Negative electrode for secondary battery and secondary battery

Abstract

A secondary battery includes: a positive electrode; a negative electrode comprising a plurality of first fibrous portions, a plurality of particle portions, and a plurality of second fibrous portions, and having a plurality of voids; and an electrolyte. The plurality of first fibrous portions are interconnected to form a three-dimensional network structure with a plurality of voids, each of the plurality of first fibrous portions containing carbon as a constituent element. The plurality of particle portions cover the surfaces of each of the plurality of first fibrous portions, a portion of which is interconnected, each of which contains silicon as a constituent element. At least a portion of the plurality of second fibrous portions is connected to the surfaces of the plurality of particle portions, each of which contains carbon as a constituent element. The average fiber diameter of the plurality of first fibrous portions is 50 nm or more and 7000 nm or less, the average fiber diameter of the plurality of second fibrous portions is 1 nm or more and 200 nm or less, and the porosity of the negative electrode is 42% by volume or more and 73% by volume or less.

Description

Technical Field

[0001] This technology relates to the negative electrode for secondary batteries and secondary batteries themselves. Background Technology

[0002] With the widespread use of mobile phones and other electronic devices, the development of secondary batteries, which are small, lightweight, and capable of producing high energy density, is underway. These secondary batteries possess a positive electrode, a negative electrode, and an electrolyte, and various studies have been conducted regarding their structure.

[0003] Specifically, as the forming material of the negative electrode for lithium-ion secondary batteries, a porous conductive substrate (carbon), a conductive material (carbon nanotubes, etc.) and an active material (silicon, etc.) are used, and the porosity (void ratio) of the negative electrode is specified (for example, see Patent Document 1).

[0004] As a negative electrode forming material for lithium-ion secondary batteries, a conductive substrate on which carbon fibers derived from a protofibrous polymer are formed on carbon paper and silicon carbide derived from polysilane is formed on the conductive substrate (for example, see Patent Document 2).

[0005] As a negative electrode forming material for lithium-ion secondary batteries, a porous silicon material with a three-dimensional network structure, consisting of a copper current collector and a conductive material such as carbon, is used, and the average porosity of the porous silicon is specified (for example, see Patent Document 3).

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2007-335283

[0009] Patent Document 2: Japanese Patent Publication No. 2015-531977

[0010] Patent Document 3: Japanese Patent Application Publication No. 2012-084521 Summary of the Invention

[0011] Although various studies have been conducted on the structure of secondary batteries, their initial capacity characteristics, expansion characteristics, load characteristics, and cycle characteristics are still insufficient, and therefore there is room for improvement.

[0012] Therefore, there is a need for a negative electrode and a secondary battery that can achieve excellent initial capacity characteristics, excellent expansion characteristics, excellent load characteristics, and excellent cycle characteristics.

[0013] One embodiment of this technology provides a negative electrode for a secondary battery comprising a plurality of first fiber portions, a plurality of particle portions, and a plurality of second fiber portions, and having a plurality of voids. The plurality of first fiber portions are interconnected to form a three-dimensional network structure with a plurality of voids, each of the plurality of first fiber portions containing carbon as a constituent element. A plurality of particle portions cover the surface of each of the plurality of first fiber portions, a portion of which is interconnected, each of which contains silicon as a constituent element. At least a portion of the plurality of second fiber portions is connected to the surface of the plurality of particle portions, each of which contains carbon as a constituent element. The average fiber diameter of the plurality of first fiber portions is 50 nm or more and 7000 nm or less, the average fiber diameter of the plurality of second fiber portions is 1 nm or more and 200 nm or less, and the porosity is 42% by volume or more and 73% by volume or less.

[0014] One embodiment of the present technology provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode has the same structure as the negative electrode of the secondary battery described in one embodiment of the present technology.

[0015] The details (definitions and calculation steps) of the above-mentioned "average fiber diameter of multiple first fiber sections", "average fiber diameter of multiple second fiber sections" and "porosity" will be described later.

[0016] According to one embodiment of the present technology, a negative electrode for a secondary battery or a secondary battery includes the aforementioned plurality of first fiber portions, plurality of particle portions and plurality of second fiber portions, and has a plurality of voids. The average fiber diameter of the plurality of first fiber portions, the average fiber diameter of the plurality of second fiber portions and the porosity satisfy the aforementioned conditions, so excellent initial capacity characteristics, excellent expansion characteristics, excellent load characteristics and excellent cycle characteristics can be obtained.

[0017] It should be noted that the effects of this technology are not necessarily limited to those described herein, but can be any of the series of effects associated with this technology described later. Attached Figure Description

[0018] Figure 1 This is a schematic diagram illustrating the structure of the negative electrode for a secondary battery in one embodiment of this technology.

[0019] Figure 2 It is an enlarged representation Figure 1 The diagram shows cross-sectional views of the structures of the large-diameter carbon fiber section, the small-diameter carbon fiber section, and the particle section.

[0020] Figure 3 This is a perspective view showing the structure of a secondary battery in one embodiment of the present technology.

[0021] Figure 4 It is an enlarged representation Figure 3 The diagram shows a cross-sectional view of the structure of the battery element.

[0022] Figure 5 This is a schematic diagram showing the structure of the negative electrode for a secondary battery in Modified Example 1.

[0023] Figure 6 This is a schematic diagram showing the structure of the negative electrode for the secondary battery in Modified Example 2.

[0024] Figure 7 This is a schematic diagram showing the structure of the negative electrode for the secondary battery in Modified Example 3.

[0025] Figure 8 This is a schematic diagram showing other structures of the negative electrode for the secondary battery in Modified Example 3.

[0026] Figure 9 This is a schematic diagram showing another structure of the negative electrode for the secondary battery in Modified Example 3.

[0027] Figure 10 This is a block diagram illustrating the structure of a secondary battery application example. Detailed Implementation

[0028] The following is a detailed description of one embodiment of the present technology with reference to the accompanying drawings. It should be noted that the description is presented in the following order.

[0029] 1. The negative terminal of a secondary battery

[0030] 1-1. Structure

[0031] 1-2. Manufacturing method

[0032] 1-3. Functions and Effects

[0033] 2. Secondary battery

[0034] 2-1. Structure

[0035] 2-2. Actions

[0036] 2-3. Manufacturing method

[0037] 2-4. Functions and Effects

[0038] 3. Variations

[0039] 4. Uses of secondary batteries

[0040] <1. Negative electrode for secondary batteries>

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

[0042] This negative electrode is used as a secondary battery in an electrochemical device. Alternatively, the negative electrode can also be used in other electrochemical devices besides secondary batteries. The types of other electrochemical devices are not particularly limited; specifically, they include capacitors, etc.

[0043] Furthermore, in the aforementioned electrochemical devices such as secondary batteries, the negative electrode undergoes insertion and extraction of electrode reaction materials during the electrode reaction. The types of electrode reaction materials are not particularly limited; specifically, they are light metals such as alkali metals and alkaline earth metals. Alkali metals include lithium, sodium, and potassium, while alkaline earth metals include beryllium, magnesium, and calcium.

[0044] <1-1. Structure>

[0045] Figure 1 The structure of negative electrode 10, as an example of negative electrode, is schematically shown. Figure 2 Enlarged Figure 1 The cross-sectional structures of the large-diameter carbon fiber section 1, the small-diameter carbon fiber section 2, and the particle section 3 are shown.

[0046] In addition, Figure 2 The image shows a large-diameter carbon fiber section 1, a small-diameter carbon fiber section 2, and multiple particle sections 3 covering the surface of the large-diameter carbon fiber section 1. Additionally, in... Figure 2 The image shows cross-sections of the large-diameter carbon fiber section 1, the small-diameter carbon fiber section 2, and the particle section 3, which intersect the long side direction of the large-diameter carbon fiber section 1 and the small-diameter carbon fiber section 2, respectively.

[0047] like Figure 1 as well as Figure 2 As shown, the negative electrode 10 includes multiple large-diameter carbon fiber sections 1, multiple small-diameter carbon fiber sections 2, and multiple particle sections 3, and has multiple voids 10G. That is, the negative electrode 10 does not contain current collectors such as metal foil (hereinafter referred to as "metal current collectors"), and is therefore a so-called metal-free current collector electrode.

[0048] [Multiple large-diameter carbon fiber sections]

[0049] like Figure 1 As shown, the plurality of large-diameter carbon fiber portions 1 are plurality of first fiber portions having an average fiber diameter AD1 that is larger than the average fiber diameter AD2 of the plurality of small-diameter carbon fiber portions 2, such as Figure 2 As shown, each of the plurality of large-diameter carbon fiber sections 1 has a fiber diameter D1. The plurality of large-diameter carbon fiber sections 1 are interconnected to form a three-dimensional mesh structure having the aforementioned plurality of voids 10G.

[0050] exist Figure 1In order to simplify the illustration, the case where each of the multiple large-diameter carbon fiber sections 1 is straight is shown. However, the state (shape) of each of the multiple large-diameter carbon fiber sections 1 is not particularly limited, and is therefore not limited to being straight. It can be curved, branched, or a mixture of two or more of them.

[0051] Here, as described above, multiple large-diameter carbon fiber sections 1 are interconnected to form a three-dimensional network structure; more specifically, they are randomly wound together. It should be noted that the multiple large-diameter carbon fiber sections 1 can be bonded together via carbides (not shown) such as polymer compounds, or they can be interconnected via one or more small-diameter carbon fiber sections 2. Thus, the multiple large-diameter carbon fiber sections 1 have multiple connection points at which they are electrically connected to each other.

[0052] The average fiber diameter AD1 of the multiple large-diameter carbon fiber sections 1 is 50 nm to 7000 nm. This is because, in the multiple large-diameter carbon fiber sections 1 that are the main part of the negative electrode 10, the fiber diameter D1 becomes sufficiently large. As a result, a sufficiently conductive network (three-dimensional mesh structure) is formed inside the negative electrode 10, thus improving the conductivity of the negative electrode 10.

[0053] The steps for calculating the average fiber diameter AD1 are as follows. First, after recovering the negative electrode 10, the negative electrode 10 is cleaned using a cleaning solvent such as dimethyl carbonate. It should be noted that when a secondary battery containing the negative electrode 10 is obtained, the negative electrode 10 is recovered by disassembling the secondary battery. Next, the negative electrode 10 is cut using an ion milling device or the like to expose its cross-section.

[0054] Next, the cross-section of the negative electrode 10 is observed using a scanning electron microscope (SEM) or a transmission electron microscope (TEM) to obtain the observation results (observation images). This allows for the identification of multiple large-diameter carbon fiber sections 1 within the observation images. Observation conditions such as accelerating voltage and magnification can be arbitrarily set.

[0055] Next, after selecting any 20 large-diameter carbon fiber sections 1, the fiber diameter D1 of each of the 20 large-diameter carbon fiber sections 1 is measured. Finally, the average value of the 20 fiber diameters D1 is calculated as the average fiber diameter AD1.

[0056] It should be noted that the average fiber length of each of the multiple large-diameter carbon fiber sections 1 is not particularly limited. This is because if the multiple large-diameter carbon fiber sections 1 having the above-mentioned average fiber diameter AD1 are interconnected, a sufficiently conductive network (three-dimensional mesh structure) can be formed regardless of the fiber length.

[0057] Each of the multiple large-diameter carbon fiber sections 1 contains carbon as a constituent element, and therefore contains so-called carbon-containing materials. This term "carbon-containing material" is a general term for materials containing carbon as a constituent element.

[0058] Specifically, the multiple large-diameter carbon fiber sections 1 contain carbon paper. This is because the multiple large-diameter carbon fiber sections 1 are sufficiently interconnected, and the average fiber diameter AD1 is sufficiently increased, thus forming a sufficiently conductive network (three-dimensional mesh structure).

[0059] Alternatively, the multiple large-diameter carbon fiber sections 1 can also be materials formed by processing multiple fibrous carbon materials having the aforementioned average fiber diameter AD1 into a three-dimensional network structure. The type of fibrous carbon material is not particularly limited; specifically, it can be vapor-grown carbon fiber (VGCF) or carbon nanofiber (CNF). Furthermore, the type of fibrous carbon material can also be multilayer carbon nanotubes (multi-walled carbon nanotubes (MWCNTs)) such as double-walled carbon nanotubes (DWCNTs).

[0060] [Multiple small-diameter carbon fiber sections]

[0061] like Figure 1 As shown, the plurality of small-diameter carbon fiber portions 2 are plurality of second fiber portions having an average fiber diameter AD2 that is smaller than the average fiber diameter AD1 of the plurality of large-diameter carbon fiber portions 1, such as Figure 2 As shown, each of the plurality of small-diameter carbon fiber portions 2 has a fiber diameter D2. Here, since each of the plurality of small-diameter carbon fiber portions 2 is fixed to the surface of the plurality of particle portions 3, it is connected to the surface of the plurality of particle portions 3.

