Negative electrode for secondary battery, and secondary battery

Abstract

Provided is a secondary battery with which excellent battery characteristics can be obtained. This secondary battery is provided with: a positive electrode; a negative electrode including a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent; and an electrolyte solution. The negative electrode active material contains a silicon-containing material, the negative electrode binder contains an N-vinyl acetamide polymer, and the negative electrode conductive agent contains a fibrous carbon material. In analysis of the negative electrode conductive agent using Raman spectroscopy, an absorption peak is detected within a Raman shift range of 120 cm-1 to 300 cm-1, and the half-value width of the absorption peak is 10 cm-1 or more.

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 provide a high energy density. This secondary battery includes a positive electrode, a negative electrode (negative electrode for secondary battery), and an electrolyte, and various studies have been conducted on the structure of this secondary battery.

[0003] Specifically, the negative electrode contains two types of negative electrode active materials and a binder (a polymer having an amide structural unit), and the mass ratio of the two types of negative electrode active materials is specified (for example, refer to Patent Document 1). The first negative electrode active material contains a carbon material, and the second negative electrode active material contains a material containing an element capable of inserting and extracting lithium ions (however, excluding carbon materials).

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2013-149395 Summary of the Invention

[0007] 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.

[0008] Therefore, a negative electrode for a secondary battery and a secondary battery that can achieve excellent battery characteristics are desired.

[0009] The negative electrode for a secondary battery according to one embodiment of the present technology includes a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent. The negative electrode active material contains a silicon-containing material, the negative electrode binder contains an N-vinylacetamide polymer, and the negative electrode conductive agent contains a fibrous carbon material. In the analysis of the negative electrode conductive agent using Raman spectroscopy, an absorption peak is detected in the range where the Raman shift is 120 cm -1 or more and 300 cm -1 or less, and the full width at half maximum of this absorption peak is 10 cm -1 or more.

[0010] In addition, a secondary battery according to one embodiment of the present technology includes a positive electrode, a negative electrode, and an electrolyte, and the negative electrode has the same structure as the negative electrode for a secondary battery according to one embodiment of the present technology described above.

[0011] Here, the "silicon-containing material" is a material containing silicon as a constituent element, and the "N-vinylacetamide polymer" is either or both of a homopolymer of N-vinylacetamide and a copolymer of N-vinylacetamide. In addition, details of each of the silicon-containing material and the N-vinylacetamide polymer will be described below.

[0012] In addition, the "half-value width" is the so-called full width at half maximum (FWHM (full width at half maximum)). In addition, details of the half-value width 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, the negative electrode for a secondary battery includes a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent. The negative electrode active material includes a silicon-containing material, the negative electrode binder includes an N-vinylacetamide polymer, and the negative electrode conductive agent includes a fibrous carbon material. In the analysis of the negative electrode conductive agent using Raman spectroscopy, the half-value width of the absorption peak detected in the range of 120 cm -1 or more and 300 cm -1 or less is 10 cm -1 or more, so 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 is a cross-sectional view showing the structure of a negative electrode for a secondary battery according to an embodiment of the present technology.

[0016] Figure 2 is a diagram showing an example of the analysis result of a negative electrode conductive agent using Raman spectroscopy.

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

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

[0019] Figure 5 is a block diagram showing the structure of an application example of a secondary battery.

[0020] Figure 6 is a cross-sectional view showing the structure of a test secondary battery. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] Hereinafter, an embodiment of the present technology will be described in detail with reference to the accompanying drawings. In addition, the order of description is as follows.

[0022] 1. Negative electrode for secondary battery

[0023] 1-1. Structure

[0024] 1-2. Physical properties

[0025] 1-3. Operation

[0026] 1-4. Manufacturing method

[0027] 1-5. Function and effect

[0028] 2. Secondary battery

[0029] 2-1. Structure

[0030] 2-2. Operation

[0031] 2-3. Manufacturing method

[0032] 2-4. Function and effect

[0033] 3. Modification example

[0034] 4. Use of secondary battery

[0035] <1. Negative electrode for secondary battery>

[0036] First, a negative electrode for a secondary battery (hereinafter simply referred to as "negative electrode") according to an embodiment of the present technology will be described.

[0037] 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.

[0038] During operation (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.

[0039] 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.

[0040] <1-1. Structure>

[0041] Figure 1 The cross-sectional structure of the negative electrode 1 as an example of the negative electrode is shown. As Figure 1As shown, the negative electrode 1 includes a negative electrode current collector 1A and a negative electrode active material layer 1B.

[0042] [Negative electrode current collector]

[0043] The negative electrode current collector 1A has a pair of surfaces on which the negative electrode active material layer 1B is provided. The negative electrode current collector 1A contains a conductive material such as a metal material, and specific examples of the conductive material are copper and the like.

[0044] 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 the negative electrode active material layer 1B 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.

[0045] [Negative electrode active material layer]

[0046] The negative electrode active material layer 1B contains a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent.

[0047] Here, the negative electrode active material layer 1B is provided on both sides of the negative electrode current collector 1A. However, the negative electrode active material layer 1B may also be provided only on one side of the negative electrode current collector 1A. In addition, the method of forming the negative electrode active material layer 1B is not particularly limited. Specifically, it is a coating method or the like.

[0048] (Negative electrode active material)

[0049] The negative electrode active material is a material for intercalating and deintercalating lithium, and contains any one or two or more of silicon-containing materials. This is because silicon has excellent lithium intercalation ability, so a high energy density can be obtained.

[0050] 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 monomer 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 of their phases. 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.

[0051] The monomer of silicon only refers to a general monomer, so it may also contain trace amounts of impurities. That is, the purity of the monomer of silicon is not necessarily limited to 100%.

[0052] The types of silicon alloys are not particularly limited. Specifically, as elements other than silicon, silicon alloys contain any one or more of the metal elements such as tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium as constituent elements.

[0053] However, silicon alloys are not limited to containing one or more metal elements as constituent elements, and may also contain one or more metal elements and one or more metalloid elements as constituent elements. In addition, silicon alloys may also contain one or more non-metal elements as constituent elements.

[0054] The types of silicon compounds are not particularly limited. Specifically, as elements other than silicon, silicon compounds contain any one or more of the non-metal elements such as oxygen and carbon as constituent elements. In addition, silicon compounds may also contain any one or more of the series of metal elements contained as constituent elements in the above-mentioned silicon alloys as constituent elements.

[0055] Specific examples of silicon alloys and silicon compounds are SiB 4 、SiB 6 、Mg 2 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 silicon alloys and silicon compounds are not limited to the compositions described herein and can be arbitrarily changed.

[0056] Here, when using silicon oxide (SiO xWhen it is a compound of silicon, during charge and discharge of the secondary battery using the negative electrode 1, there is a tendency for the irreversible capacity to increase. Therefore, when using silicon oxide as the compound of silicon, lithium can also be pre-doped in the silicon oxide. That is, in the state before the secondary battery is charged and discharged, lithium can also be pre-doped in the silicon oxide. This is because during charge and discharge of the secondary battery, a decrease in battery capacity caused by the irreversible capacity can be suppressed.

[0057] The crystalline state of the silicon-containing material is not particularly limited, and among them, an amorphous state is preferred. More specifically, in the analysis of the silicon-containing material using the X-ray diffraction method (XRD), it is preferably not to detect a crystalline peak at an attachment where the diffraction angle 2θ is 28° to 29°. This is because the formation of side reactants that are difficult to participate in the electrode reaction can be suppressed.

[0058] In addition, the surface of the silicon-containing material can also be covered with carbon. This is because the conductivity of the negative electrode active material is improved. In this case, carbon can cover the entire surface of the silicon-containing material, and carbon can also cover only a part of the surface of the silicon-containing material.

