Secondary battery

Abstract

To provide a secondary battery excellent in long-term stability and safety. And to provide a vehicle, an unmanned transport machine, an unmanned aerial vehicle, an electronic device, and a stationary power supply including the secondary battery.SOLUTION: A secondary cell comprising a positive electrode, a negative electrode, and an ion-conducting polymer membrane, wherein the ion-conducting polymer membrane is disposed between the positive electrode and the negative electrode, and the polymer membrane has an average lithium-element content of 3 to 45atomic% and an average fluorine-element content of 3 to 45atomic% in a region from a face of the polymer membrane facing the negative electrode to the 100nm of the polymer membrane in the thickness direction.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a secondary battery, and also to a vehicle, an unmanned transport aircraft, an unmanned aerial vehicle, an electronic device, or a stationary power source that includes the secondary battery. [Background technology]

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

[0003] In recent years, as devices have become smaller and more functional, there has been a demand for higher energy density in the secondary batteries that power them. If metallic lithium could be used for the negative electrode of a secondary battery, it would be possible to achieve a significantly higher capacity than current lithium-ion batteries. However, with metallic lithium negative electrodes, the morphology and composition of the SEI (semiconductor interface) formed on the surface of the negative electrode change during charge and discharge, increasing the interfacial resistance between the negative electrode and the separator and significantly reducing the battery cycle. Furthermore, lithium dendrites that grow with repeated charge and discharge can penetrate the separator and reach the positive electrode, potentially causing a short circuit, thermal runaway, and fire.

[0004] That is, to realize a secondary battery using metallic lithium as the anode, a structure that can achieve both the stability of the coating and the suppression of dendrite growth, which are issues with metallic lithium anodes, is required.

[0005] Forming a protective film on the surface of a metallic lithium negative electrode has been investigated as a method for improving the interfacial stability between the metallic lithium negative electrode and the separator (Patent Documents 1 and 2). In addition, a separator in which a layer containing inorganic particles and a resin material is provided on the surface of a porous film has been used as a method for suppressing dendrite growth (Patent Document 3). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 3989303 [Patent Document 2] Special Publication No. 2019-522879 [Patent Document 3] Patent No. 5994354 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the case of the protective films disclosed in Patent Documents 1 and 2, the lithium fluoride layer formed on the surface of the negative electrode changes in its constituent components due to repeated charge and discharge cycles, or its thickness repeatedly increases and decreases, making the surface morphology unstable and prone to becoming uneven.

[0008] Furthermore, in the case of the separator disclosed in Patent Document 3, since the substrate and surface layer are porous, there is a problem in that dendrites grow along the pores.

[0009] Therefore, in view of the above problems, the present invention provides a secondary battery that is excellent in long-term stability and safety. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention has the following features. [I] A secondary battery having a positive electrode, a negative electrode, and an ion-conductive polymer membrane, wherein the ion-conductive polymer membrane is disposed between the positive electrode and the negative electrode, and the average lithium content of the polymer membrane within a range of 100 nm in the thickness direction from the surface facing the negative electrode is 3 to 45 atomic %, and the average fluorine content is 3 to 45 atomic %. [II] The secondary battery according to [I], wherein the average content ratio of lithium element to fluorine element in the polymer film within a range of 100 nm from the surface facing the negative electrode in the thickness direction is 1:0.8 to 1:1.2. [III] The secondary battery according to [I], wherein the polymer film contains a lithium fluoride component in a range of up to 100 nm in the thickness direction from the surface on the side facing the negative electrode. [IV] The secondary battery according to [I], wherein the thickness of the polymer film is 0.1 μm or more and 10.0 μm or less, and the cross section of the polymer film has a substantially non-porous structure. [V] The secondary battery according to [I], wherein the polymer film is in contact with the negative electrode, and the polymer film is not in contact with the positive electrode. [VI] The secondary battery according to [I], wherein the polymer membrane is in contact with the negative electrode, and at least one selected from a microporous membrane, a nonwoven fabric, a solid electrolyte membrane, a membrane containing an inorganic particle layer, and a membrane containing an organic particle layer is provided between the polymer membrane and the positive electrode. [VII] The secondary battery according to [I], wherein the polymer film contains at least one polymer selected from the group consisting of aromatic polyamides, aromatic polyimides, and aromatic polyamideimides. [VIII] The secondary battery according to [I], wherein the negative electrode is metallic lithium. [IX] A vehicle, unmanned transport aircraft, unmanned flying object, electronic device, or stationary power source comprising the secondary battery according to any one of [I] to [VIII]. [Effects of the Invention]

[0011] According to the present invention, a secondary battery can be provided that can suppress an increase or fluctuation in resistance at the interface between the negative electrode and the polymer film and prevent short circuits caused by dendrites. Also, vehicles, unmanned transport vehicles, unmanned aerial vehicles, electronic devices, and stationary power sources that include the secondary battery can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below. The present invention relates to a secondary battery having a positive electrode, a negative electrode, and an ion-conducting polymer membrane, the ion-conducting polymer membrane being disposed between the positive electrode and the negative electrode, and the average lithium content of the polymer membrane within a thickness direction of 100 nm from the surface facing the negative electrode is 3 to 45 atomic % and the average fluorine content is 3 to 45 atomic %. To achieve the effects of the present invention, it is necessary to simultaneously satisfy these characteristics.

