Cylindrical battery

Abstract

In a cylindrical battery that is one exemplary embodiment, a negative electrode (12) comprises, in order from a negative electrode terminal (12e) side: a both-surfaces-exposed section (42) in which both surfaces of a negative electrode core (40) are exposed; a mixture-layer-formed-on-one-surface section (43) in which the outer surface of the negative electrode core (40) facing outward in the radial direction of an electrode body (14A) is exposed and a negative electrode mixture layer (41) is formed on the inner surface of the negative electrode core (40) facing inward in the radial direction; and a mixture-layer-formed-on-both-surfaces section (44) in which the negative electrode mixture layer (41) is formed on both surfaces of the negative electrode core (40). At least one of a first separator (13x) and a second separator (13y) is wound one or more turns from a position facing a positive electrode terminal (11e) to the winding end side of the electrode body (14A). The negative electrode mixture layer (41) contains, as a negative electrode active material, a silicon material having a porosity of 10% or more.

Description

Cylindrical battery

[0001] This disclosure relates to a cylindrical battery, and more particularly to a cylindrical battery equipped with a wound electrode body.

[0002] A cylindrical battery comprises a wound electrode body in which a positive electrode and a negative electrode are wound in a spiral shape with a separator in between (see, for example, Patent Document 1). As disclosed in Patent Document 1, the positive electrode and negative electrode constituting the wound electrode body have a core body and a composite layer formed on the core body. The negative electrode composite layer is always arranged in the area facing the positive electrode composite layer in the radial direction of the electrode body. For this reason, the end of the positive electrode composite layer, which is the end of the positive electrode composite layer at the winding end of the electrode body, is sandwiched from both radial sides of the electrode body by the negative electrode composite layer via a separator.

[0003] Japanese Patent Publication No. 2001-185201

[0004] Our investigations have revealed that deformation of the negative electrode is likely to occur near the end of the positive electrode mixture layer. Generally, the negative electrode extends beyond the end of the positive electrode mixture layer towards the end of the electrode body's winding, and a large gap corresponding to the thickness of the positive electrode mixture layer is formed between the radially opposing negative electrodes near the end of the positive electrode mixture layer. The electrode body expands and contracts during charging and discharging of the battery, and at this time, stress concentrates near the end of the positive electrode mixture layer where the gap exists, which is thought to cause deformation of the negative electrode. Since deformation of the negative electrode can lead to non-uniformity of the electrode reaction, localized short circuits, etc., suppressing deformation of the negative electrode is an important issue.

[0005] The cylindrical battery according to this disclosure comprises an electrode body in which a positive electrode and a negative electrode are wound with a separator between them, and a bottomed cylindrical outer casing for housing the electrode body, wherein the positive electrode has a positive electrode core and a positive electrode mixture layer formed on the positive electrode core, and the negative electrode has a negative electrode core and a negative electrode mixture layer formed on the negative electrode core, and starting from the negative electrode end side which is the end of the winding of the electrode body, both sides of the negative electrode core are exposed and constitute a double-sided exposed portion which comprises 0.5 times or more of the outermost circumference of the electrode body, the outer surface of the negative electrode core facing radially outward of the electrode body is exposed and the negative electrode mixture layer is formed on the inner surface of the negative electrode core facing radially inward, and the negative electrode core The electrode body includes a double-sided compound layer forming section on both sides of the body, wherein the negative electrode compound layer contains a silicon material with a porosity of 10% or more as a negative electrode active material, the single-sided compound layer forming section and the double-sided compound layer forming section are arranged to sandwich the positive electrode compound layer end, which is the end of the positive electrode compound layer on the winding end side of the electrode body, from both radial sides of the electrode body, the separator includes a first separator located radially inward of the positive electrode compound layer end and a second separator located radially outward of the positive electrode compound layer end, and at least one of the first and second separators is wound around the electrode body at least once from a position opposite to the positive electrode compound layer end toward the winding end side.

[0006] According to the cylindrical battery described herein, deformation of the negative electrode near the end of the positive electrode mixture layer can be effectively suppressed.

[0007] This is an axial cross-sectional view of a cylindrical battery, which is an example of an embodiment. This is a diagram showing a part of the radial cross-section of the electrode body of the first embodiment. This is a diagram showing a part of the radial cross-section of the electrode body of the second embodiment. This is a diagram showing a part of the radial cross-section of the electrode body of the third embodiment. This is a diagram showing a part of the radial cross-section of the electrode body of the fourth embodiment.

[0008] Hereinafter, an example of an embodiment of the cylindrical battery according to this disclosure will be described in detail with reference to the drawings. Note that the cylindrical battery according to this disclosure is not limited to the embodiments described below. Furthermore, forms obtained by selectively combining the various components of the multiple embodiments and modifications described below are also included in this disclosure.

[0009] Figure 1 is a schematic diagram showing an axial cross-section including the central axis of a cylindrical battery 10, which is an example of an embodiment. As shown in Figure 1, the cylindrical battery 10 includes a positive electrode 11, a negative electrode 12, and a separator 13, and comprises an electrode body 14 in which the positive electrode 11 and the negative electrode 12 are wound around the separator 13, and a bottomed cylindrical outer casing 16 that houses the electrode body 14. The cylindrical battery 10 also includes an electrolyte housed in the outer casing 16 and a sealing body 17 that closes the opening of the outer casing 16. The outer casing 16 has grooves 22 formed in its side wall, and the sealing body 17 is supported by the grooves 22 and closes the opening of the outer casing 16. In the following description, for convenience, the side of the cylindrical battery 10 with the sealing body 17 will be considered the top, and the bottom side of the outer casing 16 will be considered the bottom.

[0010] The electrolyte may be an aqueous electrolyte, but in this embodiment, a non-aqueous electrolyte is used. The non-aqueous electrolyte has lithium-ion conductivity. The non-aqueous electrolyte may be a liquid electrolyte (electrolyte solution) or a solid electrolyte. The cylindrical battery 10 is, for example, a non-aqueous electrolyte secondary battery, and among these, a lithium-ion battery is preferred.

[0011] A liquid electrolyte (electrolyte solution) comprises a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and mixtures of two or more of these. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixtures thereof. The non-aqueous solvent may also contain halogen-substituted solvents (e.g., fluoroethylene carbonate) in which at least some of the hydrogen atoms of the solvent are replaced with halogen atoms such as fluorine. Examples of electrolyte salts include LiPF4. ６ Lithium salts such as these are used.

[0012] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc., can be used. As the inorganic solid electrolyte, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. Examples of polymer materials include fluororesins, acrylic resins, polyether resins, etc.

[0013] As described above, the electrode body 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound in a spiral shape via a separator 13. The positive electrode 11, the negative electrode 12, and the separator 13 are all elongated strip-shaped bodies that are alternately stacked in the radial direction of the electrode body 14 by being wound in a spiral shape. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer in both the length and width directions than the positive electrode 11. The separator 13 is formed to be at least slightly larger than the positive electrode 11, and for example, two separators are arranged so as to sandwich the positive electrode 11.

