Resin composition for polymer solid electrolyte and polymer solid electrolyte membrane for all-solid secondary battery comprising same

Abstract

The present invention relates to: a resin composition for polymer solid electrolyte, comprising: a lithium salt; and a blended polymer of a polyacrilonitrile (PAN) polymer and a poly(acrylonitrile-co-methyl methacrylate) (PMMA) copolymer; and a polymer solid electrolyte membrane for an all-solid secondary battery, comprising same.

Description

Resin composition for polymer solid electrolyte and polymer solid electrolyte membrane for all-solid-state secondary battery comprising the same

[0001] The present invention relates to a resin composition for a polymer solid electrolyte and a polymer solid electrolyte membrane for an all-solid-state secondary battery comprising the same.

[0002] All-solid-state secondary batteries, which are attracting attention as next-generation batteries, use a solid material that allows lithium ions to move between the positive and negative electrodes instead of the separator and liquid electrolyte used in existing LiBs. This reduces the risk of lithium dendrites and prevents side reactions with the liquid electrolyte, showing the potential for high-power, high-stability batteries. The solid electrolyte materials for all-solid-state secondary batteries currently under development include sulfide, oxide, and polymer electrolytes. Sulfide solid electrolytes have the disadvantage of high interfacial resistance, requiring compression at high temperatures and pressures, and are vulnerable to moisture. Oxide solid electrolytes have the disadvantage of relatively low ionic conductivity. In contrast, polymer solid electrolytes are easy to manufacture and operate at room temperature, and thus, extensive research is being conducted on them.

[0003] [Prior Art Literature]

[0004] [Patent Document]

[0005] (Patent Document 1) Republic of Korea Patent Publication No. 10-2022-0026768

[0006] The present invention aims to provide a polymer solid electrolyte resin composition having high stability and capable of improving capacity retention rate according to charge and discharge, and a polymer solid electrolyte membrane for an all-solid-state secondary battery comprising the same.

[0007] One embodiment of the present invention provides a resin composition for a polymer solid electrolyte, comprising a lithium salt; and a blended polymer of a PAN (polyacrilonitrile) polymer and a PAN-co-PMMA (poly(acrylonitrile-co-methyl methacrylate)) copolymer.

[0008] Another embodiment of the present invention provides a polymer solid electrolyte membrane for an all-solid-state secondary battery comprising the resin composition for the polymer solid electrolyte.

[0009] Another embodiment of the present invention provides an all-solid-state secondary battery including the polymer solid electrolyte membrane for the all-solid-state secondary battery.

[0010] A polymer solid electrolyte membrane for an all-solid-state secondary battery comprising a polymer solid electrolyte resin composition according to the present invention has high lithium ion conductivity and enables uniform deposition of lithium ions during charge and discharge, thereby improving battery stability and lifespan.

[0011] Figure 1 is a schematic diagram showing the mixing of a PAN polymer and a PAN-co-PMMA copolymer of a blending polymer according to the present invention.

[0012] Figure 2 shows the surface of a lithium metal negative electrode after evaluating the discharge retention rate of a coin cell according to Comparative Example 1.

[0013] Figure 3 shows the surface of a lithium metal negative electrode after evaluation of the discharge retention rate of a coin cell according to Example 1.

[0014] Figure 4 shows the results of evaluating the discharge capacity retention rate of coin cells according to Example 1 and Comparative Examples 1 to 3.

[0015] In this specification, when a part is said to "include" a certain component, this does not mean that it excludes other components, but rather that it may include other components, unless specifically stated otherwise.

[0016] In this specification, when it is said that a member is located "on" another member, this includes not only cases where the member is in contact with the other member, but also cases where another member exists between the two members.

[0017] In this specification, the unit “parts by weight” may mean the weight ratio between each component.

[0018] While PAN (polyacrilonitrile) polymers have shown promise as conventional polymer-based solid electrolytes, their low ionic conductivity necessitates improvement. To address this issue, the inventors of the present invention have continued their research on PAN-based solid polymer electrolyte membranes, resulting in the invention described below.

[0019] Hereinafter, the present invention will be described in detail.

[0020] One embodiment of the present invention provides a resin composition for a polymer solid electrolyte, comprising a lithium salt; and a blended polymer of a PAN (polyacrilonitrile) polymer and a PAN-co-PMMA (poly(acrylonitrile-co-methyl methacrylate)) copolymer.