[0013] First, the secondary battery having a positive electrode, a negative electrode, and an ion-conducting polymer film in the present invention is a battery having a configuration in which a polymer film is interposed between 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 or a metal negative electrode, and in which charging and discharging are performed by the movement of lithium ions between the positive and negative electrodes.

[0014] The active material of the positive electrode of the present invention is not particularly limited, and examples thereof include 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, elemental sulfur, and solid Li2S. n (n is an integer of 1 or more), organic sulfur, a sulfur-based compound such as a carbon-sulfur composite polymer, or air, and can be selected according to the configuration of the battery. If necessary, a binder resin or a conductive additive may be used in combination, and for example, a material laminated by a known method such as coating on a positive electrode current collector such as aluminum metal foil can be suitably used.

[0015] The negative electrode of the present invention can be a metal foil such as Li, or a negative electrode material consisting of an active material and a binder resin laminated on a current collector. The active material is not particularly limited, and can be a metal material such as Li, a carbon material such as artificial graphite, natural graphite, hard carbon, or soft carbon, a lithium alloy material such as tin or silicon, or lithium titanate (Li4Ti5O 12) and the like. Examples of binder resins that can be used include fluororesins, acrylic resins, and styrene-butadiene resins. Metal foils are suitable for the current collector, and copper foils are often used in particular. Furthermore, metallic lithium can be preferably used for the purpose of producing a high-energy density secondary battery.

[0016] The ion-conducting polymer membrane of the present invention is a polymer membrane that allows lithium ions to migrate between the positive electrode and the negative electrode. The mechanism by which ions migrate is not particularly limited, and examples include a membrane with physically continuous pores, such as a microporous membrane, or a membrane with a substantially non-porous structure in which lithium ions pass through the gaps between the polymer molecular chains. Examples of polymers that can be used to form the polymer membrane include polyamide, polyimide, polyamideimide, polyetherimide, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, polysulfone, polyethersulfone, polyphenylsulfone, polyketone, polyetherketone, polycarbonate, polyacetal, polyphenylene sulfide, polymethyl methacrylate, polyetheretherketone, polyethersulfone, polyethylene oxide, and urethane (meth)acrylate. These polymers may be used alone or in combination, or may be copolymerized and cured.

[0017] For example, from the viewpoint of ion conductivity, it is preferable to use a polymer obtained by curing urethane (meth)acrylate as a polymer membrane that has excellent swelling in an electrolyte solution. Furthermore, the number average molecular weight of the urethane (meth)acrylate is preferably 5,000 or more, more preferably 10,000 or more. By curing a urethane (meth)acrylate with a number average molecular weight of a certain level or more, it is possible to obtain a polymer membrane that can maintain strength even when thinned, that is easily permeated with an electrolyte solution, and that has high ion conductivity.

[0018] The number of functional groups of the urethane (meth)acrylate is not particularly limited, but from the viewpoint of achieving both ionic conductivity and polymer strength, it is preferable that the number be two or more. Furthermore, the polymer film may be a cured product of a mixture of a polyfunctional urethane (meth)acrylate compound and a monofunctional acrylate compound. When the polymer film is a mixture of a polyfunctional urethane (meth)acrylate compound and a monofunctional acrylate compound, it may be more easily swollen by the electrolyte solution, resulting in increased ionic conductivity.

[0019] The polymer having a urethane (meth)acrylate structure preferably contains an antioxidant, a polymerization initiator, a curing agent, and a catalyst. For example, the polymerization initiator and catalyst can be used to promote crosslinking of the polymer, improve strength, or control flexibility. The polymerization initiator is not particularly limited as long as it promotes crosslinking of the polymer. Suitable initiators include those that can initiate or promote polymerization, condensation, or crosslinking reactions of components contained in the coating composition, such as anionic, cationic, or radical polymerization reactions.

[0020] Various polymerization initiators, curing agents, and catalysts can be used. The polymerization initiators, curing agents, and catalysts may be used alone, or multiple polymerization initiators, curing agents, and catalysts may be used simultaneously. Furthermore, an acidic catalyst or a thermal polymerization initiator may be used in combination. Examples of acidic catalysts include aqueous hydrochloric acid, formic acid, and acetic acid. Examples of thermal polymerization initiators include peroxides and azo compounds. Examples of photopolymerization initiators include alkylphenone compounds, sulfur-containing compounds, acylphosphine oxide compounds, and amine compounds. Examples of crosslinking catalysts that promote the urethane bond-forming reaction include dibutyltin dilaurate and dibutyltin diethylhexoate.