[0059] 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 can contain both the silicon-containing material and the carbon material. This is because while ensuring the battery capacity of the secondary battery using the negative electrode 1, damage to the negative electrode active material layer 1B can be suppressed.

[0060] 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, while obtaining a high theoretical capacity, the expansion and contraction of the negative electrode active material layer 1B during charge and discharge can be suppressed. Thus, as described above, damage to the negative electrode active material layer 1B can be suppressed while ensuring the battery capacity.

[0061] Specific examples of the carbon material are easily graphitizable carbon, hardly graphitizable carbon, and graphite (natural graphite and artificial graphite), etc.

[0062] When the negative electrode active material contains both the silicon-containing material and the carbon material, the mixing ratio of the silicon-containing material and the carbon material is not particularly limited. Among them, the weight ratio M of the weight M1 of the silicon-containing material to the sum of the weight M1 of the silicon-containing material and the weight M2 of the carbon material is preferably 30% by weight or more. This is because while further improving the battery capacity of the secondary battery using the negative electrode 1, damage to the negative electrode active material layer 1B can be further suppressed. This weight ratio M is calculated based on the calculation formula of weight ratio M = [M1 / (M1 + M2)] × 100.

[0063] In addition, the upper limit value of the weight ratio M is not particularly limited. Among them, it is preferably that the weight ratio M is 70% by weight or less. This is because the breakage of the negative electrode active material layer 1B can be sufficiently and stably suppressed.

[0064] (Negative electrode binder)

[0065] The negative electrode binder is a material that binds the negative electrode active material, the negative electrode conductive agent, etc. to each other, and contains any one or two or more of N-vinylacetamide polymers. This is because the physical strength of the negative electrode active material layer 1B is improved, so even if the electrode reaction is repeated, the negative electrode active material layer 1B will not break and is easy to maintain. Thereby, the generation of cracks in the negative electrode active material layer 1B can be suppressed, and the detachment of the negative electrode active material layer 1B from the negative electrode current collector 1A can also be suppressed.

[0066] As described above, the "N-vinylacetamide polymer" is one 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.

[0067] The copolymer of N-vinylacetamide is a compound copolymerized from N-vinylacetamide and one or two or more monomers (however, N-vinylacetamide is excluded). 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, and alkaline earth metal methacrylate, etc.

[0068] Specific examples of the alkali metal acrylate are lithium acrylate, sodium acrylate, and potassium acrylate, etc. Specific examples of the alkaline earth metal acrylate are calcium acrylate and magnesium acrylate, etc. Specific examples of the alkali metal methacrylate are lithium methacrylate, sodium methacrylate, and potassium methacrylate, etc. Specific examples of the alkaline earth metal methacrylate are calcium methacrylate and magnesium methacrylate, etc.

[0069] The copolymerization amount of the monomer in the copolymer of N-vinylacetamide is not particularly limited, and thus can be arbitrarily set.

[0070] Among them, the copolymer of N-vinylacetamide preferably contains a copolymer of N-vinylacetamide and an alkali metal acrylate. This is because, since the physical strength of the negative electrode active material layer 1B is sufficiently improved, even if the electrode reaction is repeated, the negative electrode active material layer 1B will not be sufficiently broken and is easy to maintain.

[0071] (Negative electrode conductive agent)

[0072] The negative electrode conductive agent is a material that improves the conductivity of the negative electrode active material layer 1B and includes any one or two or more of fibrous carbon materials. This is because, since the negative electrode active materials are easily electrically connected to each other via the negative electrode conductive agent, it is easy to form a conductive network inside the negative electrode active material layer 1B.

[0073] The type of the fibrous carbon material is not particularly limited. Specifically, it is a carbon nanotube or the like.

[0074] Among them, the fibrous carbon material preferably includes single-walled carbon nanotubes (SWCNT), and the purity of the single-walled carbon nanotubes is preferably high enough. This is because it is easier to form a conductive network inside the negative electrode active material layer 1B, so the conductivity of the negative electrode active material layer 1B is sufficiently improved.

[0075] The average fiber diameter of the fibrous carbon material is not particularly limited. Specifically, it is 5 nm or less. The content of the negative electrode conductive agent (fibrous carbon material) in the negative electrode active material layer 1B is not particularly limited. Among them, it is preferably 2% by weight or less. This is because, in the manufacturing process of the negative electrode 1 described later (when preparing the negative electrode mixture slurry), the dispersibility of the negative electrode conductive agent is improved, so the stability over time of the negative electrode mixture slurry is improved.

[0076] In particular, the negative electrode conductive agent containing the fibrous carbon material has specified physical properties determined by the analysis of the negative electrode conductive agent using Raman spectroscopy. In addition, the details of the physical properties of the negative electrode conductive agent will be described below (see Figure 2 ).

[0077] (Other materials)

[0078] In addition, the negative electrode active material layer 1B may further include any one or two or more of other materials.

[0079] Specific examples of the other materials are other negative electrode active materials, and the other negative electrode active materials include any one or two or more of metal-based materials. However, the above-mentioned silicon-containing materials are not included in the metal-based materials described herein.

[0080] The metal-based material is a material containing any one or two or more of metal elements and metalloid elements that can form an alloy with lithium as constituent elements. Specific examples of the metal elements and metalloid elements are tin and the like. The metal-based material can 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.

[0081] In addition, specific examples of other materials are other negative electrode binders, which include any one or two or more of synthetic rubbers and high molecular compounds. However, the above-mentioned N-acetamide polymer is not included in the other negative electrode binders described herein. Specific examples of synthetic rubbers are styrene-butadiene rubbers, fluorine rubbers, and ethylene-propylene-diene rubbers, etc. Specific examples of high molecular compounds are polyvinylidene fluoride, polyimide, and carboxymethyl cellulose, etc.

[0082] In addition to the N-vinylacetamide polymer, as other negative electrode binders, it is preferable to add styrene-butadiene rubber, polyimide, and carboxymethyl cellulose salts (sodium salt, potassium salt, lithium salt). By adding these other negative electrode binders, the cycle retention rate is improved. This is because, for styrene-butadiene rubber and polyimide, the network maintenance of electron conductivity is improved by the effect of increasing the adhesion force between active material particles and the current collector foil. In addition, carboxymethyl cellulose salt acts as a dispersant, whereby carbon nanotubes can be further dispersed in the electrode, thus improving the network maintenance of electron conductivity between active materials. As the addition amount of styrene-butadiene rubber, polyimide, and carboxymethyl cellulose salt, it is preferably 0.1 to 10% by weight, more preferably 0.2 to 5% by weight.

[0083] In addition, specific examples of other materials are other negative electrode conductive agents, which include any one or two or more of carbon materials, metal materials, and conductive high molecular compounds. However, the above-mentioned fibrous carbon material is not included in the other negative electrode conductive agents described herein. Specific examples of carbon materials are particulate carbon materials such as graphite, carbon black, acetylene black, and Ketjen black, etc. In addition, specific examples of carbon materials are other fibrous carbon materials such as carbon fibers and carbon nanofibers.

[0084] <1-2. Physical properties>

[0085] Figure 2 An example of the analysis result of a negative electrode conductive agent using Raman spectroscopy is shown. In Figure 2 , the horizontal axis represents the Raman shift (cm -1 ), and the vertical axis represents the Raman intensity (a.u. (arbitrary unit)).

[0086] [Physical property conditions]

[0087] When analyzing a negative electrode conductive agent containing a fibrous carbon material using Raman spectroscopy, the analysis result (Raman spectrum) shown in Figure 2 can be obtained. In this case, regarding the analysis result of the negative electrode conductive agent using Raman spectroscopy, it satisfies the specified physical property conditions.

