Solid polymer electrolytes based on a high dielectric polymer and ionic liquids for lithium batteries
João C. Barbosa, Rafael S. Pinto, Daniela M. Correia, Carmen R. Tubío, Renato Gonçalves, Carlos M. Costa, S. Lanceros‐Méndez
Abstract
Solid-state batteries were produced using new solid polymer electrolytes (SPEs) based on the high dielectric constant polymer poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene), P(VDF-TrFE-CFE) and 40 wt% of different ionic liquids (IL) sharing the same bis(trifluoromethylsulfonyl)imide [TFSI] anion and different cations. The morphological, thermal, mechanical and electrochemical properties of the SPEs were investigated, as a function of the interaction between IL and polymer matrix. The addition of IL increased the amorphous phase of the polymer with respect to the neat polymer, leading to room temperature ionic conductivity values between 2.3 × 10−5 and 1.4 × 10−4 S cm−1, depending on the specific IL. Further, the highest lithium transference number of 0.71 was obtained for the [PMPyrr][TFSI] sample. Li/LiFePO4 half batteries using these SPEs show excellent and stable battery performance at room temperature at different C-rates. The highest discharge capacity value is achieved for the [PMPyrr][TFSI] sample, reaching 137 mAh.g−1 and 117 mAh.g−1 at C/10 and C/2 rates, respectively, with high coulombic efficiency (∼100%) and low capacity fade after 100 cycles. The use of P(VDF-TrFE-CFE) allows the development of room temperature solid-state lithium-ion batteries and the improved results are associated to the high polymer dielectric constant which facilitates IL ions dissociation, improving SPE ionic mobility.