[0021] Furthermore, a leveling agent, a lubricant, an antistatic agent, etc. may be added to the coating composition used to form the polymer film, as long as the effects of the present invention are not impaired. This allows the polymer film to contain a leveling agent, a lubricant, an antistatic agent, etc. Examples of leveling agents include acrylic copolymers, silicone-based leveling agents, and fluorine-based leveling agents. Examples of antistatic agents include metal salts such as lithium salts, sodium salts, potassium salts, rubidium salts, cesium salts, magnesium salts, and calcium salts.

[0022] Furthermore, polyamide, polyimide, or polyamideimide is preferred because the self-supporting property and strength of the polymer film are particularly excellent. In particular, the polymer film of the present invention more preferably contains at least one polymer selected from the group consisting of aromatic polyamide, aromatic polyimide, and aromatic polyamideimide.

[0023] In the case of aromatic polyamides, they contain a structure represented by the following chemical formula (1) and / or chemical formula (2). Ar1 and Ar2 in chemical formula (1) and Ar3 in chemical formula (2) are groups containing an aromatic group, and each may be a single group or a multi-component copolymer with multiple groups. Furthermore, the bonds constituting the main chain on the aromatic ring may be either meta-oriented or para-oriented. Furthermore, some of the hydrogen atoms on the aromatic ring may be substituted with any group.

[0024] In the aromatic polyamide, at least a portion of the aromatic groups of Ar1 and Ar2 in chemical formula (1) or Ar3 in chemical formula (2) is preferably substituted with an electron-withdrawing group. Preferably, 30 to 100 mol % of the total aromatic groups are aromatic groups substituted with electron-withdrawing groups, more preferably 50 to 100 mol %. A content of 30 mol % or more improves solubility in organic solvents. Here, the electron-withdrawing group in the present invention refers to a group with an electronegativity of 2.5 or more. Examples of electron-withdrawing groups include halogen groups such as fluoro, chloro, and bromo groups, halogenated alkyl groups such as trifluoromethyl, nitro, cyano, cyanate, phenyl, and sulfone groups.

[0025] [ka]

[0026] [ka]

[0027] Specific examples of aromatic diamines include paraphenylenediamine, metaphenylenediamine, orthophenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 2,2'-ditrifluoromethyl-4,4'-diaminobiphenyl, 2,2'-ditrichloromethyl-4,4'-diaminobiphenyl, 4,4'-diaminobenzophenone, 3,3'-diaminobenzophenone, 2-chloro-1,4-phenylenediamine, 2-trifluoromethyl-1,4-phenylenediamine, 5-trifluoromethyl-1,3-phenylenediamine, 4,'-oxybis(3-trifluoromethyl)aniline, 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene, 1,5'-naphthalenediamine, and 4,4'-diaminodiphenyl sulfone, but are not limited thereto.

[0028] Specific examples of aromatic dicarboxylic acid halides include terephthalic acid chloride, 2-chloroterephthalic acid chloride, 2-fluoroterephthalic acid chloride, isophthalic acid chloride, 2-chloroisophthalic acid chloride, 2-fluoroisophthalic acid chloride, 2,3,5,6-tetrachloroisophthalic acid chloride, 2,3,5,6-tetrafluoroisophthalic acid chloride, 2,6'-naphthalenedicarboxylic acid chloride, and trimesic acid chloride, but are not limited to these.

[0029] The secondary battery of the present invention has an average lithium content of 3 to 45 atomic % and an average fluorine content of 3 to 45 atomic % in the range from the surface of the polymer film facing the negative electrode to 100 nm in the thickness direction. The average lithium content is preferably 5 to 30 atomic % and 5 to 30 atomic % of fluorine, and more preferably 8 to 25 atomic % and 8 to 25 atomic % of fluorine. By setting the average lithium and fluorine contents within these ranges, resistance increases and fluctuations at the interface between the negative electrode and the polymer film are suppressed, resulting in a secondary battery with high ionic conductivity. The average lithium and fluorine contents in the polymer film can be measured by composition analysis during ion etching from the surface facing the negative electrode using X-ray photoelectron spectroscopy (XPS), as described below.

[0030] When the average lithium content of the polymer film is 3 to 45 atomic % and the average fluorine content is 3 to 45 atomic % within 100 nm of the surface facing the negative electrode in the thickness direction, the polymer film contains lithium ions or lithium compounds, and fluorine ions or fluorine compounds within specific ranges. The presence of lithium components within these ranges is effective in enhancing lithium ion conductivity within the polymer film, while the presence of fluorine components within these ranges is effective in attracting highly affinity lithium ions into the polymer film and facilitating their migration between the electrodes. Furthermore, lithium fluoride, a compound of lithium and fluorine, has high ionic conductivity and a stable structure even in the electrolyte. Therefore, its presence near the surface of the polymer film facing the negative electrode can suppress an increase in the interfacial resistance between the negative electrode and the polymer film.