[0062] exist Figure 1 In this illustration, for the sake of simplicity, each of the multiple small-diameter carbon fiber sections 2 is shown as being in a straight line. However, the state (shape) of each of the multiple small-diameter carbon fiber sections 2 is not particularly limited, just as the state of the multiple large-diameter carbon fiber sections 1 described above is.

[0063] The reason why the negative electrode 10 includes multiple large-diameter carbon fiber portions 1 and multiple small-diameter carbon fiber portions 2 is that the multiple large-diameter carbon fiber portions 1 form a conductive network, and the multiple small-diameter carbon fiber portions 2 also form a dense conductive network, thus significantly improving the conductivity of the negative electrode 10.

[0064] Preferably, some or all of the plurality of small-diameter carbon fiber portions 2 (the plurality of small-diameter carbon fiber portions 2R) are connected to each of two or more large-diameter carbon fiber portions 1 via a portion of the plurality of particle portions 3. This is because the two or more large-diameter carbon fiber portions 1 are electrically connected to each other via the small-diameter carbon fiber portions 2R. As a result, a denser conductive network is formed, and thus the conductivity of the negative electrode 10 is further improved.

[0065] The average fiber diameter AD2 of the plurality of small-diameter carbon fiber portions 2 is smaller than the average fiber diameter AD1 of the plurality of large-diameter carbon fiber portions 1. Specifically, it is 1 / 10000 to 1 / 2 of the average fiber diameter AD1, preferably 1 / 300 to 1 / 5.

[0066] More specifically, the average fiber diameter AD2 is 1 nm to 200 nm. This is because, in a system where multiple large-diameter carbon fiber portions 1 and multiple small-diameter carbon fiber portions 2 coexist, the average fiber diameter AD2 is sufficiently small relative to the average fiber diameter AD1, thus allowing the multiple small-diameter carbon fiber portions 2 to easily disperse within the negative electrode 10. Consequently, a dense conductive network is formed through the multiple small-diameter carbon fiber portions 2, thereby further improving the conductivity of the negative electrode 10.

[0067] Except for measuring the fiber diameter D2 of each of the 20 small-diameter carbon fiber portions 2 and taking the average of these 20 fiber diameters D2 as the average fiber diameter AD2, the steps for calculating the average fiber diameter AD2 are the same as those for calculating the average fiber diameter AD1 described above. Furthermore, when the fiber diameter D2 is small, TEM is preferable to SEM for observing the cross-section of the negative electrode 10.

[0068] It should be noted that the average fiber length of each of the multiple small-diameter carbon fiber portions 2 is not particularly limited. This is because if the multiple small-diameter carbon fiber portions 2 having the aforementioned average fiber diameter AD2 are present inside the negative electrode 10, a dense conductive network can be formed regardless of fiber length.

[0069] Each of the multiple small-diameter carbon fiber sections 2 contains carbon as a constituent element, and therefore contains carbon-containing material in the same way as each of the multiple large-diameter carbon fiber sections 1.

[0070] Specifically, each of the multiple small-diameter carbon fiber sections 2 contains fibrous carbon materials such as carbon nanotubes, vapor-grown carbon fibers (VGCF), and carbon nanofibers (CNF). This is because, inside the negative electrode 10, the multiple small-diameter carbon fiber sections 2 are easily and sufficiently dispersed, and easily form a dense conductive network.

[0071] There are no particular limitations on the types of carbon nanotubes; they can be either single-walled carbon nanotubes (SWCNTs) or multilayer carbon nanotubes (MWCNTs). Specific examples of multilayer carbon nanotubes include double-walled carbon nanotubes (DWCNTs).

[0072] Each of the plurality of small-diameter carbon fiber portions 2 is preferably one or both of monolayer carbon nanotubes and vapor-grown carbon fibers. This is because, since the average fiber diameter AD2 becomes sufficiently small, the plurality of small-diameter carbon fiber portions 2 are sufficiently dispersed inside the negative electrode 10, forming a denser conductive network.

[0073] [Multiple Particle Sections]

[0074] like Figure 1 As shown, multiple particle sections 3 cover the surface of each of multiple large-diameter carbon fiber sections 1, and have an average particle size AP1. (As shown...) Figure 2 As shown, each of the plurality of particle sections 3 has a particle size P1.

[0075] Here, the plurality of particle sections 3 are so-called primary particles 3A, and some or all of these particle sections 3 (the plurality of primary particles 3A) are interconnected. That is, some or all of the plurality of primary particles 3A are densely packed together, thereby forming a plurality of aggregates (secondary particles 3B). A plurality of pores 3G are formed inside the secondary particles 3B, and the pores 3G are gaps between the plurality of primary particles 3A. The inner diameter of the pores 3G is smaller than the inner diameter of the pores 10G.

[0076] It should be noted that the number of primary particles 3A forming secondary particle 3B only needs to be two or more, without any particular limitation. Similarly, the number of secondary particles 3B only needs to be two or more, without any particular limitation. Figure 2 The case of forming multiple secondary particles 3B is shown.

[0077] Since the particle size P1 mentioned above is the particle size of secondary particle 3B, the average particle size AP1 mentioned above is the average particle size of secondary particle 3B.

[0078] The plurality of particle portions 3 may cover the entire surface of each of the plurality of large-diameter carbon fiber portions 1, or may only cover a portion of the surface of each of the plurality of large-diameter carbon fiber portions 1. In the latter case, the plurality of particle portions 3 may also cover the surface of the large-diameter carbon fiber portion 1 at multiple mutually separated locations. Figure 1 In order to simplify the illustration, it is shown that multiple particle sections 3 cover a portion of the surface of each of multiple large-diameter carbon fiber sections 1.

[0079] Thus, the surfaces of the plurality of large-diameter carbon fiber portions 1, each having a relatively large average fiber diameter AD1, are covered by the plurality of particle portions 3, while the surfaces of the plurality of small-diameter carbon fiber portions 2, each having a relatively small average fiber diameter AD2, are not covered by the plurality of particle portions 3.

[0080] The reason why the negative electrode 10 includes multiple particle sections 3 is that, while obtaining a high energy density, the electrode reactants are easily inserted and de-inserted.

[0081] In detail, since each of the multiple particle sections 3 contains the silicon-containing material described later, a high energy density can be obtained.

[0082] Furthermore, since the multiple particle portions 3 cover the respective surfaces of the multiple large-diameter carbon fiber portions 1, the initial inner diameter of the multiple voids 10G formed by these multiple large-diameter carbon fiber portions 1 randomly narrows. Therefore, in the completed negative electrode 10, multiple voids 10G with different inner diameters are easily formed, allowing the electrode reactant material to easily move through these multiple voids 10G. In this case, in particular, even if the current value increases during the electrode reaction, the electrode reactant material can easily move smoothly. Therefore, during the electrode reaction at the negative electrode 10, the electrode reactant material is easily inserted and deintercalated.

[0083] In this case, in particular, the secondary particle 3B is formed from multiple particle sections 3 (primary particles 3A), and multiple pores 3G with inner diameters smaller than the inner diameter of the void 10G are formed inside the secondary particle 3B. That is, the negative electrode 10 has two spaces of different sizes inside, namely, the void 10G with a relatively large inner diameter and the pores 3G with a relatively small inner diameter. Thus, during the electrode reaction, the expansion and contraction of the particle section 3 is suppressed not only by utilizing the void 10G but also by utilizing the pores 3G, and similarly, the electrode reactants are facilitated to move easily not only by utilizing the void 10G but also by utilizing the pores 3G.

[0084] The average particle size AP1 of the plurality of particle portions 3 is not particularly limited, but is preferably 30 nm to 2000 nm. This is because the surface coverage of the plurality of large-diameter carbon fiber portions 1 formed by the plurality of particle portions 3 becomes sufficiently large, so that sufficient energy density can be obtained in the negative electrode 10 while ensuring the conductivity of the negative electrode 10.

[0085] The steps for calculating the average particle size AP1 are as follows. First, by following the same steps as for calculating the average fiber diameter AD1, an observation of the cross-section of the negative electrode 10 is obtained (observation image). Next, after selecting any 10 particle sections 3, the particle size P1 of each of the 10 particle sections 3 is measured. It should be noted that, in the case where the particle size P1 varies depending on the location within a single particle section 3, the minimum value of that particle size P1 is selected. Finally, the average value of the 10 particle sizes P1 is calculated as the average particle size AP1.

[0086] Furthermore, each of the multiple particle sections 3 contains silicon as a constituent element, thus containing so-called silicon-containing materials. This is because silicon has excellent intercalation / deintercalation electrode reactants, thus enabling the attainment of high energy densities.

[0087] Silicon-containing materials are a general term for materials containing silicon as a constituent element. Therefore, silicon-containing materials can be silicon monomers, silicon alloys, silicon compounds, mixtures of two or more of them, or materials containing one or more of their phases. Silicon monomers may contain trace amounts of impurities. That is, the purity of the silicon monomer may not be 100%. These impurities are those accidentally introduced during the manufacturing process of the silicon monomer, as well as oxides accidentally formed due to oxygen in the atmosphere. The content of impurities in the silicon monomer is preferably as low as possible, more preferably 5% by weight or less.

[0088] Silicon alloys contain one or more of the following metallic elements besides silicon: tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium. Silicon compounds contain one or more of the following non-metallic elements besides silicon: carbon and oxygen. Additionally, silicon compounds may contain one or more of the following metallic elements as described in the section on silicon alloys.

[0089] Specific examples of silicon alloys include Mg₂Si, Ni₂Si, TiSi₂, MoSi₂, CoSi₂, NiSi₂, CaSi₂, CrSi₂, Cu₅Si, FeSi₂, MnSi₂, NbSi₂, TaSi₂, VSi₂, WSi₂, ZnSi₂, and SiC. Furthermore, the composition of silicon alloys (the mixing ratio of silicon to other metallic elements) can be arbitrarily changed.

[0090] Specific examples of silicon compounds are SiB4, SiB6, Si3N4, Si2N2O, and SiO. v (0<v≤2) and LiSiO. Where v can be in the range of 0.2<v<1.4.

[0091] The silicon-containing material is preferably silicon monomer. This is because a higher energy density can be obtained. In this case, the silicon content in each of the plurality of particle portions 3, i.e., the silicon content (purity) in the silicon-containing material, is not particularly limited, but is preferably 80% by weight or more, more preferably 80% by weight to 100% by weight. This is because a significantly higher energy density can be obtained.

[0092] The weight ratio M (wt%) of the plurality of particle portions 3 relative to the sum of the weights M1 of the plurality of large-diameter carbon fiber portions 1, M2 of the plurality of small-diameter carbon fiber portions 2, and M3 of the plurality of particle portions 3 is not particularly limited, but is preferably 40 wt% to 76 wt%. This is because, in the negative electrode 10, the relationship between the weight of the carbon component (the plurality of large-diameter carbon fiber portions 1 and the plurality of small-diameter carbon fiber portions 2) and the weight of the silicon component (the plurality of particle portions 3) is appropriately optimized, thus ensuring sufficient energy density while maintaining conductivity. This weight ratio M is calculated based on the formula M = [M3 / (M1+M2+M3)] × 100.

[0093] The steps for calculating the weight ratio M are as follows. First, after recovering the negative electrode 10, the negative electrode 10 is cleaned using a cleaning solvent such as dimethyl carbonate. Next, the negative electrode 10 is analyzed using thermogravimetric differential thermal analysis (TG-DTA) to determine the weights M1, M2, and M3. It should be noted that any TG-DTA apparatus can be used for analyzing the negative electrode 10.

[0094] In the analysis of the negative electrode 10, the weight loss when the heating temperature is raised to approximately 450°C is the weight of the electrolyte and binder, etc., and the weight loss when the heating temperature is raised to approximately 450°C to approximately 1350°C is the weight of the carbon component (multiple large-diameter carbon fiber portions 1 and multiple small-diameter carbon fiber portions 2) (weights M1, M2). Therefore, the weight of the remaining components is the weight of the silicon component (multiple particle portions 3) (weight M3).

[0095] It should be noted that the temperature at which the weight loss caused by the electrolyte, etc., is detected (approximately 450°C) sometimes varies depending on the type of adhesive. Specifically, in the case of polyvinylidene fluoride as the adhesive, if the minimum value of the differential curve of DTA is taken as the disappearance temperature, then the disappearance temperature is approximately 460°C.

[0096] Finally, using weights M1, M2, and M3, the weight ratio M is calculated based on the above formula.

[0097] It should be noted that, although not specifically illustrated here, some or all of the surfaces of each of the multiple particle sections 3 may be further covered by a coating layer. This coating layer contains one or more conductive materials, such as carbon-containing materials and metallic materials. This is because it can further improve the conductivity of the negative electrode 10. Details regarding the carbon-containing materials are as described above. The type of metallic material is not particularly limited.

