Negative electrode for secondary battery and secondary battery

Abstract

This secondary battery comprises a positive electrode, a negative electrode, and an electrolytic solution. The negative electrode comprises a carbon-containing layer and a negative electrode active substance layer provided on the carbon-containing layer. The negative electrode active substance layer comprises: a negative electrode active substance including a silicon-containing material; and a negative electrode binder comprising a N-vinyl acetamide polymer.

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 power sources that can provide high energy density. These secondary batteries contain a positive electrode, a negative electrode (secondary battery negative electrode), and an electrolyte solution, and various studies have been conducted on the configuration of these secondary batteries.

[0003] Specifically, the negative electrode contains a negative electrode active material (Si), a negative electrode binder (a water-soluble polyimide-based material), and a water-soluble thickener (poly-N-vinylacetamide), and the content of the negative electrode binder and the content of the water-soluble thickener are specified (see, for example, Patent Document 1). Also, the negative electrode contains a negative electrode active material (Si and a carbon material) and a negative electrode binder (poly-N-vinylacetamide), and the physical properties of the negative electrode binder and the peel strength of the negative electrode are specified (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-060605 [Patent Document 2] Japanese Patent Publication No. 2021-166199 Summary of the Invention

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

[0006] There is a demand for a negative electrode for a secondary battery and a secondary battery that can provide excellent battery characteristics.

[0007] According to one embodiment of the present disclosure, a secondary battery negative electrode includes a carbon-containing layer and a negative electrode active material layer provided on the carbon-containing layer. The negative electrode active material layer includes a negative electrode active material containing a silicon-containing material and a negative electrode binder containing an N-vinylacetamide polymer.

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

[0009] Here, the "carbon-containing layer" is a layer containing a carbon material, and the "silicon-containing material" is a material containing silicon as a constituent element. The "N-vinylacetamide polymer" is one or both of an N-vinylacetamide homopolymer and an N-vinylacetamide copolymer. Details of the carbon material, the silicon-containing material, and the N-vinylacetamide polymer will be described later.

[0010] According to the secondary battery negative electrode or secondary battery of one embodiment of the present technology, the secondary battery negative electrode includes a carbon-containing layer and a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material and a negative electrode binder, the negative electrode active material includes a silicon-containing material, and the negative electrode binder includes an N-vinylacetamide polymer, so that excellent battery characteristics can be obtained.

[0011] 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 explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view illustrating a configuration of a negative electrode for a secondary battery according to a first embodiment of the present technology. [Figure 2] FIG. 4 is a cross-sectional view illustrating a configuration of a negative electrode for a secondary battery according to a second embodiment of the present technology. [Figure 3] 1 is a perspective view illustrating a configuration of a secondary battery according to an embodiment of the present technology. [Figure 4] FIG. 4 is an enlarged cross-sectional view showing the configuration of the battery element shown in FIG. [Figure 5] 5 is another enlarged cross-sectional view showing the configuration of the battery element shown in FIG. 4. FIG. [Figure 6] 1 is a cross-sectional view illustrating the configuration of a negative electrode for a secondary battery according to Modification 1. FIG. [Figure 7] FIG. 1 is a block diagram illustrating a configuration of an application example of a secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present technology will be described in detail with reference to the drawings. The description will be made in the following order. 1. Negative electrode for secondary battery (first embodiment) 1-1.Configuration 1-2.Operation 1-3. Manufacturing method 1-4. Action and effects 2. Negative electrode for secondary battery (second embodiment) 2-1.Configuration 2-2.Operation 2-3. Manufacturing method 2-4. Action and effects 3. Secondary battery 3-1.Configuration 3-2.Operation 3-3. Manufacturing method 3-4. Action and effects 4. Variations 5. Uses of secondary batteries

[0014] <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.

[0015] The negative electrode described here is used in a secondary battery, which is an electrochemical device. However, the negative electrode may also be used in electrochemical devices other than secondary batteries. Specific examples of other electrochemical devices include primary batteries and capacitors.

[0016] The negative electrode absorbs and releases an electrode reactant during an electrode reaction. The type of electrode reactant is not particularly limited, but specifically, it is a light metal such as an alkali metal or alkaline earth metal. Specific examples of alkali metals include lithium, sodium, and potassium, and specific examples of alkaline earth metals include magnesium and calcium.

[0017] In the following, an example will be given in which the electrode reactant is lithium, whereby lithium is absorbed and released in an ionic state at the negative electrode during the electrode reaction.

[0018] <1-1.Configuration> Fig. 1 shows a cross-sectional structure of a negative electrode 1, which is an example of a negative electrode according to the first embodiment. As shown in Fig. 1, the negative electrode 1 includes a negative electrode current collector 1A, a base layer 1B, and a negative electrode active material layer 1C.

[0019] [Negative electrode current collector] Negative electrode current collector 1A has a pair of surfaces on which underlayer 1B and negative electrode active material layer 1C are provided. Negative electrode current collector 1A contains a metal material, and a specific example of the metal material is copper.

[0020] The surface of the negative electrode current collector 1A is preferably roughened. This is because the adhesion of the base layer 1B and the negative electrode active material layer 1C to the negative electrode current collector 1A is improved by utilizing the so-called anchor effect. The roughening method is not particularly limited, but specifically, it is a method of forming fine particles on the surface of a metal foil using an electrolytic treatment. This electrolytic treatment is a method of forming unevenness on the surface of the metal foil by forming fine particles on the surface of the metal foil using an electrolytic method in an electrolytic bath.

[0021] [Base layer] The underlayer 1B is the carbon-containing layer of the first embodiment.

[0022] This underlayer 1B is provided on the negative electrode current collector 1A. As a result, the underlayer 1B is interposed between the negative electrode current collector 1A and the negative electrode active material layer 1C. The thickness of the underlayer 1B is not particularly limited and can be set arbitrarily.

[0023] Here, the underlayer 1B is provided on one surface of the negative electrode current collector 1A, but the underlayer 1B may be provided on both surfaces of the negative electrode current collector 1A.

[0024] As described above, the underlayer 1B is a carbon-containing layer and therefore contains one or more types of carbon materials. The types of carbon materials are not particularly limited, but specific examples include graphitizable carbon, non-graphitizable carbon, and graphite (natural graphite and artificial graphite).

[0025] The method for forming the underlayer 1B is not particularly limited, but specifically includes one or more of a coating method, a vapor phase method, a liquid phase method, etc. Specific examples of the vapor phase method include a sputtering method and a chemical vapor deposition (CVD) method.

[0026] The reason why the underlayer 1B, which is a carbon-containing layer, is interposed between the negative electrode current collector 1A and the negative electrode active material layer 1C is as follows.

[0027] First, the interfacial resistance at the interface between the negative electrode current collector 1A and the negative electrode active material layer 1C is reduced, which improves the electrical conductivity (electronic conductivity) between the negative electrode current collector 1A and the negative electrode active material layer 1C, thereby improving the electrical conductivity of the negative electrode 1.

[0028] Second, the adhesion of the negative electrode active material layer 1C to the negative electrode current collector 1A is improved, which makes the negative electrode active material layer 1C less likely to fall off from the negative electrode current collector 1A, even if the negative electrode active material layer 1C contains a large amount of a silicon-containing material that tends to expand and contract during an electrode reaction.

[0029] The underlayer 1B may further contain one or more of the other materials.

[0030] When the underlayer 1B is formed by a coating method, a specific example of the other material is a binder. Hereinafter, the binder contained in the underlayer 1B will be referred to as the "underlayer binder" to distinguish it from the binder (negative electrode binder) contained in the negative electrode active material layer 1C described later. This underlayer binder is a binder contained in the underlayer 1B, which is a single-layer containing layer, and is therefore a so-called carbon binder.

[0031] The base binder contains one or more of synthetic rubbers and polymeric compounds. Specific examples of synthetic rubbers include styrene-butadiene rubbers, fluorine-containing rubbers, and ethylene-propylene-diene. Specific examples of polymeric compounds include polyvinylidene fluoride, polyimide, carboxymethyl cellulose, and N-vinylacetamide polymers. Details of N-vinylacetamide polymers will be described later.

[0032] In particular, the base binder preferably contains an N-vinylacetamide polymer. As will be described later, the anode binder contained in the anode active material layer 1C contains an N-vinylacetamide polymer, and therefore the type of the base binder and the type of the anode binder are the same. This improves the adhesion between the base binder and the anode binder, thereby improving the adhesion between the base layer 1B and the anode active material layer 1C.

[0033] As described above, the method for forming the base layer 1B containing the carbon material and the base binder is not particularly limited, but specifically includes a coating method, etc. The base layer 1B formed by the coating method is a so-called primer coat layer.

[0034] [Negative electrode active material layer] The negative electrode active material layer 1C is provided on the base layer 1B and contains a negative electrode active material and a negative electrode binder, so that the negative electrode active material layer 1C is electrically connected to the negative electrode current collector 1A via the base layer 1B.

[0035] Here, the negative electrode active material layer 1C is provided on one surface of the negative electrode current collector 1A, but the negative electrode active material layer 1C may be provided on both surfaces of the negative electrode current collector 1A.

