Aqueous-based coating composition and separator for secondary battery using the same

Abstract

The present invention relates to a water-based coating composition for a coating separator that provides stable thermal shrinkage and lifespan characteristics, and a separator for a secondary battery using the same. The water-based coating composition for a coating separator of a secondary battery according to the present invention comprises a linear polymer containing carboxyl groups and two types of crosslinking monomers. When the water-based coating composition is coated to form a coating separator having a network structure, the crosslinking monomers form secondary bonds with the linear polymer, thereby increasing the bonding strength between the coating materials, suppressing detachment of the coating materials, and providing improved thermal shrinkage and lifespan characteristics.

Description

Technology Field

[0001] The present invention relates to a separator for a secondary battery, and more specifically, to a water-based coating composition for a coating separator that provides stable thermal shrinkage characteristics and lifespan characteristics, and a separator for a secondary battery using the same. Background Technology

[0002] With the recent advancement of the information and communication industry leading to the miniaturization, lightweighting, thinning, and portability of electronic devices, there is a growing demand for higher energy density in the batteries used as power sources for these devices. Lithium-ion batteries are the best batteries to meet these demands, and active research is currently underway in this regard.

[0003] A lithium secondary battery is manufactured by injecting a non-aqueous electrolyte containing a lithium salt and an organic solvent into an electrode structure composed of a positive electrode, a negative electrode, and a separator interposed between the positive and negative electrodes, and is a secondary battery that generates electrical energy through oxidation-reduction reactions when lithium ions are inserted into and extracted from the positive and negative electrodes.

[0004] These lithium-ion batteries are currently gaining attention due to advantages such as higher operating voltage and significantly higher energy density compared to conventional batteries that use aqueous electrolytes, such as Ni-MH batteries, Ni-Cd batteries, and lead-acid batteries.

[0005] The separator, which can be considered to play the most important role among the components of a lithium-ion battery, is responsible for the safety of the battery by preventing electrical short circuits caused by physical contact between the anode and cathode, and must possess excellent thermal stability, chemical stability, and mechanical strength.

[0006] These membranes include coated membranes formed on a base membrane through a coating process based on a single polymer or a composite composition of a mixture of polymer and inorganic material. These coated membranes have an interpenetrating base structure utilizing crosslinking monomers.

[0007] However, conventional coated separators have the disadvantage that the coating material detaches or severe thermal shrinkage occurs due to adhesion issues. Prior art literature

[0008] Published Patent Application No. 2020-0046591 (May 7, 2020) The problem to be solved

[0009] Therefore, the objective of the present invention is to provide a water-based coating composition for a coating separator that increases the bonding strength between coating materials to suppress detachment of the coating materials and provides improved thermal shrinkage characteristics, and a separator for a secondary battery using the same. means of solving the problem

[0010] To achieve the above objective, the present invention provides a water-based coating composition for a coating separator of a secondary battery comprising: a linear polymer containing a carboxyl group; and two types of crosslinking monomers.

[0011] The water-based coating composition for a coating separator of a secondary battery according to the present invention may comprise 1 to 20 wt% of the linear polymer and 80 to 99 wt% of the crosslinking monomer.

[0012] At least one of the two types of crosslinking monomers above may include two or more multi-component functional groups.

[0013] The above multi-component functional group may include vinyl groups and acrylate groups.

[0014] At least one of the two types of crosslinking monomers above may include one of a vinyl group, an acrylate group, and a methacrylate group, and an epoxy group.

[0015] The present invention also relates to a coating separator for a secondary battery formed by coating with a water-based coating composition, wherein the water-based coating composition comprises: a linear polymer containing a carboxyl group; and two types of crosslinking monomers, and forms a network structure between the linear polymer and the crosslinking monomers during the coating process.

[0016] The present invention provides a separator for a secondary battery comprising: a porous base separator; and a coating separator formed by coating the base separator with a water-based coating composition. Effects of the invention

[0017] Since the water-based coating composition according to the present invention includes a crosslinking monomer capable of forming mutual secondary bonds between coating materials when forming a network structure through a coating process, the manufactured coating separation membrane can increase the bonding strength between coating materials to suppress detachment of the coating materials and provide improved thermal shrinkage characteristics.

[0018] As a result, a secondary battery to which a coating separator according to the present invention is applied can provide improved lifespan characteristics.

