Lithium battery diaphragm with uniform pore diameter and preparation method thereof

Abstract

The invention belongs to the technical field of lithium battery diaphragms, and particularly relates to a lithium battery diaphragm with a uniform pore diameter and a preparation method thereof. The lithium battery diaphragm comprises a core layer and surface layers disposed on both sides of the core layer. The core layer comprises, 91 to 96.5% of polyethylene, 2.5 to 6% of epoxy resin, 1 to 3% iflinear high-density polyethylene. Each surface layer includes, by weight percentage, 98.5 to 99.5% of polypropylene and 0.5 to 1.5% of polypropylene copolymer. By adding a small amount of linear high-density polyethylene and epoxy resin to the polyethylene composition of the core layer, and by adding a small amount of polypropylene copolymer to the polypropylene composition of the surface layers,the molding rate of the crystal can be increased and the crystal integrity can be improved during the crystallization process of casting a cast piece, thereby forming a lithium battery diaphragm witha uniform pore diameter in a process of longitudinal stretching and transverse stretching pore formation.

Description

technical field [0001] The invention belongs to the technical field of lithium battery diaphragms, and in particular relates to a lithium battery diaphragm with uniform pore size and a preparation method thereof. Background technique [0002] The lithium battery diaphragm is one of the key inner components of the lithium battery. Its main function is to separate the positive and negative electrodes of the lithium battery to prevent the two poles from contacting and short-circuiting; although the material of the lithium battery diaphragm is non-conductive, it has The function of allowing electrolyte ions to pass through; the performance of the separator determines the interface structure and internal resistance of the lithium battery, which directly affects the capacity, cycle and safety performance of the lithium battery. Under overcharge / overdischarge or other extreme conditions, the internal temperature of the lithium battery will rise rapidly. When the internal temperatur...

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Problems solved by technology

However, the thickness of the multi-layer film prepared by this ex-situ composite technology of forming a microporous membrane and then recombining is relatively large; at the same time, in order not to damage the microporous structure of the lithium battery separator, the thermal composite temperature is low, polyethylene / polyethylene Insufficient bonding of propylene leads to delamination behavior of lithium battery separators under elevated temperature operating conditions; for non-layered composite technology, Tang haolin et al. (J Power Sources2013, 241, 203) adopted PVDF-HFP (Vinylidene fluoride-hexafluoropropylene copolymer) is compounded with ePTFE (expanded polytetrafluoroethylene) porous network, and the closed cell temperature of the prepared PVDF-HFP / ePTFE composite diaphragm is ~150 ° C, because ePTFE forms a continuous network structure, its melting temperature (membrane rupture temperature) reaches ~350°C

However, the cost of this composite technology based on the porous network is too high to meet the needs of large-scale industrial production

[0004] The method of multi-layer co-extrusion to manufacture ultra-thin films has the advantages of high efficiency and low cost. However, for lithium battery separators that require extremely high pore structure indicators, due to the melt fluidity, crystallization and crystallization of each component at a similar temperature Transformation into differences in pore properties, multi-layer co-extrusion presents a certain technical complexity

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