Negative electrode for secondary battery, and secondary battery

Abstract

The secondary battery includes a positive electrode, a negative electrode, and an electrolyte solution. The 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 including a silicon-containing material; and a negative electrode binder including an 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 Art

[0002] Since various electronic devices such as mobile phones are becoming widespread, development of secondary batteries is underway as a power source that is small, lightweight, and can achieve a high energy density. This secondary battery includes a positive electrode, a negative electrode (negative electrode for a secondary battery), and an electrolytic solution, and various studies have been conducted on the structure of this secondary battery.

[0003] Specifically, the negative electrode contains a negative electrode active material (Si), a negative electrode binder (water-soluble polyimide-based material), and a water-soluble thickener (poly-N-vinylacetamide), and the content of this negative electrode binder and the content of the water-soluble thickener are specified (for example, refer to Patent Document 1). In addition, 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 this negative electrode binder and the peel strength of the negative electrode are specified (for example, refer to Patent Document 2).

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2018-060605

[0007] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2021-166199 Summary of the Invention

[0008] Although various studies have been conducted on the structure of secondary batteries, the battery characteristics of these secondary batteries are still insufficient, and thus there is room for improvement.

[0009] There is a desire for a negative electrode for a secondary battery and a secondary battery that can achieve excellent battery characteristics.

[0010] A negative electrode for a secondary battery according to an embodiment of the present technology includes: a carbon-containing layer; and a negative electrode active material layer provided on the carbon-containing layer. The negative electrode active material layer contains: a negative electrode active material containing a silicon-containing material; and a negative electrode binder containing an N-vinylacetamide polymer.

[0011] In addition, a secondary battery according to an embodiment of the present technology includes a positive electrode, a negative electrode, and an electrolytic solution, and the negative electrode has the same structure as the structure of the negative electrode for a secondary battery according to an embodiment of the present technology described above.

[0012] 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 a homopolymer of N-vinylacetamide and a copolymer of N-vinylacetamide. In addition, details of each of the carbon material, the silicon-containing material, and the N-vinylacetamide polymer will be described below.

[0013] According to a negative electrode for a secondary battery or a secondary battery according to an embodiment of the present technology, since the negative electrode for a secondary battery includes a carbon-containing layer and a negative electrode active material layer, the negative electrode active material layer contains a negative electrode active material and a negative electrode binder, the negative electrode active material contains a silicon-containing material, and the negative electrode binder contains an N-vinylacetamide polymer, excellent battery characteristics can be obtained.

[0014] In addition, the effects of the present technology are not necessarily limited to the effects described herein, and may be any of a series of effects related to the present technology described later. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a cross-sectional view showing the structure of a negative electrode for a secondary battery in the first embodiment of the present technology.

[0016] Figure 2 It is a cross-sectional view showing the structure of a negative electrode for a secondary battery in the second embodiment of the present technology.

[0017] Figure 3 It is a perspective view showing the structure of a secondary battery in an embodiment of the present technology.

[0018] Figure 4 It is Figure 3 a cross-sectional view showing an enlarged structure of the battery element shown.

[0019] Figure 5 It is Figure 4 another cross-sectional view showing an enlarged structure of the battery element shown.

[0020] Figure 6 It is a cross-sectional view showing the structure of a negative electrode for a secondary battery in Modification 1.

[0021] Figure 7 It is a block diagram showing the structure of an application example of a secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, an embodiment of the present technology will be described in detail with reference to the drawings. In addition, the order of description is as follows.

[0023] 1. Negative electrode for secondary battery (first embodiment)

[0024] 1-1. Structure

[0025] 1-2. Action

[0026] 1-3. Manufacturing method

[0027] 1-4. Function and effect

[0028] 2. Negative electrode for secondary battery (second embodiment)

[0029] 2-1. Structure

[0030] 2-2. Action

[0031] 2-3. Manufacturing method

[0032] 2-4. Function and effect

[0033] 3. Secondary battery

[0034] 3-1. Structure

[0035] 3-2. Action

[0036] 3-3. Manufacturing method

[0037] 3-4. Function and effect

[0038] 4. Modification example

[0039] 5. Use of secondary battery

[0040] <1. Negative electrode for secondary battery (first embodiment)>

[0041] First, the negative electrode for a secondary battery according to the first embodiment of the present technology (hereinafter simply referred to as "negative electrode") will be described.

[0042] The negative electrode described here is used for a secondary battery as an electrochemical device. However, the negative electrode can also be used for other electrochemical devices other than secondary batteries. Specific examples of other electrochemical devices are primary batteries and capacitors, etc.

[0043] During the electrode reaction, this negative electrode inserts and extracts an electrode reaction substance. The type of the electrode reaction substance is not particularly limited. Specifically, it is a light metal such as an alkali metal and an alkaline earth metal. Specific examples of the alkali metal are lithium, sodium, potassium, etc., and specific examples of the alkaline earth metal are magnesium, calcium, etc.

[0044] Hereinafter, the case where the electrode reaction substance is lithium will be taken as an example. Thus, in the negative electrode, during the electrode reaction, lithium is inserted and extracted in an ionic state.

[0045] <1-1. Structure>

[0046] Figure 1The cross-sectional structure of the negative electrode 1, which is an example of the negative electrode of the first embodiment, is shown. As Figure 1 shown, the negative electrode 1 includes a negative electrode current collector 1A, a base layer 1B, and a negative electrode active material layer 1C.

[0047] [Negative electrode current collector]

[0048] The negative electrode current collector 1A has a pair of surfaces on which the base layer 1B and the negative electrode active material layer 1C are provided. The negative electrode current collector 1A contains a metal material, and specific examples of the metal material are copper and the like.

[0049] The surface of the negative electrode current collector 1A is preferably roughened. This is because, by means of the so-called anchoring effect, the adhesion of each of the base layer 1B and the negative electrode active material layer 1C to the negative electrode current collector 1A is improved. The method of roughening is not particularly limited. Specifically, it is a method of forming fine particles on the surface of a metal foil using electrolytic treatment. This electrolytic treatment is a method of forming fine particles on the surface of a metal foil by using electrolysis in an electrolytic cell, thereby providing irregularities on the surface of the metal foil.

[0050] [Base layer]

[0051] The base layer 1B is a carbon-containing layer of the first embodiment.

[0052] The base layer 1B is provided on the negative electrode current collector 1A. Thus, the base layer 1B is interposed between the negative electrode current collector 1A and the negative electrode active material layer 1C. The thickness of the base layer 1B is not particularly limited, and thus can be arbitrarily set.

[0053] Here, the base layer 1B is provided on one side of the negative electrode current collector 1A. However, the base layer 1B may also be provided on both sides of the negative electrode current collector 1A.

[0054] As described above, since the base layer 1B is a carbon-containing layer, it contains any one or two or more of carbon materials. The type of carbon material is not particularly limited. Specifically, it is easily graphitizable carbon, hardly graphitizable carbon, and graphite (natural graphite and artificial graphite), etc.

[0055] The method of forming the base layer 1B is not particularly limited. Specifically, it is any one or two or more of a coating method, a vapor phase method, and a liquid phase method, etc. Specific examples of the vapor phase method are a sputtering method and a chemical vapor deposition method (CVD), etc.

[0056] The reason why the base layer 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.

[0057] First, this is because the interfacial resistance at the interface between the negative electrode current collector 1A and the negative electrode active material layer 1C is reduced. As a result, the conductivity (electron conductivity) between the negative electrode current collector 1A and the negative electrode active material layer 1C is improved, and thus the conductivity of the negative electrode 1 is improved.

[0058] Second, this is because the adhesion of the negative electrode active material layer 1C to the negative electrode current collector 1A is improved. As a result, even if the negative electrode active material layer 1C contains a large amount of a silicon-containing material that is prone to expansion and contraction during the electrode reaction, the negative electrode active material layer 1C is difficult to peel off from the negative electrode current collector 1A.

[0059] In addition, the base layer 1B may further contain any one or two or more of other materials.

[0060] In the case where the formation method of the base layer 1B is a coating method, a specific example of the other material is a binder. Hereinafter, in order to distinguish from the binder (negative electrode binder) contained in the negative electrode active material layer 1C described later, the binder contained in the base layer 1B is referred to as a "base binder". This base binder is a binder contained in the base layer 1B as a single-layer-containing layer, and is thus a so-called carbon binder.

[0061] The base binder contains any one or two or more of synthetic rubber and polymer compounds. Specific examples of the synthetic rubber are styrene-butadiene rubber, fluorine rubber, and ethylene propylene diene monomer rubber, etc. Specific examples of the polymer compound are polyvinylidene fluoride, polyimide, carboxymethyl cellulose, and N-vinylacetamide polymer, etc. In addition, the details of the N-vinylacetamide polymer will be described later.

[0062] Among them, the base binder preferably contains an N-vinylacetamide polymer. This is because, as described later, the negative electrode binder contained in the negative electrode active material layer 1C contains an N-vinylacetamide polymer, so the types of the base binder and the negative electrode binder are mutually common. As a result, the adhesion between the base binder and the negative electrode binder is improved, and thus the adhesion between the base layer 1B and the negative electrode active material layer 1C is improved.

[0063] The formation method of the base layer 1B containing a carbon material and a base binder is as described above and is not particularly limited. Specifically, it is a coating method or the like. The base layer 1B formed by the coating method is a so-called undercoat layer.

[0064] [Negative electrode active material layer]

[0065] 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. As a result, the negative electrode active material layer 1C is electrically connected to the negative electrode current collector 1A via the base layer 1B.

[0066] Here, the negative electrode active material layer 1C is provided on one side of the negative electrode current collector 1A. However, the negative electrode active material layer 1C may also be provided on both sides of the negative electrode current collector 1A.

[0067] The method for forming the negative electrode active material layer 1C is not particularly limited, but specifically, it is any one or two or more of coating methods, vapor phase methods, liquid phase methods, thermal spraying methods, and firing methods (sintering methods).