[0014] Here, we will explain the positive electrode 11 and the negative electrode 12 in detail.

[0015] [Positive Electrode] The positive electrode 11 has a long positive electrode core 30 and a positive electrode mixture layer 31 formed on the positive electrode core 30. The positive electrode core 30 can be made of a metal foil that is stable in the potential range of the positive electrode 11, such as aluminum, aluminum alloy, stainless steel, or titanium, or a film with the metal arranged on its surface. The positive electrode mixture layer 31 contains a positive electrode active material, a conductive agent, and a binder, and is preferably formed on both sides of the positive electrode core 30, except for the core exposed portion described later.

[0016] The thickness of the positive electrode 11 is, for example, 150 μm to 230 μm. In this embodiment, the thickness of the positive electrode 11 is substantially constant except for the core body exposed portion. The thickness of the positive electrode core body 30 is, for example, 10 μm to 30 μm. The thickness of the positive electrode mixture layer 31 is, for example, 70 μm to 100 μm on one side of the positive electrode core body 30. The positive electrode 11 can be manufactured by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder onto the positive electrode core body 30, drying the coating film, and then compressing it to form the positive electrode mixture layer 31 on both sides of the positive electrode core body 30.

[0017] The positive electrode active material is a lithium transition metal composite oxide containing transition metal elements such as Ni, Co, and Mn. Examples of metal elements contained in the composite oxide include Ni, Co, Mn, Al, Be, B, Na, Mg, Si, K, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, In, Sn, Sb, Ba, Ta, W, Pb, and Bi. Among these, it is preferable to contain at least one of Ni, Co, and Mn. The lithium transition metal composite oxide has, for example, a layered rock salt structure. One type of lithium transition metal composite oxide may be used alone, or multiple types may be used in combination. The content of the positive electrode active material is, for example, 90% by mass or more and 99.8% by mass or less based on the mass of the positive electrode mixture layer 31.

[0018] Examples of conductive agents included in the positive electrode mixture layer 31 include carbon black such as acetylene black and Ketjenblack, graphite, carbon nanotubes (CNTs), carbon nanofibers, graphene, metal fibers, metal powders, and conductive whiskers. One type of conductive agent may be used alone, or multiple types may be used in combination. The content of the conductive agent is not particularly limited, but is, for example, 0.1% by mass or more and 5% by mass or less, relative to the mass of the positive electrode mixture layer 31.

[0019] Examples of binders included in the positive electrode mixture layer 31 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), olefin resins such as polyethylene, polypropylene, ethylene-propylene-isoprene copolymer and ethylene-propylene-butadiene copolymer, and acrylic resins such as polyacrylonitrile (PAN), polyimide, polyamide, and ethylene-acrylic acid copolymer. These resins may also be used in combination with carboxymethylcellulose (CMC) or its salts, polyethylene oxide (PEO), etc. The binder may be used alone or in combination of multiple types. The binder content is not particularly limited, but is, for example, 0.1% to 5% by mass relative to the mass of the positive electrode mixture layer 31.

[0020] [Negative Electrode] The negative electrode 12 has a long negative electrode core 40 and a negative electrode mixture layer 41 formed on the negative electrode core 40. The negative electrode core 40 can be made of a metal foil that is stable in the potential range of the negative electrode 12, such as copper, copper alloy, stainless steel, nickel, or nickel alloy, or a film with the metal arranged on its surface. The negative electrode mixture layer 41 contains a negative electrode active material and a binder such as styrene-butadiene rubber (SBR), and is preferably formed on both sides of the negative electrode core 40, except for the core exposed portion described later.

[0021] The thickness of the negative electrode 12 is, for example, 145 μm to 235 μm. In this embodiment, the thickness of the negative electrode 12 is substantially constant except for the exposed core portion. The thickness of the negative electrode core 40 is, for example, 5 μm to 15 μm. The thickness of the negative electrode mixture layer 41 is, for example, 70 μm to 110 μm on one side of the negative electrode core 40. The negative electrode 12 can be manufactured in the same way as the positive electrode 11 by applying a negative electrode mixture slurry containing a negative electrode active material and a binder onto the negative electrode core 40, drying the coating film, and then compressing it to form the negative electrode mixture layer 41 on both sides of the negative electrode core 40.

[0022] The binder contained in the negative electrode mixture layer 41 may be a fluororesin, olefin resin, PAN, polyimide, polyamide, acrylic resin, etc., as in the case of the positive electrode 11, but polyvinyl acetate, styrene-butadiene rubber (SBR), etc. may also be used. Among these, the use of SBR is preferred. One type of binder may be used alone, or multiple types may be used in combination. Furthermore, the negative electrode mixture layer 41 preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), etc. The binder content is not particularly limited, but is, for example, 0.1% by mass or more and 5% by mass or less of the mass of the negative electrode mixture layer 41.

[0023] The negative electrode mixture layer 41 contains a silicon material with a porosity of 10% or more as the negative electrode active material. As will be described in detail later, by using a silicon material with a porosity of 10% or more, deformation of the negative electrode 12 is highly suppressed due to the synergistic effect with the separator 13 that extends for one or more turns from the position opposite the end of the positive electrode mixture layer toward the end of the winding of the electrode body 14. It is possible to use silicon material alone as the negative electrode active material, but from the viewpoint of achieving both high capacity and high durability of the battery, it is preferable that the negative electrode active material contains both silicon material and carbon material. The content of silicon material with a porosity of 10% or more is preferably 2% by mass or more and 30% by mass or less of the total mass of the negative electrode active material. For the sake of explanation below, the silicon material with a porosity of 10% or more will be referred to as "silicon material Z".

[0024] In this specification, the porosity of a silicon material refers to the ratio of the volume of voids inside a particle to the volume of the particle itself, and can be calculated, for example, based on the volume of voids measured by 3D tomography using a transmission electron microscope (TEM).

[0025] The content of silicon material Z is more preferably 2% by mass or more and 25% by mass or less, and particularly preferably 3% by mass or more and 15% by mass or less, relative to the total mass of the negative electrode active material. If the content of silicon material Z is within this range, deformation of the negative electrode 12 can be effectively suppressed while achieving both high capacity and high durability of the battery. The negative electrode active material may also contain silicon materials other than silicon material Z, i.e., a second silicon material with a porosity of less than 10%, to the extent that it does not impair the purpose of this disclosure.

[0026] If the porosity of the silicon material Z is 10% or more, the deformation suppression effect of the negative electrode 12 can be obtained. However, in order to efficiently suppress the deformation of the negative electrode 12 while increasing the capacity of the battery, the porosity is preferably 50% or less, more preferably 40% or less, and particularly preferably 30% or less. As will be described in more detail later, the silicon material Z preferably includes a silicon-carbon composite material with a porosity of 10% or more and 30% or less.

[0027] The carbon material that functions as the negative electrode active material is, for example, at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, and hard carbon. In particular, it is preferable to use artificial graphite such as bulk artificial graphite (MAG) or graphitized mesophase carbon microbeads (MCMB), natural graphite such as flake graphite, bulk graphite, or earthy graphite, or a mixture thereof as the carbon material.

