Battery

Abstract

To provide a new polymer porous membrane.SOLUTION: A polymer porous membrane includes a first layer and a second layer. The first layer is porous. The first layer has a three-dimensional network structure. The second layer is non-porous in an image at a magnification of 50000 times. The ratio of the second layer is larger than 0% and less than 10%. The ratio of the second layer is determined by the formula "the ratio of the second layer (%)=(t2 / t0)×100." t0 represents the thickness of the polymer porous membrane. t2 represents the thickness of the second layer.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a polymer porous membrane, a separator for a battery, an electrode unit, an electrode framework, a battery, and a method for manufacturing a polymer porous membrane.

Background Art

[0002] Japanese Unexamined Patent Application Publication No. 2020-123453 (Patent Document 1) discloses forming a separator layer by a phase separation method.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] It has been proposed to form a polymer porous membrane by phase separation (hereinafter also referred to as "dry-induced phase separation") induced during the drying process of a multicomponent solution. The polymer porous membrane can be used, for example, as a separator for a battery. Hereinafter, the polymer porous membrane may be abbreviated as "porous membrane".

[0005] The multicomponent solution contains a polymer material, a good solvent, and a poor solvent. During drying, the solvent vaporizes from the surface of the solution. As a result, a composition difference may occur between the surface layer of the solution and the bulk of the solution. Consequently, the porous membrane can be formed to include a first layer and a second layer. The first layer is the base layer of the porous membrane. The first layer may have a three-dimensional network structure. The second layer can be formed on the outermost surface of the porous membrane. The second layer is non-porous. The presence of pores cannot be confirmed even in a SEM (Scanning Electron Microscope) image with a magnification of 50,000 times.

[0006] Within a battery, the second layer (non-porous layer) may inhibit ion permeability. In other words, if a porous membrane includes a second layer, the porous membrane may not function as a separator.

[0007] The purpose of this disclosure is to provide a novel porous polymer film. [Means for solving the problem]

[0008] The technical configuration and effects of this disclosure are described below. However, the mechanisms of action described herein include assumptions. The mechanisms of action do not limit the technical scope of this disclosure.

[0009] 1. The polymer porous membrane comprises a first layer and a second layer. The first layer is porous. The first layer has a three-dimensional network structure. The second layer is nonporous in images at a magnification of 50,000x. The proportion of the second layer is greater than 0% and less than 10%. The proportion of the second layer can be determined by the following formula (I). Percentage of the second layer (%) = (t2 / t0) × 100 (I) "t0" indicates the thickness of the porous polymer film. "t2" indicates the thickness of the second layer.

[0010] According to the new findings in this disclosure, when the proportion of the second layer (non-porous layer) to the entire membrane is less than 10%, the second layer becomes ion-permeable. In other words, a porous membrane containing a second layer at a proportion of less than 10% can function as a separator. Furthermore, it has been found that the presence of the second layer offers advantages. Specifically, the presence of the second layer is expected to improve the short-circuit resistance of the battery. This is thought to be because the second layer inhibits the growth of dendrites.

[0011] 2. The second layer may have a proportion of, for example, 2-8%.

[0012] 3. The second layer may have a thickness of, for example, 0.5 to 1.5 μm.

[0013] 4. The first layer may have an average pore diameter of, for example, 500 to 2000 nm.

[0014] 5. The three-dimensional network structure may include, for example, a continuous pore structure.

[0015] For example, a three-dimensional network structure may be formed by partial overlap of bubble-like pores.

[0016] 6. The polymer porous membrane may include, for example, at least one selected from the group consisting of ethylene-vinyl alcohol copolymer (EVOH), polyvinylidene fluoride (PVDF), and polyvinyl alcohol (PVA).

[0017] The raw material of the porous membrane may be a water-insoluble polymer or a water-soluble polymer.

[0018] 7. The polymer porous membrane may have, for example, an air permeability of 32 to 600 s / 100 ml.

[0019] 8. The polymer porous membrane may have, for example, a porosity of 50 to 72%.

[0020] 9. The polymer porous membrane may have, for example, a thickness of 16 to 25 μm.

[0021] 10. The separator for a battery includes a polymer porous membrane.

[0022] The porous membrane may be used, for example, as a separator for a battery. Hereinafter, "separator for a battery" may be abbreviated as "separator".

[0023] 11. The electrode unit includes a polymer porous membrane and an electrode. The polymer porous membrane adheres to the surface of the electrode.

[0024] The porous membrane may be used, for example, in an electrode unit. The electrode unit is a member in which a separator and an electrode are integrated.

[0025] 12. The electrode framework includes a polymer porous membrane.

[0026] 13. The battery includes a first electrode, a separator, a second electrode, and an electrolyte. The second electrode has a polarity different from that of the first electrode. The separator separates the second electrode from the first electrode. The separator includes a polymer porous membrane.

