Negative electrode for secondary battery and secondary battery

Abstract

A secondary battery according to the present invention comprises a positive electrode, a negative electrode, and an electrolytic solution, wherein the negative electrode contains an inorganic metal salt and an organic fiber compound.

Description

[Technical field]

[0001] The present technology relates to a negative electrode for a secondary battery and a secondary battery. [Background technology]

[0002] Due to the widespread use of various electronic devices such as mobile phones, secondary batteries have been developed as small, lightweight, and high-energy-density power sources. These secondary batteries have a positive electrode, a negative electrode (secondary battery negative electrode), and an electrolyte solution, and various studies have been conducted on the structure of the secondary battery.

[0003] Specifically, in order to suppress an increase in internal resistance, etc., cellulose fibers are used as a binder for binding electrode active material particles (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-228456 A Summary of the Invention

[0005] Although various studies have been conducted on the battery characteristics of secondary batteries, the cycle characteristics and electrical resistance characteristics of the secondary batteries are still insufficient, and there is room for improvement.

[0006] Therefore, there is a demand for a negative electrode for a secondary battery and a secondary battery that are capable of achieving excellent cycle characteristics and excellent electrical resistance characteristics.

[0007] A negative electrode for a secondary battery according to an embodiment of the present technology includes an inorganic metal salt and an organic fiber compound.

[0008] A secondary battery according to an embodiment of the present technology includes an electrolyte solution together with a positive electrode and a negative electrode, and the negative electrode has a configuration similar to that of the negative electrode for a secondary battery according to the embodiment of the present technology described above.

[0009] According to the negative electrode for a secondary battery or the secondary battery of one embodiment of the present technology, since the negative electrode for a secondary battery contains an inorganic metal salt and an organic fiber compound, excellent cycle characteristics and excellent electrical resistance characteristics can be obtained.

[0010] Note that the effects of the present technology are not necessarily limited to the effects described here, but may be any of a series of effects related to the present technology described below. [Brief description of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view illustrating a configuration of a negative electrode for a secondary battery in a first embodiment of the present technology. [Diagram 2] 5 is an enlarged cross-sectional view showing the configuration of a negative electrode active material particle in a negative electrode for a secondary battery according to a second embodiment of the present technology. FIG. [Diagram 3] 1 is a perspective view illustrating a configuration of a secondary battery according to an embodiment of the present technology. [Figure 4] 4 is a cross-sectional view illustrating the configuration of the battery element shown in FIG. [Diagram 5] FIG. 1 is a block diagram showing a configuration of an application example of a secondary battery. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present technology will be described in detail with reference to the drawings. The description will be given in the following order. 1. Negative electrode for secondary battery (first embodiment) 1-1.Configuration 1-2. Manufacturing method 1-3. Actions and Effects 2. Negative electrode for secondary battery (second embodiment) 2-1.Configuration 2-2. Manufacturing method 2-3. Actions and Effects 3. Secondary battery 3-1.Configuration 3-2.Operation 3-3. Manufacturing method 3-4. Actions and Effects 4. Variations 5. Uses of secondary batteries

[0013] <1. Negative electrode for secondary battery (first embodiment)> First, a negative electrode for a secondary battery (hereinafter simply referred to as "negative electrode") according to a first embodiment of the present technology will be described.

[0014] This negative electrode is used in a secondary battery, which is an electrochemical device. However, the negative electrode may be used in other electrochemical devices other than the secondary battery. The type of other electrochemical device is not particularly limited, but specifically, it is a capacitor or the like.

[0015] In addition, the negative electrode absorbs and releases an electrode reactant during an electrode reaction in an electrochemical device such as the secondary battery. The type of the electrode reactant is not particularly limited, but specifically, it is a light metal such as an alkali metal or an alkaline earth metal. The alkali metal is lithium, sodium, potassium, etc., and the alkaline earth metal is beryllium, magnesium, calcium, etc.

[0016] In the following, an example will be given in which the electrode reactant is lithium. That is, the negative electrode absorbs and releases lithium during the electrode reaction. In this case, lithium is absorbed and released in an ionic state.

[0017] <1-1. Configuration> FIG. 1 shows a cross-sectional configuration of a negative electrode in the first embodiment.

[0018] This negative electrode contains an inorganic metal salt and an organic fiber compound. More specifically, as shown in Fig. 1, the negative electrode contains a negative electrode current collector 110 and a negative electrode active material layer 120, and the negative electrode active material layer 120 contains the above-mentioned inorganic metal salt and organic fiber compound. In this case, each of the inorganic metal salt and the organic fiber compound is dispersed in the negative electrode active material layer 120.

[0019] The negative electrode, more specifically, the negative electrode active material layer 120 contains an inorganic metal salt and an organic fiber compound, and the inorganic metal salt and the organic fiber compound are each dispersed in the negative electrode active material layer 120 because, in a secondary battery using the negative electrode, the ionic conductivity of lithium is ensured while an increase in electrical resistance is suppressed and decomposition of the electrolyte is also suppressed.

[0020] In detail, when the negative electrode active material layer 120 contains both an inorganic metal salt and an organic fiber compound, the inorganic metal salt having electrical conductivity is disposed on the surface of the negative electrode active material described later, and the organic fiber compound having a porous structure coats the surface of the negative electrode active material in the negative electrode active material layer 120. As a result, the surface of the negative electrode active material is electrochemically protected by the organic fiber compound while ensuring ion conductivity (a lithium migration path) by utilizing the porous structure, and the decomposition reaction of the electrolyte is suppressed on the surface of the reactive electrode reactant while ensuring smooth absorption and release of lithium. Moreover, the electrical conductivity between the negative electrode active materials is improved by utilizing the electrical conductivity of the inorganic metal salt, and an increase in electrical resistance is suppressed.

[0021] This ensures lithium ionic conductivity and suppresses an increase in electrical resistance and decomposition of the electrolyte, compared to when the negative electrode active material layer 120 contains only either an inorganic metal salt or an organic fiber compound.

[0022] [Negative electrode current collector] The negative electrode current collector 110 has a pair of surfaces on which the negative electrode active material layer 120 is provided. The negative electrode current collector 110 contains one or more types of conductive materials such as metal materials, and the metal materials are copper, aluminum, nickel, stainless steel, etc. The negative electrode current collector 110 may be a single layer or a multilayer.

[0023] The surface of the negative electrode current collector 110 is preferably roughened by electrolysis or the like. This is because the adhesion of the negative electrode active material layer 120 to the negative electrode current collector 110 is improved by utilizing the so-called anchor effect. However, the negative electrode current collector 110 may be omitted.

[0024] [Negative electrode active material layer] The negative electrode active material layer 120 contains the above-mentioned inorganic metal salt and organic fiber compound in addition to the negative electrode active material that absorbs and releases lithium.

[0025] The negative electrode active material layer 120 is provided on both sides of the negative electrode current collector 110. However, the negative electrode active material layer 120 may be provided on only one side of the negative electrode current collector 110. The negative electrode active material layer 120 may further contain one or more types of other materials such as a negative electrode binder and a negative electrode conductive agent.

[0026] The method for forming the negative electrode active material layer 120 is not particularly limited, but specifically includes one or more of a coating method, a gas phase method, a liquid phase method, a thermal spraying method, and a firing method (sintering method).

[0027] (Negative electrode active material) The type of the negative electrode active material is not particularly limited, but specifically, it is one or more of carbon materials and metal-based materials. That is, the negative electrode active material may be only a carbon material, only a metal-based material, or both a carbon material and a metal-based material. This is because a high energy density can be obtained. However, the type of the negative electrode active material may be a material other than the carbon material and the metal-based material.