[0031] The secondary battery of the present invention preferably contains a lithium fluoride component within a thickness direction of 100 nm from the surface of the polymer film facing the negative electrode. Generally, lithium fluoride as a coating formed on the surface of the negative electrode is known to have high ionic conductivity and to inhibit decomposition of the electrolyte. However, coatings composed of inorganic components can develop cracks and breakages due to repeated charge and discharge, resulting in increased or fluctuating interfacial resistance. By including a lithium fluoride component on the surface of the polymer film facing the negative electrode, the battery can achieve the same effects as a coating while solving the problem of cracks and breakages and enabling stable charge and discharge operation over a long period of time.

[0032] In the secondary battery of the present invention, the average content ratio of lithium element to fluorine element in the area from the surface of the polymer film facing the negative electrode to 100 nm in the thickness direction is preferably 1:0.8 to 1:1.2, more preferably 1:0.9 to 1:1.1. When the average content ratio of lithium element to fluorine element is close to 1:1, this indicates that a large amount of lithium fluoride component with excellent ionic conductivity is present on the surface facing the negative electrode, which suppresses resistance increases and fluctuations at the interface between the negative electrode and the polymer film and enables stable charge and discharge operation over a long period of time. There are no particular limitations on the method for producing a secondary battery containing lithium fluoride component on the surface of the polymer film facing the negative electrode, but examples include methods using the polymer film and battery production techniques described below.

[0033] The polymer film of the present invention preferably has a thickness of 0.1 μm or more and 10.0 μm or less, and the cross section of the polymer film preferably has a substantially non-porous structure. The substantially non-porous structure means a structure in which the cross section of the polymer film has no pores within 1 μm when observed by a known method such as a field emission scanning electron microscope. 2This means that there are 10 or fewer pore structures of 100 nm or more per unit area, and the pores are not continuous. If the cross section of the polymer film has a non-porous structure, short circuits due to lithium dendrites can be prevented, resulting in a polymer film with excellent safety. Furthermore, the thickness of the polymer film is more preferably 0.3 μm or more and 7.0 μm or less, and even more preferably 0.5 μm or more and 6.0 μm or less. By setting the thickness of the polymer film within this range, it is possible to obtain a polymer film with an excellent balance between film strength and film resistance.

[0034] The polymer membrane of the present invention has an ionic conductivity of 1×10 -5 S / cm or more is preferable. When the polymer film has a laminated structure of two or more layers, it is preferable to achieve this by laminating all materials placed 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 should be 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.

[0035] In the secondary battery of the present invention, it is preferable that the polymer film is in contact with the negative electrode but not in contact with the positive electrode. Contact of the polymer film with the negative electrode reduces the interfacial resistance during charge and discharge, and not being in contact with the positive electrode prevents oxidation degradation of the polymer film, thereby improving the life characteristics of the secondary battery.

[0036] Furthermore, in the secondary battery of the present invention, the polymer membrane is in contact with the negative electrode, and preferably has at least one selected from a microporous membrane, a nonwoven fabric, a solid electrolyte membrane, a membrane containing an inorganic particle layer, and a membrane containing an organic particle layer between the polymer membrane and the positive electrode. The presence of these membranes prevents contact between the polymer membrane and the positive electrode without impairing charge / discharge characteristics, thereby effectively suppressing oxidative degradation of the polymer membrane. The microporous membrane, nonwoven fabric, solid electrolyte membrane, membrane containing an inorganic particle layer, and membrane containing an organic particle layer disposed between the polymer membrane and the positive electrode are not particularly limited in terms of material, structure, layering configuration, or thickness, as long as they do not impair charge / discharge. For example, in the case of a microporous membrane, a porous substrate made of an olefin material such as polyethylene or polypropylene, a battery separator film "Setira" (registered trademark) manufactured by Toray Industries, Inc., or a CCS film with an alumina particle layer can be suitably used.

[0037] The polymer film of the present invention can be suitably used in various forms, such as a single film, a film pre-laminated on the surface of a metallic lithium negative electrode, or a film pre-laminated on the surface of a microporous membrane, as long as the configuration of the secondary battery of the present invention is satisfied. For example, in the case of a single film, it can be inserted between the metallic lithium negative electrode and the positive electrode. In addition, in the case of a film laminated on the surface of a metallic lithium negative electrode, it may be directly applied to the surface of the negative electrode by a known method and molded, or a polymer film molded on a release film may be transferred to the surface of the negative electrode. In addition, in the case of a film laminated on the surface of a microporous membrane, it may be directly applied to the surface of the microporous membrane by a known method and molded, or a polymer film molded on a release film may be transferred to the surface of the microporous membrane.

[0038] One embodiment of the secondary battery of the present invention is a secondary battery containing an electrolytic solution. The electrolytic solution in the present invention is a place in the battery where ions move between the positive electrode and the negative electrode, and is configured by dissolving an electrolyte in an organic solvent. Examples of the electrolyte include LiPF6, LiTFSI, LiFSI, LiBF4, and LiClO4, and two or more types of electrolytes may be used in combination.

[0039] Examples of organic solvents for the electrolyte include diethyl carbonate (DEC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), gamma butyrolactone (γBL), and sulfolane (SL), and two or more of these organic solvents may be mixed and used.

