Negative electrode for secondary battery and secondary battery

Abstract

This secondary batter comprises: a positive electrode; a plurality of first fiber parts; a negative electrode including a plurality of particle parts and a plurality of second fiber parts, and having a plurality of gaps; and an electrolyte. The plurality of first fiber parts, by being connected to each other, form a three-dimensional network structure having a plurality of gaps, and each among the plurality of first fiber parts includes carbon as a constituent element. The plurality of particle parts cover the surface of each among the plurality of first fiber parts, some among the plurality of particle parts are connected to each other, and each among the plurality of particle parts contains silicon as a constituent element. At least some among the plurality of the second fiber parts are connected to the surfaces of the plurality of particle parts, and each among the plurality of second fiber parts contains carbon as a constituent element. The average fiber diameter of the plurality of first fiber parts is 50 to 7,000 nm, inclusive, the average fiber diameter of the plurality of second fiber parts is 1 to 200 nm, inclusive, and the porosity of the negative electrode is 42 to 73 volume%, inclusive.

Description

[Technical Field]

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

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

[0003] Specifically, the materials used to form the negative electrode for a lithium ion secondary battery are a porous conductive substrate (carbon), a conductive material (such as carbon nanotubes), and an active material (such as silicon), and the porosity (void fraction) of the negative electrode is specified (see, for example, Patent Document 1).

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

[0005] Materials used to form the negative electrode for a lithium ion secondary battery include a copper current collector and porous silicon having a three-dimensional network structure coated with a conductive substance such as a carbon material, and the average porosity of the porous silicon is specified (see, for example, Patent Document 3). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-335283 [Patent Document 2] Special Publication No. 2015-531977 [Patent Document 3] Japanese Patent Application Laid-Open No. 2012-084521 Summary of the Invention

[0007] Although various studies have been conducted on the configuration of secondary batteries, the initial capacity characteristics, swelling characteristics, load characteristics, and cycle characteristics of the secondary batteries are still insufficient, and there is room for improvement.

[0008] Therefore, there is a demand for a negative electrode for a secondary battery and a secondary battery that can provide excellent initial capacity characteristics, excellent swollenness characteristics, excellent load characteristics, and excellent cycle characteristics.

[0009] According to one embodiment of the present technology, a secondary battery negative electrode includes a plurality of first fibrous portions, a plurality of particle portions, and a plurality of second fibrous portions, and has a plurality of voids. The plurality of first fibrous portions are connected to each other to form a three-dimensional network structure having a plurality of voids, and each of the plurality of first fibrous portions contains carbon as a constituent element. The plurality of particle portions cover the surfaces of the plurality of first fibrous portions, and some of the plurality of particle portions are connected to each other, and each of the plurality of particle portions contains silicon as a constituent element. At least some of the plurality of second fibrous portions are connected to the surfaces of the plurality of particle portions, and each of the plurality of second fibrous portions contains carbon as a constituent element. The average fiber diameter of the plurality of first fibrous portions is 50 nm to 7000 nm, the average fiber diameter of the plurality of second fibrous portions is 1 nm to 200 nm, and the porosity is 42 vol% to 73 vol%.

[0010] A secondary battery according to an embodiment of the present technology includes a positive electrode, a negative electrode, and an electrolyte solution, and the negative electrode has a configuration similar to that of the negative electrode for a secondary battery according to the embodiment of the present technology described above.

[0011] The details (definitions, calculation procedures, etc.) of the "average fiber diameter of the plurality of first fiber portions," "average fiber diameter of the plurality of second fiber portions," and "porosity" will be described later.

[0012] According to the negative electrode for a secondary battery or the secondary battery of one embodiment of the present technology, the negative electrode for a secondary battery includes the above-mentioned plurality of first fibrous portions, plurality of particle portions, and plurality of second fibrous portions, and has a plurality of voids. The above-mentioned conditions are satisfied with respect to the average fiber diameter of the plurality of first fibrous portions, the average fiber diameter of the plurality of second fibrous portions, and the porosity, and therefore excellent initial capacity characteristics, excellent swollenness characteristics, excellent load characteristics, and excellent cycle characteristics can be obtained.

[0013] Note that the effects of the present technology are not necessarily limited to the effects described here, but may be any of a series of effects related to the present technology described below. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic diagram illustrating a configuration of a negative electrode for a secondary battery according to an embodiment of the present technology. [Figure 2] 2 is an enlarged cross-sectional view showing the configuration of each of a large diameter carbon fiber portion, a small diameter carbon fiber portion, and a particle portion shown in FIG. 1. FIG. [Figure 3] 1 is a perspective view illustrating a configuration of a secondary battery according to an embodiment of the present technology. [Figure 4] FIG. 4 is an enlarged cross-sectional view showing the configuration of the battery element shown in FIG. [Figure 5] 1 is a schematic diagram illustrating the configuration of a negative electrode for a secondary battery according to Modification 1. FIG. [Figure 6] 10 is a schematic diagram illustrating the configuration of a negative electrode for a secondary battery according to Modification 2. FIG. [Figure 7] 10 is a schematic diagram illustrating the configuration of a negative electrode for a secondary battery according to Modification 3. FIG. [Figure 8] 10 is a schematic diagram showing another configuration of a negative electrode for a secondary battery according to Modification 3. FIG. [Figure 9] 10 is a schematic diagram showing still another configuration of the negative electrode for a secondary battery according to Modification 3. FIG. [Figure 10] FIG. 1 is a block diagram illustrating a configuration of an application example of a secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present technology will be described in detail with reference to the drawings. The description will be made in the following order. 1.Negative electrode for secondary batteries 1-1.Configuration 1-2. Manufacturing method 1-3. Action and effects 2. Secondary battery 2-1.Configuration 2-2.Operation 2-3. Manufacturing method 2-4. Action and effects 3. Variations 4. Uses of secondary batteries

[0016] <1. Negative electrode for secondary batteries> First, a negative electrode for a secondary battery (hereinafter simply referred to as "negative electrode") according to one embodiment of the present technology will be described.

[0017] This negative electrode is used in a secondary battery, which is an electrochemical device. However, the negative electrode may also be used in other electrochemical devices besides secondary batteries. The type of other electrochemical device is not particularly limited, but specifically includes a capacitor.

[0018] In addition, in electrochemical devices such as the secondary battery, the negative electrode absorbs and releases an electrode reactant during an electrode reaction. The type of electrode reactant is not particularly limited, but specifically, it is a light metal such as an alkali metal or alkaline earth metal. The alkali metal includes lithium, sodium, potassium, etc., and the alkaline earth metal includes beryllium, magnesium, calcium, etc.

[0019] <1-1.Configuration> Fig. 1 shows a schematic diagram of a negative electrode 10, which is an example of a negative electrode. Fig. 2 shows enlarged cross-sectional views of the large-diameter carbon fiber portion 1, the small-diameter carbon fiber portion 2, and the particle portion 3 shown in Fig. 1.

[0020] 2 shows one large diameter carbon fiber portion 1 and one small diameter carbon fiber portion 2, as well as a plurality of particle portions 3 covering the surface of the one large diameter carbon fiber portion 1. Also, FIG. 2 shows cross sections of the large diameter carbon fiber portion 1, the small diameter carbon fiber portion 2, and the particle portion 3 that intersect with the longitudinal direction of the large diameter carbon fiber portion 1 and the small diameter carbon fiber portion 2, respectively.

[0021] 1 and 2, this 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 also has a plurality of voids 10G. That is, the negative electrode 10 does not include a current collector such as a metal foil (hereinafter referred to as a "metal current collector"), and is therefore a so-called metal current collector-less electrode.

[0022] [Multiple large diameter carbon fiber sections] As shown in Fig. 1, the large diameter carbon fiber portions 1 are a plurality of first fiber portions having an average fiber diameter AD1 larger than the average fiber diameter AD2 of the small diameter carbon fiber portions 2, and each of the large diameter carbon fiber portions 1 has a fiber diameter D1 as shown in Fig. 2. The large diameter carbon fiber portions 1 are connected to each other to form the three-dimensional network structure having the above-described plurality of voids 10G.

[0023] 1 shows a case where each of the plurality of large diameter carbon fiber portions 1 is linear for the sake of simplicity. However, the state (shape) of each of the plurality of large diameter carbon fiber portions 1 is not particularly limited, and therefore may be curved or branched, or may be a mixture of two or more of these.

[0024] Here, as described above, the plurality of large diameter carbon fiber portions 1 are connected to one another to form a three-dimensional network structure, more specifically, are randomly entangled with one another. The plurality of large diameter carbon fiber portions 1 may be bonded to one another via a carbide (not shown) such as a polymer compound, or may be connected to one another via one or more small diameter carbon fiber portions 2. As a result, the plurality of large diameter carbon fiber portions 1 have a plurality of connection points, and the large diameter carbon fiber portions 1 are electrically connected to one another at the connection points.

[0025] The average fiber diameter AD1 of the plurality of large diameter carbon fiber portions 1 is 50 nm to 7000 nm. This is because the fiber diameter D1 is sufficiently large in the plurality of large diameter carbon fiber portions 1 that are the main portions of the negative electrode 10. As a result, a sufficient conductive network (three-dimensional mesh structure) is formed inside the negative electrode 10, improving the conductivity of the negative electrode 10.

[0026] The procedure for calculating the average fiber diameter AD1 is as follows. First, the negative electrode 10 is collected and then washed using a washing solvent such as dimethyl carbonate. When a secondary battery including the negative electrode 10 is obtained, the secondary battery is disassembled to collect the negative electrode 10. Next, the negative electrode 10 is cut using an ion milling device or the like to expose a cross section of the negative electrode 10.

[0027] Next, a cross section of the negative electrode 10 is observed using a scanning electron microscope (SEM) or a transmission electron microscope (TEM) to obtain an observation result (observation image) of the cross section. This makes it possible to identify multiple large-diameter carbon fiber portions 1 in the observation image. Observation conditions such as acceleration voltage and magnification can be set arbitrarily.

[0028] Next, 20 randomly selected large diameter carbon fiber portions 1 are measured for the fiber diameter D1 of each of the 20 large diameter carbon fiber portions 1. Finally, the average value of the 20 fiber diameters D1 is calculated to obtain the average fiber diameter AD1.

[0029] There is no particular limitation on the average fiber length of each of the plurality of large diameter carbon fiber portions 1. This is because, as long as the plurality of large diameter carbon fiber portions 1 having the above-described average fiber diameter AD1 are connected to each other, a sufficient conductive network (three-dimensional mesh structure) is formed regardless of the fiber length.

[0030] Each of the plurality of large diameter carbon fiber portions 1 contains carbon as a constituent element, and therefore contains a so-called carbon-containing material, which is a general term for materials that contain carbon as a constituent element.

[0031] Specifically, the plurality of large diameter carbon fiber portions 1 contain carbon paper because the plurality of large diameter carbon fiber portions 1 are sufficiently connected to each other and the average fiber diameter AD1 is sufficiently large, so that a sufficient conductive network (three-dimensional mesh structure) is formed.

[0032] However, the plurality of large diameter carbon fiber portions 1 may be a material obtained by processing a plurality of fibrous carbon materials having the above-mentioned average fiber diameter AD1 to form a three-dimensional network structure. The type of this fibrous carbon material is not particularly limited, but specific examples include vapor grown carbon fiber (VGCF) and carbon nanofiber (CNF). In addition, the type of fibrous carbon material may be a multi-walled carbon nanotube (multi-walled carbon nanotube (MWCNT)) such as a double-walled carbon nanotube (DWCNT).

[0033] [Multiple small diameter carbon fiber sections] As shown in Fig. 1, the plurality of small diameter carbon fiber portions 2 are a plurality of second fiber portions having an average fiber diameter AD2 smaller than the average fiber diameter AD1 of the plurality of large diameter carbon fiber portions 1, and each of the plurality of small diameter carbon fiber portions 2 has a fiber diameter D2 as shown in Fig. 2. Here, each of the plurality of small diameter carbon fiber portions 2 is fixed to the surface of the plurality of particle portions 3, and is therefore connected to the surface of the plurality of particle portions 3.

[0034] 1 shows a case where each of the plurality of small diameter carbon fiber portions 2 is linear for the sake of simplicity. However, the state (shape) of each of the plurality of small diameter carbon fiber portions 2 is not particularly limited, as in the case of the state of the plurality of large diameter carbon fiber portions 1 described above.

