The invention discloses a microporous diaphragm for a low-electrical-impedance
lithium battery and a preparation method of the microporous diaphragm. The diaphragm comprises: a base film layer, wherein the base film layer is of a microporous structure formed by biaxially stretching
polypropylene and / or
polyethylene; the surface of the base film layer is coated with the functional
coating, and the functional
coating contains mixed
slurry of
inorganic nanoparticles and a binder; the
surface modification layer is formed by introducing a hydrophilic
electrolyte group on the surface of the functional
coating through
plasma treatment or chemical
grafting. The base
membrane layer forms a uniform micropore structure through a two-way stretching process, the functional coating is formed by compounding
nano silicon dioxide or aluminum
oxide and
polyvinylidene fluoride according to a specific proportion, a
porous layer with gradient
pore diameter is formed, the pore size of the
porous layer is smaller than that of the base
membrane layer, and efficient
permeation of
electrolyte is ensured.
Electrolyte-philic groups such as sulfonic groups are introduced into the
surface modification layer, so that the wettability of the diaphragm to an
electrolyte is remarkably improved. During preparation, the base membrane is formed through
melt blending, two-way stretching and pore-forming agent extraction, and then the functional layer is constructed through
slurry coating and a low-temperature
plasma treatment or sulfonation process. The diaphragm combines gradient aperture design,
inorganic filler enhancement and
surface chemical modification, and realizes
low impedance, high
thermal stability and excellent
mechanical strength.