Lithium ion secondary battery

Abstract

The lithium ion secondary battery according to the present disclosure has a positive electrode, a negative electrode, and an electrolyte disposed between the positive electrode and the negative electrode, and the electrolyte contains a polymer electrolyte, and the polymer electrolyte contains a vinylene carbonate-based polymer and a lithium salt of a compound containing a fluorosulfonyl group.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a lithium ion secondary battery. BACKGROUND

[0002] The electrolyte used for the lithium ion secondary battery which is being actively developed in recent years not only has a large influence on the battery characteristics such as charge-discharge rate, charge-discharge cycle life characteristics, storage characteristics, but also has a large influence on safety. Therefore, improvement of the battery characteristics is sought by improving the electrolyte.

[0003] The liquid electrolyte is composed of a solvent and a supporting salt containing lithium, and from the viewpoint of improving the energy density, a non-aqueous solvent having a wider potential window than water is often used. However, the liquid electrolyte has a problem in safety such as a risk of leakage from the battery cell or ignition in a flammable electrolyte. In order to solve such a problem and improve safety, research on solid electrolytes is being conducted.

[0004] The polymer solid electrolyte can be formed into a film shape, and therefore does not have inter-particle voids. Furthermore, the polymer solid electrolyte has flexibility and can be thinned into a film, and therefore improvement in assembly to electronic devices and improvement in design freedom of electronic devices can also be expected. As the polymer solid electrolyte, polyethylene oxide-based polymers have been studied. It is considered that in the polyethylene oxide-based polymer, lithium ions are coordinated to oxygen atoms included in the main chain skeleton, and the lithium ions are transported by hopping through the molecules of the polymer chain.

[0005] Patent Literature 1 discloses a battery including a vinylene carbonate-based as a precursor of a polymer electrolyte. Patent Literature 2 discloses a battery in which the electrolyte includes a copolymer containing a polymerization unit based on a fluoroolefin and a polymerization unit based on a vinylene carbonate.

[0006] Prior Art Documents

[0007] Patent Literature

[0008] Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No. 2001-283911

[0009] Patent Literature 2: Japanese Patent Application Laid-Open (JP-A) No. Hei 10-334945

[0010] Non-Patent Literature

[0011] Non-Patent Literature 1: J. Chai, Z. Liu, et al. Adv. Sci. 10 November 2016, Volume 4, 1600377 SUMMARY

[0012] The present disclosure provides a lithium ion secondary battery with high output.

[0013] The lithium ion secondary battery of one aspect of the present disclosure has:

[0014] a positive electrode,

[0015] a negative electrode, and

[0016] an electrolyte disposed between the positive electrode and the negative electrode,

[0017] the electrolyte contains a polymer electrolyte,

[0018] the polymer electrolyte contains a vinylene carbonate-based polymer and a lithium salt of a compound containing a fluorosulfonyl group.

[0019] According to the present disclosure, a lithium ion secondary battery with high output can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 A schematic diagram showing the outline configuration of the lithium ion secondary battery of the present embodiment.

[0021] Figure 2 A graph showing the ion conductivity σ calculated from the impedance measurement results of Example 1 and Comparative Example 1.

[0022] Figure 3 A graph showing the ion conductivity σ calculated from the impedance measurement results of Example 2. DETAILED DESCRIPTION

[0023] (Basic Insight of the Present Disclosure)

[0024] A polyethylene oxide-based polymer has high crystallinity, which hinders the transport of lithium ions, and therefore has a problem of low ion conductivity.

[0025] In this regard, research has been conducted to improve the amorphousness of the polymer to improve ion conductivity, by adding a solvent or an electrolyte as a plasticizer, for example. However, even in the case of improved ion conductivity, the amount of solvent retained in the polymer itself is small, or the amount of solvent added is as much as at least 50 mass% or more (see Patent Literature 1, Patent Literature 2). Therefore, the same problem of liquid leakage as in the case of a battery using an electrolyte occurs.

[0026] Therefore, there is a need for an electrolyte with high ion conductivity and which can reduce the amount of added liquid such as an electrolyte or a solvent.

[0027] Research on an organic ion conductor in which vinylene carbonate is the main component is reported (Non-Patent Literature 1). In the above report, for an electrolyte containing lithium difluoro(oxalato)borate (LiDFOB) at a concentration of 1 mol / L, an ion conductivity of 9.82 x 10 -5S / cm. However, LiDFOB has low solubility in vinylene carbonate, and dissolves only up to about 3 mol / L or less. Therefore, it is difficult to further improve the ion conductivity.

[0028] The lithium ion secondary battery according to the present disclosure aims to improve the ion conductivity of the polymer electrolyte itself. The lithium ion secondary battery according to the present disclosure contains, as an electrolyte, a polymer having a polar structure that forms a conduction path in which lithium ions easily jump, and vinylene carbonate or a derivative thereof as a main chain skeleton, and the ion conductivity is high even at room temperature.

[0029] The lithium ion secondary battery according to the present disclosure contains, for example, a polymer electrolyte that has a higher ion conductivity than conventional materials without leakage by synthesizing a polymer after dissolving a lithium salt having high solubility in a vinylene carbonate-based compound.

