Fusion type composite separation membrane for lithium secondary battery, and preparation method therefor
The present invention relates to a composite separation membrane for a lithium secondary battery having excellent lifetime and safety improvement effects, and a preparation method therefor and, more specifically, to a composite separation membrane for a lithium secondary battery, including: a porous base layer; a heat resistant layer formed on one surface or both surfaces of the porous base layer; and a fusion layer formed on the outermost layer. Inorganic particles in the heat resistant layer are connected and fixed by a binder polymer, and the fusion layer is prepared by comprising amorphous polymer particles having a glass transition temperature of 30 to 90° C. and a difference between a fusion temperature and the glass transition temperature of 60° C. or lower.
1. A composite separation membrane for a lithium secondary battery comprising:
a porous base layer;
a heat-resistant layer including inorganic particles connected and fixed by a binder polymer, and formed on the porous base layer; and
a fusion layer including amorphous polymer particles having a glass transition temperature of 30° C. or higher to 90° C. or lower, and formed on the heat-resistant layer.
2. The composite separation membrane for a lithium secondary battery of claim 1 , wherein a difference between the glass transition temperature of the amorphous polymer particles and a fusion temperature at the time of fusion of the composite separation membrane with electrodes is 60° C. or lower.
3. The composite separation membrane for a lithium secondary battery of claim 1 , further comprising:
an interfacial layer formed between the heat-resistant layer and the fusion layer and having the inorganic particles and the amorphous polymer particles mixed therein.
4. The composite separation membrane for a lithium secondary battery of claim 1 , wherein the inorganic particles of the heat-resistant layer have a size of 0.1 to 2.0 μm.
5. The composite separation membrane for a lithium secondary battery of claim 1 , wherein the amorphous polymer particles of the fusion layer have a size of 0.05 to 0.8 μm.
6. The composite separation membrane for a lithium secondary battery of claim 1 , wherein the fusion layer has a thickness of 2 μm or less.
7. The composite separation membrane for a lithium secondary battery of claim 1 , wherein the amorphous polymer is formed of an acrylate-based polymer, a methacrylate-based polymer, or a copolymer thereof.
8. The composite separation membrane for a lithium secondary battery of claim 1 , wherein the heat-resistant layer includes one or two or more inorganic particles selected from aluminum oxide, barium titanium oxide, titanium oxide, magnesium oxide, clay, glass powder, boron nitride, and aluminum nitride.
9. A preparation method for a composite separation membrane for a lithium secondary battery comprising:
applying a heat-resistant layer coating liquid including inorganic particles and a binder polymer to one side or both sides of a porous base; and
applying a fusion layer coating liquid including amorphous polymer particles having a glass transition temperature of 30° C. or higher to 90° C. or lower on the applied heat-resistant layer coating liquid.
10. The preparation method of claim 9 , wherein the heat-resistant layer coating liquid is applied, and then the fusion layer coating liquid is applied without drying the heat-resistant layer coating liquid, thereby performing simultaneous coating.
11. The preparation method of claim 9 , wherein a difference between the glass transition temperature of the amorphous polymer particles and a fusion temperature of the fusion layer is 60° C. or lower.