[0098] When forming this capping layer, silane coupling agents and polymeric materials can be used. This is to ensure that the capping layer can adequately cover the surface of the particle portion 3. By adequately covering the surface of the particle portion 3 with the capping layer, the decomposition reaction of the electrolyte on the surface of the particle portion 3 containing silicon material can be suppressed.

[0099] Porosity

[0100] As described above, the negative electrode 10 comprises a three-dimensional mesh structure formed by multiple large-diameter carbon fiber portions 1, and thus has multiple voids 10G.

[0101] The porosity R of the negative electrode 10, determined by the multiple voids 10G, is 42% to 73% by volume. This is because, since the amount of the multiple voids 10G inside the negative electrode 10 is appropriately optimized, even if each of the multiple particle portions containing silicon material expands and contracts during the electrode reaction, the internal stress (deformation) caused by this expansion and contraction can be appropriately mitigated by the multiple voids 10G. Therefore, even with repeated electrode reactions, the expansion and contraction of the particle portions 3 can be suppressed, thus suppressing the degradation of the negative electrode 10. The degradation of the negative electrode 10 refers to defects and cuts in the large-diameter carbon fiber portion 1, defects and breaks in the small-diameter carbon fiber portion 2, and the collapse and detachment of the particle portions 3.

[0102] The steps for calculating the porosity R are as follows. Following the same steps as for calculating the average fiber diameter AD1 described above, after recovering and cleaning the negative electrode 10, a three-dimensional image of the negative electrode 10 is obtained using focused ion beam scanning electron microscopy (FIB-SEM), and the porosity R is calculated based on the three-dimensional image using image analysis processing. In this image analysis processing, the innovative materials development and comprehensive packaging software GeoDict, manufactured by Math2Market GmbH, can be used.

[0103] [Other Materials]

[0104] It should be noted that the negative electrode 10 may also contain any one or more other materials.

[0105] There are no particular limitations on the types of other materials; specifically, adhesives are an example. This is because each of the multiple large-diameter carbon fiber portions 1, the multiple small-diameter carbon fiber portions 2, and the multiple particle portions 3 is firmly connected to each other via an adhesive, thus forming a strong conductive network.

[0106] The binder contains one or more polymeric compounds, such as polyimide, polyvinylidene fluoride, polyacrylic acid, styrene-butadiene rubber, and carboxymethyl cellulose. When the negative electrode 10 contains the binder, a portion of the multiple small-diameter carbon fiber sections 2 may also be free from the surface of the particle section 3.

[0107] <1-2. Manufacturing Method>

[0108] The negative electrode 10 is manufactured through the steps described below. Here, the use of carbon paper as multiple large-diameter carbon fiber sections 1 will be explained.

[0109] First, carbon paper is prepared to serve as multiple large-diameter carbon fiber sections 1. Multiple large-diameter carbon fiber sections 1 are interconnected within this carbon paper to form a three-dimensional mesh structure with multiple voids 10G.

[0110] Next, silicon-containing material powder is added to a solvent. This disperses the silicon-containing material powder in the solvent, thus preparing a first dispersion. The solvent can be an aqueous solvent or a non-aqueous solvent (organic solvent). In this case, a binder can be added to the solvent. Details regarding the binder are as described above.

[0111] Next, multiple small-diameter carbon fiber segments 2 are added to another solvent. This disperses the multiple small-diameter carbon fiber segments 2 in the solvent, thereby preparing a second dispersion. In this case, a binder can be added to the solvent. Details regarding the solvent and binder are as described above.

[0112] Next, a dispersion is prepared by mixing the first dispersion and the second dispersion together. As described above, the dispersion contains silicon-containing material powder and multiple small-diameter carbon fiber segments 2.

[0113] Next, after coating the multiple large-diameter carbon fiber portions 1 with a dispersion liquid, the dispersion liquid is dried. As a result, since the dispersion liquid permeates the interior of the multiple large-diameter carbon fiber portions 1, the silicon-containing material powder is fixed to the surface of each of the multiple large-diameter carbon fiber portions 1, and the multiple small-diameter carbon fiber portions 2 are fixed to the surface of the silicon-containing material powder. Therefore, multiple particle portions 3 are formed covering the surface of each of the multiple large-diameter carbon fiber portions 1, and the multiple small-diameter carbon fiber portions 2 are connected to the surface of the multiple particle portions 3. Alternatively, instead of coating the multiple large-diameter carbon fiber portions 1 with a dispersion liquid, the multiple large-diameter carbon fiber portions 1 can be impregnated in the dispersion liquid.

[0114] When the plurality of particle sections 3 are formed, the inner diameter of some or all of the plurality of voids 10G decreases, thus reducing the porosity R (the so-called initial porosity R) before the formation of the plurality of particle sections 3. However, if the initial porosity R is set large enough, even if the plurality of particle sections 3 are formed, some or all of the plurality of voids 10G will not disappear and will remain, so the porosity R can be calculated even after the plurality of particle sections 3 are formed. That is, the porosity R can be controlled by adjusting the concentration of the silicon-containing material in the first dispersion.

[0115] Thus, a negative electrode 10 comprising multiple large-diameter carbon fiber sections 1, multiple small-diameter carbon fiber sections 2, and multiple particle sections 3 is produced.

[0116] It should be noted that, in the case where multiple small-diameter carbon fiber portions 2 are bonded to the surfaces of multiple particle portions 3, the multiple small-diameter carbon fiber portions 2 can be formed directly on the surfaces of the multiple particle portions 3 instead of indirectly forming them using a dispersion liquid. In this case, after a metal catalyst is placed on the surfaces of the multiple particle portions 3, the multiple small-diameter carbon fiber portions 2 are grown using a chemical vapor deposition (CVD) method or the like. Thus, each of the multiple small-diameter carbon fiber portions 2 is firmly bonded to the surfaces of the multiple particle portions 3, thereby forming a robust conductive network.

[0117] Finally, as needed, the negative electrode 10 is stamped using a press or similar instrument, and then fired. In this case, the porosity R can be controlled by adjusting the stamping pressure. The firing temperature can be set arbitrarily.

[0118] Thus, a negative electrode 10 comprising multiple large-diameter carbon fiber sections 1, multiple small-diameter carbon fiber sections 2, and multiple particle sections 3, and having multiple voids 10G, is completed. In manufacturing this negative electrode 10, the weight ratio M can be controlled by adjusting the concentration of the silicon-containing material in the first dispersion and the concentration of the multiple small-diameter carbon fiber sections 2 in the second dispersion.

[0119] It should be noted that, in the case of manufacturing the negative electrode 10, after obtaining multiple large-diameter carbon fiber portions 1 having multiple particle portions 3 through the above steps, a papermaking process using multiple large-diameter carbon fiber portions 1 and multiple small-diameter carbon fiber portions 2 having these multiple particle portions 3 can be employed. In this case, a wet process such as papermaking can be used, or a dry process using a wire mesh can be used. In this case, a negative electrode 10 containing multiple large-diameter carbon fiber portions 1, multiple small-diameter carbon fiber portions 2, and multiple particle portions 3 and having multiple voids 10G can also be manufactured.

[0120] <1-3. Functions and Effects>

[0121] According to the negative electrode 10, the negative electrode 10 includes a plurality of large-diameter carbon fiber portions 1, a plurality of small-diameter carbon fiber portions 2 and a plurality of particle portions 3, and has a plurality of voids 10G. Each of the plurality of large-diameter carbon fiber portions 1 and the plurality of small-diameter carbon fiber portions 2 contains carbon-containing material, and each of the plurality of particle portions 3 contains silicon-containing material. The average fiber diameters AD1 and AD2 and the porosity R satisfy the above conditions (AD1 = 50 nm to 7000 nm, AD2 = 1 nm to 2000 nm and R = 42 vol% to 73 vol%).

[0122] In this case, as described above, in a system comprising multiple large-diameter carbon fiber sections 1, multiple small-diameter carbon fiber sections 2, and multiple particle sections 3, the average fiber diameters AD1 and AD2 and the porosity R are appropriately adjusted, thus obtaining a series of effects as described below.

[0123] First, inside the negative electrode 10, a conductive network (three-dimensional mesh structure) is formed by multiple large-diameter carbon fiber portions 1 containing conductive carbon material, and a dense conductive network is also formed by multiple small-diameter carbon fiber portions 2 containing conductive carbon material.

[0124] Second, since each of the multiple particle sections 3 contains a silicon-containing material with excellent intercalation and deintercalation properties of the electrode reactive material, a high energy density can be obtained.

[0125] Third, by covering the surfaces of multiple large-diameter carbon fiber portions 1 with multiple particle portions 3, multiple voids 10G with different inner diameters are formed, so that the electrode reactant can easily move through these multiple voids 10G. As a result, even if the current value increases during the electrode reaction, the electrode reactant can easily be inserted and de-intercalated.

[0126] Fourth, even if each of the plurality of particle sections 3 contains silicon-containing material, during the electrode reaction, i.e., when the plurality of particle sections 3 expand and contract respectively, the internal stress generated inside the negative electrode 10 is mitigated by the plurality of voids 10G, thus suppressing the expansion and contraction of the negative electrode 10. Therefore, the degradation of the negative electrode 10 caused by the internal stress generated when the plurality of particle sections 3 expand and contract respectively can be suppressed. In this case, in particular, even if the silicon content in the silicon-containing material is large, the expansion and contraction of the negative electrode 10 can be sufficiently suppressed, thus effectively suppressing the degradation of the negative electrode 10.

[0127] Fifth, secondary particles 3B are formed from multiple particle sections 3 (primary particles 3A), and multiple pores 3G are formed inside the secondary particles 3B. Therefore, during the electrode reaction, the expansion and contraction of the particle section 3 are suppressed not only by using the pores 10G but also by using the pores 3G. Similarly, the electrode reactant is made to move easily not only by using the pores 10G but also by using the pores 3G.

[0128] Based on the above, while ensuring energy density and the intercalation / deintercalation properties of the electrode reactants, the expansion and contraction of the negative electrode 10 can be suppressed during the electrode reaction, and the discharge capacity is not easily reduced even with repeated electrode reactions. Therefore, in secondary batteries using the negative electrode 10, excellent initial capacity characteristics, excellent expansion characteristics, excellent load characteristics, and excellent cycle characteristics can be obtained.

[0129] It should be noted that in the above-mentioned negative electrode 10, since no metal current collector is required, it is possible to achieve weight reduction and increase the weight energy density (Wh / kg) compared with the case of using a metal current collector.

[0130] In particular, if the weight ratio M is 40% to 76% by weight, the relationship between the weight of the carbon component (multiple large-diameter carbon fiber sections 1 and multiple small-diameter carbon fiber sections 2) and the weight of the silicon component (multiple particle sections 3) in the negative electrode 10 is appropriate. As a result, sufficient energy density can be obtained while ensuring conductivity, thus achieving higher performance.

[0131] Furthermore, if the silicon content in each of the multiple particle sections 3 (containing silicon material) is 80% by weight or more, a significantly higher energy density can be obtained while ensuring conductivity, thus achieving a higher performance.

[0132] Furthermore, if a portion or all of the multiple small-diameter carbon fiber sections 2 are connected to each of two or more large-diameter carbon fiber sections 1 via a portion of the multiple particle sections 3, then the two or more large-diameter carbon fiber sections 1 are electrically connected to each other via the small-diameter carbon fiber sections 2. This forms a denser conductive network, thus achieving a higher efficiency.

[0133] Here, when the porosity R has a large value (42% to 73% vol%), the conductive network tends to become sparse. Furthermore, since the silicon-containing particle portions 3 expand and contract during the electrode reaction, the conductive network is easily cut. However, as described above, if a portion or all of the plurality of small-diameter carbon fiber portions 2 are connected to each of two or more small-diameter carbon fiber portions 2 via a portion of the plurality of particle portions 3, a dense conductive network is easily formed, and this conductive network is difficult to cut.

[0134] Furthermore, if the average particle size AP1 of the multiple particle sections 3 is 30nm to 2000nm, sufficient energy density can be obtained while ensuring conductivity, thus achieving higher performance.

[0135] Furthermore, if the multiple large-diameter carbon fiber sections 1 contain carbon paper, these multiple large-diameter carbon fiber sections 1 are sufficiently interconnected, and the average fiber diameter AD1 is sufficiently increased. Therefore, due to the formation of a sufficiently conductive network (three-dimensional network structure), a higher performance can be obtained.

[0136] Furthermore, if the multiple small-diameter carbon fiber sections 2 contain one or both of monolayer carbon nanotubes and vapor-grown carbon fibers, the average fiber diameter AD2 becomes sufficiently small. Therefore, within the negative electrode 10, the multiple small-diameter carbon fiber sections 2 are easily and sufficiently dispersed, and a denser conductive network is easily formed, thus achieving higher performance.

[0137] <2. Secondary batteries>

[0138] Next, a secondary battery according to one embodiment of the present technology will be described, and more specifically, an example of a secondary battery using the above-described negative electrode 10 will be described.

