Preparation and properties of aerogel sodium ion battery separator with carboxy methyl cellulose cross-linked polyacrylic acid

Objective  The aerogel sodium ion battery separator with electrochemical performance exceeding that of glass fiber was prepared using carboxy methyl cellulose sodium (CMC) and polyacrylic acid (PAA) as raw materials, and the effect of cross-linking temperature on pore structure of the separator was explored to realize the electrochemistry performance exceeding that of glass fibre.

Method  The sol-gel method and freeze-drying method were used to prepare CMC-PAA aerogel sheets, supplemented by high temperature cross-linking to stabilize the pore structure. The influence of temperature on the diaphragm was explored through microscopic testing and mechanical performance characterization. The charge-discharge specific capacities of sodium ion half cell with separators of CMC-PAA and glass fibre were compared.

Result  With the increase of cross-linking temperature, the cross-linking degree of the carboxyl group of PAA and the hydroxyl group of CMC in the diaphragm increased. As a result, the pore size and porosity of the diaphragm slightly decreased; The elongation at break of the separator appeared to first increase and then to decrease. When the aerogel battery separator was prepared with a mass ratio of CMC︰PAA=1︰1 and a cross-linking temperature of 130 ℃, the charge-discharge specific capacity of the sodium ion battery exhibited 345.8, 317.3, 274.2, 136.8, 84.8, 61.8 and 341.4 mA·h/g at charge-discharge rates of 25, 50, 100, 250, 500, 1 000 and 25 mA/g current densities, showing better properties than those of glass fibres (279.0, 233.1, 190.5, 105.9, 69.6, 49.4, and 275.1 mA·h/g) under the same conditions. 130 ℃-CMC-PAA exhibited a much higher electrochemistry performance than conventional commercial polyolefin diaphragms due to its smaller electrolyte leakage rate, which resulted in an ionic conductivity of 1.877 mS/cm and a resistance of 5.52 Ω.

Conclusion  The application of battery separators made of two water-soluble materials of CMC and PAA under 130 ℃ cross-linking in sodium ion batteries has good potentials, having better electrochemistry performance than glass fiber.