[0035] The reason why the negative electrode 10 includes a plurality of small diameter carbon fiber portions 2 together with a plurality of large diameter carbon fiber portions 1 is that the plurality of large diameter carbon fiber portions 1 form a conductive network, and the plurality of small diameter carbon fiber portions 2 also form a dense conductive network, thereby significantly improving the conductivity of the negative electrode 10.

[0036] In particular, it is preferable that some or all of the plurality of small diameter carbon fiber portions 2 (plurality of small diameter carbon fiber portions 2R) are each connected to two or more large diameter carbon fiber portions 1 via some of the plurality of particle portions 3. This is because two or more large diameter carbon fiber portions 1 are electrically connected to each other via the small diameter carbon fiber portions 2R. This forms a denser conductive network, further improving the conductivity of the negative electrode 10.

[0037] 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 described above, and specifically, is 1 / 10,000 to 1 / 2, and preferably 1 / 300 to 1 / 5, of the average fiber diameter AD1.

[0038] More specifically, the average fiber diameter AD2 is 1 nm to 200 nm. In a system in which a plurality of large diameter carbon fiber portions 1 and a plurality of small diameter carbon fiber portions 2 coexist, the average fiber diameter AD2 is sufficiently smaller than the average fiber diameter AD1, and therefore the plurality of small diameter carbon fiber portions 2 are easily dispersed inside the negative electrode 10. As a result, a dense conductive network is formed by the plurality of small diameter carbon fiber portions 2, and the conductivity of the negative electrode 10 is further improved.

[0039] The procedure for calculating the average fiber diameter AD2 is the same as the procedure for calculating the average fiber diameter AD1 described above, except that the fiber diameter D2 of any 20 small-diameter carbon fiber portions 2 is measured, and the average value of the fiber diameters D2 of the 20 small-diameter carbon fiber portions 2 is used as the average fiber diameter AD2. However, when the fiber diameter D2 is small, it is preferable to use a TEM rather than an SEM to observe the cross section of the negative electrode 10.

[0040] There is no particular limitation on the average fiber length of each of the plurality of small diameter carbon fiber portions 2. This is because, as long as the plurality of small diameter carbon fiber portions 2 having the above-described average fiber diameter AD2 are present inside the negative electrode 10, a dense conductive network is formed regardless of the fiber length.

[0041] Each of the plurality of small diameter carbon fiber portions 2 contains carbon as a constituent element, and therefore, like each of the plurality of large diameter carbon fiber portions 1, contains a carbon-containing material.

[0042] Specifically, each of the plurality of small diameter carbon fiber portions 2 contains a fibrous carbon material such as carbon nanotubes, vapor grown carbon fibers (VGCF), and carbon nanofibers (CNF), because this facilitates the sufficient dispersion of the plurality of small diameter carbon fiber portions 2 within the negative electrode 10 and the formation of a dense conductive network.

[0043] The type of carbon nanotube is not particularly limited, and may be a single-walled carbon nanotube (SWCNT) or a multi-walled carbon nanotube (MWCNT). A specific example of a multi-walled carbon nanotube is a double-walled carbon nanotube (DWCNT).

[0044] In particular, it is preferable that each of the plurality of small-diameter carbon fiber portions 2 is one or both of single-walled carbon nanotubes and vapor-grown carbon fibers, because the average fiber diameter AD2 becomes sufficiently small, and the plurality of small-diameter carbon fiber portions 2 are sufficiently dispersed inside the negative electrode 10, and a denser conductive network is formed.

[0045] [Multiple particle parts] 1, the plurality of particle portions 3 cover the surfaces of the plurality of large diameter carbon fiber portions 1, and have an average particle size AP1. Each of the plurality of particle portions 3 has a particle size P1, as shown in FIG.

[0046] Here, the plurality of particle portions 3 are so-called primary particles 3A, and some or all of the plurality of particle portions 3 (plurality of primary particles 3A) are connected to one another. That is, some or all of the plurality of primary particles 3A are densely packed together to form 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 voids 10G.

[0047] The number of primary particles 3A forming secondary particle 3B is not particularly limited as long as it is 2 or more. The number of secondary particles 3B is also not particularly limited as long as it is 2 or more. Fig. 2 shows a case where a plurality of secondary particles 3B are formed.

[0048] The particle size P1 is the particle size of the secondary particles 3B, and therefore the average particle size AP1 is the average particle size of the secondary particles 3B.

[0049] 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 cover only 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 cover the surface of the large diameter carbon fiber portion 1 at a plurality of locations that are spaced apart from one another. In FIG. 1, for the sake of simplicity, the case where the plurality of particle portions 3 cover a portion of the surface of each of the plurality of large diameter carbon fiber portions 1 is shown.

[0050] As a result, each of the plurality of large-diameter carbon fiber portions 1 having a relatively large average fiber diameter AD1 is covered on the surface with a plurality of particle portions 3, while each of the plurality of small-diameter carbon fiber portions 2 having a relatively small average fiber diameter AD2 is not covered on the surface with a plurality of particle portions 3.

[0051] The reason why the negative electrode 10 includes a plurality of particle portions 3 is that a high energy density can be obtained while the electrode reactant can be easily absorbed and released.

[0052] Specifically, since each of the plurality of particle portions 3 contains a silicon-containing material, which will be described later, a high energy density can be obtained.

[0053] Moreover, because the plurality of particle portions 3 cover the surfaces of the plurality of large-diameter carbon fiber portions 1, the initial inner diameters of the plurality of voids 10G formed by the plurality of large-diameter carbon fiber portions 1 are randomly narrowed. As a result, in the completed negative electrode 10, a plurality of voids 10G having different inner diameters are likely to be formed, and the electrode reactant material is likely to move through the plurality of voids 10G. In this case, the electrode reactant material is likely to move smoothly, particularly even if the current value during the electrode reaction increases. Therefore, the electrode reactant material is likely to be occluded and released during the electrode reaction of the negative electrode 10.

[0054] In this case, in particular, secondary particles 3B are formed from a plurality of particle portions 3 (primary particles 3A), and a plurality of pores 3G having an inner diameter smaller than the inner diameter of voids 10G are formed inside the secondary particles 3B. That is, the negative electrode 10 has two types of spaces different in size inside, namely, voids 10G having a relatively large inner diameter and pores 3G having a relatively small inner diameter. As a result, during the electrode reaction, expansion and contraction of the particle portions 3 is suppressed by utilizing not only the voids 10G but also the pores 3G, and similarly, the electrode reactant is easily moved by utilizing not only the voids 10G but also the pores 3G.

[0055] The average particle size AP1 of the plurality of particle portions 3 is not particularly limited, but is preferably 30 nm to 2000 nm, because the amount of coverage of each surface of the plurality of large diameter carbon fiber portions 1 with the plurality of particle portions 3 becomes sufficiently large, and therefore the conductivity of the negative electrode 10 is ensured while a sufficient energy density can be obtained in the negative electrode 10.

[0056] The procedure for calculating the average particle diameter AP1 is as follows. First, an observation result (observation image) of the cross section of the negative electrode 10 is obtained using the same procedure as in calculating the average fiber diameter AD1 described above. Next, 10 arbitrary particle portions 3 are selected, and the particle diameter P1 of each of the 10 particle portions 3 is measured. Note that if the particle diameter P1 varies depending on the location within a single particle portion 3, the smallest value of the particle diameter P1 is selected. Finally, the average value of the 10 particle diameters P1 is calculated to obtain the average particle diameter AP1.

[0057] Furthermore, each of the plurality of particle portions 3 contains silicon as a constituent element, and therefore contains a so-called silicon-containing material, because silicon has an excellent ability to absorb and release electrode reactants, and therefore a high energy density can be obtained.

[0058] The silicon-containing material is a general term for materials containing silicon as a constituent element. Therefore, the silicon-containing material may be silicon itself, a silicon alloy, a silicon compound, a mixture of two or more of these, or a material containing one or more of these phases. However, the silicon itself may contain trace amounts of impurities. That is, the purity of the silicon itself does not have to be 100%. These impurities include impurities unintentionally contained in the manufacturing process of the silicon itself and oxides unintentionally formed due to oxygen in the atmosphere. The impurity content in the silicon itself is preferably as low as possible, more preferably 5% by weight or less.

[0059] The silicon alloy contains, as constituent elements other than silicon, any one or more of metallic elements such as tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium. The silicon compound contains, as constituent elements other than silicon, any one or more of non-metallic elements such as carbon and oxygen. However, the silicon compound may further contain any one or more of the series of metallic elements described for the silicon alloy as constituent elements other than silicon.

[0060] Specific examples of the silicon alloy include Mg2Si, Ni2Si, TiSi2, MoSi2, CoSi2, NiSi2, CaSi2, CrSi2, Cu5Si, FeSi2, MnSi2, NbSi2, TaSi2, VSi2, WSi2, ZnSi2, and SiC. However, the composition (mixing ratio of silicon and metallic elements) of the silicon alloy can be arbitrarily changed.

[0061] Specific examples of the silicon compound include SiB4, SiB6, Si3N4, Si2N2O, SiO v (0 < v ≦ 2) and LiSiO. However, the range of v may be 0.2 < v < 1.4.

[0062] Among them, the silicon-containing material is preferably elemental silicon. 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, that is, the silicon content (purity) in the silicon-containing material is not particularly limited, but among them, it is preferably 80% by weight or more, and more preferably 80% by weight to 100% by weight. This is because a significantly high energy density can be obtained.

[0063] The weight percentage M (wt%), which is the ratio of the weight M3 of the plurality of particle portions 3 to the sum of the weight M1 of the plurality of large-diameter carbon fiber portions 1, the weight M2 of the plurality of small-diameter carbon fiber portions 2, and the weight M3 of the plurality of particle portions 3, is not particularly limited, but is preferably 40 wt% to 76 wt%. This is because 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) in the negative electrode 10 is optimized, thereby ensuring electrical conductivity and achieving sufficient energy density. This weight percentage M is calculated based on the formula M=[M3 / (M1+M2+M3)]×100.

[0064] The procedure for calculating the weight percentage M is as follows. First, the negative electrode 10 is collected and then washed using a washing 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. Note that any TG-DTA device can be used to analyze the negative electrode 10.

[0065] In the analysis of this negative electrode 10, the weight loss when the heating temperature was increased to approximately 450°C was the weight of the electrolyte, binder, etc., and the weight loss when the heating temperature was increased to approximately 450°C to approximately 1350°C was the weight (weights M1 and M2) of the carbon components (plurality of large-diameter carbon fiber portions 1 and plural small-diameter carbon fiber portions 2). As a result, the weight of the remaining components was the weight (weight M3) of the silicon component (plurality of particle portions 3).

[0066] The temperature (approximately 450°C) at which the weight loss due to the electrolyte and other factors is detected may vary depending on the type of binder. Specifically, when the binder is polyvinylidene fluoride, the minimum value of the DTA differential curve is taken as the disappearance temperature, which is approximately 460°C.

[0067] Finally, the weight ratio M is calculated using the weights M1, M2, and M3 based on the above formula.

[0068] Although not specifically shown here, a part or all of the surface of each of the plurality of particle portions 3 may be further coated with a coating layer. This coating layer contains one or more types of conductive materials such as carbon-containing materials and metal materials. This is because the conductivity of the negative electrode 10 is further improved. Details regarding the carbon-containing material are as described above. The type of metal material is not particularly limited.

[0069] When forming this coating layer, a silane coupling agent, a polymer-based material, or the like is used to ensure that the surface of the particle portion 3 can be sufficiently covered with the coating layer. By sufficiently covering the surface of the particle portion 3 with the coating layer, the decomposition reaction of the electrolyte on the surface of the particle portion 3 containing the silicon-containing material is suppressed.

[0070] [Porosity] As described above, the negative electrode 10 includes a three-dimensional network structure formed by a plurality of large-diameter carbon fiber portions 1, and therefore has a plurality of voids 10G.

