Beyond fluorine: sustainable ternary polymer electrolytes for lithium batteries

Abstract

In the state-of-the-art lithium-ion battery, sustainability and safety have often been ‘sacrificed’ in favor of ‘performance’ and ‘cost’. Regarding the electrolyte, volatile and flammable solvents and highly toxic fluorinated lithium salts need replacements. Thus, the first fluorine-free ternary polyethylene oxide-based polymer electrolyte plasticized with ionic liquid (IL) is hereby presented using the non-fluorinated 4,5-dicyano-1,2,3-triazolate (DCTA) as the anion for both conducting lithium salt and the IL plasticizer, respectively. Due to its low molecular weight, membranes with a high molar percentage of IL can be achieved, up to a PEO : LiDCTA : Pyr₁₄DCTA ratio of 20 : 2 : 4, without crosslinking the polymer part. DCTA membranes feature glass transition temperatures (T_gs) and ionic conductivities in the same range as their bis(trifluoromethanesulfonyl)imide (TFSI) analogs and much higher transference numbers. The 20 : 2 : 4 membrane has a T_g of −55.4 °C and an ionic conductivity of 5.2 × 10 4 S cm⁻¹ at 40 °C. LFP||Li metal cells devoid of any critical raw materials and including this non-fluorinated TSPE were successfully cycled 300 times.