Composite diaphragm for lithium batteries and preparation method of composite diaphragm for lithium batteries

Abstract

The invention provides a composite diaphragm for lithium batteries. The composite diaphragm is in a three-layer structure, two side surface layers are high-strength polypropylene microporous membranes, and a core layer is a low-melting-point self-turn-off polyethylene microporous membrane. The high-strength polypropylene microporous membranes are made from polypropylene resin, wherein the molecular weight is 300000-1000000, a molecular weight distribution index Mw / Mn is 4-8, isotacticity is larger than 96%, and the melt flow rate is 1.3-3.3. The low-melting-point self-turn-off polyethylene microporous membrane is made from high-density polyethylene, wherein the molecular weight is 100000-300000, a molecular weight distribution index Mw / Mn is 4-8, and the melt flow rate is 0.2-0.8. The composite diaphragm for the lithium batteries is low in pore closing temperature, high in membrane rupture temperature, wide in self-turn-off safety window, great in mechanical performance, high in puncture strength, high in safety in lithium ion battery production and utilization processes, appropriate in microporous diameter size, uniform in distribution and high in connectivity, the batteries are low in internal resistance, and improvement of operating efficiency of the batteries is benefited.

Description

technical field [0001] The invention relates to a composite separator for lithium batteries and a preparation method thereof, belonging to the technical field of lithium batteries. Background technique [0002] Lithium-ion battery separator is an important component in lithium-ion batteries. It is a thin film material with nano-scale pores, which plays a role in blocking the positive and negative electrodes in the battery and preventing the internal short circuit of the battery; at the same time, it must allow ions The current passes quickly to ensure the rapid transmission of lithium ions between the positive and negative electrodes during battery charging and discharging. The microporous structure, physical properties, chemical properties, and thermal properties of the separator determine the interface structure and internal resistance of the battery, which directly affect the capacity, cycle performance, and safety performance of the battery. A separator with excellent pe...

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Problems solved by technology

In the wet production of microporous membranes, the pore size and porosity are easier to control, and the tortuosity of the pores is relatively high, but a large amount of solvent is required, the process is complicated, and the environmental pollution is large; the process of dry production is simple, and the tortuosity of the pores is relatively high. Low, not only single-layer diaphragms can be produced, but also multi-layer composite diaphragms can be produced to improve production efficiency, but the pore size is difficult to control