[0139] As described above, the secondary battery described here is a secondary battery in which battery capacity is obtained by intercalation and deintercalation of electrode reactants, and it includes a positive electrode, a negative electrode, a separator, and an electrolyte in liquid form. As mentioned above, the types of electrode reactants are not particularly limited.

[0140] The following example uses lithium as the electrode reactant. A secondary battery that utilizes the insertion and extraction of lithium to obtain battery capacity is called a lithium-ion secondary battery. In this lithium-ion secondary battery, lithium is inserted and extracted in an ionic state.

[0141] In this case, the charging capacity of the negative electrode is greater than the discharging capacity of the positive electrode. That is, the electrochemical capacity per unit area of ​​the negative electrode is set to be greater than that of the positive electrode. This is to prevent electrode reactants from depositing on the surface of the negative electrode during charging.

[0142] <2-1. Structure>

[0143] Figure 3 The three-dimensional structure of a secondary battery is shown. Figure 4 Enlarged Figure 3 The cross-sectional structure of the battery element 30 is shown. Additionally, Figure 3 The outer packaging film 20 and the battery element 30 are shown separated from each other. Figure 4 Only a portion of battery element 30 is shown. Refer below for details already provided. Figure 1 as well as Figure 2 Furthermore, the constituent elements of the negative electrode 10, which have already been explained, are cited.

[0144] like Figure 3 as well as Figure 4 As shown, the secondary battery includes an outer packaging film 20, a battery element 30, a positive electrode lead 41, a negative electrode lead 42, and sealing films 51 and 52. The secondary battery described here is a laminated film type secondary battery that uses a flexible (or supple) outer packaging film 20.

[0145] [Outer packaging film]

[0146] like Figure 3 As shown, the outer packaging film 20 is a flexible outer packaging component that houses the battery element 30, and has a bag-like structure that is sealed when the battery element 30 is housed inside. Therefore, the outer packaging film 20 houses the positive electrode 31, the negative electrode 32, and the electrolyte, which will be described later.

[0147] Here, the outer packaging film 20 is a thin film component that is folded in the folding direction F. A recess 20U (so-called deep stretch portion) for accommodating the battery element 30 is provided on the outer packaging film 20.

[0148] Specifically, the outer packaging film 20 is a laminated film consisting of three layers stacked sequentially from the inside: a weld layer, a metal layer, and a surface protective layer. When the outer packaging film 20 is folded, the outer peripheries of the opposing weld layers are welded together. The weld 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.

[0149] In addition, there is no particular limitation on the structure (number of layers) of the outer packaging film 20; it can be 1 layer, 2 layers, or more than 4 layers.

[0150] [Battery Components]

[0151] like Figure 3 as well as Figure 4 As shown, the battery element 30 is a power generation element that includes a positive electrode 31, a negative electrode 32, a separator 33, and an electrolyte (not shown), and is housed inside the outer packaging film 20.

[0152] Since the battery element 30 is a so-called stacked electrode body, the positive electrode 31 and the negative electrode 32 are stacked on top of each other with a separator 33 in between. There is no particular limitation on the number of stacks of the positive electrode 31, the negative electrode 32 and the separator 33. Here, multiple positive electrodes 31 and multiple negative electrodes 32 are stacked alternately with a separator 33 in between.

[0153] (positive electrode)

[0154] like Figure 4 As shown, the positive electrode 31 includes a positive current collector 31A and a positive active material layer 31B.

[0155] The positive current collector 31A has one side with a positive active material layer 31B disposed thereon. The positive current collector 31A contains a conductive material such as a metal, and a specific example of the metal material is aluminum.

[0156] It should be noted that, as Figure 3 As shown, the positive current collector 31A includes a protrusion 31AT without a positive active material layer 31B, and multiple protrusions 31AT are connected to each other in a lead-like manner. Here, the protrusion 31AT is integrated with the portion other than the protrusion 31AT. Alternatively, the protrusion 31AT may be separate from the portion other than the protrusion 31AT, and thus connected to the portion other than the protrusion 31AT.

[0157] The positive electrode active material layer 31B comprises any one or more positive electrode active materials capable of lithium insertion / extraction. Additionally, the positive electrode active material layer 31B may also comprise any one or more other materials such as a positive electrode binder and a positive electrode conductive agent.

[0158] Here, the positive electrode active material layer 31B is disposed on both sides of the positive electrode current collector 31A. Alternatively, the positive electrode active material layer 31B may be disposed on only one side of the positive electrode current collector 31A, opposite to the negative electrode 32. The method for forming the positive electrode active material layer 31B is not particularly limited; specifically, it may be any one or more of the following methods: coating method, etc.

[0159] There are no particular limitations on the type of positive electrode active material; specifically, it can be lithium-containing compounds. These lithium-containing compounds are compounds that contain one or more transition metal elements as constituent elements along with lithium, and may also contain one or more other elements as constituent elements. The other elements can be any elements other than lithium and the transition metal elements themselves; there are no particular limitations. Specifically, they must belong to groups 2 to 15 of the long-period periodic table. There are no particular limitations on the type of lithium-containing compound; specifically, it can be oxides, phosphoric acid compounds, silicate compounds, and borate compounds, etc.

[0160] Specific examples of oxides are LiNiO2, LiCoO2, and LiCo. 0.98 Al 0.01 Mg 0.01 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, Li 1.2 Mn 0.52 Co 0.175 Ni 0.1 O2, Li 1.15 (Mn 0.65 Ni 0.22 Co 0.13 O2 and LiMn2O4, etc. Specific examples of phosphoric acid compounds are LiFePO4, LiMnPO4, and LiFe 0.5 Mn 0.5 PO4 and LiFe 0.3 Mn 0.7 PO4, etc.

[0161] The positive electrode binder includes any one or more of synthetic rubbers and polymeric compounds. Specific examples of synthetic rubbers include styrene-butadiene rubber, fluorinated rubbers, and ethylene propylene diene monomer (EPDM) rubber. Specific examples of polymeric compounds include polyvinylidene fluoride (PVDF), polyimide, and carboxymethyl cellulose.

[0162] The positive electrode conductive agent includes one or more conductive materials such as carbon materials. Specific examples of carbon materials include graphite, carbon black, acetylene black, Ketjen black, and carbon nanotubes. In addition, conductive materials can also be metallic materials and polymer compounds.

[0163] (negative electrode)

[0164] like Figure 4 As shown, the negative electrode 32 is positioned opposite the positive electrode 31 across a separator 33, and is capable of lithium insertion / extraction. This negative electrode 32 has the same structure as the negative electrode 10 described above, and therefore includes multiple large-diameter carbon fiber portions 1, multiple small-diameter carbon fiber portions 2, and multiple particle portions 3. In this negative electrode 32, lithium insertion / extraction is primarily performed in each of the multiple particle portions 3. Furthermore, lithium insertion / extraction can also be performed not only in each of the multiple particle portions 3, but also in one or both of the multiple large-diameter carbon fiber portions 1 and the multiple small-diameter carbon fiber portions 2.

[0165] It should be noted that, as Figure 3 As shown, the negative electrode 32 includes a protrusion 31AT composed of a portion of a large-diameter carbon fiber portion 1 without multiple particle portions 3, and the multiple protrusions 31AT are joined together in a manner that forms a lead wire.

[0166] (Diaphragm)

[0167] like Figure 4 As shown, the separator 33 is an insulating porous membrane located between the positive electrode 31 and the negative electrode 32, which prevents contact (short circuit) between the positive electrode 31 and the negative electrode 32 while allowing lithium ions to pass through. The separator 33 contains a polymer compound such as polyethylene.

[0168] (electrolyte)

[0169] An electrolyte, comprising a solvent and an electrolyte salt, is impregnated in each of the positive electrode 31, the negative electrode 32, and the separator 33.

[0170] The solvent includes any one or more of the following non-aqueous solvents (organic solvents): carbonate compounds, carboxylic acid ester compounds, and lactone compounds, and the electrolyte containing such non-aqueous solvent is called a non-aqueous electrolyte.

[0171] Carbonate compounds include cyclic carbonates and chain carbonates. Specific examples of cyclic carbonates are ethylene carbonate and propylene carbonate. Specific examples of chain carbonates are dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0172] Carboxylic acid esters are chain-like carboxylic acid esters. Specific examples of chain-like carboxylic acid esters include methyl acetate, ethyl acetate, methyl trimethylacetate, methyl propionate, ethyl propionate, and propyl propionate.

[0173] Lactone compounds include lactones. Specific examples of lactones include γ-butyrolactone and γ-valerolactone.

[0174] Electrolyte salts contain one or more of light metal salts such as lithium salts.

[0175] Specific examples of lithium salts include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiN(FSO2)2), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2), lithium bis(oxalate)borate (LiB(C2O4)2), lithium difluoro(oxalate)borate (LiB(C2O4)F2), lithium monofluorophosphate (Li2PFO3), and lithium difluorophosphate (LiPF2O2), etc.

[0176] There is no particular limit to the content of the electrolyte salt, but specifically, it is 0.3 mol / kg to 3.0 mol / kg relative to the solvent. This is because it allows for higher ionic conductivity.

[0177] It should be noted that the electrolyte may also contain one or more additives. There are no particular limitations on the types of additives; specifically, they include unsaturated cyclic carbonates, halocarbonates, phosphate esters, acid anhydrides, nitrile compounds, and isocyanate compounds, etc.

[0178] Specific examples of unsaturated cyclic carbonates include vinylene carbonate, vinyl ethylene carbonate, and methylene ethylene carbonate. Specific examples of halocarbonates include halogenated cyclic carbonates and halogenated chain carbonates. Specific examples of halogenated cyclic carbonates include monofluoroethylene carbonate and difluoroethylene carbonate. Specific examples of halogenated chain carbonates include fluoromethyl methyl carbonate. Specific examples of phosphate esters include trimethyl phosphate and triethyl phosphate.

[0179] Acid anhydrides include dicarboxylic acid anhydrides, disulfonic acid anhydrides, and carboxylic acid sulfonic anhydrides. Specific examples of dicarboxylic acid anhydrides include succinic anhydride. Specific examples of disulfonic acid anhydrides include ethane disulfonic anhydride. Specific examples of carboxylic acid sulfonic anhydrides include sulfobenzoic anhydride.

[0180] Nitrile compounds include mononitrile compounds, dinitrile compounds, and trinitrile compounds. Specific examples of mononitrile compounds include acetonitrile. Specific examples of dinitrile compounds include succinate. Specific examples of trinitrile compounds include 1,2,3-propanetrionitrile. Specific examples of isocyanate compounds include hexamethylene diisocyanate.

[0181] [Positive lead]

[0182] like Figure 3 As shown, the positive electrode lead 41 is the positive terminal connected to the junction of the plurality of protrusions 31AT in the positive electrode 31, and extends from the inside of the outer packaging film 20 to the outside. The positive electrode lead 41 contains a conductive material such as a metal, specifically aluminum. The shape of the positive electrode lead 41 is not particularly limited; specifically, it can be any of the following: a thin plate or a mesh.

[0183] [Negative lead]

[0184] like Figure 3 As shown, the negative electrode lead 42 is a negative terminal connected to the junction of multiple protrusions 32AT in the negative electrode 32, and extends from the inside of the outer packaging film 20 to the outside. Preferably, the negative electrode lead 42 is connected to the large-diameter carbon fiber portion 1 in the negative electrode 32. This is because it improves the electrical conductivity between the negative electrode 32 and the negative electrode lead 42. The negative electrode lead 42 contains a conductive material such as a metal, a specific example of which is copper. Here, the lead-out direction of the negative electrode lead 42 is the same as that of the positive electrode lead 41. The details regarding the shape of the negative electrode lead 42 are the same as the details regarding the shape of the positive electrode lead 41.

[0185] [Sealing film]

[0186] Sealing film 51 is inserted between outer packaging film 20 and positive lead 41, and sealing film 52 is inserted between outer packaging film 20 and negative lead 42. Alternatively, one or both of sealing films 51 and 52 may be omitted.

[0187] The sealing film 51 is a sealing component that prevents external gases from entering the interior of the outer packaging film 20. Furthermore, the sealing film 51 contains a polymer compound such as a polyolefin that has a tight seal with respect to the positive electrode lead 41; specific examples of this polyolefin include polypropylene.

[0188] The sealing membrane 52, except that it is a sealing component that provides a tight seal relative to the negative electrode lead 42, has the same structure as the sealing membrane 51. That is, the sealing membrane 52 contains a polymer compound such as polyolefin that provides a tight seal relative to the negative electrode lead 42.

[0189] <2-2. Actions>

[0190] During charging of the secondary battery, lithium is deintercalated from the positive electrode 31 in the battery element 30 and intercalated into the negative electrode 32 via the electrolyte. Conversely, during discharging of the secondary battery, lithium is deintercalated from the negative electrode 32 in the battery element 30 and intercalated into the positive electrode 31 via the electrolyte. During these charging and discharging processes, lithium is intercalated and deintercalated in an ionic state.