[0088] Specifically, in the analysis of a negative electrode conductive agent using Raman spectroscopy, it is detected that at a Raman shift of 120 cm -1~300 cm -1 has a Raman peak (absorption peak P that bulges upward) with a vertex within the range of. In Figure 2 it shows a case where the Raman shift is 120 cm -1 ~300 cm -1 is shaded and 1 absorption peak P is detected.

[0089] The half-width HW of this absorption peak P is 10 cm -1 or more. In addition, the upper limit value of the half-width HW is not particularly limited. Specifically, it is preferably that the half-width HW is 50 cm -1 or less. As described above, this "half-width HW" is the full width at half maximum (FWHM). That is, the half-width HW is the width of the absorption peak P at the position where the difference between the minimum value and the maximum value of the Raman intensity (= maximum value of the Raman intensity - minimum value of the Raman intensity) is halved, and the width of this absorption peak P is the difference between the maximum value and the minimum value of the Raman shift (= maximum value of the Raman shift - minimum value of the Raman shift).

[0090] However, as Figure 2 shown, the minimum value of the Raman intensity is determined based on the baseline BL. This baseline BL is a line segment along the Raman spectrum in a state where the Raman spectrum is substantially horizontal due to the minimum (substantially constant) Raman intensity. That is, the baseline BL is a line segment extending substantially along the horizontal axis.

[0091] Regarding the physical properties of the negative electrode conductive agent containing the fibrous carbon material (analysis results of the negative electrode conductive agent using Raman spectroscopy), the physical property conditions are satisfied because the state of the negative electrode conductive agent is optimized. In this case, inside the negative electrode active material layer 1B, a conductive network is also formed by the negative electrode conductive agent in the minute regions between the negative electrode active materials, so the electron conductivity between the negative electrode active materials is significantly improved. Moreover, even if the negative electrode active material layer 1B containing a silicon-containing material expands and contracts due to repeated electrode reactions, the conductive network is not broken and is easily maintained. As a result, the conductivity of the negative electrode active material layer 1B is stably improved.

[0092] In particular, as described above, the fibrous carbon material preferably contains single-walled carbon nanotubes. This is because it is easy to satisfy the physical property conditions for the fibrous carbon material, so as described above, the conductivity of the negative electrode active material layer 1B can be sufficiently improved.

[0093] However, it is considered that whether the absorption peak P is detected depends on the purity of the single-walled carbon nanotubes. Specifically, it is considered that the absorption peak P is detected when the purity of the single-walled carbon nanotubes is sufficiently high, and in contrast, the absorption peak P cannot be detected when the purity of the single-walled carbon nanotubes is not high enough.

[0094] [Analysis steps]

[0095] Details of the analysis steps for the negative electrode conductive agent using Raman spectroscopy are as described below.

[0096] As the analysis device, a Raman spectroscopy device RAMAN-11 manufactured by Nanophoton Co., Ltd. etc. can be used. At the time of analysis, a laser (wavelength = 532 nm) and a spectroscope (600 gr / mm) are used, and the analysis range is set so that the entire negative electrode conductive agent to be analyzed is within the range. In addition, as described above, the full width at half maximum HW can be calculated based on the Raman intensity of the absorption peak P with respect to the baseline BL.

[0097] The steps for analyzing the negative electrode conductive agent using a secondary battery using the negative electrode conductive agent are as described below.

[0098] First, the negative electrode 1 is recovered by disassembling the secondary battery. Next, the negative electrode 1 is washed with a washing solvent to remove the electrolyte adhering to the negative electrode 1. The type of the washing solvent is not particularly limited, and specifically, it is any one or two or more of organic solvents (aprotic solvents) such as carbonate solvents, ketone solvents, and ester solvents. In addition, when there is a film remaining on the surface of the negative electrode 1, the negative electrode 1 can be further washed with an aqueous solvent such as water. Finally, as described above, Raman spectroscopy is used to analyze the negative electrode conductive agent contained in the negative electrode 1. Thus, it is investigated whether the absorption peak P (full width at half maximum HW ≥ 10 cm -1 ) is detected.

[0099] When investigating whether the absorption peak P is detected, in order to improve the detection accuracy of the absorption peak P, the steps of investigating whether the absorption peak P is detected can be repeated multiple times. In this case, in order to improve the calculation accuracy of the full width at half maximum HW, the steps of calculating the full width at half maximum HW can also be repeated multiple times, and the average value is adopted as the full width at half maximum HW.

[0100] In addition, in Figure 2 , as described above, the case where one absorption peak P is detected is shown. However, in some cases, a composite peak may be detected. This composite peak is a peak formed by the synthesis of two or more absorption peaks P, and has two or more vertices in the range of Raman shift of 120 cm -1 ~300 cm -1 .

[0101] In this case, by using an existing peak separation method to separate the synthesized peak, after obtaining two or more absorption peaks P, one absorption peak P with the largest Raman intensity (so-called peak intensity) is selected from the two or more absorption peaks P, and thus this one absorption peak P is adopted as the absorption peak P for calculating the full width at half maximum HW.

[0102] <1-3. Operation>

[0103] During the electrode reaction of the negative electrode 1, in the negative electrode active material layer 1B, lithium is intercalated into the negative electrode active material, and lithium is deintercalated from the negative electrode active material. In this case, lithium is intercalated and deintercalated in an ionic state.

[0104] <1-4. Manufacturing method>

[0105] The negative electrode 1 is manufactured by the steps of an example described below.

[0106] First, a negative electrode mixture is made by mixing 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 containing a fibrous carbon material. In this case, a fibrous carbon material that satisfies the above physical property conditions is used.

[0107] Next, the negative electrode mixture is put into a solvent to prepare a paste-like negative electrode mixture slurry. This solvent is an aqueous solvent such as ion-exchanged water.

[0108] Next, the negative electrode mixture slurry is coated on both sides of the negative electrode current collector 1A to form the negative electrode active material layer 1B. In this case, the negative electrode mixture slurry is also heated as needed.

[0109] Finally, the negative electrode active material layer 1B is compression-molded using a roll press or the like. In this case, the negative electrode active material layer 1B can be heated, and the compression molding can be repeated multiple times.

[0110] Thereby, the negative electrode active material layer 1B is formed on both sides of the negative electrode current collector 1A, and thus the negative electrode 1 is completed.

[0111] <1-5. Function and effect>

[0112] According to this negative electrode 1, the negative electrode 1 contains a negative electrode active material (silicon-containing material), a negative electrode binder (N-vinylacetamide polymer), and a negative electrode conductive agent (fibrous carbon material), and the full width at half maximum HW of the absorption peak P detected in the analysis of the negative electrode conductive agent using Raman spectroscopy is 10 cm -1 or less.

[0113] In this case, as described above, a series of operations described below can be obtained. First, since the negative electrode active material contains a silicon-containing material, a high energy density can be obtained. Second, since the negative electrode binder contains an N-vinylacetamide polymer, the physical strength of the negative electrode active material layer 1B is improved. Thus, even if the electrode reaction is repeated, the negative electrode active material layer 1B is not damaged and is easily maintained. Third, the negative electrode conductive agent contains a fibrous carbon material, and the physical property conditions are satisfied for this negative electrode conductive agent. Thus, inside the negative electrode active material layer 1B, a conductive network is formed using the negative electrode conductive agent even in a minute region between the negative electrode active materials, and even if the electrode reaction is repeated, the conductive network is not broken and is easily maintained.

[0114] According to the above, since the conductivity of the negative electrode active material layer 1B is stably improved, the battery characteristics of the secondary battery using the negative electrode 1 are improved. Thus, by using the negative electrode 1, a secondary battery having excellent battery characteristics can be realized.