[0021] In the case of PAN (polyacrilonitrile) polymer, there was a problem that its performance was insufficient for application as a polymer solid electrolyte membrane due to low ionic conductivity. Therefore, a method to form an amorphous region within the PAN polymer structure to facilitate the movement of lithium ions was studied. In the case of a blended polymer that mixes PAN polymer and PMMA polymer, the polymer does not mix but exists as a separate phase, so the movement of lithium ions is not smooth, and the surface unevenness is too high when manufactured into a polymer solid electrolyte membrane, making it impossible to apply it to a polymer solid electrolyte membrane. In contrast, in the case of blending PAN polymer and PAN-co-PMMA (poly(acrylonitrile-co-methyl methacrylate)) copolymer as in the present invention, it was discovered that the PAN unit and the PAN polymer in the PAN-co-PMMA copolymer can be mixed with each other, thereby minimizing the problem of insolubility between different polymers.

[0022] Figure 1 is a schematic diagram showing the PAN polymer and PAN-co-PMMA copolymer of the blending polymer according to the present invention being mixed with each other. Specifically, the blending polymer of the present invention can be mixed by inserting the PAN polymer into the crystalline chain section of the PAN-co-PMMA copolymer, and the amorphous chain section of the PAN-co-PMMA copolymer can serve as a nanochannel for the movement of lithium ions, thereby facilitating the movement of lithium ions more smoothly. Specifically, since the PMMA unit of the PAN-co-PMMA copolymer has an acrylic functional group that activates the dissociation of lithium salts, the movement of lithium ions is smooth, and due to its elastic properties, it can also have a dendrite-blocking effect. Furthermore, since the blending polymer according to the present invention has high miscibility, it can be manufactured into a smooth membrane by minimizing surface unevenness when forming a polymer solid electrolyte membrane.

[0023] According to one embodiment of the present invention, the weight ratio of the PAN polymer and the PAN-co-PMMA copolymer in the blending polymer may be 6:4 to 9.5:0.5. Specifically, the weight ratio of the PAN polymer and the PAN-co-PMMA copolymer in the blending polymer may be 6.5:3.5 to 9.5:0.5, 7:3 to 9.5:0.5, 7.5:2.5 to 9.5:0.5, 8:2 to 9.5:0.5, 8.5:1.5 to 9.5:0.5, 8.7:1.3 to 9.3:0.7, 8.8:1.2 to 9.2:0.8, or about 9:1. Within the weight ratio range of the above PAN polymer and PAN-co-PMMA copolymer, the lithium ion conductivity of the polymer solid electrolyte membrane can be excellent and the decrease in capacity retention rate due to charge and discharge can be minimized.

[0024] According to one embodiment of the present invention, the weight average molecular weight of the PAN-co-PMMA copolymer may be 5000 g / mol or more and 250,000 g / mol or less. If the weight average molecular weight of the PAN-co-PMMA copolymer is less than the above range, the polymer solid electrolyte membrane may have excessively elastic properties and may not be able to function as a polymer solid electrolyte membrane. In addition, if the weight average molecular weight of the PAN-co-PMMA copolymer exceeds the above range, the copolymer may not dissolve in a solvent or the viscosity may increase excessively, which may cause a problem in that film casting is difficult.

[0025] According to one embodiment of the present invention, the weight average molecular weight of the PAN polymer may be 100,000 g / mol or more and 200,000 g / mol or less. If the weight average molecular weight of the PAN polymer is less than the above range, the mechanical properties of the electrolyte membrane, such as tensile strength, may deteriorate, and if it exceeds the above range, the problem of ionic conductivity deteriorating due to crystallinity may occur. Therefore, if the weight average molecular weight of the PAN polymer is within the above range, the mechanical properties and ionic conductivity required for a polymer solid electrolyte membrane can be satisfied.

[0026] According to one embodiment of the present invention, the lithium salt may be selected from LiFSI (lithium bis(fluorosulfonyl) imide), LiTFSI (lithium bis(trifluoromethane sulfonyl) imide), LiPF6, LiBF4, LiAsF6, LiClO4, LiCsPF6, LiNO3, LiPO2F2, LiBr, LiBOB (lithium bis(oxalato) borate), LiDFOB (lithium difluoro(oxalate) borate), LiCF3SO3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiN(SO3CF3)2, LiC4F9SO3, LiAlCl4, and LiTfl(lithium trifluoromethanesulfonate). The lithium salt may play a role in facilitating the movement of lithium ions in the polymer solid electrolyte membrane. Furthermore, Li, which is a cation of the lithium salt in the polymer solid electrolyte membrane, +While the movement of lithium ions is facilitated, the movement of anions is restricted within the polymer solid electrolyte membrane, so that lithium ions are evenly deposited on the negative electrode during charge and discharge of the battery, thereby suppressing the formation of lithium dendrites. In order to maximize this effect, according to one embodiment of the present invention, the content of the lithium salt may be 30 parts by weight or more and 70 parts by weight or less based on 100 parts by weight of the blended polymer. If the content of the lithium salt is less than the above range, sufficient lithium ion conductivity may not be achieved, and if it exceeds the above range, it may not be sufficiently dissolved in the solution, which may cause a problem in that it is difficult to manufacture a uniform film.

