Non-aqueous electrolyte secondary battery

Abstract

According to the present invention, a positive electrode active material contains a lithium-containing composite oxide, a negative electrode active material contains a silicon-containing material, and the discharge capacity per 1.0 g of a negative electrode mixture layer (52) is at least 0.5 Ah. A negative electrode lead (21) is connected to a winding start-side end part of a negative electrode (12). The negative electrode (12) has, on a winding start side of an electrode body (14), a non-facing part (61) that does not face a positive electrode (11), and the negative electrode mixture layer (52) is provided on at least a part of at least one surface of the non-facing part (61). When the distance between a negative electrode current collector (51) of a first starting end facing part (12a) in the negative electrode (12), which faces a winding start end (11a) of the positive electrode (11) on an outer winding side, and a negative electrode current collector (51) of a second starting end facing part (12b) in the negative electrode (12), which faces the winding start end (11a) on an inner winding side, is x, and the thickness of the negative electrode mixture layer (52) in the first starting end facing part (12a) is y, x / y>4.5 is satisfied.

Description

Nonaqueous electrolyte secondary battery

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery.

[0002] Conventional non-aqueous electrolyte secondary batteries include a cylindrical battery described in Patent Document 1. This cylindrical battery includes an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and a bottomed cylindrical outer can that houses the electrode assembly and is open on one side, the positive electrode having a positive electrode mixture layer disposed on a positive electrode current collector, and the negative electrode having a negative electrode mixture layer disposed on a negative electrode current collector.

[0003] This cylindrical battery has a first anode current collector exposed portion where the anode current collector is exposed at the winding start end of the anode, and a second anode current collector exposed portion where the anode current collector is exposed at the winding end end of the anode. A first anode lead is joined to the first anode current collector exposed portion, and a second anode lead is joined to the second anode current collector exposed portion.

[0004] JP 2012-023011 A

[0005] In the cylindrical battery, the negative electrode lead is joined to both the winding start end and the winding end end of the negative electrode, thereby shortening the current collection path and reducing battery resistance. In this way, by providing a negative electrode current collector exposed portion where the negative electrode current collector is exposed at the winding start end of the negative electrode and joining the negative electrode lead to this negative electrode current collector exposed portion, it is easy to realize a configuration that can shorten the current collection path and easily achieve high output.

[0006] However, the inventors of the present application have found that when a negative electrode lead is joined to the winding start end of the negative electrode, the gap between the negative electrodes at the winding start side of the electrode body becomes small, making it difficult for the electrolyte to permeate evenly into the electrode body, and therefore the rate of increase in resistance. Therefore, an object of the present disclosure is to provide a nonaqueous electrolyte secondary battery that can easily achieve high output and suppress the rate of increase in resistance.

[0007] In order to solve the above problems, the non-aqueous electrolyte secondary battery according to the present disclosure includes an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a non-aqueous electrolyte, and a bottomed cylindrical outer can that accommodates the electrode assembly and the non-aqueous electrolyte, wherein the positive electrode has a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector, the negative electrode has a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector, the positive electrode mixture layer contains a lithium-containing composite oxide as a positive electrode active material, and the negative electrode mixture layer contains a silicon-containing material as a negative electrode active material, and the discharge capacity per 1.0 g of the negative electrode mixture layer is 0.5 Ah or more, and the negative electrode has a non-aqueous electrolyte and a non-aqueous electrolyte. a first negative electrode current collector exposed portion to which a negative electrode lead is connected at an end portion on the winding start side and at which the negative electrode current collector is exposed, the negative electrode has a non-facing portion that does not face the positive electrode on the winding start side of the electrode body, and a negative electrode mixture layer is provided on at least a portion of at least one surface of the non-facing portion, and when x is the distance between the negative electrode current collector in a first starting end facing portion that faces the winding start end of the positive electrode on the outside of winding, and the negative electrode current collector in a second starting end facing portion that faces the winding start end of the positive electrode on the inside of winding, and y is the thickness of the negative electrode mixture layer in the first starting end facing portion, the relationship x / y > 4.5 is satisfied.

[0008] According to the nonaqueous electrolyte secondary battery according to the present disclosure, high output can be easily achieved and the rate of increase in resistance can be suppressed.

[0009] 4 is an axial cross-sectional view of a cylindrical battery according to an embodiment of the present disclosure; FIG. 5 is a perspective view of an electrode body; FIG. 6 is a schematic diagram showing an example of the structure of a negative electrode mixture layer; FIG. 7 is a schematic plan view showing the winding structure of the inner side of the electrode body; and FIG. 8 is an enlarged schematic plan view of the periphery of the starting end of the positive electrode in FIG.

