Secondary battery

Abstract

To provide a secondary battery with improved charge / discharge characteristics.SOLUTION: The secondary battery includes a positive electrode 21, a negative electrode 22, and an electrolytic solution. The electrolyte solution further contains at least one of a first compound and a second compound that is a linear ether, and a molar ratio of the first compound to the second compound is 1.8 or more. The first compound is a compound in which one of hydrogens bonded to a benzene ring of anisole is substituted with a thiol (- SH) group or an alkylthiol group (- CnH2nSH, n is an integer of 1 or more and 5 or less).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present technology relates to a secondary battery. [Background technology]

[0002] Non-Patent Document 1 discloses a secondary battery using an electrolyte solution containing anisole. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Moon, J., Kim, DO, Bekaert, L. et al. Non-fluorinated non-solvating cosolvent enabling superior performance of lithium metal negative electrode battery. Nature Communications 13, 4538 (2022). Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the secondary battery described in Non-Patent Document 1, there is a possibility that the charge-discharge characteristics will be deteriorated due to coordination of anisole with lithium ions.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide a secondary battery with improved charge / discharge characteristics. [Means for solving the problem]

[0006] A secondary battery according to one embodiment of the present invention comprises a positive electrode, a negative electrode, and an electrolyte solution, and the electrolyte solution contains at least one first compound represented by formula (1), formula (2), or formula (3).

[0007] [ka] (n is an integer between 0 and 5.) [Effects of the Invention]

[0008] According to the present invention, a secondary battery with improved charge-discharge characteristics can be provided. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view illustrating the configuration of a secondary battery according to one embodiment. [Figure 2] FIG. 2 is an enlarged cross-sectional view showing the configuration of the battery element shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present technology will be described in detail with reference to the drawings. However, the present invention is not limited to this embodiment.

[0011] <1. Secondary battery> The secondary battery according to this embodiment is a secondary battery that obtains battery capacity by utilizing the occlusion and release of an electrode reactant, and includes a positive electrode, a negative electrode, and an electrolyte solution.

[0012] The type of electrode reactant is not particularly limited, and specifically includes light metals such as alkali metals and alkaline earth metals. Specific examples of alkali metals include lithium, sodium, and potassium. Specific examples of alkaline earth metals include beryllium, magnesium, and calcium.

[0013] In the following description, an example will be given in which the electrode reactant is lithium. A secondary battery that obtains battery capacity by utilizing the absorption and desorption of lithium is, for example, a lithium ion secondary battery. In a lithium ion secondary battery, lithium is absorbed and desorbed in the ionic state.

[0014] <1-1.Configuration> Fig. 1 is a perspective view showing the configuration of a secondary battery according to one embodiment. Fig. 2 is an enlarged cross-sectional view showing the configuration of the battery element shown in Fig. 1. Fig. 1 shows a state in which an exterior film 10 and a battery element 20 are separated from each other, and the cross section of the battery element 20 is indicated by a dashed line. Fig. 2 shows the cross section of only a portion of the battery element 20.

[0015] As shown in FIGS. 1 and 2, the secondary battery 1 includes an exterior film 10, a battery element 20, a positive electrode lead 31, a negative electrode lead 32, and sealing films 41 and .

[0016] As described above, the secondary battery 1 in Fig. 1 uses the exterior film 10 as an exterior member for housing the battery element 20. Therefore, the secondary battery 1 shown in Fig. 1 is a so-called laminate film type secondary battery.

[0017] [Exterior film] 1, the exterior film 10 is a flexible or pliable exterior member, and has a sealed bag-like structure when the battery element 20 is housed therein. As a result, the exterior film 10 houses a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte solution (not shown), which will be described later.

[0018] In the example of Fig. 1, the exterior film 10 is a single film-like member that is folded in a folding direction F. The exterior film 10 is provided with a recessed portion 10U for accommodating the battery element 20. The recessed portion 10U is a so-called deep-drawn portion.

[0019] Specifically, the exterior film 10 is a three-layer laminate film in which a fusion layer, a metal layer, and a surface protection layer are laminated in this order from the inside. When the exterior film 10 is folded, the outer peripheral edges of the opposing fusion layers are fused to each other. The fusion layer contains a polymer compound such as polypropylene. The metal layer contains a metal material such as aluminum. The surface protection layer contains a polymer compound such as nylon. The configuration (number of layers) of the exterior film 10 is not particularly limited and may be one or two layers, or four or more layers.

[0020] [Battery element] The battery element 20 is housed in the space of the recess 10U of the exterior film 10. The battery element 20 is a so-called power generating element. As shown in Figures 1 and 2, the battery element 20 includes a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte (not shown).