[0028] Carbon materials are a general term for materials that contain carbon as a constituent element. This is because the crystal structure of carbon materials hardly changes during the absorption and release of lithium, so that high energy density can be obtained stably. In addition, carbon materials also function as negative electrode conductive agents, so that the conductivity of the negative electrode active material layer 120 is improved.

[0029] Specific examples of carbon materials include graphitizable carbon, non-graphitizable carbon, and graphite (natural graphite and artificial graphite). The interplanar spacing of the (002) plane of non-graphitizable carbon is not particularly limited, but is preferably 0.37 nm or more. The interplanar spacing of the (002) plane of graphite is not particularly limited, but is preferably 0.34 nm or less.

[0030] More specifically, specific examples of carbon materials include pyrolytic carbons, cokes, glassy carbon fibers, organic polymer compound calcined bodies, activated carbon, and carbon blacks. The cokes include pitch coke, needle coke, and petroleum coke. The organic polymer compound calcined bodies are calcined (carbonized) at an appropriate temperature of polymer compounds such as phenolic resin and furan resin. In addition, the carbon material may be low-crystalline carbon heat-treated at a temperature of about 1000° C. or less, or may be amorphous carbon. The shape of the carbon material is not particularly limited, but may be one or more of fibrous, spherical, granular, and scaly shapes.

[0031] Metallic materials are a general term for materials that contain one or more metal elements and / or metalloid elements that can form an alloy with lithium as constituent elements, because they can provide a higher energy density.

[0032] This metal-based material may be a simple substance, an alloy, a compound, a mixture of two or more of these, or a material containing one or more of these phases. The "simple substance" described here means a general simple substance, and may contain a trace amount of impurities. In other words, the purity of the simple substance is not necessarily limited to 100%.

[0033] However, the "alloy" described here includes not only materials containing two or more metal elements, but also materials containing one or more metal elements and one or more metalloid elements. The "alloy" may also contain one or more nonmetallic elements. The structure of the metal-based material is not particularly limited, but specifically may be one or more of a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or a mixture of two or more of these.

[0034] Specific examples of metal elements and metalloid elements include magnesium, boron, aluminum, gallium, indium, silicon, germanium, tin, lead, bismuth, cadmium, silver, zinc, hafnium, zirconium, yttrium, palladium, and platinum.

[0035] Among these, silicon is preferable because it has an excellent lithium absorption / desorption ability and therefore can provide a significantly high energy density.

[0036] Silicon alloys contain, as constituent elements other than silicon, any one or more of metal elements such as tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium. Silicon compounds contain, as constituent elements other than silicon, any one or more of nonmetal elements such as carbon and oxygen. However, silicon compounds may contain, as constituent elements other than silicon, any one or more of the series of metal elements described for silicon alloys.

[0037] An example of an alloy of silicon is SiB 4 , SiB 6 , Mg 2 Si, Ni 2 Si, TiSi 2 , MoSi 2 , CoSi 2 , NiSi 2 , CaSi 2 , CrSi 2 , Cu 5Si, FeSi 2 , MnSi 2 , NbSi 2 , TaSi 2 , VSi 2 , WSi 2 , ZnSi 2 and SiC, etc. However, the composition of the silicon alloy (mixing ratio of silicon and metal elements) can be arbitrarily changed.

[0038] Specific examples of silicon compounds are Si 3 N 4 , Si 2 N 2 O, SiO v (0 < v ≦ 2) and LiSiO, etc. However, the range of v may be, for example, 0.2 < v < 1.4.

[0039] In particular, the negative electrode active material is preferably both a carbon material and a metal-based material for the reasons described below.

[0040] Metal-based materials, particularly materials containing silicon as a constituent element, have the advantage of high theoretical capacity, but have the concern of being prone to severe expansion and contraction during charge and discharge. On the other hand, carbon materials have the concern of low theoretical capacity, but have the advantage of being less prone to expansion and contraction during charge and discharge. Therefore, by using a carbon material and a metal-based material in combination, a high theoretical capacity (i.e., battery capacity) can be obtained while suppressing the expansion and contraction of the negative electrode active material layer 120 during charge and discharge.

[0041] (Inorganic metal salt) An inorganic metal salt is a compound in which a hydrogen atom in an inorganic acid is replaced by a metal ion. The type of this inorganic metal salt may be only one type or two or more types.

[0042] The type of inorganic acid forming the inorganic metal salt is not particularly limited, but specifically, it is hydrofluoric acid, carbonic acid, nitric acid, sulfuric acid, phosphoric acid, etc.

[0043] The type of metal ion is not particularly limited, but specifically, it is an alkali metal ion, etc. Specific examples of the alkali metal ion are lithium ion, sodium ion, potassium ion, etc. Among them, when the electrode reactant is lithium, it is preferable that the alkali metal ion is a lithium ion.

[0044] Specific examples of inorganic metal salts include lithium fluoride, which is a lithium salt of hydrofluoric acid, and lithium carbonate, which is a lithium salt of carbonic acid, because the ionic conductivity of lithium is sufficiently improved and an increase in electrical resistance and decomposition of the electrolyte are sufficiently suppressed.

[0045] (Organic fiber compounds) The organic fiber compound is a fibrous polymeric compound (carbohydrate) that may contain one or more non-carbon elements such as nitrogen as constituent elements. The organic fiber compound may be of one type or of two or more types.

[0046] Specific examples of the organic fiber compound include cellulose, chitin, and chitosan, because the ionic conductivity of lithium is sufficiently improved and an increase in electrical resistance and decomposition of the electrolyte are sufficiently suppressed.

[0047] (Negative electrode binder) The negative electrode binder contains one or more of synthetic rubbers and polymeric compounds. The synthetic rubbers include styrene-butadiene rubbers, fluorine-based rubbers, and ethylene-propylene-diene rubbers. The polymeric compounds include polyvinylidene fluoride, polyimide, and carboxymethyl cellulose.

[0048] (Negative electrode conductive material) The negative electrode conductive agent contains one or more conductive materials such as carbon materials, and the carbon materials include graphite, carbon black, acetylene black, ketjen black, etc. However, the conductive material may also be a metal material, a polymer compound, etc.

[0049] In particular, the negative electrode conductive agent preferably contains a fibrous carbon material such as carbon nanotubes, because the electronic conductivity between the negative electrode active materials is improved, and the electrical resistance of the negative electrode active material layer 120 is reduced.

[0050] <1-2. Manufacturing method> When manufacturing a negative electrode, first, a negative electrode active material, an inorganic metal salt, and an organic fiber compound are mixed together to prepare a negative electrode mixture. In this case, a positive electrode binder, a positive electrode conductive agent, and the like may be added to the negative electrode mixture as necessary.

[0051] Next, the negative electrode mixture is poured into the solvent to prepare a paste-like negative electrode mixture slurry. The solvent may be an aqueous solvent or an organic solvent. In this case, the solvent may be stirred using a stirring device such as a mixer.

[0052] Finally, the negative electrode mixture slurry is applied to both sides of the negative electrode current collector 110 to form the negative electrode active material layer 120. After that, the negative electrode active material layer 120 may be compression molded using a roll press or the like. In this case, the negative electrode active material layer 120 may be heated, or the compression molding may be repeated multiple times.

[0053] As a result, the negative electrode active material layers 120 are formed on both sides of the negative electrode current collector 110, completing the negative electrode.

[0054] <1-3. Actions and Effects> The negative electrode of the first embodiment contains an inorganic metal salt and an organic fiber compound.

[0055] In this case, as described above, the conductive inorganic metal salt is disposed on the surface of the negative electrode active material, and the organic fiber compound having a porous structure coats the surface of the negative electrode active material. This ensures ion conductivity while electrochemically protecting the surface of the negative electrode active material, so that the decomposition reaction of the electrolyte is suppressed on the surface of the electrode reactant while ensuring the absorption and release of lithium. Moreover, the electronic conductivity between the negative electrode active materials is improved, so that the increase in electrical resistance is suppressed.