[0010] Hereinafter, embodiments of a nonaqueous electrolyte secondary battery according to the present disclosure will be described in detail with reference to the drawings. It is anticipated from the beginning that new embodiments may be constructed by appropriately combining the features of the embodiments and variations described below. In the following embodiments, the same components are designated by the same reference numerals in the drawings, and redundant description will be omitted. Furthermore, multiple drawings include schematic diagrams, and the dimensional ratios of the length, width, height, and other dimensions of each component between different drawings do not necessarily match. Furthermore, in this specification, the side of the sealing body 17 in the axial direction (height direction) of the cylindrical nonaqueous electrolyte secondary battery 10 is referred to as "upper," and the side of the bottom 68 of the outer can 16 in the axial direction is referred to as "lower." Among the components described below, components not recited in the independent claims representing the highest concepts are optional and not essential. Furthermore, the present disclosure is not limited to the following embodiments and their variations, and various improvements and modifications are possible within the scope of the claims of this application and their equivalents.

[0011] Fig. 1 is an axial cross-sectional view of a cylindrical nonaqueous electrolyte secondary battery 10 according to one embodiment of the present disclosure, and Fig. 2 is a perspective view of an electrode assembly 14 of the nonaqueous electrolyte secondary battery 10. As shown in Fig. 1, the nonaqueous electrolyte secondary battery (hereinafter simply referred to as battery) 10 includes a wound electrode assembly 14, a nonaqueous electrolyte (not shown), a cylindrical metal outer can 16 with a bottom that houses the electrode assembly 14 and the nonaqueous electrolyte, and a sealing body 17 that closes the opening of the outer can 16. As shown in Fig. 2, the electrode assembly 14 has a wound structure in which a long positive electrode 11 and a long negative electrode 12 are wound with two long separators 13 interposed therebetween.

[0012] The negative electrode 12 is formed to have dimensions slightly larger than the positive electrode 11 to prevent lithium precipitation. That is, the negative electrode 12 is formed to be longer in the longitudinal direction and width direction (short direction) than the positive electrode 11. Furthermore, the two separators 13 are formed to have dimensions at least slightly larger than the positive electrode 11 and are arranged to sandwich the positive electrode 11, for example. The negative electrode 12 may form the winding start end of the electrode assembly 14. However, generally, the separator 13 extends beyond the winding start end of the negative electrode 12, and the winding start end of the separator 13 becomes the winding start end of the electrode assembly 14.

[0013] The non-aqueous electrolyte has ion conductivity (e.g., lithium ion conductivity). The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte. The liquid electrolyte (electrolytic solution) includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The non-aqueous solvent may contain a halogen-substituted compound (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. The electrolyte salt may include, for example, LiPF ６ Lithium salts such as

[0014] Examples of the solid electrolyte include solid or gel polymer electrolytes and inorganic solid electrolytes. 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. Examples of the matrix polymer include a polymer material that absorbs the non-aqueous solvent and gels. Examples of the polymer material include fluororesin, acrylic resin, and polyether resin. Examples of the inorganic solid electrolyte include materials known in all-solid-state lithium ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.).

[0015] The positive electrode 11 has a positive electrode current collector 41 (see FIG. 5 ) and positive electrode mixture layers 42 (see FIG. 5 ) disposed on both sides of the positive electrode current collector 41. The positive electrode current collector 41 can be made of a metal foil, such as aluminum or an aluminum alloy, that is stable within the potential range of the positive electrode 11, or a film with such a metal disposed on its surface. The positive electrode mixture layer 42 contains a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, and the like onto the positive electrode current collector 41, drying the coating, and then compressing it to form the positive electrode mixture layers 42 on both sides of the positive electrode current collector 41.

[0016] The positive electrode active material is composed mainly of a lithium-containing composite oxide. Examples of metal elements contained in the lithium-containing composite oxide (lithium-containing metal composite oxide) include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. An example of a preferred lithium-containing composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al. The lithium-containing composite oxide may have a spinel structure or an olivine structure. However, it is preferable that the lithium-containing composite oxide have a layered rock salt structure, as this facilitates the production of a positive electrode with a large discharge capacity.

