The effect of alkali treatment and organic modification of diatomite on the properties of diatomite composite separators

Abstract

Alkali treatment and organic modification were used to regulate the surface properties of diatomite, and diatomite composite separators were prepared by using alkali-treated diatomite and organic-modified diatomite as coating materials. The surface of diatomite was partially etched in the NaOH solution, resulting in the reduction of SiO₂ content in diatomite and the exposure of more surface Si–OH groups. The 3-Methacryloxypropyltrimethoxysilane (MPS) modifier was proved to be grafted on the surface of diatomite, and alkali treatment before organic modification could promote the grafting amount of MPS. The diatomite composite separator (OA-D/PET) prepared using organic-modified diatomite has a three-dimensional pore structure, excellent thermal stability, high porosity (51.6%) and electrolyte absorption (0.744 g cm⁻³). Both alkali treatment and organic modification of diatomite could improve the affinity of the composite separator to the organic electrolyte. The combination of alkali treatment and organic modification made the contact angle of the composite separator (OA-D/PET) reach 0°, which significantly improved the affinity of the separator and the electrolyte. The OA-D/PET composite separator also exhibited higher ionic conductivity (1.47 mS cm⁻¹). The excellent properties of the diatomite composite separator improved the rate performance and cycle performance of the assembled battery.