[0036] The method for forming the negative electrode active material layer 1C is not particularly limited, but specifically includes one or more of a coating method, a vapor phase method, a liquid phase method, a thermal spraying method, and a firing method (sintering method).

[0037] (Negative electrode active material) The negative electrode active material is a material that absorbs and releases lithium and contains one or more silicon-containing materials, because silicon has an excellent lithium absorption capacity and can provide a high energy density.

[0038] As described above, this "silicon-containing material" is a material that contains silicon as a constituent element. That is, the silicon-containing material may be silicon alone, a silicon alloy, a silicon compound, a mixture of two or more of these, or a material containing two or more of these phases. The structure of the silicon-containing material is not particularly limited, and specifically, it may be a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or a mixture of two or more of these.

[0039] The term "silicon element" refers to a general element, and may contain trace amounts of impurities. In other words, the purity of silicon element is not necessarily limited to 100%.

[0040] The type of silicon alloy is not particularly limited. Specifically, the silicon alloy contains, as a constituent element other than silicon, one or more of metal elements such as tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium.

[0041] However, the silicon alloy is not limited to containing one or more metal elements as constituent elements, and may contain one or more metal elements and one or more metalloid elements as constituent elements. In addition, the silicon alloy may further contain one or more non-metal elements as constituent elements.

[0042] The types of silicon compounds are not particularly limited. Specifically, the silicon compound contains, as elements other than silicon, any one or more of non-metal elements such as oxygen and carbon as constituent elements. In addition, the silicon compound may further contain any one or more of a series of metal elements contained as constituent elements in the above-mentioned silicon alloy as constituent elements.

[0043] Specific examples of the silicon alloy and the silicon compound are SiB4, SiB6, Mg2Si, Ni2Si, TiSi2, MoSi2, CoSi2, NiSi2, CaSi2, CrSi2, Cu5Si, FeSi2, MnSi2, NbSi2, TaSi2, VSi2, WSi2, ZnSi2, SiC, Si3N4, Si2N2O, SiO x (0 < x ≤ 2 or 0.2 < x < 1.4) and LiSiO, etc. However, the composition of each specific example of the silicon alloy and the silicon compound is not limited to the composition described here and can be arbitrarily changed.

[0044] In addition, the negative electrode active material may further contain any one or more of carbon materials. That is, the negative electrode active material may contain both a silicon-containing material and a carbon material. This is because in the secondary battery using the negative electrode 1, while ensuring the battery capacity, the damage of the negative electrode active material layer 1C is suppressed.

[0045] Specifically, silicon-containing materials have the advantage of high theoretical capacity, but the drawback is that they tend to expand and contract significantly during charging and discharging. On the other hand, carbon materials have the drawback of low theoretical capacity, but the drawback is that they tend not to expand and contract during charging and discharging. Therefore, by using a carbon material and a silicon-containing material in combination, a high theoretical capacity can be obtained while suppressing the expansion and contraction of the negative electrode active material layer 1C during charging and discharging. As a result, as described above, the battery capacity is maintained while damage to the negative electrode active material layer 1C is suppressed.

[0046] Specific examples of carbon materials include graphitizable carbon, non-graphitizable carbon, and graphite (natural graphite and artificial graphite).

[0047] The mixing ratio of the silicon-containing material to the carbon material is not particularly limited and can be set arbitrarily. In particular, the ratio of the weight of the silicon-containing material to the sum of the weight of the silicon-containing material and the weight of the carbon material is preferably 30% by weight or more. This is because sufficient battery capacity can be obtained while damage to the negative electrode active material layer 1C is sufficiently suppressed. This ratio is calculated based on the formula: ratio (wt%) = [weight of silicon-containing material / (weight of silicon-containing material + weight of carbon material)] × 100.

[0048] (Negative electrode binder) The negative electrode binder is a material that binds the negative electrode active materials together, and contains one or more types of N-vinylacetamide polymers.

[0049] The negative electrode binder contains an N-vinylacetamide polymer because it improves the physical strength of the negative electrode active material layer 1C. This makes it easier for the negative electrode active material layer 1C to be maintained without being damaged even when the electrode reaction is repeated, and also makes it less likely for the negative electrode active material layer 1C to fall off from the negative electrode current collector 1A, thereby improving the physical durability of the negative electrode 1. In this case, the generation of cracks in the negative electrode active material layer 1C is suppressed, and the negative electrode active material layer 1C is also suppressed from falling off from the negative electrode current collector 1A.

[0050] The negative electrode binder may further contain one of polyvinylidene fluoride and styrene-butadiene rubber. That is, the negative electrode binder may contain both N-vinylacetamide polymer and polyvinylidene fluoride, or may contain both N-vinylacetamide polymer and styrene-butadiene rubber. This is because the physical strength of the negative electrode active material layer 1C is further improved, making the negative electrode active material layer 1C less susceptible to damage even when the electrode reaction is repeated.

[0051] As described above, this "N-vinylacetamide polymer" is one or both of an N-vinylacetamide homopolymer and an N-vinylacetamide copolymer. This N-vinylacetamide homopolymer is so-called poly-N-vinylacetamide.

[0052] N-vinylacetamide copolymers are compounds obtained by copolymerizing N-vinylacetamide with one or more monomers (excluding N-vinylacetamide). The types of the monomers are not particularly limited, but specific examples include acrylic acid, methacrylic acid, alkali metal acrylates, alkaline earth metal acrylates, alkali metal methacrylates, and alkaline earth metal methacrylates.

[0053] Specific examples of alkali metal acrylates include lithium acrylate, sodium acrylate, and potassium acrylate. Specific examples of alkaline earth metal acrylates include calcium acrylate and magnesium acrylate. Specific examples of alkali metal methacrylates include lithium methacrylate, sodium methacrylate, and potassium methacrylate. Specific examples of alkaline earth metal methacrylates include calcium methacrylate and magnesium methacrylate.

[0054] The copolymerization amount of the monomer in the N-vinylacetamide copolymer is not particularly limited and can be set arbitrarily.

[0055] (Other materials) The negative electrode active material layer 1C may further contain one or more of the other materials.

[0056] A specific example of the other material is another negative electrode active material, which includes one or more metal-based materials, except that the silicon-containing materials described above are excluded from the metal-based materials described here.

[0057] This metallic material is a material containing, as a constituent element, one or more of metallic elements and semi-metallic elements that can form an alloy with lithium, and a specific example of the metallic element and semi-metallic element is tin, etc. This metallic material may be a simple substance, an alloy, a compound, a mixture of two or more of these, or a material containing two or more of these phases.

[0058] Specific examples of other materials include other negative electrode binders, which include one or more of synthetic rubbers and polymeric compounds. However, the above-mentioned N-vinylacetamide polymer, polyvinylidene fluoride, and styrene butadiene rubber are excluded from the other negative electrode binders described here. Specific examples of synthetic rubbers include fluorine-based rubbers and ethylene propylene dienes. Specific examples of polymeric compounds include polyimides and carboxymethyl cellulose.

[0059] Furthermore, a specific example of the other material is a negative electrode conductive agent, which contains one or more of a carbon material, a metal material, and a conductive polymer compound. This carbon material may be a fibrous carbon material, a particulate carbon material, or both. Specific examples of the fibrous carbon material include carbon fiber, carbon nanofiber, and carbon nanotube. Specific examples of the particulate carbon material include graphite, carbon black, acetylene black, and ketjen black.

[0060] <1-2. Operation> In the negative electrode 1, during the electrode reaction, lithium is absorbed into the negative electrode active material contained in the negative electrode active material layer 1C, and lithium is released from the negative electrode active material. In this case, lithium is absorbed and released in an ionic state.

[0061] <1-3. Manufacturing method> The negative electrode 1 is produced by the following example procedure.

[0062] First, a carbon material and a base binder are mixed together to form a base mixture. Then, the base mixture is poured into a solvent to prepare a paste-like base mixture slurry. This solvent may be an aqueous solvent or an organic solvent. Next, the base mixture slurry is applied to one side of the negative electrode current collector 1A to form the base layer 1B.

[0063] Next, a negative electrode active material containing a silicon-containing material, a negative electrode binder containing an N-vinylacetamide polymer, and a negative electrode conductive agent are mixed together to form a negative electrode mixture. The negative electrode mixture is then poured into a solvent to prepare a paste-like negative electrode mixture slurry. This solvent may be an aqueous solvent or an organic solvent. The negative electrode mixture slurry is then applied to the surface of the base layer 1B to form a negative electrode active material layer 1C.

[0064] Finally, the negative electrode active material layer 1C is compression molded using a roll press etc. In this case, the negative electrode active material layer 1C may be heated, and the compression molding may be repeated multiple times.

[0065] As a result, the underlayer 1B and the negative electrode active material layer 1C are formed on the negative electrode current collector 1A, and thus the negative electrode 1 is completed.