[0028] The carbon material content is, for example, 60% to 99% by mass relative to the total mass of the negative electrode active material, preferably 70% to 98% by mass, and more preferably 85% to 97% by mass, from the viewpoint of achieving both high capacity and high durability of the battery. That is, the silicon material content is preferably 2% to 30% by mass, and more preferably 3% to 15% by mass, relative to the total mass of the negative electrode active material. The silicon material may contain a second silicon material with a porosity of less than 10%, but the proportion of silicon material Z in the total silicon material is preferably 40% by mass or more.

[0029] The above-mentioned soft carbon and hard carbon are classified as amorphous carbon in which the graphite crystal structure is not well developed. More specifically, they refer to carbon components in which the d(002) interplanar spacing determined by X-ray diffraction is 0.342 nm or greater. Soft carbon is also called easily graphitizable carbon, and is carbon that graphitizes more easily than hard carbon when treated at high temperatures. Hard carbon is also called poorly graphitizable carbon. Note that there is no need to clearly distinguish between soft carbon and hard carbon. As a negative electrode active material, graphite and at least one of amorphous carbon, either soft carbon or hard carbon, may be used in combination.

[0030] The volume-based median diameter (D50) of the carbon material is, for example, 1 μm to 30 μm, preferably 5 μm to 25 μm. D50 represents the particle size at which the cumulative frequency of the smallest particle size accounts for 50% in the volume-based particle size distribution. The particle size distribution of the carbon material can be measured using a laser diffraction particle size distribution analyzer (for example, Shimadzu Corporation, SALD-2000A) with water as the dispersion medium.

[0031] The silicon material Z, which functions as the negative electrode active material, can be any material containing Si, and examples include silicon alloys, silicon compounds, and composite materials containing Si. Among these, composite materials containing Si are preferred. The D50 of silicon material Z is generally smaller than that of graphite. The volume-based D50 of silicon material Z is, for example, 1 μm or more and 20 μm or less, and preferably 1 μm or more and 15 μm or less.

[0032] A suitable composite material is a composite particle comprising an ionic conducting phase and a Si phase dispersed in the ionic conducting phase. The ionic conducting phase is, for example, at least one selected from the group consisting of silicate phase, carbon phase, silicide phase, and silicon oxide phase. The ionic conducting phase may also contain at least one selected from the group consisting of Group 1 and Group 2 elements of the periodic table, or it may be a Li-doped silicon oxide phase. The silicide phase is a compound phase consisting of Si and an element more electrically positive than Si, such as NiSi and Mg. ２ Si, TiSi ２ These are some examples.

[0033] The Si phase is formed by dispersing Si in the form of fine particles. The ion-conducting phase is a continuous phase composed of, for example, an aggregate of particles finer than those in the Si phase. The average size (crystallite size) of the Si phase is preferably between 1 nm and 200 nm, and more preferably between 1 nm and 100 nm. The average size of the Si phase is calculated from the full width at half maximum of the peak (2θ = 28.4°) attributable to Si in the XRD pattern using the formula D = kλ / Bcosθ (k = 0.89, λ = 0.15418, 2θ = 28.4°, B is the full width at half maximum). The average size of the Si phase may also be, for example, between 1 nm and 10 nm. By reducing the size of the Si phase, particle expansion associated with charging and discharging can be suppressed while maintaining high capacity.

[0034] An example of a suitable composite material containing Si is a silicon-carbon composite material, which comprises a carbon phase and a Si phase dispersed in the carbon phase. The silicon-carbon composite material is a composite particle having a sea-island structure in which fine Si particles are dispersed substantially uniformly in the carbon phase. The carbon phase is preferably an amorphous carbon phase. The carbon phase may contain crystalline phase components, but it is preferable that the amorphous phase components are more abundant. The amorphous carbon phase is composed of a carbon material in which the average interplanar spacing of (002) planes, as measured by X-ray diffraction, exceeds 0.34 nm.

[0035] Another example of a suitable composite material containing Si is one having a sea-island structure in which fine Si particles are dispersed substantially uniformly in an amorphous silicon oxide phase, and the overall general formula is SiO ｘ This is a composite particle represented by (0 < x ≤ 2). The main component of silicon oxide may be silicon dioxide. The silicon oxide phase may also be doped with Li. The oxygen content ratio (x) to Si is, for example, 0.5 ≤ x < 2.0, and preferably 0.8 ≤ x ≤ 1.5.

[0036] Another example of a suitable composite material containing Si is a composite particle having a sea-island structure in which fine Si particles are dispersed substantially uniformly in an amorphous silicate phase. A suitable silicate phase is a lithium silicate phase containing Li. The lithium silicate phase is, for example, a lithium silicate with the general formula Li ２ｚ SiO （２＋ｚ）It is a phase of a composite oxide represented by (0 < z < 2). In the lithium silicate phase, Li ４ SiO ４ (Z = 2) is preferably not contained. Li ４ SiO ４ is an unstable compound that reacts with water to exhibit alkalinity, which may deteriorate Si and cause a decrease in charge-discharge capacity. From the viewpoints of stability, productivity, Li ion conductivity, etc., the lithium silicate phase is Li ２ SiO ３ (Z = 1) or Li ２ Si ２ O ５ (Z = 1 / 2) is preferably contained as a main component.

[0037] The composite material may have a conductive layer covering the surface of the ion conductive phase. The conductive layer is composed of a material having higher conductivity than the ion conductive phase, and forms a good conductive path in the negative electrode mixture layer 41. The conductive layer is, for example, a carbon coating composed of a conductive carbon material. As the conductive carbon material, carbon black such as acetylene black and Ketjen black, graphite, amorphous carbon with low crystallinity, and the like can be used. Note that the silicon-carbon composite material containing a carbon phase may have a conductive layer different from the carbon phase, or may not have such a conductive layer.

[0038] As described above, the silicon material Z is preferably a Si-containing composite material, and among them, a silicon-carbon composite material is particularly preferred. Hereinafter, a silicon-carbon composite material having a porosity of 10% or more is referred to as "silicon-carbon composite material Z". By using the silicon-carbon composite material Z, the effect of suppressing deformation of the negative electrode 12 becomes more remarkable. As described above, the silicon-carbon composite material Z has a sea-island structure in which fine Si phases are dispersed in a continuous phase composed of amorphous carbon. The Si phase is dispersed in the amorphous carbon phase in the form of fine particles, and repeatedly absorbs and releases Li ions during charge and discharge of the battery. Although the volume of the Si phase changes with charge and discharge, since it is dispersed in the amorphous carbon phase, the stress caused by the volume change of the Si phase is relaxed by the amorphous carbon phase.

[0039] The porosity of the silicon-carbon composite material Z is preferably 10% or more and 30% or less, more preferably 13% or more and 27% or less, and particularly preferably 15% or more and 25% or less. When the porosity of the silicon-carbon composite material Z falls within the above range, deformation of the negative electrode 12 can be efficiently suppressed while increasing the capacity of the battery. Note that the voids in the silicon-carbon composite material Z exist throughout the entire particle, and are mainly present in the carbon phase and at the interface between the carbon phase and the Si phase, but voids may also be present in the Si phase.