[0040] Furthermore, methods for introducing lithium fluoride components into the surface of the polymer film facing the negative electrode include, but are not limited to, incorporating lithium fluoride into the polymer film during its manufacturing process, processing the polymer film after molding, such as vapor deposition or coating, or introducing an additive that promotes lithium fluoride generation into a battery using a polymer film and then generating lithium fluoride by charging and discharging with a weak current or by heating. However, to efficiently form a hybrid structure of polymer and lithium fluoride components on the surface of the polymer film facing the negative electrode, a method of generating lithium fluoride after battery assembly is preferred. For example, by adding FEC solvent or LiPF6 electrolyte to the electrolyte and storing the battery at 40 to 60°C for 2 to 48 hours, fluoride ions are generated from the additive, which react with the lithium components inside the battery to generate lithium fluoride components on the surface of the polymer film facing the negative electrode. In particular, by using metallic lithium as the negative electrode, lithium fluoride can be generated in a concentrated manner within a thickness range of 100 nm from the surface of the polymer film facing the metallic lithium negative electrode, suppressing increases and fluctuations in resistance at the interface between the negative electrode and the polymer film and enabling stable charge and discharge operation over the long term.

[0041] To fabricate a secondary battery, first, a cathode active material and a conductive additive are 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 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 metallic lithium foil directly or by vapor deposition or rolling onto a copper foil current collector. A polymer film is then placed between the cathode and anode thus obtained. This is then enclosed in an exterior material such as an aluminum laminate film or a coin-shaped cell. After injecting an electrolyte solution containing an electrolyte, a negative electrode lead and a safety valve are installed, and the exterior material is sealed. When metallic lithium is used for the anode, a current of 0.05 to 0.3 mA / cm is applied to activate the surface of the anode. 2 It is also preferable to perform preliminary charge / discharge for 1 to 30 minutes under the conditions for 1 to 5 cycles.

[0042] When FEC or LiPF6 is used as an additive for lithium fluoride generation, it is dissolved in the electrolyte beforehand and then introduced. The battery containing the additive is then stored in an environment of 40 to 60°C for 2 to 48 hours to generate lithium fluoride components on the surface of the polymer film facing the negative electrode. The secondary battery obtained in this way has excellent long-term stability and safety. [Example]

[0043] 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.

[0044] [Measurement method] (1) Number of pores in the cross section of the polymer membrane The polymer film was cryo-processed using a cross-section polisher (SM-9010 manufactured by JEOL Ltd.), and then cross-sections were cut in the thickness direction and width direction of the film. The film was then platinum-coated to prepare an observation sample. Next, a field emission scanning electron microscope (S-4800 manufactured by Hitachi Ltd.) was used to measure the 1 μm 2Three images of the area were taken. The accelerating voltage was 1.0 kV. The number of pores with a maximum diameter of 100 nm or more was counted in each image. The average of the numbers of pores in the three locations was taken as the number of pores in the sample.

[0045] (2) Thickness of polymer film (μm) The polymer film was cryo-processed using a cross-section polisher (SM-9010 manufactured by JEOL Ltd.), and then cross-sections were cut in the thickness direction and width direction of the film. The film was then platinum-coated to prepare an observation sample. The thickness of the sample was then measured using a field emission scanning electron microscope (S-4800 manufactured by Hitachi Ltd.).

[0046] (3) Ionic conductivity Using an HS cell (manufactured by Hosen Co., Ltd.), a cell was fabricated by stacking an electrode composite with the polymer layer facing the counter electrode, 200 μL of non-aqueous electrolyte (1 M LiTFSI ethylene carbonate (EC) / diethyl carbonate (DEC) = 1 / 1), and a SUS (stainless steel) 304 electrode.

[0047] After leaving the cell to stand for 24 hours in a 25°C environment, the AC impedance of the fabricated cell was measured using an electrochemical tester (Biologic, model number: SP-150) under conditions of 25°C, amplitude 10 mV, and frequency 1 MHz-10 mHz. The resistance value was read from a graph plotted on a complex plane and substituted into the following equation (i) to calculate the ionic conductivity. Five measurements were taken for the same polymer membrane, and the average value was used as the ionic conductivity. σ=T0 / AR (i) σ: Ionic conductivity (S / cm) T0: Thickness of polymer film (cm) A: electrode area (cm 2 ) R: Resistance value (Ω).

[0048] (4) Coin battery production The positive electrode sheet contains Li(Ni 5 / 10 Mn 2 / 10 Co 3 / 10A 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 a diameter of 15 mm. A lithium metal foil (thickness: 20 μm) with a diameter of 16 mm was used as the negative electrode. Next, the polymer film obtained in the example was punched out to a diameter of 19 mm. The sheets were stacked in the order of aluminum foil / positive electrode active material layer / polymer film / negative electrode, and arranged so that the positive electrode coating portion was entirely facing the negative electrode. The resultant was then introduced into a coin battery container, and 80 μL of the nonaqueous electrolyte described in the example was poured thereinto. After that, a spring was inserted, the lid was closed, and the product was crimped to produce a coin battery.