[0066] <1-4. Actions and Effects> According to this negative electrode 1, the negative electrode 1 includes a negative electrode current collector 1A, a base layer 1B, and a negative electrode active material layer 1C. The negative electrode current collector 1A includes a metal material. The base layer 1B is a carbon-containing layer and therefore includes a carbon material. The negative electrode active material layer 1C further includes a negative electrode active material (a silicon-containing material) and a negative electrode binder (an N-vinylacetamide polymer).

[0067] In this case, as described above, a series of actions described below are obtained.

[0068] First, since the negative electrode active material contains a silicon-containing material, a high energy density can be obtained in the negative electrode 1 .

[0069] Second, because the underlayer 1B (carbon-containing layer) is interposed between the negative electrode current collector 1A and the negative electrode active material layer 1C, the interfacial resistance at the interface between the negative electrode current collector 1A and the negative electrode active material layer 1C is reduced, and the adhesion of the negative electrode active material layer 1C to the negative electrode current collector 1A is improved. This improves the conductivity between the negative electrode current collector 1A and the negative electrode active material layer 1C, and makes it difficult for the negative electrode active material layer 1C to fall off from the negative electrode current collector 1A, so the conductivity of the negative electrode 1 is stably improved.

[0070] Third, because the negative electrode binder contains an N-vinylacetamide polymer, the physical strength of the negative electrode active material layer 1C is improved. As a result, even when the electrode reaction is repeated, the negative electrode active material layer 1C is less likely to be damaged and is less likely to fall off the negative electrode current collector 1A, thereby improving the physical durability of the negative electrode 1. In this case, the physical durability of the negative electrode 1 is effectively improved, particularly even when the negative electrode active material contains a silicon-containing material that is prone to expansion and contraction during the electrode reaction.

[0071] For these reasons, the electrical conductivity and physical durability are improved while the energy density is ensured in the negative electrode 1. Therefore, the negative electrode 1 can be used to realize a secondary battery with excellent battery characteristics.

[0072] Here, as described above, the negative electrode 1 includes the negative electrode current collector 1A together with the underlayer 1B and the negative electrode active material layer 1C, and the underlayer 1B is provided on the negative electrode current collector 1A. Therefore, the underlayer 1B can be utilized to sufficiently improve the conductivity between the negative electrode current collector 1A and the negative electrode active material layer 1C.

[0073] Furthermore, if the underlayer 1B contains an underlayer binder, and the underlayer binder contains an N-vinylacetamide polymer, the adhesion between the underlayer 1B (carbon binder) and the negative electrode active material layer 1C (negative electrode binder) is improved, thereby achieving a greater effect.

[0074] Furthermore, if the negative electrode binder further contains either polyvinylidene fluoride or styrene-butadiene rubber, the physical strength of the negative electrode active material layer 1C is further improved, making the negative electrode active material layer 1C less susceptible to damage even when electrode reactions are repeated, thereby achieving a greater effect.

[0075] Furthermore, if the negative electrode active material further contains a carbon material, damage to the negative electrode active material layer 1C is suppressed while the battery capacity is ensured in a secondary battery using the negative electrode 1, and therefore a greater effect can be obtained.

[0076] <2. Negative electrode for secondary battery (second embodiment)> Next, a negative electrode for a secondary battery (hereinafter simply referred to as "negative electrode") according to a second embodiment of the present technology will be described.

[0077] <2-1.Configuration> Fig. 2 shows a cross-sectional structure of a negative electrode 2, which is an example of a negative electrode according to the second embodiment, and corresponds to Fig. 1. As shown in Fig. 2, the negative electrode 2 has a similar structure to that of the negative electrode 1, except that it includes a negative electrode current collector 1D instead of the negative electrode current collector 1A and the underlayer 1B.

[0078] The negative electrode current collector 1D has the same configuration as the negative electrode current collector 1A, except for the points described below.

[0079] This negative electrode current collector 1D is the carbon-containing layer of the second embodiment. As a result, the negative electrode active material layer 1C is provided on the negative electrode current collector 1D, and therefore the negative electrode current collector 1D is adjacent to the negative electrode active material layer 1C. The thickness of the negative electrode current collector 1D is not particularly limited and can be set as desired.

[0080] The negative electrode current collector 1D has a pair of surfaces on which the negative electrode active material layer 1C is provided. Here, the negative electrode active material layer 1C is provided on one surface of the negative electrode current collector 1D. However, the negative electrode active material layer 1C may be provided on both surfaces of the negative electrode current collector 1D.

[0081] As described above, the negative electrode current collector 1D is a carbon-containing layer and therefore contains one or more types of carbon materials. Details regarding the carbon materials are as described above. Specifically, the negative electrode current collector 1D is a carbon material formed into a sheet shape (a so-called carbon sheet), and a specific example of the carbon sheet is a graphite sheet.

[0082] The reason why the negative electrode 2 includes the negative electrode current collector 1D is that it reduces the interfacial resistance at the interface between the negative electrode current collector 1D and the negative electrode active material layer 1C and improves the adhesion of the negative electrode active material layer 1C to the negative electrode current collector 1D. This improves the conductivity between the negative electrode current collector 1D and the negative electrode active material layer 1C and makes it difficult for the negative electrode active material layer 1C to fall off from the negative electrode current collector 1D, thereby stably improving the conductivity of the negative electrode 2.

[0083] In particular, when the negative electrode current collector 1D, which is a carbon sheet, is used, a series of advantages described below are obtained compared to when the negative electrode current collector 1A, which contains a metal material, is used.

[0084] First, the weight of negative electrode current collector 1D (carbon sheet) is smaller than the weight of negative electrode current collector 1A (metal material), and therefore the weight of negative electrode 2 is smaller than the weight of negative electrode 1. As a result, the energy density per unit weight (Wh / kg) of negative electrode 2 is greater than the energy density per unit weight of negative electrode 1.

[0085] Second, the negative electrode current collector 1D (carbon sheet) is less likely to deform, more specifically, warp, during the electrode reaction than the negative electrode current collector 1A (metal material). This makes it easier to maintain the flatness of the negative electrode 2 than the flatness of the negative electrode 1.

[0086] Third, to ensure the current collection performance of the negative electrode current collector 1D (carbon sheet), the thickness of the negative electrode current collector 1D is made thicker than the thickness of the negative electrode current collector 1A (metal material). This ensures that the heat dissipation performance of the negative electrode 2 is better than that of the negative electrode 1, even if heat is generated during the electrode reaction.

[0087] <2-2. Operation> The operation of the negative electrode 2 is the same as that of the negative electrode 1. That is, during the electrode reaction of the negative electrode 2, lithium is absorbed and released in the negative electrode active material contained in the negative electrode active material layer 1C.

[0088] <2-3. Manufacturing method> The negative electrode 2 is produced by the procedure of an example described below.

[0089] First, a negative electrode current collector 1D, which is a carbon sheet, is prepared. Next, a negative electrode mixture slurry is prepared using the procedure described in the first embodiment. Next, the negative electrode mixture slurry is applied to one side of the negative electrode current collector 1D to form a negative electrode active material layer 1C. Finally, the negative electrode active material layer 1C is compression-molded using the procedure described in the first embodiment.

[0090] As a result, the negative electrode active material layer 1C is formed on the negative electrode current collector 1D, and the negative electrode 2 is completed.

[0091] <2-4. Actions and Effects> According to this negative electrode 2, the negative electrode 2 includes a negative electrode current collector 1D and a negative electrode active material layer 1C. The negative electrode current collector 1D is a carbon-containing layer and therefore includes a carbon material. The negative electrode active material layer 1C includes a negative electrode active material (a silicon-containing material) and a negative electrode binder (an N-vinylacetamide polymer).

[0092] In this case, as described above, a series of actions described below are obtained.

[0093] First, since the negative electrode active material contains a silicon-containing material, a high energy density can be obtained in the negative electrode 2 .

[0094] Second, the interfacial resistance at the interface between the negative electrode current collector 1D and the negative electrode active material layer 1C is reduced, and the adhesion of the negative electrode active material layer 1C to the negative electrode current collector 1D is improved. This improves the conductivity between the negative electrode current collector 1D and the negative electrode active material layer 1C, and makes it difficult for the negative electrode active material layer 1C to fall off from the negative electrode current collector 1D, thereby stably improving the conductivity of the negative electrode 2.

[0095] Third, because the negative electrode binder contains an N-vinylacetamide polymer, the physical strength of the negative electrode current collector 1D is ensured even if the negative electrode current collector 1D does not contain a metal material. This makes it easier for the negative electrode current collector 1D to stably support the negative electrode active material layer 1C, even when the electrode reaction is repeated, and the negative electrode active material layer 1C is less likely to fall off the negative electrode current collector 1D, thereby improving the physical durability of the negative electrode 2. In this case, the physical durability of the negative electrode 2 is effectively improved, particularly even if the negative electrode active material contains a silicon-containing material that tends to expand and contract during the electrode reaction.

[0096] These factors ensure that the electrical conductivity and physical durability of the negative electrode 2 are improved while maintaining the energy density. Therefore, the negative electrode 2 can be used to realize a secondary battery with excellent battery characteristics.

