The PVDF was pre-mixed with the N-Methyl-2-pyrrolidone (NMP) and homogenized overnight. Subsequently the NMC and CB were added to the mixture in the weight ratios mentioned along the manuscript (90:5:5, 92:4:4 and 95:3:2, NMC:CB:PVDF). After all materials were mixed, NMP was added to the mixture to adjust the solid content to 60 % in weight. The mixing was performed in a vacuum mixer MSK-SFM-7 (MTI corp.) at a fixed mixing speed of 320 rpm. The homogenization of the mixture took place for 5 hours in a controlled environment at 20ºC in short steps of 30 minutes followed by 10 minutes of rest to avoid the heating up of the sample.