[0030] (Summary of one aspect of the present disclosure)

[0031] The lithium ion secondary battery according to the first aspect of the present disclosure includes a positive electrode, a negative electrode, and an electrolyte disposed between the positive electrode and the negative electrode,

[0032] The electrolyte contains a polymer electrolyte,

[0033] The polymer electrolyte contains a polymer of a vinylene carbonate-based compound and a lithium salt of a compound containing a fluorosulfonyl group.

[0034] According to the first aspect, a high conductivity can be obtained. Therefore, a lithium ion secondary battery with high output can be realized.

[0035] In the second aspect of the present disclosure, for example, in the lithium ion secondary battery according to the first aspect, the vinylene carbonate-based compound can be a compound represented by the following formula (1).

[0036]

[0037] (In the formula, R 1 and R 2 each independently represent a hydrogen atom, an alkyl group optionally having a substituent, an aryl group optionally having a substituent, or a halogen atom.)

[0038] In the third aspect of the present disclosure, for example, in the lithium ion secondary battery according to the first aspect or the second aspect, the polymer of the vinylene carbonate-based compound can be a homopolymer of the vinylene carbonate-based compound.

[0039] In the fourth aspect of the present disclosure, for example, in the lithium ion secondary battery according to any one of the first aspect to the third aspect, the polymer of the vinylene carbonate-based compound can be poly(vinylene carbonate).

[0040] According to the first to fourth aspects, a lithium ion secondary battery having a high-molecular electrolyte having high ionic conductivity, and high output, can be provided.

[0041] In the fifth aspect of the present disclosure, for example, in the lithium ion secondary battery according to any one of the first to fourth aspects, the lithium salt of the compound containing a fluorosulfonyl group can include lithium bis(fluorosulfonyl)imide.

[0042] According to the fifth aspect, by dissolving a lithium salt having high solubility in a vinylene carbonate-based solvent and then synthesizing a high molecule, a lithium ion secondary battery having high output without leakage can be provided. Further, according to the fifth aspect, the polymerization reaction at the time of synthesizing a high molecule is not hindered by the lithium salt as a supporting salt, and the film-forming property of the high-molecular electrolyte is excellent.

[0043] In the sixth aspect of the present disclosure, for example, in the lithium ion secondary battery according to any one of the first to fifth aspects, the high-molecular electrolyte can include less than 40 mass% of a nonaqueous solvent.

[0044] In the seventh aspect of the present disclosure, for example, in the lithium ion secondary battery according to the sixth aspect, the nonaqueous solvent can include at least one selected from the group consisting of cyclic carbonate-based solvents, chain carbonate-based solvents, and sulfolane-based solvents.

[0045] In the eighth aspect of the present disclosure, for example, in the lithium ion secondary battery according to the sixth aspect, the nonaqueous solvent can include at least one selected from the group consisting of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and sulfolane.

[0046] According to the sixth to eighth aspects, the lithium ion secondary battery according to the present disclosure has reduced risk of leakage and excellent safety.

[0047] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. The present disclosure is not limited to the following embodiments.

[0048] (Embodiments)

[0049] Figure 1is a cross-sectional view showing a schematic configuration of the battery 1000 of the present embodiment. The lithium ion secondary battery according to the present embodiment includes a positive electrode 101, an electrolyte 102, and a negative electrode 103. The electrolyte 102 is disposed between the positive electrode 101 and the negative electrode 103. The electrolyte 102 contains a polymer electrolyte. The polymer electrolyte contains a vinylene carbonate-based polymer and a lithium salt of a compound containing a fluorosulfonyl group. The electrolyte 102 can also contain the polymer electrolyte as a main component. The "main component" refers to a component contained in the largest amount in terms of mass ratio. The content of the polymer electrolyte in the electrolyte 102 can be, for example, 50% by mass or more, or 60% by mass or more. Furthermore, the content of the polymer electrolyte in the electrolyte 102 can be 80% by mass or more, can be 90% by mass or more, or can be 100% by mass. In the present disclosure, "vinylene carbonate-based" refers to vinylene carbonate or a derivative thereof. Here, the derivative of vinylene carbonate is a substance in which the hydrogen atom possessed by vinylene carbonate is substituted with a substituent.

[0050] The vinylene carbonate-based can be a compound represented by the following formula (1).

[0051]

[0052] In formula (1), R 1 and R 2 each independently represent a hydrogen atom, an alkyl group which can have a substituent, an aryl group which can have a substituent, or a halogen atom. The alkyl group can be linear or branched. The carbon number of the alkyl group of R 1 and R 2 each independently can be 1 to 8, can be 1 to 6, or can be 1 to 4. As the alkyl group, for example, a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, or the like can be exemplified. R 1 and R 2 each independently can be an unsubstituted alkyl group. In the case where the alkyl group has a substituent, the number of the substituents can be 1 to 6, can be 1 to 4, or can be 1 to 3. R 1 and R 2 each independently can be an aryl group which can have a substituent. The carbon number of the aryl group of R 1 and R 2 each independently can be 6 to 14, or can be 6 to 10. As the aryl group, for example, a phenyl group, a naphthyl group, or the like can be exemplified. R 1 and R 2 each independently can be an unsubstituted phenyl group. As the substituent possessed by the alkyl group and the aryl group, a halogen atom, an alkyl group having a carbon number of 1 to 6, a hydroxyl group, or the like can be exemplified. As the halogen atom of R 1 , R 2may be a hydrogen atom.