[0021] 1, battery element 20 is a so-called wound electrode body. Therefore, positive electrode 21 and negative electrode 22 are wound around winding axis P while facing each other with separator 23 interposed therebetween. In the following description, the direction along winding axis P may be referred to as the Y direction, the longitudinal direction of battery element 20 perpendicular to winding axis P as the X direction, and the lateral direction of battery element 20 perpendicular to winding axis P as the Z direction.

[0022] In the example of FIG. 1, the battery element 20 has a flat three-dimensional shape. That is, the shape of a cross section (cross section along the XZ plane) of the battery element 20 intersecting with the winding axis P of the battery element 20 is a flat shape defined by a major axis J1 and a minor axis J2. The major axis J1 is an imaginary axis extending in the X-axis direction and has a length greater than that of the minor axis J2. The minor axis J2 is an imaginary axis extending in the Z-axis direction and has a length smaller than that of the major axis J1. As a result, the cross-sectional shape of the battery element 20 is a flat, approximately elliptical shape. Note that the three-dimensional shape of the battery element 20 is merely an example and is not limited to the above.

[0023] (positive electrode) 2, the positive electrode 21 includes a positive electrode current collector 21A and a positive electrode active material layer 21B. However, the positive electrode current collector 21A may be omitted.

[0024] The positive electrode current collector 21A has a pair of surfaces on which the positive electrode active material layers 21B are provided. The positive electrode current collector 21A contains a conductive material such as a metal material such as aluminum.

[0025] The positive electrode active material layer 21B contains at least one positive electrode active material that absorbs and releases lithium. However, the positive electrode active material layer 21B may further contain one or more other materials, such as a positive electrode binder and a positive electrode conductive agent. The method for forming the positive electrode active material layer 21B is not particularly limited, and specifically includes a coating method.

[0026] 2, the positive electrode active material layer 21B is provided on both sides of the positive electrode current collector 21A. However, the positive electrode active material layer 21B may be provided on only one side of the positive electrode current collector 21A, where the positive electrode 21 faces the negative electrode 22.

[0027] The type of positive electrode active material is not particularly limited, and specifically includes a lithium-containing compound. The lithium-containing compound is a compound containing lithium and one or more transition metal elements as constituent elements. The lithium-containing compound may further contain one or more other elements as constituent elements. The type of other elements is not particularly limited as long as it is an element other than lithium and a transition metal element, and specifically includes elements belonging to Groups 2 to 15 of the long period periodic table. The type of lithium-containing compound is not particularly limited, and specifically includes oxides, phosphate compounds, silicate compounds, borate compounds, and the like.

[0028] Specific examples of oxides are LiNiO2, LiCoO2, LiCo 0.98 Al 0.01 Mg 0.01 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi0.33 Co 0.33 Mn 0.33 O2, Li 1.2 Mn 0.52 Co 0.175 Ni 0.1 O2, Li 1.15 (Mn 0.65 Ni 0.22 Co 0.13 )O2 and LiMn2O4. Specific examples of phosphate compounds include LiFePO4, LiMnPO4, LiFe 0.5 Mn 0.5 PO4 and LiFe 0.3 Mn 0.7 PO4, etc.

[0029] The positive electrode binder contains at least one of synthetic rubber and polymer compounds. Specific examples of synthetic rubber include styrene-butadiene rubber, fluorine-containing rubber, and ethylene-propylene-diene. Specific examples of polymer compounds include polyvinylidene fluoride, polyimide, and carboxymethyl cellulose.

[0030] The positive electrode conductive agent contains at least one conductive material such as a carbon material, a metal material, and a conductive polymer compound, and specific examples of the carbon material include graphite, carbon black, acetylene black, and ketjen black.

[0031] (Negative electrode) 2, the negative electrode 22 includes a negative electrode current collector 22A and a negative electrode active material layer 22B. However, the negative electrode current collector 22A may be omitted.

[0032] The negative electrode current collector 22A has a pair of surfaces on which the negative electrode active material layers 22B are provided. The negative electrode current collector 22A contains a conductive material such as a metal material such as copper.

[0033] The negative electrode active material layer 22B includes at least one negative electrode active material that absorbs and releases lithium. However, the negative electrode active material layer 22B may further include at least one other material such as a negative electrode binder and a negative electrode conductive agent. The method for forming the negative electrode active material layer 22B is not particularly limited, and specifically includes at least one of a coating method, a vapor phase method, a liquid phase method, a thermal spraying method, and a firing method (sintering method).

[0034] 2, the negative electrode active material layer 22B is provided on both sides of the negative electrode current collector 22A. However, the negative electrode active material layer 22B may be provided on only one side of the negative electrode current collector 22A where the negative electrode 22 faces the positive electrode 21.