[0097] In this case, in particular, because the negative electrode current collector 1D contains a carbon material, i.e., the negative electrode current collector 1D is a carbon sheet, as described above, the energy density per unit weight of the negative electrode 2 increases, the flatness of the negative electrode 2 is more easily maintained, and the heat dissipation properties of the negative electrode 2 are improved. Therefore, the battery characteristics of a secondary battery using the negative electrode 2 are improved compared to the battery characteristics of a secondary battery using the negative electrode 1.

[0098] Other functions and effects of the negative electrode 2 are the same as those of the negative electrode 1.

[0099] <3. Secondary battery> Next, a secondary battery according to an embodiment of the present technology will be described.

[0100] The secondary battery described here is a secondary battery that obtains battery capacity by absorbing and releasing an electrode reactant, and includes a positive electrode, a negative electrode, and an electrolyte. Hereinafter, as described above, the case where the electrode reactant is lithium will be taken as an example. A secondary battery that obtains battery capacity by absorbing and releasing lithium is a so-called lithium-ion secondary battery. In this lithium-ion secondary battery, lithium is absorbed and released in an ionic state.

[0101] The charge capacity of the negative electrode is preferably larger than the discharge capacity of the positive electrode. That is, the electrochemical capacity per unit area of ​​the negative electrode is preferably larger than the electrochemical capacity per unit area of ​​the positive electrode. This is to prevent lithium from being deposited on the surface of the negative electrode during charging.

[0102] <3-1. Structure> Fig. 3 shows a perspective view of the secondary battery, and Fig. 4 and Fig. 5 each show an enlarged 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 the cross section of the battery element 20 taken along the XZ plane is shown by a dashed line. Fig. 4 and Fig. 5 each show only a portion of the battery element 20.

[0103] 3, 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 or pliable exterior film 10.

[0104] [Exterior film] 3, the exterior film 10 is an 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. As a result, the exterior film 10 houses an electrolyte solution together with a positive electrode 21 and a negative electrode 22, which will be described later.

[0105] Here, 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 (so-called deep drawn portion) for accommodating the battery element 20.

[0106] 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 out, 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.

[0107] However, the configuration (number of layers) of the exterior film 10 is not particularly limited, and may be one layer, two layers, or four or more layers.

[0108] [Battery element] As shown in FIGS. 3 to 5, the battery element 20 is a power generating element that includes a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte (not shown), and is housed inside the exterior film 10.

[0109] Since this battery element 20 is a so-called laminated electrode body, the positive electrodes 21 and the negative electrodes 22 are laminated one upon the other with separators 23 interposed therebetween. The number of positive electrodes 21, negative electrodes 22, and separators 23 laminated is not particularly limited. Here, a plurality of positive electrodes 21 and a plurality of negative electrodes 22 are alternately laminated with separators 33 interposed therebetween.

[0110] (positive electrode) As shown in FIGS. 4 and 5, the positive electrode 21 includes a positive electrode current collector 21A and a positive electrode active material layer 21B.

[0111] The positive electrode current collector 21A has a pair of surfaces on which the positive electrode active material layer 21B is provided. The positive electrode current collector 21A contains a conductive material such as a metal material, and a specific example of the metal material is aluminum.

[0112] 3, the positive electrode current collector 21A includes a protrusion 21AT on which the positive electrode active material layer 21B is not provided, and the plurality of protrusions 21AT are joined to each other to form a single lead. Here, the protrusion 21AT is integrated with the portion other than the protrusion 21AT. However, since the protrusion 21AT is separate from the portion other than the protrusion 21AT, it may be joined to the portion other than the protrusion 21AT.

[0113] Here, the positive electrode active material layer 21B is provided on both sides of the positive electrode current collector 21A and contains one or more types of positive electrode active materials that absorb and release lithium. However, the positive electrode active material layer 21B may be provided on only one side of the positive electrode current 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 conductive agent. The method for forming the positive electrode active material layer 21B is not particularly limited, but specifically may be one or more types of coating methods.

[0114] The type of positive electrode active material is not particularly limited, but specifically includes a lithium-containing compound. This lithium-containing compound is a compound containing lithium and one or more transition metal elements as constituent elements, and may further contain one or more other elements as constituent elements. The type of other element is not particularly limited as long as it is an element other than lithium and transition metal elements, but 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, but specifically includes oxides, phosphate compounds, silicate compounds, borate compounds, etc.

[0115] 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, LiNi 0.33 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.

[0116] The positive electrode binder contains one or more of the following materials: synthetic rubber, polymer compound, etc. 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.

[0117] The positive electrode conductive agent contains one or more conductive materials such as carbon materials, metal materials, and conductive polymer compounds, and specific examples of the carbon materials include graphite, carbon black, acetylene black, and ketjen black.

[0118] (Negative electrode) The negative electrode 22 may have a configuration similar to that of the negative electrode 1 described above, or may have a configuration similar to that of the negative electrode 2 described above.

[0119] Specifically, the negative electrode 22 may include a negative electrode current collector 22A, a base layer 22B, and a negative electrode active material layer 22C, as shown in Fig. 4. The configurations of the negative electrode current collector 22A, the base layer 22B, and the negative electrode active material layer 22C are similar to the configurations of the negative electrode current collector 1A, the base layer 1B, and the negative electrode active material layer 1C, respectively.

[0120] In this case, as shown in FIG. 3, the negative electrode current collector 22A includes a protruding portion 22AT on which the base layer 22B and the negative electrode active material layer 22C are not provided. The protruding portions 22AT are joined together to form a single lead, thereby forming a joined body. Here, the protruding portion 22AT is integrated with the portion other than the protruding portion 22AT. However, since the protruding portion 22AT is separate from the portion other than the protruding portion 22AT, it may be joined to the portion other than the protruding portion 22AT.

[0121] Alternatively, the negative electrode 22 may include a negative electrode current collector 22D and a negative electrode active material layer 22C as shown in Fig. 5. The configurations of the negative electrode current collector 22D and the negative electrode active material layer 22C are similar to the configurations of the negative electrode current collector 1D and the negative electrode active material layer 1C, respectively.

[0122] In this case, the negative electrode current collector 22D includes a protruding portion 22AT on which the negative electrode active material layer 22C is not provided, as shown in Fig. 3. The protruding portions 22AT are joined together to form a single lead, thereby forming a joined body. As described above, the protruding portion 22AT may be integrated with the portion other than the protruding portion 22AT, or may be separated from the portion other than the protruding portion 22AT.

[0123] (separator) 4 and 5, 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.

[0124] (electrolyte) The electrolyte is a liquid electrolyte that 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.

[0125] Here, the solvent contains one or more types of non-aqueous solvents (organic solvents), and the electrolyte solution containing the non-aqueous solvent is a so-called non-aqueous electrolyte solution. The non-aqueous solvent is an ester, an ether, or the like, more specifically, a carbonate ester compound, a carboxylic acid ester compound, a lactone compound, or the like. This is because the dissociation of the electrolyte salt is improved and the mobility of ions is also improved.

[0126] The carbonate ester compounds include cyclic carbonate esters and chain carbonate esters. Specific examples of the cyclic carbonate esters include ethylene carbonate and propylene carbonate, and specific examples of the chain carbonate esters include dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0127] The carboxylic acid ester compound is a chain carboxylic acid ester, etc. Specific examples of the chain carboxylic acid ester include ethyl acetate, ethyl propionate, propyl propionate, and ethyl trimethylacetate. The lactone compound is a lactone, etc. Specific examples of the lactone include γ-butyrolactone and γ-valerolactone. The ether may be 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, etc.

[0128] The electrolyte salt contains one or more light metal salts such as lithium salts. Specific examples of lithium salts include 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 is because high battery capacity can be obtained.

[0129] 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.

[0130] The electrolyte may further contain one or more additives, which improves the electrochemical stability of the electrolyte. The type of additive is not particularly limited, but specific examples include unsaturated cyclic carbonates, fluorinated cyclic carbonates, sulfonates, phosphates, acid anhydrides, nitrile compounds, and isocyanate compounds.

[0131] 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 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.

[0132] [Positive and negative leads] 3 to 5, the positive electrode lead 31 is a positive electrode terminal connected to the assembly of the multiple protrusions 21AT of the positive electrode 21, and is led out of the exterior film 10. The positive electrode lead 31 contains a conductive material such as a metal material, and a specific example of the metal material is aluminum. The shape of the positive electrode lead 31 is not particularly limited, but specifically may be either a thin plate shape or a mesh shape.

[0133] 3 to 5, the negative electrode lead 32 is a negative electrode terminal connected to the assembly of the multiple protrusions 22AT of the negative electrode 22, and is led out of the exterior film 10. The negative electrode lead 32 contains a conductive material such as a metal material, and a specific example of the metal material is copper. Here, the details regarding the lead-out direction and shape of the negative electrode lead 32 are the same as the details regarding the lead-out direction and shape of the positive electrode lead 31.

[0134] [Sealing film] 3, 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.

[0135] 3, 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 also contains a polymer compound such as polyolefin that has adhesiveness to the positive electrode lead 31, and a specific example of the polyolefin is polypropylene.

