Separator for secondary battery and secondary battery including the same

Abstract

The present invention relates to a separator for a secondary battery, which includes a separator body having a porous structure and a particulate polymer embedded in the separator body, wherein the particulate polymer is made of a material that is more heat resistant than the separator body, and which can provide a thin separator with improved heat shrinkage.

Description

[Technical field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0157028 dated November 15, 2021, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a separator for a secondary battery and a secondary battery including the same. More particularly, the present invention relates to a separator for a secondary battery having improved thermal properties by introducing a heat-resistant polymer into a porous separator, and a secondary battery including the same. [Background technology]

[0003] Lithium secondary batteries prevent short circuits caused by contact between the positive and negative electrodes by interposing a separator between them. In addition to heat generation during normal charging and discharging, lithium secondary batteries can also cause short circuits between the positive and negative electrodes due to external impacts. Therefore, in order to improve the heat resistance of the separator, a coating layer containing an inorganic material is added to the outer surface of a separator substrate having a porous structure.

[0004] However, the lithium secondary battery has drawbacks such as low output and safety issues due to side reactions of the electrolyte at high temperatures, and therefore there is an increasing need to find an alternative technology.

[0005] In addition, in order to achieve a high energy density of a secondary battery, attempts are being made to manufacture a separator with a thin thickness. At the same time, various researches are being conducted to prevent the occurrence of an internal short circuit by improving the strength of the separator and reducing the thermal shrinkage rate.

[0006] In this regard, Patent Document 1 discloses a separator for electronic components which is composed of a porous substrate made of a substance having a melting point of 180°C or higher and a resin structure provided on at least one surface and / or inside the substrate, and which contains filler particles having a melting point of 180°C or higher or having substantially no melting point.

[0007] Patent Document 1 provides a separator for electronic components that has very little thermal shrinkage when overheated and is highly reliable, but the separator in Patent Document 1 forms an integrated structure by adding a porous resin structure onto a porous substrate, and therefore it is difficult to manufacture a secondary battery with improved energy density by producing a thin separator.

[0008] Patent Document 2 discloses a separator for a secondary battery in which pressure plastic polymer powder is filled into the pores of a porous nonwoven fabric substrate, and the pores are filled by compression bonding during assembly of the secondary battery.

[0009] In Patent Document 2, a separator for a secondary battery is interposed between a positive electrode and a negative electrode, and is compressed by a hot press process, thereby preventing the pressure-plastic polymer powder from being detached from the porous nonwoven fabric substrate and providing an adhesive force between the separator and the electrodes.

[0010] However, in the separation membrane of Patent Document 2, a part of the pressure plastic polymer melts at a high temperature of 200°C or less to block the pores of the porous nonwoven fabric substrate, thereby preventing internal short circuits. However, in such a case, since the pressure plastic polymer melts, it is difficult to ensure the strength of the separation membrane.

[0011] Therefore, there is a strong need for technology that can reduce the overall thickness of the separation membrane while ensuring the strength and thermal shrinkage rate of the separation membrane by not adding a coating layer that was previously added to the outer surface of the separation membrane substrate. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] JP 2005-302341 A [Patent Document 2] Korean Patent Publication No. 2018-0075003 [Patent Document 3] JP 2013-145717 A Summary of the Invention [Problem to be solved by the invention]

[0013] The present invention has been made to solve the above problems, and aims to provide a separator for a secondary battery having excellent heat resistance and improved strength while minimizing an increase in the total thickness of the separator by incorporating a highly heat-resistant particulate polymer into a separator body having a porous structure, and a secondary battery including the same. [Means for solving the problem]

[0014] To achieve the above object, the separator for a secondary battery according to the present invention includes a separator body having a porous structure and a particulate polymer embedded in the separator body, and the particulate polymer may be made of a material having a higher heat resistance than the separator body.

[0015] The separation membrane body may be made of a porous membrane or a nonwoven fabric.

[0016] At least a portion of the particulate polymer may be inserted into the pores of the separator body.

[0017] The weight of the particulate polymer may be 10% to 80% based on the weight of the separation membrane body.

[0018] The volume of the particulate polymer may be 10% to 80% based on the total volume of the pores of the separation membrane body.

[0019] Based on the air permeability of the separation membrane body alone, the increase in air permeability of the separation membrane body incorporating the particulate polymer may be 30% or less.

[0020] The pore size of the separation membrane body may be 110% to 1,000% of the particle size of the particulate polymer.