[0191] <2-3. Manufacturing Method>

[0192] In the case of manufacturing a secondary battery, after the positive electrode 31 and the negative electrode 32 are fabricated and the electrolyte is prepared by following the steps of an example described below, the secondary battery is assembled, and after the assembly, the secondary battery is stabilized.

[0193] [The production of the positive electrode]

[0194] First, a mixture (positive electrode paste) consisting of positive electrode active material, positive electrode binder, and positive electrode conductive agent is added to a solvent to prepare a paste-like positive electrode paste slurry. This solvent can be an aqueous solvent or an organic solvent. Next, the positive electrode paste slurry is coated onto both sides (excluding the protrusions 31AT) of the positive electrode current collector 31A, thereby forming a positive electrode active material layer 31B. Finally, the positive electrode active material layer 31B is compressed and molded using a roller press or the like. In this case, the positive electrode active material layer 31B can be heated, or the compression molding process can be repeated multiple times. Thus, the positive electrode active material layer 31B is formed on both sides of the positive electrode current collector 31A, thereby fabricating the positive electrode 31.

[0195] [Making the negative electrode]

[0196] The negative electrode 32, which includes the protrusion 32AT, is manufactured by following the same steps as those for manufacturing the negative electrode 10 described above.

[0197] [Preparation of Electrolyte]

[0198] An electrolyte salt is added to a solvent. The electrolyte salt is then dispersed or dissolved in the solvent, thus preparing an electrolyte solution.

[0199] [Assembly of a secondary battery]

[0200] First, the positive electrode 31 and the negative electrode 32 are alternately stacked with a separator 33 in between, thereby creating a laminate (not shown). This laminate has the same structure as the battery element 30, except that no electrolyte is impregnated in any of the positive electrode 31, the negative electrode 32, and the separator 33.

[0201] Next, the multiple protrusions 31AT are joined together, and the multiple protrusions 32AT are joined together. Next, the positive lead 41 is joined to the joint of the multiple protrusions 31AT, and the negative lead 42 is connected to the joint of the multiple protrusions 32AT.

[0202] Next, the laminate is housed inside the recess 20U, and then the outer packaging film 20 (welded layer / metal layer / surface protective layer) is folded so that the outer packaging films 20 are facing each other. Next, using a heat fusion method or the like, the outer peripheral portions of two sides of the facing outer packaging films 20 (welded layers) are joined together, thereby housing the laminate inside the bag-shaped outer packaging film 20.

[0203] Finally, the electrolyte is injected into the inside of the pouch-shaped outer packaging film 20, and then the outer periphery of the remaining side of the outer packaging film 20 (welded layer) is joined together using a heat fusion method or the like. In this case, the sealing film 51 is inserted between the outer packaging film 20 and the positive electrode lead 41, and the sealing film 52 is inserted between the outer packaging film 20 and the negative electrode lead 42.

[0204] Therefore, an electrolyte is impregnated into the laminate to create a battery element 30, which serves as the laminated electrode body. The battery element 30 is then sealed inside a pouch-shaped outer packaging film 20 to assemble a secondary battery.

[0205] Stabilization of secondary batteries

[0206] The assembled secondary battery is then charged and discharged. Various conditions, such as ambient temperature, number of charge / discharge cycles, and charging / discharging conditions, can be arbitrarily set. This forms a coating on the surfaces of both the positive electrode 31 and the negative electrode 32, thereby stabilizing the electrochemical state of the secondary battery. Thus, the secondary battery is completed.

[0207] <2-4. Functions and Effects>

[0208] According to this secondary battery, the negative electrode 32 has the same structure as the negative electrode 10 described above. Therefore, for the same reasons as described with respect to the negative electrode 10, excellent initial capacity characteristics, excellent expansion characteristics, excellent load characteristics, and excellent cycle characteristics can be obtained.

[0209] In addition, if the secondary battery is a lithium-ion secondary battery, sufficient battery capacity can be stably obtained by utilizing the insertion and extraction of lithium, thus achieving higher performance.

[0210] Apart from this, the function and effect of the secondary battery are the same as those of the negative electrode 10 mentioned above.

[0211] <3. Variations>

[0212] Next, we will explain the variations.

[0213] As explained below, the structures of the negative electrode 10 and the secondary battery can be modified appropriately, as described below. Furthermore, any two or more of the variations described below can be combined with each other.

[0214] [Variation Example 1]

[0215] As with Figure 2 corresponding Figure 5 As shown, some or all of the plurality of particle sections 3 (primary particles 3A) may include a central section 3X and a covering section 3Y. The covering section 3Y has a thickness T. Figure 5 In, with Figure 2 The difference is that only particle section 3 is shown in magnification.

[0216] The central part 3X has the same as Figure 2 The structure of particle section 3 (primary particle 3A) shown is the same, therefore it contains silicon-containing material.

[0217] The covering portion 3Y covers the surface of the central portion 3X. This covering portion 3Y may cover the entire surface of the central portion 3X, or it may only cover a portion of the surface of the covering portion 3Y. In the latter case, the covering portion 3Y may also cover the surface of the central portion 3X at multiple mutually separated locations. Figure 5 In order to simplify the illustration, the case where the covering part 3Y covers the entire surface of the central part 3X is shown.

[0218] (The material forming the cover is a carbon-containing material)

[0219] Here, the covering part 3Y may also contain any one or more carbon-containing materials. Specific examples of carbon-containing materials are amorphous carbon and graphite, etc.

[0220] The average thickness AT of the cover portion 3Y is not particularly limited and can therefore be set arbitrarily. The steps for calculating the average thickness AT of the cover portion 3Y are as follows. First, by following the same steps as when calculating the average fiber diameter AD1, an observation result (observation image) of the cross-section of the negative electrode 10 is obtained. Next, after selecting any 20 cover portions 3Y, the thickness T of each of the 20 cover portions 3Y is measured. It should be noted that when the thickness of a cover portion 3Y varies depending on the location, the maximum value of its thickness T is selected. Finally, the average of the 20 thicknesses T is calculated as the average thickness AT.

[0221] In forming a plurality of particle portions 3 including the central portion 3X and the cover portion 3Y (containing carbon material), a silicon-containing material powder is prepared as the central portion 3X, and then the carbon-containing material is deposited on the surface of the central portion 3X using a vapor phase method, thereby forming the cover portion 3Y. The type of vapor phase method is not particularly limited, but specifically, it is any one or more of vacuum evaporation, CVD, and sputtering methods.

[0222] In this case, the conductivity of each of the multiple particle sections 3 increases. As a result, the conductivity of the negative electrode 10 is further improved, thus achieving a higher efficiency.

[0223] (The material forming the cover = ion-conducting material)

[0224] Alternatively, the covering portion 3Y may also contain any one or more ion-conducting materials. Specific examples of ion-conducting materials are lithium phosphate nitride and solid electrolytes such as lithium phosphate. The composition of the lithium phosphate nitride is not particularly limited; specifically, it is Li. 3.30 PO 3.90 N 0.17 wait.

[0225] Another specific example of ion-conducting materials is a gel electrolyte in which the electrolyte is held in place by a matrix polymer compound. The structure of the electrolyte is as described above. Specific examples of the matrix polymer compound are polyethylene oxide and polyvinylidene fluoride, etc.

[0226] The details regarding the average thickness AT of the cover portion 3Y are as described above.

[0227] The steps for forming multiple particle portions 3, including the central portion 3X and the cover portion 3Y (ion-conducting material), are as follows. When using a solid electrolyte as the ion-conducting material, the cover portion 3Y is directly formed on the surface of each of the multiple central portions 3X using a vapor-phase method such as sputtering. When using a gel electrolyte as the ion-conducting material, a solution containing an electrolyte, a matrix polymer compound, and a diluent is coated onto the surface of each of the multiple central portions 3X, and then the solution is dried. Alternatively, the multiple central portions 3X can be impregnated in a solution.

[0228] In this case, since ion-conducting materials are used in each of the multiple particle sections 3 to improve the ion conductivity of the electrode reactants, a higher effect can be obtained.

[0229] In particular, by utilizing the multiple particle portions 3 containing ion-conducting material in the covering portion 3Y, the negative electrode 10 can be applied to an all-solid-state battery. This is because, since the expansion and contraction of the negative electrode 10 can be suppressed, the increase in the interfacial resistance between the negative electrode 10 and the solid electrolyte can be suppressed. Thus, the all-solid-state battery can achieve both ensuring safety and improving energy density.

[0230] [Variation Example 2]

[0231] As with Figure 5 corresponding Figure 6 As shown, some or all of the multiple particle parts 3 (primary particles 3A) may include an inner covering part 3Y1 and an outer covering part 3Y2 while including a central part 3X.

[0232] The structure of the central portion 3X is as described above. One of the inner covering portion 3Y1 and the outer covering portion 3Y2 contains a carbon-containing material, and the other of the inner covering portion 3Y1 and the outer covering portion 3Y2 contains an ion-conducting material. That is, the inner covering portion 3Y1 may contain a carbon-containing material, and the outer covering portion 3Y2 may contain an ion-conducting material. Alternatively, the inner covering portion 3Y1 may contain an ion-conducting material, and the outer covering portion 3Y2 may contain a carbon-containing material.

[0233] The details of the carbon-containing material and the ion-conducting material are as described above. Furthermore, the average thickness of the inner cover portion 3Y1 and the average thickness of the outer cover portion 3Y2 are the same as the average thickness AT described above. Additionally, the forming methods of the inner cover portion 3Y1 and the outer cover portion 3Y2 are the same as the forming method of the cover portion 3Y.

[0234] In this case, since the conductivity and ionic conductivity are improved in each of the multiple particle sections 3, a higher effect can be obtained.

[0235] [Variation Example 3]

[0236] As with Figure 2 corresponding Figures 7-9 As shown, some or all of the multiple particle portions 3 (primary particles 3A) can form composite secondary particles 3BP, which include a portion of multiple small-diameter carbon fiber portions 2 and one or both of multiple ion-conducting materials 4. The composite secondary particles 3BP have a particle size P2. Figures 7-9 In, with Figure 2 The difference is that only particle section 3 (composite secondary particle 3BP) is shown in enlarged form.

[0237] (Composite secondary particles containing multiple small-diameter carbon fiber sections)

[0238] Specifically, such as Figure 7As shown, since multiple particle sections 3 (primary particles 3A) are granulated together with a portion of multiple small-diameter carbon fiber sections, the multiple primary particles 3A and the multiple small-diameter carbon fiber sections 2 can also be intertwined in the composite secondary particles 3BP formed by the multiple particle sections 3. Thus, the multiple primary particles 3A are electrically connected to each other and physically connected to each other via the multiple small-diameter carbon fiber sections 2.

[0239] The average particle size AP2 of the composite secondary particles 3BP is not particularly limited, but is preferably 300 nm to 10000 nm. This is because it can effectively suppress the expansion and contraction of the particle portion 3 while ensuring conductivity, and the electrode reactant can move easily and sufficiently.

[0240] The steps for calculating the average particle size AP2 are the same as those for calculating the average particle size AP1, except that after measuring the particle size P2 of any 10 composite secondary particles 3BP, the average of the 10 particle sizes P2 is taken as the average particle size AP2.

[0241] In forming composite secondary particles 3BP comprising the plurality of small-diameter carbon fiber portions 2, after preparing a dispersion comprising the plurality of particle portions 3, the plurality of small-diameter carbon fiber portions 2, and a solvent for dilution, the dispersion is spray-dried using a spray drying method. Details regarding the solvent are described above. The dispersion may contain a binder, details of which are described above. Thus, by using the dispersion for granulation, granules comprising the plurality of particle portions 3 and the plurality of small-diameter carbon fiber portions 2 are formed (composite secondary particles 3BP).

[0242] In this case, since the multiple particle parts 3 and the multiple small-diameter carbon fiber parts 2 are firmly connected to each other, the conductivity of the negative electrode 10 is improved more stably.

[0243] (Composite secondary particles containing multiple ion-conducting materials)

[0244] In addition, such as Figure 8 As shown, since multiple particle units 3 (primary particles 3A) are granulated together with multiple ion-conducting materials 4, in the composite secondary particles 3BP formed by the multiple particle units 3, two or more primary particles 3A can be electrically connected to each other and physically linked to each other through one or more ion-conducting materials 4.

[0245] Detailed information regarding the average particle size AP2 of the composite secondary particles 3BP and Figure 7 The situation is the same as shown. That is, the average particle size AP2 of the composite secondary particles 3BP is preferably 300 nm to 10000 nm.

[0246] Except for replacing the multiple small-diameter carbon fiber sections 2 with ion-conducting materials, the formation steps of the composite secondary particles 3BP containing the multiple ion-conducting materials 4 are the same as... Figure 7 The situation is the same as shown.

[0247] In this case, since the multiple particle sections 3 are firmly connected to the multiple ion-conducting materials 4, the ion conductivity of the negative electrode 10 is improved more stably.