[0027] The battery described in "13." above may include at least one of the separator described in "10." and the electrode unit described in "11."

[0028] 14. The battery includes a first electrode, a second electrode, and an electrolyte. The second electrode has a polarity different from that of the first electrode. The second electrode includes an electrode framework. The second electrode is configured to be charged by a metal deposition reaction in the voids within the first layer and discharged by a metal dissolution reaction.

[0029] The present disclosure also provides a novel use of the porous membrane. In a dissolution-precipitation type battery, the electrode framework provides a reaction field for the active material (metal). The metal can dissolve and precipitate in the voids within the electrode framework (the first layer). The dissolution-precipitation type battery is expected to have a high capacity. Conventionally, dendrite is an issue in dissolution-precipitation type batteries. That is, when metal dendrites grow, there is a possibility of internal short circuit. For example, it is expected that when metal precipitates in the pores (bubbly pores) of the first layer, the metal will not become dendrites but will become块状. Also, it is expected that the volume change of the electrode accompanying the dissolution and precipitation of the metal will be alleviated. Furthermore, due to the presence of the second layer, it is expected that the metal will be confined within the first layer.

[0030] 15. The method for manufacturing a polymer porous membrane includes the following (a) to (c). (a) Prepare a polymer solution by mixing a polymer material, a good solvent, and a poor solvent. (b) Form a liquid film of the polymer solution. (c) Manufacture a polymer porous membrane by drying the liquid film. Poor solvents have higher boiling points compared to good solvents. The polymer porous membrane comprises a first layer and a second layer. The first layer is porous. The first layer has a three-dimensional network structure. The second layer is nonporous in an image at a magnification of 50,000x. The thickness ratio of the second layer is greater than 0% and less than 10%. The thickness ratio of the second layer can be determined by the above formula (I).

[0031] Porous membranes can be formed by drying-induced phase separation. For example, the proportion of the second layer can be adjusted by combinations of factors such as "types of polymer material, good solvent, and poor solvent," "combination of materials," "mixing ratio of materials," and "drying conditions."

[0032] Embodiments of the present disclosure (hereinafter abbreviated as "Embodiments") and examples of the present disclosure (hereinafter abbreviated as "Examples") are described below. However, these embodiments and examples do not limit the technical scope of the present disclosure. [Brief explanation of the drawing]

[0033] [Figure 1] Figure 1 shows an example of a cross-sectional SEM image of a porous polymer membrane in this embodiment. [Figure 2] Figure 2 is a schematic cross-sectional view showing the polymer porous membrane in this embodiment. [Figure 3] Figure 3 is a schematic flowchart of the method for producing a porous polymer membrane in this embodiment. [Figure 4] Figure 4 is a schematic cross-sectional view showing the configuration of the first battery in this embodiment. [Figure 5] Figure 5 is a schematic cross-sectional view showing the configuration of the second battery in this embodiment. [Figure 6] Figure 6 shows cross-sectional and surface SEM images of Nos. 1-5. [Figure 7] Figure 7 shows cross-sectional and surface SEM images of Nos. 6-8. [Figure 8] Figure 8 is a graph showing the measurement results of the DC internal resistance. [Figure 9]Figure 9 is a graph showing the results of the initial charge and discharge cycle. [Figure 10] Figure 10 shows cross-sectional SEM images of Nos. 9-11. [Modes for carrying out the invention]

[0034] <Definitions of Terms, etc.> The phrases “compose,” “include,” “have,” and variations thereof (e.g., “composed of,” etc.) are open-ended. Open-ended descriptions may or may not include additional elements in addition to the required elements. The phrase “consist of” is closed-ended. However, even in closed-ended descriptions, additional elements that are usually incidental or irrelevant to the disclosed technology are not excluded. The phrase “substantially consists of…” is semi-closed. Semi-closed descriptions allow for the addition of elements that do not substantially affect the fundamental and novel characteristics of the disclosed technology.

[0035] Expressions such as "may do" and "may be" are used in a permissive sense, meaning "there is a possibility," rather than in an obligatory sense, meaning "it must be done."

[0036] Elements expressed in the singular form, unless otherwise specified, also include the plural form. For example, "particle" can mean not only "a single particle" but also "an aggregate of particles (powder, powder, group of particles)."

[0037] Unless otherwise specified, the order in which the various steps, actions, and operations included in each method are executed is not limited to the order in which they are described. For example, multiple steps may occur simultaneously. For example, multiple steps may occur one after the other.