[0115] In particular, if the fibrous carbon material contains single-walled carbon nanotubes, the negative electrode conductive agent easily satisfies the physical property conditions. Thus, since the conductivity of the negative electrode active material layer 1B is sufficiently improved, a higher effect can be obtained.

[0116] Furthermore, if the negative electrode active material further contains a carbon material, while ensuring the battery capacity of the secondary battery using the negative electrode 1, breakage of the negative electrode active material layer 1B can be suppressed, and thus a higher effect can be obtained.

[0117] In this case, if the weight ratio of the silicon-containing material is 30% by weight or more, while the battery capacity of the secondary battery using the negative electrode 1 can be further improved, breakage of the negative electrode active material layer 1B can be further suppressed, and thus a higher effect can be obtained.

[0118] <2. Secondary battery>

[0119] Next, a secondary battery according to an embodiment of the present technology to which the negative electrode 1 is applied will be described.

[0120] The secondary battery described herein is a secondary battery that can obtain a battery capacity by 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 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.

[0121] In addition, the charging capacity of the negative electrode is preferably greater than the discharging capacity of the positive electrode. That is, preferably, the electrochemical capacity per unit area of the negative electrode is greater than that of the positive electrode. This is to prevent lithium from depositing on the surface of the negative electrode during the charging process.

[0122] <2-1. Structure>

[0123] Figure 3 The three-dimensional structure of the secondary battery is shown, Figure 4 and the cross-sectional structure of the battery element 20 shown is enlarged. Figure 3 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 addition, in Figure 4 , only a part of the battery element 20 is shown.

[0124] As Figure 3 and Figure 4 shown, this 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 here is a laminated film type secondary battery using a flexible or pliable outer packaging film 10.

[0125] [Outer packaging film]

[0126] 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 in a state where the battery element 20 is housed inside. Thus, the outer packaging film 10 houses the positive electrode 21, the negative electrode 22, and the electrolyte described later.

[0127] Here, the outer packaging film 10 is a thin film-like component that is folded along the folding direction F. A recessed portion 10U (so-called deep drawing portion) for housing the battery element 20 is provided on the outer packaging film 10.

[0128] 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 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.

[0129] However, since the structure (number of layers) of the outer packaging film 10 as a laminated film is not particularly limited, it may be 1 layer or 2 layers, or may be 4 layers or more.

[0130] [Battery element]

[0131] As Figure 3 andFigure 4 As shown, the battery element 20 is a power generation element including a positive electrode 21, a negative electrode 22, a separator 23, and an electrolytic solution (not shown), and is housed inside the outer packaging film 10.

[0132] The battery element 20 is a so-called wound electrode body. That is, the positive electrode 21 and the negative electrode 22 are laminated on each other with the separator 23 interposed therebetween, and while facing each other with the separator 23 interposed therebetween, they are wound around a winding axis P. The winding axis P is an imaginary axis extending in the Y-axis direction.

[0133] The three-dimensional shape of the battery element 20 is not particularly limited. Here, since the battery element 20 is flat, the shape of the cross-section of the battery element 20 (the cross-section along the XZ plane) intersecting the winding axis P is a flat shape defined by a major axis J1 and a minor axis J2. The major axis J1 is an imaginary axis extending in the X-axis direction and having a length greater than that of the minor axis J2, and the minor axis J2 is an imaginary axis extending in the Z-axis direction intersecting the X-axis direction and having a length smaller than that of the major axis J1. Here, since the three-dimensional shape of the battery element 20 is a flat cylindrical shape, the cross-sectional shape of the battery element 20 is a flat approximate ellipse.

[0134] (Positive electrode)

[0135] As Figure 4 shown, the positive electrode 21 includes a positive electrode current collector 21A and a positive electrode active material layer 21B.

[0136] The positive electrode current collector 21A has a pair of surfaces on which the positive electrode active material layer 21B is provided. The positive electrode current collector 21A contains a conductive material such as a metal material, and specific examples of the conductive material are aluminum and the like.

[0137] 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 two or more of the positive electrode active materials that intercalate and deintercalate lithium. However, it may be 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 may be that the positive electrode active material layer 21B also contains any one or two 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 a coating method or the like.

[0138] The type of the positive electrode active material is not particularly limited. Specifically, it is a lithium-containing compound or 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 not particularly limited as long as it is an element other than lithium and transition metal elements respectively. 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. Specifically, it is an oxide, a phosphate compound, a silicate compound, a borate compound or the like.

[0139] 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 0.33 O 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 )O 2 and LiMn 2 O 4 etc. Specific examples of the phosphate compound are LiFePO 4 , LiMnPO 4 , LiFe 0.5 Mn 0.5 PO 4 and LiFe 0.3 Mn 0.7 PO 4 etc.

[0140] The positive electrode binder includes any one or two or more of materials such as synthetic rubber and polymer compounds. Specific examples of the synthetic rubber are styrene-butadiene rubber, fluorine rubber, ethylene-propylene-diene rubber, etc. Specific examples of the polymer compound are polyvinylidene fluoride, polyimide, carboxymethyl cellulose, etc.

[0141] The positive electrode conductive agent includes any one or two or more of conductive materials such as carbon materials, metal materials, and conductive polymer compounds. Specific examples of the carbon materials are graphite, carbon black, acetylene black, and Ketjen black, etc.

[0142] (Negative electrode)

[0143] The negative electrode 22 has the same structure as that of the above-mentioned negative electrode 1. That is, as Figure 4 shown, the negative electrode 22 includes a negative electrode current collector 22A and a negative electrode active material layer 22B. The structure of the negative electrode current collector 22A is the same as that of the negative electrode current collector 1A, and the structure of the negative electrode active material layer 22B is the same as that of the negative electrode active material layer 1B.

[0144] (Separator)

[0145] As Figure 4 shown, the separator 23 is an insulating porous membrane between the positive electrode 21 and the negative electrode 22, which prevents contact (short circuit) between the positive electrode 21 and the negative electrode 22 while allowing lithium ions to pass through. The separator 23 contains a polymer compound such as polyethylene.

[0146] (Electrolyte solution)

[0147] 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.

[0148] Here, the solvent includes 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, and lactone-based compounds, etc. This is because the dissociation of the electrolyte salt is improved, and the ion mobility is also improved.

[0149] 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.

[0150] The carboxylate-based compounds are chain carboxylates, etc. Specific examples of the chain carboxylates are ethyl acetate, ethyl propionate, propyl propionate, and ethyl trimethylacetate, etc. The lactone-based compounds are lactones, etc. Specific examples of the lactones are γ-butyrolactone and γ-valerolactone, etc. In addition, the ethers can also be 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, and 1,4-dioxane, etc.

[0151] The electrolyte salt includes any one or two or more of light metal salts such as lithium salts. Specific examples of the lithium salts are lithium hexafluorophosphate (LiPF6 ), lithium tetrafluoroborate (LiBF 4 ), lithium trifluoromethanesulfonate (LiCF 3 SO 3 ), lithium bis(fluorosulfonyl)imide (LiN(FSO 2 )) 2 ), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF 3 SO 2 )) 2 ), lithium tris(trifluoromethanesulfonyl)methide (LiC(CF 3 SO 2 )) 3 ), lithium bis(oxalato)borate (LiB(C 2 O 4 )) 2 ), lithium monofluorophosphate (Li 2 PFO 3 ), and lithium difluorophosphate (LiPF 2 O 2 ), etc. This is because a high battery capacity can be obtained.

[0152] 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.

[0153] In addition, the electrolyte can also contain any one or two or more of the additives. This is because the electrochemical stability of the electrolyte is improved. The types of additives are not particularly limited. Specifically, they are unsaturated cyclic carbonates, fluorinated cyclic carbonates, sulfonates, phosphates, acid anhydrides, nitrile compounds, and isocyanate compounds, etc.

