Battery

Abstract

To provide batteries with excellent long-term stability.SOLUTION: A battery includes a metallic lithium negative electrode, a porous layer, and a positive electrode arranged in this order, and the porous layer satisfies the following requirements (1) and (2). (1) The average pore diameter P1 of the cross section in the region from the surface of the metallic lithium negative electrode to a depth of 1 μm in the thickness direction is 0.5 μm or more and 30.0 μm or less, and the average porosity V1 is 30% or more and 70% or less. (2) The average pore diameter P2 of the cross section in the region from the surface of the positive electrode to a depth of 1 μm in the thickness direction and the average porosity V2 satisfy the following formulas. P1>P2 (1). V1>V2 (2).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a battery comprising a metallic lithium anode, a porous layer, and a cathode. [Background technology]

[0002] Secondary batteries such as lithium-ion batteries are widely used in portable digital devices such as smartphones, tablets, mobile phones, laptops, digital cameras, digital video cameras, and portable game consoles; portable devices such as power tools, electric motorcycles, and electrically assisted bicycles; and automotive applications such as electric vehicles, hybrid vehicles, and plug-in hybrid vehicles.

[0003] Lithium-ion batteries generally have a configuration in which a positive electrode, in which a positive electrode active material is laminated on a positive electrode current collector, and a negative electrode, in which a negative electrode active material is laminated on a negative electrode current collector, are sandwiched between a secondary battery separator and an electrolyte. Furthermore, lithium-ion batteries are required to have even higher energy densities, and studies are underway to use metallic lithium, which has the highest theoretical capacity, as the negative electrode active material.

[0004] If a polyolefin-based porous substrate, which is the mainstream separator for lithium-ion secondary batteries, is used as is in a secondary battery with a metallic lithium anode, lithium dendrites generated during charging and discharging will cause a short circuit, resulting in the battery not functioning properly. Furthermore, as batteries become larger in capacity, secondary battery separators are required to have long-life stability and safety features.

[0005] In response to these demands, Patent Document 1 proposes impregnating a porous membrane with an ion-conductive polymer material as a protective membrane for the negative electrode, while Patent Document 2 proposes disposing a porous layer containing a heat-resistant resin to impart heat resistance to the separator. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-133940 [Patent Document 2] International Publication No. 2018-155287 Summary of the Invention [Problem to be solved by the invention]

[0007] Patent Document 1 proposes impregnating a porous membrane with a polymeric material having ionic conductivity, such as a homopolymer of vinylidene fluoride or a copolymer with hexafluoropropylene. However, such polymeric materials swell in organic electrolyte solutions and are insufficiently strong against lithium dendrites, resulting in poor long-term stability.

[0008] In Patent Document 2, because the membrane is fine and porous, when a metallic lithium negative electrode is used, lithium dendrites tend to form fine needle-like structures, which tend to trace the pores in the porous membrane and cause short circuits.

[0009] Therefore, in view of the above problems, an object of the present invention is to provide a thin battery with excellent long-term stability. [Means for solving the problem]

[0010] In order to solve the above problems, the battery of the present invention has the following configuration. [1] A battery comprising a metallic lithium negative electrode, a porous layer, and a positive electrode arranged in this order, wherein the porous layer satisfies the following requirements (I) and (II): (I) The average pore size P1 in the cross section in the region from the surface of the metallic lithium negative electrode to a depth of 1 μm in the thickness direction is 0.5 μm or more and 30.0 μm or less, and the average porosity V1 is 30% or more and 70% or less. (II) The average pore diameter P2 and average porosity V2 of the cross section in the region from the surface on the positive electrode side to a depth of 1 μm in the thickness direction satisfy the following formula. P1>P2...Equation (1) V1>V2...Equation (2) [2] The battery according to [1], wherein the average pore diameter P2 is 0.001 μm or more and less than 1.0 μm, and the average porosity V2 is 20% or more and 60% or less. [3] The battery according to [1], wherein the porous layer is composed of at least two layers and is arranged so as to be in contact with the metallic lithium anode and cathode. [4] The battery according to [3], wherein the porous layer comprises a first porous layer made of a fibrous sheet having a thickness of 1 to 30 μm and in contact with the metallic lithium negative electrode, and a second porous layer made of a porous membrane having a thickness of 1 to 30 μm and in contact with the positive electrode. [5] The battery according to [4], wherein the distance between the interface between the metallic lithium negative electrode and the first porous layer and the interface between the positive electrode and the second porous layer is 5 to 60 μm. [6] The battery according to [4] or [5], wherein the first porous layer contains any one of cellulose fibers, polyolefin fibers, polyester fibers, aramid fibers, polyphenylene sulfide fibers, vinyl fibers, plant fibers, and animal fibers. [7] The battery according to [4] or [5], wherein the second porous layer contains one of polyolefin, polyamide, polyamideimide, and polyimide. [Effects of the Invention]