[0027] According to one embodiment of the present invention, the polymer solid electrolyte resin composition may further include a plasticizer. The plasticizer may enable smoother movement of ions within the coating layer.

[0028] According to one embodiment of the present invention, the plasticizer may include at least one selected from the group consisting of gamma-Butyrolactone (GBL), glutaronitrile (GN), and succinonitrile (SN). Specifically, the plasticizer may be glutaronitrile (GN).

[0029] According to one embodiment of the present invention, the resin composition for the polymer solid electrolyte may further include a solvent. Specifically, according to one embodiment of the present invention, the solvent may be an organic solvent. More specifically, the organic solvent may include at least one selected from the group consisting of N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolan, formamide, dimethylformamide, dioxolan, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphoric acid, trimethoxy methane, dioxolan derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyrropionate and ethyl propionate.

[0030] Another embodiment of the present invention provides a polymer solid electrolyte membrane for an all-solid-state secondary battery, comprising the polymer solid electrolyte resin composition. The polymer solid electrolyte membrane for an all-solid-state secondary battery may comprise a cured product of the polymer solid electrolyte resin composition, and specifically, may be a cured product of the polymer solid electrolyte resin composition.

[0031] Another embodiment of the present invention provides a method for manufacturing a polymer solid electrolyte membrane for an all-solid-state secondary battery using the polymer solid electrolyte resin composition. Specifically, the method includes the steps of: preparing a polymer solid electrolyte resin composition in which a lithium salt and a blended polymer of a polyacrilonitrile (PAN) polymer and a poly(acrylonitrile-co-methyl methacrylate) (PAN-co-PMMA) copolymer are dissolved in a solvent; and forming a polymer solid electrolyte membrane using the polymer solid electrolyte resin composition using a wet coating method. In this case, the polymer solid electrolyte resin composition includes the configuration and contents as described above.

[0032] According to one embodiment of the present invention, the wet coating method may be to apply the resin composition for the polymer solid electrolyte by bar coating, doctor blade coating, spray coating, flow coating, roll coating, spin coating or gravure coating, and then dry it.

[0033] According to one embodiment of the present invention, the coating thickness of the polymer solid electrolyte resin composition in the wet coating method may be 10 ㎛ to 50 ㎛, 15 ㎛ to 40 ㎛, or 20 ㎛ to 35 ㎛. Within the above thickness range, the surface unevenness of the polymer solid electrolyte membrane after drying can be minimized and the necessary rigidity, etc. When the coating thickness is set as described above, the surface of the coating layer can rise and increase in thickness due to the surface tension of the polymer solid electrolyte resin composition after coating, and the thickness of the polymer solid electrolyte membrane after final drying can be 50 ㎛ to 150 ㎛ or 80 ㎛ to 100 ㎛.

[0034] Another embodiment of the present invention provides an all-solid-state secondary battery comprising the polymer solid electrolyte membrane for the all-solid-state secondary battery. The all-solid-state secondary battery comprises a positive electrode and a negative electrode provided via the above-described polymer solid electrolyte membrane. The all-solid-state secondary battery may be a lithium metal all-solid-state secondary battery that applies the polymer solid electrolyte membrane and applies lithium metal to the negative electrode. However, the present invention is not limited thereto, and components of the positive electrode, negative electrode, and all-solid-state secondary battery may be applied according to the purpose as known in the art.

[0035] Hereinafter, the present invention will be described in detail using examples. However, the examples according to the present invention may be modified in various ways, and the scope of the present invention is not limited to the examples described below. The examples in this specification are provided to more fully explain the present invention to those of ordinary skill in the art.