[0056] Therefore, in a secondary battery using a negative electrode, the ionic conductivity of lithium is ensured while an increase in electrical resistance is suppressed and decomposition of the electrolyte is also suppressed, thereby achieving excellent cycle characteristics and excellent electrical resistance characteristics.

[0057] In particular, if the inorganic metal salt contains lithium fluoride or the like and the organic fiber compound contains cellulose or the like, the ionic conductivity of lithium is sufficiently improved and the increase in electrical resistance and the decomposition of the electrolyte are sufficiently suppressed, thereby achieving even greater effects.

[0058] Furthermore, if the negative electrode active material layer 120 contains an inorganic metal salt and an organic fiber compound together with the negative electrode active material, the inorganic metal salt and the organic fiber compound are each dispersed in the negative electrode active material layer 120. Therefore, as described above, the inorganic metal salt having electrical conductivity is easily arranged on the surface of the negative electrode active material, and the organic fiber compound having a porous structure is easily able to cover the surface of the negative electrode active material, thereby achieving a higher effect.

[0059] <2. Negative electrode for secondary battery (second embodiment)> Next, a negative electrode for a secondary battery (negative electrode) according to a second embodiment of the present technology will be described.

[0060] <2-1. Configuration> The negative electrode of the second embodiment has a similar configuration to that of the negative electrode of the first embodiment, except that the configuration of the negative electrode active material layer 120 is different. The configuration of this negative electrode is similar to that of the negative electrode of the first embodiment, except as described below. In the following, reference will be made to FIG. 1, which has already been described.

[0061] Fig. 2 shows an enlarged cross-sectional configuration of a negative electrode active material particle 121 in the negative electrode of the second embodiment. As shown in Fig. 2, the negative electrode active material layer 120 contains a plurality of particulate negative electrode active materials (negative electrode active material particles 121), and each negative electrode active material particle 121 includes a central portion 121X and a covering portion 121Y.

[0062] [Center] The central portion 121X contains one or more of a carbon material, a metal-based material, etc., for absorbing and releasing lithium. Details of the carbon material and the metal-based material are as described above.

[0063] [Coating] The coating portion 121Y contains an inorganic metal salt and an organic fiber compound. The details of the inorganic metal salt and the organic fiber compound are as described above. The coating portion 121Y may cover the entire surface of the central portion 121X, or may cover only a part of the surface of the central portion 121X. In the latter case, a plurality of coating portions 121Y spaced apart from each other may cover the surface of the central portion 121X.

[0064] That is, in the second embodiment, unlike the first embodiment in which the inorganic metal salt and the organic fiber compound were each dispersed in the negative electrode active material layer 120, the inorganic metal salt and the organic fiber compound are each localized on the surface of the central portion 121X.

[0065] Thus, when the coating portion 121Y of the negative electrode active material particle 121 contains an inorganic metal salt and an organic fiber compound, the same advantages as those of the first embodiment can be obtained. That is, the inorganic metal salt having electrical conductivity is disposed on the surface of the central portion 121X, and the organic fiber compound having a porous structure coats the surface of the central portion 121X. This improves the ion conductivity of lithium, and suppresses both an increase in electrical resistance and decomposition of the electrolyte.

[0066] In this case, since the inorganic metal salt and the organic fiber compound are each localized on the surface of the central portion 121X, the inorganic metal salt is more likely to be disposed on the surface of the central portion 121X, and the organic fiber compound is more likely to cover the surface of the central portion 121X. Therefore, compared to the first embodiment in which the inorganic metal salt and the organic fiber compound are not localized on the surface of the negative electrode active material, the ion conductivity of lithium is further improved, and an increase in electrical resistance and decomposition of the electrolyte are further suppressed.

[0067] [Other materials] Of course, the negative electrode active material layer 120 may further contain one or more of other materials such as a negative electrode binder and a negative electrode conductor. Details of the negative electrode binder and the negative electrode conductor are as described above.

[0068] <2-2. Manufacturing method> The method for producing the negative electrode of the second embodiment is similar to the method for producing the negative electrode of the first embodiment, except that the procedure for forming the negative electrode active material layer 120 is different.

[0069] When forming the negative electrode active material layer 120, first, the central portion 121X and the inorganic metal salt and the organic fiber compound, which are raw materials for forming the coating portion 121Y, are mixed together to form a mixture. The central portion 121X is any one or more of a powdered carbon material and a powdered metal-based material. Then, the mixture is poured into a solvent to prepare a mixed solution. The solvent may be an aqueous solvent or an organic solvent. In this case, the solvent may be stirred using a stirring device such as a mixer.

[0070] Next, the mixed solution is sprayed using a spraying device such as a spray dryer, etc. As a result, coating portion 121Y containing an inorganic metal salt and an organic fiber compound is formed on the surface of center portion 121X, thereby obtaining a plurality of negative electrode active material particles 121.

[0071] Finally, as described above, a negative electrode mixture slurry is prepared using the plurality of negative electrode active material particles 121, and then the negative electrode active material layer 120 is formed using the negative electrode mixture slurry.

[0072] <2-3. Actions and Effects> The negative electrode of the second embodiment contains an inorganic metal salt and an organic fiber compound. Therefore, for the same reason as in the first embodiment, in a secondary battery using the negative electrode, the ion conductivity of lithium is ensured, while the increase in electrical resistance is suppressed and decomposition of the electrolyte is also suppressed, so that excellent cycle characteristics and excellent electrical resistance characteristics can be obtained.

[0073] In particular, if the surface of the central portion 121X that absorbs and releases lithium is covered with the covering portion 121Y and the covering portion 121Y contains an inorganic metal salt and an organic fiber compound, as described above, the inorganic metal salt and the organic fiber compound are each localized on the surface of the central portion 121X. This further improves the ion conductivity of lithium, and further suppresses the increase in electrical resistance and the decomposition of the electrolyte, thereby achieving a greater effect.

[0074] Other functions and effects of the negative electrode of the second embodiment are similar to those of the negative electrode of the first embodiment.

[0075] <3. Secondary battery> Next, a secondary battery using the above-mentioned negative electrode will be described.

[0076] The secondary battery described here is a secondary battery in which battery capacity is obtained by utilizing the occlusion and release of an electrode reactant, and includes a positive electrode, a negative electrode, and an electrolytic solution which is a liquid electrolyte.

[0077] In this secondary battery, the charge capacity of the negative electrode is larger than the discharge capacity of the positive electrode. That is, the electrochemical capacity per unit area of ​​the negative electrode is set to be larger than the electrochemical capacity per unit area of ​​the positive electrode. This is to prevent deposition of electrode reactants on the surface of the negative electrode during charging.

[0078] Details regarding the type of electrode reactant are as described above. In the following, as in the case of the negative electrode, an example will be given in which the electrode reactant is lithium. A secondary battery that obtains battery capacity by utilizing the absorption and release of lithium is a so-called lithium ion secondary battery. In this lithium ion secondary battery, lithium is absorbed and released in an ionic state.

[0079] <3-1. Configuration> Fig. 3 shows a perspective view of a secondary battery, and Fig. 4 shows a cross-sectional view of the battery element 20 shown in Fig. 3. However, Fig. 3 shows a state in which the exterior film 10 and the battery element 20 are separated from each other, and shows a cross section of the battery element 20 along the XZ plane by a broken line. Fig. 4 shows only a part of the battery element 20.

[0080] 3 and 4, this secondary battery includes an exterior film 10, a battery element 20, a positive electrode lead 31, a negative electrode lead 32, and sealing films 41 and 42. The secondary battery described here is a laminate film type secondary battery that uses a flexible exterior film 10.