[0035] The type of negative electrode active material is not particularly limited, and specific examples include carbon materials and metal-based materials. This allows for high energy density. Specific examples of carbon materials include graphitizable carbon, non-graphitizable carbon, and graphite. Graphite may be either or both of natural graphite and artificial graphite. Metal-based materials are a general term for materials containing at least one metal element and / or metalloid element that can form an alloy with lithium as a constituent element. Specific examples of metal elements and metalloid elements include silicon and tin. Metal-based materials may be simple substances, alloys, or compounds. Furthermore, metal-based materials may be mixtures of two or more materials or materials containing two or more phases. Furthermore, simple substances may contain any amount of impurities. Specific examples of metal-based materials are TiSi2 and SiO x (0 <x≦2)などである。

[0036] The negative electrode binder may be made of the same material as the positive electrode binder described above, and the negative electrode conductive agent may be made of the same material as the positive electrode conductive agent described above.

[0037] (separator) As shown in FIG. 2, the separator 23 is an insulating porous film interposed between the positive electrode 21 and the negative electrode 22. The separator 23 allows lithium to pass through in an ionic state while preventing short circuits caused by contact between the positive electrode 21 and the negative electrode 22. The separator 23 contains at least one insulating polymer compound. A specific example of the insulating polymer compound is polyethylene.

[0038] (electrolyte) The electrolyte is impregnated into each of the positive electrode 21, the negative electrode 22, and the separator 23. Details of the electrolyte will be described later.

[0039] [Positive lead] 1 and 2, the positive electrode lead 31 is a positive electrode wiring connected to the positive electrode current collector 21A of the positive electrode 21, and is drawn out to the exterior of the exterior film 10. The positive electrode lead 31 includes at least one type of conductive material such as a metal material, and a specific example of the conductive material is aluminum. The shape of the positive electrode lead 31 is not particularly limited, and may be, for example, a thin plate or a mesh shape.

[0040] [Negative lead] As shown in FIGS. 1 and 2, the negative electrode lead 32 is a negative electrode wiring connected to the negative electrode current collector 22A of the negative electrode 22 and is drawn out to the outside of the exterior film 10. The negative electrode lead 32 includes at least one type of conductive material such as a metal material. A specific example of the conductive material is copper. The shape of the negative electrode lead 32 is not particularly limited and may be, for example, a thin plate or a mesh shape.

[0041] [Sealing film] As shown in Fig. 1, the sealing film 41 is inserted between the exterior film 10 and the positive electrode lead 31. Furthermore, as shown in Fig. 1, the sealing film 42 is inserted between the exterior film 10 and the negative electrode lead 32. However, one or both of the sealing films 41 and 42 may be omitted.

[0042] The sealing film 41 is a sealing member that prevents outside air and the like from entering the inside of the exterior film 10. The sealing film 41 contains a polymer compound such as polyolefin that has adhesiveness to the positive electrode lead 31. A specific example of the polymer compound is polypropylene.

[0043] The sealing film 42 is a sealing member that prevents outside air and the like from entering the inside of the exterior film 10. The sealing film 41 contains a polymer compound such as polyolefin that has adhesiveness to the negative electrode lead 32. A specific example of the polymer compound is polypropylene.

[0044] <2. Electrolyte> The electrolyte solution according to this embodiment will be described in detail below.

[0045] <2-1.Configuration> The electrolyte solution includes a solvent and an electrolyte salt.

[0046] [solvent] (First Compound) The solvent contains at least one of the first compounds represented by formula (1), formula (2), or formula (3). The number of carbon atoms n in formula (1), formula (2), and formula (3) is 0 or more and 5 or less. That is, the first compound is a compound in which one of the hydrogen atoms bonded to the benzene ring of anisole is a thiol group (-SH) or an alkylthiol group (-C n H 2n The first compound is a compound substituted with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 112, 113, 114, 115, 116, 117, 118, 120, 121, 122, 123, 124, 125, 126, 127, 128, 130, 131, 132, 133, 134,

[0047] [ka]

[0048] Here, the alkylthiol group in the formula (1), the formula (2), and the formula (3) is an alkyl group (-C n H 2n+1 It refers to a functional group in which one hydrogen atom in an alkyl group (where n is an integer of 1 to 5) has been substituted with a thiol group (-SH). Specific examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, and a pentyl group. The alkyl group may be linear or branched. Thus, for example, the propyl group may be an n-butyl group, a sec-butyl group, an isobutyl group, or a tert-butyl group.

[0049] The number of carbon atoms n in formulas (1), (2), and (3) is preferably 0 or 1. That is, the solvent preferably contains, as the first compound, at least one compound in which one of the hydrogen atoms bonded to the benzene ring of anisole is substituted with a thiol group (-SH) or a methylthiol group (-CHSH). This can improve the solubility of the solute in the first compound and the compatibility with the solvent, such as the second compound.

[0050] Specific examples of the first compound include compounds represented by formulas (4) to (6).