[0136] The configuration of the sealing film 42 is the same as the configuration of the sealing film 41, except that the sealing film 42 is a sealing member that has adhesiveness to the negative electrode lead 32. That is, the sealing film 42 contains a polymer compound such as polyolefin that has adhesiveness to the negative electrode lead 32.

[0137] <3-2. Operation> The secondary battery operates as follows during charging and discharging.

[0138] During charging, lithium is released from the positive electrode 21 of the battery element 20 and is absorbed into the negative electrode 22 via the electrolyte. During discharging, lithium is released from the negative electrode 22 of the battery element 20 and is absorbed into the positive electrode 21 via the electrolyte. During charging and discharging, lithium is absorbed and released in an ionic state.

[0139] <3-3. Manufacturing method> When manufacturing a secondary battery, the positive electrode 21 and the negative electrode 22 are each produced and an electrolyte solution is prepared according to the procedure described below as an example. Then, the positive electrode 21, the negative electrode 22, and the electrolyte solution are used to assemble a secondary battery, and a stabilization process is performed on the assembled secondary battery.

[0140] [Preparation of positive electrode] First, a paste-like cathode mixture slurry is prepared by adding a mixture (cathode mixture) of a cathode active material, a cathode binder, and a cathode conductive agent to a solvent. This solvent may be an aqueous solvent or an organic solvent. Next, the cathode mixture slurry is applied to both surfaces (excluding the protrusions 21AT) of the cathode current collector 21A including the protrusions 21AT to form the cathode active material layer 21B. Finally, 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 surfaces of the cathode current collector 21A, thereby producing the cathode 21.

[0141] [Preparation of negative electrode] Using a procedure similar to that for producing the negative electrode 1 described above, the negative electrode 22 is produced by forming the base layer 22B and the negative electrode active material layer 22C on both surfaces (excluding the protrusion 22AT) of the negative electrode current collector 22A including the protrusion 22AT.

[0142] Alternatively, the negative electrode 22 is fabricated by forming the negative electrode active material layers 22C on both sides of the negative electrode current collector 22D using a procedure similar to that for fabricating the negative electrode 2 described above.

[0143] [Preparation of electrolyte] An electrolyte salt is added to a solvent, whereby the electrolyte salt is dispersed or dissolved in the solvent, thereby preparing an electrolytic solution.

[0144] [Secondary battery assembly] First, positive electrodes 21 and negative electrodes 22 are alternately stacked with separators 23 interposed therebetween to prepare a stack (not shown).

[0145] Next, the plurality of protrusions 21AT are joined to one another using a joining method such as welding to form a joined body, and the plurality of protrusions 22AT are joined to one another to form a joined body. Next, the positive electrode lead 31 is joined to the joined body of the plurality of protrusions 21AT using a joining method such as welding, and the negative electrode lead 32 is joined to the joined body of the plurality of protrusions 22AT.

[0146] Next, after the roll is housed inside the recess 10U, the exterior film 10 (fusion layer / metal layer / surface protection layer) is folded to face each other. Next, the outer peripheral edges of two sides of the facing fusion layers are joined together using an adhesive method such as heat sealing, thereby housing the roll inside the bag-shaped exterior film 10.

[0147] Finally, an electrolyte solution is poured into the bag-shaped exterior film 10, and then the outer peripheral edges of the remaining sides of the opposing fusion layers are joined together using an adhesive method such as heat fusion. 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.

[0148] This allows the wound body to be impregnated with the electrolyte, producing a wound electrode body, the battery element 20. The battery element 20 is then sealed inside the bag-shaped exterior film 10, and a secondary battery is assembled.

[0149] [Secondary battery stabilization] The assembled secondary battery is charged and discharged. Conditions such as the ambient temperature, the number of charge / discharge cycles (number of cycles), and the charge / discharge conditions can be set arbitrarily. This forms a coating on the surface of each of the positive electrode 21 and the negative electrode 22, electrochemically stabilizing the state of the battery element 20. This completes the secondary battery.

[0150] <3-4. Actions and Effects> This secondary battery includes a negative electrode 22, which has a configuration similar to that of the negative electrode 1 or the negative electrode 2. Therefore, for the reasons described above, the energy density of the negative electrode 22 is ensured while the electrical conductivity and physical durability are improved, thereby achieving excellent battery characteristics.

[0151] In particular, 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, and therefore a greater effect can be obtained.

[0152] Other functions and effects of this secondary battery are the same as those of negative electrode 1 or negative electrode 2.

[0153] <4. Modifications> Next, a modified example will be described.

[0154] The configurations of the negative electrode for a secondary battery and the secondary battery can be modified as appropriate, as described below. Note that the series of modifications described below may be combined with each other.

[0155] [Variation 1] In FIG. 1, the negative electrode 1 includes an underlayer 1B, whereas in FIG. 2, the negative electrode 2 does not include an underlayer 1B.

[0156] However, as shown in Fig. 6 corresponding to Fig. 2, the negative electrode 2 may further include an underlayer 1B. As a result, the negative electrode 2 includes a negative electrode current collector 1D, an underlayer 1B, and a negative electrode active material layer 1C, and the negative electrode current collector 1D and the underlayer 1B are the carbon-containing layers of Modification 1.

[0157] The negative electrode 2 shown in Fig. 6 has the same configuration as the negative electrode 2 shown in Fig. 2, except that an underlayer 1B is interposed between a negative electrode current collector 1D and a negative electrode active material layer 1C. The configuration of the underlayer 1B is as described above.

[0158] In this case, the underlayer 1B significantly reduces the interfacial resistance at the interface between the negative electrode current collector 1D and the negative electrode active material layer 1C, significantly improving the conductivity between the negative electrode current collector 1D and the negative electrode active material layer 1C, thereby significantly improving the conductivity of the negative electrode 2 and achieving even greater effects.

[0159] [Variation 2] In Fig. 3, the secondary battery includes a battery element 20 that is a laminated electrode body. However, although not specifically shown here, the secondary battery may also include a battery element that is a wound electrode body.

[0160] In the battery element, which is a wound electrode body, a positive electrode 21 and a negative electrode 22 are wound around a winding axis, which is an imaginary axis, while facing each other with a separator 23 interposed therebetween.

[0161] The three-dimensional shape of the battery element is not particularly limited. For example, since the battery element is flat, the cross-sectional shape of the battery element intersecting the winding axis is a flat shape defined by a major axis and a minor axis. In this case, the three-dimensional shape of the battery element is a flat cylindrical shape, and the cross-sectional shape of the battery element is a flat, approximately elliptical shape.

[0162] When a battery element is produced in the manufacturing process of a secondary battery, the positive electrode 21 and the negative electrode 22 are stacked one on top of the other with the separator 23 interposed therebetween, and then the positive electrode 21, the negative electrode 22, and the separator 23 are wound to produce a wound body (not shown). Next, the wound body is pressed using a press or the like to form a flat shape. This wound body has the same configuration as the battery element, except that the positive electrode 21, the negative electrode 22, and the separator 23 are not impregnated with an electrolyte solution.

[0163] Even when a battery element that is a wound electrode body is used, the battery capacity is obtained by utilizing the absorption and release of lithium, and therefore the same effect can be obtained.

[0164] [Variation 3] A porous film separator 23 was used. However, although not specifically shown here, a laminated separator including a polymer compound layer may also be used.

[0165] Specifically, the laminated separator includes a porous membrane having a pair of surfaces and a polymer compound layer provided on one or both surfaces of the porous membrane. This is because the separator improves adhesion to each of the positive electrode 21 and the negative electrode 22, thereby preventing miswinding of the battery element 20. This prevents 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. Polyvinylidene fluoride has excellent physical strength and is electrochemically stable.

[0166] One or both of the porous film and the polymer compound layer may contain a plurality of insulating particles. This is because the plurality of insulating particles promotes heat dissipation when the secondary battery generates heat, thereby 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.

[0167] When fabricating a laminated separator, 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 membrane. In this case, instead of applying the precursor solution to the porous membrane, the porous membrane may be immersed in the precursor solution. In addition, multiple insulating particles may be added to the precursor solution.

[0168] Even when this laminated separator is used, the same effect can be obtained because lithium becomes 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 greater effect can be obtained.

[0169] [Variation 4] An electrolyte solution, which is a liquid electrolyte, was used, but although not specifically shown here, an electrolyte layer, which is a gel electrolyte, may also be used.

[0170] In the battery element 20 including the electrolyte layer, the positive electrode 21 and the negative electrode 22 are stacked 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 together. The electrolyte layer is interposed between the positive electrode 21 and the separator 23, and also between the negative electrode 22 and the separator 23. However, the electrolyte layer may be interposed only between the positive electrode 21 and the separator 23, or may be interposed only between the negative electrode 22 and the separator 23.

[0171] This electrolyte layer contains a polymer compound together with an electrolytic solution, and the electrolytic solution is held by the polymer compound. This is because leakage of the electrolytic solution is prevented. The composition of the electrolytic solution is as described above. The polymer compound includes polyvinylidene fluoride, etc. When forming the electrolyte layer, a precursor solution containing the electrolytic solution, the polymer compound, and a solvent is prepared, and then the precursor solution is applied to one or both surfaces of each of the positive electrode 21 and the negative electrode 22.