[0068] (Negative electrode active material)

[0069] The negative electrode active material is a material for inserting and extracting lithium, and contains any one or two or more of silicon-containing materials. This is because silicon has excellent lithium insertion ability, so a high energy density can be obtained.

[0070] As described above, the "silicon-containing material" is a material containing silicon as a constituent element. That is, the silicon-containing material can be a single substance of silicon, an alloy of silicon, a compound of silicon, a mixture of two or more of them, or a material containing two or more phases of them. In addition, the structure of the silicon-containing material is not particularly limited. Specifically, it can be a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or a coexistence of two or more of them.

[0071] The single substance of silicon only refers to a general single substance, so it may also contain trace impurities. That is, the purity of the single substance of silicon is not necessarily limited to 100%.

[0072] The type of the alloy of silicon is not particularly limited. Specifically, as elements other than silicon, the alloy of silicon contains any one or two or more of metal elements such as tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium as constituent elements.

[0073] However, the alloy of silicon is not limited to the case of containing one or two or more metal elements as constituent elements, and may also contain one or two or more metal elements and one or two or more semi-metal elements as constituent elements. In addition, the alloy of silicon may also contain one or two or more non-metal elements as constituent elements.

[0074] The type of the compound of silicon is not particularly limited. Specifically, as elements other than silicon, the compound of silicon contains any one or two or more of non-metal elements such as oxygen and carbon as constituent elements. In addition, the compound of silicon may also contain any one or two or more of a series of metal elements contained as constituent elements in the above-mentioned alloy of silicon as constituent elements.

[0075] Specific examples of each of the alloy of silicon and the compound of silicon are SiB 4 、SiB 6 、Mg2 Si, Ni 2 Si, TiSi 2 , MoSi 2 , CoSi 2 , NiSi 2 , CaSi 2 , CrSi 2 , Cu 5 Si, FeSi 2 , MnSi 2 , NbSi 2 , TaSi 2 , VSi 2 , WSi 2 , ZnSi 2 , SiC, Si 3 N 4 , Si 2 N 2 O, SiO x (0 < x ≤ 2 or 0.2 < x < 1.4) and LiSiO, etc. However, the compositions of the specific examples of the alloys and compounds of silicon are not limited to the compositions described herein and can be arbitrarily changed.

[0076] In addition, the negative electrode active material may further contain any one or two 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, the breakage of the negative electrode active material layer 1C can be suppressed while ensuring the battery capacity.

[0077] Specifically, the silicon-containing material has the advantage of a high theoretical capacity but has a risk point of being prone to severe expansion and contraction during charge and discharge. On the other hand, the carbon material has a risk point of a low theoretical capacity but has the advantage of being difficult to expand and contract during charge and discharge. Therefore, by using the carbon material and the silicon-containing material together, the expansion and contraction of the negative electrode active material layer 1C during charge and discharge can be suppressed while obtaining a high theoretical capacity. Thus, as described above, the breakage of the negative electrode active material layer 1C can be suppressed while ensuring the battery capacity.

[0078] Specific examples of the carbon material are easily graphitizable carbon, difficult-to-graphitize carbon, and graphite (natural graphite and artificial graphite), etc.

[0079] The mixing ratio of the silicon-containing material and the carbon material is not particularly limited and can therefore be arbitrarily set. Among them, the proportion of the weight of the silicon-containing material relative 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 the breakage of the negative electrode active material layer 1C can be sufficiently suppressed while sufficiently obtaining the battery capacity. This ratio is calculated based on the calculation formula of ratio (% by weight) = [weight of silicon-containing material / (weight of silicon-containing material + weight of carbon material)] × 100.

[0080] (Negative electrode binder)

[0081] The negative electrode binder is a material that binds negative electrode active materials to each other and includes any one or two or more of N-vinylacetamide polymers.

[0082] The negative electrode binder contains N-vinylacetamide polymer because the physical strength of the negative electrode active material layer 1C is improved. Thus, even if the electrode reaction is repeated, the negative electrode active material layer 1C is not damaged and is easily maintained, and the negative electrode active material layer 1C is difficult to peel off from the negative electrode current collector 1A. Therefore, the physical durability of the negative electrode 1 is improved. In this case, generation of cracks in the negative electrode active material layer 1C can be suppressed, and peeling of the negative electrode active material layer 1C from the negative electrode current collector 1A can also be suppressed.

[0083] In addition, the negative electrode binder may further contain either polyvinylidene fluoride or 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, since the physical strength of the negative electrode active material layer 1C is further improved, the negative electrode active material layer 1C is more difficult to be damaged even if the electrode reaction is repeated.

[0084] As described above, the "N-vinylacetamide polymer" is either or both of a homopolymer of N-vinylacetamide and a copolymer of N-vinylacetamide. The homopolymer of N-vinylacetamide is so-called poly-N-vinylacetamide.

[0085] The copolymer of N-vinylacetamide is a compound copolymerized from N-vinylacetamide and one or two or more monomers (excluding N-vinylacetamide). The type of the monomer is not particularly limited. Specifically, it is acrylic acid, methacrylic acid, alkali metal acrylate, alkaline earth metal acrylate, alkali metal methacrylate, alkaline earth metal methacrylate, etc.

[0086] Specific examples of the alkali metal acrylate are lithium acrylate, sodium acrylate, potassium acrylate, etc. Specific examples of the alkaline earth metal acrylate are calcium acrylate, magnesium acrylate, etc. Specific examples of the alkali metal methacrylate are lithium methacrylate, sodium methacrylate, potassium methacrylate, etc. Specific examples of the alkaline earth metal methacrylate are calcium methacrylate, magnesium methacrylate, etc.

[0087] The copolymerization amount of the monomer in the copolymer of N-vinylacetamide is not particularly limited, and thus can be arbitrarily set.

[0088] (Other materials)

[0089] In addition, the negative electrode active material layer 1C may further contain one or more of other materials.

[0090] Specific examples of the other materials are other negative electrode active materials, and the other negative electrode active materials include any one or more of metal-based materials. However, the above-mentioned silicon-containing materials are not included in the metal-based materials described herein.

[0091] The metal-based material is a material containing any one or more of a metal element capable of forming an alloy with lithium and a metalloid element as constituent elements, and specific examples of the metal element and the metalloid element are tin and the like. The metal-based material may be a monomer, an alloy, a compound, a mixture of two or more of them, or a material containing two or more phases of them.

[0092] In addition, specific examples of the other materials are other negative electrode binders, and the other negative electrode binders include any one or more of synthetic rubbers and polymer compounds. However, the above-mentioned N-vinylacetamide polymer, polyvinylidene fluoride, and styrene-butadiene rubber are not included in the other negative electrode binders described herein. Specific examples of the synthetic rubber are fluorine-based rubber and ethylene propylene diene monomer rubber, etc. Specific examples of the polymer compound are polyimide and carboxymethyl cellulose, etc.

[0093] In addition, specific examples of the other materials are negative electrode conductive agents, and the negative electrode conductive agents include any one or more of carbon materials, metal materials, and conductive polymer compounds. The carbon material may be a fibrous carbon material, a particulate carbon material, or both. Specific examples of the fibrous carbon material are carbon fiber, carbon nanofiber, and carbon nanotube, etc. Specific examples of the particulate carbon material are graphite, carbon black, acetylene black, and Ketjen black, etc.

[0094] <1-2. Operation>

[0095] In the negative electrode 1, during the electrode reaction, lithium is intercalated into the negative electrode active material contained in the negative electrode active material layer 1C, and lithium is deintercalated from the negative electrode active material. In this case, lithium is intercalated and deintercalated in an ionic state.

[0096] <1-3. Manufacturing method>

[0097] The negative electrode 1 is manufactured by the steps of an example described below.

[0098] First, a carbon material and a base binder are mixed with each other to prepare a base mixture. Next, the base mixture is put into a solvent to prepare a paste-like base mixture slurry. The solvent may be an aqueous solvent or an organic solvent. Next, the base mixture slurry is coated on one side of the negative electrode current collector 1A to form a base layer 1B.

[0099] 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 with each other to form a negative electrode mixture. Next, the negative electrode mixture is put into a solvent to prepare a paste-like negative electrode mixture slurry. The solvent can be an aqueous solvent or an organic solvent. Next, the negative electrode mixture slurry is coated on the surface of the base layer 1B to form a negative electrode active material layer 1C.

[0100] Finally, the negative electrode active material layer 1C is compression-molded using a roll press or the like. In this case, the negative electrode active material layer 1C can be heated, and the compression molding can be repeated multiple times.

[0101] Thereby, the base layer 1B and the negative electrode active material layer 1C are formed on the negative electrode current collector 1A, and the negative electrode 1 is completed.

[0102] <1-4. Functions and effects>

[0103] 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. In addition, since the base layer 1B is a carbon-containing layer, it includes a carbon material. In addition, the negative electrode active material layer 1C includes a negative electrode active material (silicon-containing material) and a negative electrode binder (N-vinylacetamide polymer).

[0104] In this case, as described above, a series of functions described below can be obtained.

[0105] First, since the negative electrode active material contains a silicon-containing material, a high energy density can be obtained in the negative electrode 1.

[0106] Second, since there is a base layer 1B (carbon-containing layer) 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. As a result, the conductivity between the negative electrode current collector 1A and the negative electrode active material layer 1C is improved, and the negative electrode active material layer 1C is difficult to peel off from the negative electrode current collector 1A, so the conductivity of the negative electrode 1 is stably improved.

[0107] Third, since 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 if the electrode reaction is repeated, the negative electrode active material layer 1C is difficult to break, and the negative electrode active material layer 1C is difficult to peel off from the negative electrode current collector 1A, so the physical durability of the negative electrode 1 is improved. In this case, in particular, even if the negative electrode active material contains a silicon-containing material that is likely to expand and contract during the electrode reaction, the physical durability of the negative electrode 1 is effectively improved.