[0038] For example, numerical ranges such as "m~n%" include upper and lower limits unless otherwise specified. That is, "m~n%" indicates a numerical range of "m% or more and n% or less". Also, "m% or more and n% or less" includes "greater than m% and less than n%". "Greater than m%" can also be written as "greater than m%". Furthermore, a number arbitrarily selected from within the numerical range may be set as a new upper or lower limit. For example, a new numerical range may be set by arbitrarily combining a number within the numerical range with a number listed in another part of this specification, in a table, in a figure, etc.

[0039] All numerical values ​​are modified by the term "approximately." The term "approximately" may mean, for example, ±5%, ±3%, ±1%, etc. All numerical values ​​may be approximations that vary depending on how the technology disclosed herein is used. All numerical values ​​may be expressed with significant figures. Measured values ​​may be the average of multiple measurements. The number of measurements may be three or more, five or more, or ten or more. Generally, the reliability of the average value is expected to improve with a larger number of measurements. Measured values ​​may be rounded to the nearest significant figure. Measured values ​​may include errors, for example, those associated with the detection limit of the measuring device.

[0040] When a compound is represented by a stoichiometric formula (e.g., "LiCoO2"), this formula is merely a representative example of the compound. The compound may have a non-stoichiometric composition. For example, when lithium cobaltate is represented as "LiCoO2", unless otherwise specified, lithium cobaltate is not limited to a composition ratio of "Li / Co / O = 1 / 1 / 2", but may contain Li, Co, and O in any composition ratio. Furthermore, doping and substitution with trace elements may also be permitted.

[0041] Geometric terms (e.g., "parallel," "perpendicular," "orthogonal," etc.) should not be interpreted strictly. For example, "parallel" may deviate slightly from the strict definition of "parallel." Geometric terms used herein may include tolerances, errors, etc., for example, in design, operation, or manufacturing. Dimensional relationships in the figures may not correspond to actual dimensional relationships. Dimensional relationships (length, width, thickness, etc.) in the figures may be altered to aid in understanding the disclosed technology. Furthermore, some components may be omitted.

[0042] The thickness of a porous membrane can be measured using a constant-pressure thickness gauge. For example, the "PG-01" (or an equivalent product) manufactured by Tech-Lock Corporation can be used. The measurement pressure is 0.8 N.

[0043] The structure of a porous membrane can be determined by the following procedure: A sample of a predetermined size is cut from the porous membrane. The sample is coated with platinum (Pt) to reduce its charge. The sample is placed in liquid nitrogen. The sample is cooled sufficiently. After cooling, the sample is fractured. The fracture surface of the sample is observed using a field emission scanning electron microscope (FE-SEM). For example, a JEOL product named "JSM-7100F" (or an equivalent product) may be used.

[0044] Figure 1 shows an example of a cross-sectional SEM image of a porous polymer membrane in this embodiment. The surface layer of the porous membrane is observed at a magnification of 50,000x. If no open pores are found opening on the surface of the porous membrane at 10 randomly selected locations, it is considered that a second layer exists that is "non-porous in the image at a magnification of 50,000x". However, since ions are permeating through the second layer, it is possible that nanoscale pores that cannot be seen at 50,000x magnification are formed in the second layer. For example, pores with a maximum Ferret diameter of 100 nm or less may be formed.

[0045] The thickness of the second layer (t2) is measured. The thickness of the porous film (t0) is measured using the constant-pressure thickness measuring instrument described above. The proportion of the second layer is determined using the above formula (I).

[0046] The "average pore diameter" is determined by the following procedure: A cross-sectional SEM image of the first layer is prepared. The image magnification may be, for example, 2,000 to 5,000 times. The first layer is observed in the cross-sectional SEM image. The maximum ferret diameter of 100 pores (bubble pores) is measured. The arithmetic mean of the 100 maximum ferret diameters is considered to be the average pore diameter.

[0047] "Air permeability" refers to "air resistance" as defined in "JIS P8117". Air permeability can be measured using a Gurley tester. For example, a Gurley densometer (or equivalent) manufactured by Toyo Seiki Seisakusho can be used.

[0048] Porosity is measured by the following procedure: A sample of a predetermined size is cut from the porous membrane. For example, a punch may be used. The mass and thickness of the sample are measured. The volume of the sample is determined from the area and thickness of the sample. The apparent density is determined from the mass and volume of the sample. The porosity is determined by the following formula (II). Porosity (%)={1-ρ / ρ0}×100 (II) "ρ" indicates the apparent density of the sample. "ρ0" represents the true density of the polymer material (the constituent material of the sample).

[0049] Whether a liquid material is a "good solvent" or a "poor solvent" for a polymer material can be determined by the following criteria: A liquid material is considered a good solvent if 2.5 parts by mass or more of the polymer material can dissolve in 100 parts by mass of the liquid material. A liquid material is considered a poor solvent if 1 part by mass or more of the polymer material cannot dissolve in 100 parts by mass of the liquid material.