[0017] Examples of the conductive agent contained in the positive electrode mixture layer 42 include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. Examples of the binder contained in the positive electrode mixture layer 42 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resin, acrylic resin, and polyolefin resin. These resins may be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), and the like.

[0018] The negative electrode 12 has a negative electrode current collector 51 (see FIG. 5 ) and a negative electrode mixture layer 52 (see FIG. 5 ) disposed on both sides of the negative electrode current collector 51. The negative electrode current collector 51 can be made of a metal foil, such as copper or a copper alloy, that is stable within the potential range of the negative electrode 12, or a film having such a metal disposed on its surface. The negative electrode mixture layer 52 contains a negative electrode active material and a binder. The negative electrode 12 can be produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the negative electrode current collector 51, drying the coating, and then compressing it to form the negative electrode mixture layer 52 on both sides of the negative electrode current collector 51.

[0019] The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. Preferred carbon materials are graphites such as natural graphite, such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite, such as lump artificial graphite and graphitized mesophase carbon microbeads. The discharge capacity per 1.0 g of the negative electrode mixture layer 52 is 0.5 Ah or more. To effectively increase the discharge capacity per 1.0 g of the negative electrode mixture layer 52, the negative electrode mixture layer 52 preferably contains a silicon-containing material containing silicon (Si) as the negative electrode active material.

[0020] FIG. 3 is a schematic diagram illustrating an example of the structure of the negative electrode mixture layer 52. As shown in FIG. 3, the negative electrode mixture layer 52 preferably includes graphite 60 and a silicon-containing material 70. The silicon-containing material 70 includes, for example, an ion-conducting phase 71 and an Si phase 72 dispersed in the ion-conducting phase 71. The weight ratio of the Si phase 72 in the silicon-containing material 70 is preferably 30% or more because this increases the discharge capacity and facilitates high output of the battery 10. Furthermore, the weight ratio of the Si phase 72 in the silicon-containing material 70 is preferably 60% or less because this reduces the volume change of the negative electrode mixture layer 52 during charging and discharging, thereby suppressing the expansion and contraction of the electrode body 14 during charging and discharging, thereby facilitating excellent durability of the battery 10. The ion-conducting phase 71 may be composed of, for example, an amorphous carbon phase, a lithium silicate phase, a silicon oxide phase, a titanium oxide phase, a zirconium oxide phase, or the like. However, in order to suppress the volume change of the negative electrode active material during charge and discharge and to increase the charge and discharge efficiency, it is preferable that the ion-conducting phase 71 contains an amorphous carbon phase.

[0021] From the viewpoint of the weight ratio of elemental silicon to the anode mixture layer 52, the weight ratio of elemental silicon to the anode mixture layer 52 is preferably 7% by mass or more, and more preferably 12% by mass or more, because this increases the discharge capacity and results in high output of the battery 10. Furthermore, the weight ratio of elemental silicon to the anode mixture layer 52 is preferably 50% by mass or less, because this reduces the volume change of the anode mixture layer 52 during charging and discharging, thereby suppressing expansion and contraction of the electrode body 14 during charging and discharging, thereby improving the durability of the battery 10. When the anode mixture layer 52 contains a silicon-containing material 70, the mass of the elemental silicon may be approximately the same as the mass of the Si phase 72. That is, the weight ratio of the Si phase 72 to the anode mixture layer 52 may be 7% by mass or more and 50% by mass or less. The anode active material may be a metal other than Si that alloys with lithium, an alloy containing such a metal, a compound containing such a metal, or the like.

[0022] As in the case of the positive electrode 11, fluororesin, PAN, polyimide resin, acrylic resin, polyolefin resin, or the like may be used as the binder contained in the negative electrode mixture layer 52, but styrene-butadiene rubber (SBR) or a modified product thereof is preferably used. In addition to SBR or the like, the negative electrode mixture layer 52 may also contain, for example, CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, or the like.

[0023] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Preferred materials for the separator 13 include polyolefin resins such as polyethylene and polypropylene, and cellulose. The separator 13 may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be disposed on the surface of the separator 13.