[0040] As described above, the silicon material Z may contain silicon materials other than the silicon-carbon composite material Z, for example, a Si-containing composite material with a porosity of less than 10%. The content of the silicon-carbon composite material Z is preferably 40% by mass or more, more preferably 80% by mass or more, based on the total mass of the silicon material, and may be substantially 100% by mass. When the content of the silicon-carbon composite material Z is 40% by mass or more and 100% by mass or less, the effect of suppressing deformation of the negative electrode 12 is more remarkable.

[0041] The Si content in the silicon-carbon composite material Z is, for example, 40% by mass or more and 70% by mass or less. If the Si content is too low, the capacity will decrease. Therefore, the Si content relative to the mass of the silicon-carbon composite material Z is more preferably 50% by mass or more. On the other hand, if the Si content is too high, for example, the volume change of the particles accompanying charge and discharge becomes large, and particle cracking is prone to occur. As a result, a side reaction between the non-aqueous electrolyte and Si occurs, which tends to reduce the durability of the battery.

[0042] The average particle diameter of the Si phase, at least before the initial charge and discharge, is preferably 500 nm or less, more preferably 200 nm or less, and particularly preferably 50 nm or less. By refining and dispersing the Si phase, the volume change of the silicon-carbon composite material Z during charge and discharge is reduced, and the stability of the particle structure is further improved. The average particle diameter of the Si phase is determined by observing the cross-section of particles of the silicon-carbon composite material Z using a scanning electron microscope (SEM). Specifically, 100 arbitrary Si phases are selected from an SEM image of the particle cross-section, the diameter of the circumscribed circle of each Si phase is measured, and the average of the measured values is obtained.

[0043] The amorphous carbon phase is obtained by heat-treating pitch at a temperature of 700°C to 900°C. The amorphous carbon phase may also contain metal oxides that do not react with Li, such as zirconium oxide, aluminum oxide, titanium oxide, nickel oxide, and yttrium oxide. The silicon-carbon composite material Z can be produced, for example, by mixing Si powder with amorphous carbon such as pitch, and then heat-treating and pulverizing the mixture. The mixing and heat treatment of the raw materials are preferably carried out in an inert atmosphere (for example, in an atmosphere of argon, nitrogen, etc.). For example, a ball mill can be used to mix the raw materials.

[0044] The above heat treatment is performed in an inert atmosphere at a temperature of 450°C to 1000°C. Within this range, a sea-island structure in which minute Si phases are dispersed within a less crystalline amorphous carbon phase can be easily formed. The heat treatment temperature is preferably 600°C to 950°C, and more preferably 700°C to 900°C. The heat treatment time is, for example, 1 hour to 10 hours. The porosity of the silicon-carbon composite material Z can be controlled, for example, by the softening point of the pitch. When a pitch with a low softening point is used, carbon is more easily filled between Si particles, resulting in a lower porosity. On the other hand, when a pitch with a high softening point is used, carbon is less easily filled between Si particles, resulting in a higher porosity.

[0045] The elemental content in the amorphous carbon phase can be measured by inductively coupled plasma atomic emission spectroscopy (ICP). Specifically, silicon-carbon composite material Z is dissolved in a heated acid solution (a mixed acid of hydrofluoric acid, nitric acid, and sulfuric acid), and the carbon residue in the solution is filtered out. The elemental content in the amorphous carbon phase can then be determined by analyzing the resulting filtrate with ICP. Alternatively, the carbon content in silicon-carbon composite material Z can be measured using a carbon-sulfur analyzer (for example, EMIA-520, manufactured by Horiba, Ltd.).

[0046] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator 13 include polyethylene, polyolefins such as polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. Furthermore, a highly heat-resistant resin layer, such as aramid resin, may be formed on the surface of the separator 13.

[0047] The electrode body 14 has a positive electrode lead 20 connected to a positive electrode 11 and a negative electrode lead 21 connected to a negative electrode 12. In this embodiment, the positive electrode mixture layer 31 is absent in the longitudinal center of the positive electrode 11, and a core exposed portion is formed where the surface of the positive electrode core 30 is exposed. The positive electrode lead 20 is connected to this exposed portion. On the other hand, the negative electrode lead 21 is provided at one longitudinal end of the negative electrode 12, which is located on the winding start side of the electrode body 14. At one longitudinal end of the negative electrode 12, the negative electrode mixture layer 41 is absent, and a first core exposed portion (not shown) is formed where the surface of the negative electrode core 40 is exposed. The negative electrode lead 21 is connected to this core exposed portion.

[0048] Insulating plates 18 and 19 are positioned above and below the electrode body 14, respectively. In the example shown in Figure 1, the positive electrode lead 20 extends through a through-hole in the insulating plate 18 towards the sealing body 17, and the negative electrode lead 21 extends through a through-hole in the insulating plate 19 towards the bottom of the outer can 16. The positive electrode lead 20 is connected to the lower surface of the internal terminal plate 23 of the sealing body 17 by welding or the like, and the cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, becomes the positive electrode terminal. The negative electrode lead 21 is connected to the inner bottom surface of the outer can 16 by welding or the like, and the outer can 16 becomes the negative electrode terminal.

[0049] The outermost surface of the electrode body 14 is provided with a negative electrode 12 and a double-sided exposed portion 42, which is a second core exposed portion where the surface of the negative electrode core body 40 is exposed. The double-sided exposed portion 42 is in contact with the inner surface of the outer casing 16. By the double-sided exposed portion 42 contacting the inner surface of the outer casing 16, both ends in the longitudinal direction of the negative electrode 12 and the outer casing 16 are electrically connected, ensuring good current collection on the negative electrode side. A winding stopper tape may be attached to the outermost surface of the electrode body 14 to maintain the winding structure.

[0050] The outer casing 16 is a bottomed cylindrical metal container. A gasket 28 is provided between the outer casing 16 and the sealing body 17 to seal the inside of the battery. The outer casing 16 has a grooved portion 22 that supports the sealing body 17, which is formed, for example, by pressing the side surface from the outside. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the outer casing 16, and its upper surface supports the sealing body 17. The upper end of the outer casing 16 is bent inward and crimped to the peripheral edge of the sealing body 17.

[0051] The sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked in order from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each component except the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, with the insulating member 25 interposed between their respective peripheries. When the internal pressure of the battery rises due to abnormal heat generation, the lower valve body 24 deforms and ruptures, pushing the upper valve body 26 towards the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 ruptures, and gas is discharged from the opening of the cap 27.

[0052] The embodiments of the electrode body will be described in detail below with reference to Figures 2 to 5. Figures 2 to 5 show a portion of the radial cross-section of the electrode bodies 14A to 14D of the first to fourth embodiments, cut in a direction perpendicular to the central axis, and show the cross-section at the end of the winding. Note that any of the electrode bodies 14A to 14D can be applied to the electrode body 14 of the cylindrical battery 10 shown in Figure 1.