[0050] The rate of current over time is represented by the symbol "C". A current of "1C" discharges the battery to its rated capacity in one hour. In charge / discharge conditions, "CC (Constant Current)" indicates a constant current method, and "CCCV (Constant Current - Constant Voltage)" indicates a constant current-constant voltage method.

[0051] The term "electrode" is a general term for both positive and negative electrodes. An electrode may be either a positive or negative electrode.

[0052] The "average degree of polymerization" can be measured by general methods. For example, the average degree of polymerization of a polymer material may be measured by NMR (Nuclear Magnetic Resonance).

[0053] "Water-insoluble polymers" refer to polymers whose solubility in water at 25°C is less than 1% by mass fraction. The solubility of water-insoluble polymers may be 0.5% or less, 0.2% or less, or 0.1% or less. "Water-soluble polymers" refer to polymers whose solubility in water at 25°C is 1% or more by mass fraction.

[0054] <Porous polymer membrane> Figure 2 is a schematic cross-sectional view showing a polymer porous membrane in this embodiment. The porous membrane 5 includes a first layer 1 and a second layer 2. The porous membrane 5 can be used in any application. The porous membrane 5 may have arbitrary membrane properties depending on the application, for example. For example, the suitable membrane properties may differ between the separator described later and the electrode framework.

[0055] 《Film Thickness》 The porous membrane 5 may have a thickness of, for example, 1 to 100 μm, 5 to 50 μm, 10 to 30 μm, or 16 to 25 μm.

[0056] Air permeability The porous membrane 5 may have, for example, an air permeability of 10 to 1000 s / 100 ml, an air permeability of 32 to 600 s / 100 ml, an air permeability of 125 to 385 s / 100 ml, or an air permeability of 125 to 300 s / 100 ml.

[0057] 《Porosity》 The porous membrane 5 may have, for example, a porosity of 10-90%, 40-80%, 50-80%, 50-72%, or 64-72%.

[0058] "composition" The porous membrane 5 may be composed of any polymer material. The polymer material may be, for example, water-insoluble or water-soluble. The polymer material may be electrically insulating. The polymer material may be, for example, nonionic conductive. The polymer material may be, for example, non-swelling. The polymer material may include, for example, at least one selected from the group consisting of EVOH, PVDF, and PVA.

[0059] 《1st layer》 The first layer 1 is the base layer of the porous membrane 5. The porous membrane 5 may include a second layer 2 that is more than 0% but less than 10% in thickness, and the remainder being the first layer 1. The first layer 1 is porous. The first layer 1 has a three-dimensional network structure. For example, the three-dimensional network structure may be formed by the partial overlapping of bubble-like pores. That is, the three-dimensional network structure may include a continuous pore structure. The average pore diameter in the first layer 1 may be, for example, 100 to 5000 nm, 500 to 2000 nm, or 500 to 1000 nm.

[0060] 《Second layer》 The second layer 2 is the surface layer of the porous membrane 5. The second layer 2 is formed on one of the main surfaces of the porous membrane 5. The second layer 2 is laminated on the first layer 1. The second layer 2 is nonporous when observed at 50,000x magnification. The second layer 2 is ion permeable. The second layer 2 may inhibit dendrite growth.

[0061] The proportion of the second tier 2 is greater than 0% but less than 10%. The proportion of the second tier 2 could be, for example, 2-8%, 2-7%, 2-6%, or 2-5%. The proportion of the second tier 2 could be, for example, 4-8%, 5-8%, 6-8%, or 7-8%.

[0062] The second layer 2 may have a thickness of, for example, 0.1 to 2 μm, 0.5 to 1.5 μm, 0.5 to 1.0 μm, or 1.0 to 1.5 μm.

[0063] <Method for manufacturing porous polymer membranes> Figure 3 is a schematic flowchart of the method for producing a polymer porous membrane in this embodiment. Hereinafter, "the method for producing a polymer porous membrane in this embodiment" may be abbreviated as "this manufacturing method". This manufacturing method includes "(a) preparation of polymer solution", "(b) formation of liquid film", and "(c) drying".

[0064] (a) Preparation of polymer solution This manufacturing method includes preparing a polymer solution by mixing a polymer material with a good solvent and a poor solvent. The polymer material may have, for example, an average degree of polymerization of 70 to 500,000, or an average degree of polymerization of 100 to 200,000.

[0065] The good solvent and the poor solvent are selected according to the type of polymer material. The poor solvent has a higher boiling point than the good solvent. The boiling point of the poor solvent may be, for example, 10°C or more higher than the boiling point of the good solvent. The boiling point of the poor solvent may be, for example, 90 to 300°C higher than the boiling point of the good solvent.