[0248] (Composite secondary particles containing multiple small-diameter carbon fiber sections and multiple ion-conducting materials)

[0249] In addition, such as Figure 9 As shown, since multiple particle portions 3 (primary particles 3A) are granulated together with a portion of multiple small-diameter carbon fiber portions 2 and multiple ion-conducting materials 4, the composite secondary particles 3BP formed by these multiple particle portions 3 can include both the multiple small-diameter carbon fiber portions 2 and the multiple ion-conducting materials 4. Details regarding the structure of the composite secondary particles 3BP comprising each of the multiple small-diameter carbon fiber portions 2 and the multiple ion-conducting materials 4 are as described above (see [reference]). Figure 7 as well as Figure 8 ).

[0250] Detailed information regarding the average particle size AP2 of the composite secondary particles 3BP and Figure 7 The situation is the same as shown. That is, the average particle size AP2 of the composite secondary particles 3BP is preferably 300 nm to 10000 nm.

[0251] The formation steps of the composite secondary particle 3BP, which includes multiple small-diameter carbon fiber portions 2 and multiple ion-conducting materials 4, involve using multiple small-diameter carbon fiber portions 2 and ion-conducting materials 4, in addition to using ion-conducting materials. Figure 7 The situation is the same as shown.

[0252] In this case, since the multiple particle parts 3, the multiple small-diameter carbon fiber parts 2, and the multiple ion-conducting materials 4 are firmly connected to each other, the conductivity and ion conductivity of the negative electrode 10 are steadily improved.

[0253] (Other composite secondary particles)

[0254] Although there is no specific illustration here, Figure 5 as well as Figure 6 The structures of the particle section 3 (primary particle 3A) shown respectively can be compared with... Figures 7-9 The structures of the composite secondary particles 3BP shown are combined with each other. Specifically, Figure 5 The multiple particle units 3 (primary particles 3A) shown can be formed Figures 7-9 The composite secondary particles 3BP are shown separately. Figure 6The multiple particle units 3 (primary particles 3A) shown can be formed Figures 7-9 The composite secondary particles 3BP shown separately can also exist in a mixture. In these cases, the same effect can be obtained.

[0255] [Variation Example 4]

[0256] A septum 33 was used as a porous membrane. However, although not specifically illustrated here, a laminated septum containing layers of polymer compounds may be used instead of septum 33.

[0257] Specifically, the laminated separator comprises a porous membrane with one and two opposite surfaces and a polymer compound layer disposed on one or both surfaces of the porous membrane. This is because, due to the improved adhesion of the separator to each of the positive electrode 31 and the negative electrode 32, the winding misalignment of the battery element 30 can be suppressed. Therefore, even if an electrolyte decomposition reaction occurs, the secondary battery is less prone to expansion. The structure of the porous membrane is the same as that described for separator 33. The polymer compound layer comprises a polymer compound such as polyvinylidene fluoride (PVDF). This is because PVDF and similar compounds possess excellent physical strength and excellent electrochemical stability.

[0258] It should be noted that one or both of the porous membrane and the polymer compound layer may contain any one or more types of insulating particles. This is because multiple insulating particles promote heat dissipation when the secondary battery heats up, thus improving the safety (heat resistance) of the secondary battery. Insulating particles can be one or both of inorganic particles and resin particles. Specific examples of inorganic particles include alumina, aluminum nitride, boehmite, silicon dioxide, titanium dioxide, magnesium oxide, and zirconium oxide. Specific examples of resin particles include acrylic resin and styrene resin.

[0259] In the case of fabricating a layered membrane, a precursor solution containing a polymer compound and a solvent is prepared, and then the precursor solution is coated onto one or both sides of a porous membrane. Alternatively, the porous membrane can be impregnated in the precursor solution instead of coating the porous membrane with the precursor solution. It should be noted that the precursor solution may also contain multiple insulating particles.

[0260] When using this layered separator, lithium ions can also move between the positive electrode 31 and the negative electrode 32, thus achieving the same effect. In this case, especially as described above, even greater performance can be achieved due to the improved safety of the secondary battery.

[0261] [Variation Example 5]

[0262] An electrolyte solution, which is a liquid electrolyte, was used. However, although not specifically illustrated here, an electrolyte layer, which is a gel electrolyte, can also be used instead of the electrolyte solution.

[0263] In the battery element 30 using an electrolyte layer, the positive electrode 31 and the negative electrode 32 are alternately stacked with a separator 33 and an electrolyte layer in between. In this case, the electrolyte layer is located between the positive electrode 31 and the separator 33, and the electrolyte layer is located between the negative electrode 32 and the separator 33. Alternatively, the electrolyte layer may be located only between the positive electrode 31 and the separator 33, or only between the negative electrode 32 and the separator 33.

[0264] Specifically, the electrolyte layer comprises an electrolyte and a polymer compound, and the electrolyte is held in place by the polymer compound. This is to prevent leakage of the electrolyte. The structure of the electrolyte is as described above. The polymer compound includes polyvinylidene fluoride, etc. In forming the electrolyte layer, a precursor solution comprising the electrolyte, the polymer compound, and a solvent for dilution is prepared, and then the precursor solution is coated on one or both sides of each of the positive electrode 31 and the negative electrode 32. Details regarding the solvent are as described above.

[0265] When this electrolyte layer is used, lithium ions can also move between the positive electrode 31 and the negative electrode 32 via the electrolyte layer, thus achieving the same effect. In this case, in particular, as described above, even better performance can be obtained because electrolyte leakage can be prevented.

[0266] <4. Uses of Secondary Batteries>

[0267] Finally, the uses (application examples) of secondary batteries will be explained.

[0268] There are no particular limitations on the uses of secondary batteries. As a power source, a secondary battery can be the main power source for electronic devices and electric vehicles, or it can be an auxiliary power source. The main power source is the power source used preferentially, regardless of the availability of other power sources. An auxiliary power source is a power source used in place of the main power source, or a power source switched from the main power source.

[0269] Specific examples of applications for rechargeable batteries are as follows: electronic devices such as camcorders, digital still cameras, mobile phones, laptops, stereo headphones, portable radios, and portable information terminals; backup power supplies and storage devices such as memory cards; power tools such as electric drills and chainsaws; battery packs integrated into electronic devices; medical electronic devices such as pacemakers and hearing aids; electric vehicles (including hybrid vehicles); and power storage systems such as household or industrial battery systems that pre-store power in preparation for emergencies. In these applications, one or multiple rechargeable batteries can be used.

[0270] Battery packs can use single cells or battery arrays. Electric vehicles are vehicles that operate (drive) using a secondary battery as a power source, and can also be hybrid vehicles that have a power source other than the secondary battery. In household electricity storage systems, electricity stored in a secondary battery that serves as an electricity storage source can be used to operate household electrical products, etc.

[0271] Here, we will specifically illustrate one application example of a secondary battery. The structure described below is only an example and can be modified as appropriate.

[0272] Figure 10 This describes the frame structure of the battery pack. The battery pack described here is a pouch cell that uses a rechargeable battery and is used in electronic devices such as smartphones.

[0273] like Figure 10 As shown, the battery pack includes a power supply 61 and a circuit board 62. The circuit board 62 is connected to the power supply 61 and includes a positive terminal 63, a negative terminal 64, and a temperature detection terminal 65.

[0274] The power supply 61 includes a secondary battery. In this secondary battery, the positive lead is connected to the positive terminal 63, and the negative lead is connected to the negative terminal 64. The power supply 61 is connected to an external source via the positive terminal 63 and the negative terminal 64, thus enabling charging and discharging. The circuit board 62 includes a control unit 66, a switch 67, a thermistor (PTC) element 68, and a temperature detection unit 69. Alternatively, the PTC element 68 may be omitted.

[0275] The control unit 66 includes a central processing unit (CPU) and memory, and controls the overall operation of the battery pack. The control unit 66 detects and controls the operating status of the power supply 61 as needed.

[0276] It should be noted that when the voltage of power supply 61 (secondary battery) reaches the overcharge detection voltage or over-discharge detection voltage, control unit 66 cuts off switch 67 to prevent charging current from flowing through the current path of power supply 61. The overcharge detection voltage is not particularly limited, but is specifically 4.2 ± 0.05 V, and the over-discharge detection voltage is also not particularly limited, but is specifically 2.4 ± 0.1 V.

[0277] Switch 67 includes a charging control switch, a discharging control switch, a charging diode, and a discharging diode, etc., and switches the connection between power supply 61 and external devices according to the instructions of control unit 66. Switch 67 includes a field-effect transistor (MOSFET) using metal-oxide-semiconductor, and the charging and discharging current is detected based on the on-resistance of switch 67.

[0278] The temperature detection unit 69 includes temperature detection elements such as a thermistor, measures the temperature of the power supply 61 using the temperature detection terminal 65, and outputs the temperature measurement result to the control unit 66. The temperature measurement result measured by the temperature detection unit 69 is used for situations such as when the control unit 66 performs charge / discharge control in case of abnormal heating, and when the control unit 66 performs correction processing when calculating the remaining capacity.

[0279] Example

[0280] The embodiments of this technology are described below.

[0281] <Examples 1-7 and Comparative Examples 1, 2>

[0282] After the secondary battery was manufactured, its characteristics were evaluated. To evaluate these characteristics, two types of secondary batteries (a first secondary battery and a second secondary battery) were manufactured.

[0283] [Making First and Secondary Batteries]

[0284] The first and second-generation batteries (Examples 1-7) were fabricated using the steps described below. These first and second-generation batteries are... Figure 3 as well as Figure 4 The image shows a laminated film type lithium-ion secondary battery (battery capacity = 7mAh~12mAh).

[0285] It should be noted that in the following explanation, the manufacturing process of the negative electrode 32 will be referenced frequently to illustrate the process. Figure 1 as well as Figure 2 The constituent elements of the negative electrode 10 shown.

[0286] (The production of the positive electrode)

[0287] First, 97 parts by mass of the positive electrode active material (LiNi) 0.8 Co 0.15 Al 0.05 O2), 2.2 parts by weight of positive electrode binder (polyvinylidene fluoride), and 0.8 parts by weight of positive electrode conductive agent (Ketjen Black) are mixed together to prepare a positive electrode mixture. Next, the positive electrode mixture is added to a solvent (N-methyl-2-pyrrolidone as the organic solvent), and the solvent is stirred using a rotary mixer to prepare a paste-like positive electrode mixture slurry. Next, the positive electrode mixture slurry is coated onto both sides (excluding the protrusions 31AT) of the positive electrode current collector 31A (aluminum foil, thickness = 15 μm) containing the protrusions 31AT using a coating apparatus, and then the positive electrode mixture slurry is dried (drying temperature = 120°C) to form a positive electrode active material layer 31B. Finally, the positive electrode active material layer 31B is compressed and molded using a hand press (bulk density of positive electrode active material layer 31B = 3.5 g / cm³). 3Thus, a positive electrode 31 containing a protrusion 31AT was manufactured.

[0288] (Making the negative electrode)

[0289] First, carbon paper (CP, thickness = 50 μm) was prepared, comprising multiple large-diameter carbon fiber sections 1 including protrusions 32AT. This carbon paper has a three-dimensional mesh structure formed by the multiple large-diameter carbon fiber sections 1, and therefore has multiple voids 10G. The inner diameter of each of the multiple voids 10G is larger than the inner diameter of the negative electrode 32 after completion. It should be noted that the average fiber diameter AD1 (nm) of the multiple large-diameter carbon fiber sections 1 is shown in Table 1.

[0290] Next, a dispersion was prepared by mixing a first dispersion containing silicon-containing material with a second dispersion containing carbon-containing material (multiple small-diameter carbon fiber portions 2).

[0291] The first dispersion is prepared by mixing silicon-containing material powder (silicon monomer (Si, purity = 95%), binder (polyimide), and solvent (N-methyl-2-pyrrolidone as an organic solvent) with each other and stirring the solvent using a rotary mixer.

[0292] The second dispersion is prepared by mixing multiple small-diameter carbon fiber segments 2 (single-layer carbon nanotubes (SWCNTs) or vapor-grown carbon fibers (VGCF)), a binder (polyvinylidene fluoride), and a solvent (N-methyl-2-pyrrolidone as an organic solvent) and stirring the solvent using a rotary mixer. It should be noted that the average fiber diameter AD2 (nm) of the multiple small-diameter carbon fiber segments 2 is shown in Table 1.

[0293] The composition (by weight) of the dispersion is: silicon-containing material powder: binder (polyimide): multiple small-diameter carbon fiber parts 2: binder (polyvinylidene fluoride) = 85:10 (converted to solid components): 0.8:4.2.