[0108] As described above, in the negative electrode 1, conductivity and physical durability can be improved while ensuring the energy density. Therefore, by using the negative electrode 1, a secondary battery having excellent battery characteristics can be realized.

[0109] Here, as described above, the negative electrode 1 includes a base layer 1B, a negative electrode active material layer 1C, and a negative electrode current collector 1A. The base layer 1B is provided on the negative electrode current collector 1A, so that the conductivity between the negative electrode current collector 1A and the negative electrode active material layer 1C can be sufficiently improved by using the base layer 1B.

[0110] In addition, if the base layer 1B contains a base binder, and the base binder contains an N-vinylacetamide polymer, the adhesion between the base layer 1B (carbon binder) and the negative electrode active material layer 1C (negative electrode binder) is improved, so that a higher effect can be obtained.

[0111] In addition, 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. Therefore, even if the electrode reaction is repeated, the negative electrode active material layer 1C is more difficult to break, so that a higher effect can be obtained.

[0112] In addition, if the negative electrode active material further contains a carbon material, in the secondary battery using the negative electrode 1, breakage of the negative electrode active material layer 1C can be suppressed while ensuring the battery capacity, so that a higher effect can be obtained.

[0113] <2. Negative electrode for secondary battery (second embodiment)>

[0114] Next, a negative electrode for a secondary battery according to the second embodiment of the present technology (hereinafter simply referred to as "negative electrode") will be described.

[0115] <2-1. Structure>

[0116] Figure 2 The cross-sectional structure of a negative electrode 2, which is an example of the negative electrode of the second embodiment, is shown, corresponding to Figure 1 . As Figure 2 shown, except that a negative electrode current collector 1D is included instead of the negative electrode current collector 1A and the base layer 1B, the negative electrode 2 has the same structure as that of the negative electrode 1.

[0117] Except for the content described below, the negative electrode current collector 1D has the same structure as that of the negative electrode current collector 1A.

[0118] The negative electrode current collector 1D is the carbon-containing layer of the second embodiment. Therefore, since the negative electrode active material layer 1C is provided on the negative electrode current collector 1D, 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 thus can be arbitrarily set.

[0119] 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 also be provided on both surfaces of the negative electrode current collector 1D.

[0120] In addition, as described above, since the negative electrode current collector 1D is a carbon-containing layer, it contains any one or two or more of carbon materials. The details of the carbon material are as described above. Specifically, the negative electrode current collector 1D is a carbon material formed into a sheet (so-called carbon sheet), and specific examples of the carbon sheet are graphite sheets and the like.

[0121] The negative electrode 2 includes the negative electrode current collector 1D because 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. Thereby, the conductivity between the negative electrode current collector 1D and the negative electrode active material layer 1C is improved, and the negative electrode active material layer 1C is difficult to peel off from the negative electrode current collector 1D, so the conductivity of the negative electrode 2 is stably improved.

[0122] In particular, in the case of using the negative electrode current collector 1D as a carbon sheet, a series of advantages described below can be obtained compared with the case of using the negative electrode current collector 1A containing a metal material.

[0123] First, since the weight of the negative electrode current collector 1D (carbon sheet) is less than the weight of the negative electrode current collector 1A (metal material), the weight of the negative electrode 2 is less than the weight of the negative electrode 1. Thereby, the energy density per unit weight (Wh / kg) in the negative electrode 2 is increased compared with the energy density per unit weight in the negative electrode 1.

[0124] Second, the negative electrode current collector 1D (carbon sheet) is less likely to deform during the electrode reaction compared with the negative electrode current collector 1A (metal material), and more specifically, is less likely to warp. Thereby, the flatness of the negative electrode 2 is more easily maintained stably than the flatness of the negative electrode 1.

[0125] Third, in order to ensure the current collecting property of the negative electrode current collector 1D (carbon sheet), the thickness of the negative electrode current collector 1D is greater than the thickness of the negative electrode current collector 1A (metal material). Thereby, even when heat is generated during the electrode reaction, the heat dissipation property of the negative electrode 2 is improved compared with the heat dissipation property of the negative electrode 1.

[0126] <2-2. Operation>

[0127] 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 ions are intercalated and deintercalated in the negative electrode active material contained in the negative electrode active material layer 1C.

[0128] <2-3. Manufacturing method>

[0129] The negative electrode 2 is manufactured through the steps of an example described below.

[0130] First, a negative electrode current collector 1D in the form of a carbon sheet is prepared. Next, a negative electrode mixture slurry is prepared through the steps described in the first embodiment. Next, the negative electrode mixture slurry is coated on one side of the negative electrode current collector 1D, thereby forming the negative electrode active material layer 1C. Finally, the negative electrode active material layer 1C is compression-molded through the steps described in the first embodiment.

[0131] Thereby, the negative electrode active material layer 1C is formed on the negative electrode current collector 1D, thus completing the negative electrode 2.

[0132] <2-4. Function and effect>

[0133] 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. Since the negative electrode current collector 1D is a carbon-containing layer, it contains a carbon material. The negative electrode active material layer 1C contains a negative electrode active material (containing a silicon material) and a negative electrode binder (N-vinylacetamide polymer).

[0134] In this case, as described above, a series of functions described below can be obtained.

[0135] First, since the negative electrode active material contains a silicon-containing material, a high energy density can be obtained in the negative electrode 2.

[0136] 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. Thereby, the conductivity between the negative electrode current collector 1D and the negative electrode active material layer 1C is improved, and the negative electrode active material layer 1C is difficult to peel off from the negative electrode current collector 1D, so the conductivity of the negative electrode 2 is stably improved.

[0137] Third, since the negative electrode binder contains an N-vinylacetamide polymer, the physical strength of the negative electrode current collector 1D can be ensured even if the negative electrode current collector 1D does not contain a metal material. Thereby, even if the electrode reaction is repeated, the negative electrode current collector 1D can easily and stably support the negative electrode active material layer 1C, and the negative electrode active material layer 1C is difficult to peel off from the negative electrode current collector 1D, so the physical durability of the negative electrode 2 is improved. In this case, in particular, even if the negative electrode active material contains a silicon-containing material that is prone to expansion and contraction during the electrode reaction, the physical durability of the negative electrode 2 is effectively improved.

[0138] As described above, in the negative electrode 2, while ensuring the energy density, the conductivity and physical durability are improved. Therefore, by using the negative electrode 2, a secondary battery having excellent battery characteristics can be realized.

[0139] In this case, in particular, the negative electrode current collector 1D contains a carbon material, that is, the negative electrode current collector 1D is a carbon sheet. Therefore, as described above, the energy density per unit weight in the negative electrode 2 increases, the flatness of the negative electrode 2 is easily and stably maintained, and the heat dissipation of the negative electrode 2 is improved. Therefore, compared with the battery characteristics of the secondary battery using the negative electrode 1, the battery characteristics of the secondary battery using the negative electrode 2 are improved.

[0140] In addition, other functions and effects of the negative electrode 2 are the same as those of the negative electrode 1.

[0141] <3. Secondary battery>

[0142] Next, a secondary battery according to an embodiment of the present technology will be described.

[0143] The secondary battery described herein is a secondary battery that can obtain a battery capacity by the insertion and extraction of an electrode reaction material, and includes a positive electrode, a negative electrode, and an electrolyte. Hereinafter, as described above, the case where the electrode reaction material is lithium will be taken as an example. A secondary battery that obtains a battery capacity by the insertion and extraction of lithium is a so-called lithium ion secondary battery. In this lithium ion secondary battery, lithium is inserted and extracted in an ionic state.

[0144] In addition, the charging capacity of the negative electrode is preferably greater than the discharging capacity of the positive electrode. That is, it is preferable that the electrochemical capacity per unit area of the negative electrode is greater than the electrochemical capacity per unit area of the positive electrode. This is to prevent lithium from precipitating on the surface of the negative electrode during the charging process.

[0145] <3-1. Structure>

[0146] Figure 3 The three-dimensional structure of the secondary battery is shown, and Figure 4 and Figure 5 respectively magnify and show Figure 3 the cross-sectional structure of the battery element 20 shown. In addition, in Figure 3 , the state where the outer packaging film 10 and the battery element 20 are separated from each other is shown, and the cross-section of the battery element 20 along the XZ plane is shown by a dashed line. In Figure 4 and Figure 5 each, only a part of the battery element 20 is shown.

[0147] As Figure 3As shown, the secondary battery includes an outer packaging 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 herein is a laminated film type secondary battery using a flexible or pliable outer packaging film 10.

[0148] [Outer packaging film]

[0149] As Figure 3 shown, the outer packaging film 10 is an outer packaging component that houses the battery element 20 and has a bag-like structure that is sealed when the battery element 20 is housed inside. Thus, the outer packaging film 10 houses the positive electrode 21, negative electrode 22, and electrolyte described below.

[0150] Here, the outer packaging film 10 is a single film-like component that is folded along the folding direction F. A recessed portion 10U (so-called deep draw portion) for housing the battery element 20 is provided on the outer packaging film 10.

[0151] Specifically, the outer packaging film 10 is a three-layer laminated film having a welding layer, a metal layer, and a surface protective layer laminated in that order from the inside. In a state where the outer packaging film 10 is folded, the outer peripheral edge portions of the welding layers facing each other are welded to each other. The welding layer contains a polymer compound such as polypropylene. The metal layer contains a metal material such as aluminum. The surface protective layer contains a polymer compound such as nylon.

[0152] However, the structure (number of layers) of the outer packaging film 10 is not particularly limited and may be 1 layer, 2 layers, or 4 layers or more.

[0153] [Battery element]

[0154] As Figures 3 - 5 shown, the battery element 20 is a power generation element including a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte (not shown) and is housed inside the outer packaging film 10.