[0066] For example, when the polymer material is EVOH, PVA, etc., the good solvent may include at least one selected from the group consisting of, for example, water, alcohol, and dimethyl sulfoxide (DMSO). The good solvent may include at least one selected from the group consisting of, for example, water, n-propyl alcohol (nPA), and iso-propyl alcohol (iPA). The poor solvent may include at least one selected from the group consisting of, for example, cyclic esters, alcohols, diols, and ethers. The poor solvent may include at least one selected from the group consisting of, for example, γ-butyrolactone (GBL), hexylene glycol (HG), and diethylene glycol monomethyl ether (DEGEE).

[0067] For example, when the polymer material is PVDF, the good solvent may include at least one selected from the group consisting of N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), and DMSO. The poor solvent may include at least one selected from the group consisting of alcohols and ethers. The poor solvent may also include at least one selected from the group consisting of 1,4-butanediol and glycerin.

[0068] A polymer material, a good solvent, and a poor solvent are mixed in a predetermined proportion. The amount of the good solvent may be, for example, 2 to 10 parts by mass, 4 to 8 parts by mass, or 5 to 6.6 parts by mass per 1 part by mass of polymer material. The amount of the poor solvent may be, for example, 1 to 5 parts by mass, 1 to 3 parts by mass, 1.5 to 2.3 parts by mass, or 1.5 to 2.0 parts by mass per 1 part by mass of polymer material.

[0069] The polymer material, a good solvent, and a poor solvent are mixed so that the polymer material is completely dissolved. To promote the dissolution of the polymer material, the polymer solution may be heated, for example. The heating temperature may be, for example, 80-90°C. After the polymer material has dissolved, the polymer solution may be cooled to room temperature (25°C). The polymer solution may form a homogeneous phase.

[0070] (b) Formation of a liquid film This manufacturing method involves forming a liquid film of a polymer solution. For example, the liquid film may be formed by coating the surface of a substrate with the polymer solution. The coating method is arbitrary. For example, the polymer solution may be coated by a casting method, a spin coating method, etc. For example, the thickness of the polymer porous film can be adjusted by the thickness of the liquid film. The substrate may be, for example, a metal foil. The substrate may also be, for example, a battery electrode.

[0071] 《(c) Drying》 This manufacturing method includes producing a polymer porous film by drying a liquid film. The drying method is arbitrary. For example, the liquid film may be dried on a hot plate. The drying temperature may be, for example, 80 to 150°C. By drying the liquid film, a porous film 5 can be formed. For example, it is thought that a three-dimensional network structure is formed by the following mechanism.

[0072] During drying, the good solvent may vaporize before the poor solvent because the boiling point of the poor solvent is higher than that of the good solvent. As the good solvent decreases, the concentration of the poor solvent in the polymer solution relatively increases. Since the polymer material dissolves selectively in the good solvent, the separation of the phase consisting of the polymer material and the good solvent from the phase consisting of the poor solvent is promoted. This separation may also be spinodal decomposition. Through phase separation, the polymer material forms a three-dimensional network structure framework. In the initial stages of drying, the good solvent-rich solvent vaporizes. As drying progresses, the proportion of the poor solvent increases. In the later stages of drying, the poor solvent-rich solvent vaporizes. As the solvent decreases, the polymer material precipitates. Furthermore, as the poor solvent vaporizes, voids are formed.

[0073] The porous membrane 5 is formed to include a first layer 1 and a second layer 2. In this manufacturing method, various conditions are adjusted so that the proportion of the second layer 2 is greater than 0% and less than 10%. For example, the proportion of the second layer 2 can be adjusted by combinations of "types of polymer material, good solvent, and poor solvent," "combination of materials," "mixing ratio of materials," and "drying conditions."

[0074] After the formation of the porous film 5, the substrate may be removed. For example, if the substrate is a metal foil, the metal foil may be removed by an etching solution. By removing the substrate, the porous film 5 (self-supporting film) may be formed. For example, an electrode unit may be manufactured by forming the porous film 5 on the surface of an electrode.

[0075] <First Battery> The porous membrane 5 can be used as a separator, for example. Figure 4 is a schematic cross-sectional view showing the configuration of the first battery in this embodiment. The first battery 100 may be, for example, a lithium-ion secondary battery. The first battery 100 may include a sealed container (not shown). The sealed container may contain a first electrode 10, a separator 30, a second electrode 20, and an electrolyte (not shown). The second electrode 20 has a different polarity from the first electrode 10. For example, when the first electrode 10 is the positive electrode, the second electrode 20 is the negative electrode. The first electrode 10 may be either the negative electrode or the positive electrode. Each electrode contains an active material. Each electrode may contain, for example, an insertion material. The positive electrode may contain, for example, lithium nickel cobalt manganese oxide (NCM). The negative electrode may contain, for example, natural graphite (NG). Each electrode may further contain, for example, a conductive material. Each electrode may contain, for example, acetylene black (AB). Each electrode may further contain, for example, a binder. Each electrode may contain, for example, PVDF, carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR), etc.

