Challenges of using recycled ethyl methyl carbonate in lithium-ion batteries: Effects of residual alcohols on performance

Residual impurities – particularly alcohols – pose challenges for using recycled carbonate solvents in lithium-ion cells. Understanding and quantifying their effect on the electrochemical performance is key to enabling the use of recycled materials. We investigate the influence of such alcohols on NCM811/graphite cells, focusing on the formation of the solid electrolyte interphase (SEI) and cycling over 250 cycles. Model electrolytes were prepared by systematically adding methanol and ethanol (0.01–1 wt%, relative to EMC) to a ‘battery grade’ electrolyte containing 1 M LiPF 6 in EC:EMC (3:7). High alcohol concentrations led to a rise in interphase resistance (2.8–72.6 Ω) and continued irreversible losses over 40 cycles, attributed to hindered SEI passivation and ongoing decomposition via nucleophilic attack of alkoxides. At lower concentrations (<0.2 wt%), resistance increase and capacity losses during formation were moderate. Nevertheless, beyond the formation phase no significant cyclic ageing occurred in contaminated cells. Recycled EMC samples with purities of 99.40 % and 98.30 % containing 0.14 wt% and 0.16 wt% residual alcohols showed consistent performance with the model electrolytes, confirming alcohol content as a key quality factor. Overall, while alcohol residues affect initial cell formation, sufficiently purified recycled solvents with residual alcohol levels <0.2 wt% may still be viable for practical application. • Residual alcohols limit the quality of recycled solvents in lithium-ion batteries. • Alcohol residues in recycled EMC strongly impact SEI formation and cell resistance. • Model systems and real recycled samples show consistent electrochemical trends. • Industrially relevant concentrations allow stable cycling after careful formation.