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