[0071] The porosity R of the negative electrode 10, determined based on the plurality of voids 10G, is 42% to 73% by volume. Because the number of voids 10G present within the negative electrode 10 is optimized, even if each of the plurality of particle portions 3 containing a silicon-containing material expands and contracts during an electrode reaction, the internal stress (strain) generated by the expansion and contraction is appropriately alleviated by utilizing the plurality of voids 10G. This suppresses the expansion and contraction of the particle portions 3 even when the electrode reaction is repeated, thereby suppressing deterioration of the negative electrode 10. Deterioration of the negative electrode 10 includes chipping and cutting of the large-diameter carbon fiber portion 1, chipping and breakage of the small-diameter carbon fiber portion 2, and collapse and shedding of the particle portions 3.

[0072] The procedure for calculating the porosity R is as follows. After recovering and cleaning the negative electrode 10 using the same procedure as in calculating the average fiber diameter AD1 described above, a three-dimensional image of the negative electrode 10 is acquired using a focused ion beam scanning electron microscope (FIB-SEM), and the porosity R is calculated based on the three-dimensional image using image analysis processing. This image analysis processing can use GeoDict, an innovative materials development comprehensive package software from Math2Market GmbH.

[0073] [Other materials] The negative electrode 10 may further contain one or more of the other materials.

[0074] The type of other material is not particularly limited, but specifically, it is a binder, etc. This is because the plurality of large-diameter carbon fiber portions 1, the plurality of small-diameter carbon fiber portions 2, and the plurality of particle portions 3 are firmly connected to each other via the binder, thereby forming a strong conductive network.

[0075] The binder contains one or more polymer compounds, and specific examples of the polymer compounds include polyimide, polyvinylidene fluoride, polyacrylic acid, styrene-butadiene rubber, and carboxymethyl cellulose. When the negative electrode 10 contains a binder, some of the small-diameter carbon fiber portions 2 may be free and not connected to the surface of the particle portion 3.

[0076] <1-2. Manufacturing method> The negative electrode 10 is manufactured by the following procedure, which will be described below with reference to the case where carbon paper is used as the plurality of large diameter carbon fiber portions 1.

[0077] First, prepare carbon paper that is a plurality of large diameter carbon fiber portions 1. In this carbon paper, the plurality of large diameter carbon fiber portions 1 are connected to each other, so that a three-dimensional network structure having a plurality of voids 10G is formed.

[0078] Next, a powder of the silicon-containing material is added to the solvent. This disperses the powder of the silicon-containing material in the solvent, thereby preparing a first dispersion. This solvent may be an aqueous solvent or a non-aqueous solvent (organic solvent). In this case, a binder may be added to the solvent. Details regarding this binder are as described above.

[0079] Next, the plurality of small-diameter carbon fiber parts 2 are introduced into another solvent. As a result, the plurality of small-diameter carbon fiber parts 2 are dispersed in the solvent, and a second dispersion liquid is prepared. In this case, a binder may be added to the solvent. Details regarding the solvent and the binder are as described above.

[0080] Subsequently, the first dispersion and the second dispersion are mixed together to prepare a dispersion containing the silicon-containing material powder and the plurality of small-diameter carbon fiber parts 2, as described above.

[0081] Next, the dispersion liquid is applied to the plurality of large diameter carbon fiber portions 1, and then the dispersion liquid is dried. As a result, the dispersion liquid is impregnated into the interiors of the plurality of large diameter carbon fiber portions 1, so that the powder of the silicon-containing material is fixed to the surface of each of the plurality of large diameter carbon fiber portions 1, and the plurality of small diameter carbon fiber portions 2 are fixed to the surface of the powder of the silicon-containing material. Therefore, a plurality of particle portions 3 are formed that cover the surface of each of the plurality of large diameter carbon fiber portions 1, and the plurality of small diameter carbon fiber portions 2 are connected to the surfaces of the plurality of particle portions 3. However, instead of applying the dispersion liquid to the plurality of large diameter carbon fiber portions 1, the plurality of large diameter carbon fiber portions 1 may be immersed in the dispersion liquid.

[0082] When the plurality of particle portions 3 are formed, the inner diameter of some or all of the plurality of voids 10G decreases, and the porosity R before the formation of the plurality of particle portions 3 (so-called initial porosity R) decreases. However, if the initial porosity R is set to be sufficiently large, some or all of the plurality of voids 10G remain even after the formation of the plurality of particle portions 3, and therefore the porosity R can be calculated even after the formation of the plurality of particle portions 3. In other words, the porosity R can be controlled by adjusting the concentration of the silicon-containing material in the first dispersion.

[0083] As a result, the negative electrode 10 including 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 is produced.

[0084] When connecting a plurality of small-diameter carbon fiber portions 2 to the surfaces of a plurality of particle portions 3, instead of indirectly forming a plurality of small-diameter carbon fiber portions 2 on the surfaces of a plurality of particle portions 3 using a dispersion liquid, a plurality of small-diameter carbon fiber portions 2 may be formed directly on the surfaces of the plurality of particle portions 3. In this case, a metal catalyst is disposed on the surfaces of the plurality of particle portions 3, and then the plurality of small-diameter carbon fiber portions 2 are grown using a chemical vapor deposition (CVD) method or the like. As a result, each of the plurality of small-diameter carbon fiber portions 2 is firmly connected to the surfaces of the plurality of particle portions 3, forming a strong conductive network.

[0085] Finally, if necessary, the negative electrode 10 is pressed using a press or the like, and then the negative electrode 10 is fired. In this case, the porosity R can be controlled by adjusting the pressing pressure. The firing temperature can be set arbitrarily.

[0086] This completes the negative electrode 10, which 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. When producing 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 plurality of small-diameter carbon fiber portions 2 in the second dispersion.

[0087] In addition, when producing the negative electrode 10, a plurality of large-diameter carbon fiber portions 1 each having a plurality of particle portions 3 formed thereon may be obtained by the above-described procedure, and then a papermaking process may be used using the plurality of large-diameter carbon fiber portions 1 each having a plurality of particle portions 3 formed thereon and the plurality of small-diameter carbon fiber portions 2. In this case, a wet process such as papermaking may be used, or a dry process using a web or the like may be used. In this case, the negative electrode 10 is produced, which 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.

[0088] <1-3. Actions and Effects> This 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 containing a carbon-containing material, and each of the plurality of particle portions 3 containing a silicon-containing material, and the above-mentioned conditions for the average fiber diameters AD1, AD2 and the porosity R (AD1=50 nm to 7000 nm, AD2=1 nm to 200 nm, and R=42 vol% to 73 vol%) are satisfied.

[0089] In this case, as described above, the average fiber diameters AD1 and AD2 and the porosity R are each optimized in a system including 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 therefore, a series of actions described below are obtained.

[0090] First, inside the negative electrode 10, a conductive network (three-dimensional mesh structure) is formed by a plurality of large-diameter carbon fiber parts 1 containing a conductive carbon-containing material, and a dense conductive network is also formed by a plurality of small-diameter carbon fiber parts 2 similarly containing a conductive carbon-containing material.

[0091] Secondly, since each of the plurality of particle portions 3 contains a silicon-containing material that is excellent in occlusion and release of an electrode reactant, a high energy density can be obtained.

[0092] Third, since the surfaces of the plurality of large-diameter carbon fiber portions 1 are respectively covered with the plurality of particle portions 3, a plurality of voids 10G having different inner diameters are formed, and the electrode reactant can easily move through the plurality of voids 10G. As a result, even if the current value during the electrode reaction increases, the electrode reactant can easily be occluded and released.

[0093] Fourth, even if each of the plurality of particle portions 3 contains a silicon-containing material, the internal stress generated inside the negative electrode 10 during the electrode reaction, i.e., when each of the plurality of particle portions 3 expands and contracts, is alleviated by utilizing the plurality of voids 10G, thereby suppressing expansion and contraction of the negative electrode 10. This suppresses deterioration of the negative electrode 10 due to the internal stress generated when each of the plurality of particle portions 3 expands and contracts. In this case, even if the silicon content in the silicon-containing material is particularly high, the expansion and contraction of the negative electrode 10 is sufficiently suppressed, and therefore deterioration of the negative electrode 10 is effectively suppressed.

[0094] Fifth, secondary particles 3B are formed from multiple particle portions 3 (primary particles 3A), and multiple pores 3G are formed inside the secondary particles 3B. Therefore, during the electrode reaction, not only the voids 10G but also the pores 3G are utilized to suppress expansion and contraction of the particle portions 3, and similarly, not only the voids 10G but also the pores 3G are utilized to facilitate the movement of electrode reaction substances.

[0095] As a result, the energy density and the occlusion / desorption properties of the electrode reactant are ensured, while the expansion and contraction of the negative electrode 10 during the electrode reaction is suppressed, and the discharge capacity is less likely to decrease even when the electrode reaction is repeated. Therefore, a secondary battery using the negative electrode 10 can achieve excellent initial capacity characteristics, excellent swelling characteristics, excellent load characteristics, and excellent cycle characteristics.

[0096] In addition, since the above-described negative electrode 10 does not require a metal current collector, it is possible to reduce the weight and increase the weight energy density (Wh / kg) compared to when a metal current collector is used.

[0097] In particular, when the weight ratio M is 40% by weight to 76% by weight, the relationship between the weight of the carbon component (plurality of large-diameter carbon fiber portions 1 and plural small-diameter carbon fiber portions 2) and the weight of the silicon component (plurality of particle portions 3) in the negative electrode 10 is optimized. Therefore, sufficient energy density can be obtained while ensuring electrical conductivity, and thus a greater effect can be obtained.

[0098] Furthermore, if the silicon content in each of the plurality of particle parts 3 (silicon-containing material) is 80% by weight or more, a significantly high energy density can be obtained while ensuring electrical conductivity, thereby achieving a greater effect.

[0099] Furthermore, if some or all of the plurality of small diameter carbon fiber portions 2 are connected to two or more large diameter carbon fiber portions 1 via some of the plurality of particle portions 3, the two or more large diameter carbon fiber portions 1 are electrically connected to each other via the small diameter carbon fiber portions 2. Therefore, a denser conductive network is formed, and a greater effect can be obtained.

[0100] Here, when the porosity R has the above-mentioned large value (= 42 volume % to 73 volume %), the conductive network is likely to become sparse. Moreover, since the particle portion 3 containing the silicon-containing material expands and contracts during the electrode reaction, the conductive network is likely to be disconnected. However, as described above, when some or all of the plurality of small-diameter carbon fiber portions 2 are connected to two or more small-diameter carbon fiber portions 2 via some of the plurality of particle portions 3, a dense conductive network is likely to be formed and the conductive network is less likely to be disconnected.

[0101] Furthermore, if the average particle size AP1 of the plurality of particle portions 3 is 30 nm to 2000 nm, a sufficient energy density can be obtained while ensuring electrical conductivity, and therefore a higher effect can be obtained.

[0102] Furthermore, if the plurality of large diameter carbon fiber portions 1 contain carbon paper, the plurality of large diameter carbon fiber portions 1 are sufficiently connected to each other and have a sufficiently large average fiber diameter AD1, thereby forming a sufficient conductive network (three-dimensional mesh structure), thereby achieving a higher effect.

[0103] Furthermore, if the plurality of small-diameter carbon fiber portions 2 contain one or both of single-walled carbon nanotubes and vapor-grown carbon fibers, the average fiber diameter AD2 becomes sufficiently small. Therefore, the plurality of small-diameter carbon fiber portions 2 are easily dispersed in the negative electrode 10, and a denser conductive network is easily formed, thereby achieving a greater effect.

[0104] <2. Secondary battery> Next, a secondary battery according to an embodiment of the present technology, more specifically, an example of a secondary battery using the above-described negative electrode 10 will be described.

[0105] As described above, the secondary battery described here is a secondary battery that obtains battery capacity by utilizing the occlusion and release of an electrode reactant, and includes a positive electrode, a negative electrode, a separator, and an electrolytic solution that is a liquid electrolyte. As described above, the type of electrode reactant is not particularly limited.

[0106] In the following, we will take the case where the electrode reactant is lithium as an example. A secondary battery that obtains battery capacity by utilizing the absorption and desorption of lithium is called a lithium ion secondary battery. In this lithium ion secondary battery, lithium is absorbed and desorbed in the ionic state.

