high voltage conditions. DFT results revealed that the HOMO-LUMO energy gap (∆E) for the EC/DEC electrolyte (8.3604 eV) increases when EC/DEC is combined with DMSO (8.6680 eV) or formamide (8.6663 eV), suggesting improved electrochemical stability. DFT calculations revealed that the addition of formamide and DMSO enhances the stability of the interaction between Li⁺ and EC/DEC, facilitating Li⁺ dissociation and improving its transport within the electrolyte. However, electrochemical cycling performance testing for the EC/DEC in DMSO electrolyte shows a decline in the later stages, indicating reduced electrochemical reversibility, likely due to solid electrolyte interphase (SEI) degradation in the presence of DMSO. This highlights the need to optimize the additive concentration in the EC/DEC electrolyte to achieve optimal electrochemical performance and extended cycle life.