[0053] [First Embodiment] As shown in Figure 2, the electrode body 14A of the first embodiment has a winding structure in which the negative electrode 12 and separator 13 extend toward the end of the winding of the electrode body 14A beyond the positive electrode end 11e, which is the end of the positive electrode 11 at the end of the winding of the electrode body 14A. As described above, the negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition, and the negative electrode mixture layer 41 is always arranged in the area facing the positive electrode mixture layer 31 via the separator 13. The negative electrode mixture layer 41 is arranged to sandwich the positive electrode end 11e from both radial sides of the electrode body 14A.

[0054] In this embodiment, the positive electrode mixture layer end, which is the end of the positive electrode mixture layer 31 at the winding end of the electrode body 14A, and the positive electrode end 11e, which is the end of the positive electrode 11, coincide. That is, there is no exposed portion of the positive electrode core 30 at the winding end of the electrode body 14A, and the positive electrode end 11e can be rephrased as the positive electrode mixture layer end. In the following, for the sake of explanation, the radially outer side of the electrode body may be simply referred to as the "outside," and the radially inner side of the electrode body may be simply referred to as the "inside."

[0055] The negative electrode 12 includes, in order along the winding direction from the negative electrode end 12e, which is the end of the negative electrode 12 at the winding end of the electrode body 14A, a double-sided exposed portion 42, a single-sided composite layer forming portion 43, and a double-sided composite layer forming portion 44. The double-sided exposed portion 42 exposes both sides of the negative electrode core 40 and constitutes at least 0.5 turns of the outermost surface of the electrode body 14A. As described above, the double-sided exposed portion 42 abuts against the inner surface of the outer casing 16, and the negative electrode 12 and the outer casing 16 are electrically connected at the winding end of the electrode body 14A. If at least 0.5 turns of the outermost surface of the electrode body 14A is the double-sided exposed portion 42, good current collection performance on the negative electrode side can be ensured.

[0056] The single-sided compound layer forming portion 43 is the portion in which the outer surface of the negative electrode core 40 facing radially outward of the electrode body 14A is exposed, and the negative electrode compound layer 41 is formed on the inner surface of the negative electrode core 40 facing radially inward of the electrode body 14A. The single-sided compound layer forming portion 43 is formed in a region where the positive electrode 11 is facing radially inward of the electrode body 14A via the separator 13, and where the positive electrode 11 is not present on the radially outward side of the electrode body 14A. In this embodiment, the single-sided compound layer forming portion 43 is positioned slightly towards the end of the winding from the position where it faces the positive electrode end 11e via the separator 13 outside the positive electrode end 11e, and extends for a length of approximately one full turn.

[0057] The double-sided compound layer forming section 44 is the portion of the negative electrode core body 40 in which the negative electrode compound layer 41 is formed on both sides. The double-sided compound layer forming section 44 is formed on both radial sides of the electrode body 14A via the separator 13, in the area facing the positive electrode 11. Specifically, the double-sided compound layer forming section 44 is positioned slightly towards the end of the winding from the position facing the positive electrode end 11e via the separator 13 inside the positive electrode end 11e, and extends to a position facing the positive electrode compound layer starting end, which is the end of the positive electrode compound layer 31 on the winding starting side of the electrode body 14A, via the separator 13. The single-sided compound layer forming section 43 and the double-sided compound layer forming section 44 are positioned to sandwich the positive electrode end 11e from both radial sides of the electrode body 14A, as described above.

[0058] The electrode body 14A includes a first separator 13x and a second separator 13y as separators 13. The two separators are wound around the positive electrode 11, with the first separator 13x positioned radially inward of the electrode body 14A and facing the positive electrode end 11e, and the second separator 13y positioned radially outward of the electrode body 14A and facing the positive electrode end 11e. The first separator 13x and the second separator 13y can be made of the same type of porous sheet having the same width. As will be described in detail later, in this embodiment, the lengths of the first separator 13x and the second separator 13y are different, with the length of the second separator 13y being longer than that of the first separator 13x.

[0059] As described above, the electrode body 14A has a structure in which a single-sided composite layer forming section 43 is positioned outside the positive electrode end 11e via a second separator 13y, and a double-sided composite layer forming section 44 is positioned inside the positive electrode end 11e via a first separator 13x. The negative electrode composite layers 41 of the single-sided composite layer forming section 43 and the double-sided composite layer forming section 44, which sandwich the positive electrode end 11e, are positioned slightly towards the end of the winding of the electrode body 14A rather than at the position facing the positive electrode end 11e via the separator 13, in order to more reliably prevent lithium deposition.

[0060] In this embodiment, the end of the single-sided compound layer forming section 43 and the end of the double-sided compound layer forming section 44 on the winding end side of the electrode body 14A are arranged substantially side by side in the radial direction of the electrode body 14A. The ends of the single-sided compound layer forming section 43 and the double-sided compound layer forming section 44 are located, for example, within a range of 0.1 to 0.2 turns from the position facing the positive electrode end 11e via the separator 13 toward the winding end side of the electrode body 14A. Since the double-sided exposed section 42, the single-sided compound layer forming section 43, and the double-sided compound layer forming section 44 of the negative electrode 12 are formed in this order continuously from the negative electrode end 12e side, the end of the single-sided compound layer forming section 43 is the starting end of the double-sided exposed section 42, and the end of the double-sided compound layer forming section 44 is the starting end of the single-sided compound layer forming section 43.

[0061] The electrode body 14A further has a structure in which a second separator 13y is wound around the electrode body 14A at least once from a position facing the positive electrode end 11e toward the winding end side. Preferably, the second separator 13y extends beyond the position facing the positive electrode end 11e outside the single-sided compound layer forming section 43 toward the winding end side of the electrode body 14A. In this embodiment, the entire outer surface of the single-sided compound layer forming section 43 is covered by the second separator 13y, and the second separator 13y constitutes a part of the outermost surface of the electrode body 14A. On the other hand, the end of the first separator 13x on the winding end side of the electrode body 14A is located at a position facing the end of the double-sided compound layer forming section 44, or in its vicinity.

[0062] Here, for example, "the second separator 13y is wound around the electrode body 14A from the position opposite the positive electrode end 11e to the winding end side" means that, in the radial cross-section of the electrode body 14A, the second separator 13y is wound 360° around the winding center of the electrode body 14A, starting from the position opposite the positive electrode end 11e.

[0063] In electrode body 14A, it is not necessary to extend the separator far beyond the positive electrode end 11e towards the winding end of electrode body 14A in order to prevent short circuits between the positive and negative electrodes. However, the second separator 13y extends at least one extra turn from the position opposite the positive electrode end 11e towards the winding end. In this case, two or more layers of the second separator 13y are arranged outside the positive electrode end 11e, effectively suppressing deformation of the negative electrode mixture layer 41 near the positive electrode end 11e. The second separator 13y is thought to function as a buffer layer against radial stress on electrode body 14, reducing the pressure acting on the negative electrode 12 near the positive electrode end 11e.