[0154] Specific examples of the unsaturated cyclic carbonates are vinylene carbonate, ethylene vinyl carbonate, and methylene vinyl carbonate, etc. Specific examples of the fluorinated cyclic carbonates are fluoroethylene carbonate and difluoroethylene carbonate, etc. Specific examples of the sulfonates are propane sultone and propene sultone, etc. Specific examples of the phosphates are trimethyl phosphate and triethyl phosphate, etc. Specific examples of the acid anhydrides are succinic anhydride, 1,2-ethanedisulfonic anhydride, and 2-sulfobenzoic anhydride, etc. Specific examples of the nitrile compounds are succinonitrile, etc. Specific examples of the isocyanate compounds are hexamethylene diisocyanate, etc.

[0155] [Positive electrode lead and negative electrode lead]

[0156] As Figure 3 and Figure 4As shown, the positive electrode lead 31 is a positive electrode terminal connected to the positive electrode current collector 21A of the positive electrode 21 and is led out to the outside of the outer packaging film 10. The positive electrode lead 31 contains a conductive material such as a metal material, and specific examples of such a conductive 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, etc.

[0157] [Negative electrode lead]

[0158] As Figure 3 and Figure 4 shown, the negative electrode lead 32 is a negative electrode terminal connected to the negative electrode current collector 22A of the negative electrode 22 and is led out to the outside of the outer packaging film 10. The negative electrode lead 32 contains a conductive material such as a metal material, and specific examples of such a conductive 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.

[0159] [Sealing film]

[0160] 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.

[0161] 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. Specifically, the sealing film 41 contains a polymer compound such as polyolefin having adhesiveness to the positive electrode lead 31, and specific examples of such a polyolefin are polypropylene and the like.

[0162] 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 contains a polymer compound such as polyolefin having adhesiveness to the negative electrode lead 32.

[0163] <2-2. Operation>

[0164] The secondary battery operates as follows during charge and discharge.

[0165] 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.

[0166] <2-3. Manufacturing method>

[0167] In the case of manufacturing a secondary battery, after separately fabricating a positive electrode 21 and a negative electrode 22 through the steps of an example described below and preparing an electrolytic solution, the secondary battery is assembled using the positive electrode 21, the negative electrode 22, and the electrolytic solution, and the assembled secondary battery is subjected to a stabilization treatment.

[0168] [Fabrication of Positive Electrode]

[0169] 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 surfaces of the positive electrode current collector 21A, 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 compression molding can be repeated multiple times. Thus, the positive electrode active material layer 21B is formed on both surfaces of the positive electrode current collector 21A, thereby fabricating the positive electrode 21.

[0170] [Fabrication of Negative Electrode]

[0171] Using the same steps as those for fabricating the above-described negative electrode 1, a negative electrode active material layer 22B is formed on both surfaces of the negative electrode current collector 22A, thereby fabricating the negative electrode 22.

[0172] [Preparation of Electrolytic Solution]

[0173] An electrolyte salt is put into a solvent. Thus, the electrolyte salt is dispersed or dissolved in the solvent, thereby preparing the electrolytic solution.

[0174] [Assembly of Secondary Battery]

[0175] First, using a joining method such as a welding method, a positive electrode lead 31 is connected to the positive electrode current collector 21A of the positive electrode 21, and using a joining method such as a welding method, a negative electrode lead 32 is connected to the negative electrode current collector 22A of the negative electrode 22.

[0176] Next, the positive electrode 21 and the negative electrode 22 are stacked on top of each other with a separator 23 interposed therebetween, and then the positive electrode 21, the negative electrode 22, and the separator 23 are wound, thereby fabricating a wound body (not shown). Next, the wound body is pressed using a press or the like, thereby molding the wound body into a flat shape. Except that the positive electrode 21, the negative electrode 22, and the separator 23 are not impregnated with the electrolytic solution, the wound body has the same structure as that of the battery element 20.

[0177] Next, after housing the wound body inside the recessed portion 10U, the outer packaging film 10 (welding layer / metal layer / surface protective layer) is folded so that the outer packaging films 10 face each other. Next, using an adhesion method such as a hot melt method, the outer peripheral edge portions of two sides in the welding layers facing each other are joined to each other, thereby housing the wound body inside the bag-shaped outer packaging film 10.

[0178] Finally, after injecting the electrolytic solution 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 using an adhesion method such as a hot melt 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.

[0179] Thereby, the electrolytic solution is impregnated into the wound body, thereby manufacturing the battery element 20 as a wound electrode body, and the battery element 20 is sealed inside the bag-shaped outer packaging film 10, thereby assembling a secondary battery.

[0180] [Stabilization of secondary battery]

[0181] 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 stable. Thereby, the secondary battery is completed.

[0182] <2-4. Function and effect>

[0183] According to this secondary battery, the secondary battery includes a negative electrode 22 having the same structure as that of the negative electrode 1. Therefore, for the above reasons, the conductivity of the negative electrode active material layer 22B is stably improved, and thus excellent battery characteristics can be obtained.

[0184] 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 obtained.

[0185] Other functions and effects related to this secondary battery are the same as other functions and effects related to the negative electrode 1.

[0186] <3. Modification example>

[0187] Next, a modification example of the above secondary battery will be described.

[0188] As described below, the structure of the secondary battery can be appropriately changed. In addition, a series of modification examples described below can also be combined with each other.

[0189] [Modification Example 1]

[0190] The separator 23 which is a porous membrane is used. However, although not specifically illustrated here, a laminated separator including a polymer compound layer may also be used.

[0191] 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, so that the winding deviation of the battery element 20 can be suppressed. Thus, 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.

[0192] 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, so that 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, silica, titanium oxide, magnesium oxide, and zirconia. Specific examples of the resin materials are acrylic resin and styrene resin.

[0193] In the case of manufacturing the laminated separator, a precursor solution containing a polymer compound and a solvent is prepared, and then the precursor solution is coated on one or both surfaces of the 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.

[0194] In the case where the laminated separator is used, lithium can also move between the positive electrode 21 and the negative electrode 22, so that 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.

[0195] [Modification Example 2]

[0196] An electrolytic solution which is a liquid electrolyte is used. However, although not specifically illustrated here, an electrolyte layer which is a gel-like electrolyte may also be used.

[0197] In a battery element 20 including an electrolyte layer, a positive electrode 21 and a negative electrode 22 are stacked on top of each other with a 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 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 only between the negative electrode 22 and the separator 23.

[0198] 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 and the like. When forming the electrolyte layer, a precursor solution containing the electrolytic solution, the polymer compound, and a solvent is prepared, and then the precursor solution is coated on one side or both sides of each of the positive electrode 21 and the negative electrode 22.

[0199] When this electrolyte layer is used, 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.

[0200] <4. Applications of the secondary battery>

[0201] Finally, the applications (application examples) of the secondary battery will be described.

[0202] The applications of the secondary battery are not particularly limited. The secondary battery used as a power source can be the main power source of electronic devices, electric vehicles, etc., or an auxiliary power source. The main power source refers to the power source that is preferentially used, regardless of the presence or absence of other power sources. The auxiliary power source can be a power source used instead of the main power source or a power source switched from the main power source.

[0203] Specific examples of the applications of the secondary battery are as follows: electronic devices such as cameras, digital still cameras, mobile phones, laptop computers, stereo headphones, portable radios, and portable information terminals; storage devices such as backup power sources 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 cars (including hybrid vehicles); power storage systems such as household or industrial battery systems that store electricity in advance to prepare for emergencies, etc. In these applications, one secondary battery or multiple secondary batteries can be used.