[0051] [ka]

[0052] Whether the electrolyte solution contains the first compound can be determined by analyzing the electrolyte solution. Specifically, the secondary battery 1 is disassembled, and the electrolyte solution is recovered using a centrifuge and analyzed. This allows the types of components contained in the electrolyte solution, such as the first compound, to be identified. The method for analyzing the electrolyte solution is not particularly limited, and specifically includes at least one of inductively coupled plasma (ICP) optical emission spectroscopy, nuclear magnetic resonance spectroscopy (NMR), and gas chromatography mass spectrometry (GC-MS).

[0053] (Second Compound) Preferably, the solvent further contains at least one second compound. The second compound is a linear ether. In the present disclosure, linear ether refers to a linear compound having at least one ether bond. Here, linear ethers include those in which hydrogen is replaced by a carbon-free substituent. Specific examples of linear ethers include 1,2-dimethoxyethane (DME), diethyl ether (DEE), diethylene glycol dimethyl ether (G2), triethylene glycol dimethyl ether (G3), etc. More preferably, the solvent contains 1,2-dimethoxyethane (DME). This reduces the viscosity of the electrolyte solution, improves the electrolytic properties of the electrolyte salt, and improves the mobility of ions in the electrolyte solution, thereby improving charge / discharge characteristics.

[0054] Whether or not the electrolyte solution contains the second compound can be determined by analyzing the electrolyte solution using the same procedure as for determining the presence or absence of the first compound described above.

[0055] (Mixing ratio) In this embodiment, the molar ratio of the first compound to the second compound in the electrolyte solution is preferably 1.8 or more, and more preferably 2.0 or more. The molar ratio of the first compound to the second compound in the electrolyte solution is calculated by dividing the total amount (mol) of the first compound contained in the electrolyte solution by the total amount (mol) of the second compound contained in the electrolyte solution. This improves the effect of the first compound, i.e., the effect of forming a coating derived from the anions of the electrolyte solution on the negative electrode, while improving the physical properties of the electrolyte solution with the second compound, thereby further improving charge / discharge characteristics.

[0056] The molar ratio of the first compound to the second compound can be determined by analyzing the electrolyte solution. Specifically, the secondary battery 1 is disassembled, and the electrolyte solution is recovered using a centrifuge and analyzed. This allows the amounts of the first compound and the second compound contained in the electrolyte solution to be measured. The electrolyte solution can be analyzed by at least one of ICP atomic emission spectroscopy, NMR, and GC-MS.

[0057] (Other solvents) The solvent may further contain a solvent other than the first compound or the second compound.

[0058] Specifically, the other solvents include esters and cyclic ethers, and more specifically, carbonate ester compounds, carboxylic acid ester compounds, and lactone compounds. Carbonate ester compounds include cyclic carbonate esters and chain carbonate esters. Specific examples of cyclic carbonate esters include ethylene carbonate and propylene carbonate. Specific examples of chain carbonate esters include dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Carboxylate ester compounds include chain carboxylic acid esters. Specific examples of chain carboxylic acid esters include ethyl acetate, ethyl propionate, propyl propionate, and ethyl trimethylacetate. Lactone compounds include lactones. Specific examples of lactones include γ-butyrolactone and γ-valerolactone. Cyclic ethers include 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, and 1,4-dioxane.

[0059] Other solvents may include unsaturated cyclic carbonates, fluorinated cyclic carbonates, sulfonates, phosphates, acid anhydrides, nitrile compounds, and isocyanate compounds. This improves the electrochemical stability of the electrolyte. Specific examples of unsaturated cyclic carbonates include vinylene carbonate, vinylethylene carbonate, and methyleneethylene carbonate. Specific examples of fluorinated cyclic carbonates include monofluoroethylene carbonate and difluoroethylene carbonate. Specific examples of sulfonates include propane sultone and propene sultone. Specific examples of phosphate esters include trimethyl phosphate and triethyl phosphate. Specific examples of acid anhydrides include succinic anhydride, 1,2-ethanedisulfonic anhydride, and 2-sulfobenzoic anhydride. Specific examples of nitrile compounds include succinonitrile. Specific examples of isocyanate compounds include hexamethylene diisocyanate.

[0060] [Electrolyte salt] The electrolyte salt includes a cation and an anion.

[0061] Examples of the cation of the electrolyte salt include alkali metal ions such as potassium ions, lithium ions, and sodium ions.

[0062] The anion of the electrolyte salt is hexafluorophosphate ion (PC6 - ), tetrafluoroboric acid (BF4 - ), trifluoromethanesulfonate ion (CF3SO3 - ), bis(trifluoromethanesulfonyl)imide ion (N(CF3SO2)2 - ), tris(trifluoromethanesulfonyl)methide ion (C(CF3SO2)3 - ), bis(oxalato)borate ion (B(C2O4)2 - ) and nitrate ions (NO3 - ) is preferably contained. This allows a coating containing an inorganic substance such as LiF or Li3N to be formed on the surface of the negative electrode by decomposition of the anions of the electrolyte salt.