[0064] In addition to the buffering function of the second separator 13y, using a silicon material Z with a porosity of 10% or more as the negative electrode active material significantly improves the deformation suppression effect of the negative electrode 12. Even when silicon material Z is not used, the buffering function of the second separator 13y can suppress large deformations that would cause the negative electrode 12 to break, but in that case, traces of stretching of the negative electrode 12 in the axial direction of the electrode body 14 can be observed after the charge-discharge cycle. In contrast, when silicon material Z is used, such traces are not observed, suggesting that silicon material Z suppresses the force acting in the axial direction of the electrode body 14. In other words, the deformation of the negative electrode 12 is more effectively suppressed by the synergistic effect of the second separator 13y and silicon material Z (see the examples described later for details).

[0065] Preferably, the second separator 13y is wound more than one turn from the position facing the positive electrode end 11e toward the end of the winding of the electrode body 14A. In this case, the second separator 13y functions more effectively as a buffer layer, and the effect of suppressing deformation of the negative electrode 12 becomes more pronounced. The second separator 13y only needs to be wound from the position directly facing the positive electrode end 11e to the position facing the positive electrode end 11e via the single-sided composite layer forming portion 43, but in this embodiment, it extends beyond the position facing the positive electrode end 11e to a position that covers the outer surface of the double-sided exposed portion 42.

[0066] A suitable length for the second separator 13y extending from the position opposite the positive electrode end 11e to the winding end of the electrode body 14A is, for example, more than 1.0 turn but no more than 2.0 turns, more than 1.0 turn but no more than 1.5 turns, or more than 1.1 turns but no more than 1.5 turns in the winding direction of the electrode body 14A. Even if the second separator 13y is wound for more than 2.0 turns, the deformation suppression effect of the negative electrode 12 plateaus, while the volumetric energy density of the electrode body 14A decreases. For this reason, the upper limit of the length of the second separator 13y is set to, for example, 2.0 turns.

[0067] The double-sided exposed portion 42 of the negative electrode 12 abuts against the inner circumferential surface of the outer casing 16 and constitutes more than 50% of the circumference of the outermost surface of the electrode body 14A. In this case, good current collection performance on the negative electrode side can be ensured. In this embodiment, the double-sided exposed portion 42 does not extend radially to a position overlapping with the positive electrode end 11e of the electrode body 14A, and the outermost surface of the electrode body 14A is composed of the double-sided exposed portion 42 and the second separator 13y.

[0068] [Second Embodiment] As shown in Figure 3, the electrode body 14B of the second embodiment differs from the electrode body 14A in that both the first separator 13x and the second separator 13y are wound around the end of the winding of the electrode body 14A at least once, starting from a position facing the positive electrode end 11e. In the following, redundant explanations of content common to the above embodiment will be omitted, and the differences will be explained mainly (the same applies to subsequent embodiments). In the electrode body 14B, the first separator 13x and the second separator 13y directly face each other and directly overlap each other on the end of the winding of the electrode body 14B, beyond the positive electrode end 11e. Outside the positive electrode end 11e, the second separator 13y, the single-sided composite layer forming portion 43, the first separator 13x, and the second separator 13y are stacked in that order.

[0069] The end positions of the first separator 13x and the second separator 13y may be far apart, but in the electrode body 14B, the end positions of each separator are aligned. In this case, the productivity of the electrode body 14B is improved because the first separator 13x and the second separator 13y can be cut at the same position during production. The first separator 13x is wound more than one turn from the position opposite the positive electrode end 11e toward the winding end side of the electrode body 14B, and extends to a position that covers the outer surface of the double-sided exposed portion 42. A suitable length of the separator 13 extending from the position directly opposite the positive electrode end 11e toward the winding end side of the electrode body 14B is, for example, more than 1.1 turns but no more than 1.5 turns in the winding direction of the electrode body 14B.

[0070] With electrode body 14B, three or more separators 13, which function as buffer layers, are arranged outside the positive electrode terminal 11e, thereby more effectively suppressing deformation of the negative electrode 12 near the positive electrode terminal 11e.

[0071] [Third Embodiment] As shown in Figure 4, the electrode body 14C of the third embodiment differs from the electrode body 14A in that the negative electrode 12 is wound at least once from a position facing the positive electrode end 11e via the second separator 13y toward the end of the winding of the electrode body 14C. In the electrode body 14C, the double-sided exposed portion 42 of the negative electrode 12 is wound to a position facing the positive electrode end 11e via at least the second separator 13y and the single-sided compound layer forming portion 43. In this case, the double-sided exposed portion 42 functions as a buffer layer together with the second separator 13y, and deformation of the portion of the negative electrode 12 where the negative electrode compound layer 41 is formed is effectively suppressed. Furthermore, by extending the double-sided exposed portion 42, the contact area between the negative electrode 12 and the outer can 16 is increased, improving current collection performance.

[0072] Preferably, the double-sided exposed portion 42 is wound beyond the position facing the positive electrode end 11e via the second separator 13y and the single-sided mixture layer forming portion 43. In the electrode body 14C, the double-sided exposed portion 42 is wound beyond one turn from the end of the single-sided mixture layer forming portion 43. Furthermore, it is preferable that the end position of the double-sided exposed portion 42 coincides with the end position of the second separator 13y, or is located on the winding end side of the electrode body 14C than the end position of the second separator 13y. In this case, the second separator 13y is not arranged on the outermost periphery of the electrode body 14C, and the effect of improving current collection performance becomes more pronounced.

[0073] [Fourth Embodiment] As shown in Figure 5, the electrode body 14D of the fourth embodiment is similar to the electrode body 14B in that both the first separator 13x and the second separator 13y are wound around the end of the electrode body 14A at least once from a position facing the positive electrode end 11e. The electrode body 14D is also similar to the electrode body 14C in that the double-sided exposed portion 42 of the negative electrode 12 is wound around to a position facing the positive electrode end 11e via the separator 13 and the single-sided composite layer forming portion 43. In other words, in the electrode body 14D, a total of four or more layers are arranged as a buffer layer on the outside of the positive electrode end 11e, consisting of one or more layers of the first separator 13x, two or more layers of the second separator 13y, and one or more layers of the double-sided exposed portion 42.

[0074] It is preferable that the first separator 13x, the second separator 13y, and the double-sided exposed portion 42 are wound beyond the position where they overlap with the positive electrode end 11e outside the positive electrode end 11e, and further beyond the end position of the single-sided mixture layer forming portion 43. Furthermore, it is preferable that the end position of the double-sided exposed portion 42 coincides with the end positions of the first separator 13x and the second separator 13y, or is located on the winding end side of the electrode body 14D, similar to the case of the electrode body 14C.

[0075] The above embodiments can be modified as appropriate without impairing the purpose of this disclosure. For example, in electrode bodies 14A and 14C, the second separator 13y is wound around the electrode body at least once from a position facing the end of the positive electrode mixture layer toward the end of the winding, but the separator wound around at least once may be the first separator 13x.