[0204] The battery pack may include a single battery or a battery pack. An electric vehicle is a vehicle that runs using a secondary battery as a driving power source, and may also be a hybrid vehicle that simultaneously has a driving source other than the secondary battery. In a household power storage system, the power stored in the secondary battery as a power storage source can be used to operate household electrical products.

[0205] Here, an example of the use of the secondary battery will be specifically described. The structures described below are merely examples, and thus can be appropriately changed.

[0206] Figure 5 The module structure of a battery pack as an application example of the secondary battery is shown. The battery pack described here is a battery pack (so-called soft pack) that uses one secondary battery and is mounted in electronic devices typified by a smartphone.

[0207] As Figure 5 shown, the battery pack includes a power source 51 and a circuit board 52. The circuit board 52 is connected to the power source 51 and includes a positive terminal 53, a negative terminal 54, and a temperature detection terminal 55.

[0208] The power source 51 includes one secondary battery. In this secondary battery, the positive lead is connected to the positive terminal 53, and the negative lead is connected to the negative terminal 54. Since the power source 51 is connected to an external power source via the positive terminal 53 and the negative terminal 54, charging and discharging can be performed. The circuit board 52 includes a control unit 56, a switch 57, a thermistor element (so-called PTC element) 58, and a temperature detection unit 59. However, the PTC element 58 may be omitted.

[0209] 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 source 51 as needed.

[0210] In addition, when the voltage of the power source 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 source 51. The overcharge detection voltage is not particularly limited, specifically 4.20V ± 0.05V, and the overdischarge detection voltage is not particularly limited, specifically 2.40V ± 0.10V.

[0211] 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 source 51 and an external device according to an instruction from 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.

[0212] 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 heat generation and in cases where the control unit 56 performs correction processing when calculating the remaining capacity, etc.

[0213] Example

[0214] Examples of the present technology will be described.

[0215] <Experimental Examples 1 to 13 and Comparative Examples 1 to 6>

[0216] After manufacturing the secondary battery, the characteristics of the secondary battery were evaluated.

[0217] [Manufacture of Secondary Battery]

[0218] The secondary battery (laminated film type lithium ion secondary battery) shown in Figure 3 and Figure 4 was manufactured through the steps described below.

[0219] (Manufacture of Positive Electrode)

[0220] First, 95 parts by mass of a positive electrode active material (lithium cobaltate (LiCoO 2 ), which is a lithium-containing compound (oxide)), 3 parts by mass of a positive electrode binder (polyvinylidene fluoride), and 2 parts by mass of a positive electrode conductive agent (Ketjenblack, which is an amorphous carbon powder) were mixed with each other to prepare a positive electrode mixture. Next, the positive electrode mixture was put into a solvent (N-methyl-2-pyrrolidone, which is an organic solvent), and then the solvent was stirred to prepare a paste-like positive electrode mixture slurry.

[0221] Next, the positive electrode mixture slurry was coated on both surfaces of a positive electrode current collector 21A (aluminum foil with a thickness of 10 μm), and then the positive electrode mixture slurry was dried with hot air to form a positive electrode active material layer 21B.

[0222] Finally, the positive electrode active material layer 21B was compression-molded using a roll press, and then the positive electrode current collector 21A having the positive electrode active material layer 21B formed thereon was cut into strips (width = 70 mm × length = 800 mm). Thus, the positive electrode 21 was manufactured.

[0223] (Manufacture of Negative Electrode)

[0224] First, 94 parts by mass of a negative electrode active material (a mixture of a silicon material and a carbon material, or a silicon material), 5 parts by mass of a negative electrode binder (an N-vinylacetamide (NVA) polymer), 0.3 parts by mass of a negative electrode conductive agent (single-walled carbon nanotubes (SWCNT) as a fibrous carbon material), and 0.7 parts by mass of another negative electrode conductive agent (carbon black as a particulate carbon material) are mixed with each other to obtain a negative electrode mixture. In addition, in Table 1 and Table 2, the description of the other negative electrode conductive agent is omitted.

[0225] When using a mixture of a silicon material and a carbon material as the negative electrode active material, silicon oxide (SiO x ) is used as the silicon material, and mesocarbon microbeads (MCMB) are used as the carbon material. When using only a silicon material as the negative electrode active material, as the silicon material, silicon monomer (Si), silicon-titanium alloy (SiTi 0.01 ) as an alloy of silicon, or silicon oxide (SiO) as a compound of silicon is used. The mixing ratio (content (wt%)) of the negative electrode active material is as shown in Table 1 and Table 2.

[0226] As the negative electrode binder (N-vinylacetamide polymer), a homopolymer of N-vinylacetamide (poly-N-vinylacetamide (PNVA)) or a copolymer of N-vinylacetamide is used, and as the copolymer of N-vinylacetamide, a copolymer of N-vinylacetamide and an alkali metal salt of acrylic acid is used.

[0227] As the copolymer of N-vinylacetamide and an alkali metal salt of acrylic acid, a copolymer of N-vinylacetamide and lithium acrylate (NVA-AALi), a copolymer of N-vinylacetamide and sodium acrylate (NVA-AANa), or a copolymer of N-vinylacetamide and potassium acrylate (NVA-AAK) is used. The copolymerization amount of the monomer (lithium acrylate, sodium acrylate, or potassium acrylate) in the copolymer of N-vinylacetamide is 10 wt%.

[0228] In particular, when using a mixture of a silicon material and a carbon material as the negative electrode active material, by changing the mixing ratio of the silicon material and the carbon material, as shown in Table 1 and Table 2, the weight ratio (wt%) of the silicon material is adjusted.

[0229] In addition, as other negative electrode binders, styrene-butadiene rubber (SBR) is further added in Example 11, polyimide (PI) is further added in Example 12, and carboxymethyl cellulose salt (CMCN) is further added in Example 13, and their contents (wt%) are as shown in Table 1, respectively.

[0230] In addition, as the negative electrode conductive agent, a fibrous carbon material (high-purity single-walled carbon nanotube) in which an absorption peak P (half-value width HW ≥ 10 cm -1 ) was detected in the analysis of the negative electrode conductive agent using Raman spectroscopy was used.

[0231] Next, the negative electrode mixture was put into a solvent (ion-exchanged water as an aqueous solvent), and then the solvent was kneaded and stirred using a rotation-revolution mixer, thereby preparing a paste-like negative electrode mixture slurry.

[0232] Next, the negative electrode mixture slurry was coated on both surfaces of the negative electrode current collector 22A (copper foil with a thickness of 8 μm), and then the negative electrode mixture slurry was dried by hot air, thereby forming the negative electrode active material layer 22B.

[0233] Finally, the negative electrode active material layer 22B was compression-molded using a roll press, and then the negative electrode current collector 22A having the negative electrode active material layer 22B formed thereon was cut into strips (width = 72 mm × length = 810 mm). Thus, the negative electrode 22 was fabricated.

[0234] In addition, for comparison, as shown in Table 2, except that a fibrous carbon material (low-purity single-walled carbon nanotube) in which absorption peak P (half-peak width HW ≥ 10 cm -1 ) was not detected was used as the negative electrode conductive agent, the negative electrode 22 was fabricated through the same steps. In the column of "absorption peak" shown in Table 1 and Table 2, "detected" means that absorption peak P was detected, and "not detected" means that absorption peak P was not detected.

[0235] In addition, for comparison, as shown in Table 2, polyacrylic acid (PAA) was used as the negative electrode conductive agent instead of the N-vinylacetamide polymer, and the negative electrode 22 was fabricated through the same steps except for this.