[0053] The vinylene carbonate-based polymer can be a homopolymer of vinylene carbonate or a copolymer. The copolymer can be a copolymer of vinylene carbonate and a fluoroolefin. The fluoroolefin can be tetrafluoroethylene, chlorotrifluoroethylene, vinylidene fluoride, or hexafluoropropylene. The copolymer can include a monomer unit other than the structural unit of vinylene carbonate and the fluoroolefin. As the other monomer, for example, vinyl fluoride, trifluoroethylene, hexafluoroacetone, perfluoro(methyl vinyl ether), perfluoro(propyl vinyl ether), (perfluorobutyl)ethylene, (perfluorooctyl)propylene, ethylene, propylene, isobutylene, vinyl pivalate, vinyl acetate, vinyl benzoate, ethyl vinyl ether, butyl vinyl ether, cyclohexyl vinyl ether, chloroethyl vinyl ether, ethyl allyl ether, cyclohexyl allyl ether, norbornadiene, crotonic acid and its esters, acrylic acid and its alkyl esters, methacrylic acid and its alkyl esters, and the like can be exemplified. Two or more selected from among them can be used in combination.

[0054] The compound containing a fluorosulfonyl group can contain only a fluorosulfonyl group represented by -SO2F. The compound containing a fluorosulfonyl group can be bis(fluorosulfonyl)imide. The lithium salt of the compound containing a fluorosulfonyl group can have a molecular weight of 500 or less, 300 or less, or 250 or less. The lithium salt of the compound containing a fluorosulfonyl group according to the present disclosure has excellent film formability. In addition, the lithium salt of the compound containing a fluorosulfonyl group according to the present disclosure has excellent solubility in vinylene carbonate. Furthermore, the polymer electrolyte containing the lithium salt of the compound containing a fluorosulfonyl group according to the present disclosure has a high ionic conductivity at room temperature.

[0055] The lithium salt of the compound containing a fluorosulfonyl group can include lithium bis(fluorosulfonyl)imide. The concentration of the lithium salt of the compound containing a fluorosulfonyl group in the polymer electrolyte can be 1 mol / L or more and 7 mol / L or less, or 2 mol / L or more and 6 mol / L or less.

[0056] The polymer electrolyte in the present embodiment can also include less than 40 mass% of a non-aqueous solvent. The content of the non-aqueous solvent can be less than 35 mass%, less than 30 mass%, less than 20 mass%, or less than 10 mass%. In the past, the ionic conductivity of the polymer electrolyte was low, and therefore, 50 mass% or more of a non-aqueous solvent was required in order to obtain a high ionic conductivity. On the other hand, since a large amount of non-aqueous solvent was used, there was a risk of liquid leakage. In contrast, the polymer electrolyte used in the lithium ion secondary battery according to the present disclosure has a significantly improved ionic conductivity at room temperature, and therefore, the amount of non-aqueous solvent can be reduced. The lithium ion secondary battery according to the present disclosure has a reduced risk of liquid leakage due to the small amount of non-aqueous solvent, and therefore, has excellent safety.

[0057] The non-aqueous solvent in the present embodiment can include at least one selected from the group consisting of cyclic carbonates, chain carbonates, and sulfolanes. As the cyclic carbonates, for example, ethylene carbonate, fluoroethylene carbonate, propylene carbonate, butylene carbonate, and the like can be listed. As the chain carbonates, for example, dimethyl carbonate, ethyl methyl carbonate, fluoroethyl methyl carbonate, diethyl carbonate, and the like can be listed. As the sulfolanes, for example, 3-methyl sulfolane, 2,4-dimethyl sulfolane, and the like can be listed. The non-aqueous solvent can include at least one selected from the group consisting of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and sulfolane.

[0058] The shape of the polymer electrolyte in the present embodiment is not limited. The shape of the polymer electrolyte can be listed as particles, plates, films, and the like. In the case where the polymer electrolyte in the present embodiment is a film, the thickness of the film can be 1 μm or more and 100 μm or less.

[0059] The method for producing the polymer electrolyte in the present embodiment is not particularly limited. As the method for producing the polymer electrolyte, for example, a method in which a lithium salt of a compound containing a fluorosulfonyl group is dissolved in a vinylene carbonate as a monomer, and polymerization is performed by a publicly known method can be listed. As the polymerization method, for example, thermal polymerization, photopolymerization can be listed. As the polymerization initiator used for the polymerization, a publicly known substance can be used. As the polymerization initiator, for example, an azo-based polymerization initiator, a peroxide-based initiator, and the like can be listed. As the azo-based polymerization initiator, for example, 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), and the like can be listed. As the peroxide-based initiator, for example, a ketone peroxide, hydrogen peroxide, a diacyl peroxide, a dialkyl peroxide, a peroxide ketal, a peroxide ester, a peroxydicarbonate, and the like can be listed. As another method for producing the polymer electrolyte, for example, a method in which a lithium salt of a compound containing a fluorosulfonyl group and a vinylene carbonate are dissolved in a non-aqueous solvent, and polymerization is performed by a publicly known method can be listed.