[0076] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited to these examples.

[0077] <Example 1> [Preparation of the positive electrode] Lithium nickel cobalt oxide containing aluminum was used as the positive electrode active material. The positive electrode active material, acetylene black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 98:1:1, and N-methyl-2-pyrrolidone (NMP) was used as the dispersion medium to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to both sides of a positive electrode core made of 15 μm thick aluminum foil, and the coating was dried. The coating was compressed with a rolling mill, and the core was cut to a predetermined electrode size to obtain a positive electrode in which a positive electrode mixture layer was formed on both sides of the positive electrode core. An exposed portion was provided approximately in the center of the length of the positive electrode, where the surface of the positive electrode core was exposed, and an aluminum positive electrode lead was welded to this exposed portion.

[0078] [Fabrication of the negative electrode] As the negative electrode active material, a mixture of graphite and silicon material in a mass ratio of 94:6 was used. The graphite was natural graphite with a D50 of 15 μm. The silicon material was of the general formula SiO ｘA composite material represented by (hereinafter referred to as "Si-O") and a silicon-carbon composite material (hereinafter referred to as "Si-C") were mixed in a mass ratio of 60:40. Si-O consists of particles with a Si content of 60 mass%, a porosity of 0%, and a D50 of 5 μm, and has a sea-island structure in which fine Si particles are dispersed almost uniformly in an amorphous silicon oxide phase. Si-C consists of particles with a Si content of 53 mass%, a porosity of 15%, and a D50 of 8 μm, and has a sea-island structure in which fine Si particles are dispersed almost uniformly in an amorphous carbon phase.

[0079] A negative electrode slurry was prepared by mixing a negative electrode active material, styrene-butadiene rubber (SBR), and sodium carboxymethylcellulose (CMC-Na) in a mass ratio of 98:1:1, and using water as a dispersion medium. Next, the negative electrode slurry was applied to both sides of a negative electrode core made of 8 μm thick copper foil, and the coating was dried. The coating was compressed with a rolling mill, and the core was cut to a predetermined electrode size to produce a negative electrode in which a negative electrode slurry layer was formed on both sides of the negative electrode core. Exposed portions were provided at both ends of the negative electrode in the longitudinal direction, and a nickel negative electrode lead was welded to one of the exposed portions.

[0080] [Preparation of Non-Aqueous Electrolyte] 100 parts by mass of a mixed solvent prepared by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 3:7, to which 5 parts by mass of vinylene carbonate (VC) is added, and further lithium hexafluoride phosphate (LiPF) is added. ６ A non-aqueous electrolyte was prepared by dissolving ) at a concentration of 1.3 mol / liter.

[0081] [Electrode Fabrication] A wound electrode body was fabricated by winding the positive and negative electrodes in a spiral shape via a polyethylene separator. At this time, the negative electrode was positioned so that the negative electrode lead (one exposed portion formed at both ends in the longitudinal direction of the negative electrode) was located on the winding start side of the electrode body. Two separators were placed on either side of the positive electrode, and the second separator, which is located radially outside the winding structure and facing the positive electrode end, was extended by at least one extra turn from the position facing the end of the positive electrode mixture layer toward the winding end of the winding structure. Similarly, the exposed portions on both sides of the negative electrode (the other exposed portion formed at both ends in the longitudinal direction of the negative electrode) were extended by at least one extra turn from the position facing the end of the positive electrode mixture layer toward the winding end of the winding structure via the second separator (see Figure 4).

[0082] [Fabrication of Cylindrical Battery] Insulating plates were placed above and below the electrode body, and the electrode body was housed in a bottomed cylindrical metal casing. The negative electrode lead was welded to the inner surface of the bottom of the casing, and the positive electrode lead was welded to the sealing body. Then, a non-aqueous electrolyte was injected into the casing, and the opening of the casing was sealed with the sealing body via a gasket to obtain a cylindrical battery.

[0083] <Example 2> A cylindrical battery was manufactured in the same manner as in Example 1, except that the mass ratio of Si-O to Si-C was changed to 17:83 in the fabrication of the negative electrode.

[0084] <Example 3> A cylindrical battery was manufactured in the same manner as in Example 1, except that only Si-C was used as the silicon material in the fabrication of the negative electrode, and the mass ratio of graphite to silicon material was changed to 91:9.

[0085] <Example 4> A cylindrical battery was fabricated in the same manner as in Example 3, except that Si-C with a porosity of 25% was used instead of the Si-C used in Example 1 for the negative electrode.

[0086] <Comparative Example 1> A cylindrical battery was manufactured in the same manner as in Example 1, except that only Si-O was used as the silicon material in the fabrication of the negative electrode.

[0087] <Comparative Example 2> A cylindrical battery was manufactured in the same manner as in Example 1, except that only Si-O was used as the silicon material in the fabrication of the negative electrode, and the mass ratio of graphite to silicon material was changed to 91:9.

[0088] <Comparative Example 3> In the preparation of the electrode body, a second separator was added that faced the end of the positive electrode mixture layer at a radially outer position of the winding structure beyond the end of the positive electrode mixture layer, and the exposed portions of both sides of the negative electrode facing the end of the positive electrode mixture layer via the second separator were wound from the position facing the end of the positive electrode mixture layer toward the end of the winding structure for a length of less than one full turn.

[0089] For each cylindrical battery in the examples and comparative examples, the presence or absence of negative electrode deformation after charge-discharge cycles was confirmed. The evaluation results, along with the presence or absence of separator-negative electrode extension, the content of silicon material (Si material) in the negative electrode active material, the Si-C content in the Si material, and the Si-C porosity, are shown in Table 1. Note that the presence or absence of separator-negative electrode extension means whether the second separator facing the end of the positive electrode mixture layer radially outside the winding structure beyond the end of the positive electrode mixture layer, and the exposed portions on both sides of the negative electrode facing the end of the positive electrode mixture layer via the second separator, extend toward the end of the winding by one turn or more.

[0090] [Evaluation of Negative Electrode Deformation] For each battery in the examples and comparative examples, constant current charging was performed at a current value of 0.3C relative to the design capacity at a temperature of 45°C until the battery voltage reached 4.2V. After that, the batteries were discharged at a current value of 0.5C until the battery voltage reached 2.85V. After performing this charge-discharge cycle 400 times, the batteries were disassembled and the state of the negative electrode was observed. The observation location for the negative electrode was the part facing the radially outer side of the electrode body via the end of the positive electrode mixture layer and the second separator. If deformation of the negative electrode is observed at this location, deformation usually also occurs in the part located inside it (such as the single-sided mixture layer formation area).

[0091]

[0092] As shown in Table 1, no deformation of the negative electrode was observed in the cylindrical battery of the example after the above charge-discharge cycle. On the other hand, deformation of the negative electrode was observed in the cylindrical batteries of Comparative Examples 1 to 3, which did not use a silicon material (Si-C) with a porosity of 10% or more as the negative electrode active material. In particular, in the battery of Comparative Example 3, in which the separator and negative electrode were not extended by more than one turn from the position opposite the end of the positive electrode mixture layer, significant deformation of the negative electrode was observed, and fracture of the negative electrode was confirmed. In the batteries of Comparative Examples 1 and 2, although no fracture of the negative electrode was observed, traces of stretching in the axial direction of the electrode body were confirmed on the negative electrode.