[0049] When a polymer film and a microporous film were used in a laminated state, they were all punched out to a diameter of 19 mm and laminated in the following order: aluminum foil / positive electrode active material layer / microporous film / polymer film / negative electrode.

[0050] When the lithium metal foil onto which the polymer film had been transferred was used as the negative electrode, it was punched out to a diameter of 16 mm, and a microporous membrane punched out to a diameter of 19 mm was used as a separator, and the layers were stacked in the following order: aluminum foil / positive electrode active material layer / microporous membrane / polymer membrane / negative electrode.

[0051] The fabricated coin battery was charged at 0.1 mA / cm under a 25°C environment. 2 10 minutes of charging under conditions of 0.1mA / cm 2 Each battery was discharged for 10 minutes under the conditions described in the examples, and then stored under the conditions described in the examples to obtain the desired coin batteries.

[0052] (5) Lithium and fluorine content (atomic%) The polymer film was removed from the inside of the coin battery fabricated in (4) above and washed by immersing it in diethyl carbonate for 10 seconds. The washed polymer film was then dried in a vacuum dryer at 25°C for 30 minutes. The dried polymer film was subjected to composition analysis using XPS while ion etching from the surface facing the negative electrode, and the composition in the depth direction of the polymer film was profiled. The atomic species of lithium and fluorine were analyzed from the peak positions of the binding energy of each atom, and the ratio of the elements contained in the polymer film was calculated from the peak intensities. The peaks that appeared at 55 eV for Li+ ions and 684 eV for F- ions were used. The measurement conditions and ion etching conditions are as follows: The ion-etched depth was calculated from the etching rate when ion etching was performed using methyl methacrylate (PMMA) as the reference material and the etching time per etching.

[0053] The element ratios in the etching depth range of 0 to 100 nm were averaged to obtain the content of the element. The ratio of lithium element to fluorine element was calculated by taking the lithium element content as 1. [Measurement conditions] Equipment: PHI Genesis (Ulvac-PHI) Excited X-ray: monochromatic Al Kα 1,2 rays (1486.6 eV) X-ray diameter: 200 μm Photoelectron detection angle: 90° (detector angle relative to sample surface) [Ion etching conditions] Ion species: Ar gas cluster ions (Ar-GCIB) Voltage: 10kV Etching time per cycle: 0.4 min Etching rate: 54.2 nm / min (PMMA equivalent value).

[0054] (6) Cycle characteristics The coin battery prepared in (4) above was subjected to a cycle test according to the following procedure, and the discharge capacity retention rate was evaluated. The ambient temperature was 25°C, and the charging condition was 2 mA / cm. 2 , 4.2V constant current charge, discharge condition 2mA / cm 2 The battery was subjected to 100 cycles of constant current discharge at 2.5 V, and the discharge capacity retention rate was calculated using equation (ii).

[0055] Discharge capacity retention rate (%) = (discharge capacity after 100 cycles) / (first discharge capacity) × 100 (ii) The evaluation criteria were A: 70% or more, B: 60% or more but less than 70%, and C: less than 60%, with B or more being considered a pass.

[0056] (7) Dendrite resistance In the cycle test conducted in the same manner as in (6) above, whether or not the test was interrupted due to a sudden rise or fall in voltage was judged. If there was no interruption, it was judged as pass (○), and if there was an interruption, it was judged as fail (×).

[0057] (Reference Example 1) Polymer stock solution P-1 2,2'-Ditrifluoromethyl-4,4'-diaminobiphenyl (diamine) was dissolved in dehydrated N-methyl-2-pyrrolidone (hereinafter referred to as NMP) under a nitrogen stream and cooled to below 30°C. To this solution, 2-fluoroterephthalic acid chloride (acid dichloride) equivalent to 98.8 mol% of the total amount of diamine was added over 30 minutes while maintaining the system at below 30°C under a nitrogen stream. After the complete addition, the mixture was stirred for approximately 2 hours to polymerize an aromatic polyamide polymer solution (P-1). The resulting polymerization solution was neutralized with 90.7 mol% of lithium carbonate (acid dichloride) and further neutralized with 8 mol% of diethanolamine to obtain a polymer stock solution with an aromatic polyamide concentration of 8% by mass. The intrinsic viscosity (ηinh) of the resulting polymer was 4.0 dL / g.

[0058] (Reference Example 2) Polymer stock solution P-2 The polymer stock solution P-1 was poured into purified water in an amount of 10 times by weight or more, and the solvent and neutralization salt were extracted into the water. The precipitated polymer was separated and then vacuum dried at 80°C for 10 hours to obtain aromatic polyamide P-1 powder. The polymer was then redissolved in dehydrated NMP to a polymer concentration of 2% by mass to obtain polymer stock solution P-2.