[0060] The electrolyte including the polymer electrolyte related to the present disclosure is used as a lithium ion conductive film. The polymer electrolyte itself can also be used as the lithium ion conductive film. The thickness of the lithium ion conductive film is not particularly limited. The thickness of the lithium ion conductive film can be 0.1 μm or more, can be 1 μm or more, or can be 10 μm or more. Further, the thickness of the lithium ion conductive film can be 1000 μm or less, can be 800 μm or less, or can be 500 μm or less.

[0061] The positive electrode 101 contains a material capable of absorbing and releasing lithium ions. For example, the positive electrode 101 may contain a positive electrode active material. The shape of the positive electrode active material is not particularly limited; it can be in particulate, powder, or granular form. The positive electrode active material can be fixed using a binder. Examples of binders include resins such as polyvinylidene fluoride, polypropylene, polyethylene, and polyimide.

[0062] Examples of positive electrode active materials include lithium-containing transition metal oxides, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, or transition metal oxynitrides. Examples of lithium-containing transition metal oxides are Li(NiCoAl)O2, Li(NiCoMn)O2, or LiCoO2.

[0063] When the positive electrode 101 contains a positive electrode active material, this positive electrode active material may contain a transition metal oxyfluoride. Based on the above configuration, the charge and discharge efficiency of the battery can be improved.

[0064] Transition metal oxyfluorides may also contain at least O (oxygen) and F (fluorine) as anions. p Me q O m F n The compound is represented by the formula Li. Here, Me is at least one element selected from the group consisting of Mn, Co, Ni, Fe, Al, Cu, V, Nb, Mo, Ti, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, Ag, Ru, W, B, Si, and P. Furthermore, it satisfies 0.5 ≤ p ≤ 1.5, 0.5 ≤ q ≤ 1.0, 1 ≤ m < 2, and 0 < n ≤ 1. As a compound represented by the formula Li... p Me q O m F n Transition metal oxyfluorides, represented by Li, can be expressed using Li 1.05 (Ni 0.35 Co 0.35 Mn 0.3 ) 0.95 O 1.9 F 0.1 Based on the above configuration, the charging and discharging efficiency of the battery can be further improved.

[0065] The positive electrode active material can include lithium phosphate. By using lithium phosphate, a cheaper and safer battery can be provided.

[0066] The lithium ion secondary battery according to the present embodiment can also contain another electrolyte material different from the high-molecular electrolyte according to the present disclosure. Examples of the other electrolyte material are Li2MgX4, Li2FeX4, Li(Al, Ga, In)X4, Li3(Al, Ga, In)X6, or LiI. Here, X is at least one element selected from the group consisting of F, Cl, Br, and I.

[0067] The negative electrode 103 contains a material capable of occluding and releasing lithium ions. The negative electrode 103 can contain, for example, a negative electrode active material. The shape of the negative electrode active material is not particularly limited, and can be in the form of particles, can be in the form of powder, or can be in the form of granules. The negative electrode active material can also be fixed with a binder. As the binder, a resin such as polyvinylidene fluoride, polypropylene, polyethylene, or polyimide can be cited.

[0068] Examples of the negative electrode active material are a metal material, a carbon material, an oxide, a nitride, a tin compound, or a silicon compound. The metal material can be a simple metal or an alloy. Examples of the metal material are lithium metal or a lithium alloy. Examples of the carbon material are natural graphite, coke, partially graphitized carbon, carbon fiber, spherical carbon, artificial graphite, or amorphous carbon. From the viewpoint of capacity density, silicon (Si), tin (Sn), a silicon compound, or a tin compound can be used.

[0069] The negative electrode active material can be, for example, an active material that occludes and releases lithium ions at 0.27 V or more with respect to lithium. Examples of the negative electrode active material are a titanium oxide, an indium metal, or a lithium alloy. Examples of the titanium oxide are Li4Ti5O12, LiTi2O4, or TiO2. According to the above configuration, the charge and discharge efficiency of the battery can be improved. 12

[0070] The negative electrode 103 can also contain a sulfide solid electrolyte material and a negative electrode active material. According to the above configuration, the internal resistance of the battery can be reduced by the electrochemically stable sulfide solid electrolyte material.

[0071] ​For the purpose of improving ion conductivity, a solid electrolyte material different from the high molecular electrolyte relating to the present embodiment can also be contained in at least one selected from the group consisting of the positive electrode 101, the electrolyte 102, and the negative electrode 103. Examples of the solid electrolyte material different from the high molecular electrolyte relating to the present embodiment are a sulfide solid electrolyte material, an oxide solid electrolyte material, or a halide solid electrolyte material. In the present disclosure, the "sulfide solid electrolyte material" refers to a solid electrolyte material containing sulfur. In the present disclosure, the "oxide solid electrolyte material" refers to a solid electrolyte material containing oxygen. Here, the oxide solid electrolyte material can further contain anions other than sulfur and halogen elements as anions other than oxygen. In the present disclosure, the "halide solid electrolyte material" refers to a solid electrolyte material containing halogen and not containing sulfur. Here, the halide solid electrolyte material can further contain oxygen as anions other than halogen.