[0011] According to the present invention, a thin battery with excellent long-term stability can be obtained. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below. The battery of the present invention is a battery in which a metallic lithium negative electrode, a porous layer, and a positive electrode are arranged in this order.

[0013] First, the metallic lithium negative electrode of the present invention can suitably be one obtained by forming metallic lithium into a foil, or by laminating metallic lithium on the surface of a negative electrode current collector such as copper by a known method such as rolling, sputtering, vapor deposition, or coating.

[0014] The positive electrode of the present invention may be made of any active material, including layered lithium-containing transition metal oxides such as LiCoO2, LiNiO2, and Li(NiCoMn)O2, spinel-type manganese oxides such as LiMn2O4, iron-based compounds such as LiFePO4, sulfur-based compounds such as elemental sulfur, solid Li2Sn (n is an integer of 1 or greater), organic sulfur, and carbon-sulfur composite polymers, or air, and may be selected according to the battery configuration. A binder resin and a conductive additive may also be used as needed, and examples of suitable materials include those laminated by known methods, such as coating, on a positive electrode current collector such as aluminum metal foil.

[0015] The porous layer of the present invention has a cross-sectional average pore diameter P1 of 0.5 μm to 30.0 μm, preferably 1 μm to 25 μm, and most preferably 5 μm to 20 μm, in a region from the surface on the metallic lithium negative electrode side to a depth of 1 μm in the thickness direction. By setting the average pore diameter P1 within this range, the size of lithium deposited near the interface between the metallic lithium negative electrode and the porous layer can be made uniform.

[0016] The average porosity V1 is 30% or more and 70% or less, preferably 35% or more and 67% or less, and more preferably 40% or more and 65% or less. By setting the average porosity V1 in this range, the mass of the porous layer can be reduced, resulting in a lightweight battery.

[0017] Furthermore, in the porous layer of the present invention, the average pore size P2 and average porosity V2 of the cross section in the region from the surface on the positive electrode side to a depth of 1 μm in the thickness direction must satisfy the following formula. P1>P2...Equation (1) V1>V2...Equation (2)

[0018] Here, P2 and V2 may be substantially free of vacancies as long as they satisfy the requirements of formula 1 and formula 2 and have a structure that conducts lithium ions.

[0019] The average pore diameter P2 is preferably in the range of 0.001 μm or more and less than 1.0 μm, and more preferably 0.01 μm or more and less than 1.0 μm. If the average pore diameter P2 satisfies the formula 1, the precipitated lithium is less likely to become needle-like crystals, and a battery with excellent short-circuit suppression can be obtained.

[0020] Furthermore, the average porosity V2 is preferably in the range of 20% to 60%, more preferably 30% to 60%. If the average porosity V2 satisfies formula 2, the resistance of the porous layer can be reduced, resulting in a battery with excellent ion conductivity. In order to achieve the effects of the present invention, it is preferable that the above characteristics are satisfied simultaneously.