[0172] Even when this electrolyte layer is used, the same effect can be obtained because lithium can move between the positive electrode 21 and the negative electrode 22 via the electrolyte layer. In this case, leakage of the electrolyte solution is prevented as described above, and therefore a greater effect can be obtained.

[0173] <5. Uses of secondary batteries> Finally, the uses (application examples) of the secondary battery will be described.

[0174] The use 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, electric vehicles, etc., or 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 may be a power source used in place of the main power source, or a power source that can be switched from the main power source.

[0175] Specific examples of uses for secondary batteries are as follows: Electronic devices such as video cameras, digital still cameras, mobile phones, laptop computers, headphone stereos, portable radios, and portable information terminals. Storage devices such as backup power supplies and memory cards. Power tools such as power drills and power saws. Battery packs installed in 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.

[0176] The battery pack may include a single cell or a battery pack. The electric vehicle is a vehicle that runs on 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, household electrical appliances can be powered by using the power stored in the secondary battery, which is a power storage source.

[0177] Here, an example of the use of the secondary battery will be specifically described. The configuration described below is merely an example and can be modified as appropriate.

[0178] Figure 7 shows the block diagram of a battery pack, which is an application example of a secondary battery. 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.

[0179] 7, the battery pack includes a power supply 51 and a circuit board 52. The circuit board 52 is connected to the power supply 51 and includes a positive terminal 53, a negative terminal 54, and a temperature detection terminal 55.

[0180] Power source 51 includes one secondary battery. In this secondary battery, a positive electrode lead is connected to positive electrode terminal 53, and a negative electrode lead is connected to negative electrode terminal 54. Power source 51 is connected to an external power source via positive electrode terminal 53 and negative electrode terminal 54, and is therefore capable of charging and discharging. Circuit board 52 includes control unit 56, switch 57, PTC element 58, which is a thermosensitive resistor, and temperature detection unit 59. However, PTC element 58 may be omitted.

[0181] The control unit 56 includes a central processing unit (CPU) and a memory, and controls the operation of the battery pack. The control unit 56 detects and controls the usage state of the power source 51 as necessary.

[0182] When the voltage of power supply 51 (secondary battery) reaches the overcharge detection voltage or the overdischarge detection voltage, control unit 56 turns off switch 57 to prevent charging current from flowing through the current path of power supply 51. The overcharge detection voltage is not particularly limited, but specifically is 4.20V±0.05V, and the overdischarge detection voltage is not particularly limited, but specifically is 2.40V±0.10V.

[0183] Switch 57 includes a charge control switch, a discharge control switch, a charge diode, a discharge diode, etc., and switches between the presence and absence of a connection between power supply 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 the charge / discharge current is detected based on the ON resistance of switch 57.

[0184] Temperature detection unit 59 includes a temperature detection element such as a thermistor. Temperature detection unit 59 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 controls charging and discharging in the event of abnormal heat generation, and when control unit 56 performs correction processing when calculating the remaining capacity. [Example]

[0185] An embodiment of the present technology will be described.

[0186] <Examples 1 to 6 and Comparative Examples 1 to 7> First, a secondary battery was fabricated to which the negative electrode 1 of the first embodiment was applied, and then the battery characteristics of the secondary battery were evaluated. Here, two types of secondary batteries (a first secondary battery and a second secondary battery) were fabricated to evaluate the battery characteristics.

[0187] [Preparation of the first secondary battery] A first secondary battery (a laminate film type lithium ion secondary battery shown in FIGS. 3 and 4, battery capacity=7 mAh to 12 mAh) was fabricated according to the procedure described below.

[0188] (Preparation of positive electrode) First, the positive electrode active material (lithium-containing compound (oxide) LiNi 0.8 Co 0.15 Al 0.05 A positive electrode mixture was prepared by mixing 97 parts by mass of ethylenediamine fluoride (O2), 2.2 parts by mass of a positive electrode binder (polyvinylidene fluoride), and 0.8 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.

[0189] Next, using a coating device, the positive electrode mixture slurry was applied to one side (excluding the protrusion 21AT) of the positive electrode current collector 21A (a strip-shaped aluminum foil with a thickness of 15 μm) including the protrusion 21AT, and then the positive electrode mixture slurry was heated and dried (heating temperature = 120°C) to form the positive electrode active material layer 21B.

[0190] Finally, the positive electrode active material layer 21B was compression-molded using a hand press, and then dried in a vacuum atmosphere. In this case, the volume density of the positive electrode active material layer 21B was 3.5 g / cm 3 In this way, the positive electrode 21 was produced.

[0191] (Preparation of negative electrode) First, 60 parts by mass of carbon material (graphite, median diameter D50 = 0.5 μm) and 40 parts by mass of base binder were mixed together to prepare a base mixture. The base binder consisted of polyvinylidene fluoride (PVDF) and N-vinylacetamide polymer (poly N-vinylacetamide (PNVA), a homopolymer of N-vinylacetamide). The base mixture was then poured into a solvent (pure water, an aqueous solvent), and the solvent was kneaded and stirred using a planetary mixer to prepare a paste-like base mixture slurry.

[0192] Next, using a coating device, the base mixture slurry was applied to one side (excluding the protrusions 22AT) of the negative electrode current collector 22A containing a metal material and including the protrusions 22AT, and the base mixture slurry was then dried to form the base layer 22B (thickness = 0.2 μm to 0.4 μm). Copper foil (thickness = 6 μm) and stainless steel (SUS304, thickness = 6 μm) were used as the negative electrode current collector 22A.

[0193] Next, 94.4 parts by mass of the negative electrode active material, 4 parts by mass of the negative electrode binder, and 1.6 parts by mass of the negative electrode conductive agent were mixed together to prepare a negative electrode mixture.

[0194] The negative electrode active material used was a mixture of 66.1 parts by mass of pre-doped silicon oxide (median diameter D50=7 μm) as a silicon-containing material and 28.3 parts by mass of graphite (median diameter D50=21 μm) as a carbon material.

[0195] The negative electrode binders used were N-vinylacetamide polymer (poly N-vinylacetamide (PNVA)), a mixture of poly N-vinylacetamide and polyvinylidene fluoride (PNVA + PVDF), and a mixture of poly N-vinylacetamide and styrene-butadiene rubber (PNVA + SBR). The weight ratio of the mixtures was poly N-vinylacetamide:polyvinylidene fluoride or styrene-butadiene rubber = 3:1.

[0196] The negative electrode conductive agent was a mixture of 1 part by mass of carbon black, a particulate carbon material, and an aqueous dispersion (solid concentration = 0.6%) containing carbon nanotubes, a fibrous carbon material. This aqueous dispersion contained 0.4 parts by mass of carbon nanotubes (average fiber diameter = 2 nm) and 0.6 parts by mass of carboxymethyl cellulose, a dispersant.

[0197] Next, the negative electrode mixture was added to a solvent (pure water, which is an aqueous solvent), and then the solvent was mixed and stirred using a planetary mixer to prepare a paste-like negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to the surface of the base layer 22B using a coating device, and then the negative electrode mixture slurry was dried to form the negative electrode active material layer 22C.

[0198] Finally, the negative electrode active material layer 22C was compression-molded using a hand press, and then dried in a vacuum atmosphere. In this case, the volume density of the negative electrode active material layer 22C was 1.6 g / cm 3 In this way, the negative electrode 22 was produced.

[0199] For comparison, a negative electrode 22 was fabricated using the same procedure except that the underlayer 22B was not formed. For comparison, a negative electrode 22 was fabricated using the same procedure except that polyvinylidene fluoride was used as the negative electrode binder. For comparison, a negative electrode 22 was fabricated using the same procedure except that a mixture of styrene-butadiene rubber and carboxymethyl cellulose (SBR+CMC) was used as the negative electrode binder. The mixing ratio (weight ratio) of the mixture was styrene-butadiene rubber:carboxymethyl cellulose = 50:50.

[0200] (Preparation of Electrolyte) An electrolyte salt (lithium hexafluorophosphate (LiPF6) which is a lithium salt) was added to the solvent, and then the solvent with the electrolyte salt added was stirred. The solvent used was a mixture of ethylene carbonate which is a cyclic carbonate, dimethyl carbonate which is a chain carbonate, and monofluoroethylene carbonate which is a fluorinated cyclic carbonate. In this case, the mixing ratio (weight ratio) of the solvents was ethylene carbonate:dimethyl carbonate:monofluoroethylene carbonate = 30:60:10, and the content of the electrolyte salt was 1 mol / kg relative to the solvent. In this way, an electrolyte solution was prepared.

[0201] (First secondary battery assembly) First, a positive electrode 21 including a protrusion 21AT and a negative electrode 22 including a protrusion 22AT were stacked together with a separator 23 (microporous polyethylene film, thickness = 20 μm) in between to prepare a laminate (positive electrode 21 / separator 23 / negative electrode 22).