[0076] The electrolyte includes, for example, a lithium (Li) salt and a solvent. The Li salt may include, for example, LiPF6. The concentration of the Li salt may be, for example, 0.5 to 2 mol / L. The solvent may include, for example, at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and diethyl carbonate (DEC).

[0077] Battery separator At least a portion of the separator 30 is interposed between the first electrode 10 and the second electrode 20. The separator 30 separates the second electrode 20 from the first electrode 10.

[0078] The separator 30 includes a porous membrane 5. The separator 30 may consist of a single porous membrane 5. The separator 30 may include multiple porous membranes 5. For example, the separator 30 may be formed by stacking multiple porous membranes 5. For example, multiple porous membranes 5 may be stacked sequentially such that a first layer 1 is stacked on top of a second layer 2. For example, two porous membranes 5 may be stacked so that they are in contact with each other. In this case, the second layer 2 will be positioned near the center of the separator 30.

[0079] The separator 30 may further include additional components in addition to the porous membrane 5. For example, a heat-resistant layer (not shown) may be formed on the surface of the porous membrane 5. For example, the heat-resistant layer may be formed by coating the surface of the porous membrane 5 with ceramic particles.

[0080] The porous membrane 5 includes a first layer 1 (porous layer) and a second layer 2 (non-porous layer). The presence of the second layer 2 between the positive and negative electrodes is expected to improve short-circuit resistance. This is thought to be because the second layer 2 inhibits the growth of dendrites extending from the negative electrode towards the positive electrode. A desired battery resistance can be achieved by having the proportion of the second layer 2 be less than 10%. The second layer 2 may face either the positive or negative electrode.

[0081] Electrode Unit The separator 30 (porous film 5) may be attached to the surface of the first electrode 10. By integrating the separator 30 with the first electrode 10, an electrode unit 40 is formed. That is, the electrode unit 40 includes the porous film 5 and the first electrode 10. Of course, the first electrode 10 may be a positive electrode or a negative electrode. For example, the electrode unit 40 can be manufactured by using the first electrode 10 as a substrate and manufacturing the porous film 5 on its surface. By integrating the separator 30 with the electrode, for example, a reduction in the number of parts and simplification of battery assembly can be expected.

[0082] The first electrode 10 may include, for example, a first current collector 11 and a first active material layer 12. The first current collector 11 may include, for example, a metal foil. The first current collector 11 may include, for example, an aluminum (Al) foil. The first active material layer 12 contains an active material. The active material may be particles. The first active material layer 12 may further include, for example, a conductive material, a binder, etc. The porous film 5 may be attached to the surface of the first active material layer 12, for example.

[0083] <Second Battery> The porous membrane 5 can be used, for example, as an electrode framework. Figure 5 is a schematic cross-sectional view showing the configuration of the second battery in this embodiment. The second battery 200 is of the elution-discharge type. The second battery 200 may be, for example, a lithium metal secondary battery. The second battery 200 may include a sealed container (not shown). The sealed container may contain a first electrode 10, a second electrode 20, and an electrolyte (not shown). A separator 30 may be placed between the first electrode 10 and the second electrode 20. The separator 30 may include, for example, a porous membrane made of polyolefin, a nonwoven fabric, etc. The separator 30 may be manufactured, for example, by a stretching method.

[0084] The second electrode 20 has a different polarity from the first electrode 10. The second electrode 20 may be, for example, a negative electrode. The second electrode 20 includes an electrode framework 23. The second electrode 20 may further include a second current collector 21. The second current collector 21 may include, for example, copper (Cu) foil. The electrode framework 23 may be supported by the second current collector 21. The electrode framework 23 may be attached to the surface of the second current collector 21.

[0085] The second electrode 20 contains a dissolving and eluting type active material. The active material may include, for example, at least one selected from the group consisting of Li metal, magnesium (Mg) metal, calcium (Ca) metal, and Al metal.

[0086] The electrode framework 23 includes a porous membrane 5. The porous membrane 5 includes a first layer 1 (porous layer) and a second layer 2 (non-porous layer). When the second electrode 20 is charged, metal (active material) may precipitate in the voids within the first layer 1. When the second electrode 20 is discharged, the metal may dissolve in the electrolyte within the voids within the first layer 1. Dissolved and ejectable active material (metal) tends to form dendrites upon deposition. It is expected that the deposition of metal in the voids (bubble-like pores) of the first layer 1 will result in a lumpy metal deposition form.

[0087] Typically, electrodes of the dissolution and extraction type undergo a significant volume change during charging and discharging (dissolution and extraction of metal). It is expected that the volume change of the second electrode 20 will be mitigated by the dissolution and extraction of metal occurring within the first layer 1 (three-dimensional network structure).