[0021] The porous layer of the present invention may be either a single membrane or a laminate, so long as P1 and P2, and V1 and V2, satisfy the requirements of Formula 1 and Formula 2. For example, in the case of a single membrane, a membrane having a pore structure that is graded or stepwise different between the front and back can be used. Such a porous layer can also be obtained by forming a solvent-dissolved polymer liquid, such as polyolefin, polyester, acrylic, or aromatic polyamide, into a sheet and then rendering it porous by known techniques such as phase separation or extraction.

[0022] In the battery of the present invention, the porous layer preferably comprises at least two layers, which are arranged so as to be in contact with the metallic lithium anode and cathode. By combining porous layers with different pore structures, the size of the deposited lithium can be easily controlled.

[0023] Furthermore, in the porous layer of the present invention, when the porous layer in contact with the metallic lithium negative electrode is designated as the first porous layer and the porous layer in contact with the positive electrode is designated as the second porous layer, the first porous layer is preferably a fibrous sheet having a thickness of 1 to 30 μm. Here, the fibrous sheet refers to cloth, nonwoven fabric, paper, etc. made primarily from synthetic fibers, semi-synthetic fibers, or natural fibers. The thickness of the film of the first porous layer is preferably 2 to 25 μm, more preferably 3 to 20 μm. If the thickness of the first porous layer exceeds 30 μm, the film resistance may increase. If the thickness is less than 1 μm, the lithium deposition morphology may become unstable, film production may become difficult, and sufficient mechanical properties may not be obtained.

[0024] The first porous layer of the present invention preferably contains any one of cellulose fibers, polyolefin fibers, polyester fibers, aramid fibers, polyphenylene sulfide fibers, vinyl fibers, plant fibers, and animal fibers. In particular, fibers containing polar groups with high affinity for lithium, such as oxygen groups, amide groups, sulfone groups, carboxy groups, and fluorine groups, are preferred as the composition of the fibers, and cellulose fibers, aramid fibers, polyphenylene sulfide fibers, and the like are preferably used.

[0025] The second porous layer of the present invention is preferably a porous membrane having a thickness of 1 to 30 μm. Here, the term "porous membrane" refers to a sheet or film in which pores are intentionally formed during the manufacturing process, and known methods can be used for manufacturing the porous membrane, such as forming pores by layer separation, substitution, or exposure, or stretching and fibrillating a polymer membrane. The thickness of the second porous layer is preferably 2 to 28 μm, more preferably 3 to 25 μm. If the thickness of the first porous layer exceeds 30 μm, the membrane resistance may increase, resulting in a battery with poor initial characteristics. If the thickness is less than 1 μm, manufacturing becomes difficult and sufficient mechanical properties may not be obtained.

[0026] The second porous layer of the present invention preferably contains one of polyolefin, polyamide, polyamideimide, and polyimide, and the composition may be a single material or a composite of two or more materials. Among these, polyolefin porous films containing polyolefin are preferred. Specific examples of polyolefin include polyethylene, polypropylene, their copolymers, and mixtures thereof. Examples include single-layer polyolefin porous films containing 90% by mass or more of polyethylene, and multilayer polyolefin porous films composed of polyethylene and polypropylene. Examples of methods for producing polyolefin porous films include a method in which a polyolefin resin is formed into a sheet and then stretched to make it porous, and a method in which a polyolefin resin is dissolved in a solvent such as liquid paraffin, formed into a sheet, and then the solvent is extracted to make it porous. Toray Industries, Inc.'s polyethylene porous film "Setira" can also be suitably used.

[0027] The air permeability of the second porous layer of the present invention is preferably 40 seconds / 100cc or more and 1,000 seconds / 100cc or less, more preferably 40 seconds / 100cc or more and 500 seconds / 100cc or less. If the air permeability is greater than 1,000 seconds / 100cc, sufficient ion mobility may not be obtained, resulting in a deterioration in battery characteristics. If the air permeability is less than 40 seconds / 100cc, sufficient mechanical properties may not be obtained.