[0036] [Examples and Comparative Examples]

[0037] A resin composition for a polymer solid electrolyte was prepared with the composition shown in Table 1 below. Specifically, ethylene carbonate was prepared as a solvent for dissolving the polymer, and glutaronitrile (GN) as a plasticizer was added thereto. Then, PAN polymer (Aldrich, Mw: 150,000 g / mol) and PAN-co-PMMA copolymer (Aldrich, PAN 94 wt% and PMMA 6 wt%, Mw: 200,000 g / mol) were dissolved in the prepared solvent, and then lithium salt (LiPF6) was added and dissolved to prepare a resin composition for a polymer solid electrolyte.

[0038] PAN / PAN-co-PMMA (weight ratio)PAN (weight ratio)PAN-co-PMMA (weight ratio)Solvent (weight ratio)Lithium salt (weight ratio)Comparative example 110100855Example 19 / 191855Reference example 18 / 282855Reference example 27 / 373855

[0039] The manufactured polymer solid electrolyte resin composition was cast onto a glass substrate using a doctor blade at a set thickness of 10 μm. Then, the polymer solid electrolyte membrane was obtained by drying in a vacuum oven at about 70°C for about 1 hour.

[0040] Then, coin cells of the size of CR2032 (diameter 20 mm, thickness 32 mm) were manufactured and the ionic conductivity and discharge capacity retention rate were evaluated. NCM811 was used as the positive electrode, Li metal foil was used as the negative electrode, and a polymer solid electrolyte membrane was manufactured between the positive and negative electrodes. The ionic conductivity of the manufactured coin cells and the discharge capacity retention rate were evaluated at a rate of 0.3 C charge and discharge, and the results are shown in Table 2 below.

[0041] PAN / Copolymer Weight Specific Ion Conductivity Discharge Capacity Retention Rate Comparison Example 110 / 01.180%@80cycle Example 19 / 11.894%@100cycle Example 28 / 21.588%@80cycle Example 37 / 31.686%@80cycle

[0042] Fig. 2 shows the surface of a lithium metal anode after the discharge retention rate evaluation of a coin cell according to Comparative Example 1. And, Fig. 3 shows the surface of a lithium metal anode after the discharge retention rate evaluation of a coin cell according to Example 1. Referring to Figs. 2 and 3, it can be confirmed that the polymer solid electrolyte according to Example 1 evenly deposits lithium ions onto the anode during charge and discharge due to its high lithium ion conductivity. It can be inferred that such even lithium deposition suppresses the formation of lithium dendrites, thereby contributing to the improvement of the lifespan of the battery.

[0043] Figure 4 shows the results of evaluating the discharge capacity retention rate of coin cells according to Example 1 and Comparative Examples 1 to 3. Specifically, Examples 1 to 3, in which a blended polymer of a PAN polymer and a PAN-co-PMMA copolymer was applied to a polymer solid electrolyte membrane, exhibited improved ion conductivity and battery life characteristics compared to Comparative Example 1, in which only a PAN polymer was applied to the polymer solid electrolyte membrane. This means that lithium ions move more freely through the PAN polymer and the PAN-co-PMMA copolymer PMMA. Among the examples, Example 1, in which the weight ratio of the PAN polymer and the PAN-co-PMMA copolymer was 9:1, exhibited the best battery characteristics. This is because the content of the PAN polymer and the PAN-co-PMMA copolymer was optimized and blended, resulting in the smoothest movement of lithium ions.

Claims

1. Lithium salt; and PAN (polyacrilonitrile) polymer and A resin composition for a polymer solid electrolyte, comprising a blended polymer of a PAN-co-PMMA (poly(acrylonitrile-co-methyl methacrylate)) copolymer.

2. In claim 1, A resin composition for a polymer solid electrolyte, wherein the weight ratio of the PAN polymer and the PAN-co-PMMA copolymer in the blended polymer is 6:4 to 9.5:0.

5.

3. In claim 1, A resin composition for a polymer solid electrolyte, wherein the weight average molecular weight of the PAN-co-PMMA copolymer is 5,000 g / mol or more and 250,000 g / mol or less.

4. In claim 1, A resin composition for a polymer solid electrolyte, wherein the weight average molecular weight of the PAN polymer is 100,000 g / mol or more and 200,000 g / mol or less.

5. In claim 1, A resin composition for a polymer solid electrolyte, wherein the content of the lithium salt is 30 parts by weight or more and 70 parts by weight or less with respect to 100 parts by weight of the blended polymer.

6. A polymer solid electrolyte membrane for an all-solid-state secondary battery, comprising a resin composition for a polymer solid electrolyte according to claim 1.

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