[0063] The anion of the electrolyte salt is hexafluorophosphate ion (PC6 - ), tetrafluoroboric acid (BF4 - ), trifluoromethanesulfonate ion (CF3SO3 - ), bis(trifluoromethanesulfonyl)imide ion (N(CF3SO2)2 - ) and tris(trifluoromethanesulfonyl)methide ion (C(CF3SO2)3 - ) is more preferably contained. This allows a fluorine-containing SEI to be formed on the surface of the negative electrode.

[0064] The anion of the electrolyte salt more preferably contains at least one anion having an imide bond, such as lithium bis(fluorosulfonyl)imide (LiN(FSO2)2) or lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2). This allows for the formation of a good ion pair between the electrolyte anion and the alkali metal ion in the electrolytic solution, facilitating the formation of an SEI.

[0065] Specific examples of electrolyte salts include lithium salts such as lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium trifluoromethanesulfonate (LiCFSO), lithium bis(fluorosulfonyl)imide (LiN(FSO)), lithium bis(trifluoromethanesulfonyl)imide (LiN(CFSO)), lithium tris(trifluoromethanesulfonyl)methide (LiC(CFSO)), lithium bis(oxalato)borate (LiB(CO)), lithium monofluorophosphate (LiPFO), and lithium difluorophosphate (LiPFO). This allows for high battery capacity.

[0066] The content of the electrolyte salt is not particularly limited, but specifically, it is preferably 0.3 mol / kg or more and 3.0 mol / kg or less relative to the solvent, which can improve the ionic conductivity of the electrolyte solution.

[0067] <3.Operation> The secondary battery 1 according to this embodiment operates in the battery element 20 as follows.

[0068] During charging, lithium is released from the positive electrode 21 and is absorbed into the negative electrode 22 via the electrolyte. On the other hand, during discharging, lithium is released from the negative electrode 22 and is absorbed into the positive electrode 21 via the electrolyte. During both discharging and charging, lithium is absorbed and released in an ionic state.

[0069] <4. Manufacturing method> When manufacturing the secondary battery 1 according to this embodiment, the positive electrode 21, the negative electrode 22, and the electrolyte solution are each prepared using the procedure described below as an example, and then the secondary battery 1 is assembled and subjected to a stabilization process. Note that the manufacturing method of the secondary battery 1 described below is merely an example and is not limited to this.

[0070] [Preparation of positive electrode] First, a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent are mixed together to form a positive electrode mixture. Then, the positive electrode mixture is added to a solvent to prepare a paste-like positive electrode mixture slurry. The solvent may be an aqueous solvent or an organic solvent.

[0071] Finally, the positive electrode active material layer 21B is formed by applying the positive electrode mixture slurry to both surfaces of the positive electrode current collector 21A. When forming the positive electrode active material layer 21B, the positive electrode active material layer 21B may be compression-molded using a compression device such as a roll press. When compression-molding the positive electrode active material layer 21B, the positive electrode active material layer 21B may be heated, or the compression molding may be repeated multiple times. Through the above procedure, the positive electrode active material layer 21B is formed on both surfaces of the positive electrode current collector 21A, and the positive electrode 21 is produced.

[0072] [Preparation of negative electrode] The negative electrode 22 is formed by a procedure similar to that for producing the positive electrode 21 described above. Specifically, a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent are mixed together to produce a negative electrode mixture, and the resulting mixture is poured into a solvent to prepare a paste-like negative electrode mixture slurry. The solvent may be an aqueous solvent or an organic solvent. The negative electrode mixture slurry is then applied to both surfaces of the negative electrode current collector 22A to form the negative electrode active material layer 22B. Thereafter, the negative electrode active material layer 22B may be compression-molded. When forming the negative electrode active material layer 22B, it may be compression-molded in the same manner as the positive electrode active material layer 21B. By the above procedure, the negative electrode active material layers 22B are formed on both surfaces of the negative electrode current collector 22A, and the negative electrode 22 is produced.

[0073] [Preparation of electrolyte] When producing an electrolytic solution, an electrolyte salt is added to a solvent containing a first compound and a second compound. In this case, the mixing ratio of the first compound to the second compound is adjusted so that the molar ratio of the first compound to the second compound falls within the above-mentioned range. This disperses or dissolves the electrolyte salt in the solvent, preparing the electrolytic solution.

[0074] [Secondary battery assembly] First, the positive electrode lead 31 is connected to the positive electrode current collector 21A of the positive electrode 21 using a joining method such as welding, and the negative electrode lead 32 is connected to the negative electrode current collector 22A of the negative electrode 22 using a joining method such as welding.