[0236] (Preparation of electrolyte solution)

[0237] An electrolyte salt (lithium hexafluorophosphate (LiPF 6 )) was added to a solvent (ethylene carbonate as a cyclic carbonate and ethyl methyl carbonate as a chain carbonate), and then the solvent was stirred. In this case, the mixing ratio (mass ratio) of the solvents was ethylene carbonate:ethyl methyl carbonate = 50:50, and the content of the electrolyte salt relative to the solvent was 1 mol / l (= 1 mol / dm 3 ). Thus, the electrolyte solution was prepared.

[0238] (Assembly of secondary battery)

[0239] First, the positive electrode lead 31 (aluminum foil) is welded to the positive electrode current collector 21A of the positive electrode 21, and the negative electrode lead 32 (copper foil) is welded to the negative electrode current collector 22A of the negative electrode 22.

[0240] Next, the positive electrode 21 and the negative electrode 22 are stacked on top of each other with the separator 23 (a microporous polyethylene film with a thickness of 25 μm) in between, and then the positive electrode 21, the negative electrode 22, and the separator 23 are wound around each other to fabricate a wound body. Next, the wound body is pressed using a press to form the wound body into a flat shape.

[0241] Next, the outer packaging film 10 is folded in such a way as to sandwich the wound body accommodated inside the recessed portion 10U. As the outer packaging film 10, an aluminum laminated film is used which has, from the inside, a fusion layer (a polypropylene film with a thickness of 30 μm), a metal layer (an aluminum foil with a thickness of 40 μm), and a surface protective layer (a nylon film with a thickness of 25 μm) laminated in that order. Next, the outer peripheral edge portions of two sides in the fusion layers facing each other are heat-sealed to each other, thereby accommodating the wound body inside the bag-shaped outer packaging film 10.

[0242] 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 fusion layers facing each other are heat-sealed to each other in a reduced-pressure environment. In this case, a sealing film 41 (a polypropylene film with a thickness of 5 μm) is inserted between the outer packaging film 10 and the positive electrode lead 31, and a sealing film 42 (a polypropylene film with a thickness of 5 μm) is inserted between the outer packaging film 10 and the negative electrode lead 32.

[0243] As a result, the electrolytic solution is impregnated into the wound body, thereby fabricating the battery element 20. Therefore, the battery element 20 is enclosed inside the outer packaging film 10 and assembled into a secondary battery.

[0244] (Stabilization of the secondary battery)

[0245] The secondary battery is charged and discharged for 1 cycle in a normal temperature environment (temperature = 23°C). During charging, constant current charging is performed at a current of 0.2C until the voltage reaches 4.4V, and then constant voltage charging is performed at the voltage of 4.4V until the current reaches 0.025C. During discharging, constant current discharging is performed at a current of 0.2C until the voltage reaches 3.0V. 0.2C refers to the current value that completely discharges the battery capacity (theoretical capacity) in 5 hours, and 0.025C refers to the current value that completely discharges the battery capacity in 40 hours.

[0246] As a result, 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 stable. Therefore, the secondary battery is completed.

[0247] (Design of the capacity ratio)

[0248] Figure 6 The cross-sectional structure of a test (coin-type) secondary battery is shown. In the case of manufacturing the above-described laminated film-type secondary battery, the capacity ratio was designed using the coin-type secondary battery through the steps described below.

[0249] In the coin-type secondary battery, as Figure 6 shown, the test electrode 61 is housed inside the container-shaped outer packaging cup 64, and the counter electrode 62 is housed inside the container-shaped outer packaging can 65. The test electrode 61 and the counter electrode 62 are stacked on top of each other with a separator 63 in between, and the outer packaging cup 64 and the outer packaging can 65 are riveted to each other with a gasket 66. The electrolyte is impregnated in each of the test electrode 61, the counter electrode 62, and the separator 63, and it has the above-described structure.

[0250] In the case of designing the capacity ratio, first, the positive electrode 21 was manufactured through the same steps except that the positive electrode active material layer 21B was formed only on one side of the positive electrode current collector 21A. In addition, the negative electrode 22 was manufactured through the same steps except that the negative electrode active material layer 22B was formed only on one side of the negative electrode current collector 22A.

[0251] Next, a coin-type first secondary battery was manufactured using the positive electrode 21 as the test electrode 61 and a lithium metal plate as the counter electrode 62. In addition, a coin-type second secondary battery was manufactured by using the negative electrode 22 as the test electrode 61 and a lithium metal plate as the counter electrode 62.

[0252] Next, the first secondary battery was charged, and thereby the capacitance was measured. Then, based on this capacitance and the thickness of the positive electrode active material layer 21B, the charging capacity of the positive electrode 21 per unit thickness of the positive electrode active material layer 21B was calculated. During charging, constant current charging was performed at a current of 0.1C until the voltage reached 4.45V, and then constant voltage charging was performed at this voltage of 4.45V until the current decreased to 1 / 10. 0.1C refers to the current value that completely discharges the battery capacity in 10 hours.

[0253] Next, the second secondary battery was charged, and thereby the capacitance was measured. Then, based on this capacitance and the thickness of the negative electrode active material layer 22B, the charging capacity of the negative electrode 22 per unit thickness of the negative electrode active material layer 22B was calculated. During charging, constant current charging was performed at a current of 0.1C until the voltage reached 0V, and then constant voltage charging was performed at this voltage of 0V until the current decreased to 1 / 10.

[0254] Finally, the capacity ratio was calculated based on the charging capacity of the positive electrode 21 and the charging capacity of the negative electrode 22. This capacity ratio is calculated based on the calculation formula of capacity ratio = charging capacity of positive electrode 21 / charging capacity of negative electrode 22.

[0255] In the case of manufacturing a secondary battery of a laminated film type, the concentrations and coating speeds of the positive electrode mixture paste and the negative electrode mixture paste were adjusted so that the capacity ratio was 0.9.

[0256] [Evaluation of battery characteristics]

[0257] Through the steps described below, as battery characteristics, the cycle characteristics and the battery capacity characteristics were evaluated, and the results shown in Table 1 and Table 2 were obtained.

[0258] [Cycle characteristics]

[0259] First, the secondary battery was charged and discharged in a normal temperature environment (temperature = 23°C), and the discharge capacity (the discharge capacity of the first cycle) was measured. Next, in the same environment, the secondary battery was repeatedly charged and discharged until the number of cycles reached 100 cycles, and the discharge capacity (the discharge capacity of the 100th cycle) was measured. Finally, based on the calculation formula of the capacity retention rate (%) = (the discharge capacity of the 100th cycle / the discharge capacity of the first cycle) × 100, the capacity retention rate, which is an index for evaluating the cycle characteristics, was calculated.

[0260] The charge-discharge conditions of the first cycle were the same as the charge-discharge conditions during the stabilization of the secondary battery. The charge-discharge conditions after the second cycle were the same as the charge-discharge conditions during the stabilization of the secondary battery except that the charging current and the discharging current were changed to 0.5C respectively. 0.5C refers to the current value that completely discharges the battery capacity in 2 hours.

[0261] [Battery capacity characteristics]

[0262] The above-mentioned secondary battery was charged and discharged, and the negative electrode capacity (mAh / g), which is an index for evaluating the battery capacity characteristics, was calculated.

[0263] Specifically, first, the secondary battery was charged. In this case, as described above, constant current charging was performed at a current of 0.1C until the voltage reached 0V, and then constant voltage charging was performed at this 0V voltage until the current decreased to 1 / 10.

[0264] Next, the secondary battery was discharged, and the discharge capacity (mAh) was measured. In this case, constant current discharge was performed at a current of 0.1C until the voltage reached 1.5V.

[0265] Finally, the discharge capacity was divided by the weight (g) of the negative electrode active material, and the negative electrode capacity was calculated. In addition, the values of the negative electrode capacity shown in Table 1 and Table 2 are values standardized with the value of the negative electrode capacity in Example 4 as 100.