[0155] The battery element 20 is a so-called laminated electrode body, and the positive electrode 21 and the negative electrode 22 are laminated with each other with the separator 23 interposed therebetween. The number of laminations of the positive electrode 21, negative electrode 22, and separator 23 is not particularly limited. Here, a plurality of positive electrodes 21 and a plurality of negative electrodes 22 are alternately laminated with the separator 33 interposed therebetween.

[0156] (Positive electrode)

[0157] As Figure 4 and Figure 5 shown, the positive electrode 21 includes a positive electrode current collector 21A and a positive electrode active material layer 21B.

[0158] The positive electrode current collector 21A has a pair of surfaces provided with a positive electrode active material layer 21B. The positive electrode current collector 21A contains a conductive material such as a metal material, and specific examples of the metal material are aluminum and the like.

[0159] In addition, as Figure 3 shown, the positive electrode current collector 21A includes protruding portions 21AT where the positive electrode active material layer 21B is not provided, and a plurality of protruding portions 21AT are joined to each other in a manner to form a single lead. Here, the protruding portions 21AT are integrated with the portions other than the protruding portions 21AT. However, since the protruding portions 21AT are separated from the portions other than the protruding portions 21AT, they can also be joined to the portions other than the protruding portions 21AT.

[0160] Here, the positive electrode active material layer 21B is provided on both surfaces of the positive electrode current collector 21A and contains any one or more of positive electrode active materials that can intercalate and deintercalate lithium. However, it is also possible that the positive electrode active material layer 21B is provided only on one surface of the positive electrode current collector 21A on the side where the positive electrode 21 faces the negative electrode 22. In addition, it is also possible that the positive electrode active material layer 21B further contains any one or more 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, and specifically, it is any one or more of coating methods and the like.

[0161] The type of the positive electrode active material is not particularly limited, and specifically, it is a lithium-containing compound and the like. The lithium-containing compound is a compound containing lithium and one or more transition metal elements as constituent elements, and may also contain one or more other elements as constituent elements. The type of the other elements is only required to be an element other than lithium and transition metal elements respectively, and is not particularly limited. Specifically, it is an element belonging to Groups 2 to 15 of the long-period type periodic table. The type of the lithium-containing compound is not particularly limited, and specifically, it is an oxide, a phosphate compound, a silicate compound, a borate compound, and the like.

[0162] Specific examples of the oxide are LiNiO 2 、LiCoO 2 、LiCo 0.98 Al 0.01 Mg 0.01 O 2 、LiNi 0.5 Co 0.2 Mn 0.3 O 2 、LiNi 0.8 Co 0.15 Al 0.05 O 2 、LiNi 0.33 Co 0.33 Mn 0.33O 2 , Li 1.2 Mn 0.52 Co 0.175 Ni 0.1 O 2 , Li 1.15 (Mn 0.65 Ni 0.22 Co 0.13 ) 2 and LiMn 2 O 4 etc. A specific example of the phosphoric acid compound is LiFePO 4 、LiMnPO 4 、LiFe 0.5 Mn 0.5 PO 4 and LiFe 0.3 Mn 0.7 PO 4 wait.

[0163] The positive electrode binder includes any one or more of materials such as synthetic rubber and polymer compounds. Specific examples of synthetic rubber are styrene-butadiene rubber, fluorine rubber, and EPDM rubber. Specific examples of polymer compounds are polyvinylidene fluoride, polyimide, and carboxymethyl cellulose.

[0164] The positive electrode conductive agent includes any one or two or more conductive materials such as carbon materials, metal materials, and conductive polymer compounds. Specific examples of the carbon material include graphite, carbon black, acetylene black, and Ketjen black.

[0165] (negative electrode)

[0166] The negative electrode 22 may have the same structure as that of the negative electrode 1 described above, or may have the same structure as that of the negative electrode 2 described above.

[0167] Specifically, it can also be, Figure 4 As shown, the negative electrode 22 includes a negative electrode collector 22A, a base layer 22B, and a negative electrode active material layer 22C. The structures of the negative electrode collector 22A, the base layer 22B, and the negative electrode active material layer 22C are the same as those of the negative electrode collector 1A, the base layer 1B, and the negative electrode active material layer 1C.

[0168] In this case, if Figure 3As shown, the negative electrode current collector 22A includes a protruding portion 22AT where the base layer 22B and the negative electrode active material layer 22C are not provided. In addition, a plurality of protruding portions 22AT are joined to each other in a manner to form a single lead shape, thereby forming a joined body. Here, the protruding portion 22AT is integrated with the portion other than the protruding portion 22AT. However, the protruding portion 22AT may be separated from the portion other than the protruding portion 22AT, and thus joined to the portion other than the protruding portion 22AT.

[0169] Alternatively, it may be that, as Figure 5 shown, the negative electrode 22 includes a negative electrode current collector 22D and a negative electrode active material layer 22C. The structures of the negative electrode current collector 22D and the negative electrode active material layer 22C are the same as the structures of the negative electrode current collector 1D and the negative electrode active material layer 1C, respectively.

[0170] In this case, as Figure 3 shown, the negative electrode current collector 22D includes a protruding portion 22AT where the negative electrode active material layer 22C is not provided. In addition, a plurality of protruding portions 22AT are joined to each other in a manner to form a single lead shape, 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.

[0171] (Separator)

[0172] As Figure 4 and Figure 5 shown, 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.

[0173] (Electrolyte solution)

[0174] The electrolyte solution is a liquid electrolyte. The electrolyte solution is impregnated in each of the positive electrode 21, the negative electrode 22, and the separator 23, and contains a solvent and an electrolyte salt.

[0175] Here, the solvent contains any one or two or more 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 esters, ethers, etc. More specifically, it is carbonate-based compounds, carboxylate-based compounds, lactone-based compounds, etc. This is because the dissociation of the electrolyte salt is improved and the ion mobility is also improved.

[0176] The carbonate-based compounds are cyclic carbonates and chain carbonates. Specific examples of the cyclic carbonates are ethylene carbonate and propylene carbonate, etc., and specific examples of the chain carbonates are dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate, etc.

[0177] The carboxylic acid ester compounds are chain carboxylic acid esters and the like. Specific examples of the chain carboxylic acid esters are ethyl acetate, ethyl propionate, propyl propionate, ethyl pivalate, and the like. The lactone compounds are lactones and the like. Specific examples of the lactones are γ-butyrolactone, γ-valerolactone, and the like. In addition, the ethers may be 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, and the like.

[0178] The electrolyte salt includes any one or more of light metal salts such as lithium salts. Specific examples of the lithium salts are lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium trifluoromethanesulfonate (LiCF 3 SO 3 ), lithium bis(fluorosulfonyl)imide (LiN(FSO 2 ) 2 ), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF 3 SO 2 ) 2 ), lithium tris(trifluoromethanesulfonyl)methide (LiC(CF 3 SO 2 ) 3 ), lithium bis(oxalato)borate (LiB(C 2 O 4 ) 2 ), lithium monofluorophosphate (Li 2 PFO 3 ), lithium difluorophosphate (LiPF 2 O 2 ), and the like. This is because a high battery capacity can be obtained.

[0179] The content of the electrolyte salt is not particularly limited. Specifically, it is 0.3 mol / kg to 3.0 mol / kg relative to the solvent. This is because high ionic conductivity can be obtained.

[0180] In addition, the electrolytic solution may further contain any one or more of additives. This is because the electrochemical stability of the electrolytic solution is improved. The types of the additives are not particularly limited. Specifically, they are unsaturated cyclic carbonates, fluorinated cyclic carbonates, sulfonates, phosphates, acid anhydrides, nitrile compounds, isocyanate compounds, and the like.

[0181] Specific examples of the unsaturated cyclic carbonate are vinylene carbonate, ethylene vinylene carbonate, and methylene vinylene carbonate. Specific examples of the fluorinated cyclic carbonate are fluoroethylene carbonate and difluoroethylene carbonate. Specific examples of the sulfonate are propane sultone and propylene sultone. Specific examples of the phosphate are trimethyl phosphate and triethyl phosphate. Specific examples of the acid anhydride are succinic anhydride, 1,2-ethanedisulfonic anhydride, and 2-sulfobenzoic anhydride. Specific examples of the nitrile compound are succinonitrile. Specific examples of the isocyanate compound are hexamethylene diisocyanate.

[0182] [Positive electrode lead and negative electrode lead]

[0183] As Figures 3 - 5 shown, the positive electrode lead 31 is a positive electrode terminal connected to the joint body of a plurality of protrusions 21AT in the positive electrode 21, and is led out to the outside of the outer packaging film 10. The positive electrode lead 31 includes a conductive material such as a metal material, and specific examples of the metal material are aluminum and the like. The shape of the positive electrode lead 31 is not particularly limited, and specifically, it is any one of a thin plate shape and a mesh shape.

[0184] As Figures 3 - 5 shown, the negative electrode lead 32 is a negative electrode terminal connected to the joint body of a plurality of protrusions 22AT in the negative electrode 22, and is led out to the outside of the outer packaging film 10. The negative electrode lead 32 includes a conductive material such as a metal material, and specific examples of the metal material are copper and the like. Here, the details of the leading-out direction and shape of the negative electrode lead 32 are the same as the details of the leading-out direction and shape of the positive electrode lead 31.

[0185] [Sealing film]

[0186] As Figure 3 shown, the sealing film 41 is inserted between the outer packaging film 10 and the positive electrode lead 31, and the sealing film 42 is inserted between the outer packaging film 10 and the negative electrode lead 32. However, one or both of the sealing films 41 and 42 may be omitted.

[0187] As Figure 3 shown, the sealing film 41 is a sealing member that prevents external gases and the like from entering the inside of the outer packaging film 10. In addition, the sealing film 41 includes a polymer compound such as polyolefin having adhesiveness to the positive electrode lead 31, and specific examples of the polyolefin are polypropylene and the like.

