The invention discloses a composite diaphragm adapting to low temperature, which comprises a base material and a functional
coating, the functional
coating is provided with tubular composite particles, and the tubular composite particles comprise tubular
boehmite,
hydroxymethyl cellulose and
lithium salt; the preparation method comprises the following steps: mixing an aluminum salt, a template agent, deionized water, a
lithium salt, a chelating agent, a pH
regulator and
hydroxymethyl cellulose, carrying out a
hydrothermal reaction, cooling after the
hydrothermal reaction is finished, washing with water, centrifuging, and
drying to obtain the low-temperature-adaptive composite diaphragm. Tubular composite particles containing tubular
boehmite,
hydroxymethyl cellulose and
lithium salt are obtained; mixing the tubular composite particles, deionized water, a dispersing agent, a binder and a
wetting agent to obtain
coating slurry; the tubular composite particles are used for providing channels for lithium
ion migration, so that the lithium
ion conductivity is improved, the
interface impedance of the diaphragm is reduced, and the
cycle rate performance of a battery is improved.