[0081] [Exterior and sealing films] 3, the exterior film 10 is a flexible exterior member that houses the battery element 20, and has a bag-like structure that is sealed when the battery element 20 is housed inside. Therefore, the exterior film 10 houses an electrolyte solution together with a positive electrode 21 and a negative electrode 22, which will be described later.

[0082] Here, the exterior film 10 is a single film-like member, and is folded in a folding direction F. This exterior film 10 is provided with a recessed portion 10U (so-called deep drawn portion) for accommodating the battery element 20 therein.

[0083] 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, and 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.

[0084] However, the configuration (number of layers) of the exterior film 10 is not particularly limited, and may be one or two layers, or may be four or more layers.

[0085] The sealing film 41 is inserted between the exterior film 10 and the positive electrode lead 31, and 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.

[0086] 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 adhesion to the positive electrode lead 31, and the polyolefin is polypropylene or the like.

[0087] The configuration of the sealing film 42 is similar to the configuration of the sealing film 41, except that the sealing film 42 is a sealing member having adhesion to the negative electrode lead 32. That is, the sealing film 42 contains a polymer compound such as polyolefin having adhesion to the negative electrode lead 32.

[0088] [Battery element] As shown in FIGS. 3 and 4, the battery element 20 is a power generating element including a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte (not shown), and is housed inside the exterior film 10.

[0089] This battery element 20 is a so-called wound electrode body. That is, in the battery element 20, the positive electrode 21 and the negative electrode 22 are stacked on top of each other with a separator 23 interposed therebetween, and the positive electrode 21, the negative electrode 22, and the separator 23 are wound around a winding axis P, which is a virtual axis extending in the Y-axis direction. As a result, the positive electrode 21 and the negative electrode 22 are wound while facing each other with the separator 23 interposed therebetween.

[0090] The three-dimensional shape of the battery element 20 is not particularly limited. Here, since the battery element 20 is flat, the cross section of the battery element 20 intersecting with the winding axis P (cross section along the XZ plane) has a flat shape defined by a major axis J1 and a minor axis J2. The major axis J1 is an imaginary axis that extends in the X-axis direction and has a length greater than that of the minor axis J2, and the minor axis J2 is an imaginary axis that extends in the Z-axis direction intersecting with the X-axis direction and has a length smaller than that of the major axis J1. Here, since the three-dimensional shape of the battery element 20 is a flat cylindrical shape, the cross section of the battery element 20 has a flattened, approximately elliptical shape.

[0091] (positive electrode) As shown in FIG. 4, the positive electrode 21 includes a positive electrode current collector 21A and a positive electrode active material layer 21B.

[0092] Positive electrode current collector 21A has a pair of surfaces on which positive electrode active material layer 21B is provided. Positive electrode current collector 21A contains a conductive material such as a metal material, and the metal material is aluminum or the like.

[0093] Here, the positive electrode active material layer 21B is provided on both sides of the positive electrode collector 21A, and contains one or more types of positive electrode active materials capable of absorbing and releasing lithium. However, the positive electrode active material layer 21B may be provided only on one side of the positive electrode collector 21A on the side where the positive electrode 21 faces the negative electrode 22. The positive electrode active material layer 21B may further contain one or more types of other materials such as a positive electrode binder and a positive electrode conductor. The method of forming the positive electrode active material layer 21B is not particularly limited, and specifically, it is one or more types of coating methods.

[0094] The type of the positive electrode active material is not particularly limited, but specifically includes a lithium-containing compound. The lithium-containing compound is a compound that contains one or more transition metal elements as constituent elements together with lithium, and may further contain one or more other elements as constituent elements. The type of the other elements is not particularly limited as long as it is an element other than lithium and transition metal elements, but specifically includes an element belonging to Groups 2 to 15 of the long periodic table. The type of the lithium-containing compound is not particularly limited, but specifically includes an oxide, a phosphate compound, a silicate compound, a borate compound, etc.

[0095] A specific example of an oxide is LiNiO 2 , LiCoO 2 , LiCo 0.98 Al 0.01 Mg 0.01 O 2 , LiNi 0.5 Co 0.2 Mn 0.3 O 2 , LiNi0.8 Co 0.15 Al 0.05 O 2 , LiNi 0.33 Co 0.33 Mn 0.33 O 2 , Li 1.2 Mn 0.52 Co 0.175 Ni 0.1 O 2 , Li 1.15 (M 0.65 Ni 0.22 Co 0.13 )O 2 and LiMn 2 O 4 A specific example of a phosphate compound is LiFePO 4 , LiMnPO 4 , Life 0.5 Mn 0.5 PO 4 and Life 0.3 Mn 0.7 PO 4 And so on.

[0096] The details of the positive electrode binder and the positive electrode conductive agent are the same as the details of the negative electrode binder and the negative electrode conductive agent described above.

[0097] (Negative electrode) The configuration of the negative electrode 22 is the same as that of the negative electrode described above. That is, the negative electrode 22 contains an inorganic metal salt and an organic fiber compound. More specifically, as shown in FIG. 4, the negative electrode 22 contains a negative electrode current collector 22A corresponding to the negative electrode current collector 110 and a negative electrode active material layer 22B corresponding to the negative electrode active material layer 120.

[0098] The negative electrode 22 may have a configuration similar to that of the negative electrode of the first embodiment, or may have a configuration similar to that of the negative electrode of the second embodiment.

[0099] (Separator) 4, the separator 23 is an insulating porous film interposed between the positive electrode 21 and the negative electrode 22, and allows lithium ions to pass through while preventing contact (short circuit) between the positive electrode 21 and the negative electrode 22. The separator 23 contains a polymer compound such as polyethylene.

[0100] (electrolyte) The electrolyte is impregnated into each of the positive electrode 21, the negative electrode 22, and the separator 23, and contains a solvent and an electrolyte salt.

[0101] The solvent contains one or more of non-aqueous solvents (organic solvents), and the electrolyte containing the non-aqueous solvent is a so-called non-aqueous electrolyte. The non-aqueous solvent is an ester or ether, more specifically, a carbonate ester compound, a carboxylate ester compound, a lactone compound, etc. This is because the dissociation of the electrolyte salt and the mobility of the ions are improved.

[0102] The carbonate ester compounds are cyclic carbonate esters and chain carbonate esters. Specific examples of the cyclic carbonate esters are ethylene carbonate and propylene carbonate, and specific examples of the chain carbonate esters are dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0103] The carboxylate compound is a chain carboxylate, etc. Specific examples of the chain carboxylate are ethyl acetate, ethyl propionate, propyl propionate, and ethyl trimethylacetate.

[0104] The lactone compound is lactone, etc. Specific examples of lactone are γ-butyrolactone and γ-valerolactone, etc.

[0105] The ethers may be, in addition to the lactone compounds mentioned above, 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, and the like.

[0106] Among these, the solvent preferably contains a chain carboxylate, because this further suppresses an increase in electrical resistance and further suppresses the decomposition reaction of the electrolyte.

[0107] The electrolyte salt contains one or more types of light metal salts such as lithium salts. A specific example of the lithium salt is lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium trifluoromethanesulfonate (LiCF 3 SO 3 ), lithium bis(fluorosulfonyl)imide (LiN(FSO 2 ) 2 ), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF 3 SO 2 ) 2 ), lithium tris(trifluoromethanesulfonyl)methide (LiC(CF 3 SO 2 ) 3 ), lithium bis(oxalato)borate (LiB(C 2 O 4 ) 2 ), lithium monofluorophosphate (Li 2 PFO 3 ) and lithium difluorophosphate (LiPF 2 O 2 ) This is because it allows for high battery capacity.

[0108] Among these, it is preferable that the electrolyte salt contains one or both of lithium monofluorophosphate and lithium difluorophosphate, because this further suppresses an increase in electrical resistance and further suppresses the decomposition reaction of the electrolyte.