[0021] The separation membrane body may be at least one selected from the group consisting of polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, polyacrylonitrile, cellulose, polyethylene naphthalene, and mixtures thereof.

[0022] The material of the particulate polymer may be at least one selected from the group consisting of polyethylene terephthalate, polyimide, polyamide, polysulfone, polyetheretherketone, polyphenylene sulfide, polytetrafluoroethylene, polyetherimide, and polyamide-imide, in a range in which the glass transition temperature (Tg) or melting point (Tm) is higher than that of the material of the separation membrane body.

[0023] The thickness of the separation membrane body not including the particulate polymer may be the same as the thickness of the separation membrane body including the particulate polymer.

[0024] The present invention provides a secondary battery including the separator for a secondary battery.

[0025] Moreover, the present invention can also be provided in the form of a combination of various means for solving the above problems. Effect of the Invention

[0026] As described above, since the separator for a secondary battery according to the present invention includes a particulate polymer inside the pores in the separator body having a porous structure, it is possible to manufacture a thin separator with a minimal increase in thickness when comparing a separator body before the particulate polymer is included and a separator body including the particulate polymer.

[0027] In addition, since the particulate polymer is made of a material having excellent heat resistance, a separator having an improved heat shrinkage rate can be produced.

[0028] In addition, since the particulate polymer is interposed within the separator body having a porous structure, the strength of the separator can be improved. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, when describing the operation principle of the preferred embodiments of the present invention in detail, detailed descriptions of related well-known functions or configurations may unnecessarily obscure the gist of the present invention, and such detailed descriptions will be omitted.

[0030] Throughout the specification, when a part is said to be connected to another part, this includes not only the case where the part is directly connected to another part, but also the case where the part is indirectly connected via another element in between. In addition, when a part includes a certain component, it does not mean that the other component is excluded, but that the part may further include the other component, unless otherwise specified.

[0031] Furthermore, descriptions that limit or add specific elements are applicable to all inventions and are not limited to a particular invention unless otherwise specified.

[0032] Furthermore, throughout the description of the present invention and the claims, the singular includes the plural unless otherwise stated.

[0033] In addition, throughout the description of the present invention and the claims, unless otherwise stated, "or" includes "and." Therefore, "including A or B" means three cases: including A, including B, or including both A and B.

[0034] The separator for a secondary battery according to the present invention includes a separator body having a porous structure and a particulate polymer embedded therein, the particulate polymer being made of a material having a higher heat resistance than the separator body.

[0035] Since the separator contains a particulate polymer having a higher heat resistance than the separator body, the heat resistance is improved compared to a case where the separator is composed only of the separator body, and therefore the heat shrinkage of the separator at high temperatures can be reduced.

[0036] In addition, since the separation membrane body has a porous structure, at least a portion of the particulate polymer having high heat resistance can be inserted and positioned inside the pores of the separation membrane body, thereby providing a separation membrane having a smaller thickness than a conventional separation membrane having a coating layer added to the outer surface of a separation membrane substrate having a porous structure.

[0037] The separator body is an insulating thin film having high ion permeability and mechanical strength, and may be, for example, a polyolefin-based porous membrane or a nonwoven fabric made of a polyolefin-based material, but is not limited thereto.

[0038] Examples of the polyolefin-based porous membrane include membranes formed from polyolefin-based polymers such as polyethylene (e.g., high density polyethylene, linear low density polyethylene, low density polyethylene, ultra-high molecular weight polyethylene), polypropylene, polybutylene, and polypentene, either alone or in combination.

[0039] Examples of the material of the nonwoven fabric include, in addition to the polyolefin-based materials, nonwoven fabrics containing one or more materials selected from the group consisting of polyethylene terephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, polyacrylonitrile, cellulose, polyethylenenaphthalene, and mixtures thereof.

[0040] The nonwoven fabric may be a spunbond or meltblown nonwoven fabric made from long fibers.

[0041] The particulate polymer is made of a material having a higher heat resistance than the separation membrane body, and the material of the particulate polymer has a lower glass transition temperature (T g ) or melting point (T m) in a high range, the polymerizable compound may be one or more selected from the group consisting of polyethylene terephthalate, polyimide, polyamide, polysulfone, polyetheretherketone, polyphenylene sulfide, polytetrafluoroethylene, polyetherimide, and polyamide-imide.