[0028] The second porous layer of the present invention preferably has a shutdown function from the viewpoint of improving the safety of the battery, and the shutdown temperature is preferably 100 to 140° C. If the shutdown temperature is 140° C. or less, the shutdown function can operate sufficiently even if the heat generation initiation temperature decreases when the capacity and power of the secondary battery are increased. From the viewpoint of further decreasing the heat generation initiation temperature when the capacity and power of the secondary battery are increased, the shutdown temperature is more preferably 100 to 135° C.

[0029] The porous layer of the present invention may be a laminated film having a coating layer provided on the surface of the film for the purpose of improving battery characteristics such as heat resistance, dendrite resistance, ionic conductivity, oxidation resistance, and reduction resistance. The coating method may be a known method, such as dip coating, gravure coating, slit die coating, knife coating, comma coating, kiss coating, roll coating, bar coating, spray coating, immersion coating, spin coating, screen printing, inkjet printing, pad printing, or other types of printing. The coating method is not limited to these, and may be selected according to the preferred conditions of the resin, inorganic particles, dispersant, leveling agent, solvent used, porous film, etc.

[0030] In the battery of the present invention, the distance between the interface between the metallic lithium negative electrode and the first porous layer and the interface between the positive electrode and the second porous layer is preferably 5 to 60 μm, more preferably 7 to 50 μm, and even more preferably 8 to 40 μm. By setting the distance between the interface between the metallic lithium negative electrode and the first porous layer and the interface between the positive electrode and the second porous layer in such ranges, a thin and lightweight battery can be obtained.

[0031] The porous layer used in the battery of the present invention has an ionic conductivity of 1×10 -5 S / cm or more is preferable. When the porous layer has a laminated structure of two or more layers, it is preferable to achieve this by laminating all materials disposed between the positive electrode and the negative electrode. From the viewpoint of the initial capacity and long-term stability of the battery characteristics, the ionic conductivity is 5 × 10 -5 S / cm or more is preferable, and 1×10 -4 The upper limit of the ionic conductivity is substantially 1×10 -1 It becomes S / cm.

[0032] The electrolyte in the battery of the present invention is a medium for ion transfer between the positive and negative electrodes in the secondary battery, and is composed of an electrolyte dissolved in an organic solvent. Examples of electrolytes include LiPF6, LiTFSI, LiFSI, LiBF4, and LiClO4, with LiPF6 being preferred in terms of solubility in organic solvents and ionic conductivity. Examples of organic solvents include diethyl carbonate, propylene carbonate, fluorodiethyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, gamma butyrolactone, and sulfolane. Two or more of these organic solvents may be mixed and used.

[0033] To fabricate a battery, a cathode active material and a conductive additive are first dispersed in a binder solution to prepare an electrode coating solution. This coating solution is then applied to an aluminum foil current collector, and the solvent is then dried to obtain a cathode. The thickness of the coating film after drying is preferably 50 μm to 500 μm. The anode is obtained by laminating a metallic lithium foil directly or by vapor deposition or rolling onto a copper foil current collector. A porous layer is then placed between the cathode and anode, with the side of the porous layer with the largest pore size and volume porosity in contact with the anode. This is then enclosed in an exterior material such as an aluminum laminate film or a coin-shaped cell. After the electrolyte is injected, a negative electrode lead and a safety valve are installed, and the exterior material is sealed. The resulting battery exhibits excellent battery characteristics and allows for the production of lightweight batteries. [Example]

[0034] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto. The measurement methods used in these examples are as follows.

[0035] [Measurement method] (1) Average pore size of the porous layer (μm) The porous layer obtained in the examples was cryo-processed using a cross-section polisher (JEOL SM-9010), followed by cross-section cutting in the width and thickness directions of the film, and then platinum-coated to prepare an observation sample. Next, using a Hitachi field emission scanning electron microscope (S-4800), 10 locations were observed, covering the area from the surface of the sample to 1 μm in the thickness direction, and obtaining continuous images of 100 μm or more in the width direction. The magnification was 10,000x, and the accelerating voltage during observation was 1.0 kV. The obtained image data was stitched together, and the longest diameter of the pores present within the plane from 100 μm in the width direction and from the surface of the sample to 1 μm in the thickness direction was measured and used as the pore diameter. The average pore diameter of the pores within the plane was calculated, and this was used as the average pore diameter of the sample.