[0109] The content of the electrolyte salt is not particularly limited, but specifically, it is 0.3 mol / kg to 3.0 mol / kg relative to the solvent, because high ionic conductivity can be obtained.

[0110] The electrolytic solution may further contain one or more of the additives, which are not particularly limited, and specifically include unsaturated cyclic carbonates, halogenated cyclic carbonates, sulfonates, phosphates, acid anhydrides, nitrile compounds, and isocyanates.

[0111] Specific examples of unsaturated cyclic carbonates include vinylene carbonate, vinylethylene carbonate, and methyleneethylene carbonate. Specific examples of halogenated cyclic carbonates include monofluoroethylene carbonate and difluoroethylene carbonate. Specific examples of sulfonic acid esters 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.

[0112] [Positive and negative leads] 3, the positive electrode lead 31 is a positive electrode terminal connected to the positive electrode 21, and more specifically, is connected to the positive electrode current collector 21A. This positive electrode lead 31 is led out from the inside to the outside of the exterior film 10, and contains a conductive material such as aluminum. The shape of the positive electrode lead 31 is not particularly limited, and specifically, it is either a thin plate shape, a mesh shape, or the like.

[0113] As shown in FIG. 3, the negative electrode lead 32 is a negative electrode terminal connected to the negative electrode 22, and more specifically, is connected to the negative electrode current collector 22A. The negative electrode lead 32 is led out from the inside to the outside of the exterior film 10, and contains a conductive material such as copper. Here, the lead-out direction of the negative electrode lead 32 is the same as the lead-out direction of the positive electrode lead 31. The details of the shape of the negative electrode lead 32 are the same as the details of the shape of the positive electrode lead 31.

[0114] <3-2. Operation> When the secondary battery is charged, in the battery element 20, lithium is released from the positive electrode 21 and the lithium is absorbed in the negative electrode 22 via the electrolyte. On the other hand, when the secondary battery is discharged, in the battery element 20, lithium is released from the negative electrode 22 and the lithium is absorbed in the positive electrode 21 via the electrolyte. During these charging and discharging times, lithium is absorbed and released in an ionic state.

[0115] <3-3. Manufacturing method> When manufacturing a secondary battery, the positive electrode 21 and the negative electrode 22 are produced by the procedure described below, and then the positive electrode 21, the negative electrode 22, and an electrolyte are used to manufacture the secondary battery.

[0116] [Preparation of positive electrode] First, a mixture (cathode mixture) in which a cathode active material, a cathode binder, and a cathode conductive agent are mixed together is poured into a solvent to prepare a paste-like cathode mixture slurry. This solvent may be an aqueous solvent or an organic solvent. Next, the cathode mixture slurry is applied to both sides of the cathode current collector 21A to form the cathode active material layer 21B. After this, the cathode active material layer 21B may be compression molded using a roll press or the like. In this case, the cathode active material layer 21B may be heated, or the compression molding may be repeated multiple times. As a result, the cathode active material layer 21B is formed on both sides of the cathode current collector 21A, and thus the cathode 21 is produced.

[0117] [Preparation of negative electrode] Using the same procedure as the above-mentioned negative electrode preparation procedure, the negative electrode active material layer 22B is formed on both sides of the negative electrode current collector 22A to prepare the negative electrode 22. In this case, the same procedure as the negative electrode preparation procedure of the first embodiment may be used, or the same procedure as the negative electrode preparation procedure of the second embodiment may be used.

[0118] [Preparation of electrolyte] An electrolyte salt is added to a solvent, whereby the electrolyte salt is dispersed or dissolved in the solvent, and an electrolyte solution is prepared.

[0119] [Secondary battery assembly] First, the positive electrode lead 31 is connected to the positive electrode current collector 21A of the positive electrode 21 by welding or the like, and the negative electrode lead 32 is connected to the negative electrode current collector 22A of the negative electrode 22 by welding or the like.

[0120] Next, the positive electrode 21 and the negative electrode 22 are stacked on each other with the separator 23 interposed therebetween, and then the positive electrode 21, the negative electrode 22, and the separator 23 are wound to prepare a wound body. This wound body has a configuration similar to that of the battery element 20, except that the positive electrode 21, the negative electrode 22, and the separator 23 are not impregnated with an electrolyte. Next, the wound body is pressed using a press or the like to mold the wound body into a flat shape.

[0121] Next, after the roll is accommodated inside the recessed portion 10U, the exterior film 10 (adhesive layer / metal layer / surface protection layer) is folded to face the exterior films 10. Next, the outer peripheral edges of two sides of the opposing exterior films 10 (adhesive layers) are joined to each other using a heat fusion method or the like, thereby accommodating the roll inside the bag-shaped exterior film 10.

[0122] Finally, after injecting an electrolyte solution into the bag-shaped exterior film 10, the outer peripheral edges of the remaining side of the exterior film 10 (bonding layer) are joined to each other using a heat fusion method or the like. In this case, 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. As a result, the electrolyte solution is impregnated into the wound body, so that the battery element 20, which is a wound electrode body, is produced, and the battery element 20 is sealed inside the bag-shaped exterior film 10, so that a secondary battery is assembled.

[0123] [Stabilization of secondary batteries] The assembled secondary battery is charged and discharged. Various conditions such as the environmental temperature, the number of charge / discharge cycles (number of cycles), and the charge / discharge conditions can be set arbitrarily. As a result, a coating is formed on the surface of each of the positive electrode 21 and the negative electrode 22, so that the state of the secondary battery is electrochemically stabilized. Thus, the secondary battery is completed.

[0124] <3-4. Actions and Effects> In this secondary battery, the negative electrode 22 has a configuration similar to that of the negative electrode described above. Therefore, while ensuring the ionic conductivity of lithium, an increase in electrical resistance is suppressed and decomposition of the electrolyte is also suppressed, so that excellent cycle characteristics and excellent electrical resistance characteristics can be obtained.

[0125] Furthermore, if the secondary battery is a lithium ion secondary battery, a sufficient battery capacity can be stably obtained by utilizing the absorption and release of lithium, so that a higher effect can be obtained.

[0126] Other functions and effects of this secondary battery are similar to those of the negative electrode described above.

[0127] <4. Modifications> The configuration of the secondary battery described above can be modified as appropriate, as described below, although any two or more of the series of modifications described below may be combined with each other.

[0128] [Variation 1] In the first embodiment, since the negative electrode does not include the coating portion 121Y, the inorganic metal salt and the organic fiber compound are each dispersed in the negative electrode active material layer 120. In the second embodiment, since the negative electrode (negative electrode active material particles 121) includes the coating portion 121Y, in the negative electrode active material layer 120, the inorganic metal salt and the organic fiber compound are each localized on the surface of the central portion 121X.

[0129] However, the negative electrode configuration in the first embodiment and the negative electrode configuration in the second embodiment may be combined with each other. Specifically, the negative electrode active material layer 120 may contain an inorganic metal salt and an organic fiber compound together with a plurality of negative electrode active material particles 121 (central portion 121X and coating portion 121Y). That is, in the negative electrode active material layer 120, the inorganic metal salt and the organic fiber compound may each be localized on the surface of the central portion 121X, and the inorganic metal salt and the organic fiber compound may each be dispersed around the negative electrode active material particles 121.

[0130] In this case, too, the use of inorganic metal salts and organic fiber compounds ensures the ionic conductivity of lithium while suppressing the increase in electrical resistance and the decomposition of the electrolyte, thereby achieving the same effects.

[0131] [Variation 2] A porous membrane separator 23 was used. However, although not specifically shown here, a laminated separator including a polymer compound layer may also be used.