[0059] (Reference Example 3) Polymer stock solution P-3 A four-neck flask equipped with a thermometer, a condenser, and a stirrer was charged with 15.8 parts by mass of polycaprolactone triol (manufactured by Daicel Corporation, "PLACCEL" (registered trademark) 312) and 47.6 parts by mass of polycaprolactone diol (manufactured by Daicel Corporation, "PLACCEL" (registered trademark) L212AL) ​​as component A, and 32.2 parts by mass of an allophanate-modified hexamethylene diisocyanate (manufactured by Covestro AG, "Desmodur" (registered trademark) XP2580), 0.03 parts by mass of dibutyltin laurate (manufactured by Nitto Kasei Co., Ltd., "Neostan" (registered trademark) U-100), and 67 parts by mass of methyl isobutyl ketone (hereinafter referred to as MIBK) as component B. The internal temperature was maintained at 60°C while nitrogen was blown in, and the reaction was carried out for 5 hours. Next, 4.4 parts by mass of 2-hydroxyethyl acrylate (HEA manufactured by Osaka Organic Chemical Industry Co., Ltd.) and 0.1 parts by mass of hydroquinone monomethyl ether were added as component C, and the mixture was reacted at the same temperature for 3 hours while blowing in air. After that, the isocyanate group content was confirmed to be 0.1% or less according to the method of JIS K7301 (1995), and polymer P-3 was obtained, which had a weight-average molecular weight of 9,300 and a functionality of 3. The molecular weight of polymer P-3 was measured using a GPC apparatus HLC-8220 (manufactured by Tosoh Corporation).

[0060] 167 parts by mass of the obtained polymer, 3.0 parts by mass of an α-hydroxyacetophenone-based photopolymerization initiator (manufactured by IGM Resins BV, product name: "Omnirad" (registered trademark) 184), 0.2 parts by mass of a non-silicone-based leveling agent (manufactured by BYK Additives & Instruments, product name: BYK-3560), and 36.5 parts by mass of a solvent (methyl ethyl isobutyl ketone) were uniformly mixed to obtain polymer stock solution P-3.

[0061] Example 1 A solution was prepared by dispersing lithium fluoride nanoparticles (average particle size 100 nm) in dehydrated NMP to a solids concentration of 10% by mass. Next, polymer stock solution P-1 and the lithium fluoride nanoparticle solution were mixed so that the solids in each solution were in a 50:50 ratio to prepare a polymer solution. The polymer solution was cast onto a glass support and dried in hot air at 130°C until the polymer film became self-supporting. The polymer film was then peeled off from the glass, attached to a metal frame, and placed in a water bath at 25°C for 10 minutes. The water on the surface of the polymer film was then wiped off, and the film was heat-treated in a hot air oven at 180°C for 1 minute, yielding a polymer film with a thickness of 4.7 μm.

[0062] A coin battery was fabricated using the resulting polymer film and a 1M non-aqueous electrolyte solution with LiTFSI as the electrolyte and EC / DEC = 1 / 1 (volume ratio) as the solvent, and was stored at 25°C for 24 hours before evaluation. The characteristics of the polymer film and the battery are shown in Table 1. The ionic conductivity and cycle characteristics were good.

[0063] Example 2 Using polymer stock solution P-1, the polymer solution was cast onto a glass support and dried in hot air at 130°C until the polymer film became self-supporting. Next, the polymer film was peeled off from the glass, attached to a metal frame, and placed in a water bath at 25°C for 10 minutes. After that, the water on the surface of the polymer film was wiped off, and the film was heat-treated in a hot air oven at 180°C for 1 minute to obtain a polymer film with a thickness of 4.6 μm.

[0064] A coin battery was fabricated using the resulting polymer film and a 1M non-aqueous electrolyte solution with LiTFSI as the electrolyte and EC / DEC / FEC = 7 / 7 / 1 (volume ratio) as the solvent, and was stored at 30°C for 24 hours before evaluation. The characteristics of the polymer film and the battery are shown in Table 1. The ionic conductivity and cycle characteristics were good.

[0065] Example 3 A coin battery was fabricated using a 1M nonaqueous electrolyte solution with a weight ratio of LiTFSI / LiPF6 of 9 / 1 and a volume ratio of EC / DEC of 1 / 1 as the solvent, and the polymer membrane obtained in Example 2. The battery was stored at 60°C for 24 hours and evaluated. The characteristics of the polymer membrane and the battery are shown in Table 1. The ionic conductivity and cycle characteristics were good.

[0066] Example 4 A coating solution was obtained by diluting polymer stock solution P-1 with dehydrated NMP to a polymer concentration of 4% by mass. The resulting coating solution was applied to one side of a polyethylene porous membrane substrate (12 μm thick, Gurley coefficient 161 seconds / 100 cc, manufactured by Toray Industries, Inc.), immersed in a 20°C water bath within 10 seconds, removed from the water bath after 30 seconds of immersion, and dried at 65°C for 60 seconds to obtain a composite film with a 1.1 μm-thick polymer membrane formed on the porous membrane substrate. A battery was fabricated and evaluated in the same manner as in Example 3, except that the polymer membrane-laminated side of the composite film was used as the surface facing the negative electrode. The characteristics of the polymer membrane and battery are shown in Table 1. The ionic conductivity and dendrite resistance were excellent.