[0088] Furthermore, because the porous membrane 5 includes a second layer 2 (non-porous layer), it is expected that the metal will be trapped within the first layer 1. This trapping of the metal within the first layer 1 is expected to improve, for example, the cycle life. [Examples]

[0089] <Experiment 1> In Experiment 1, porous membranes corresponding to No. 1 to 8 were manufactured using water-insoluble polymers as raw materials. Hereafter, for example, "porous membrane corresponding to No. 1" may be abbreviated as "No. 1".

[0090] Manufacturing of porous membranes No.1 The following materials were prepared. Polymer material: EVOH (product name "EVAL L171B", manufactured by Kuraray Co., Ltd.) Good solvents: Water, nPA, iPA Poor solvents: GBL, HG Base material: Cu foil

[0091] One part by mass of EVOH, 3.3 parts by mass of water, 3.3 parts by mass of iPA, and 2.0 parts by mass of HG were placed in a sample container. The sample container was heated to 80-90°C. The mixture was stirred at a rotation speed of 350 rpm until the EVOH was completely dissolved, as confirmed by visual inspection. A polymer solution was obtained. The polymer solution was then cooled to 25°C.

[0092] The cooled polymer solution was applied to the surface of the substrate by a casting method, forming a liquid film. The substrate with the liquid film was placed in a hot plate dryer (set temperature: 100°C). The liquid film was dried for 20 minutes. A porous film was formed on the surface of the substrate as the good and poor solvents vaporized. The porous film was separated from the substrate using an etching solution.

[0093] No. 2-8 As shown in Table 1 below, porous films were manufactured in the same manner as in No. 1, except that the type and amount of good solvent, the type and amount of poor solvent, and the drying temperature were changed. It can be seen that the proportion of the second layer changes with the changes in various conditions.

[0094] "evaluation" Film properties The "porous membrane thickness," "porosity," "air permeability," and "average pore diameter" were measured using the method described above. The results are shown in Table 1 below. In the "air permeability" column, ">600" indicates a value greater than 600, and "10<" indicates a value less than 10.

[0095] Percentage of the second layer The "thickness of the second layer" and the "proportion of the second layer" were measured using the method described above. The results are shown in Table 1 below.

[0096] Battery characteristics The DC internal resistance was measured in a test battery (coin cell). The configuration of the test battery was as follows:

[0097] positive electrode Shape: Disc-shaped (Diameter: 14mm) Active material layer composition: NCM / AB / PVDF = 88.8 / 9.4 / 1.8 (mass ratio) Current collector: Al foil

[0098] Separator Shape: Disc-shaped (Diameter: 19mm) Composition: Porous membranes related to No. 1-8 Orientation: The porous membrane is positioned between the positive and negative electrodes so that the second layer faces the negative electrode.

[0099] negative electrode Shape: Disc-shaped (Diameter: 16mm) Composition: NG / SBR / CMC=98.8 / 0.7 / 0.5 (mass ratio) Current collector: Cu foil

[0100] electrolyte Li salt: LiPF6 (concentration: 1.1 ml / L) Solvent: EC / DMC / EMC = 3 / 4 / 3 (volume ratio)

[0101] The internal resistance of the test battery was measured under the following conditions. 1C corresponds to 1.5mA.

[0102] Initial charge / discharge Ambient temperature: 25℃ CCCV charging: 0.2C, 4.1V CC discharge: 0.2C, 3.0V

[0103] Resistance measurement After the initial charge and discharge, the following charge and discharge procedures were performed again under the conditions described below. Ambient temperature: 25℃ CCCV charging: 0.2C, 4.1V CC discharge: 0.2C, 3.0V

[0104] The DC internal resistance was determined from the difference between the voltage at the start of discharge and the voltage 10 seconds after the start of discharge. Of the DC internal resistance, the component from 0 to 0.1 seconds was considered to be "DC + reaction resistance". Of the DC internal resistance, the component from 0.1 to 10 seconds was considered to be "diffusion resistance".

[0105] [Table 1]

[0106] "result" Figure 6 shows cross-sectional and surface SEM images of samples No. 1-5. In samples No. 1-5, a thin second layer (non-porous layer) was formed on the outermost surface of the porous membrane.

[0107] Figure 7 shows cross-sectional and surface SEM images of samples No. 6-8. In sample No. 6, a thick second layer (non-porous layer) was formed on the outermost surface of the porous membrane. In samples No. 7 and 8, open pores were observed on the surface of the porous membrane. In other words, the second layer (non-porous layer) was not formed in samples No. 7 and 8.