[0188] Except that the sealing film 42 is a sealing member having adhesiveness to the negative electrode lead 32, the structure of the sealing film 42 is the same as the structure of the sealing film 41. That is, the sealing film 42 includes a polymer compound such as polyolefin having adhesiveness to the negative electrode lead 32.

[0189] <3-2. Operation>

[0190] The secondary battery operates as follows during charge and discharge.

[0191] During charging, in the battery element 20, lithium is deintercalated from the positive electrode 21, and this lithium is intercalated into the negative electrode 22 via the electrolyte. On the other hand, during discharging, in the battery element 20, lithium is deintercalated from the negative electrode 22, and this lithium is intercalated into the positive electrode 21 via the electrolyte. During charging and discharging, lithium is intercalated and deintercalated in an ionic state, respectively.

[0192] <3-3. Manufacturing method>

[0193] In the case of manufacturing a secondary battery, after separately producing the positive electrode 21 and the negative electrode 22 through the steps of an example described below and preparing an electrolyte, the secondary battery is assembled using the positive electrode 21, the negative electrode 22, and the electrolyte, and the assembled secondary battery is subjected to a stabilization treatment.

[0194] [Manufacture of positive electrode]

[0195] First, a mixture (positive electrode mixture) obtained by mixing a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent is put into a solvent, thereby preparing a paste-like positive electrode mixture slurry. The solvent can be an aqueous solvent or an organic solvent. Next, the positive electrode mixture slurry is coated on both sides (excluding the protruding portion 21AT) of the positive electrode current collector 21A including the protruding portion 21AT, thereby forming a positive electrode active material layer 21B. Finally, the positive electrode active material layer 21B can be compression-molded using a roll press or the like. In this case, the positive electrode active material layer 21B can be heated, or the compression molding can be repeated multiple times. Thus, the positive electrode active material layer 21B is formed on both sides of the positive electrode current collector 21A, thereby manufacturing the positive electrode 21.

[0196] [Manufacture of negative electrode]

[0197] Using the same steps as those for manufacturing the above-described negative electrode 1, a base layer 22B and a negative electrode active material layer 22C are formed on both sides (excluding the protruding portion 22AT) of the negative electrode current collector 22A including the protruding portion 22AT, thereby manufacturing the negative electrode 22.

[0198] Alternatively, using the same steps as those for manufacturing the above-described negative electrode 2, a negative electrode active material layer 22C is formed on both sides of the negative electrode current collector 22D, thereby manufacturing the negative electrode 22.

[0199] [Preparation of electrolyte]

[0200] An electrolyte salt is put into a solvent. Thereby, the electrolyte salt is dispersed or dissolved in the solvent, thereby preparing an electrolyte.

[0201] [Assembly of secondary battery]

[0202] First, the positive electrode 21 and the negative electrode 22 are alternately laminated with the separator 23 interposed therebetween to fabricate a laminate (not shown).

[0203] Next, a plurality of protruding portions 21AT are joined to each other by a joining method such as a welding method to form a joined body, and a plurality of protruding portions 22AT are joined to each other by a joining method such as a welding method to form a joined body. Next, the positive electrode lead 31 is joined to the joined body of the plurality of protruding portions 21AT, and the negative electrode lead 32 is joined to the joined body of the plurality of protruding portions 22AT by a joining method such as a welding method.

[0204] Next, after the wound body is housed inside the recessed portion 10U, the outer packaging film 10 (welding layer / metal layer / surface protection layer) is folded so that the outer packaging film 10 faces each other. Next, by a bonding method such as a hot melt bonding method, the outer peripheral edge portions of two sides in the welding layers facing each other are joined to each other, and thereby the wound body is housed inside the bag-shaped outer packaging film 10.

[0205] Finally, after the electrolytic solution is injected into the bag-shaped outer packaging film 10, the outer peripheral edge portions of the remaining one side in the welding layers facing each other are joined to each other by a bonding method such as a hot melt bonding method. In this case, the sealing film 41 is inserted between the outer packaging film 10 and the positive electrode lead 31, and the sealing film 42 is inserted between the outer packaging film 10 and the negative electrode lead 32.

[0206] Thereby, the electrolytic solution is impregnated into the wound body, and thus the battery element 20 as a wound electrode body is fabricated. Therefore, the battery element 20 is sealed inside the bag-shaped outer packaging film 10 to assemble a secondary battery.

[0207] [Stabilization of the secondary battery]

[0208] The assembled secondary battery is charged and discharged. Conditions such as the ambient temperature, the number of charge and discharge cycles (cycle number), and the charge and discharge conditions can be arbitrarily set. Thereby, a coating film is formed on the surface of each of the positive electrode 21 and the negative electrode 22, and thus the state of the battery element 20 is electrochemically stabilized. Thereby, the secondary battery is completed.

[0209] <3-4. Function and effect>

[0210] According to this secondary battery, the secondary battery includes the negative electrode 22 having the same structure as that of the negative electrode 1 or the negative electrode 2. Therefore, for the above reasons, while ensuring the energy density in the negative electrode 22, the conductivity and physical durability are improved, and thus excellent battery characteristics can be obtained.

[0211] In particular, if the secondary battery is a lithium ion secondary battery, sufficient battery capacity can be stably obtained by the insertion and extraction of lithium, and thus higher effects can be achieved.

[0212] Other functions and effects related to the secondary battery are the same as those related to the negative electrode 1 or the negative electrode 2.

[0213] <4. Modification example>

[0214] Next, the modification example will be described.

[0215] As described below, the structure of the negative electrode for the secondary battery and the secondary battery itself can be appropriately changed. In addition, a series of modification examples described below can also be combined with each other.

[0216] [Modification example 1]

[0217] In Figure 1 , the negative electrode 1 includes the base layer 1B. In contrast, in Figure 2 , the negative electrode 2 does not include the base layer 1B.

[0218] However, as shown in Figure 2 corresponding to Figure 6 , the negative electrode 2 may further include the base layer 1B. Thus, the negative electrode 2 includes the negative electrode current collector 1D, the base layer 1B, and the negative electrode active material layer 1C, and the negative electrode current collector 1D and the base layer 1B are carbon-containing layers of the modification example 1.

[0219] Figure 6 The negative electrode 2 shown in Figure 2 has the same structure as the negative electrode 2 shown in Figure 2 , except that the base layer 1B is interposed between the negative electrode current collector 1D and the negative electrode active material layer 1C. In addition, the constitution of the base layer 1B is as described above.

[0220] In this case, by using the base layer 1B, the interfacial resistance at the interface between the negative electrode current collector 1D and the negative electrode active material layer 1C is significantly reduced, and thus the conductivity between the negative electrode current collector 1D and the negative electrode active material layer 1C is significantly improved. Therefore, the conductivity of the negative electrode 2 is significantly improved, and thus higher effects can be achieved.

[0221] [Modification example 2]

[0222] In Figure 3 , the secondary battery includes the battery element 20 as a laminated electrode body. However, although not specifically shown here, the secondary battery may also include a battery element as a wound electrode body.

[0223] In the battery element as a wound electrode body, the positive electrode 21 and the negative electrode 22 face each other with the separator 23 interposed therebetween, and are wound around a winding axis as an imaginary axis.

[0224] The three-dimensional shape of the battery element is not particularly limited. For example, the battery element is flat, and thus the cross-sectional shape of the battery element intersecting the winding axis is a flat shape defined by the major axis and the minor axis. In this case, since the three-dimensional shape of the battery element is a flat cylindrical shape, the shape of the cross-section of the battery element is a substantially flat ellipse.

[0225] In the case of manufacturing a battery element in the manufacturing process of a secondary battery, the positive electrode 21 and the negative electrode 22 are laminated with each other with a 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 the wound body into a flat shape. The wound body has the same structure as that of the battery element except that the positive electrode 21, the negative electrode 22, and each of the separators 23 are not impregnated with an electrolytic solution.

[0226] In the case of using the battery element as the wound electrode body, since the battery capacity can be obtained by the insertion and extraction of lithium, the same effect can also be obtained.

[0227] [Modification Example 3]

[0228] The separator 23 used is a porous membrane. However, although not specifically shown here, a laminated separator including a polymer compound layer may also be used.

[0229] 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 adhesion of the separator to each of the positive electrode 21 and the negative electrode 22 is improved, and thus the winding deviation of the battery element 20 can be suppressed. Thereby, even if a decomposition reaction of the electrolytic solution occurs, the swelling of the secondary battery can be suppressed. The polymer compound layer contains a polymer compound such as polyvinylidene fluoride. This is because polyvinylidene fluoride has excellent physical strength and is electrochemically stable.

[0230] In addition, one or both of the porous membrane and the polymer compound layer may contain a plurality of insulating particles. This is because when the secondary battery generates heat, the plurality of insulating particles promote heat dissipation, and thus the safety (heat resistance) of the secondary battery is improved. The insulating particles contain any one or two or more of inorganic materials and resin materials. Specific examples of the inorganic materials are alumina, aluminum nitride, boehmite, silicon oxide, titanium oxide, magnesium oxide, and zirconium oxide. Specific examples of the resin materials are acrylic resin and styrene resin.

[0231] In the case of manufacturing a laminated separator, a precursor solution containing a polymer compound and a solvent or the like is prepared, and then the precursor solution is coated on one or both sides of a porous membrane. In this case, instead of coating the precursor solution on the porous membrane, the porous membrane may be immersed in the precursor solution. In addition, a plurality of insulating particles may be added to the precursor solution.

[0232] In the case of using such a laminated separator, lithium can also move between the positive electrode 21 and the negative electrode 22, and thus the same effect can be obtained. In this case, in particular, as described above, since the safety of the secondary battery is improved, a higher effect can be obtained.

[0233] [Modification Example 4]

[0234] An electrolytic solution as a liquid electrolyte is used. However, although not specifically illustrated here, an electrolyte layer as a gel-like electrolyte may also be used.