[0132] Specifically, the laminated separator includes a porous film having a pair of surfaces, and a polymer compound layer disposed on one or both surfaces of the porous film. This is because the adhesiveness of the separator to each of the positive electrode 21 and the negative electrode 22 is improved, thereby suppressing misalignment (winding misalignment) of the battery element 20. This suppresses swelling of the secondary battery even if a decomposition reaction of the electrolyte occurs. The polymer compound layer includes a polymer compound such as polyvinylidene fluoride. This is because polyvinylidene fluoride and the like have excellent physical strength and are electrochemically stable.

[0133] One or both of the porous film and the polymer compound layer may contain one or more of a plurality of insulating particles. This is because the insulating particles dissipate heat when the secondary battery generates heat, improving the safety (heat resistance) of the secondary battery. The insulating particles contain one or more of inorganic materials and resin materials. 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.

[0134] When a laminated separator is produced, a precursor solution containing a polymer compound and a solvent is prepared, and then the precursor solution is applied to one or both sides of a porous film. In this case, a plurality of insulating particles may be added to the precursor solution as necessary.

[0135] Even when this laminated separator is used, the same effect can be obtained because lithium ions are movable between the positive electrode 21 and the negative electrode 22. In this case, as described above, the safety of the secondary battery is particularly improved, and therefore, a higher effect can be obtained.

[0136] [Variation 3] An electrolyte solution that is a liquid electrolyte is used, but an electrolyte layer that is a gel electrolyte may also be used, although this is not specifically shown.

[0137] In the battery element 20 using the electrolyte layer, the positive electrode 21 and the negative electrode 22 are laminated with the separator 23 and the electrolyte layer interposed therebetween, and the positive electrode 21, the negative electrode 22, the separator 23, and the electrolyte layer are wound. The electrolyte layer is interposed between the positive electrode 21 and the separator 23, and is also interposed between the negative electrode 22 and the separator 23.

[0138] Specifically, the electrolyte layer contains a polymer compound together with an electrolyte solution, and the electrolyte solution is held by the polymer compound. This is because leakage of the electrolyte solution is prevented. The composition of the electrolyte solution is as described above. The polymer compound contains polyvinylidene fluoride and the like. When forming the electrolyte layer, a precursor solution containing an electrolyte solution, a polymer compound, a solvent, and the like is prepared, and then the precursor solution is applied to one or both sides of each of the positive electrode 21 and the negative electrode 22.

[0139] Even when this electrolyte layer is used, the same effect can be obtained because lithium ions can move between the positive electrode 21 and the negative electrode 22 via the electrolyte layer. In this case, leakage of the electrolyte is particularly prevented as described above, so that a higher effect can be obtained.

[0140] <5. Uses of secondary batteries> The use (application example) of the secondary battery is not particularly limited. The secondary battery used as a power source may be a main power source for electronic devices and electric vehicles, or may be an auxiliary power source. A main power source is a power source that is used preferentially regardless of the presence or absence of other power sources. An auxiliary power source is a power source that is used in place of a main power source, or a power source that is switched from a main power source.

[0141] Specific examples of uses of secondary batteries are as follows: Electronic devices such as video cameras, digital still cameras, mobile phones, notebook computers, headphone stereos, portable radios, and portable information terminals. Storage devices such as backup power sources and memory cards. Power tools such as power drills and power saws. Battery packs mounted on electronic devices. Medical electronic devices such as pacemakers and hearing aids. Electric vehicles such as electric cars (including hybrid cars). Power storage systems such as home or industrial battery systems that store power in preparation for emergencies. In these uses, one secondary battery may be used, or multiple secondary batteries may be used.

[0142] The battery pack may use a single cell or a battery pack. The electric vehicle is a vehicle that operates (runs) using a secondary battery as a driving power source, and may be a hybrid vehicle that also includes a driving source other than the secondary battery. In a home power storage system, it is possible to use home electrical appliances and the like by utilizing the power stored in the secondary battery, which is a power storage source.

[0143] Here, an example of an application of the secondary battery will be specifically described. The configuration of the application described below is merely an example and can be modified as appropriate.

[0144] Figure 5 shows the block configuration of a battery pack. The battery pack described here is a battery pack (a so-called soft pack) that uses one secondary battery, and is installed in electronic devices such as smartphones.

[0145] 5, the battery pack includes a power source 51 and a circuit board 52. The circuit board 52 is connected to the power source 51, and includes a positive terminal 53, a negative terminal 54, and a temperature detection terminal 55.

[0146] The power source 51 includes one secondary battery. In this secondary battery, a positive electrode lead is connected to a positive electrode terminal 53, and a negative electrode lead is connected to a negative electrode terminal 54. This power source 51 can be connected to the outside via the positive electrode terminal 53 and the negative electrode terminal 54, and therefore can be charged and discharged. The circuit board 52 includes a control unit 56, a switch 57, a thermosensitive resistor (PTC element) 58, and a temperature detection unit 59. However, the PTC element 58 may be omitted.

[0147] The control unit 56 includes a central processing unit (CPU) and a memory, and controls the operation of the entire battery pack. The control unit 56 detects and controls the usage state of the power source 51 as necessary.

[0148] When the voltage of power source 51 (secondary battery) reaches the overcharge detection voltage or the overdischarge detection voltage, control unit 56 turns off switch 57 to prevent a charging current from flowing through the current path of power source 51. The overcharge detection voltage is not particularly limited, but specifically, is 4.2V±0.05V, and the overdischarge detection voltage is not particularly limited, but specifically, is 2.4V±0.1V.

[0149] Switch 57 includes a charge control switch, a discharge control switch, a charge diode, and a discharge diode, and switches between the presence and absence of a connection between power source 51 and an external device in response to an instruction from control unit 56. Switch 57 includes a field effect transistor (MOSFET) using a metal oxide semiconductor, and a charge / discharge current is detected based on the ON resistance of switch 57.

[0150] Temperature detection unit 59 includes a temperature detection element such as a thermistor, measures the temperature of power supply 51 using temperature detection terminal 55, and outputs the temperature measurement result to control unit 56. The temperature measurement result measured by temperature detection unit 59 is used when control unit 56 performs charge / discharge control in the event of abnormal heat generation, and when control unit 56 performs correction processing when calculating remaining capacity. EXAMPLES

[0151] An embodiment of the present technology will be described.

[0152] <Experimental Examples 1 to 8 and Comparative Examples 1 to 3> As described below, after the secondary battery was fabricated, the battery characteristics of the secondary battery were evaluated.

[0153] [Preparation of secondary battery] The laminate film type lithium ion secondary battery shown in FIGS. 3 and 4 was fabricated by the following procedure.

[0154] (Preparation of positive electrode) First, the positive electrode active material (LiCoO, a lithium-containing compound (oxide)) 2A positive electrode mixture was prepared by mixing 95 parts by mass of a positive electrode binder (polyvinylidene fluoride), 3 parts by mass of a positive electrode conductive agent (Ketjen black), and 2 parts by mass of a positive electrode conductive agent (Ketjen black). The positive electrode mixture was then added to a solvent (N-methyl-2-pyrrolidone, an organic solvent), and the solvent was stirred to prepare a paste-like positive electrode mixture slurry.

[0155] Next, the cathode mixture slurry was applied to both sides of the cathode current collector 21A (aluminum foil with a thickness of 10 μm) using a coating device, and then the cathode mixture slurry was dried to form the cathode active material layer 21B. Finally, the cathode active material layer 21B was compression molded using a roll press machine, and then the cathode current collector 21A on which the cathode active material layer 21B was formed was cut into a strip shape (width = 70 mm × length = 800 mm). In this way, the cathode 21 was produced.

[0156] (Preparation of negative electrode) Here, negative electrodes 22 having two types of structures (dispersion type and coating type) were produced.