[0108] Figure 8 is a graph showing the measured DC internal resistance. No. 6 has a very high DC internal resistance. In No. 6, the proportion of the second layer is 10% or more (see Table 1 above). Nos. 1 to 5 showed the desired DC internal resistance. In Nos. 1 to 5, the proportion of the second layer is less than 10% (see Table 1 above). Note that the DC internal resistance of Nos. 7 and 8 was not measured because they were short-circuited during the initial charging.

[0109] Figure 9 is a graph showing the results of the initial charge and discharge. No. 7 experienced a short circuit during charging. The percentage of the second layer in No. 7 was 0% (see Table 1 above). No. 1 was able to be charged and discharged. The percentage of the second layer in No. 1 was greater than 0% (see Table 1 above).

[0110] <Experiment 2> In Experiment 2, porous membranes corresponding to Nos. 9-11 were manufactured using water-soluble polymers as raw materials.

[0111] Manufacturing of porous membranes No. 9 The following materials were prepared. Polymer material: PVA (product name "POVA PVA117", manufactured by Kuraray Co., Ltd.) Good solvent: water Poor solvent: DEGEE Base material: Cu foil

[0112] 1.5 parts by mass of PVA, 10 parts by mass of water, and 6 parts by mass of DEGEE were placed in a sample container. The sample container was heated to 80-90°C. The mixture was stirred at a rotation speed of 350 rpm until the PVA was completely dissolved, as confirmed by visual inspection. A polymer solution was obtained. The polymer solution was then cooled to 25°C.

[0113] The cooled polymer solution was applied to the surface of the substrate by a casting method, forming a liquid film. The substrate with the liquid film was placed in a hot plate dryer (set temperature: 140°C). The liquid film was dried for 20 minutes. A porous film was formed on the surface of the substrate as the good and poor solvents vaporized. The porous film was separated from the substrate using an etching solution.

[0114] No. 10, 11 As shown in Table 2 below, porous films were manufactured in the same manner as in No. 1, except that the amount of poor solvent used and the drying temperature were changed. It can be seen that the proportion of the second layer changes with the changes in various conditions.

[0115] "evaluation" Using the method described above, the "thickness of the porous membrane," "porosity," and "proportion of the second layer" were measured. The results are shown in Table 2 below.

[0116] [Table 2]

[0117] "result" Figure 10 shows cross-sectional SEM images of samples No. 9-11. It can be seen that porous membranes containing a first and second layer can be manufactured even when water-soluble polymers are used as raw materials.

[0118] These embodiments and examples are illustrative in all respects. These embodiments and examples are not restrictive. The technical scope of this disclosure includes all modifications in the sense and scope equivalent to the claims. For example, it is intended from the outset that any configuration may be extracted from these embodiments and examples and combined in any way. [Explanation of symbols]

[0119] 1 First layer, 2 Second layer, 5 Porous membrane, 10 First electrode, 20 Second electrode, 21 Current collector, 22 Active material layer, 23 Electrode framework, 30 Separator, 40 Electrode unit, 100 First battery, 200 Second battery.

Claims

1. First electrode and, The second electrode and Electrolyte and Includes, The second electrode has a different polarity from the first electrode. The aforementioned second electrode includes a current collector and an electrode framework. The electrode framework includes a polymer porous membrane, The polymer porous membrane is disposed between the first electrode and the current collector. The polymer porous membrane comprises a first layer and a second layer, The first layer is positioned between the current collector and the second layer. The first layer is porous, The first layer has a three-dimensional network structure, The aforementioned second layer is nonporous in an image with a magnification of 50,000 times. The following formula (I): The percentage of the second layer (%) = (t 2 / t 0 ) × 100 (I) (t 0 t indicates the thickness of the polymer porous film, 2 (This indicates the thickness of the second layer.) The percentage of the second layer obtained by this method is greater than 0% and less than 10%, The second electrode is configured to be charged by a metal deposition reaction in the void within the first layer and discharged by a metal dissolution reaction. battery.

2. The aforementioned second layer has a proportion of 2-8%, The battery according to claim 1.

3. The second layer has a thickness of 0.5 to 1.5 μm. The battery according to claim 1 or claim 2.

4. The first layer has an average pore size of 500 to 2000 nm. The battery according to any one of claims 1 to 3.

5. The polymer porous membrane, the three-dimensional network structure, includes a continuous porous structure. The battery according to any one of claims 1 to 4.

6. The polymer porous membrane comprises at least one selected from the group consisting of ethylene-vinyl alcohol copolymer, polyvinylidene fluoride, and polyvinyl alcohol. The battery according to any one of claims 1 to 5.

7. The polymer porous membrane has an air permeability of 32 to 600 s / 100 ml. The battery according to any one of claims 1 to 6.

8. The polymer porous membrane has a porosity of 50 to 72%. The battery according to any one of claims 1 to 7.

9. The polymer porous membrane has a thickness of 16 to 25 μm. The battery according to any one of claims 1 to 8.

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