[0235] In the battery element 20 including the electrolyte layer, the positive electrode 21 and the negative electrode 22 are laminated on each other with the separator 23 and the electrolyte layer interposed therebetween, and the positive electrode 21, the negative electrode 22, the separator 23, and the electrolyte layer are wound. The electrolyte layer is interposed between the positive electrode 21 and the separator 23, and is also interposed between the negative electrode 22 and the separator 23. 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.

[0236] The electrolyte layer contains an electrolytic solution and a polymer compound, and the electrolytic solution is held by the polymer compound. This is because leakage of the electrolytic solution can be prevented. The structure of the electrolytic solution is as described above. The polymer compound includes polyvinylidene fluoride or the like. In the case of 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 coated on one or both sides of each of the positive electrode 21 and the negative electrode 22.

[0237] In the case of using such an electrolyte layer, lithium can also move between the positive electrode 21 and the negative electrode 22 via the electrolyte layer, and thus the same effect can be obtained. In this case, in particular, as described above, since leakage of the electrolytic solution can be prevented, a higher effect can be obtained.

[0238] <5. Uses of the secondary battery>

[0239] Finally, the uses (application examples) of the secondary battery will be described.

[0240] The use of secondary batteries is not particularly limited. Secondary batteries used as power sources can be the main power source of electronic equipment and electric vehicles, etc., or they can be auxiliary power sources. The main power source refers to the power source that is used preferentially, regardless of the presence or absence of other power sources. The auxiliary power source can be a power source that replaces the main power source, or it can be a power source that is switched from the main power source.

[0241] Specific examples of the use of secondary batteries are as follows: electronic devices such as video cameras, digital still cameras, mobile phones, laptop computers, stereo headphones, portable radios, and portable information terminals; storage devices such as backup power supplies and memory cards; power tools such as electric drills and electric saws; battery packs mounted on electronic devices, etc.; medical electronic devices such as pacemakers and hearing aids; electric vehicles such as electric vehicles (including hybrid vehicles); power storage systems such as household or industrial battery systems that store electricity in advance in case of emergencies. In these uses, one secondary battery or multiple secondary batteries can be used.

[0242] The battery pack may include a single cell or a battery pack. An electric vehicle is a vehicle that uses a secondary battery as a driving power source, or a hybrid vehicle that also has a driving source other than the secondary battery. In a home power storage system, the power stored in the secondary battery as a power storage source can be used to use home electrical products.

[0243] Here, an example of the use of the secondary battery is described in detail. The structure described below is just an example and can be changed appropriately.

[0244] Figure 7 The module structure of a battery pack as an application example of a secondary battery is shown. The battery pack described here is a battery pack (so-called soft pack) using one secondary battery, and is mounted in electronic devices such as smartphones.

[0245] like Figure 7 As shown in FIG. 1 , the battery pack includes a power source 51 and a circuit board 52 . The circuit board 52 is connected to the power source 51 and includes a positive electrode terminal 53 , a negative electrode terminal 54 , and a temperature detection terminal 55 .

[0246] The power source 51 includes a secondary battery. In the secondary battery, the positive lead is connected to the positive terminal 53, and the negative lead is connected to the negative terminal 54. The power source 51 is connected to an external power source via the positive terminal 53 and the negative terminal 54, so that charging and discharging are possible. The circuit substrate 52 includes a control unit 56, a switch 57, a PTC element 58 as a thermistor element, and a temperature detection unit 59. However, the PTC element 58 may be omitted.

[0247] 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 performs detection and control related to the usage state of the power supply 51 as needed.

[0248] In addition, when the voltage of the power supply 51 (secondary battery) reaches the overcharge detection voltage or the overdischarge detection voltage, the control unit 56 cuts off the switch 57 to prevent the charging current from flowing through the current path of the power supply 51. The overcharge detection voltage is not particularly limited, specifically 4.20 V ± 0.05 V, and the overdischarge detection voltage is not particularly limited, specifically 2.40 V ± 0.10 V.

[0249] The switch 57 includes a charge control switch, a discharge control switch, a charging diode, a discharging diode, etc., and switches the connection between the power supply 51 and the external device according to the instruction of the control unit 56. The switch 57 includes a metal oxide semiconductor field effect transistor (MOSFET), and the charge and discharge current is detected based on the on-resistance of the switch 57.

[0250] The temperature detection unit 59 includes a temperature detection element such as a thermistor. The temperature detection unit 59 measures the temperature of the power supply 51 using the temperature detection terminal 55, and outputs the measurement result of the temperature to the control unit 56. The measurement result of the temperature measured by the temperature detection unit 59 is used in cases where the control unit 56 performs charge and discharge control during abnormal heating and cases where the control unit 56 performs correction processing when calculating the remaining capacity.

[0251] Examples

[0252] Examples of the present technology will be described.

[0253] <Examples 1 to 6 and Comparative Examples 1 to 7>

[0254] First, a secondary battery applying the negative electrode 1 of the first embodiment was fabricated, and then the battery characteristics of the secondary battery were evaluated. Here, in order to evaluate the battery characteristics, two secondary batteries (the first secondary battery and the second secondary battery) were fabricated.

[0255] [Fabrication of the First Secondary Battery]

[0256] The first secondary battery ( Figure 3 and Figure 4 the laminated film type lithium ion secondary battery shown, battery capacity = 7 mAh to 12 mAh) was fabricated through the steps described below.

[0257] [Fabrication of the Positive Electrode]

[0258] First, 97 parts by mass of a positive electrode active material (LiNi as a lithium-containing compound (oxide)) 0.8 Co0.15 Al 0.05 O 2 (5), 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) are mixed with each other to prepare a positive electrode mixture. Next, the positive electrode mixture is put into a solvent (N-methyl-2-pyrrolidone as an organic solvent), and then the solvent is stirred to prepare a paste-like positive electrode mixture slurry.

[0259] Next, using a coating device, the positive electrode mixture slurry is coated on one side of the positive electrode current collector 21A (a strip-shaped aluminum foil with a thickness of 15 μm) including the protruding portion 21AT (excluding the protruding portion 21AT), and then the positive electrode mixture slurry is heated and dried (heating temperature = 120 °C) to form a positive electrode active material layer 21B.

[0260] Finally, the positive electrode active material layer 21B is compression-molded using a hand press, and then the positive electrode active material layer 21B is dried in a vacuum atmosphere. In this case, the bulk density of the positive electrode active material layer 21B is 3.5 g / cm 3 . Thus, the positive electrode 21 is manufactured.

[0261] (Manufacture of negative electrode)

[0262] First, 60 parts by mass of a carbon material (graphite, median diameter D50 = 0.5 μm) and 40 parts by mass of a base binder are mixed with each other to prepare a base mixture. As the base binder, polyvinylidene fluoride (PVDF) and N-vinylacetamide polymer (poly-N-vinylacetamide (PNVA) as a homopolymer of N-vinylacetamide) are used. Next, the base mixture is put into a solvent (pure water as an aqueous solvent), and then the solvent is kneaded and stirred using a rotary mixer to prepare a paste-like base mixture slurry.

[0263] Next, using a coating device, the base mixture slurry is coated on one side of the negative electrode current collector 22A including a metal material and including the protruding portion 22AT (excluding the protruding portion 22AT), and then the base mixture slurry is dried to form a base layer 22B (thickness = 0.2 μm to 0.4 μm). As the negative electrode current collector 22A, a copper foil (thickness = 6 μm) and stainless steel (SUS304, thickness = 6 μm) are used.

[0264] Next, 94.4 parts by mass of a negative electrode active material, 4 parts by mass of a negative electrode binder, and 1.6 parts by mass of a negative electrode conductive agent are mixed with each other to prepare a negative electrode mixture.

[0265] As the negative electrode active material, 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 was used.

[0266] As the negative electrode binder, a mixture of 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) was used. The mixing ratio (weight ratio) of the mixture was poly-N-vinylacetamide: polyvinylidene fluoride or styrene-butadiene rubber = 3:1.

[0267] As the negative electrode conductive agent, a mixture of 1 part by mass of carbon black as a particulate carbon material and an aqueous dispersion containing carbon nanotubes as a fibrous carbon material (solid component concentration = 0.6%) was used. The aqueous dispersion contained 0.4 part by mass of carbon nanotubes (average fiber diameter = 2 nm) and 0.6 part by mass of carboxymethyl cellulose as a dispersant.

[0268] Next, the negative electrode mixture was put into a solvent (pure water as an aqueous solvent), and then the solvent was kneaded and stirred using a planetary mixer, thereby preparing a paste-like negative electrode mixture slurry. Next, the negative electrode mixture slurry was coated on the surface of the base layer 22B using a coating device, and then the negative electrode mixture slurry was dried, thereby forming a negative electrode active material layer 22C.

[0269] Finally, the negative electrode active material layer 22C was compression-molded using a hand press, and then the negative electrode active material layer 22C was dried in a vacuum atmosphere. In this case, the bulk density of the negative electrode active material layer 22C was 1.6 g / cm 3 . Thus, the negative electrode 22 was fabricated.

[0270] In addition, for comparison, the negative electrode 22 was fabricated through the same steps except that the base layer 22B was not formed. Further, for comparison, the negative electrode 22 was fabricated through the same steps except that polyvinylidene fluoride was used as the negative electrode binder. Further, for comparison, the negative electrode 22 was fabricated through the same steps 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.

[0271] (Preparation of the electrolyte solution)

[0272] An electrolyte salt (lithium hexafluorophosphate (LiPF 6), and then the solvent containing the electrolyte salt was stirred. As the solvent, a mixture of ethylene carbonate as a cyclic carbonate, dimethyl carbonate as a chain carbonate, and fluoroethylene carbonate as a fluorinated cyclic carbonate was used. In this case, the mixing ratio (weight ratio) of the solvents was ethylene carbonate:dimethyl carbonate:fluoroethylene carbonate = 30:60:10, and the content of the electrolyte salt was 1 mol / kg relative to the solvent. Thus, an electrolytic solution was prepared.