[0072] Examples of the sulfide solid electrolyte material are Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, Li 3.25 Ge 0.25 P 0.75 S4, or Li 10 GeP2S 12 Two or more selected from among them can also be used in combination.

[0073] Examples of the oxide solid electrolyte material are a NASICON-type solid electrolyte represented by LiTi2(PO4)3and an elemental substitution body thereof, a perovskite-type solid electrolyte of the (LaLi)TiO3system, a LISICON-type solid electrolyte represented by Li 14 ZnGe4O 16 , Li4SiO4, LiGeO4, and an elemental substitution body thereof, a garnet-type solid electrolyte represented by Li7La3Zr2O 12 and an elemental substitution body thereof, or Li3PO4and an N substitution body thereof. Two or more selected from among them can also be used in combination.

[0074] Examples of the halide solid electrolyte material are Li a Me b Y cX6represents a compound. Here, a + mb + 3c = 6 and c > 0 are satisfied, Me is at least one selected from the group consisting of metal elements and semi-metal elements other than Li and Y, and m represents the valence number of Me. The "semi-metal elements" refer to B, Si, Ge, As, Sb, and Te. The "metal elements" are all elements included in Groups IA to IIB of the periodic table (Groups 1 to 12 of the Japanese Periodic Table) (excluding hydrogen), and all elements included in Groups IIIA to VIA of the periodic table (Groups 13 to 16 of the Japanese Periodic Table) (excluding B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se). That is, the "metal elements" are a group of elements that can become cations when forming inorganic compounds with halides. Me can be at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Zr, Hf, Ti, Sn, Ta, and Nb. As the halide solid electrolyte material, for example, Li3YCl6or Li3YBr6may be used. Two or more selected from them can also be used in combination.

[0075] For the purpose of easy transfer of lithium ions and improvement of the output characteristics of the battery, a non-aqueous electrolytic solution, a gel electrolyte, or an ionic liquid can also be contained in the positive electrode 101 or the negative electrode 103.

[0076] The non-aqueous electrolytic solution can also contain a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. The non-aqueous electrolytic solution contains a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent can include cyclic carbonate-based solvents, chain carbonate-based solvents, cyclic ether solvents, chain ether solvents, cyclic ester solvents, chain ester solvents, or fluorine solvents. As the cyclic carbonate-based solvents, for example, ethylene carbonate, fluoroethylene carbonate, propylene carbonate, butylene carbonate, or the like can be listed. As the chain carbonate-based solvents, for example, dimethyl carbonate, methyl ethyl carbonate, fluoro-methyl ethyl carbonate, diethyl carbonate, or the like can be listed. As the cyclic ether solvents, for example, tetrahydrofuran, 1,4-dioxane, or 1,3-dioxolane can be listed. As the chain ether solvents, for example, 1,2-dimethoxyethane or 1,2-diethoxyethane can be listed. An example of the cyclic ester solvent is γ-butyrolactone. As the chain ester solvent, for example, methyl acetate can be listed. Examples of the fluorine solvents are fluoroethylene carbonate, fluoro-methyl propionate, fluorobenzene, fluoro-methyl ethyl carbonate, or fluoro-dimethyl carbonate. One non-aqueous solvent selected from them can be used alone. A mixture of two or more non-aqueous solvents selected from them can also be used. The lithium salt can also be a lithium salt of a compound containing a fluorosulfonyl group. The non-aqueous electrolytic solution can also contain a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. The non-aqueous electrolytic solution contains a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent can include cyclic carbonate-based solvents, chain carbonate-based solvents, cyclic ether solvents, chain ether solvents, cyclic ester solvents, chain ester solvents, or fluorine solvents. As the cyclic carbonate-based solvents, for example, ethylene carbonate, fluoroethylene carbonate, propylene carbonate, butylene carbonate, or the like can be listed. As the chain carbonate-based solvents, for example, dimethyl carbonate, methyl ethyl carbonate, fluoro-methyl ethyl carbonate, diethyl carbonate, or the like can be listed. As the cyclic ether solvents, for example, tetrahydrofuran, 1,4-dioxane, or 1,3-dioxolane can be listed. As the chain ether solvents, for example, 1,2-dimethoxyethane or 1,2-diethoxyethane can be listed. An example of the cyclic ester solvent is γ-butyrolactone. As the chain ester solvent, for example, methyl acetate can be listed. Examples of the fluorine solvents are fluoroethylene carbonate, fluoro-methyl propionate, fluorobenzene, fluoro-methyl ethyl carbonate, or fluoro-dimethyl carbonate. One non-aqueous solvent selected from them can be used alone. A mixture of two or more non-aqueous solvents selected from them can also be used. The lithium salt can also be a lithium salt of a compound containing a fluorosulfonyl group.

