The invention which discloses a diaphragm for a high
thermal safety temperature
lithium ion cell and a preparation method thereof belongs to the field of diaphragm materials for
lithium ion cells. The diaphragm is mainly formed by a high strength
expanded polytetrafluoroethylene matrix membrane and a porous filled
polymer with the
melting point of 125-160DEG C, the thermal closure temperature of the diaphragm is 125-160DEG C, and the
thermal safety temperature of the diaphragm reaches 338DEG C, wherein the tensile strength of the matrix membrane is 60-150MPa, the thickness of the membrane is 2-20mum, the membrane has a through dendritic pore structure, the
porosity is 50-80%, and the average pore size is 1-5mum. The preparation method comprises the following steps: mixing a 125-160DEG
melting point different
polymerization degree
polyvinylidene fluoride-hexafluoropropene,
polyethylene or
polypropylene resin, and a pore forming agent, preparing a homogeneous diaphragm
casting liquid in an
organic solvent, immersing the matrix membrane in the diaphragm
casting liquid, taking out the matrix membrane, extracting the pore forming agent from the matrix membrane by an extractant, and
drying the matrix membrane to obtain the diaphragm. The composite diaphragm prepared in the invention has the advantages of high infiltration performance, high
thermal safety temperature and high thermomechanical performance, so the safety of the diaphragm in the power
lithium ion cell is improved.