[0294] Next, a dispersion liquid is coated onto multiple large-diameter carbon fiber portions 1 (excluding protrusions 32AT), thereby allowing the dispersion liquid to penetrate the interior of the three-dimensional network structure formed by the multiple large-diameter carbon fiber portions 1. As a result, silicon-containing material powder is fixed onto the surface of each of the multiple large-diameter carbon fiber portions 1, thus forming multiple particle portions 3, and multiple small-diameter carbon fiber portions 2 are fixed onto the surface of the multiple particle portions 3, thereby connecting the multiple small-diameter carbon fiber portions 2 to the surface of the multiple particle portions 3. In this case, the multiple particle portions 3 (primary particles 3A) are interconnected to form multiple secondary particles 3B. It should be noted that the average particle size AP1 (nm) of the multiple particle portions 3 (secondary particles 3B) is shown in Table 1. Thus, a negative electrode 32 including protrusions 32AT is fabricated.

[0295] Finally, the negative electrode 32 was stamped at room temperature (temperature = 23°C), and then heated in a nitrogen (N2) atmosphere (heating temperature = 350°C, heating time = 3 hours). Under these conditions, the porosity R (volume %) was varied by adjusting the stamping pressure, as shown in Table 1.

[0296] Thus, a negative electrode 10 comprising multiple large-diameter carbon fiber sections 1, multiple small-diameter carbon fiber sections 2, and multiple particle sections 3, and having multiple voids 10G, was completed. In manufacturing this negative electrode 10, the weight ratio M (wt%) was varied by adjusting the concentration of the silicon-containing material in the first dispersion and the concentration of the multiple small-diameter carbon fiber sections 2 in the second dispersion, as shown in Table 1.

[0297] (Preparation of electrolyte)

[0298] An electrolyte salt (lithium hexafluorophosphate) was added to a solvent, and the solvent was then stirred. The solvent used included ethylene carbonate as a cyclic carbonate, dimethyl carbonate as a chain carbonate, and monofluoroethylene carbonate as an additive (halogenated cyclic carbonate). The solvent mixing ratio (by weight) was ethylene carbonate:dimethyl carbonate:monofluoroethylene carbonate = 30:60:10. The electrolyte salt concentration was 1 mol / kg relative to the solvent. Thus, an electrolyte was prepared.

[0299] (Assembly of primary and secondary batteries)

[0300] First, a laminate (positive electrode 31 / separator 33 / negative electrode 32) is fabricated by stacking a positive electrode 31 containing protrusion 31AT and a negative electrode 32 containing protrusion 32AT on each other with a separator 33 (microporous polyethylene membrane, thickness = 20μm) in between.

[0301] Next, the positive lead 41 (aluminum foil) is bonded to the protrusion 31AT, and the negative lead 42 (copper foil) is bonded to the protrusion 32AT.

[0302] Next, the outer packaging film 20 (welding layer / metal layer / surface protective layer) is folded in such a way that the laminated body housed inside the recess 20U is clamped, and then the outer periphery of two sides of the outer packaging film 20 (welding layer) is heat-fused together, thereby housing the laminated body inside the bag-shaped outer packaging film 20. As the outer packaging film 20, an aluminum laminate film is used, which consists of a welding layer (polypropylene film, thickness = 30 μm), a metal layer (aluminum foil, thickness = 40 μm), and a surface protective layer (nylon film, thickness = 25 μm) stacked sequentially from the inside.

[0303] Finally, after injecting the electrolyte into the pouch-shaped outer packaging film 20, the outer periphery of the remaining edge of the outer packaging film 20 (welded layer) is thermally fused together under reduced pressure. In this case, a sealing film 51 (polypropylene film, thickness = 5 μm) is inserted between the outer packaging film 20 and the positive electrode lead 41, and a sealing film 52 (polypropylene film, thickness = 5 μm) is inserted between the outer packaging film 20 and the negative electrode lead 42.

[0304] Thus, the electrolyte permeates into the laminate, thereby creating the battery element 30. The battery element 30 is then sealed inside the outer packaging film 20, thereby assembling a first and second-generation battery.

[0305] It should be noted that, in the case of assembling the first and second batteries, the thickness of the positive electrode active material layer 31B was adjusted so that the capacity ratio, that is, the ratio of the positive electrode charging capacity to the negative electrode charging capacity (=positive electrode charging capacity / negative electrode charging capacity), became 0.7.

[0306] (Stabilization of the first and second batteries)

[0307] The first and second batteries were subjected to one charge-discharge cycle at room temperature (temperature = 23℃). During charging, a constant current of 0.1C was used until the voltage reached 4.2V, followed by constant voltage charging at that 4.2V until the current reached 0.025C. During discharging, a constant current of 0.1C was used until the voltage reached 2.0V. 0.1C refers to the current value required to fully discharge the battery capacity (theoretical capacity) in 10 hours, and 0.025C refers to the current value required to fully discharge the battery capacity in 40 hours.

[0308] Thus, a coating is formed on the surfaces of both the positive electrode 31 and the negative electrode 32, thereby achieving electrochemical stability in the first and second batteries. This completes the first and second batteries.

[0309] [Making a Secondary Battery]

[0310] Except for using a lithium metal plate (thickness = 100 μm) to replace the positive electrode 31, a second secondary battery (battery capacity = 10 mAh to 15 mAh) was manufactured by following the same steps as the first secondary battery manufacturing steps described above.

[0311] Here, the first secondary battery that uses the positive electrode 31 as the counter electrode of the negative electrode 32 is called a full cell, while the second secondary battery that uses a lithium metal plate as the counter electrode of the negative electrode 32 is called a half cell.

[0312] [Making a secondary battery for comparison]

[0313] For comparison purposes, two types of secondary batteries (Comparative Examples 1 and 2) were fabricated using the same steps, except that a negative electrode for comparison was made using a metal current collector.

[0314] In the fabrication of this negative electrode, firstly, 82 parts by mass of the negative electrode active material (silicon monomer (Si), purity = 95%, median particle size D50 = 50 nm), 10 parts by mass of the negative electrode binder (polyimide) (converted to solid content), 3 parts by mass of the negative electrode conductive agent (carbon black), and 5 parts by mass of other negative electrode conductive agents (carbon nanotube dispersion) are mixed to form a negative electrode mixture. This carbon nanotube dispersion comprises 0.8 parts by mass of carbon nanotubes (the aforementioned plurality of small-diameter carbon fiber portions 2) and 4.2 parts by mass of the dispersion medium (polyvinylidene fluoride).

[0315] Next, the negative electrode mixture is added to a solvent (N-methyl-2-pyrrolidone as the organic solvent), and the organic solvent is stirred using a rotary mixer to prepare a paste-like negative electrode mixture slurry. Next, the negative electrode mixture slurry is coated onto both sides of the negative electrode current collector (copper foil (Cu), thickness = 10 μm or 6 μm) as a metal current collector using a coating device, and then the negative electrode mixture slurry is dried to form a layer of negative electrode active material. Thus, the negative electrode is assembled.

[0316] Finally, the negative electrode was stamped at room temperature (temperature = 23°C), and then heated in a nitrogen atmosphere (heating temperature = 350°C, heating time = 3 hours). Under these conditions, as shown in Table 1, the porosity R of the negative electrode active material layer was varied by adjusting the stamping pressure.

[0317] It should be noted that the "Metal Current Collector (Thickness)" column in Table 1 indicates whether a metal current collector is present or not, and if the metal current collector is used, the material and thickness (μm) are shown.

[0318] [Characteristics Evaluation of Secondary Batteries]

[0319] The characteristics of the secondary battery (initial capacity characteristics, expansion characteristics, load characteristics, and cycle characteristics) were evaluated, and the results are shown in Table 1.

[0320] In this case, the initial capacity characteristics were evaluated using a second secondary battery (half-cell) and the expansion characteristics, load characteristics, and cycle characteristics were evaluated using a first secondary battery (full-cell) through the steps described below.

[0321] (Initial capacity characteristics)

[0322] In a normal temperature environment (temperature = 23℃), the secondary battery was subjected to pressure while undergoing one charge-discharge cycle, and the discharge capacity was measured. Based on the formula: initial capacity (mAh / g) = discharge capacity (mAh) / total weight of negative electrode 32 (g), the initial capacity, used as an indicator to evaluate initial capacity characteristics, was calculated.

[0323] In this case, pressure is applied to the secondary battery in the direction in which the positive electrode 31 and the negative electrode 32 are stacked together with the separator 33 in between, thereby allowing the secondary battery to charge and discharge while the positive electrode 31 and the negative electrode 32 are tightly sealed together with the separator 33 in between. It should be noted that when a metal current collector is used, the total weight of the negative electrode 32 includes the weight of the metal current collector; conversely, when a metal current collector is not used, the total weight of the negative electrode 32 does not include the weight of the metal current collector.

[0324] During charging, a constant current of 0.1C is used for charging until the voltage reaches 0.005V, and then a constant voltage of 0.005V is used for charging until the current reaches 0.01C. During discharging, a constant current of 0.1C is used for discharging until the voltage reaches 1.5V. 0.01C refers to the current value required to fully discharge the battery within 100 hours.

[0325] (Expansion characteristics)

[0326] First, the thickness of the secondary battery (thickness before charging) was measured in a normal temperature environment (temperature = 23℃).

[0327] Next, the secondary battery was charged while pressure was applied, and then the thickness of the secondary battery (the thickness after charging) was measured.

[0328] In this case, similar to the evaluation of the initial capacity characteristics described above, pressure is applied to the secondary battery, thereby charging the secondary battery while the positive electrode 31 and the negative electrode 32 are sealed together through the separator 33. During charging, constant current charging is performed at 0.1C until the voltage reaches 4.2V, and then constant voltage charging is performed at this 4.2V until the current reaches 0.01C.

[0329] Finally, based on the formula expansion rate (%) = [(thickness after charging - thickness before charging) / thickness before charging] × 100, the expansion rate, which is used as an indicator to evaluate expansion characteristics, is calculated.

[0330] (Load characteristics)

[0331] First, the secondary battery was charged and discharged for one cycle at room temperature (temperature = 23°C), and the discharge capacity (discharge capacity of the first cycle) was determined.

[0332] During charging, the battery is charged at a constant current of 0.2C until the voltage reaches 4.2V, and then charged at a constant voltage of 4.2V until the current reaches 0.025C. During discharging, the battery is discharged at a constant current of 0.2C until the voltage reaches 2.5V. 0.2C refers to the current value required to fully discharge the battery within 5 hours.

[0333] Next, the discharge capacity (discharge capacity of the second cycle) was measured by subjecting the secondary battery to one charge-discharge cycle in the same environment. The charge-discharge conditions were the same as those of the first cycle, except that the charging current and the discharging current were changed to 5C. 5C refers to the current value at which the battery capacity is fully discharged in 0.2 hours.

[0334] Finally, based on the formula that load maintenance rate (%) = (discharge capacity of the second cycle / discharge capacity of the first cycle) × 100, the load maintenance rate, which is used as an indicator to evaluate load characteristics, is calculated.

[0335] (Cyclic Characteristics)

[0336] First, the secondary battery was charged and discharged for one cycle at room temperature (temperature = 23°C), and the discharge capacity (discharge capacity of the first cycle) was measured. Next, the secondary battery was charged and discharged for 199 cycles at the same environment, and the discharge capacity (discharge capacity of the 200th cycle) was measured. The charge and discharge conditions were the same as those for the first cycle when the load characteristics described above were evaluated.

[0337] Finally, based on the formula that capacity retention (%) = (discharge capacity of the 200th cycle / discharge capacity of the 1st cycle) × 100, the capacity retention rate, which is used as an indicator to evaluate cycle characteristics, is calculated.

[0338] (Standardization of characteristic values)

[0339] It should be noted that the initial capacity values ​​shown in Table 1 are standardized values ​​with the initial capacity of the secondary battery of Comparative Example 1, which uses a metal current collector (copper foil with a thickness of 10 μm), set to 100. The values ​​of expansion rate, load retention rate, and capacity retention rate are also standardized values ​​based on the secondary battery of Comparative Example 1.

[0340] [Table 1]

[0341]

[0342] [Inspection]

[0343] As shown in Table 1, the initial capacity, expansion rate, load maintenance rate, and capacity maintenance rate vary significantly depending on the structure of the negative electrode. Hereinafter, the values ​​of each of the initial capacity, expansion rate, load maintenance rate, and capacity maintenance rate in Comparative Example 1 will be used as the comparison benchmark.

[0344] Specifically, when a metal current collector is used, if the thickness of the metal current collector is reduced (Comparative Example 2), the initial capacity increases, but the expansion rate increases, and the load maintenance rate and capacity maintenance rate decrease, respectively.

[0345] In contrast, when multiple large-diameter carbon fiber sections 1, multiple small-diameter carbon fiber sections 2, and multiple particle sections 3 are used without using a metal current collector (Examples 1-7), the average fiber diameters AD1 and AD2 and the porosity R meet appropriate conditions (AD1 = 50 nm to 7000 nm, AD2 = 1 nm to 200 nm, R = 42 vol% to 73 vol%), thereby increasing the initial capacity, load retention rate, and capacity retention rate, and decreasing the expansion rate.