[0077] The gel electrolyte can use a substance in which a nonaqueous electrolyte solution is contained in a high molecular material. As the high molecular material, for example, polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, a polymer having an ethylene oxide bond, a polymer in which a high molecular electrolyte is involved in a vinylene carbonate type, or the like can be exemplified.

[0078] Examples of the cation contained in the ionic liquid are tetraalkylammonium and tetraalkylphosphonium , and the like aliphatic chain quaternary ammonium, pyrrolidinium , morpholinium , imidazolinium , tetrahydro-pyrimidinium , piperazinium , and piperidinium , and the like aliphatic cyclic ammonium, or pyridinium , and imidazole , and the like nitrogen-containing heterocyclic aromatic cation. Examples of the anion contained in the ionic liquid are PF6 - , BF4 - , SbF6 - , AsF6 - , SO3CF3 - , N(SO2CF3)2 - , N(SO2C2F5)2 - , N(SO2F)2 - , N(SO2CF3)(SO2C4F9) - , or C(SO2CF3)3 - , and also N(SO2F)2 - . The ionic liquid can also contain a lithium salt. The lithium salt can also be a lithium salt of a compound containing a fluorosulfonyl group.

[0079] In order to reduce the electrode resistance, the positive electrode 101 or the negative electrode 103 can also contain a conductive aid.

[0080] Examples of the conductive aid are graphite such as natural graphite and artificial graphite, carbon black such as acetylene black and ketjen black, conductive fiber such as carbon fiber and metal fiber, metal powder such as fluorinated carbon and aluminum, conductive whisker such as zinc oxide and potassium titanate, conductive metal oxide such as titanium oxide, conductive high molecular compound such as polyaniline, polypyrrole, or polythiophene. By using a carbon conductive aid as the conductive aid, cost reduction can be sought.

[0081] Examples of the shape of the lithium ion secondary battery are coin type, cylindrical type, square type, sheet type, button type, flat type, or stacked type.

[0082] Embodiment

[0083] The present disclosure will be described more specifically below based on examples, but the present disclosure is not limited by any of these examples, and those skilled in the art can make various modifications within the scope of the technical idea of the present disclosure.

[0084] [Example 1]

[0085] <Production of polymer electrolyte>

[0086] Lithium bis(fluorosulfonyl)imide (Kishida Chemical Co., Ltd.) was dissolved in 10 mL of vinylene carbonate (Aldrich) so as to be 2.0 mol / L, 3.0 mol / L. Next, 10 mg of 2,2'-azobis(isobutyronitrile) (Tokyo Chemical Industry Co., Ltd.) was further added, and the resulting substance was clamped with a glass plate and heated at 60°C for 24 hours. Then, further heating was performed at 80°C for 10 hours. Thus, a film-shaped polymer electrolyte was produced.

[0087] <Measurement of ionic conductivity>

[0088] The working electrode was set to a Ni plate, and the counter electrode was set to a Ni plate. The produced polymer electrolyte was punched into φ 9 mm. Next, the polymer electrolyte was clamped with the working electrode and the counter electrode, and a battery evaluation test cell (Swagelok cell) was assembled to produce a test cell. Impedance measurement was performed at room temperature (25°C) using VSP-300 (Bio-Logic) with a frequency range of 0.1 MHz or more and 7 MHz or less. The results of the measurement are shown in Figure 2 . Figure 2 In Table 1, "LiFSI" indicates Example 1.

[0089] [Comparative Example 1]

[0090] <Production of polymer electrolyte>

[0091] Instead of lithium bis(fluorosulfonyl)imide, lithium difluoro(oxalato)borate (Tokyo Chemical Industry Co., Ltd.) was used, and otherwise, the same operation as in Example 1 was performed to produce a film-shaped polymer electrolyte. The concentration of lithium difluoro(oxalato)borate was also set to 2.0 mol / L, 3.0 mol / L, like Example 1.

[0092] <Measurement of ionic conductivity>

[0093] The same operation as in Example 1 was performed, and the ionic conductivity σ was measured for the obtained polymer electrolyte. The results of the measurement are shown in Figure 2 . Figure 2 In Table 1, "LiDFOB" indicates Comparative Example 1. Figure 2In the figure, the vertical axis represents the ionic conductivity σ. The unit of the vertical axis is S / cm. The horizontal axis represents the supporting salt concentration. The unit of the horizontal axis is mol / L. The supporting salt was lithium bis(fluorosulfonyl)imide in Example 1 and lithium difluorooxalate borate in Comparative Example 1.

[0094] Figure 2 This is a graph showing the ionic conductivity σ calculated from impedance measurements for Example 1 and Comparative Example 1. Figure 2 It is clear that in Example 1, the concentration of the supporting salt was 2.0 mol / L and 3.0 mol / L, and as the concentration of the supporting salt increased, the ionic conductivity at room temperature increased. On the other hand, in Comparative Example 1, even when the concentration of the supporting salt was changed to 2.0 mol / L and 3.0 mol / L, the ionic conductivity remained as low as about 1.00E-05, showing almost no change.