[0107] In this case, the charge capacity of the negative electrode is larger than the discharge capacity of the positive electrode. That is, the electrochemical capacity per unit area of ​​the negative electrode is set to be larger than the electrochemical capacity per unit area of ​​the positive electrode. This is to prevent deposition of electrode reactants on the surface of the negative electrode during charging.

[0108] <2-1.Configuration> Fig. 3 shows a perspective view of a secondary battery. Fig. 4 shows an enlarged cross-sectional view of the battery element 30 shown in Fig. 3. However, Fig. 3 shows a state in which the exterior film 20 and the battery element 30 are separated from each other, and Fig. 4 shows only a portion of the battery element 30. Below, reference will be made occasionally to Figs. 1 and 2, which have already been described, and the components of the negative electrode 10, which have already been described, will be cited.

[0109] 3 and 4, this secondary battery includes an exterior 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 laminate film type secondary battery that uses a flexible exterior film 20.

[0110] [Exterior film] 3, the exterior film 20 is a flexible exterior member that houses the battery element 30, and has a sealed bag-like structure with the battery element 30 housed inside. Therefore, the exterior film 20 houses an electrolyte solution together with a positive electrode 31 and a negative electrode 32, which will be described later.

[0111] Here, the exterior film 20 is a single film-like member that is folded in a folding direction F. The exterior film 20 is provided with a recessed portion 20U (so-called deep drawn portion) for accommodating the battery element 30.

[0112] Specifically, the exterior film 20 is a three-layer laminate film in which a fusion layer, a metal layer, and a surface protection layer are laminated in this order from the inside, and when the exterior film 20 is folded, the outer peripheral edges of the opposing fusion layers are fused to each other. The fusion layer contains a polymer compound such as polypropylene. The metal layer contains a metal material such as aluminum. The surface protection layer contains a polymer compound such as nylon.

[0113] However, the configuration (number of layers) of the exterior film 20 is not particularly limited, and may be one layer, two layers, or four or more layers.

[0114] [Battery element] As shown in FIGS. 3 and 4, the battery element 30 is a power generating element that includes a positive electrode 31, a negative electrode 32, a separator 33, and an electrolyte (not shown), and is housed inside the exterior film 20.

[0115] This battery element 30 is a so-called laminated electrode body, and therefore the positive electrodes 31 and the negative electrodes 32 are laminated one upon the other with separators 33 interposed therebetween. The number of positive electrodes 31, negative electrodes 32, and separators 33 laminated is not particularly limited. Here, a plurality of positive electrodes 31 and a plurality of negative electrodes 32 are alternately laminated with separators 33 interposed therebetween.

[0116] (positive electrode) As shown in FIG. 4, the positive electrode 31 includes a positive electrode current collector 31A and a positive electrode active material layer 31B.

[0117] The positive electrode current collector 31A has a pair of surfaces on which the positive electrode active material layer 31B is provided. The positive electrode current collector 31A contains a conductive material such as a metal material, and a specific example of the metal material is aluminum.

[0118] 3, the positive electrode current collector 31A includes a protrusion 31AT on which the positive electrode active material layer 31B is not provided, and the plurality of protrusions 31AT are joined to each other to form a single lead. Here, the protrusion 31AT is integrated with the portion other than the protrusion 31AT. However, since the protrusion 31AT is separate from the portion other than the protrusion 31AT, it may be joined to the portion other than the protrusion 31AT.

[0119] The positive electrode active material layer 31B contains one or more types of positive electrode active materials capable of absorbing and releasing lithium, but may also contain one or more types of other materials such as a positive electrode binder and a positive electrode conductive agent.

[0120] Here, the positive electrode active material layer 31B is provided on both sides of the positive electrode current collector 31A. However, the positive electrode active material layer 31B may be provided on only one side of the positive electrode current collector 31A, on the side where the positive electrode 31 faces the negative electrode 32. The method for forming the positive electrode active material layer 31B is not particularly limited, and specifically, it may be one or more of coating methods or the like.

[0121] The type of positive electrode active material is not particularly limited, but specifically includes a lithium-containing compound. This lithium-containing compound is a compound containing lithium and one or more transition metal elements as constituent elements, and may further contain one or more other elements as constituent elements. The type of other element is not particularly limited as long as it is an element other than lithium and transition metal elements, but specifically includes elements belonging to Groups 2 to 15 of the long period periodic table. The type of lithium-containing compound is not particularly limited, but specifically includes oxides, phosphate compounds, silicate compounds, borate compounds, etc.

[0122] Specific examples of oxides are LiNiO2, LiCoO2, LiCo 0.98 Al 0.01 Mg 0.01 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, Li 1.2 Mn 0.52 Co 0.175 Ni 0.1 O2, Li 1.15 (Mn 0.65 Ni 0.22 Co 0.13 )O2 and LiMn2O4. Specific examples of phosphate compounds include LiFePO4, LiMnPO4, LiFe 0.5 Mn 0.5 PO4 and LiFe 0.3 Mn 0.7 PO4, etc.

[0123] The positive electrode binder contains one or more of synthetic rubbers and polymeric compounds. Specific examples of synthetic rubbers include styrene-butadiene rubber, fluorine-containing rubber, and ethylene-propylene-diene. Specific examples of polymeric compounds include polyvinylidene fluoride, polyimide, and carboxymethyl cellulose.

[0124] The positive electrode conductive agent contains one or more conductive materials such as carbon materials, and specific examples of the carbon materials include graphite, carbon black, acetylene black, ketjen black, and carbon nanotubes. However, the conductive material may also be a metal material or a polymer compound.

[0125] (Negative electrode) As shown in FIG. 4, the negative electrode 32 faces the positive electrode 31 via a separator 33 and is capable of absorbing and desorbing lithium. This negative electrode 32 has a configuration similar to that of the above-described negative electrode 10, and therefore 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. In this negative electrode 32, lithium is absorbed and desorbed mainly in each of the plurality of particle portions 3. However, lithium may be absorbed and desorbed not only in each of the plurality of particle portions 3, but also in one or both of the plurality of large-diameter carbon fiber portions 1 and the plurality of small-diameter carbon fiber portions 2.

[0126] As shown in FIG. 3, the negative electrode 32 includes a protrusion 31AT consisting of a portion of the large-diameter carbon fiber portion 1 on which a plurality of particle portions 3 are not provided, and the plurality of protrusions 31AT are joined to each other to form a single lead.

[0127] (separator) 4, the separator 33 is an insulating porous film interposed between the positive electrode 31 and the negative electrode 32, and allows lithium ions to pass through while preventing contact (short circuit) between the positive electrode 31 and the negative electrode 32. The separator 33 contains a polymer compound such as polyethylene.

[0128] (electrolyte) The electrolyte solution is impregnated into each of the positive electrode 31, the negative electrode 32, and the separator 33, and contains a solvent and an electrolyte salt.

[0129] The solvent contains one or more of non-aqueous solvents (organic solvents) such as carbonate ester compounds, carboxylic acid ester compounds, and lactone compounds, and the electrolyte solution containing such non-aqueous solvents is a so-called non-aqueous electrolyte solution.

[0130] Carbonate compounds include cyclic carbonates and chain carbonates. Specific examples of cyclic carbonates include ethylene carbonate and propylene carbonate. Specific examples of chain carbonates include dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0131] The carboxylic acid ester compound is a chain carboxylic acid ester, etc. Specific examples of the chain carboxylic acid ester include methyl acetate, ethyl acetate, trimethylmethyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

[0132] The lactone compound is a lactone, etc. Specific examples of lactones include γ-butyrolactone and γ-valerolactone.

[0133] The electrolyte salt contains one or more types of light metal salts such as lithium salts.

[0134] Specific examples of lithium salts include lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium bis(fluorosulfonyl)imide (LiN(FSO)), lithium bis(trifluoromethanesulfonyl)imide (LiN(CFSO)), lithium bis(oxalato)borate (LiB(C0)), lithium difluoro(oxalato)borate (LiB(C0)F), lithium monofluorophosphate (LiPFO), and lithium difluorophosphate (LiPF0).

[0135] The content of the electrolyte salt is not particularly limited, but specifically, it is 0.3 mol / kg to 3.0 mol / kg relative to the solvent, because high ionic conductivity can be obtained.

[0136] The electrode solution may further contain one or more additives, including, but not limited to, unsaturated cyclic carbonates, halogenated carbonates, phosphates, acid anhydrides, nitrile compounds, and isocyanate compounds.

[0137] Specific examples of unsaturated cyclic carbonates include vinylene carbonate, vinylethylene carbonate, and methyleneethylene carbonate. Specific examples of halogenated carbonates 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 fluoromethylmethyl carbonate. Specific examples of phosphates include trimethyl phosphate and triethyl phosphate.

[0138] Acid anhydrides include dicarboxylic acid anhydrides, disulfonic acid anhydrides, and carboxylic acid sulfonic acid anhydrides. A specific example of a dicarboxylic acid anhydride is succinic acid anhydride. A specific example of a disulfonic acid anhydride is ethanedisulfonic acid anhydride. A specific example of a carboxylic acid sulfonic acid anhydride is sulfobenzoic acid anhydride.

[0139] Nitrile compounds include mononitrile compounds, dinitrile compounds, and trinitrile compounds. A specific example of a mononitrile compound is acetonitrile. A specific example of a dinitrile compound is succinonitrile. A specific example of a trinitrile compound is 1,2,3-propanetricarbonitrile. A specific example of an isocyanate compound is hexamethylene diisocyanate.

[0140] [Positive lead] As shown in Fig. 3, the positive electrode lead 41 is a positive electrode terminal connected to the assembly of the multiple protrusions 31AT of the positive electrode 31, and is led from the inside to the outside of the exterior film 20. The positive electrode lead 41 contains a conductive material such as a metal material, and a specific example of the metal material is aluminum. The shape of the positive electrode lead 41 is not particularly limited, but specifically may be either a thin plate shape or a mesh shape.

[0141] [Negative lead] As shown in FIG. 3 , the negative electrode lead 42 is a negative electrode terminal connected to the assembly of the multiple protrusions 32AT of the negative electrode 32, and is led from the inside to the outside of the exterior film 20. In particular, the negative electrode lead 42 is preferably connected to the large-diameter carbon fiber portion 1 of the negative electrode 32. This is because electrical conductivity between the negative electrode 32 and the negative electrode lead 42 is improved. The negative electrode lead 42 contains a conductive material such as a metal material, and a specific example of the metal material is copper. Here, the lead-out direction of the negative electrode lead 42 is the same as the lead-out direction 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.

[0142] [Sealing film] The sealing film 51 is inserted between the exterior film 20 and the positive electrode lead 41, and the sealing film 52 is inserted between the exterior film 20 and the negative electrode lead 42. However, one or both of the sealing films 51 and 52 may be omitted.

[0143] The sealing film 51 is a sealing member that prevents outside air and the like from entering the inside of the exterior film 20. The sealing film 51 also contains a polymer compound such as polyolefin that has adhesiveness to the positive electrode lead 41, and a specific example of the polyolefin is polypropylene.

[0144] The configuration of the sealing film 52 is the same as the configuration of the sealing film 51, except that the sealing film 52 is a sealing member that has adhesiveness to the negative electrode lead 42. That is, the sealing film 52 contains a polymer compound such as polyolefin that has adhesiveness to the negative electrode lead 42.

[0145] <2-2. Operation> When the secondary battery is charged, lithium is released from the positive electrode 31 in the battery element 30 and is absorbed into the negative electrode 32 via the electrolyte. On the other hand, when the secondary battery is discharged, lithium is released from the negative electrode 32 in the battery element 30 and is absorbed into the positive electrode 31 via the electrolyte. During these charging and discharging times, lithium is absorbed and released in an ionic state.

[0146] <2-3. Manufacturing method> When manufacturing a secondary battery, the positive electrode 31 and the negative electrode 32 are each produced and the electrolyte solution is prepared according to the procedure described below as an example, and then the secondary battery is assembled and subjected to a stabilization process after assembly.

[0147] [Preparation of positive electrode] First, a paste-like cathode mixture slurry is prepared by adding a mixture (cathode mixture) of a cathode active material, a cathode binder, and a cathode conductive agent to a solvent. This solvent may be an aqueous solvent or an organic solvent. Next, the cathode mixture slurry is applied to both surfaces (excluding the protrusions 31AT) of the cathode current collector 31A including the protrusions 31AT to form the cathode active material layer 31B. Finally, the cathode active material layer 31B is compression-molded using a roll press or the like. In this case, the cathode active material layer 31B may be heated, or the compression molding may be repeated multiple times. As a result, the cathode active material layer 31B is formed on both surfaces of the cathode current collector 31A, thereby producing the cathode 31.