[0346] In this case, in particular, if the weight ratio M is 40% to 76% by weight, the expansion rate is sufficiently reduced, and the initial capacity, load retention rate, and capacity retention rate are sufficiently increased. Furthermore, if the average particle size AP is 30 nm to 2000 nm, the expansion rate is sufficiently reduced, and the initial capacity, load retention rate, and capacity retention rate are sufficiently increased.

[0347] <Examples 8-11>

[0348] As shown in Table 2, except that multiple particle portions 3, including a central portion 3X and a covering portion 3Y, were formed in the fabrication process of the negative electrode 32, a secondary battery was fabricated using the same steps as in Example 1, and then the characteristics of the secondary battery were evaluated.

[0349] As the forming material for the 3Y cover portion, a carbon-containing material or an ion-conducting material was used, and as the ion-conducting material, a solid electrolyte or a gel electrolyte was used. As the carbon-containing material, amorphous carbon (AC) was used. As the ion-conducting material (solid electrolyte), lithium phosphate nitride (Li₂O₃) was used. 3.30 PO 3.90 N 0.17 Alternatively, lithium phosphate (Li3PO4) or lithium phosphate (Li3PO4) may be used. As a gel electrolyte, a mixture of electrolyte and matrix polymer (polyvinylidene fluoride (PVDF)) is used. In this gel electrolyte, the electrolyte is held in place by the matrix polymer. It should be noted that the average thickness AT (nm) of the covering portion 3Y is shown in Table 2.

[0350] In the case where multiple particle portions 3 containing carbon-containing material are formed in the cover portion 3Y, carbon-containing material (amorphous carbon) is deposited on the surface of each of the multiple central portions 3X (as silicon monomers containing silicon material, purity = 95%) using the CVD method.

[0351] In the case where multiple particle portions 3 containing a solid electrolyte (lithium phosphate) are formed in the cover portion 3Y, lithium phosphate is deposited on the surface of each of the multiple center portions 3X (which are silicon monomers containing silicon material with a purity of 95%) using a sputtering method targeting lithium phosphate.

[0352] In the case where multiple particle portions 3 containing a solid electrolyte (lithium nitride) are formed in the cover portion 3Y, lithium phosphate nitride is deposited on the surface of each of the multiple central portions 3X (as silicon monomers containing silicon material, purity = 95%) in a nitrogen atmosphere using a sputtering method targeting lithium phosphate.

[0353] In the case where the covering portion 3Y forms multiple particle portions 3 containing a gel electrolyte (electrolyte and matrix polymer compound), firstly, an electrolyte salt (lithium hexafluorophosphate) is added to a solvent (ethylene carbonate and propylene carbonate), and the solvent is stirred to prepare an electrolyte. Next, the electrolyte is mixed with a matrix polymer compound (polyvinylidene fluoride) to prepare a precursor solution. The mixing ratio (by weight) of this precursor solution is ethylene carbonate:propylene carbonate:lithium hexafluorophosphate:polyvinylidene fluoride = 42:42:13:3. Finally, the precursor solution is coated onto the surface of each of the multiple central portions 3X (as silicon monomers containing silicon, purity = 95%), and then the precursor solution is dried.

[0354] [Table 2]

[0355]

[0356] As shown in Table 2, when multiple particle portions 3, including a central portion 3X and a covering portion 3Y, are used (Examples 8 to 11), compared with the case where the covering portion 3Y is not used (Example 1), the initial capacity, load maintenance rate, and capacity maintenance rate can be increased while the increase in expansion rate is sufficiently suppressed, or the load maintenance rate and capacity maintenance rate can be increased respectively.

[0357] <Examples 12-16>

[0358] As shown in Table 3, except that in the fabrication process of the negative electrode 32, each of the plurality of particle portions 3 is formed as a composite secondary particle 3BP containing a plurality of small-diameter carbon fiber portions 2, the secondary battery was fabricated by the same steps as in Example 1, and then the characteristics of the secondary battery were evaluated.

[0359] In forming the composite secondary particles 3BP, firstly, silicon-containing material powder (silicon monomer, purity = 95%), multiple small-diameter carbon fiber segments 2 (SWCNT), and binder (lithium polyacrylate) are added to a solvent (pure water as an aqueous solvent), and then the solvent is stirred to prepare a dispersion. The mixing ratio (weight ratio) of the dispersion is silicon-containing material powder: multiple small-diameter carbon fiber segments 2: binder = 94:1:4. Next, the dispersion is sprayed using a spray drying device, and the sprayed material (granules) is dried.

[0360] [Table 3]

[0361]

[0362] As shown in Table 3, when using composite secondary particles 3BP containing multiple small-diameter carbon fiber portions 2 (Examples 12-16), compared with the case where the composite secondary particles 3BP are not used (Example 1), one or more of the initial capacity, expansion rate, load retention rate, and capacity retention rate are improved. In particular, when using composite secondary particles 3BP, if the average particle size AP2 is 100 nm to 10000 nm, the expansion rate is sufficiently reduced, and the initial capacity, load retention rate, and capacity retention rate are sufficiently increased.

[0363] <Examples 17-21>

[0364] As shown in Table 4, except that in the fabrication process of the negative electrode 32, each of the plurality of particle parts 3 forms a composite secondary particle 3BP containing an ion-conducting material (gel electrolyte), a secondary battery was fabricated by the same steps as in Example 1, and then the characteristics of the secondary battery were evaluated.

[0365] In the formation of the composite secondary particles 3BP, firstly, an electrolyte salt (lithium hexafluorophosphate) is added to a solvent (ethylene carbonate and propylene carbonate), and the solvent is stirred to prepare an electrolyte. Next, the electrolyte is mixed with a matrix polymer compound (polyvinylidene fluoride) to prepare a precursor solution. The mixing ratio (by weight) of this precursor solution is ethylene carbonate:propylene carbonate:lithium hexafluorophosphate:polyvinylidene fluoride = 42:42:13:3. Next, a silicon-containing material powder (silicon monomer, purity = 95%) is mixed with the precursor solution, and the precursor solution is stirred to prepare a dispersion. Finally, the dispersion is sprayed using a spray dryer to dry the sprayed material (granules).

[0366] [Table 4]

[0367]

[0368] As shown in Table 4, even when using composite secondary particles 3BP containing ion-conducting materials (gel electrolytes), the same results were obtained as when using composite secondary particles 3BP containing multiple small-diameter carbon fiber portions 2 (Table 3). That is, when using composite secondary particles 3BP containing ion-conducting materials (Examples 17-21), compared to not using composite secondary particles 3BP (Example 1), any one or more of the initial capacity, expansion rate, load retention rate, and capacity retention rate were improved. In particular, when using composite secondary particles 3BP, if the average particle size AP2 is 100 nm to 10000 nm, the expansion rate is sufficiently reduced, and the initial capacity, load retention rate, and capacity retention rate are sufficiently increased.

[0369] [Summarize]

[0370] As shown in Tables 1 to 4, when the negative electrode 32 (negative electrode 10) comprises multiple large-diameter carbon fiber sections 1, multiple small-diameter carbon fiber sections 2, and multiple particle sections 3, and has multiple voids 10G, with each of the multiple large-diameter carbon fiber sections 1 and the multiple small-diameter carbon fiber sections 2 containing carbon-containing material and each of the multiple particle sections 3 containing silicon-containing material, and the average fiber diameters AD1 and AD2 and the porosity R satisfy the above-mentioned appropriate conditions, the initial capacity, load retention rate, and capacity retention rate increase respectively, and the expansion rate decreases. Therefore, in the secondary battery, excellent initial capacity characteristics, excellent expansion characteristics, excellent load retention rate, and excellent cycle characteristics can be obtained.

[0371] The above describes one implementation method and an embodiment of the present technology. However, the structure of the present technology is not limited to the structure described in one implementation method and embodiment, and various modifications can be made.

[0372] Specifically, the case of a laminated film type battery structure for secondary batteries has been described. However, since the battery structure of secondary batteries is not particularly limited, other battery structures such as cylindrical, square, coin-shaped, and button-shaped batteries can be used.

[0373] Furthermore, the case where the battery element structure is a stacked type has been explained. However, since the element structure of the battery element is not particularly limited, other element structures such as wound type and repeatedly folded type can be used. In the wound type, the positive and negative electrodes are wound with a separator in between, and in the repeatedly folded type, the positive and negative electrodes are placed opposite each other with a separator in between and folded into a Z-shape.

[0374] Furthermore, while the use of lithium as the electrode reactant has been described, it is not particularly limited. Specifically, as mentioned above, the electrode reactant can be other alkali metals such as sodium and potassium, or alkaline earth metals such as beryllium, magnesium, and calcium. Additionally, other light metals such as aluminum can also be used as the electrode reactant.

[0375] The effects described in this specification are merely illustrative, and therefore the effects of this technology are not limited to those described herein. Thus, other effects can also be obtained with this technology.

Claims

1. A secondary battery, comprising: positive electrode; The negative electrode comprises multiple first fiber sections, multiple particle sections, and multiple second fiber sections, and has multiple voids; and Electrolyte The plurality of first fiber portions are interconnected to form a three-dimensional network structure with the plurality of voids, and each of the plurality of first fiber portions contains carbon as a constituent element. The plurality of particle portions cover the surfaces of the plurality of first fiber portions, at least a portion of the plurality of particle portions are interconnected, and each of the plurality of particle portions contains silicon as a constituent element. At least a portion of the plurality of second fiber portions is connected to the surface of the plurality of particle portions, and each of the plurality of second fiber portions contains carbon as a constituent element. The average fiber diameter of the plurality of first fiber portions is 50 nm or more and 7000 nm or less. The average fiber diameter of the plurality of second fiber sections is 1 nm or more and 200 nm or less, and the porosity of the negative electrode is 42% or more and 73% or less by volume.

2. The secondary battery according to claim 1, wherein, The weight of the plurality of particle portions relative to the sum of the weights of the plurality of first fiber portions, the plurality of particle portions, and the plurality of second fiber portions is 40% by weight or more and 76% by weight or less.

3. The secondary battery according to claim 1 or 2, wherein, The silicon content in each of the plurality of particle sections is 80% by weight or more.

4. The secondary battery according to any one of claims 1 to 3, wherein, At least a portion of the plurality of second fiber portions is connected to each of two or more first fiber portions via a portion of the plurality of particle portions.

5. The secondary battery according to any one of claims 1 to 4, wherein, Each of the plurality of particle units is a primary particle. At least a portion of the plurality of particle units are interconnected to form a plurality of secondary particles. The average particle size of the plurality of secondary particles is greater than 30 nm and less than 2000 nm.

6. The secondary battery according to any one of claims 1 to 4, wherein, At least a portion of the plurality of particle units includes: The central part contains silicon as a constituent element; and The surface of the central portion is covered, and the covering contains carbon as a constituent element.

7. The secondary battery according to any one of claims 1 to 4, wherein, At least a portion of the plurality of particle units includes: The central part contains silicon as a constituent element; and A covering portion that covers the surface of the central portion and contains an ion-conducting material.

8. The secondary battery according to claim 7, wherein, The ion-conducting material contains at least one of lithium nitride and lithium phosphate.

9. The secondary battery according to any one of claims 1 to 8, wherein, Each of the plurality of particle units is a primary particle. At least a portion of the plurality of particle portions forms a plurality of secondary particles, including a portion of the plurality of second fiber portions. The average particle size of the plurality of secondary particles is greater than 300 nm and less than 10,000 nm.

10. The secondary battery according to any one of claims 1 to 8, wherein, Each of the plurality of particle units is a primary particle. At least a portion of the plurality of particle sections forms a plurality of secondary particles comprising a plurality of ion-conducting materials. The average particle size of the plurality of secondary particles is greater than 300 nm and less than 10,000 nm.

11. The secondary battery according to any one of claims 1 to 10, wherein, The plurality of first fiber sections comprise carbon paper. Each of the plurality of second fiber sections comprises at least one of a single-layer carbon nanotube and a vapor-grown carbon fiber.

12. The secondary battery according to any one of claims 1 to 11, The secondary battery is a lithium-ion secondary battery.

13. A negative electrode for a secondary battery, It comprises multiple first fiber sections, multiple particle sections, and multiple second fiber sections, and has multiple voids. The plurality of first fiber portions are interconnected to form a three-dimensional network structure with the plurality of voids, and each of the plurality of first fiber portions contains carbon as a constituent element. The plurality of particle portions cover the surfaces of the plurality of first fiber portions, at least a portion of the plurality of particle portions are interconnected, and each of the plurality of particle portions contains silicon as a constituent element. At least a portion of the plurality of second fiber portions is connected to the surface of the plurality of particle portions, and each of the plurality of second fiber portions contains carbon as a constituent element. The average fiber diameter of the plurality of first fiber portions is 50 nm or more and 7000 nm or less. The average fiber diameter of the plurality of second fiber portions is 1 nm or more and 200 nm or less. The porosity is above 42% by volume and below 73% by volume.

Images