[0075] Next, the positive electrode 21 and the negative electrode 22 are stacked with the separator 23 interposed therebetween to form a laminate. Next, the laminate is wound around the winding axis P shown in FIG. 2 to form a wound body, and then the wound body is pressed using a compression device such as a press to form the wound body into a flat shape. As a result, the shape of the wound body after molding becomes the same as the shape of the battery element 20.

[0076] Next, after the roll is accommodated in the recess 10U, the exterior film 10 is folded so that the two exterior films 10 face each other in the Z direction. Next, the outer peripheral edges of two sides of the opposing fusion layers are joined together using an adhesive method such as heat fusion, thereby accommodating the roll in the bag-shaped exterior film 10.

[0077] Finally, the electrolyte solution prepared above is poured into the bag-shaped exterior film 10, and then the outer peripheral edges of the remaining side of the opposing fusion layers are joined together using an adhesive method such as heat sealing. When joining the outer peripheral edges of the remaining side, a sealing film 41 is inserted between the exterior film 10 and the positive electrode lead 31, and a sealing film 42 is inserted between the exterior film 10 and the negative electrode lead 32. This allows the wound body to be impregnated with the electrolyte solution, and the battery element 20 is produced.

[0078] As a result of the above, the battery element 20 is sealed in the bag-shaped exterior film 10, and the secondary battery 1 according to this embodiment is assembled.

[0079] [Stabilization process for secondary batteries after assembly] The assembled secondary battery 1 is subjected to a stabilization treatment by charging and discharging. The stabilization conditions, such as the ambient temperature, the number of charge / discharge cycles (number of cycles), and the charge / discharge conditions, can be set arbitrarily. The stabilization treatment forms the above-mentioned coating on the surface of the negative electrode 22, completing the secondary battery 1 in which the battery element 20 is electrochemically stabilized.

[0080] <5. Action and Effects> As described above, the secondary battery 1 according to this embodiment includes the positive electrode 21, the negative electrode 22, and an electrolyte solution. The electrolyte solution contains at least one of the first compounds represented by formula (1), formula (2), or formula (3).

[0081] [ka] (n is an integer between 0 and 5.)

[0082] This increases the boiling point of the electrolyte solution by the first compound, reducing its volatility and flammability, and improving safety. Furthermore, the first compound is less likely to coordinate with alkali metal ions such as lithium ions, reducing the ionic conductivity of the electrolyte solution and improving charge-discharge characteristics.

[0083] In a desirable embodiment, n in formula (1), formula (2), or formula (3) is 0 or 1. This can improve the solubility of the solute in the first compound and the compatibility with the solvent of the second compound, etc.

[0084] In a preferred embodiment, the electrolyte further contains at least one second compound that is a linear ether, which reduces the viscosity of the electrolyte solution, improves the electrolytic properties of the electrolyte salt, and improves the mobility of ions in the electrolyte solution, thereby improving charge / discharge characteristics.

[0085] In a more preferred embodiment, the molar ratio of the first compound to the second compound in the electrolyte solution is 1.8 or more, which allows the first compound to promote film formation on the negative electrode, while the second compound can improve the physical properties of the electrolyte solution, thereby further improving charge-discharge characteristics.

[0086] <6. Variations> Next, modified examples will be described. The configuration of the secondary battery according to this embodiment can be modified as appropriate, as described below. Note that the series of modified examples described below may be combined with each other.

[0087] [First Modification] The secondary battery according to the first modification differs from the above-described secondary battery 1 in that it is a secondary battery that utilizes deposition and dissolution of lithium, a so-called lithium metal secondary battery.

[0088] The secondary battery according to the first modification has the same configuration as the secondary battery 1 described above, except that the negative electrode 22 contains elemental lithium, i.e., lithium metal. Specifically, the negative electrode 22 is a lithium metal foil or the like. However, the lithium metal may contain any amount of impurities.

[0089] In the secondary battery according to the first modification, when lithium is released in an ionic state from the positive electrode 21 during charging, metallic lithium is deposited on the surface of the negative electrode 22. Furthermore, in the secondary battery according to the first modification, when lithium metal is eluted from the negative electrode 22 during discharging, lithium is absorbed in an ionic state in the positive electrode 21.

[0090] The method for manufacturing the secondary battery according to the first modification is the same as the method for manufacturing the secondary battery 1 described above, except that lithium metal is used as the negative electrode 22.

[0091] In the secondary battery according to the first modification, the battery capacity is also obtained by utilizing the deposition and dissolution of lithium, and therefore the same effects as those of the secondary battery 1 described above can be obtained.

[0092] [Second Modification] The second modification differs from the secondary battery 1 described above in that a laminated separator including a polymer compound layer is used instead of the separator 23 which is a porous film.