[0148] [Preparation of negative electrode] The negative electrode 32 including the protrusion 32AT is produced by a procedure similar to that for producing the negative electrode 10 described above.

[0149] [Preparation of electrolyte] An electrolyte salt is added to a solvent, whereby the electrolyte salt is dispersed or dissolved in the solvent, thereby preparing an electrolytic solution.

[0150] [Secondary battery assembly] First, a laminate (not shown) is prepared by alternately stacking positive electrodes 31 and negative electrodes 32 with separators 33 interposed therebetween. This laminate has the same configuration as that of the battery element 30, except that the positive electrodes 31, negative electrodes 32, and separators 33 are not impregnated with an electrolyte solution.

[0151] Next, the plurality of protrusions 31AT are joined to one another, and the plurality of protrusions 32AT are joined to one another. Next, the positive electrode lead 41 is joined to the joined body of the plurality of protrusions 31AT, and the negative electrode lead 42 is connected to the joined body of the plurality of protrusions 32AT.

[0152] Next, after the laminate is housed inside the recessed portion 20U, the exterior films 20 (adhesive layer / metal layer / surface protection layer) are folded to face each other. Next, the outer peripheral edges of two sides of the facing exterior films 20 (adhesive layers) are joined together using a heat fusion method or the like, thereby housing the laminate inside the bag-shaped exterior film 20.

[0153] Finally, after injecting an electrolyte solution into the bag-shaped exterior film 20, the outer peripheral edges of the remaining side of the exterior film 20 (bonding layer) are joined together using a heat fusion method or the like. In this case, a sealing film 51 is inserted between the exterior film 20 and the positive electrode lead 41, and a sealing film 52 is inserted between the exterior film 20 and the negative electrode lead 42.

[0154] This allows the laminate to be impregnated with the electrolyte, producing a laminated electrode body, the battery element 30. The battery element 30 is then sealed inside the bag-shaped exterior film 20, and a secondary battery is assembled.

[0155] [Secondary battery stabilization] The assembled secondary battery is charged and discharged. Various conditions, such as the ambient temperature, the number of charge / discharge cycles (number of cycles), and the charge / discharge conditions, can be set as desired. This forms a coating on the surface of each of the positive electrode 31 and the negative electrode 32, electrochemically stabilizing the state of the secondary battery. This completes the secondary battery.

[0156] <2-4. Actions and Effects> In this secondary battery, the negative electrode 32 has a configuration similar to that of the above-described negative electrode 10. Therefore, for the same reasons as those described for the negative electrode 10, excellent initial capacity characteristics, excellent swollenness characteristics, excellent load characteristics, and excellent cycle characteristics can be obtained.

[0157] Furthermore, if the secondary battery is a lithium ion secondary battery, a sufficient battery capacity can be stably obtained by utilizing the absorption and desorption of lithium, and therefore a greater effect can be obtained.

[0158] Other functions and effects of the secondary battery are the same as those of the negative electrode 10 described above.

[0159] <3. Modifications> Next, a modified example will be described.

[0160] The configurations of the negative electrode 10 and the secondary battery described above can be modified as appropriate, as described below, although any two or more of the series of modifications described below may be combined with each other.

[0161] [Variation 1] As shown in Fig. 5, which corresponds to Fig. 2, some or all of the plurality of particle portions 3 (primary particles 3A) may include a core portion 3X and a coating portion 3Y. This coating portion 3Y has a thickness T. Unlike Fig. 2, Fig. 5 shows only the particle portion 3 in an enlarged manner.

[0162] The central portion 3X has a structure similar to that of the particle portion 3 (primary particle 3A) shown in FIG. 2, and therefore contains a silicon-containing material.

[0163] 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 may cover only a portion of the surface of the covering portion 3Y. In the latter case, the covering portion 3Y may cover the surface of the central portion 3X at multiple locations that are spaced apart from one another. For the sake of simplicity, FIG. 5 shows a case in which the covering portion 3Y covers the entire surface of the central portion 3X.

[0164] (Covering material = carbon-containing material) Here, the covering portion 3Y may contain one or more types of carbon-containing materials, specific examples of which include amorphous carbon and graphite.

[0165] The average thickness AT of the covering portion 3Y is not particularly limited and can be set arbitrarily. The procedure for calculating the average thickness AT of the covering portion 3Y is as follows. First, an observation result (observation image) of the cross section of the negative electrode 10 is obtained using the same procedure as in calculating the average fiber diameter AD1 described above. Next, 20 covering portions 3Y are arbitrarily selected, and the thickness T of each of the 20 covering portions 3Y is measured. Note that if the thickness varies depending on the location within one covering portion 3Y, the maximum value of the thickness T is selected. Finally, the average value of the 20 thicknesses T is calculated to obtain the average thickness AT.

[0166] When forming a plurality of particles 3 including a core 3X and a coating 3Y (carbon-containing material), a powder of a silicon-containing material that forms the core 3X is prepared, and then the carbon-containing material is deposited on the surface of the core 3X using a vapor phase method to form the coating 3Y. The type of vapor phase method is not particularly limited, but specifically, it may be one or more of a vacuum deposition method, a CVD method, a sputtering method, etc.

[0167] In this case, the conductivity of each of the plurality of particle parts 3 is improved, and therefore the conductivity of the negative electrode 10 is further improved, and a greater effect can be obtained.

[0168] (Covering material = ion conductive material) Alternatively, the covering portion 3Y may contain one or more types of ion-conductive materials. Specific examples of ion-conductive materials include solid electrolytes such as lithium phosphate nitride and lithium phosphate. The composition of this lithium phosphate nitride is not particularly limited, but specifically, Li 3.30 PO 3.90 N 0.17 And so on.

[0169] A specific example of the ion-conductive material is a gel electrolyte in which an electrolyte solution is held by a matrix polymer compound. The composition of the electrolyte solution is as described above. Specific examples of the matrix polymer compound include polyethylene oxide and polyvinylidene fluoride.

[0170] Details regarding the average thickness AT of the covering portion 3Y are as described above.

[0171] The procedure for forming the plurality of particle portions 3 including the core portion 3X and the coating portion 3Y (ion-conductive material) is as follows. When a solid electrolyte is used as the ion-conductive material, the coating portion 3Y is directly formed on the surface of each of the plurality of core portions 3X using a gas-phase method such as sputtering. When a gel electrolyte is used as the ion-conductive material, a solution containing an electrolyte solution, a matrix polymer compound, and a dilution solvent is applied to the surface of each of the plurality of core portions 3X, and the solution is then dried. However, the plurality of core portions 3X may also be immersed in the solution.

[0172] In this case, the ion conductivity of the electrode reactant is improved by using an ion conductive material in each of the plurality of particle portions 3, and therefore a higher effect can be obtained.

[0173] In particular, by utilizing a plurality of particle portions 3 in which the coating portion 3Y contains an ion-conductive material, the negative electrode 10 can be applied to an all-solid-state battery. This is because the expansion and contraction of the negative electrode 10 is suppressed, thereby suppressing an increase in the interfacial resistance between the negative electrode 10 and the solid electrolyte. This allows the all-solid-state battery to achieve both ensuring safety and improving energy density.

[0174] [Variation 2] As shown in FIG. 6, which corresponds to FIG. 5, some or all of the plurality of particle portions 3 (primary particles 3A) may include an inner coating portion 3Y1 and an outer coating portion 3Y2 in addition to a central portion 3X.

[0175] The configuration of the center 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-conductive material. That is, the inner covering portion 3Y1 may contain a carbon-containing material, and the outer covering portion 3Y2 may contain an ion-conductive material. Alternatively, the inner covering portion 3Y1 may contain an ion-conductive material, and the outer covering portion 3Y2 may contain a carbon-containing material.

[0176] The carbon-containing material and the ion-conductive material are as described above in detail. The average thicknesses of the inner covering portion 3Y1 and the outer covering portion 3Y2 are the same as those of the average thickness AT described above. The inner covering portion 3Y1 and the outer covering portion 3Y2 are formed in the same manner as the method for forming the covering portion 3Y.

[0177] In this case, the electrical conductivity and ionic conductivity are improved in each of the plurality of particle portions 3, so that even greater effects can be obtained.

[0178] [Variation 3] As shown in Figures 7 to 9, which correspond to Figure 2, some or all of the plurality of particle portions 3 (primary particles 3A) may form composite secondary particles 3BP containing one or both of some of the plurality of small-diameter carbon fiber portions 2 and the plurality of ion-conductive materials 4. These composite secondary particles 3BP have a particle size P2. Unlike Figure 2, each of Figures 7 to 9 shows only the particle portion 3 (composite secondary particle 3BP) in an enlarged manner.

[0179] (Composite secondary particles containing multiple small diameter carbon fiber parts) 7, a plurality of particle portions 3 (primary particles 3A) are granulated together with some of a plurality of small diameter carbon fiber portions, and therefore, in a composite secondary particle 3BP formed by the plurality of particle portions 3, the plurality of primary particles 3A and the plurality of small diameter carbon fiber portions 2 may be entangled with each other. As a result, the plurality of primary particles 3A are electrically connected to each other and physically linked to each other via the plurality of small diameter carbon fiber portions 2.

[0180] The average particle size AP2 of the composite secondary particles 3BP is not particularly limited, but is preferably 300 nm to 10,000 nm, because this ensures electrical conductivity, sufficiently suppresses expansion and contraction of the particle portion 3, and facilitates the movement of the electrode reactant.

[0181] The procedure for calculating the average particle size AP2 is the same as the procedure for calculating the average particle size AP1 described above, except that the particle sizes P2 of any 10 composite secondary particles 3BP are measured, and then the average value of the particle sizes P2 of the 10 particles is taken as the average particle size AP2.

[0182] When forming composite secondary particles 3BP containing a plurality of small-diameter carbon fiber portions 2, a dispersion containing a plurality of particle portions 3, a plurality of small-diameter carbon fiber portions 2, and a dilution solvent is prepared, and then the dispersion is sprayed using a spray-drying method. Details regarding the solvent are as described above. This dispersion may contain a binder, and details regarding the binder are as described above. As a result, granulation is performed using the dispersion, and granules (composite secondary particles 3BP) containing a plurality of small-diameter carbon fiber portions 2 together with a plurality of particle portions 3 are formed.

[0183] In this case, the plurality of particle portions 3 and the plurality of small diameter carbon fiber portions 2 are firmly connected to each other, so that the conductivity of the negative electrode 10 is improved stably.

[0184] (Composite secondary particles containing multiple ion-conductive materials) Furthermore, as shown in FIG. 8, since a plurality of particle parts 3 (primary particles 3A) are granulated together with a plurality of ion-conductive materials 4, in the composite secondary particle 3BP formed by the plurality of particle parts 3, two or more primary particles 3A may be electrically connected to each other via one or two or more ion-conductive materials 4 and may also be physically linked to each other.

[0185] Details regarding the average particle size AP2 of the composite secondary particles 3BP are the same as those shown in Fig. 7. That is, the average particle size AP2 of the composite secondary particles 3BP is preferably 300 nm to 10,000 nm.

[0186] The procedure for forming the composite secondary particles 3BP containing the plurality of ion-conductive materials 4 is the same as that shown in FIG. 7, except that the plurality of small-diameter carbon fiber portions 2 are replaced with an ion-conductive material.

[0187] In this case, the plurality of particle portions 3 and the plurality of ion-conductive materials 4 are firmly connected to each other, so that the ion conductivity of the negative electrode 10 is improved stably.

[0188] (Composite secondary particles containing multiple small-diameter carbon fiber portions and multiple ion-conductive materials) 9, since the plurality of particle portions 3 (primary particles 3A) are granulated together with some of the plurality of small-diameter carbon fiber portions 2 and the plurality of ion-conductive materials 4, the composite secondary particle 3BP formed by the plurality of particle portions 3 may contain both the plurality of small-diameter carbon fiber portions 2 and the plurality of ion-conductive materials 4. Details of the configuration of the composite secondary particle 3BP containing each of the plurality of small-diameter carbon fiber portions 2 and the plurality of ion-conductive materials 4 are as described above (see FIGS. 7 and 8).