[0157] When preparing the dispersed type negative electrode 22, first, 65.4 parts by mass of a negative electrode active material (mesocarbon microbeads (MCMB), which is a carbon material), 30 parts by mass of other negative electrode active material (metal-based material), 3 parts by mass of a negative electrode binder (polyvinylidene fluoride), 1 part by mass of a negative electrode conductive agent (carbon nanotubes), 0.3 parts by mass of an inorganic metal salt, and 0.3 parts by mass of an organic fiber compound were mixed together to prepare a negative electrode mixture.

[0158] Metallic materials include silicon oxide (SiO), a compound of silicon, silicon itself (Si), and silicon-titanium alloys (SiTi 0.01 ) was used. The inorganic metal salts used were lithium fluoride (LiF) and lithium carbonate (Li 2 CO 3 As the organic fiber compounds, cellulose, chitin, and chitosan were used.

[0159] When obtaining a negative electrode mixture, the metal-based material was replaced with a carbon material as necessary, so that only the carbon material was used as the negative electrode active material without using the metal-based material.

[0160] Next, the negative electrode mixture was added to a solvent (organic solvent N-methyl-2-pyrrolidone), and the solvent was stirred using a planetary mixer to prepare a paste-like negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both sides of the negative electrode current collector 22A (copper foil with a thickness of 8 μm) using a coating device, and the negative electrode mixture slurry was dried with hot air to form the negative electrode active material layer 22B.

[0161] Finally, the negative electrode active material layer 22B was compression molded using a roll press, and then the negative electrode current collector 22A on which the negative electrode active material layer 22B was formed was cut into a strip shape (width = 72 mm × length = 810 mm), thereby producing a dispersed type negative electrode 22.

[0162] When preparing the coated negative electrode 22, first, 98 parts by mass of a powdered metal material (silicon oxide (SiO), which is a silicon compound), 1 part by mass of an inorganic metal salt (lithium fluoride), and 1 part by mass of an organic fiber compound (cellulose) were mixed together to prepare a mixture.

[0163] Next, the mixture was added to a solvent (pure water, which is an aqueous solvent), and the solvent was stirred to prepare a mixed solution. Next, the mixed solution was sprayed using a spray dryer, and the spray was dried. As a result, a coating portion 121Y containing an inorganic metal salt and an organic fiber compound was formed on the surface of the center portion 121X containing a metal-based material, and thus a plurality of negative electrode active material particles 121 were obtained.

[0164] Next, 66 parts by mass of MCMB, which is a carbon material, 30 parts by mass of the plurality of negative electrode active material particles 121 (the central portion 121X and the coating portion 121Y), 3 parts by mass of a negative electrode binder (polyvinylidene fluoride), and 1 part by mass of a negative electrode conductive agent (carbon nanotubes) were mixed together to prepare a negative electrode mixture. Next, the negative electrode mixture was poured into a solvent (N-methyl-2-pyrrolidone, which is an organic solvent), and the solvent was stirred using a planetary centrifugal mixer to prepare a paste-like negative electrode mixture slurry.

[0165] Next, the negative electrode active material layer 22B was formed and compression molded in the same manner as in the case of producing the dispersed type negative electrode 22, and then the negative electrode current collector 22A on which the negative electrode active material layer 22B was formed was cut into a strip shape, thereby producing a coated type negative electrode 22.

[0166] For comparison, a negative electrode 22 was produced in the same manner except that neither the inorganic metal salt nor the organic fiber compound was used. In this case, both the inorganic metal salt and the organic fiber compound were replaced with a negative electrode active material (metal-based material).

[0167] For comparison, a negative electrode 22 was prepared in the same manner except that only one of the inorganic metal salt and the organic fiber compound was used. In this case, each of the inorganic metal salt and the organic fiber compound was replaced with a negative electrode active material (metal-based material).

[0168] (Preparation of electrolyte) Solvents (cyclic ethylene carbonate (EC) and linear ethylene carbonate (ethyl methyl carbonate (EMC))) are mixed with electrolyte salts (lithium salts, LiPF 6 In this case, the mixing ratio (mass ratio) of the solvent was cyclic carbonate ester:chain carbonate ester=50:50, and the content of the electrolyte salt was 1 mol / dm 3 (=1 mol / l). In this way, the electrolyte was prepared.

[0169] (Secondary battery assembly) First, an aluminum positive electrode lead 31 was welded to the positive electrode current collector 21A of the positive electrode 21, and a copper negative electrode lead 32 was welded to the negative electrode current collector 22A of the negative electrode 22.

[0170] Next, the positive electrode 21 and the negative electrode 22 were laminated together with a separator 23 (a microporous polyethylene film having a thickness of 25 μm) interposed therebetween, and then the positive electrode 21, the negative electrode 22, and the separator 23 were wound to produce a wound body. Next, the wound body was pressed using a press machine to mold the wound body into a flat shape.

[0171] Next, the exterior film 10 was folded so as to sandwich the wound body accommodated in the recessed portion 10U. An aluminum laminate film was used as the exterior film 10, in which a fusion layer (a polypropylene film having a thickness of 30 μm), a metal layer (aluminum foil having a thickness of 40 μm), and a surface protection layer (a nylon film having a thickness of 25 μm) were laminated in this order from the inside. Next, the outer peripheral edges of two sides of the exterior film 10 (fusion layer) were heat-sealed to each other, thereby accommodating the wound body inside the bag-shaped exterior film 10.

[0172] Finally, after injecting the electrolyte into the bag-shaped exterior film 10, the outer peripheral edges of the remaining side of the exterior film 10 (bonding layer) were heat-sealed to each other in a reduced pressure environment. In this case, a sealing film 41 (a polypropylene film having a thickness of 5 μm) was inserted between the exterior film 10 and the positive electrode lead 31, and a sealing film 42 (a polypropylene film having a thickness of 5 μm) was inserted between the exterior film 10 and the negative electrode lead 32. As a result, the electrolyte was impregnated into the wound body, and the battery element 20, which is a wound electrode body, was produced. Thus, the battery element 20 was enclosed inside the exterior film 10, and a secondary battery was assembled.

[0173] (Stabilization of secondary batteries) The secondary battery was charged and discharged for one cycle in a room temperature environment (temperature = 23°C). During charging, the battery was charged at a constant current of 0.2C until the voltage reached 4.4V, and then charged at a constant voltage of 4.4V until the current reached 0.025C. During discharging, the battery was discharged at a constant current of 0.5C until the voltage reached 3.0V. 0.2C is the current value at which the battery capacity (theoretical capacity) is fully discharged in 5 hours. Similarly, 0.025C is the current value at which the battery capacity is fully discharged in 40 hours, and 0.5C is the current value at which the battery capacity is fully discharged in 2 hours. This completed a laminate film type secondary battery.

[0174] [Evaluation of battery characteristics] The battery characteristics (cycle characteristics and electrical resistance characteristics) of the secondary battery were evaluated, and the results shown in Table 1 were obtained. Two types of cycle characteristics (room temperature cycle characteristics and high temperature cycle characteristics) were investigated.

[0175] (Room temperature cycle characteristics) First, the discharge capacity (discharge capacity at the first cycle) was measured by charging and discharging the secondary battery in a room temperature environment (temperature = 23 ° C.). Next, the discharge capacity (discharge capacity at the 500th cycle) was measured by repeatedly charging and discharging the secondary battery in the same environment until the number of cycles reached 500. Finally, the room temperature capacity retention rate, which is an index for evaluating the room temperature cycle characteristics, was calculated based on the formula: room temperature capacity retention rate (%) = (discharge capacity at the 500th cycle / discharge capacity at the 1st cycle) x 100. The charge and discharge conditions were the same as those for stabilizing the secondary battery described above.