[0093] Specifically, the laminated separator includes a porous film and a polymer compound layer. The porous film has a pair of surfaces. The polymer compound layer is provided on one or both surfaces of the porous film. This improves the adhesion of the separator to the positive electrode 21 and the negative electrode 22, respectively, thereby preventing misalignment of the positive electrode 21, the negative electrode 22, and the separator 23 during winding. Therefore, swelling of the secondary battery is suppressed even if a decomposition reaction of the positive electrolyte occurs.

[0094] The polymer compound layer preferably contains polyvinylidene fluoride, etc. This can improve the physical strength and electrochemical stability of the polymer compound layer.

[0095] One or both of the porous film and the polymer compound layer may contain at least one type of insulating particles. This allows the insulating particles to dissipate heat when the secondary battery generates heat, thereby improving the heat resistance and safety of the secondary battery. The insulating particles contain at least one type of insulating material, such as an inorganic material or a resin material. Specific examples of inorganic materials include aluminum oxide, aluminum nitride, boehmite, silicon oxide, titanium oxide, magnesium oxide, and zirconium oxide. Specific examples of resin materials include acrylic resin and styrene resin.

[0096] The separator according to the second modification is fabricated by preparing a precursor solution containing a polymer compound and an organic solvent, and then applying the precursor solution to one or both sides of a porous film. In fabricating the separator according to the second modification, the precursor solution may contain a plurality of insulating particles.

[0097] Even when the laminated separator according to the second modification is used, lithium can move in an ionic state between the positive electrode 21 and the negative electrode 22, and therefore it is possible to obtain the same effects as those of the above-described secondary battery 1. In particular, the second modification can suppress swelling of the secondary battery.

[0098] [Third Modification] In the secondary battery according to the third modification, a gel electrolyte layer may be used instead of the liquid electrolyte solution.

[0099] In a battery element 20 using the electrolyte layer according to the third modification, a positive electrode 21 and a negative electrode 22 are wound facing each other with a separator 23 and an electrolyte layer interposed therebetween. The electrolyte layer is interposed between the positive electrode 21 and the separator 23, and between the negative electrode 22 and the separator 23.

[0100] Specifically, the electrolyte layer contains an electrolytic solution and a polymer compound. In the electrolyte layer, the electrolytic solution is held by the polymer compound. This makes it possible to prevent leakage of the electrolytic solution. The composition of the electrolytic solution is the same as that of the electrolytic solution in the secondary battery 1 described above. The polymer compound contains polyvinylidene fluoride, etc.

[0101] The electrolyte layer according to the third modification is formed by preparing a precursor solution containing an electrolytic solution, a polymer compound, and a solvent, and then applying the precursor solution to one or both surfaces of the positive electrode 21 and the negative electrode 22.

[0102] The same effect can be obtained when the electrolyte layer according to the third modification is used, because lithium can move in an ionic state between the positive electrode 21 and the negative electrode 22 via the electrolyte layer. In particular, the third modification can suppress leakage of the electrolyte solution.

[0103] Examples of the secondary battery according to this embodiment will be described below, but the secondary battery according to this embodiment is not limited to the following examples.

[0104] <Examples 1 to 5 and Comparative Example 1> In Examples 1 to 5 and Comparative Example 1, secondary batteries were manufactured in the following manner: The secondary batteries according to Examples 1 to 5 and Comparative Example 1 are simple lithium metal secondary batteries.

[0105] [Secondary battery production] The electrolytic solution was prepared by adding an electrolyte salt to a mixed solvent of the first solvent and the second solvent, and stirring the mixture.

[0106] As shown in Table 1 below, the first solvent used was the compound represented by formula (4) (2-methoxybenzenethiol) in Examples 1 to 3, the compound represented by formula (5) (4-methoxybenzenethiol) in Example 4, the compound represented by formula (6) (4-Methoxy-alpha-toluenethiol) in Example 5, and the compound represented by formula (7) (Anisole) in Comparative Example 1. That is, in Examples 1 to 5, the first compound according to this embodiment was used as the first solvent, while in Comparative Example 1, anisole was used instead of the first compound.

[0107] [ka]

[0108] The second solvent used was 1,2-dimethoxyethane (DME). That is, in Examples 1 to 5 and Comparative Example 1, the second compound according to the present embodiment was used as the second solvent. Here, the solvents were prepared so that the molar ratio of the first solvent to the second solvent was 1.8 in Example 1 and 2.0 in Examples 2 to 5 and Comparative Example 1, as shown in Table 1 below.

[0109] The electrolyte salt used was lithium bis(fluorosulfonyl)imide (LiFSI). The electrolyte solutions were prepared so that the concentration of the electrolyte salt relative to the solvent was 2 mol / L in Examples 1, 2, 4, and 5 and Comparative Example 1, and 3 mol / L in Example 3, as shown in Table 1 below.