[0189] Details regarding the average particle size AP2 of the composite secondary particles 3BP are the same as those shown in Fig. 7. That is, the average particle size AP2 of the composite secondary particles 3BP is preferably 300 nm to 10,000 nm.

[0190] The procedure for forming the composite secondary particles 3BP containing the plurality of small-diameter carbon fiber portions 2 and the plurality of ion-conductive materials 4 is the same as that shown in FIG. 7, except that an ion-conductive material is used in addition to the plurality of small-diameter carbon fiber portions 2.

[0191] In this case, the plurality of particle portions 3, the plurality of small-diameter carbon fiber portions 2, and the plurality of ion-conductive materials 4 are firmly connected to one another, so that the electrical conductivity and ion conductivity of the negative electrode 10 are each improved stably.

[0192] (Other composite secondary particles) Although not specifically shown here, the configuration of the particle portion 3 (primary particles 3A) shown in each of Figures 5 and 6 may be combined with the configuration of the composite secondary particle 3BP shown in each of Figures 7 to 9. Specifically, a plurality of particle portions 3 (primary particles 3A) shown in Figure 5 may form a composite secondary particle 3BP shown in each of Figures 7 to 9, or a plurality of particle portions 3 (primary particles 3A) shown in Figure 6 may form a composite secondary particle 3BP shown in each of Figures 7 to 9, or both may be mixed. In these cases, the same effect can be obtained.

[0193] [Variation 4] A porous film separator 33 was used. However, although not specifically shown here, a laminated separator including a polymer compound layer may be used instead of the separator 33.

[0194] Specifically, the laminated separator includes a porous membrane having a pair of surfaces and a polymer compound layer provided on one or both surfaces of the porous membrane. This is because the separators improve their adhesion to the positive electrode 31 and the negative electrode 32, respectively, thereby preventing the battery element 30 from slipping out of its winding. This reduces the likelihood of swelling of the secondary battery even if a decomposition reaction of the electrolyte occurs. The porous membrane has the same structure as the porous membrane described for the separator 33. The polymer compound layer includes a polymer compound such as polyvinylidene fluoride. This is because polyvinylidene fluoride and other polymers have excellent physical strength and are electrochemically stable.

[0195] One or both of the porous film and the polymer compound layer may contain one or more types of insulating particles. This is because the insulating particles promote heat dissipation when the secondary battery generates heat, thereby improving the safety (heat resistance) of the secondary battery. The insulating particles may be one or both of inorganic particles and resin particles. Specific examples of inorganic particles include particles of aluminum oxide, aluminum nitride, boehmite, silicon oxide, titanium oxide, magnesium oxide, and zirconium oxide. Specific examples of resin particles include particles of acrylic resin and styrene resin.

[0196] When fabricating a laminated separator, a precursor solution containing a polymer compound and a solvent is prepared, and then the precursor solution is applied to one or both sides of a porous membrane. In this case, instead of applying the precursor solution to the porous membrane, the porous membrane may be immersed in the precursor solution. The precursor solution may contain multiple insulating particles.

[0197] Even when this laminated separator is used, the same effect can be obtained because lithium ions are able to move between the positive electrode 31 and the negative electrode 32. In this case, the safety of the secondary battery is particularly improved as described above, and therefore, a greater effect can be obtained.

[0198] [Variation 5] An electrolytic solution, which is a liquid electrolyte, was used. However, although not specifically shown here, an electrolyte layer, which is a gel electrolyte, may be used instead of the electrolytic solution.

[0199] In a battery element 30 using an electrolyte layer, positive electrodes 31 and negative electrodes 32 are alternately stacked with separators 33 and electrolyte layers interposed therebetween. In this case, an electrolyte layer is interposed between the positive electrode 31 and separator 33, and an electrolyte layer is interposed between the negative electrode 32 and separator 33. However, the electrolyte layer may be interposed only between the positive electrode 31 and separator 33, or only between the negative electrode 32 and separator 33.

[0200] Specifically, the electrolyte layer contains a polymer compound together with an electrolytic solution, and the electrolytic solution is held by the polymer compound. This is because leakage of the electrolytic solution is prevented. The composition of the electrolytic solution is as described above. The polymer compound contains polyvinylidene fluoride, etc. When forming the electrolyte layer, a precursor solution containing the electrolytic solution, the polymer compound, and a dilution solvent is prepared, and then the precursor solution is applied to one or both surfaces of each of the positive electrode 31 and the negative electrode 32. Details regarding the solvent are as described above.

[0201] Even when this electrolyte layer is used, the same effect can be obtained because lithium ions can move between the positive electrode 31 and the negative electrode 32 via the electrolyte layer. In this case, leakage of the electrolyte solution is particularly prevented as described above, so that a greater effect can be obtained.

[0202] <4. Uses of secondary batteries> Finally, the uses (application examples) of the secondary battery will be described.

[0203] The use of the secondary battery is not particularly limited. The secondary battery used as a power source may be a main power source for electronic devices, electric vehicles, etc., or an auxiliary power source. A main power source is a power source that is used preferentially regardless of the presence or absence of other power sources. An auxiliary power source is a power source that is used in place of the main power source or a power source that can be switched from the main power source.

[0204] Specific examples of uses for secondary batteries are as follows: Electronic devices such as video cameras, digital still cameras, mobile phones, laptop computers, headphone stereos, portable radios, and portable information terminals. Storage devices such as backup power supplies and memory cards. Power tools such as power drills and power saws. Battery packs installed in electronic devices. Medical electronic devices such as pacemakers and hearing aids. Electric vehicles such as electric cars (including hybrid cars). Power storage systems such as home or industrial battery systems that store power in preparation for emergencies. In these uses, one secondary battery may be used, or multiple secondary batteries may be used.

[0205] The battery pack may use a single cell or a battery pack. The electric vehicle is a vehicle that operates (travels) using a secondary battery as a driving power source, and may be a hybrid vehicle that also has a driving source other than the secondary battery. In a home power storage system, the power stored in the secondary battery, which is a power storage source, can be used to power home electrical appliances, etc.

[0206] Here, an example of an application of a secondary battery will be specifically described. The configuration described below is merely an example and can be modified as appropriate.

[0207] Figure 10 shows the block diagram of a battery pack. The battery pack described here is a battery pack (a so-called soft pack) that uses one secondary battery, and is installed in electronic devices such as smartphones.

[0208] 10, 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.

[0209] The power source 61 includes one secondary battery. In this secondary battery, the positive electrode lead is connected to a positive electrode terminal 63, and the negative electrode lead is connected to a negative electrode terminal 64. The power source 61 is connected to the outside via the positive electrode terminal 63 and the negative electrode terminal 64, and is therefore capable of charging and discharging. The circuit board 62 includes a control unit 66, a switch 67, a thermosensitive resistor (PTC) element 68, and a temperature detection unit 69. However, the PTC element 68 may be omitted.

[0210] The control unit 66 includes a central processing unit (CPU) and memory, and controls the operation of the entire battery pack. The control unit 66 detects and controls the usage state of the power source 61 as necessary.

[0211] When the voltage of the power supply 61 (secondary battery) reaches the overcharge detection voltage or the overdischarge detection voltage, the control unit 66 turns off the switch 67 to prevent the charging current from flowing through the current path of the power supply 61. The overcharge detection voltage is not particularly limited, but specifically, it is 4.2±0.05V, and the overdischarge detection voltage is not particularly limited, but specifically, it is 2.4±0.1V.

[0212] Switch 67 includes a charge control switch, a discharge control switch, a charge diode, a discharge diode, etc., and switches between the presence and absence of a connection between power supply 61 and an external device in response to an instruction from control unit 66. Switch 67 includes a field effect transistor (MOSFET) using a metal oxide semiconductor, etc., and the charge / discharge current is detected based on the ON resistance of switch 67.

[0213] The temperature detection unit 69 includes a temperature detection element 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 when the control unit 66 controls charging and discharging in the event of abnormal heat generation, and when the control unit 66 performs correction processing when calculating the remaining capacity. [Example]

[0214] An embodiment of the present technology will be described.

[0215] <Examples 1 to 7 and Comparative Examples 1 and 2> After the secondary batteries were fabricated, the characteristics of the secondary batteries were evaluated. Here, two types of secondary batteries (first secondary battery and second secondary battery) were fabricated to evaluate the characteristics of the secondary batteries.

[0216] [Preparation of the first secondary battery] First secondary batteries (Examples 1 to 7) were fabricated according to the procedure described below. The first secondary batteries were laminate film-type lithium ion secondary batteries (battery capacity = 7 mAh to 12 mAh) shown in Figures 3 and 4.

[0217] In the following description, the components of the negative electrode 10 shown in FIGS. 1 and 2 will be referenced where necessary to explain the process of producing the negative electrode 32.

[0218] (Preparation of positive electrode) First, the positive electrode active material (LiNi 0.8 Co 0.15 Al 0.05A positive electrode mixture was prepared by mixing 97 parts by mass of ethylenediamine fluoride (O2), 2.2 parts by mass of a positive electrode binder (polyvinylidene fluoride), and 0.8 parts by mass of a positive electrode conductive agent (Ketjen black). The positive electrode mixture was then added to a solvent (N-methyl-2-pyrrolidone, an organic solvent), and the solvent was stirred using a planetary mixer to prepare a paste-like positive electrode mixture slurry. The positive electrode mixture slurry was then applied to both surfaces (excluding the protrusions 31AT) of a positive electrode current collector 31A (aluminum foil, thickness = 15 μm) including the protrusions 31AT using a coating device, and the positive electrode mixture slurry was then dried (drying temperature = 120°C) to form a positive electrode active material layer 31B. Finally, the positive electrode active material layer 31B was compression-molded using a hand press (volume density of the positive electrode active material layer 31B = 3.5 g / cm). 3 ) In this way, the positive electrode 31 including the protrusion 31AT was produced.

[0219] (Preparation of negative electrode) First, carbon paper (CP, thickness = 50 μm) was prepared, which was a plurality of large diameter carbon fiber portions 1 including protrusions 32AT. This carbon paper had a three-dimensional mesh structure formed by the plurality of large diameter carbon fiber portions 1, and therefore had a plurality of voids 10G. The inner diameter of each of the plurality of voids 10G was larger than the inner diameter of the negative electrode 32 after completion. The average fiber diameter AD1 (nm) of the plurality of large diameter carbon fiber portions 1 was as shown in Table 1.

[0220] Subsequently, a first dispersion containing a silicon-containing material and a second dispersion containing a carbon-containing material (a plurality of small diameter carbon fiber portions 2) were mixed together to prepare a dispersion.

[0221] The first dispersion was prepared by mixing a powder of a silicon-containing material (elemental silicon (Si), purity = 95%), a binder (polyimide), and a solvent (organic solvent N-methyl-2-pyrrolidone) together, and then stirring the solvent using a planetary mixer.

[0222] The second dispersion was prepared by mixing a plurality of small-diameter carbon fiber portions 2 (single-walled carbon nanotubes (SWCNTs) or vapor-grown carbon fibers (VGCFs)), a binder (polyvinylidene fluoride), and a solvent (N-methyl-2-pyrrolidone, an organic solvent), and then stirring the solvent using a planetary mixer. The average fiber diameters AD2 (nm) of the plurality of small-diameter carbon fiber portions 2 are as shown in Table 1.

[0223] The composition (weight ratio) of the dispersion was silicon-containing material powder: binder (polyimide): plural small diameter carbon fiber parts 2: binder (polyvinylidene fluoride) = 85:10 (solid content equivalent): 0.8:4.2.

[0224] Next, the dispersion liquid was applied to the plurality of large diameter carbon fiber portions 1 (excluding the protrusions 32AT), thereby impregnating the interior of the three-dimensional network structure formed by the plurality of large diameter carbon fiber portions 1 with the dispersion liquid. As a result, the powder of the silicon-containing material was fixed to the surfaces of each of the plurality of large diameter carbon fiber portions 1, thereby forming a plurality of particle portions 3, and at the same time, a plurality of small diameter carbon fiber portions 2 was fixed to the surfaces of the plurality of particle portions 3, thereby connecting the plurality of small diameter carbon fiber portions 2 to the surfaces of the plurality of particle portions 3. In this case, the plurality of particle portions 3 (primary particles 3A) were connected to each other, thereby forming a plurality of secondary particles 3B. The average particle diameter AP1 (nm) of the plurality of particle portions 3 (secondary particles 3B) is as shown in Table 1. Thus, a negative electrode 32 including the protrusions 32AT was produced.