[0036] (2) Average porosity of the porous layer (%) As in (1) above, 10 cross sections of the membrane in the width direction and the longitudinal direction were observed and stitched together. The obtained image data was binarized using a known image processing method, and the area ratio of the pore region present in the plane 100 μm in the width direction and 1 μm from the surface of the sample in the thickness direction was first calculated, and this was taken as the porosity in the width direction. Similarly, the area ratio of the pore region present in the plane 100 μm in the longitudinal direction and 1 μm from the surface of the sample in the thickness direction was calculated, and this was taken as the porosity in the longitudinal direction. Furthermore, the porosities in the width direction and the longitudinal direction were averaged to obtain the average porosity.

[0037] (3) Film thickness (μm) The porous layer obtained in the examples was cryo-processed using a cross-section polisher (SM-9010 manufactured by JEOL Ltd.), followed by cross-section cutting in the thickness direction in the width direction of the film and further platinum coating to prepare an observation sample. Next, the thickness of the sample was measured using a field emission scanning electron microscope (S-4800) manufactured by Hitachi, Ltd. In this case, if the porous layer was a laminate comprising layers of different materials or different forms, the thickness of those layers was also measured. In addition, the distance between the interface between the negative electrode and the first porous layer and the interface between the positive electrode and the second porous layer was taken as the sum of the thicknesses of all films disposed between the negative electrode and the positive electrode.

[0038] (4) Ionic conductivity (S / cm) The porous layer was immersed in an electrolyte (1M LiPF6 ethylene carbonate (EC) / diethyl carbonate (DEC) = 1 / 1) for 24 hours, then placed on a SUS304 electrode to cover the electrode portion, and the same electrolyte was dripped onto it. The layer was then sandwiched between another SUS electrode to create an electrode / porous layer / electrode laminate. The laminate was fixed with a silicon plate to prevent it from shifting, and an evaluation cell was created.

[0039] The AC impedance of the prepared cell was measured at 25°C using an electrochemical tester (Biologic, model number: SP-150) under conditions of an amplitude of 10 mV and a frequency of 1 MHz to 10 mHz. The resistance value was read from a graph plotted on a complex plane and substituted into equation (3) to calculate the ionic conductivity. Five measurements were taken, and the calculated average value was used as the ionic conductivity. σ=T0 / AR Equation (3) σ: Ionic conductivity (S / cm) T0: Thickness of polymer film (cm) A: electrode area (cm 2 ) R: Resistance value (Ω)

[0040] (5) Battery construction The positive electrode sheet contains Li(Ni 5 / 10 Mn 2 / 10 Co 3 / 10 A positive electrode slurry was prepared by dispersing 92 parts by mass of 1000 kJ / cm2, 2.5 parts by mass each of acetylene black and graphite as a positive electrode conductive additive, and 3 parts by mass of polyvinylidene fluoride as a positive electrode binder in N-methyl-2-pyrrolidone using a planetary mixer. The slurry was then applied to aluminum foil, dried, and rolled to prepare a positive electrode (coating weight: 9.5 mg / cm2). 2). This positive electrode sheet was punched out to 15 mm. A lithium metal foil (20 μm thick) with a diameter of 16 mm was used as the negative electrode. Next, the porous layer obtained in the example was punched out to 19 mm. The above positive and negative electrodes were stacked on both sides of the porous layer so that the active material layer separated the samples, and the positive electrode coated area was placed so that the entire area faced the negative electrode coated area. The resultant was then introduced into a coin battery container, and 75 μL of electrolyte was poured into it. After that, a spring was inserted, the lid was closed, and the battery was crimped to obtain a coin battery. The electrolyte used was a 1M LiPF6 ethylene carbonate (EC) / diethyl carbonate (DEC) = 1 / 1 solution.