[0273] (Assembly of the first secondary battery)

[0274] First, the positive electrode 21 including the protrusion 21AT and the negative electrode 22 including the protrusion 22AT were laminated with each other with the separator 23 (micro-porous polyethylene film, thickness = 20 μm) interposed therebetween, thereby producing a laminate (positive electrode 21 / separator 23 / negative electrode 22).

[0275] Next, the outer packaging film 10 was folded so as to sandwich the laminate housed inside the recess 10U. In this case, the protrusions 21AT and 22AT were led out to the outside of the outer packaging film 10. As the outer packaging film 10, an aluminum laminated film in which a welding layer (polypropylene film with a thickness of 30 μm), a metal layer (aluminum foil with a thickness of 40 μm), and a surface protective layer (nylon film with a thickness of 25 μm) were laminated in this order from the inside was used. Next, the outer peripheral edge portions of two sides in the welding layers facing each other were heat-sealed to each other, thereby housing the laminate inside the bag-shaped outer packaging film 10.

[0276] Finally, after injecting the electrolytic solution into the inside of the bag-shaped outer packaging film 10, the outer peripheral edge portions of the remaining one side in the welding layers facing each other were heat-sealed to each other in a reduced-pressure environment. In this case, a sealing film 41 (polypropylene film with a thickness of 5 μm) was inserted between the outer packaging film 10 and the protrusion 21AT, and a sealing film 42 (polypropylene film with a thickness of 5 μm) was inserted between the outer packaging film 10 and the protrusion 22AT.

[0277] Thus, the electrolytic solution was impregnated into the laminate, thereby producing the battery element 20. Therefore, the battery element 20 was sealed inside the outer packaging film 10, thereby assembling the first secondary battery.

[0278] (Stabilization of the first secondary battery)

[0279] In a normal temperature environment (temperature = 23 °C), the first secondary battery was charged and discharged for 1 cycle. During charging, constant current charging was performed at a current of 0.1C until the voltage reached 4.2V, and then constant voltage charging was performed at the voltage of 4.2V until the current reached 0.025C. During discharging, constant current discharging was performed at a current of 0.1C until the voltage reached 2.0V. 0.1C refers to the current value that completely discharges the battery capacity (theoretical capacity) within 10 hours, and 0.025C refers to the current value that completely discharges the battery capacity within 40 hours.

[0280] As a result, a coating film was formed on the surface of each of the positive electrode 21 and the negative electrode 22, so the state of the battery element 20 was electrochemically stable. Thus, the first secondary battery (battery capacity = 10 mAh) was completed. In the case of manufacturing 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 (= charging capacity of the positive electrode 21 / charging capacity of the negative electrode 22) = 0.9.

[0281] [Manufacture of the second secondary battery]

[0282] Except for using a lithium metal plate (thickness = 100 μm) instead of the positive electrode 21, a second secondary battery (battery capacity = 10 mAh to 15 mAh) was manufactured through the same steps as those for manufacturing the above-mentioned first secondary battery.

[0283] Here, the first secondary battery using the positive electrode 21 as the counter electrode with respect to the negative electrode 22 is a so-called full cell, while the second secondary battery using the lithium metal plate as the counter electrode with respect to the negative electrode 22 is a so-called half cell.

[0284] [Evaluation of battery characteristics]

[0285] Through the steps described below, as battery characteristics, the resistance characteristics, adhesion characteristics, initial charge and discharge characteristics, and cycle characteristics were evaluated, and the results shown in Table 1 were obtained.

[0286] (Resistance characteristics)

[0287] In the case of evaluating the resistance characteristics, after manufacturing the negative electrode 22 and before assembling the secondary battery using the negative electrode 22, the resistance of the negative electrode 22 was measured using an electrode resistance meter (Electrode Resistance System RM2611 manufactured by Hioki E.E. Corporation).

[0288] Specifically, in a normal temperature environment (temperature = 23 °C), using the above-mentioned electrode resistance meter, the interfacial resistance of the negative electrode 22, which is an index for evaluating the resistance characteristics, was measured.

[0289] In addition, the interfacial resistance values shown in Table 1 are values normalized with the interfacial resistance value in Comparative Example 1 being 100.

[0290] (Sealing property)

[0291] In the case of evaluating the sealing property, after manufacturing the negative electrode 22 and before assembling the secondary battery using the negative electrode 22, a peeling test of the negative electrode 22 was performed using a tensile testing machine.

[0292] Specifically, an adhesive tape (adhesive tape G9000 manufactured by Dexerials Co., Ltd.) was adhered to the surface of the negative electrode active material layer 22C, and then the adhesive tape was stretched in the 180° direction, thereby peeling the negative electrode active material layer 22C from the negative electrode current collector 22A. Thereby, the peeling strength of the negative electrode 22, which is an index for evaluating the sealing property, was measured. When stretching the adhesive tape, the stretching speed of the adhesive tape was set to 10 cm / min. In addition, when measuring the peeling strength, the average value of the peeling strength measured during a certain period after starting to stretch the adhesive tape (from 10 seconds to 40 seconds after the start of stretching) was calculated.

[0293] In addition, the peeling strength values shown in Table 1 are values normalized with the peeling strength value in Comparative Example 1 being 100. Here, the allowable range of the peeling strength is 20 or more.

[0294] (Initial charge-discharge characteristics)

[0295] In the case of evaluating the initial charge-discharge characteristics, a second secondary battery (half cell) was used.

[0296] Specifically, first, the second secondary battery was charged and discharged in a normal temperature environment (temperature = 23°C), thereby measuring the discharge capacity.

[0297] During charging, constant current charging was performed at a current of 0.1C until the voltage reached 0.005V, and then constant voltage charging was performed at the voltage of 0.005V until the current reached 0.01C. During discharging, constant current discharging was performed at a current of 0.1C until the voltage reached 1.5V. 0.01C refers to the current value that completely discharges the battery capacity in 100 hours.

[0298] Next, the second secondary battery after charge and discharge was disassembled, thereby recovering 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.

[0299] Finally, based on the calculation formula of initial capacity (mAh / g) = discharge capacity (mAh) / weight (g) of the negative electrode 22, the initial capacity, which is an index for evaluating the initial charge-discharge characteristics, was calculated.

[0300] In addition, the values of the initial capacity shown in Table 1 are the values standardized with the value of the initial capacity in Comparative Example 1 as 100.

[0301] (Cycle characteristics)

[0302] In the case of evaluating the cycle characteristics, the first secondary battery (full battery) was used.

[0303] Specifically, first, the first secondary battery was charged and discharged in a normal temperature environment (temperature = 23°C), and thus the discharge capacity (the discharge capacity of the 1st cycle) was measured. Next, in the same environment, the first secondary battery was repeatedly charged and discharged until the number of cycles reached 200 cycles, and thus the discharge capacity (the discharge capacity of the 200th cycle) was measured. Finally, based on the calculation formula of capacity retention rate (%) = (discharge capacity of the 200th cycle / discharge capacity of the 1st cycle) × 100, the capacity retention rate, which is an index for evaluating the cycle characteristics, was calculated.

[0304] When charging and discharging the first secondary battery, the first secondary battery was clamped from above and below with 2 pressing plates, and charging and discharging were performed while applying pressure to the first secondary battery. In this case, the pressure applied to the first secondary battery was set to 0.5 MPa.

[0305] During charging, constant current charging was performed at a current of 0.5C until the voltage reached 4.2V, and then constant voltage charging was performed at the voltage of 4.2V until the current reached 0.025C. During discharging, constant current discharging was performed at a current of 0.5C until the voltage reached 2.5V. 0.5C refers to the current value that completely discharges the battery capacity within 2 hours.

[0306] In addition, the values of the capacity retention rate shown in Table 1 are the values standardized with the value of the capacity retention rate in Comparative Example 1 as 100.

[0307] [Table 1]

[0308]

[0309] [Discussion]

[0310] As shown in Table 1, the interfacial resistance, peel strength, initial capacity, and capacity retention rate vary significantly according to the structure of the negative electrode 22.

[0311] Hereinafter, the interfacial resistance, peel strength, initial capacity, and capacity retention rate in the case of not using the base layer 22B and the negative electrode binder not containing the N-vinylacetamide polymer (Comparative Example 1) are used as comparative benchmarks respectively.

[0312] In the case of not using the base layer 22B and the negative electrode binder not containing the N-vinylacetamide polymer (Comparative Examples 2 and 3), the interfacial resistance, peel strength, initial capacity, and capacity retention rate were not all improved sufficiently. In particular, in some cases, the interfacial resistance increased significantly, and the peel strength and capacity retention rate decreased significantly respectively.

[0313] In addition, in the case of using the base layer 22B but the negative electrode binder not containing the N-vinylacetamide polymer (Comparative Examples 4 and 5) as well, the interfacial resistance, peel strength, initial capacity, and capacity retention rate were not all improved sufficiently. In particular, in some cases, the interfacial resistance increased significantly, and the peel strength and capacity retention rate decreased significantly respectively.

[0314] In addition, in the case of not using the base layer 22B but the negative electrode binder containing the N-vinylacetamide polymer (Comparative Examples 6 and 7) as well, the interfacial resistance, peel strength, initial capacity, and capacity retention rate were not all improved sufficiently. In particular, in some cases, the interfacial resistance increased significantly.

[0315] In contrast, in the case of using the base layer 22B and the negative electrode binder containing the N-vinylacetamide polymer (Examples 1 to 6), the interfacial resistance, peel strength, initial capacity, and capacity retention rate were all improved sufficiently. More specifically, while ensuring the peel strength within the allowable range, the interfacial resistance was sufficiently reduced, and the initial capacity and capacity retention rate increased sufficiently respectively.

[0316] In particular, in the case of using the base layer 22B and the negative electrode binder containing the N-vinylacetamide polymer, a series of tendencies described below were obtained.

