Influence of the porosity degree of poly(vinylidene fluoride-co-hexafluoropropylene) separators in the performance of Li-ion batteries

• The effect of porosity degree in P(VdF–HFP) membranes is investigated.
• Correlation among porosity, liquid uptake, tortuosity and conductivity is established.
• Room temperature conductivity above 10−3 S cm−1 is obtained for the 5/95 sample.
• From 70% to 90% of the theoretical capacity is delivered by Li/Sn–C and Li/LiFePO4 half-cells.
• A charge/discharge efficiency close to 100% is observed in Li/Sn–C and Li/LiFePO4 half-cells.

Polyvinylidenedifluoride–hexafluoropropylene, (P(VdF–HFP))-based polymer electrolytes, as separators for lithium batteries, were prepared through different polymer/solvent (N,N-dimethylformamide, DMF) ratios and physicochemically investigated. Scanning electron microscopy measurements have shown a homogeneously distributed porosity within the membranes, with moderately tortuous pathways, resulting in a liquid uptake up to 77 wt.% with respect to the overall weight and conduction values above 10−3 S cm−1 at room temperature.Prolonged cycling tests, performed on Li/Sn–C and Li/LiFePO4 half-cells based on P(VdF–HFP) polymer electrolyte separator membranes, have evidenced nominal capacities ranging from 70% to 90% of the theoretical value with very good capacity retention and charge/discharge efficiency close at 100% even at high current rates. A capacity decay is observed at high current regime, associated to the diffusion phenomena occurring within the electrode and the polymer electrolyte separator membrane.