[0042] The weight of the particulate polymer may be determined in consideration of the pore volume, air permeability, etc. of the separation membrane body. In particular, the weight of the particulate polymer may be 10% to 80% based on the weight of the separation membrane body, and more particularly, 20% to 30%.

[0043] If the weight of the particulate polymer is less than 10% based on the weight of the separation membrane body, it is difficult to expect an effect of improving heat shrinkability, and if it is more than 80%, ion conductivity may become an issue, which is not preferable.

[0044] At least a part or all of the particulate polymer is inserted and disposed in the internal pores of the separation membrane body, and the volume of the particulate polymer may be 10% to 80% based on the total volume of the pores of the separation membrane body.

[0045] If the volume of the particulate polymer is less than 10%, it is difficult to obtain the effect of improving heat resistance, and if the volume of the particulate polymer is more than 80%, problems may arise in ion conductivity and resistance increase, which is not preferable.

[0046] In this way, the present invention is configured such that at least a portion of the particulate polymer is inserted into the pores of the separation membrane body, and when the entire particulate polymer is inserted into the pores of the separation membrane body, the thickness of the separation membrane body without the particulate polymer may be the same as the thickness of the separation membrane body including the particulate polymer. Alternatively, at least a portion of the particulate polymer may be located on the surface of the separation membrane body, and the remainder may be inserted into the pores of the separation membrane body. In this case, the thickness of the separation membrane body without the particulate polymer may be smaller than the thickness of the separation membrane body including the particulate polymer.

[0047] The pore size of the separation membrane body may be 110% to 1,000% of the particle size of the particulate polymer. The particulate polymer is inserted into the pores of the separation membrane body, so that the pore size of the separation membrane body can be uniform. Therefore, the electrolyte impregnation and ion conductivity can be uniform throughout the separation membrane.

[0048] The weight ratio of the particulate polymer to the solvent may be 1:1 to 1:10.

[0049] The solution may further include a dispersant to maintain the particle-type polymer in a uniformly dispersed state. The dispersant may be, for example, one selected from the group consisting of polyvinylpyrrolidone, polyacrylic acid hydrazide, poly-N-vinyl-5-methoxazolidon, N-alkyl polyimine, polyvinyl alcohol, N-acetyl polyimine, polyacrylamide, poly-L-lysine hydrobromide, polyacroleine, benzyl-dodecyl-dimethylammonium chloride, polyacrylic acid, polyethyleneimine, 4-vinylpyridine, and methylvinylketone, or an oligomer thereof.

[0050] The present invention will be described below with reference to examples, which are provided for easier understanding of the present invention and are not intended to limit the scope of the present invention.

[0051] <Example 1> Polyether ether ketone (PEE) was used as a particulate polymer. K ) is poured into acetone to produce a particle-type polymer dispersion.

[0052] The particle-type polymer solution is coated on a porous membrane body made of polyolefin (PO) material, which is made of nonwoven fabric, by doctor blade coating to manufacture the membrane.

[0053] The separation membrane was pressed with a pressing roll to prepare a separation membrane in which the particulate polymer was inserted into the internal pores of the separation membrane body.

[0054] The thickness of the thus manufactured separation membrane was made to be the same as that of the separation membrane body.

[0055] The polyether ether ketone was coated at a weight ratio of 20% based on the weight of the separation membrane body.

[0056] <Example 2> A separation membrane was prepared in the same manner as in Example 1, except that polyetheretherketone was used as a particulate polymer in a weight ratio of 30% based on the weight of the separation membrane body.

[0057] <Example 3> A separation membrane was manufactured in the same manner as in Example 1, except that polyphenylene sulfide was used as a particulate polymer in a weight ratio of 20% based on the weight of the separation membrane body.

[0058] <Comparative Example 1> The separator was made of stretched polyolefin (PO) material alone.

[0059] <Comparative Example 2> As the separation membrane, the separation membrane body used in Example 1 was used alone.

[0060] <Comparative Example 3> A separation membrane was prepared in the same manner as in Example 1, except that polyvinylidene fluoride (PVDF) was coated at a weight ratio of 20% based on the weight of the separation membrane body, instead of coating with a particle-type polymer dispersion.

[0061] <Experimental Example 1> Air permeability measurement The air permeability was measured using an air permeability measuring device (EGO-IT, manufactured by Asahi Seiko Co., Ltd.) in accordance with JIS P8117.

[0062] [Table 1]

[0063] Comparing Comparative Example 1 with Comparative Example 2, the pore size of the nonwoven fabric was larger than that of the stretched separation membrane, so the measured air permeability was smaller.