[0202] Next, the exterior film 10 was folded so as to sandwich the laminate housed inside the recessed portion 10U. In this case, the protrusions 21AT and 22AT were led out to the outside of the exterior film 10. The exterior film 10 was an aluminum laminate film 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 opposing fusion layers were heat-sealed to each other, thereby housing the laminate inside the bag-shaped exterior film 10.

[0203] Finally, after pouring an electrolyte solution into the bag-shaped exterior film 10, the outer peripheral edges of the remaining sides of the opposing fusion layers 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 protrusion 21AT, and a sealing film 42 (a polypropylene film having a thickness of 5 μm) was inserted between the exterior film 10 and the protrusion 22AT.

[0204] As a result, the laminate was impregnated with the electrolyte solution, thereby producing the battery element 20. Thus, the battery element 20 was sealed inside the exterior film 10, and the first secondary battery was assembled.

[0205] (Stabilization of the first secondary battery) The first 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 0.1 C until the voltage reached 4.2 V, and then at a constant voltage of 0.025 C at that voltage of 4.2 V. During discharging, the battery was discharged at a constant current of 0.1 C until the voltage reached 2.0 V. 0.1 C is the current value at which the battery capacity (theoretical capacity) is fully discharged in 10 hours, and 0.025 C is the current value at which the battery capacity is fully discharged in 40 hours.

[0206] As a result, a coating was formed on each surface of the positive electrode 21 and the negative electrode 22, electrochemically stabilizing the state of the battery element 20. Thus, a first secondary battery (battery capacity = 10 mAh) was completed. When producing this first secondary battery, the thickness of the positive electrode active material layer 21B and the negative electrode active material layer 22C were adjusted so that the capacity ratio (= charge capacity of the positive electrode 21 / charge capacity of the negative electrode 22) was 0.9.

[0207] [Preparation of the second secondary battery] A second secondary battery (battery capacity = 10 mAh to 15 mAh) was fabricated using the same procedure as the first secondary battery described above, except that a lithium metal plate (thickness = 100 μm) was used instead of the positive electrode 21.

[0208] Here, the first secondary battery using the positive electrode 21 as the counter electrode for the negative electrode 22 is a so-called full cell, whereas the second secondary battery using a lithium metal plate as the counter electrode for the negative electrode 22 is a so-called half cell.

[0209] [Evaluation of battery characteristics] The battery characteristics, including electrical resistance, adhesion, initial charge / discharge characteristics, and cycle characteristics, were evaluated according to the procedures described below, and the results shown in Table 1 were obtained.

[0210] (Electrical resistance characteristics) When evaluating the electrical resistance characteristics, after preparing the negative electrode 22, the electrical resistance of the negative electrode 22 was measured using an electrode resistance meter (electrode resistance system RM2611 manufactured by Hioki Electric Industry Co., Ltd.) before assembling a secondary battery using the negative electrode 22.

[0211] Specifically, the interface resistance of the negative electrode 22, which is an index for evaluating the electrical resistance characteristics, was measured in a room temperature environment (temperature=23° C.) using the electrode resistance meter described above.

[0212] The interface resistance values ​​shown in Table 1 are normalized with the interface resistance value in Comparative Example 1 set to 100.

[0213] (adhesion properties) When evaluating the adhesion characteristics, after the negative electrode 22 was produced, a peel test was performed on the negative electrode 22 using a tensile tester before the negative electrode 22 was used to assemble a secondary battery.

[0214] Specifically, adhesive tape (G9000 adhesive tape manufactured by Dexerials Corporation) was attached to the surface of the negative electrode active material layer 22C, and then the adhesive tape was pulled in a 180° direction to peel the negative electrode active material layer 22C from the negative electrode current collector 22A. This measured the peel strength of the negative electrode 22, which is an index for evaluating adhesion properties. When pulling the adhesive tape, the pulling speed of the adhesive tape was 10 cm / min. When measuring the peel strength, the average value of the peel strengths measured over a certain period of time after starting to pull the adhesive tape (10 seconds to 40 seconds after starting to pull) was calculated.

[0215] The peel strength values ​​shown in Table 1 are normalized values ​​with the peel strength value in Comparative Example 1 set to 100. Here, the acceptable range of peel strength is 20 or more.

[0216] (Initial charge / discharge characteristics) When evaluating the initial charge / discharge characteristics, a second secondary battery (half cell) was used.

[0217] Specifically, first, the second secondary battery was charged and discharged in a room temperature environment (temperature = 23°C) to measure the discharge capacity.

[0218] During charging, the battery was charged at a constant current of 0.1 C until the voltage reached 0.005 V, and then at a constant voltage of 0.005 V, the battery was charged at a constant current of 0.1 C until the voltage reached 0.01 C. During discharging, the battery was discharged at a constant current of 0.1 C until the voltage reached 1.5 V. 0.01 C is the current value that fully discharges the battery capacity in 100 hours.

[0219] Subsequently, the second secondary battery after charging and discharging was disassembled to collect the negative electrode 22, and then the weight of the negative electrode 22 was measured. The weight of the negative electrode 22 is the sum of the weight of the negative electrode current collector 22A, the weight of the base layer 22B, and the weight of the negative electrode active material layer 22C.

[0220] Finally, the initial capacity, which is an index for evaluating the initial charge-discharge characteristics, was calculated based on the formula: initial capacity (mAh / g)=discharge capacity (mAh) / weight (g) of negative electrode 22.

[0221] The initial capacity values ​​shown in Table 1 are normalized values ​​with the initial capacity value in Comparative Example 1 set to 100.

[0222] (Cycle characteristics) When evaluating the cycle characteristics, the first secondary battery (full cell) was used.

[0223] Specifically, the first secondary battery was first charged and discharged in a room temperature environment (temperature = 23°C) to measure the discharge capacity (discharge capacity at the first cycle). Next, the first secondary battery was repeatedly charged and discharged in the same environment until the number of cycles reached 200, to measure the discharge capacity (discharge capacity at the 200th cycle). Finally, the capacity retention rate, which is an index for evaluating cycle characteristics, was calculated based on the formula: capacity retention rate (%) = (discharge capacity at the 200th cycle / discharge capacity at the first cycle) × 100.

[0224] When charging and discharging the first secondary battery, the first secondary battery was sandwiched between two press plates from above and below, and the first secondary battery was charged and discharged while applying pressure to the first secondary battery. In this case, the pressure applied to the first secondary battery was 0.5 MPa.

[0225] During charging, the battery was charged at a constant current of 0.5 C until the voltage reached 4.2 V, and then at a constant voltage of 4.2 V, the battery was charged at a constant current of 0.5 C until the voltage reached 2.5 V. During discharging, the battery was discharged at a constant current of 0.5 C until the voltage reached 2.5 V. 0.5 C is the current value that fully discharges the battery capacity in 2 hours.

[0226] The values ​​of the capacity retention rates shown in Table 1 are normalized values ​​with the value of the capacity retention rate in Comparative Example 1 set to 100.

[0227] [Table 1]

[0228] [Consideration] As shown in Table 1, the interface resistance, peel strength, initial capacity, and capacity retention rate each varied greatly depending on the configuration of the negative electrode 22.

[0229] In the following, the interfacial resistance, peel strength, initial capacity, and capacity retention rate are compared with those in the case where no underlayer 22B is used and the negative electrode binder does not contain N-vinylacetamide polymer (Comparative Example 1).

[0230] When the underlayer 22B was not used and the negative electrode binder did not contain an N-vinylacetamide polymer (Comparative Examples 2 and 3), the interfacial resistance, peel strength, initial capacity, and capacity retention rate were not all sufficiently improved. In particular, in some cases, the interfacial resistance significantly increased, and the peel strength and capacity retention rate significantly decreased.

[0231] Similarly, when the underlayer 22B was used but the negative electrode binder did not contain N-vinylacetamide polymer (Comparative Examples 4 and 5), the interfacial resistance, peel strength, initial capacity, and capacity retention rate were not all sufficiently improved. In particular, in some cases, the interfacial resistance significantly increased, and the peel strength and capacity retention rate significantly decreased.

[0232] Furthermore, in the cases where the underlayer 22B was not used but the negative electrode binder contained N-vinylacetamide polymer (Comparative Examples 6 and 7), the interfacial resistance, peel strength, initial capacity, and capacity retention rate were not all sufficiently improved. In particular, in some cases, the interfacial resistance significantly increased.

[0233] In contrast, when the underlayer 22B was used and the negative electrode binder contained an N-vinylacetamide polymer (Examples 1 to 6), the interfacial resistance, peel strength, initial capacity, and capacity retention rate were all sufficiently improved. More specifically, while the peel strength was maintained within an acceptable range, the interfacial resistance was sufficiently reduced, and the initial capacity and capacity retention rate were each sufficiently increased.

[0234] In particular, when the underlayer 22B was used and the negative electrode binder contained an N-vinylacetamide polymer, a series of trends described below were observed.

[0235] First, regardless of the type of negative electrode current collector (metal material), the interfacial resistance was sufficiently reduced while maintaining an acceptable peel strength, and the initial capacity and capacity retention rate were both significantly increased.