[0041] (6) Cycle characteristics The cycle characteristics of the prepared coin batteries were tested according to the following procedure and evaluated based on the discharge capacity retention rate. The ambient temperature was 25°C and the charging condition was 2mA / cm. 2 , 4.2V constant current charge, discharge condition 2mA / cm 2 , and constant current discharge at 2.5 V was performed 100 times.

[0042] [Calculation of discharge capacity retention rate] The discharge capacity retention rate was calculated as (discharge capacity after 100 cycles) / (first discharge capacity) x 100. The rating was A: 70% or more, B: 60% or more but less than 70%, and C: less than 60%.

[0043] Example 1 9,9-bis(4-aminophenyl)fluorene (diamine) was dissolved in dehydrated N-methyl-2-pyrrolidone (NMP) under a nitrogen stream and cooled to below 30°C. To this solution, 2-fluoroterephthaloyl chloride (acid dichloride) was added over 30 minutes in an amount equivalent to 100.0 mol% of the total diamine, while maintaining the system at below 30°C under a nitrogen stream. After the entire amount was added, the mixture was stirred for approximately 2 hours to polymerize an aromatic polyamide. The resulting polymerization solution was neutralized with 97 mol% lithium carbonate and 6 mol% diethanolamine, based on the total acid dichloride, to obtain an aromatic polyamide resin solution with an aromatic polyamide resin concentration of 10% by mass. The inherent viscosity (η in h) of the resulting aromatic polyamide was 1.5 dL / g.

[0044] The resulting aromatic polyamide resin solution was diluted with dehydrated NMP to a polymer concentration of 6 wt%, and the mixture was stirred and degassed using a mixer to obtain a solution. The resulting solution was applied to a glass plate cooled to 10°C and then placed in a 45°C water bath to extract the solvent and neutralized salts. The resulting hydrated polymer film was then peeled from the glass plate, fixed to a metal frame, and the surface water was wiped off. Then, the film was heat-treated in a dryer at 100°C for 1 minute to obtain a 5 μm-thick aromatic polyamide porous layer. The surface of the porous layer that had been in contact with the glass plate was placed on the positive electrode side, and a battery was fabricated and evaluated.

[0045] Example 2 Polyvinylpyrrolidone (PVP, weight-average molecular weight 900,000) was added as a thickener to the aromatic polyamide resin solution obtained in Example 1 at a resin component weight ratio of 5:5. Dehydrated NMP was then added, and the mixture was diluted to a total polymer concentration of 8 wt%. The mixture was then stirred and degassed using a mixer to obtain a solution. The resulting solution was applied to one side of a polyester nonwoven fabric (20 μm thick) using a die coater. It was then passed through an air gap at 25°C for 1 second, and then immersed in a water bath at 15°C for 1 minute to extract the solvent and neutralized salts. The mixture was dried until the solvent evaporated, yielding a porous layer with a laminate structure in which an aromatic polyamide polymer layer was formed on a cellulose nonwoven fabric. A battery was fabricated with the polymer layer facing the positive electrode and evaluated.

[0046] Example 3 The aromatic polyamide resin solution obtained in Example 1 was added to a mixer together with water, and the polymer was precipitated and extracted while stirring. The extracted polymer was washed with water and dried under reduced pressure at 120°C for 24 hours to isolate the aromatic polyamide. The obtained aromatic polyamide and polyvinylpyrrolidone (PVP, weight-average molecular weight 1.2 million) were added to NMP so that the weight ratio of the resin components was 7:3 and the total polymer concentration was 10 wt%, and the mixture was stirred at 60°C for 7 hours to obtain a polymer solution.

[0047] This polymer solution was applied to a stainless steel (SUS316) plate and treated for 1 minute in a temperature- and humidity-controlled atmosphere at 50°C and 85% RH until the coating film devitrified. The devitrified coating film was then peeled off from the stainless steel plate, fixed to a metal frame, and placed in a 60°C water bath for 2 minutes to extract the solvent. After wiping off the surface water, the film was heat-treated in a tenter at 200°C for 1 minute to obtain a 30µm-thick porous aromatic polyamide layer.