[0064] Comparing Example and Comparative Example 2, the air permeability does not change significantly even though a particulate polymer is inserted into the pores of the nonwoven fabric in Example. This is because the polymer added to the separator is in the form of a particulate polymer and is therefore unable to completely block the pore channels.

[0065] On the other hand, in the case of a non-particulate material such as Comparative Example 3, a part or a large part of the pore channels may be blocked, so that the air permeability shows a high value.

[0066] Therefore, when comparing the air permeability of only the separation membrane body as in Comparative Example 2 with the air permeability of the separation membrane body containing the particulate polymer, it can be confirmed that the increase is less than 30%.

[0067] On the other hand, when polyvinylidene fluoride, which is not a particulate polymer, is coated as in Comparative Example 3, the air permeability increases by about 70% or more based on the air permeability of only the separation membrane body as in Comparative Example 2, which may cause problems such as a decrease in ion conductivity and an increase in resistance.

[0068] <Experimental Example 2> Heat shrinkage measurement Total length 65mm, total width 40.5mm, area 2,632.5mm 2 Samples were prepared and subjected to heat shrinkage treatment at 130°C and 150°C for 30 minutes. After the heat shrinkage treatment, the area of ​​the sample was measured and the area reduction rate was calculated as the shrinkage rate.

[0069] [Table 2]

[0070] Comparing Comparative Example 1 and Comparative Example 2, the nonwoven fabric has better heat shrinkage properties than the stretched separator. This is because the stretched product has a tendency to return to its pre-processing state when exposed to heat due to residual stress remaining after production. On the other hand, the nonwoven fabric is not subjected to stress during production, so it basically has better heat shrinkage properties.

[0071] Therefore, it can be seen that the heat shrinkability is significantly increased in Examples 1 to 3, in which a nonwoven fabric is used as the separator body and a particulate polymer having excellent heat resistance is used.

[0072] On the other hand, the low glass transition temperature (T g ) or melting point (T m In the case of Comparative Example 3 using a polymer having the above structure, it can be seen that the improvement in heat shrinkability is only small compared to Comparative Example 2 using only nonwoven fabric.

[0073] Therefore, when a highly heat-resistant particulate polymer is inserted into a separation membrane body made of a nonwoven fabric material as in the present invention, a separation membrane with significantly improved heat resistance can be provided.

[0074] Those skilled in the art will appreciate that various applications and modifications within the scope of the present invention will be possible based on the above content.

Claims

1. A separator for a secondary battery, A separation membrane body having a porous structure; A particulate polymer contained in the internal pores of the separation membrane body; It consists of: The particulate polymer is made of a material having a higher heat resistance than the separation membrane body, The separation membrane body is made of a nonwoven fabric, The particulate polymer material has a glass transition temperature (Tg) or a melting point (Tm) higher than that of the separator body.

2. 2. The separator for a secondary battery according to claim 1, wherein at least a portion of the particulate polymer is inserted into pores of the separator body.

3. 2. The separator for a secondary battery according to claim 1, wherein a weight of the particulate polymer is 10% to 80% based on a weight of the separator body.

4. 2. The separator for a secondary battery according to claim 1, wherein a volume of the particulate polymer is 10% to 80% of a total volume of pores of the separator body.

5. 2. The separator for a secondary battery according to claim 1, wherein the increase in air permeability of the separator body having the particulate polymer embedded therein is 30% or less based on the air permeability of the separator body alone.

6. 2. The separator for a secondary battery according to claim 1, wherein the pore size of the separator body is 110% to 1,000% of the particle size of the particulate polymer.

7. The separator body may be made of polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, etc.

2. The separator for a secondary battery according to claim 1, which is at least one selected from the group consisting of polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyacrylonitrile, cellulose, polyethylenenaphthalene, and mixtures thereof.

8. 2. The separator for a secondary battery of claim 1, wherein the particulate polymer material is at least one selected from the group consisting of polyethylene terephthalate, polyimide, polyamide, polysulfone, polyetheretherketone, polyphenylene sulfide, polytetrafluoroethylene, polyetherimide, and polyamide-imide.

9. 2. The separator for a secondary battery according to claim 1, wherein a thickness of the separator body not including the particulate polymer is the same as a thickness of the separator body including the particulate polymer.

10. A secondary battery comprising the separator for a secondary battery according to any one of claims 1 to 9.

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