[0067] Example 5 The polymer stock solution P-2 was applied to the release surface of a release film "Cerapeel" HP2 (50 μm thick, manufactured by Toray Industries, Inc.) and dried at 130°C for 2 minutes to form a 0.1 μm thick polymer film on the release film. Next, in a glove box under an argon gas atmosphere, the polymer film with the release film was placed on the surface of a lithium metal foil so that the polymer film surface faced the surface, and the release film was pressed with a hand roller to transfer the polymer film to the lithium metal foil. Then, only the release film was peeled off. The lithium metal foil with the polymer film transferred onto it was punched out to a diameter of 16 mm, and a coin battery was fabricated and evaluated using this as the negative electrode. The characteristics of the polymer film and the battery are shown in Table 1. The ionic conductivity and dendrite resistance were good.

[0068] Example 6 The polymer stock solution P-3 was applied to the release surface of a release film "Cerapeel" SY09 (50 μm thick, manufactured by Toray Industries, Inc.) and dried at 80°C for 2 minutes. After that, it was dried under a nitrogen gas atmosphere with an integrated light dose of 200 mJ / cm. 2 The polymer film was cured by UV irradiation under the conditions of

[0043] , forming a 7 μm-thick polymer film on the release film. Next, in a glove box under an argon gas atmosphere, the polymer film with the release film was placed on the surface of a lithium metal foil so that the polymer film surface faced the surface of the polymer film, and the release film was pressed onto the surface with a hand roller to transfer the polymer film to the lithium metal foil. Then, only the release film was peeled off. The lithium metal foil with the polymer film transferred onto it was punched out to a diameter of 16 mm, and a coin battery was fabricated and evaluated using this as the negative electrode. The characteristics of the polymer film and the battery are shown in Table 1. The ionic conductivity was good.

[0069] Example 7 In the same manner as in Example 6, a polymer membrane with a release film was formed, and then the polymer membrane with the release film was placed on one side of a polyethylene porous membrane substrate (thickness 5 μm, Gurley value 110 seconds / 100 cc, manufactured by Toray Industries, Inc.) with the polymer membrane surface facing the substrate. The release film was pressed with a hand roller to transfer the polymer membrane to the microporous membrane side, and then the release film alone was peeled off. The porous substrate with the transferred polymer membrane was punched out to a diameter of 19 mm, and a coin battery was fabricated and evaluated using this as a separator. The characteristics of the polymer membrane and the battery are shown in Table 1. The ionic conductivity was good.

[0070] (Comparative Example 1) A battery was fabricated and evaluated in the same manner as in Example 3, except that a polyethylene porous membrane substrate (thickness 12 μm, Gurley value 161 seconds / 100 cc, manufactured by Toray Industries, Inc.) was used as the polymer membrane. The characteristics of the polymer membrane and the battery are shown in Table 1. The battery was rejected due to poor cycle characteristics and dendrite resistance.

[0071] (Comparative Example 2) A battery was fabricated and evaluated in the same manner as in Example 4, except that the coin battery was stored in a 25°C environment for 24 hours. The characteristics of the polymer film and the battery are shown in Table 1. The battery was rejected due to poor cycle characteristics.

[0072] [Table 1]

Claims

1. A secondary battery having a positive electrode, a negative electrode, and an ion-conductive polymer membrane, wherein the ion-conductive polymer membrane is disposed between the positive electrode and the negative electrode, and the average lithium content within a range of 100 nm in a thickness direction from the surface of the polymer membrane facing the negative electrode is 3 to 45 atomic %, and the average fluorine content is 3 to 45 atomic %.

2. 2. The secondary battery according to claim 1, wherein the average content ratio of lithium element and fluorine element in the polymer film within a range of 100 nm from the surface facing the negative electrode in the thickness direction is 1:0.8 to 1:1.

2.

3. 2. The secondary battery according to claim 1, wherein the polymer film contains a lithium fluoride component in a range of up to 100 nm in a thickness direction from the surface of the polymer film facing the negative electrode.

4. 2. The secondary battery according to claim 1, wherein the polymer film has a thickness of 0.1 μm or more and 10.0 μm or less, and the cross section of the polymer film has a substantially non-porous structure.

5. The secondary battery according to claim 1 , wherein the polymer film is in contact with the negative electrode, and the polymer film is not in contact with the positive electrode.

6. 2. The secondary battery according to claim 1, wherein the polymer membrane is in contact with the negative electrode, and at least one selected from a microporous membrane, a nonwoven fabric, a solid electrolyte membrane, a membrane containing an inorganic particle layer, and a membrane containing an organic particle layer is provided between the polymer membrane and the positive electrode.

7. 2. The secondary battery according to claim 1, wherein the polymer film contains at least one polymer selected from the group consisting of aromatic polyamides, aromatic polyimides, and aromatic polyamideimides.

8. 2. The secondary battery according to claim 1, wherein the negative electrode is metallic lithium.

9. A vehicle, an unmanned transport aircraft, an unmanned flying object, an electronic device, or a stationary power source comprising the secondary battery according to any one of claims 1 to 8.

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