[0176] (High temperature cycle characteristics) The high-temperature capacity retention rate (%), which is an index for evaluating the high-temperature cycle characteristics, was calculated using the same procedure as in the examination of the room-temperature cycle characteristics, except that the secondary battery was charged and discharged in a high-temperature environment (temperature = 60°C).

[0177] (Electrical resistance characteristics) First, the secondary battery was charged and discharged in a high-temperature environment (temperature = 60°C). In this case, the secondary battery was discharged for 10 seconds at a current of 5C when the state of charge (SOC) was 50%. The voltage drop of the secondary battery was measured 10 seconds after the start of discharge, and the electrical resistance (electrical resistance at the first cycle) was calculated based on the voltage drop. 5C is the current value at which the battery capacity is fully discharged in 0.2 hours.

[0178] Next, in the same environment, the secondary battery was repeatedly charged and discharged until the number of cycles reached 500. In this case, at the time of discharging at the 500th cycle, the electrical resistance (electrical resistance at the 500th cycle) was calculated by the same procedure as in the calculation of the electrical resistance at the first cycle described above.

[0179] Finally, the high-temperature resistance increase rate, which is an index for evaluating electrical resistance characteristics, was calculated based on the formula: high-temperature resistance increase rate (%)=(electrical resistance at 500th cycle / electrical resistance at 1st cycle)×100.

[0180] The values ​​of the room temperature capacity retention shown in Table 1 are normalized by setting the value of the room temperature capacity retention of Comparative Example 1, which did not use either an inorganic metal salt or an organic fiber compound, to 1.000. Similarly, the values ​​of the high temperature capacity retention are normalized by setting the value of the high temperature capacity retention of Comparative Example 1 to 1.000, and the values ​​of the high temperature resistance increase rate are normalized by setting the value of the high temperature resistance increase rate of Comparative Example 1 to 1.000. In this case, the values ​​of the room temperature capacity retention rate, the high temperature capacity retention rate, and the high temperature resistance increase rate are each rounded off to the fourth decimal place.

[0181] [Table 1]

[0182] [Consideration] As shown in Table 1, the room temperature capacity retention rate, the high temperature capacity retention rate, and the high temperature resistance increase rate each varied greatly depending on the configuration of the negative electrode 22. In the following, the room temperature capacity retention rate, the high temperature capacity retention rate, and the high temperature resistance increase rate of Comparative Example 1, in which neither an inorganic metal salt nor an organic fiber compound was used, are used as the comparison standard.

[0183] When only the inorganic metal salt was used (Comparative Example 2), the high temperature resistance increase rate decreased, while both the room temperature capacity retention rate and the high temperature capacity retention rate decreased. When only the organic fiber compound was used (Comparative Example 3), the room temperature capacity retention rate increased, while the high temperature capacity retention rate decreased and the high temperature resistance increase rate increased.

[0184] In contrast, when both an inorganic metal salt and an organic fiber compound were used (Examples 1 to 8), the high-temperature resistance increase rate decreased and the room-temperature capacity retention rate and the high-temperature capacity retention rate each increased, regardless of the configuration (dispersion type and coating type) of the negative electrode 22. In this case, particularly when the negative electrode 22 was of the coating type, the room-temperature capacity retention rate and the high-temperature capacity retention rate each increased more, and the high-temperature resistance increase rate decreased more.

[0185] <Examples 9 to 12> Secondary batteries were produced in the same manner as in Example 1, except that the composition of the electrolyte salt and the composition of the solvent were changed as shown in Table 2, and the battery characteristics of the secondary batteries were then evaluated.

[0186] When changing the composition of the electrolyte salt, part of the hexafluorophosphate was replaced with another lithium salt. The other lithium salt was lithium monofluorophosphate (Li 2 PFO 3 ) and lithium difluorophosphate (LiPF 2 O 2 In this case, the mixing ratio (mass ratio) of the electrolyte salts was lithium hexafluorophosphate:other lithium salt=50:50.

[0187] When the solvent composition was changed, the chain carbonate ester was replaced with a chain carboxylate ester, such as ethyl propionate (EtPr) or propyl propionate (PrPr).

[0188] [Table 2]

[0189] As shown in Table 2, when the electrolyte salt contained other lithium salts (lithium monofluorophosphate or lithium difluorophosphate) (Examples 9 and 10), the room temperature capacity retention rate and the high temperature capacity retention rate each increased more, and the high temperature resistance increase rate decreased more, compared to when the electrolyte salt did not contain other lithium salts (Example 1).

[0190] Furthermore, when the solvent contained a chain carboxylic acid ester (Examples 11 and 12), the room temperature capacity retention rate and the high temperature capacity retention rate each increased more, and the high temperature resistance increase rate decreased more, compared to when the solvent did not contain a chain carboxylic acid ester (Example 1).

[0191] [summary] From the results shown in Tables 1 and 2, when the negative electrode 22 contains an inorganic metal salt and an organic fiber compound, the normal temperature cycle characteristics, the high temperature cycle characteristics, and the electrical resistance characteristics are all improved. Therefore, excellent cycle characteristics and excellent electrical resistance characteristics were obtained in the secondary battery.

[0192] Although the present technology has been described above with reference to several embodiments and examples, the configuration of the present technology is not limited to the configurations described in the respective embodiments and examples and can be modified in various ways.

[0193] Although the secondary battery has been described as having a laminate film structure, the type of the battery structure is not particularly limited. Specifically, the battery structure may be a cylindrical type, a square type, a coin type, a button type, or the like.

[0194] Although the battery element has a wound structure, the type of the element structure is not particularly limited. Specifically, the element structure may be a stacked type in which the electrodes (positive and negative electrodes) are stacked, a zigzag folded type in which the electrodes are folded, or other types.

[0195] Furthermore, although the electrode reactant is lithium, the type of the electrode reactant is not particularly limited. Specifically, as described above, the electrode reactant may be other alkali metals such as sodium and potassium, or may be alkaline earth metals such as beryllium, magnesium, and calcium. In addition, the electrode reactant may be other light metals such as aluminum.

[0196] The effects described in this specification are merely examples, and the effects of the present technology are not limited to the effects described in this specification. Therefore, other effects may be obtained with respect to the present technology.

Claims

1. A positive electrode and a negative electrode are provided together with an electrolyte solution; the negative electrode comprises an inorganic metal salt and an organic fiber compound; the inorganic metal salt includes at least one of lithium fluoride and lithium carbonate; The organic fiber compound includes at least one of cellulose, chitin, and chitosan. Secondary battery.

2. The negative electrode includes a negative electrode active material layer, the negative electrode active material layer contains the inorganic metal salt and the organic fiber compound together with the negative electrode active material, The secondary battery according to claim 1 .

3. The negative electrode includes a negative electrode active material, The negative electrode active material is A central portion that absorbs and releases an electrode reactant; a coating portion that coats the surface of the core portion and contains the inorganic metal salt and the organic fiber compound; The secondary battery according to claim 1 .

4. The electrolyte solution contains at least one of lithium monofluorophosphate and lithium difluorophosphate. The secondary battery according to claim 1 .

5. A positive electrode and a negative electrode are provided together with an electrolyte solution; the negative electrode comprises an inorganic metal salt and an organic fiber compound; The electrolyte solution contains at least one of lithium monofluorophosphate and lithium difluorophosphate. Secondary battery.

6. The electrolyte solution contains a chain carboxylate ester. The secondary battery according to claim 1 .

7. It is a lithium-ion secondary battery. The secondary battery according to claim 1 .

8. Contains inorganic metal salts and organic fiber compounds, the inorganic metal salt includes at least one of lithium fluoride and lithium carbonate; The organic fiber compound includes at least one of cellulose, chitin, and chitosan. Negative electrode for secondary batteries.

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