[0236] Second, when the negative electrode active material contained both a silicon-containing material and a carbon material, both the initial capacity and the capacity retention rate were sufficiently increased.

[0237] Third, when the negative electrode binder contained polyvinylidene fluoride or styrene butadiene rubber together with N-vinylacetamide polymer, the capacity retention rate increased more.

[0238] Fourth, when the base binder contained N-vinylacetamide polymer, the capacity retention rate increased more.

[0239] <Examples 7 to 10 and Comparative Examples 8 and 9> Next, a secondary battery was fabricated using the negative electrode 2 of the second embodiment, and the battery characteristics of the secondary battery were then evaluated. Here, the above-described two types of secondary batteries were fabricated to evaluate the battery characteristics.

[0240] [Preparation of the first secondary battery] The manufacturing procedure for the first secondary battery (the laminate film type lithium ion secondary battery shown in Figures 3 and 5) is the same as the manufacturing procedure for the above-mentioned first secondary battery (the laminate film type lithium ion secondary battery shown in Figures 3 and 4), except that the manufacturing procedure for the negative electrode 22 is different.

[0241] When producing the negative electrode 22, the negative electrode active material layer 22C was formed on both sides of the negative electrode current collector 22D (a carbon sheet having a thickness of 12 μm) containing a carbon material (graphite). A graphite sheet was used as this carbon sheet.

[0242] In addition, when producing the negative electrode 22, Modification 1 shown in FIG. 6 was adopted to form the negative electrode active material layer 22C on the surface of the negative electrode current collector 22D via the base layer 22B.

[0243] [Preparation of the second secondary battery] The procedure for producing the second secondary battery was the same as that for producing the first secondary battery described above, except that a lithium metal plate (thickness=100 μm) was used instead of the positive electrode 21.

[0244] [Evaluation of battery characteristics] The battery characteristics, including electrical resistance, adhesion, initial charge / discharge, and cycle characteristics, were evaluated, and the results are shown in Table 2. The procedures for evaluating the electrical resistance, adhesion, initial charge / discharge, and cycle characteristics were as described above.

[0245] The values ​​of the interface resistance, peel strength, initial capacity, and capacity retention rate shown in Table 2 are normalized with the values ​​of the interface resistance, peel strength, initial capacity, and capacity retention rate in Comparative Example 1 set to 100.

[0246] [Table 2]

[0247] [Consideration] As shown in Table 2, the interface resistance, peel strength, initial capacity, and capacity retention rate each varied greatly depending on the configuration of the negative electrode 22.

[0248] In the following, as described above, the interface resistance, peel strength, initial capacity, and capacity retention rate in Comparative Example 1 are used as the comparison standards.

[0249] When the negative electrode current collector 22D, which is a carbon sheet, was used but the negative electrode binder did not contain N-vinylacetamide polymer (Comparative Examples 8 and 9), the interfacial resistance, peel strength, initial capacity, and capacity retention rate were not all sufficiently improved. In particular, in some cases, the peel strength and capacity retention rate were significantly reduced.

[0250] In contrast, when the negative electrode current collector 22D, which is a carbon sheet, is used and the negative electrode binder contains an N-vinylacetamide polymer (Examples 7 to 10), the interfacial resistance, peel strength, initial capacity, and capacity retention rate are all sufficiently improved. More specifically, while the peel strength is maintained within an acceptable range, the interfacial resistance is sufficiently reduced, and the initial capacity and capacity retention rate are each sufficiently increased.

[0251] In particular, when the negative electrode current collector 22D, which is a carbon sheet, is used and the negative electrode binder contains an N-vinylacetamide polymer, a series of trends described below were observed.

[0252] First, when the negative electrode active material contained both a silicon-containing material and a carbon material, both the initial capacity and the capacity retention rate were sufficiently increased.

[0253] Second, when the negative electrode binder contained polyvinylidene fluoride or styrene butadiene rubber together with N-vinylacetamide polymer, the capacity retention rate increased more.

[0254] Third, when the negative electrode 22 further includes the underlayer 22B, the initial capacity and the capacity retention rate both increase more.

[0255] [summary] From the results shown in Tables 1 and 2, when the negative electrode 22 includes the negative electrode current collector 22A (metal material), the base layer 22B (carbon material), and the negative electrode active material layer 22C, and the negative electrode active material layer 22C includes the negative electrode active material (silicon-containing material) and the negative electrode binder (N-vinylacetamide polymer), the electrical resistance characteristics, adhesion characteristics, initial charge / discharge characteristics, and cycle characteristics were all improved, and a secondary battery with excellent battery characteristics was obtained.

[0256] This tendency for excellent battery characteristics to be obtained was also obtained when the negative electrode 22 included a negative electrode current collector 22D (carbon material) and a negative electrode active material layer 22C, and the negative electrode active material layer 22C included a negative electrode active material (silicon-containing material) and a negative electrode binder (N-vinylacetamide polymer).

[0257] The present technology has been described above using several embodiments and examples, but the configuration of the present technology is not limited to the configurations described in those embodiments and examples and can be modified in various ways.

[0258] Specifically, the battery structure of the secondary battery has been described as being a laminate film type and a coin type. However, the battery structure of the secondary battery is not particularly limited, and may be a cylindrical type, a square type, a button type, or the like.

[0259] The battery element has been described as having a wound structure. However, the structure of the battery element is not particularly limited, and may be a stacked structure or a zigzag structure. In the stacked structure, the positive and negative electrodes are stacked on top of each other, and in the zigzag structure, the positive and negative electrodes are folded in a zigzag pattern.

[0260] Furthermore, although the electrode reactant is lithium in the above description, 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 alkaline earth metals such as beryllium, magnesium, and calcium. In addition, the electrode reactant may be other light metals such as aluminum.

[0261] 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.

[0262] The present technology can also be configured as follows. <1> a positive electrode, a negative electrode, and an electrolyte; The negative electrode is a carbon-containing layer; a negative electrode active material layer provided on the carbon-containing layer; Including, The negative electrode active material layer is a negative electrode active material including a silicon-containing material; a negative electrode binder containing an N-vinylacetamide polymer; A secondary battery comprising: <2> the negative electrode further includes a negative electrode current collector containing a metal material, the carbon-containing layer is a base layer provided on the negative electrode current collector; <1> The secondary battery according to claim 1. <3> the carbon-containing layer further contains a carbon binder; The carbon binder includes an N-vinylacetamide polymer. <2> The secondary battery according to claim 1. <4> the negative electrode further includes a negative electrode current collector, the carbon-containing layer is the negative electrode current collector; <1> The secondary battery according to claim 1. <5> The negative electrode further comprises a negative electrode current collector; a base layer provided on the negative electrode current collector; Including, the carbon-containing layer is the negative electrode current collector and the underlayer; <1> The secondary battery according to claim 1. <6> the negative electrode binder further contains one of polyvinylidene fluoride and styrene-butadiene rubber, <1> Or <5> 10. The secondary battery according to claim 9, wherein the second electrode is a conductor. <7> The negative electrode active material further contains a carbon material. <1> Or <6> 10. The secondary battery according to claim 9, wherein the second electrode is a conductor. <8> It is a lithium-ion secondary battery. <1> Or <7> 10. The secondary battery according to claim 9, wherein the second electrode is a conductor. <9> a carbon-containing layer; a negative electrode active material layer provided on the carbon-containing layer; Including, The negative electrode active material layer is a negative electrode active material including a silicon-containing material; a negative electrode binder containing an N-vinylacetamide polymer; A negative electrode for a secondary battery comprising:

Claims

1. a positive electrode, a negative electrode, and an electrolyte; The negative electrode is a carbon-containing layer; a negative electrode active material layer provided on the carbon-containing layer; Including, The negative electrode active material layer is a negative electrode active material including a silicon-containing material; a negative electrode binder containing an N-vinylacetamide polymer; A secondary battery comprising:

2. the negative electrode further includes a negative electrode current collector containing a metal material, the carbon-containing layer is a base layer provided on the negative electrode current collector; The secondary battery according to claim 1 .

3. the carbon-containing layer further contains a carbon binder; The carbon binder includes an N-vinylacetamide polymer. The secondary battery according to claim 2 .

4. the negative electrode further includes a negative electrode current collector, the carbon-containing layer is the negative electrode current collector; The secondary battery according to claim 1 .

5. The negative electrode further comprises a negative electrode current collector; a base layer provided on the negative electrode current collector; Including, the carbon-containing layer is the negative electrode current collector and the underlayer; The secondary battery according to claim 1 .

6. the negative electrode binder further contains one of polyvinylidene fluoride and styrene-butadiene rubber, The secondary battery according to any one of claims 1 to 5.

7. The negative electrode active material further contains a carbon material. The secondary battery according to any one of claims 1 to 5.

8. It is a lithium-ion secondary battery. The secondary battery according to any one of claims 1 to 5.

9. a carbon-containing layer; a negative electrode active material layer provided on the carbon-containing layer; Including, The negative electrode active material layer is a negative electrode active material including a silicon-containing material; a negative electrode binder containing an N-vinylacetamide polymer; A negative electrode for a secondary battery comprising:

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