[0266] [Table 1]

[0267]

[0268] [Table 2]

[0269]

[0270] [Investigation]

[0271] As shown in Table 1 and Table 2, the capacity retention rate varies significantly depending on the structure of the negative electrode binder and the physical properties of the negative electrode conductive agent.

[0272] Hereinafter, the case where the negative electrode binder does not contain an N-vinylacetamide polymer and no absorption peak P (half-value width HW≥10 cm -1 ) is detected in the analysis of the negative electrode conductive agent (fibrous carbon material) using Raman spectroscopy (Comparative Example 1) is used as a comparison reference.

[0273] When the negative electrode binder does not contain an N-vinylacetamide polymer but an absorption peak P is detected in the analysis of the negative electrode conductive agent using Raman spectroscopy (Comparative Example 2), the capacity retention rate slightly increases. The increase ratio of the capacity retention rate in this case is 25%.

[0274] In addition, when the negative electrode binder contains an N-vinylacetamide polymer but no absorption peak P is detected in the analysis of the negative electrode conductive agent using Raman spectroscopy (Comparative Example 3), the capacity retention rate slightly increases. The increase ratio of the capacity retention rate in this case is approximately 15%.

[0275] Thus, when the negative electrode binder contains an N-vinylacetamide polymer and an absorption peak P is detected in the analysis of the negative electrode conductive agent using Raman spectroscopy, it is expected that the capacity retention rate will slightly increase. In this case, the expected increase ratio of the capacity retention rate is approximately 40% (=25% + 15%).

[0276] However, in fact, a result that contradicts the above expectation was obtained. That is, when the negative electrode binder contains an N-vinylacetamide polymer and an absorption peak P is detected in the analysis of the negative electrode conductive agent using Raman spectroscopy (Example 1), the capacity retention rate significantly slightly increases. The increase ratio of the capacity retention rate in this case is approximately 79%, which is approximately twice the expected increase ratio (= approximately 40%).

[0277] Thus, even when the type and composition of the negative electrode active material are changed (Examples 2 to 13), a significantly high capacity retention rate is obtained.

[0278] In particular, when the negative electrode binder contains an N-vinylacetamide polymer and an absorption peak P is detected in the analysis of the negative electrode conductive agent using Raman spectroscopy (Examples 1 to 13), a series of tendencies described below were obtained.

[0279] First, when using single-walled carbon nanotubes as the negative electrode conductive agent (fibrous carbon material), a sufficiently high capacity retention rate was obtained. Second, regardless of the type of the negative electrode binder (N-vinylacetamide polymer) (homopolymer of N-vinylacetamide or copolymer of N-vinylacetamide), a sufficiently high capacity retention rate was obtained. Third, compared with the case of using only a silicon-containing material as the negative electrode active material, when both a silicon-containing material and a carbon material are used as the negative electrode active material, the capacity retention rate further increases. Fourth, when both a silicon-containing material and a carbon material are used as the negative electrode active material, if the weight ratio is 30% by weight or more, the negative electrode capacity can be further increased while maintaining a high capacity retention rate.

[0280] In addition, it was confirmed that, in addition to the N-vinylacetamide polymer, by adding styrene-butadiene rubber (SBR), polyimide (PI), or carboxymethylcellulose salt (CMCN) as other negative electrode binders, the capacity retention rate was improved (Examples 11 to 13).

[0281] [Summary]

[0282] According to the results shown in Table 1 and Table 2, if the negative electrode 22 contains a negative electrode active material (silicon-containing material), a negative electrode binder (N-vinylacetamide polymer), and a negative electrode conductive agent (fibrous carbon material), and the half-value width HW of the absorption peak P detected in the analysis of the negative electrode conductive agent using Raman spectroscopy is 10 cm -1 , a high capacity retention rate can be obtained. Therefore, the cycle characteristics are improved, and a secondary battery having excellent battery characteristics is obtained.

[0283] As described above, one embodiment and one example of the present technology have been described, but the structure of the present technology is not limited to the structures described in one embodiment and one example, and thus various modifications can be made.

[0284] 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.

[0285] 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 can be a stacked type, a repeatedly folded type, or the like. 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.

[0286] 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, or alkaline earth metals such as beryllium, magnesium, and calcium. In addition, the electrode reaction material can also be other light metals such as aluminum.

[0287] The effects described in this specification are only 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 with respect to the present technology.

[0288] In addition, the following structure can also be adopted for the present technology.

[0289] <1>

[0290] A secondary battery comprising:

[0291] A positive electrode;

[0292] A negative electrode including a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent; and

[0293] An electrolytic solution,

[0294] wherein the negative electrode active material contains a silicon-containing material,

[0295] the negative electrode binder contains an N-vinylacetamide polymer,

[0296] the negative electrode conductive agent contains a fibrous carbon material,

[0297] in the analysis of the negative electrode conductive agent using Raman spectroscopy, an absorption peak is detected in the range where the Raman shift is 120 cm -1 or more and 300 cm -1 or less,

[0298] and the half-value width of the absorption peak is 10 cm -1 or more.

[0299] <2>

[0300] The secondary battery according to <1>,

[0301] wherein the fibrous carbon material contains single-walled carbon nanotubes.

[0302] <3>

[0303] The secondary battery according to <1> or <2>

[0304] The negative electrode active material further includes a carbon material.

[0305] <4>

[0306] The secondary battery according to <3>

[0307] 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 30% by weight or more.

[0308] <5>

[0309] The secondary battery according to any one of <1> to <4>

[0310] The secondary battery is a lithium ion secondary battery.

[0311] <6>

[0312] A negative electrode for a secondary battery

[0313] comprising a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent

[0314] The negative electrode active material includes a silicon-containing material

[0315] The negative electrode binder includes an N-vinylacetamide polymer

[0316] The negative electrode conductive agent includes a fibrous carbon material

[0317] In the analysis of the negative electrode conductive agent using Raman spectroscopy, an absorption peak is detected in the range where the Raman shift is 120 cm -1 or more and 300 cm -1 or less

[0318] The half-value width of the absorption peak is 10 cm -1 or more.

Claims

1. A secondary battery, comprising: a positive electrode; a negative electrode including a negative active material, a negative binder, and a negative conductive agent; and an electrolyte, wherein the negative active material includes a silicon-containing material, the negative binder includes an N-vinylacetamide polymer, the negative conductive agent includes a fibrous carbon material, In the analysis of the negative electrode conductive agent using Raman spectroscopy, an absorption peak is detected in the range where the Raman shift is 120 cm -1 or more and 300 cm -1 or less. The full width at half maximum of the absorption peak is 10 cm -1 or more.

2. The secondary battery according to claim 1, wherein the fibrous carbon material includes single-walled carbon nanotubes.

3. The secondary battery according to claim 1 or 2, wherein the negative active material further includes a carbon material.

4. The secondary battery according to claim 3, wherein the ratio of the weight of the silicon-containing material to the sum of the weights of the silicon-containing material and the carbon material is 30% by weight or more.

5. The secondary battery according to any one of claims 1 to 4, wherein the secondary battery is a lithium ion secondary battery.

6. A negative electrode for a secondary battery, including a negative active material, a negative binder, and a negative conductive agent, wherein the negative active material includes a silicon-containing material, the negative binder includes an N-vinylacetamide polymer, the negative conductive agent includes a fibrous carbon material, In the analysis of the negative electrode conductive agent using Raman spectroscopy, an absorption peak is detected in the range where the Raman shift is 120 cm -1 or more and 300 cm -1 or less. The full width at half maximum of the absorption peak is 10 cm -1 or more.

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