[0095] [Example 2]

[0096] <Preparation of Polymer Electrolytes>

[0097] Lithium bis(fluorosulfonyl)imide (Kishida Chemical Co., Ltd.) was dissolved in 10 mL of vinylene carbonate (Aldrich) at two concentrations: 4.0 mol / L and 5.0 mol / L. Next, solutions containing 10 mg of 2,2'-azobis(isobutyronitrile) (Tokyo Chemical Industry Co., Ltd.) were prepared. Ethylene carbonate (EC) was added to these solutions at concentrations of 25%, 30%, 35%, 40%, 45%, and 50% by mass, and the resulting substances were held in a glass plate and heated at 60°C for 24 hours. Then, the mixture was further heated at 80°C for 10 hours. This produced a film-like polymeric electrolyte.

[0098] <Determination of Ionic Conductivity>

[0099] The ionic conductivity σ of the obtained polymeric electrolyte was measured using the same procedure as in Example 1. The measurement results are shown below. Figure 3 . Figure 3 A graph showing the change in ionic conductivity σ relative to the amount of ethylene carbonate added. Figure 3 In the text, "LiFSI 4mol / L" indicates the result of setting lithium bis(fluorosulfonyl)imide to 4.0mol / L, and "LiFSI 5mol / L" indicates the result of setting lithium bis(fluorosulfonyl)imide to 5.0mol / L.

[0100] [Experimental Example]

[0101] On the basis of lithium bis(fluorosulfonyl)imide (LiFSI) used in Example 1 and Example 2, lithium difluoro(oxalato)borate (LiDFOB) of Comparative Example 1, comparative experiments were performed using lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as Comparative Example 2. In the comparative experiments, the solubility in vinylene carbonate (VC), the film-forming property, and the ionic conductivity σ of these lithium salts were evaluated. The ionic conductivity σ was measured by the same method as in Example 1.

[0102] Specifically, the measurement was performed by the following method. Each of the three kinds of lithium salts was dissolved in vinylene carbonate at a concentration in the range of 1 mol / L to 5 mol / L to prepare a solution. To 1 mL of the obtained solution, 1 mg of 2,2'-azobis(isobutyronitrile) (Tokyo Chemical Industry Co., Ltd.) was further added, and the obtained substance was sandwiched with glass plates and heated at 60°C for 24 hours. Subsequently, further heating was performed at 80°C for 10 hours. In this way, a film-shaped polymer electrolyte was produced. Note that, in the case of LiTFSI, since a self-standing film could not be produced at 1 mol / L, attempts were also made to form a film at a concentration of 0.1 mol / L, 0.5 mol / L, and 0.75 mol / L. In the case of LiTFSI, a self-standing film was obtained at a concentration of 0.1 mol / L and 0.5 mol / L. The ionic conductivity of LiTFSI was measured at 0.1 mol / L at which a battery evaluation test cell capable of measuring the ionic conductivity could be formed.

[0103] The solubility in vinylene carbonate (VC) of the supporting salt of the electrolyte and the film-forming property of the polymer electrolyte were evaluated in accordance with the following evaluation criteria.

[0104] < Solubility in vinylene carbonate (VC) of the supporting salt of the electrolyte >

[0105] O: solubility could be confirmed by visual observation when added at a concentration exceeding 5.0 mol / L

[0106] Δ: although an undissolved substance could be confirmed by visual observation when added at a concentration of 5.0 mol / L, solubility could be confirmed by visual observation when added at a concentration of 2.0 mol / L or less

[0107] < Film-forming property of the polymer electrolyte >

[0108] O: film-forming into a self-standing film was possible when added to VC at a concentration exceeding 5.0 mol / L

[0109] Δ: film-forming into a self-standing film was not possible when added to VC at a concentration of 5.0 mol / L, but film-forming into a self-standing film was possible when added to VC at a concentration of 0.5 mol / L or less

[0110] The evaluation results relating to the solubility in vinylene carbonate (VC) of the supporting salt as electrolyte, the film-forming property of the polymer electrolyte, and the ionic conductivity at room temperature are shown in Table 1 below.

[0111] [Table 1]

[0112] Table 1

[0113]

[0114] The lithium bisfluorosulfonylimide of Comparative Example 1 did not dissolve in vinylene carbonate at a concentration exceeding about 3 mol / L. In addition, the ionic conductivity was low. The lithium bis(trifluoromethanesulfonyl)imide of Comparative Example 2 dissolved in vinylene carbonate even at a concentration of 5 mol / L. However, the lithium bis(trifluoromethanesulfonyl)imide of Comparative Example 2 was at a level where a self-standing film was obtained with difficulty at a concentration of 0.5 mol / L, and the film-forming property was poor.

[0115] As shown in Table 1, it can be confirmed that the solubility in vinylene carbonate or the film-forming property of the polymer electrolyte greatly varies depending on the kind of the supporting salt.