[0093] In the battery of the example, it is believed that the deformation of the negative electrode was highly suppressed due to the synergistic effect of the separator, which extends at least one turn from the position opposite the end of the positive electrode mixture layer toward the end of the electrode body winding, and the silicon material with a porosity of 10% or more. It is thought that the extra-extended separator functions as a buffer layer outside the end of the positive electrode mixture layer, and that the silicon material used in the example suppresses the force acting in the axial direction of the electrode body, resulting in effective suppression of the deformation of the negative electrode. In this example, evaluation results using silicon materials with a porosity of 15% or 25% are shown, but various studies have confirmed that the effect of suppressing negative electrode deformation is specifically obtained when the porosity of the silicon material is 10% or more.

[0094] This disclosure is further described by the following embodiments. Configuration 1: A cylindrical battery comprising an electrode body in which a positive electrode and a negative electrode are wound with a separator between them, and a bottomed cylindrical outer casing for housing the electrode body, wherein the positive electrode has a positive electrode core and a positive electrode mixture layer formed on the positive electrode core, and the negative electrode has a negative electrode core and a negative electrode mixture layer formed on the negative electrode core, and starting from the negative electrode end side which is the end of the negative electrode at the winding end of the electrode body, both sides of the negative electrode core are exposed and constitute a double-sided exposed portion which comprises 0.5 or more of the outermost circumference of the electrode body, the outer surface of the negative electrode core facing radially outward is exposed and the negative electrode mixture layer is formed on the inner surface of the negative electrode core facing radially inward, and both sides of the negative electrode core A cylindrical battery comprising a double-sided compound layer forming section on which the negative electrode compound layer is formed, wherein the negative electrode compound layer contains a silicon material with a porosity of 10% or more as a negative electrode active material, the single-sided compound layer forming section and the double-sided compound layer forming section are arranged to sandwich the positive electrode compound layer end, which is the end of the positive electrode compound layer on the winding end side of the electrode body, from both radial sides of the electrode body, the separator comprises a first separator located radially inside the positive electrode compound layer end and a second separator located radially outside the positive electrode compound layer end, and at least one of the first and second separators is wound around the electrode body at least once from a position opposite to the positive electrode compound layer end toward the winding end side. Configuration 2: The cylindrical battery according to Configuration 1, wherein the negative electrode active material comprises the silicon material and a carbon material, and the content of the silicon material is 2% by mass or more and 30% by mass or less of the total mass of the negative electrode active material. Configuration 3: The cylindrical battery according to Configuration 1 or 2, wherein the silicon material includes a silicon-carbon composite material with a porosity of 10% or more and 30% or less. Configuration 4: The cylindrical battery according to Configuration 4, wherein the content of the silicon-carbon composite material is 40% by mass or more relative to the total mass of the silicon material and the second silicon material having a porosity of less than 10% that functions as the negative electrode active material. Configuration 5: The cylindrical battery according to any one of Configurations 1 to 4, wherein the first and second separators are wound one or more times from a position opposite to the end of the positive electrode mixture layer toward the end of the winding of the electrode body.Configuration 6: The cylindrical battery according to any one of Configurations 1 to 5, wherein the negative electrode is wound one or more times from a position facing the end of the positive electrode mixture layer via the second separator toward the end of the winding of the electrode body. Configuration 7: The cylindrical battery according to Configuration 6, wherein the double-sided exposed portion is arranged facing the outside of the end of the positive electrode mixture layer via the separator and the single-sided mixture layer forming portion.

[0095] 10 Cylindrical battery, 11 Positive electrode, 11e Positive electrode terminal, 12 Negative electrode, 12e Negative electrode terminal, 13 Separator, 13x First separator, 13y Second separator, 14, 14A, 14B, 14C, 14D Electrode body, 16 Outer can, 17 Sealing body, 18 Upper insulating plate, 19 Lower insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Grooved section, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket, 30 Positive electrode core, 31 Positive electrode mixture layer, 40 Negative electrode core, 41 Negative electrode mixture layer, 42 Double-sided exposed section, 43 Single-sided mixture layer forming section, 44 Double-sided mixture layer forming section

Claims

1. A cylindrical battery comprising an electrode body in which a positive electrode and a negative electrode are wound with a separator in between, and a bottomed cylindrical outer casing for housing the electrode body, wherein the positive electrode has a positive electrode core and a positive electrode mixture layer formed on the positive electrode core, and the negative electrode has a negative electrode core and a negative electrode mixture layer formed on the negative electrode core, and starting from the negative electrode end side which is the end of the winding of the electrode body, both sides of the negative electrode core are exposed and constitute 0.5 times or more of the outermost circumference of the electrode body, a single-sided mixture layer forming portion where the outer surface of the negative electrode core facing radially outward is exposed and the negative electrode mixture layer is formed on the inner surface of the negative electrode core facing radially inward, and a double-sided mixture layer forming portion where the negative electrode mixture layer is formed on both sides of the negative electrode core, the negative electrode mixture layer contains a silicon material with a porosity of 10% or more as a negative electrode active material. The cylindrical battery is characterized in that the single-sided compound layer forming portion and the double-sided compound layer forming portion are arranged to sandwich the positive electrode compound layer end, which is the end of the positive electrode compound layer on the winding end side of the electrode body, from both radial sides of the electrode body, and the separator includes a first separator located radially inward of the positive electrode compound layer end and a second separator located radially outward of the positive electrode compound layer end, and at least one of the first and second separators is wound around the electrode body one or more times from a position opposite to the positive electrode compound layer end toward the winding end side.

2. The cylindrical battery according to claim 1, wherein the negative electrode active material comprises the silicon material and the carbon material, and the content of the silicon material is 2% by mass or more and 30% by mass or less based on the total mass of the negative electrode active material.

3. The cylindrical battery according to claim 2, wherein the silicon material includes a silicon-carbon composite material with a porosity of 10% or more and 30% or less.

4. The cylindrical battery according to claim 3, wherein the content of the silicon-carbon composite material is 40% by mass or more relative to the total mass of the silicon material and the second silicon material having a porosity of less than 10% that functions as the negative electrode active material.

5. The cylindrical battery according to any one of claims 1 to 3, wherein the first and second separators are wound one or more times from a position opposite to the end of the positive electrode mixture layer toward the end of the winding of the electrode body.

6. The cylindrical battery according to any one of claims 1 to 3, wherein the negative electrode is wound one or more times from a position facing the end of the positive electrode mixture layer via the second separator toward the end of the winding of the electrode body.

7. The cylindrical battery according to claim 6, wherein the double-sided exposed portion is arranged opposite to the end of the positive electrode mixture layer via the separator and the single-sided mixture layer forming portion.

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