[0225] Finally, the negative electrode 32 was pressed in a room temperature environment (temperature = 23 °C), and then heated in a nitrogen (N2) atmosphere (heating temperature = 350 °C, heating time = 3 hours). In this case, the porosity R (volume %) was changed by adjusting the pressing pressure, as shown in Table 1.

[0226] This resulted in the completion of a negative electrode 32 that included 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, as well as a plurality of voids 10G. When producing this negative electrode 10, the weight percentage M (wt%) was changed as shown in Table 1 by adjusting the concentration of the silicon-containing material in the first dispersion and the concentration of the plurality of small-diameter carbon fiber portions 2 in the second dispersion.

[0227] (Preparation of Electrolyte) After adding an electrolyte salt (lithium hexafluorophosphate) to the solvent, the solvent was stirred. The solvent used was a mixture of ethylene carbonate, a cyclic carbonate, dimethyl carbonate, a chain carbonate, and monofluoroethylene carbonate, an additive (halogenated cyclic carbonate). The mixing ratio (weight ratio) of the solvents was ethylene carbonate:dimethyl carbonate:monofluoroethylene carbonate = 30:60:10. The content of the electrolyte salt relative to the solvent was 1 mol / kg. In this way, an electrolytic solution was prepared.

[0228] (First secondary battery assembly) First, a positive electrode 31 including a protrusion 31AT and a negative electrode 32 including a protrusion 32AT were stacked together with a separator 33 (microporous polyethylene film, thickness = 20 μm) in between to prepare a laminate (positive electrode 31 / separator 33 / negative electrode 32).

[0229] Subsequently, a positive electrode lead 41 (aluminum foil) was joined to the protruding portion 31AT, and a negative electrode lead 42 (copper foil) was joined to the protruding portion 32AT.

[0230] Next, the exterior film 20 (adhesive layer / metal layer / surface protection layer) was folded so as to sandwich the laminate housed inside the recessed portion 20U, and then the outer peripheral edges of two sides of the exterior film 20 (adhesive layer) were heat-sealed to each other, thereby housing the laminate inside the bag-shaped exterior film 20. The exterior film 20 used was an aluminum laminate film in which a adhesive layer (polypropylene film, thickness = 30 μm), a metal layer (aluminum foil, thickness = 40 μm), and a surface protection layer (nylon film, thickness = 25 μm) were laminated in this order from the inside.

[0231] Finally, after pouring the electrolyte solution into the bag-shaped exterior film 20, the outer peripheral edges of the remaining side of the exterior film 20 (bonding layer) were heat-sealed together in a reduced pressure environment. In this case, a sealing film 51 (polypropylene film, thickness = 5 μm) was inserted between the exterior film 20 and the positive electrode lead 41, and a sealing film 52 (polypropylene film, thickness = 5 μm) was inserted between the exterior film 20 and the negative electrode lead 42.

[0232] As a result, the laminate was impregnated with the electrolyte solution, thereby producing the battery element 30. Thus, the battery element 30 was sealed inside the exterior film 20, and the first secondary battery was assembled.

[0233] When assembling the first secondary battery, the thickness of the positive electrode active material layer 31B was adjusted so that the capacity ratio, i.e., the ratio of the positive electrode charge capacity to the negative electrode charge capacity (= positive electrode charge capacity / negative electrode charge capacity), was 0.7.

[0234] (Stabilization of the first secondary battery) The first secondary battery was charged and discharged for one cycle in a room temperature environment (temperature = 23°C). During charging, the battery was charged at a constant current of 0.1 C until the voltage reached 4.2 V, and then at a constant voltage of 4.2 V, the battery was charged at a constant current of 0.1 C until the voltage reached 2.0 V. 0.1 C is the current value at which the battery capacity (theoretical capacity) is fully discharged in 10 hours, and 0.025 C is the current value at which the battery capacity is fully discharged in 40 hours.

[0235] As a result, a coating was formed on the surface of each of the positive electrode 31 and the negative electrode 32, and the state of the first secondary battery was electrochemically stabilized, thereby completing the first secondary battery.

[0236] [Preparation of the second secondary battery] A second secondary battery (battery capacity = 10 mAh to 15 mAh) was fabricated using the same procedure as the first secondary battery described above, except that a lithium metal plate (thickness = 100 μm) was used instead of the positive electrode 31.

[0237] Here, the first secondary battery using the positive electrode 31 as the counter electrode for the negative electrode 32 is a so-called full cell, whereas the second secondary battery using a lithium metal plate as the counter electrode for the negative electrode 32 is a so-called half cell.

[0238] [Preparation of a secondary battery for comparison] For comparison, two types of secondary batteries for comparison (Comparative Examples 1 and 2) were fabricated in the same manner except that a metal current collector was used to fabricate a comparative negative electrode.

[0239] To fabricate this negative electrode, 82 parts by mass of a negative electrode active material (silicon (Si), purity = 95%, median diameter D50 = 50 nm), 10 parts by mass (solid content equivalent) of a negative electrode binder (polyimide), 3 parts by mass of a negative electrode conductive agent (carbon black), and 5 parts by mass of another negative electrode conductive agent (carbon nanotube dispersion) were mixed together to form a negative electrode mixture. This carbon nanotube dispersion contained 0.8 parts by mass of carbon nanotubes (the above-mentioned plurality of small-diameter carbon fiber parts 2) and 4.2 parts by mass of a dispersion medium (polyvinylidene fluoride).

[0240] Next, the negative electrode mixture was added to a solvent (organic solvent N-methyl-2-pyrrolidone), and the organic solvent was stirred using a planetary mixer to prepare a paste-like negative electrode mixture slurry. The negative electrode mixture slurry was then applied to both sides of a metal current collector (copper foil (Cu), thickness = 10 μm or 6 μm) using a coating device, and the negative electrode mixture slurry was then dried to form a negative electrode active material layer. This completed the assembly of the negative electrode.

[0241] Finally, the negative electrode was pressed in a room temperature environment (temperature = 23 °C) and then heated in a nitrogen atmosphere (heating temperature = 350 °C, heating time = 3 hours). In this case, the porosity R of the negative electrode active material layer was changed by adjusting the pressing pressure, as shown in Table 1.

[0242] In addition, the column "Metal current collector (thickness)" in Table 1 indicates whether or not a metal current collector is used, and if so, the material and thickness (μm) of the metal current collector.

[0243] [Characteristic evaluation of secondary batteries] The characteristics of the secondary battery (initial capacity characteristics, swelling characteristics, load characteristics, and cycle characteristics) were evaluated, and the results shown in Table 1 were obtained.

[0244] In this case, the initial capacity characteristics were evaluated using the second secondary battery (half cell) and the swelling characteristics, load characteristics and cycle characteristics were evaluated using the first secondary battery (full cell) according to the procedures described below.

[0245] (Initial capacity characteristics) The discharge capacity was measured by charging and discharging the secondary battery for one cycle while applying pressure to the secondary battery in a room temperature environment (temperature = 23 ° C.) From this, the initial capacity, which is an index for evaluating the initial capacity characteristics, was calculated based on the formula: initial capacity (mAh / g) = discharge capacity (mAh) / total weight (g) of the negative electrode 32.

[0246] In this case, pressure was applied to the secondary battery in the direction in which the positive electrode 31 and the negative electrode 32 were stacked together with the separator 33 interposed therebetween, and the secondary battery was charged and discharged while the positive electrode 31 and the negative electrode 32 were in close contact with each other via the separator 33. Note that the total weight of the negative electrode 32 described above includes the weight of a metal current collector when one is used, whereas it does not include the weight of the metal current collector when one is not used.

[0247] During charging, the battery was charged at a constant current of 0.1 C until the voltage reached 0.005 V, and then at a constant voltage of 0.005 V, the battery was charged at a constant current of 0.1 C until the voltage reached 0.01 C. During discharging, the battery was discharged at a constant current of 0.1 C until the voltage reached 1.5 V. 0.01 C is the current value that fully discharges the battery capacity in 100 hours.

[0248] (Swelling characteristics) First, the thickness of the secondary battery (thickness before charging) was measured in a room temperature environment (temperature = 23°C).

[0249] Subsequently, the secondary battery was charged while pressure was being applied to the secondary battery, and then the thickness of the secondary battery (thickness after charging) was measured.

[0250] In this case, similarly to the case of evaluating the initial capacity characteristics described above, the secondary battery was charged while applying pressure to the secondary battery to bring the positive electrode 31 and the negative electrode 32 into close contact with each other via the separator 33. During charging, the secondary battery was charged at a constant current of 0.1 C until the voltage reached 4.2 V, and then at the same voltage of 4.2 V, the battery was charged at a constant voltage of 0.01 C until the current reached 0.01 C.

[0251] Finally, the swelling ratio, which is an index for evaluating swelling characteristics, was calculated based on the formula: swelling ratio (%) = [(thickness after charging - thickness before charging) / thickness before charging] × 100.

[0252] (Load characteristics) First, the secondary battery was charged and discharged for one cycle in a room temperature environment (temperature=23°C) to measure the discharge capacity (discharge capacity at the first cycle).

[0253] During charging, the battery was charged at a constant current of 0.2 C until the voltage reached 4.2 V, and then at a constant voltage of 0.025 C at that voltage. During discharging, the battery was discharged at a constant current of 0.2 C until the voltage reached 2.5 V. 0.2 C is the current value that fully discharges the battery capacity in 5 hours.

[0254] Next, the secondary battery was charged and discharged for one cycle in the same environment to measure the discharge capacity (discharge capacity at the second cycle). The charge and discharge conditions were the same as those for the first cycle, except that the charge and discharge currents were both changed to 5C. 5C is the current value at which the battery capacity is fully discharged in 0.2 hours.

[0255] Finally, the load retention rate, which is an index for evaluating load characteristics, was calculated based on the formula: load retention rate (%)=(discharge capacity at second cycle / discharge capacity at first cycle)×100.

[0256] (Cycle characteristics) First, the secondary battery was charged and discharged for one cycle in a room temperature environment (temperature = 23°C) to measure the discharge capacity (discharge capacity at the first cycle). Next, the secondary battery was charged and discharged for 199 cycles in the same environment to measure the discharge capacity (discharge capacity at the 200th cycle). The charge and discharge conditions were the same as those for the first cycle when the load characteristics were evaluated.

[0257] Finally, the capacity retention rate, which is an index for evaluating cycle characteristics, was calculated based on the formula: capacity retention rate (%)=(discharge capacity at 200th cycle / discharge capacity at 1st cycle)×100.

[0258] (Normalization of characteristic values) The initial capacity values ​​shown in Table 1 are normalized values ​​with the initial capacity value for the secondary battery of Comparative Example 1 using a metal current collector (copper foil with a thickness of 10 μm) set to 100. The same applies to the values ​​of the swollenness ratio, load retention ratio, and capacity retention ratio, which are normalized based on the secondary battery of Comparative Example 1.

[0259] [Table 1]

[0260] [Consideration] As shown in Table 1, the initial capacity, swelling rate, load retention rate, and capacity retention rate each varied significantly depending on the configuration of the negative electrode. In the following, the initial capacity, swelling rate, load retention rate, and capacity retention rate values ​​in Comparative Example 1 are used as the comparison standard.

[0261] Specifically, when a metal current collector was used, reducing the thickness of the metal current collector (Comparative Example 2) increased the initial capacity, but the swollenness rate increased and the load retention rate and capacity retention rate both decreased.

[0262] In contrast, when a plurality of large-diameter carbon fiber sections 1, a plurality of small-diameter carbon fiber sections 2, and a plurality of particle sections 3 were used without using a metal current collector (Examples 1 to 7), the appropriate conditions for the average fiber diameters AD1 and AD2 and the porosity R (AD1 = 50 nm to 7000 nm, AD2 = 1 nm to 200 nm, R = 42 vol% to 73 vol%) were satisfied, and therefore the initial capacity, load retention rate, and capacity retention rate all increased, and the swelling rate decreased.