[0317] First, regardless of the type of the negative electrode current collector (metal material), while ensuring the peel strength within the allowable range, the interfacial resistance was sufficiently reduced, and the initial capacity and capacity retention rate increased sufficiently respectively.

[0318] Second, when the negative electrode active material contains both a silicon-containing material and a carbon material, the initial capacity and capacity retention rate increased sufficiently respectively.

[0319] Third, when the negative electrode binder contains the N-vinylacetamide polymer and polyvinylidene fluoride or styrene-butadiene rubber, the capacity retention rate increased further.

[0320] Fourth, when the base binder contains an N-vinylacetamide polymer, the capacity retention rate further increases.

[0321] <Examples 7 to 10 and Comparative Examples 8 and 9>

[0322] Next, after manufacturing a secondary battery using the negative electrode 2 of the second embodiment, the battery characteristics of the secondary battery were evaluated. Here, in order to evaluate the battery characteristics, the above two types of secondary batteries were fabricated.

[0323] [Fabrication of the First Secondary Battery]

[0324] The fabrication steps of the first secondary battery ( Figure 3 and Figure 5 the laminated film type lithium ion secondary battery shown) were the same as those of the above first secondary battery ( Figure 3 and Figure 4 the laminated film type lithium ion secondary battery shown), except that the fabrication steps of the negative electrode 22 were different.

[0325] In the case of fabricating the negative electrode 22, a negative electrode active material layer 22C was formed on both surfaces of a negative electrode current collector 22D (carbon sheet with a thickness of 12 μm) containing a carbon material (graphite). As the carbon sheet, a graphite sheet was used.

[0326] In addition, in the case of fabricating the negative electrode 22, the modified example 1 shown in Figure 6 was adopted, whereby the negative electrode active material layer 22C was formed on the surface of the negative electrode current collector 22D with a base layer 22B interposed therebetween.

[0327] [Fabrication of the Second Secondary Battery]

[0328] The fabrication steps of the second secondary battery were the same as those of the above first secondary battery, except that a lithium metal plate (thickness = 100 μm) was used instead of the positive electrode 21.

[0329] [Evaluation of Battery Characteristics]

[0330] As battery characteristics, the resistance characteristics, adhesion characteristics, initial charge-discharge characteristics, and cycle characteristics were evaluated, and the results shown in Table 2 were obtained. In addition, the evaluation steps for the resistance characteristics, adhesion characteristics, initial charge-discharge characteristics, and cycle characteristics were as described above.

[0331] In addition, the respective values of the interfacial resistance, peel strength, initial capacity, and capacity retention rate shown in Table 2 are values standardized by setting the respective values of the interfacial resistance, peel strength, initial capacity, and capacity retention rate in Comparative Example 1 to 100.

[0332] [Table 2]

[0333]

[0334] [Investigation]

[0335] As shown in Table 2, the interfacial resistance, peel strength, initial capacity, and capacity retention rate vary significantly depending on the structure of the negative electrode 22.

[0336] Hereinafter, as described above, the interfacial resistance, peel strength, initial capacity, and capacity retention rate in Comparative Example 1 are used as the comparison benchmarks, respectively.

[0337] In the case of using the negative electrode current collector 22D as a carbon sheet but the negative electrode binder does not contain an N-vinylacetamide polymer (Comparative Examples 8 and 9), none of the interfacial resistance, peel strength, initial capacity, and capacity retention rate are sufficiently improved. In particular, in some cases, the peel strength is significantly reduced, and the capacity retention rate is significantly reduced.

[0338] In contrast, in the case of using the negative electrode current collector 22D as a carbon sheet and the negative electrode binder contains an N-vinylacetamide polymer (Examples 7 to 10), all of the interfacial resistance, peel strength, initial capacity, and capacity retention rate are sufficiently improved. More specifically, while ensuring the peel strength within an allowable range, the interfacial resistance is sufficiently reduced, and the initial capacity and capacity retention rate are increased sufficiently, respectively.

[0339] In particular, in the case of using the negative electrode current collector 22D as a carbon sheet and the negative electrode binder contains an N-vinylacetamide polymer, a series of tendencies described below are obtained.

[0340] First, when the negative electrode active material contains both a silicon-containing material and a carbon material, the initial capacity and capacity retention rate are increased sufficiently, respectively.

[0341] Second, when the negative electrode binder contains an N-vinylacetamide polymer and polyvinylidene fluoride or styrene-butadiene rubber, the capacity retention rate is further increased.

[0342] Third, when the negative electrode 22 further includes a base layer 22B, the initial capacity and capacity retention rate are increased further, respectively.

[0343] [Summary]

[0344] According to the results shown in Table 1 and Table 2, when the negative electrode 22 includes a negative electrode current collector 22A (metal material), a base layer 22B (carbon material), and a negative electrode active material layer 22C, and the negative electrode active material layer 22C contains a negative electrode active material (silicon-containing material) and a negative electrode binder (N-vinylacetamide polymer), all of the resistance characteristics, adhesion characteristics, initial charge-discharge characteristics, and cycle characteristics are improved, and thus a secondary battery with excellent battery characteristics is obtained.

[0345] The tendency to obtain such excellent battery characteristics is also achieved when the negative electrode 22 includes a negative electrode current collector 22D (carbon material) and a negative electrode active material layer 22C, and the negative electrode active material layer 22C contains a negative electrode active material (silicon-containing material) and a negative electrode binder (N-vinylacetamide polymer).

[0346] As described above, several embodiments and examples have been described regarding the present technology. However, the structure of the present technology is not limited to the structures described in these embodiments and examples, and thus various modifications can be made.

[0347] Specifically, the case where the battery structure of the secondary battery is a laminated film type and a coin type has been described. However, since the battery structure of the secondary battery is not particularly limited, it can be a cylindrical type, a square type, a button type, etc.

[0348] In addition, the case where the element structure of the battery element is a wound type has been described. However, the element structure of the battery element is not particularly limited, and thus it can be a stacked type, a repeatedly folded type, etc. In the stacked type, the positive electrode and the negative electrode are stacked on each other, and in the repeatedly folded type, the positive electrode and the negative electrode are folded in a Z shape.

[0349] In addition, although the case where the electrode reaction material is lithium has been described, the type of the electrode reaction material is not particularly limited. Specifically, as described above, the electrode reaction material can be other alkali metals such as sodium and potassium, and can also be alkaline earth metals such as beryllium, magnesium, and calcium. In addition, the electrode reaction material can also be other light metals such as aluminum.

[0350] The effects described in this specification are merely examples, and thus the effects of the present technology are not limited to the effects described in this specification. Therefore, other effects can also be obtained regarding the present technology.

[0351] In addition, the present technology can also adopt the following structure.

[0352] <1>

[0353] A secondary battery,

[0354] comprising a positive electrode, a negative electrode, and an electrolyte,

[0355] The negative electrode includes:

[0356] a carbon-containing layer; and

[0357] a negative electrode active material layer provided on the carbon-containing layer,

[0358] The negative electrode active material layer contains:

[0359] The negative electrode active material includes a silicon-containing material; and

[0360] The negative electrode binder includes an N-vinylacetamide polymer.

[0361] <2>

[0362] The secondary battery according to <1>,

[0363] The negative electrode further includes a negative electrode current collector containing a metal material,

[0364] The carbon-containing layer is a base layer provided on the negative electrode current collector.

[0365] <3>

[0366] The secondary battery according to <2>,

[0367] The carbon-containing layer further includes a carbon binder,

[0368] The carbon binder includes an N-vinylacetamide polymer.

[0369] <4>

[0370] The secondary battery according to <1>,

[0371] The negative electrode further includes a negative electrode current collector,

[0372] The carbon-containing layer is the negative electrode current collector.

[0373] <5>

[0374] The secondary battery according to <1>,

[0375] The negative electrode further includes:

[0376] A negative electrode current collector; and

[0377] A base layer provided on the negative electrode current collector,

[0378] The carbon-containing layer is the negative electrode current collector and the base layer.

[0379] <6>

[0380] The secondary battery according to any one of <1> to <5>,

[0381] The negative electrode binder further includes any one of polyvinylidene fluoride and styrene-butadiene rubber.

[0382] <7>

[0383] The secondary battery according to any one of <1> to <6>,

[0384] The negative electrode active material further includes a carbon material.

[0385] <8>

[0386] The secondary battery according to any one of <1> to <7>

[0387] The secondary battery is a lithium ion secondary battery.

[0388] <9>

[0389] A negative electrode for a secondary battery, comprising:

[0390] A carbon-containing layer; and

[0391] A negative electrode active material layer provided on the carbon-containing layer,

[0392] The negative electrode active material layer contains:

[0393] A negative electrode active material containing a silicon-containing material; and

[0394] A negative electrode binder containing an N-vinylacetamide polymer.

Claims

1. A secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode comprises: a carbon-containing layer; and a negative electrode active material layer disposed on the carbon-containing layer, wherein the negative electrode active material layer comprises: a negative electrode active material containing a silicon-containing material; and a negative electrode binder containing an N-vinylacetamide polymer.

2. The secondary battery according to claim 1, wherein the negative electrode further comprises a negative electrode current collector containing a metal material, and the carbon-containing layer is a base layer disposed on the negative electrode current collector.

3. The secondary battery according to claim 2, wherein the carbon-containing layer further comprises a carbon binder, and the carbon binder contains an N-vinylacetamide polymer.

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

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

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

7. The secondary battery according to any one of claims 1 to 6, wherein the negative electrode active material further comprises a carbon material.

8. The secondary battery according to any one of claims 1 to 7, wherein the secondary battery is a lithium-ion secondary battery.

9. A negative electrode for a secondary battery, comprising: a carbon-containing layer; and a negative electrode active material layer disposed on the carbon-containing layer, wherein the negative electrode active material layer comprises: a negative electrode active material containing a silicon-containing material; and a negative electrode binder containing an N-vinylacetamide polymer.

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