[0048] A battery was fabricated and evaluated using this aromatic polyamide porous membrane as the first porous layer and a polyethylene porous membrane "Setira" manufactured by Toray Industries, Inc. (thickness: 12 μm, air permeability: 160 sec / 100 cc) as the second porous layer.

[0049] Example 4 A battery was fabricated and evaluated using a PTFE nonwoven fabric "Poreflon" HP series (thickness: 30 μm) manufactured by Sumitomo Electric Fine Polymers, Inc. as the first porous layer and a polyethylene porous membrane "Setira" manufactured by Toray Industries, Inc. (thickness: 12 μm, air permeability: 160 seconds / 100 cc) as the second porous layer.

[0050] Example 5 A battery was fabricated and evaluated using a cellulose nonwoven fabric "Cellulion" (thickness: 10 μm) manufactured by Nippon Kodoshi Co., Ltd. as the first porous layer and a polyethylene porous membrane "Setira" (thickness: 12 μm, air permeability: 160 seconds / 100 cc) manufactured by Toray Industries, Inc. as the second porous layer.

[0051] (Comparative Example 1) A battery was fabricated and evaluated using only a Toray Industries, Inc. polyethylene porous film "Setira" (thickness: 12 μm, air permeability: 160 seconds / 100 cc) as the porous layer.

[0052] (Comparative Example 2) A battery was fabricated and evaluated using only a cellulose nonwoven fabric "Cellulion" (thickness 10 μm) manufactured by Nippon Kodoshi Co., Ltd. as the porous layer.

[0053] [Table 1]

[0054] As can be seen from Table 1, all of the Examples exhibited sufficient ionic conductivity and the long-term battery characteristics were excellent, whereas the Comparative Examples exhibited insufficient battery characteristics. [Industrial Applicability]

[0055] The battery of the present invention can be widely used as a lithium-ion battery for portable digital devices such as smartphones, tablets, mobile phones, laptop computers, digital cameras, digital video cameras, and portable game consoles; portable devices such as power tools, electric motorcycles, and electrically assisted bicycles; and automotive applications such as electric vehicles, hybrid vehicles, and plug-in hybrid vehicles.

Claims

1. A battery comprising a metallic lithium negative electrode, a porous layer, and a positive electrode arranged in this order, wherein the porous layer satisfies the following requirements (1) and (2): (1) The average pore diameter P1 of the cross section in the region from the surface of the metallic lithium negative electrode to a depth of 1 μm in the thickness direction is 0.5 μm or more and 30.0 μm or less, and the average porosity V1 is 30% or more and 70% or less. (2) The average pore diameter P2 and the average porosity V2 of the cross section in the region from the surface on the positive electrode side to a depth of 1 μm in the thickness direction satisfy the following formula: P1>P2...Formula (1) V1>V2...Formula (2)

2. The battery according to claim 1, wherein the average pore diameter P2 is 0.001 μm or more and less than 1.0 μm, and the average porosity V2 is 20% or more and 60% or less.

3. 2. The battery according to claim 1, wherein the porous layer is composed of at least two layers and is arranged so as to be in contact with the metallic lithium negative electrode and the positive electrode.

4. The battery according to claim 3, wherein the porous layer comprises a first porous layer made of a fibrous sheet having a thickness of 1 to 30 μm in contact with the metallic lithium negative electrode, and a second porous layer made of a porous membrane having a thickness of 1 to 30 μm in contact with the positive electrode.

5. 5. The battery according to claim 4, wherein the distance between the interface between the metallic lithium negative electrode and the first porous layer and the interface between the positive electrode and the second porous layer is 5 to 60 μm.

6. The battery according to claim 4 or 5, wherein the first porous layer contains any one of cellulose fibers, polyolefin fibers, polyester fibers, aramid fibers, polyphenylene sulfide fibers, vinyl fibers, plant fibers, and animal fibers.

7. The battery according to claim 4 or 5, wherein the second porous layer contains one of polyolefin, polyamide, polyamideimide, and polyimide.

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