[0019] Furthermore, since the coating separation membrane according to the present invention is formed from a water-based coating composition, it is environmentally friendly and exhibits superior characteristics in terms of processability. Brief explanation of the drawing

[0020] FIG. 1 is a cross-sectional view showing a separator for a secondary battery comprising a coating separator formed of a water-based coating composition according to the present invention. Figure 2 is a drawing showing an enlarged view of the coating separation membrane of Figure 1. Figure 3 is a photograph showing the thermal shrinkage characteristics of the coating separator according to the example and comparative example. Figure 4 is a graph showing the lifespan characteristics of a secondary battery containing different coated separators in the examples and comparative examples. Specific details for implementing the invention

[0021] It should be noted that in the following description, only the parts necessary for understanding the embodiments of the present invention are explained, and the description of other parts will be omitted to the extent that it does not deviate from the gist of the present invention.

[0022] The terms and words used in the specification and claims described below should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention. Accordingly, the embodiments described in this specification and the configurations illustrated in the drawings are merely preferred embodiments of the invention and do not represent all aspects of the technical spirit of the invention; therefore, it should be understood that various equivalents and modifications capable of replacing them may exist at the time of filing this application.

[0023] Hereinafter, embodiments of the present invention will be described in more detail with reference to the attached drawings.

[0024] FIG. 1 is a cross-sectional view showing a separator for a secondary battery comprising a coating separator formed of a water-based coating composition according to the present invention. FIG. 2 is an enlarged view of the coating separator of FIG. 1.

[0025] Referring to FIGS. 1 and 2, the separator (300) for a secondary battery according to the present invention includes a base separator (200) and a coated separator (100) coated on the base separator (200).

[0026] Here, the base separator (200) is a polymer membrane formed from any one polymer selected from the group consisting of polyethylene, polypropylene, polyethyleneterephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenyleneoxide, cyclic olefin copolymer, polyphenylenesulfide, and polyethylenenaphthalene, or a mixture of two or more of these. It can be a multi-layer, woven, or non-woven fabric.

[0027] And the coating separator (100) is formed by coating a base separator (200) with a water-based coating composition.

[0028] A water-based coating composition comprises a plurality of coating materials capable of forming a network structure through a coating process. That is, the water-based coating composition comprises a linear polymer (10) containing a carboxyl group and two types of crosslinking monomers (20). Here, when a network structure is formed with the linear polymer (10) and two types of crosslinking monomers (20) by coating the water-based coating composition, the crosslinking monomers (20) form a secondary bond (31) with the linear polymer (10).

[0029] The water-based coating composition according to the present invention may include 1 to 20 wt% of a linear polymer (10) and 80 to 99 wt% of a crosslinking monomer (20).

[0030] For example, PAA can be used as the linear polymer (10).

[0031] Two types of crosslinking monomers (20) include a plurality of functional groups (21).

[0032] That is, at least one of the two types of crosslinking monomers (20) includes two or more multi-component functional groups. The multi-component functional groups may include vinyl groups and acrylate groups.

[0033] At least one of the two types of crosslinking monomers (20) may include one of a vinyl group, an acrylate group and a methacrylate group, and an epoxy group.

[0034] For example, PEDGA and glycidyl methacrylate can be used as the two types of crosslinking monomers (20).

[0035] As such, the water-based coating composition according to the present invention includes a crosslinking monomer (20) capable of forming mutual secondary bonds (31) between coating materials when forming a network structure through a coating process, so the manufactured coating separation membrane (100) can increase the bonding strength between coating materials, suppress the detachment of coating materials, and provide improved thermal shrinkage characteristics.

[0036] As a result, a secondary battery to which the coating separator (100) according to the present invention is applied can provide improved lifespan characteristics.

[0037] Since the coating separation membrane (100) according to the present invention is formed from a water-based coating composition, it is environmentally friendly and exhibits superior characteristics in terms of processability.

[0038] In addition, since the coating separator (100) according to the present invention does not use inorganic particles, it also has the advantage of being lightweight in terms of energy density per weight of the cell.

[0039] [Examples and Comparative Examples]

[0040] In order to verify the thermal shrinkage characteristics and lifespan characteristics of the coating separator according to the present invention, separators according to comparative examples and examples were prepared as follows.

[0041] The base membranes of Comparative Example, Example 1, and Example 2 used polymer membranes formed of polyethylene.

[0042] In the comparative example, the base separator without a coated separator was used as is.

[0043] The separator according to Examples 1 and 2 was formed by a coating process on a base separator. PAA, PEDGA, and glycidyl methacrylate were used as water-based coating compositions.

[0044] The water-based coating composition according to Example 1 has a composition of PAA : PEDGA : glycidyl methacrylate of 1 : 3 : 4.

[0045] The water-based coating composition according to Example 2 has a composition of PAA : PEDGA : glycidyl methacrylate of 1 : 4 : 2.

[0046] To confirm the thermal shrinkage characteristics of the separator membranes according to the examples and comparative examples, the shrinkage rate was measured after exposure to 130°C for 1 hour, and the measurement results are shown in Table 1 and Figure 3. Figure 3 is a photograph showing the thermal shrinkage characteristics of the coated separator membranes according to the examples and comparative examples.

