Separator including porous bonding layer and electrochemical battery including the separator

1. A separator, comprising

a porous substrate; and

a porous bonding layer on one surface or both surfaces of the porous substrate,

wherein the porous bonding layer includes:

a first polyvinylidene fluoride-based polymer, the first polyvinylidene fluoride-based polymer including a polyvinylidene fluoride-based homopolymer or a polyvinylidene fluoride-based copolymer that includes a vinylidene fluoride repeating unit and a hexafluoropropylene repeating unit, and

a second polyvinylidene fluoride-based polymer, the second polyvinylidene fluoride-based polymer including:

a vinylidene fluoride repeating unit and a (meth)acrylate repeating unit, or

a vinylidene fluoride repeating unit and a repeating unit of a monomer that includes at least one of an epoxy group, a hydroxy group, a carboxyl group, an ester group, or an acid anhydride group,

wherein a weight ratio of the first polyvinylidene fluoride-based polymer and the second polyvinylidene fluoride-based polymer is about 2:8 to about 5:5,

wherein the first polyvinylidene fluoride-based polymer includes the polyvinylidene fluoride-based copolymer, and a content of the hexafluoropropylene of the polyvinylidene fluoride-based copolymer of the first polyvinylidene fluoride-based polymer is about 5 wt % to about 20 wt %, based on a total weight of the copolymer,

wherein a weight average molecular weight of the polyvinylidene fluoride-based copolymer including the vinylidene fluoride repeating unit and the hexafluoropropylene repeating unit of the first polyvinylidene fluoride-based polymer is less than or equal to about 800,000 gram/mole,

wherein a content of the vinylidene fluoride repeating unit of the second polyvinylidene fluoride-based polymer is greater than or equal to 87 wt %, based on a total weight of the second polyvinylidene fluoride-based polymer, and

wherein a weight average molecular weight of the second polyvinylidene fluoride-based polymer is from 800,000 to 1,500,000 gram/mole.

2. The separator as claimed in claim 1 , wherein:

a content of the (meth)acrylate repeating unit is less than or equal to about 10 wt %, based on a total weight of the second polyvinylidene fluoride-based polymer, or

a content of the repeating unit of the monomer including at least one of an epoxy group, a hydroxy group, a carboxyl group, an ester group, or an acid anhydride group is less than or equal to about 10 wt %, based on the total weight of the second polyvinylidene fluoride-based polymer.

3. The separator as claimed in claim 1 , wherein the second polyvinylidene fluoride-based polymer is a polymer including the (meth)acrylate repeating unit and the vinylidene fluoride repeating unit.

4. The separator as claimed in claim 1 , wherein the porous bonding layer further includes inorganic particles.

5. The separator as claimed in claim 4 , wherein a weight ratio of the inorganic particles to the first polyvinylidene fluoride-based polymer and the second polyvinylidene fluoride-based polymer is about 8:2 to about 2:8.

6. The separator as claimed in claim 1 , wherein an average transfer rate of positive and negative active materials into the separator is greater than or equal to about 30% after charge and discharge, as calculated by Equation 1:

Transfer rate (%)=( A 1 /A 0 )×100  Equation 1

wherein in Equation 1,

A 0 denotes the entire area of both surfaces of the separator,

A 1 denotes an area sum of positive and negative active materials transferred into the separator when a cell is manufactured by interposing the separator between positive and negative electrodes, primarily compressing them at about 95° C. to about 105° C. for about 1 to about 5 seconds with a pressure of about 1 to about 5 kgf/cm 2 , injecting an electrolyte solution into the compressed positive electrode/separator/negative electrode structure, and secondarily compressing it at about 95° C. to about 105° C. for about 25 to about 40 seconds with a pressure of about 10 to about 200 kgf/cm 2 and then, sequentially charging and discharging under the following conditions:

Charge: 4.35 V, 0.2 C, 50 mA cut-off, and 5 hours,

Discharge: 0.2 C, 3 V cut-off, and 5 hours, and

Charge: 0.5 C, 4 V cut-off, and 2 hours.

7. The separator as claimed in claim 1 , wherein an air permeability of the separator is less than or equal to about 300 sec/100 cc.

8. The separator as claimed in claim 1 , wherein an adhesion force of the porous bonding layer to the porous substrate is greater than or equal to about 0.05 N/mm.

9. An electrochemical battery, comprising:

a positive electrode;

a negative electrode;

the separator as claimed in claim 1 ; and

an electrolyte solution.

10. The electrochemical battery as claimed in claim 9 , wherein:

an adhesion force of the separator to the positive electrode is greater than or equal to about 0.5 gf/5 mm, and

an adhesion force of the separator to the negative electrode is greater than or equal to about 0.1 gf/5 mm.

11. The electrochemical battery as claimed in claim 9 , wherein the electrochemical battery is a rechargeable lithium battery.

12. The separator as claimed in claim 1 , wherein the first polyvinylidene fluoride-based polymer is different from the second polyvinylidene fluoride-based polymer.