[0116] It can be considered that the higher the concentration of lithium ions contained in the polymer electrolyte, the higher the carrier concentration, and the higher the ionic conductivity. Therefore, the lithium bisfluorosulfonylimide of Example 1 and Example 2, which dissolved in the vinylene carbonate class even at a high concentration of 5 mol / L and for which a self-standing film was obtained, showed a high ionic conductivity compared with Comparative Example 1 and Comparative Example 2. Note that the lithium bisfluorosulfonylimide of Example 1 and Example 2 dissolved in vinylene carbonate even at a concentration of 15 mol / L. In addition, it can be confirmed from Example 2 that the polymer electrolyte according to the present disclosure can show a high ionic conductivity without greatly depending on the concentration of ethylene carbonate.

[0117] Industrial applicability

[0118] The lithium ion secondary battery according to the present disclosure can be suitably used as a high-output lithium ion secondary battery.

[0119] Explanation of reference numerals

[0120] 101 positive electrode

[0121] 102 electrolyte

[0122] 103 negative electrode

Claims

1. A lithium ion secondary battery comprising: a positive electrode, a negative electrode, and a polymer electrolyte film disposed between the positive electrode and the negative electrode, wherein the polymer electrolyte film contains a vinylene carbonate-based polymer and lithium bis(fluorosulfonyl)imide, the polymer electrolyte film contains only a homopolymer of the vinylene carbonate-based polymer as a polymer component, or the vinylene carbonate-based polymer is a copolymer of the vinylene carbonate-based polymer and a fluoroolefin. The polymer electrolyte film contains only a homopolymer of the vinylene carbonate-based polymer as a polymer component, and the polymer electrolyte film is a self-supporting film. The polymer electrolyte film contains only a homopolymer of the vinylene carbonate-based polymer as a polymer component, and the concentration of lithium bis(fluorosulfonyl)imide in the polymer electrolyte film is 1 mol / L or more and 7 mol / L or less. The concentration of lithium bis(fluorosulfonyl)imide in the polymer electrolyte film is 2 mol / L or more and 6 mol / L or less. The vinylene carbonate-based compound is a compound represented by the following formula (1), The vinylene carbonate-based polymer is poly(vinylene carbonate).

2. The lithium-ion secondary battery according to claim 1, wherein The polymer electrolyte film contains less than 40 mass% of a nonaqueous solvent.

3. The lithium-ion secondary battery according to claim 1, wherein The nonaqueous solvent contains at least one selected from the group consisting of cyclic carbonates, chain carbonates, and sulfolanes.

4. The lithium-ion secondary battery according to claim 3, wherein The nonaqueous solvent contains at least one selected from the group consisting of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, and sulfolane.

5. The lithium-ion secondary battery according to claim 1, wherein The nonaqueous solvent contains ethylene carbonate. wherein R 1 and R 2 each independently represents a hydrogen atom, an alkyl group which can have a substituent, an aryl group which can have a substituent, or a halogen atom.

6. The lithium-ion secondary battery according to claim 1, wherein The polymer electrolyte film is a self-supporting film composed of the vinylene carbonate-based polymer and lithium bis(fluorosulfonyl)imide.

7. The lithium-ion secondary battery according to claim 1, wherein 12. A method for manufacturing a lithium ion secondary battery, the lithium ion secondary battery comprising a positive electrode, a negative electrode, and an electrolyte disposed between the positive electrode and the negative electrode, the electrolyte containing a polymer electrolyte, the polymer electrolyte containing a vinylene carbonate-based polymer and a lithium salt of a compound containing a fluorosulfonyl group, the lithium salt of the compound containing a fluorosulfonyl group containing lithium bis(fluorosulfonyl)imide, wherein in the method, the lithium salt of the compound containing a fluorosulfonyl group is dissolved in a vinylene carbonate-based compound as a monomer, and then a vinylene carbonate-based polymer is synthesized.

8. The lithium-ion secondary battery according to claim 7, wherein The vinylene carbonate-based compound is a compound represented by the following formula (1), 9. The lithium-ion secondary battery according to claim 7, wherein The vinylene carbonate-based polymer is a homopolymer of the vinylene carbonate-based compound.

10. The lithium-ion secondary battery according to claim 7, wherein The vinylene carbonate-based polymer is poly(vinylene carbonate).

11. The lithium-ion secondary battery according to claim 1, wherein The polymer electrolyte contains less than 40 mass% of a nonaqueous solvent. The nonaqueous solvent contains at least one selected from the group consisting of cyclic carbonates, chain carbonates, and sulfolanes. The nonaqueous solvent contains at least one selected from the group consisting of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, and sulfolane. The nonaqueous solvent contains ethylene carbonate. ​ ​ ​ 13. The method for manufacturing a lithium-ion secondary battery according to claim 12, wherein ​ wherein R 1 and R 2 each independently represents a hydrogen atom, an alkyl group which can have a substituent, an aryl group which can have a substituent, or a halogen atom.

14. The method for manufacturing a lithium-ion secondary battery according to claim 12, wherein ​ 15. The method for manufacturing a lithium-ion secondary battery according to claim 12, wherein ​ 16. The method for manufacturing a lithium-ion secondary battery according to claim 12, wherein ​ 17. The method for manufacturing a lithium-ion secondary battery according to claim 16, wherein ​ 18. The method for manufacturing a lithium-ion secondary battery according to claim 16, wherein ​ 19. The method for manufacturing a lithium-ion secondary battery according to claim 16, wherein ​

Images