[0263] In this case, when the weight ratio M was 40% by weight to 76% by weight, the swelling rate was sufficiently reduced, and the initial capacity, load retention rate, and capacity retention rate all increased sufficiently.Furthermore, when the average particle size AP was 30 nm to 2000 nm, the swelling rate was sufficiently reduced, and the initial capacity, load retention rate, and capacity retention rate all increased sufficiently.

[0264] <Examples 8 to 11> As shown in Table 2, a secondary battery was produced using the same procedure as in Example 1, except that multiple particle portions 3 including a central portion 3X and a coating portion 3Y were formed in the production process of the negative electrode 32, and then the characteristics of the secondary battery were evaluated.

[0265] The covering portion 3Y was formed from a carbon-containing material or an ion-conductive material, and the ion-conductive material was a solid electrolyte or a gel electrolyte. Amorphous carbon (AC) was used as the carbon-containing material. Lithium phosphate nitrate (Li) was used as the ion-conductive material (solid electrolyte). 3.30 PO 3.90 N 0.17 ) or lithium phosphate (Li3PO4). A mixture of an electrolyte solution and a matrix polymer compound (polyvinylidene fluoride (PVDF)) was used as the gel electrolyte. In this gel electrolyte, the electrolyte solution is held by the matrix polymer compound. The average thickness AT (nm) of the covering portion 3Y is as shown in Table 2.

[0266] When forming multiple particle portions 3 in which the coating portion 3Y contains a carbon-containing material, a carbon-containing material (amorphous carbon) was deposited on the surface of each of multiple central portions 3X (silicon-containing material, elemental silicon, purity = 95%) using the CVD method.

[0267] When forming multiple particle portions 3 in which the coating portion 3Y contains a solid electrolyte (lithium phosphate), lithium phosphate was deposited on the surface of each of multiple central portions 3X (silicon-containing material, pure silicon, purity = 95%) using a sputtering method with lithium phosphate as a target.

[0268] When forming multiple particle portions 3 in which the coating portion 3Y contains a solid electrolyte (lithium phosphate nitride), a sputtering method using lithium phosphate as a target was used to deposit lithium phosphate nitride on the surface of each of multiple core portions 3X (silicon-containing material, pure silicon, purity = 95%) in a nitrogen atmosphere.

[0269] When forming a plurality of particle portions 3 in which the coating portion 3Y contains a gel electrolyte (electrolyte solution and matrix polymer compound), an electrolyte salt (lithium hexafluorophosphate) was first added to a solvent (ethylene carbonate and propylene carbonate), and the solvent was then stirred to prepare an electrolyte solution. Next, a precursor solution was prepared by mixing the electrolyte solution with a matrix polymer compound (polyvinylidene fluoride). The mixture ratio (weight ratio) of this precursor solution was ethylene carbonate:propylene carbonate:lithium hexafluorophosphate:polyvinylidene fluoride = 42:42:13:3. Finally, the precursor solution was applied to the surface of each of a plurality of core portions 3X (silicon-containing material, elemental silicon, purity = 95%), and then the precursor solution was dried.

[0270] [Table 2]

[0271] As shown in Table 2, when multiple particle portions 3 including a central portion 3X and a coating portion 3Y were used (Examples 8 to 11), the increase in the swelling rate was sufficiently suppressed, while the initial capacity, load retention rate, and capacity retention rate each increased, or both the load retention rate and the capacity retention rate each increased, compared to when the coating portion 3Y was not used (Example 1).

[0272] <Examples 12 to 16> As shown in Table 3, a secondary battery was produced using the same procedure as in Example 1, except that composite secondary particles 3BP containing multiple small-diameter carbon fiber portions 2 were formed as each of the multiple particle portions 3 in the production process of the negative electrode 32, and then the characteristics of the secondary battery were evaluated.

[0273] To form these composite secondary particles 3BP, first, a powder of silicon-containing material (silicon element, purity = 95%), a plurality of small-diameter carbon fiber parts 2 (SWCNT), and a binder (lithium polyacrylate) were added to a solvent (pure water, which is an aqueous solvent), and the solvent was then stirred to prepare a dispersion. The mixing ratio (weight ratio) of the dispersion was silicon-containing material powder: plurality of small-diameter carbon fiber parts 2: binder = 94:1:4. Next, the dispersion was sprayed using a spray dryer, and the sprayed product (granules) was then dried.

[0274] [Table 3]

[0275] As shown in Table 3, when composite secondary particles 3BP containing a plurality of small-diameter carbon fiber portions 2 were used (Examples 12 to 16), one or more of the initial capacity, swelling rate, load retention rate, and capacity retention rate were improved compared to when the composite secondary particles 3BP were not used (Example 1). In particular, when composite secondary particles 3BP were used and the average particle size AP2 was 100 nm to 10,000 nm, the swelling rate was sufficiently reduced and the initial capacity, load retention rate, and capacity retention rate were each sufficiently increased.

[0276] <Examples 17 to 21> As shown in Table 4, a secondary battery was produced using the same procedure as in Example 1, except that composite secondary particles 3BP containing an ion-conductive material (gel electrolyte) were formed as each of the multiple particle portions 3 in the process of producing the negative electrode 32, and then the characteristics of the secondary battery were evaluated.

[0277] To form these composite secondary particles 3BP, an electrolyte solution was prepared by first adding an electrolyte salt (lithium hexafluorophosphate) to a solvent (ethylene carbonate and propylene carbonate) and then stirring the solvent. Next, a precursor solution was prepared by mixing the electrolyte solution with a matrix polymer compound (polyvinylidene fluoride). The mixing ratio (weight ratio) of this precursor solution was ethylene carbonate:propylene carbonate:lithium hexafluorophosphate:polyvinylidene fluoride = 42:42:13:3. Next, a silicon-containing material powder (elemental silicon, purity = 95%) and the precursor solution were mixed together, and the precursor solution was stirred to prepare a dispersion. Finally, the dispersion was sprayed using a spray dryer, and the sprayed product (granules) was dried.

[0278] [Table 4]

[0279] As shown in Table 4, when composite secondary particles 3BP containing an ion-conductive material (gel electrolyte) were used, the same results as when composite secondary particles 3BP containing a plurality of small-diameter carbon fiber portions 2 (Table 3) were used were obtained. That is, when composite secondary particles 3BP containing an ion-conductive material were used (Examples 17 to 21), one or more of the initial capacity, swelling rate, load retention rate, and capacity retention rate were improved compared to when the composite secondary particles 3BP were not used (Example 1). In particular, when composite secondary particles 3BP were used, when the average particle size AP2 was 100 nm to 10,000 nm, the swelling rate was sufficiently reduced, and the initial capacity, load retention rate, and capacity retention rate were each sufficiently increased.

[0280] [summary] The results shown in Tables 1 to 4 show that when the negative electrode 32 (negative electrode 10) contains a plurality of large-diameter carbon fiber sections 1, a plurality of small-diameter carbon fiber sections 2, and a plurality of particle sections 3, and has a plurality of voids 10G, each of the plurality of large-diameter carbon fiber sections 1 and the plurality of small-diameter carbon fiber sections 2 contains a carbon-containing material, each of the plurality of particle sections 3 contains a silicon-containing material, and the average fiber diameters AD1 and AD2 and porosity R satisfy the above-mentioned appropriate conditions, the initial capacity, load retention rate, and capacity retention rate all increase, and the swell rate decreases. Therefore, the secondary battery can achieve excellent initial capacity characteristics, excellent swell characteristics, excellent load retention rate, and excellent cycle characteristics.

[0281] The present technology has been described above with reference to an embodiment and examples. However, the configuration of the present technology is not limited to the configuration described in the embodiment and examples, and can be modified in various ways.

[0282] Specifically, the secondary battery has been described as having a laminate film structure, but the structure of the secondary battery is not particularly limited, and other battery structures such as a cylindrical type, a prismatic type, a coin type, and a button type may also be used.

[0283] The battery element has been described as having a stacked structure. However, the structure of the battery element is not particularly limited, and other structures such as a wound structure and a zigzag structure may be used. In the wound structure, the positive electrode and the negative electrode are wound with a separator interposed therebetween, and in the zigzag structure, the positive electrode and the negative electrode are folded in a zigzag pattern while facing each other with the separator interposed therebetween.

[0284] Furthermore, although the electrode reactant is lithium in the above description, the electrode reactant is not particularly limited. Specifically, as described above, the electrode reactant may be other alkali metals such as sodium and potassium, or alkaline earth metals such as beryllium, magnesium, and calcium. In addition, the electrode reactant may be other light metals such as aluminum.

[0285] The effects described in this specification are merely examples, and the effects of the present technology are not limited to the effects described in this specification. Therefore, other effects may be obtained with respect to the present technology.

Claims

1. A positive electrode and a negative electrode including a plurality of first fibrous portions, a plurality of particle portions, and a plurality of second fibrous portions, and having a plurality of voids; Electrolyte and Equipped with the plurality of first fiber portions are carbon paper, the plurality of first fiber parts are connected to each other to form a three-dimensional network structure having the plurality of voids, and each of the plurality of first fiber parts contains carbon as a constituent element; the plurality of particle portions cover the surfaces of the plurality of first fiber portions, at least some of the plurality of particle portions are connected to each other, and each of the plurality of particle portions contains silicon as a constituent element; the plurality of second fiber portions are carbon nanotubes, at least a portion of the plurality of second fibrous portions are connected to surfaces of the plurality of particle portions, and each of the plurality of second fibrous 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; an average fiber diameter of the plurality of second fiber portions is smaller than an average fiber diameter of the plurality of first fiber portions; the porosity of the negative electrode is 42% by volume or more and 73% by volume or less; At least some of the second fiber portions are connected to two or more of the first fiber portions via some of the particle portions. Secondary battery.

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

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

4. each of the plurality of particle portions is a primary particle, at least some of the plurality of particle portions are connected to each other to form a plurality of secondary particles, The average particle size of the plurality of secondary particles is 30 nm or more and 2000 nm or less. The secondary battery according to any one of claims 1 to 3.

5. At least a portion of the plurality of particle portions is a core containing silicon as a constituent element; a coating portion that coats the surface of the central portion and contains carbon as a constituent element; The secondary battery according to claim 1 , comprising:

6. At least a portion of the plurality of particle portions is a core containing silicon as a constituent element; a coating portion that coats the surface of the central portion and contains an ion-conductive material; The secondary battery according to claim 1 , comprising:

7. the ion-conductive material includes at least one of lithium phosphate oxynitride and lithium phosphate; The secondary battery according to claim 6.

8. each of the plurality of particle portions 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 300 nm or more and 10,000 nm or less. The secondary battery according to any one of claims 1 to 7.

9. each of the plurality of particle portions is a primary particle, at least a portion of the plurality of particle portions forms a plurality of secondary particles containing a plurality of ion-conductive materials; The average particle size of the plurality of secondary particles is 300 nm or more and 10,000 nm or less. The secondary battery according to any one of claims 1 to 7.

10. Each of the plurality of second fiber portions includes a single-walled carbon nanotube. The secondary battery according to any one of claims 1 to 9.

11. It is a lithium-ion secondary battery. The secondary battery according to any one of claims 1 to 10.

12. The fiber optics includes a plurality of first fiber portions, a plurality of particle portions, and a plurality of second fiber portions, and has a plurality of voids; the plurality of first fiber portions are carbon paper, the plurality of first fiber parts are connected to each other to form a three-dimensional network structure having the plurality of voids, and each of the plurality of first fiber parts contains carbon as a constituent element; the plurality of particle portions cover the surfaces of the plurality of first fiber portions, at least some of the plurality of particle portions are connected to each other, and each of the plurality of particle portions contains silicon as a constituent element; the plurality of second fiber portions are carbon nanotubes, at least a portion of the plurality of second fibrous portions are connected to surfaces of the plurality of particle portions, and each of the plurality of second fibrous 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; an average fiber diameter of the plurality of second fiber portions is smaller than an average fiber diameter of the plurality of first fiber portions; The porosity is 42% by volume or more and 73% by volume or less, At least some of the second fiber portions are connected to two or more of the first fiber portions via some of the particle portions. Negative electrode for secondary batteries.

Images