[0047]

[0048] Referring to Figure 3, the comparative example that did not form a coating separation film showed a shrinkage rate of 38.9%.

[0049] On the other hand, Examples 1 and 2, in which a coating separation film was formed, showed a shrinkage rate of 1.3%.

[0050] That is, it was confirmed that the separator according to Examples 1 and 2 exhibited improved heat shrinkage characteristics compared to the comparative example.

[0051] In order to examine the electrochemical characteristics of a secondary battery including a separator according to the present invention, NCM622 / graphite-based single cells were fabricated using separators according to the examples and comparative examples. The long-term lifespan of the single cells according to the examples and comparative examples at 0.5C was evaluated, and the evaluation results are shown in Fig. 4. Here, Fig. 4 is a graph showing the lifespan characteristics of a secondary battery including a coated separator according to the examples and comparative examples.

[0052] Referring to Figure 4, in the case of the comparative example, a capacity retention rate of 86.4% was confirmed after 80 cycles of operation.

[0053] On the other hand, after 80 cycles of operation, Example 1 showed a capacity retention rate of 96.5% and Example 2 showed 90.9%.

[0054] That is, it was confirmed that the battery with the separator according to Examples 1 and 2 exhibited improved lifespan characteristics compared to the comparative example.

[0055] Meanwhile, the embodiments disclosed in this specification and drawings are merely specific examples provided to aid understanding and are not intended to limit the scope of the invention. It is obvious to those skilled in the art that other variations based on the technical concept of the invention are possible in addition to the embodiments disclosed herein. Explanation of the symbols

[0056] 10: Linear polymer 20: Crosslinking monomer 21: Sensory organ 31 : Secondary combination 100 : Coating separator 200 : Base separator 300 : Separator

Claims

Claim 1 A water-based coating composition for a coating separator of a secondary battery, comprising: a linear polymer containing a carboxyl group; and two types of crosslinking monomers; wherein the linear polymer comprises PAA, and the two types of crosslinking monomers comprise PEDGA and glycidyl methacrylate; wherein a network structure is formed through mutual secondary bonding between the linear polymer and the crosslinking monomers during the coating process, and wherein lightweighting is possible in terms of energy density per weight of the cell by not using inorganic particles. Claim 2 A water-based coating composition for a coating separator of a secondary battery according to claim 1, comprising 1 to 20 wt% of the linear polymer and 80 to 99 wt% of the crosslinking monomer, wherein the composition of PAA : PEDGA : glycidyl methacrylate is 1 : 3 : 4 or 1 : 4 : 2, characterized in that it provides a capacity retention rate of 90.9% or more after 80 cycles of operation. Claim 3 delete Claim 4 delete Claim 5 delete Claim 6 A coating separator for a secondary battery formed by coating with a water-based coating composition, wherein the water-based coating composition comprises: a linear polymer containing a carboxyl group; and two types of crosslinking monomers; wherein the linear polymer comprises PAA, and the two types of crosslinking monomers comprise PEDGA and glycidyl methacrylate; wherein a network structure is formed between the linear polymer and the crosslinking monomers during the coating process, and the coating separator for a secondary battery is characterized by being lightweight in terms of energy density per unit weight of the cell by not using inorganic particles. Claim 7 A coating separator for a secondary battery according to claim 6, wherein the water-based coating composition comprises 1 to 20 wt% of the linear polymer and 80 to 99 wt% of the crosslinking monomer, and has a composition of PAA : PEDGA : glycidyl methacrylate of 1 : 3 : 4 or 1 : 4 : 2, thereby providing a capacity retention rate of 90.9% or more after 80 cycles of operation. Claim 8 delete Claim 9 delete Claim 10 delete Claim 11 A separator for a secondary battery comprising: a porous base separator; and a coated separator formed by coating the base separator with a water-based coating composition; wherein the water-based coating composition comprises: a linear polymer containing a carboxyl group; and two types of crosslinking monomers; wherein the linear polymer comprises PAA, and the two types of crosslinking monomers comprise PEDGA and glycidyl methacrylate; wherein a network structure is formed between the linear polymer and the crosslinking monomers during the coating process, and wherein lightweighting is possible in terms of energy density per unit weight of the cell by not using inorganic particles. Claim 12 A separator for a secondary battery according to claim 11, wherein the water-based coating composition comprises 1 to 20 wt% of the linear polymer and 80 to 99 wt% of the crosslinking monomer, and has a composition of PAA : PEDGA : glycidyl methacrylate of 1 : 3 : 4 or 1 : 4 : 2, thereby providing a capacity retention rate of 90.9% or more after 80 cycles of operation. Claim 13 delete

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