Electrolyte wettability determines the absorption rate and affinity of porous membrane. Figure 4b show visually the difference in wettability between PP separator and cellulose membranes, the liquid electrolyte droplet stands up on the PP separator due to the poor compatibility of non-polar polyolefin-based separators with traditional polar liquid electrolytes. By contrast, electrolyte can absolutely penetrate into cellulose/CaCO₃ membranes, which demonstrates the excellent performance of cellulose membranes in terms of electrolyte wettability. The good electrolyte wettability of membrane is conducive to the transport of lithium ions, which further affects the rate performance of battery. Besides, because the polar hydroxyl groups of cellulose have a good affinity for electrolytes, the membrane prepared by electrospinning has a loose porous structure to store a large amount of electrolyte. The cellulose/CaCO₃membranes show a significant promotion in liquid uptake, reaching 220% at a mass fraction of 0.5 wt% of nano-CaCO₃, much higher than that of the PP separator (97%) (Table 3 ). Porosity as another important parameter for separators determines the electrolyte storage capacity and the permeability of the membrane. The cellulose membranes possess high porosity of 49% due to the fibrous-network structure. Furthermore, nano-CaCO₃ has no adverse effect on porosity.

Table 3. Physical properties of PP, cellulose and cellulose/CaCO₃ membranes