[0110] The test electrode was fabricated by pressing a 0.1 mm thick lithium metal foil onto a 0.01 mm thick copper foil using a press. The counter electrode was a 0.012 mm thick copper foil. The separator was a 10 μm thick microporous polyethylene film. The separator was impregnated with the prepared electrolyte by dripping the electrolyte solution. The amount of electrolyte dripped was 0.01 mL. The test electrode, the separator impregnated with the electrolyte, and the counter electrode were then stacked in this order to fabricate a secondary battery for charge / discharge tests.

[0111] [Charge / discharge test] For the secondary batteries prepared above, a charge / discharge test was carried out by the following method to evaluate the battery characteristics, and the coulomb efficiency was measured.

[0112] In the charge-discharge test, measurements were taken by repeating multiple charge-discharge cycles. Specifically, the secondary battery was charged and discharged at a temperature of 23°C for each cycle to measure the charge capacity and discharge capacity. During charging, the current was 0.22 mA / cm. 2 The battery was charged at a current density of 1000 kJ / s for a total charging time of 3 hours, and discharged until the voltage reached 0.1 V. The coulombic efficiency was calculated for each cycle using the formula: Coulombic efficiency (%) = (discharge capacity / charge capacity) × 100.

[0113] In the charge-discharge test, the secondary battery was repeatedly charged and discharged until it reached 25 cycles, and the Coulombic efficiency was measured. The average Coulombic efficiency (%) was calculated by averaging the Coulombic efficiencies calculated for each of the 16 cycles from the 10th to the 25th cycle. Only the Coulombic efficiencies from the 10th to the 25th cycles were used to calculate the average Coulombic efficiency in order to improve the accuracy and reproducibility of the evaluation of the charge-discharge characteristics. Because the Coulombic efficiency values ​​tend to vary from the 1st to the 9th cycles, the Coulombic efficiencies from the 1st to the 9th cycles were not used to calculate the average Coulombic efficiency.

[0114] Table 1 shows the composition of the electrolyte solution and the charge / discharge characteristics of the secondary batteries according to Examples 1 to 5 and Comparative Example 1. In Table 1, "first solvent / second solvent" refers to the ratio of the amount of substance of the first solvent contained in the electrolyte to the amount of substance of the second solvent contained in the electrolyte.

[0115] [Table 1]

[0116] As shown in Table 1, in Examples 1 to 5, in which the first compound represented by any one of formulas (4) to (6) was used as the first solvent, the average Coulombic efficiency was improved compared to Comparative Example 1, in which anisole represented by formula (7) was used. Therefore, it can be seen that the charge-discharge characteristics are improved when the electrolyte solution contains the first compound.

[0117] As shown in Table 1, in Examples 1 to 5 where the ratio of the first solvent to the second solvent, i.e., the ratio of the first compound to the second compound, was 1.8 or more, the average Coulombic efficiency was 99% or more. Therefore, it can be seen that when the ratio of the first compound to the second compound is 1.8 or more, the charge-discharge characteristics are good.

[0118] As shown in Table 1, in Examples 2 to 4, in which the ratio of the first solvent to the second solvent, i.e., the ratio of the first compound to the second compound, was 2.0 or more, the average Coulombic efficiency was improved compared to Example 1, in which the ratio of the first compound to the second compound was less than 2.0. Therefore, it can be seen that the charge-discharge characteristics are further improved when the ratio of the first compound to the second compound is 2.0 or more.

[0119] The above content is intended to facilitate understanding of the present invention, and is not intended to be interpreted as limiting the present invention. The present invention may be modified or improved without departing from the spirit thereof, and equivalents thereof are also included in the present invention.

[0120] Specifically, the battery structure of the secondary battery may be cylindrical, rectangular, coin, or button type.

[0121] The battery element may have a stacked structure or a zigzag structure. In the stacked structure, positive and negative electrodes are alternately stacked with a separator interposed therebetween. In the zigzag structure, the positive and negative electrodes are folded in a zigzag pattern while facing each other with the separator interposed therebetween. [Explanation of symbols]

[0122] 1 Secondary battery 21 Positive electrode 22 Negative electrode

Claims

1. a positive electrode, a negative electrode, and an electrolyte; The secondary battery, wherein the electrolyte solution contains at least one first compound represented by formula (1), formula (2), or formula (3). 【Chemistry 1】 (n is an integer of 0 to 5.)

2. The secondary battery according to claim 1 , wherein n is 0 or 1.

3. 3. The secondary battery according to claim 1, wherein the electrolyte solution further contains at least one second compound that is a linear ether.

4. The secondary battery according to claim 3 , wherein a molar ratio of the first compound to the second compound in the electrolyte solution is 1.8 or more.

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