[0024] As shown in FIG. 1 , a positive electrode lead 20 is joined to the positive electrode 11, and a negative electrode lead 21 is joined to the end of the negative electrode 12 at the winding start side in the longitudinal direction. The battery 10 has an insulating plate 18 above the electrode body 14 and an insulating plate 19 below the electrode body 14. The positive electrode lead 20 passes through a through hole in the insulating plate 18 and extends toward the sealing body 17, and the negative electrode lead 21 passes through a through hole in the insulating plate 19 and extends toward the bottom 68 of the outer can 16. The positive electrode lead 20 is connected to the underside of the sealing plate 23 of the sealing body 17 by welding or the like. A terminal cap 27 constituting the top plate of the sealing body 17 is electrically connected to the sealing plate 23, and the terminal cap 27 serves as a positive electrode terminal. The negative electrode lead 21 is connected to the inner surface of the bottom 68 of the metal outer can 16 by welding or the like, and the outer can 16 serves as a negative electrode terminal.

[0025] The positive electrode 11 has a positive electrode current collector exposed portion where the positive electrode current collector 41 is exposed in an intermediate portion, such as the center portion, in the winding direction, and the positive electrode lead 20 is electrically connected to the positive electrode current collector exposed portion. The negative electrode 12 has a first negative electrode current collector exposed portion 51a (see FIG. 4) where the negative electrode current collector 51 is exposed at the end portion on the winding start side in the winding direction, and a second negative electrode current collector exposed portion 51b (see FIG. 1) where the negative electrode current collector 51 is exposed at the end portion on the winding end side in the winding direction. The second negative electrode current collector exposed portion 51b has a portion included in the outermost peripheral surface of the electrode body 14. The negative electrode lead 21 is electrically connected to the first negative electrode current collector exposed portion 51a, and the second negative electrode current collector exposed portion 51b includes a portion that contacts the inner surface of the outer can 16. In this way, by electrically connecting both the winding start side and the winding end side of the negative electrode 12 to the negative electrode terminal, the number of current collection paths is reduced, and electrical resistance is reduced.

[0026] Alternatively, the winding end of the negative electrode current collector in the winding direction may not be in contact with the inner surface of the outer can, and only one negative electrode lead may be electrically connected to the winding start end of the negative electrode current collector in the winding direction. Alternatively, two negative electrode leads may be joined to the electrode body, one negative electrode lead being electrically connected to the winding start end of the negative electrode current collector in the winding direction, and the other negative electrode lead being electrically connected to the winding end of the negative electrode current collector in the winding direction.

[0027] The battery 10 further includes a resin gasket 28 disposed between the exterior can 16 and the sealing body 17. The sealing body 17 is fixed to the opening of the exterior can 16 by crimping via the gasket 28, thereby sealing the internal space of the battery 10. The gasket 28 is sandwiched between the exterior can 16 and the sealing body 17, and insulates the sealing body 17 from the exterior can 16. The gasket 28 serves as a sealing material to maintain airtightness inside the battery and as an insulating material to insulate the exterior can 16 and the sealing body 17.

[0028] The outer can 16 accommodates the electrode assembly 14 and the non-aqueous electrolyte. The outer can 16 has a cylindrical portion 30 and a bottom portion 68. The cylindrical portion 30 includes a shoulder portion 38 and a grooved portion 34. The grooved portion 34 can be formed, for example, by spinning a portion of the side surface of the outer can 16 radially inward to form an annular recess radially inward. The shoulder portion 38 is formed by bending the upper end of the outer can 16 inward toward the peripheral edge 45 of the sealing body 17 when the sealing body 17 is crimped to the outer can 16.

[0029] The sealing body 17 has a structure in which, in order from the electrode body 14 side, a sealing plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a terminal cap 27 are stacked. Each member constituting the sealing body 17 has, for example, a disk or ring shape, and each member except for the insulating member 25 is electrically connected to one another. The sealing plate 23 has at least one through-hole 23a. 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 peripheral edges.

[0030] When the battery 10 generates abnormal heat and the internal pressure of the battery 10 rises, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 toward the terminal cap 27, cutting off 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 breaks and gas is released from the through-hole 27a of the terminal cap 27. This gas release prevents the internal pressure of the battery 10 from rising excessively, which could cause the battery 10 to explode, thereby improving the safety of the battery 10.

[0031] FIG. 4 is a schematic plan view showing the winding structure of the inner side of the electrode assembly 14. Note that the separator 13 is not shown in FIG. 4 . As shown in FIG. 4 , the negative electrode 12 includes a non-facing portion 61 wound from a portion of the winding start end 11a of the positive electrode 11 facing the inner side of the winding to the winding start side without facing the positive electrode 11. A negative electrode mixture layer 52 is provided on at least a portion of at least one surface of the non-facing portion 61. The negative electrode 12 has a first negative electrode current collector exposed portion 51a to which the negative electrode lead 21 is connected at the end on the winding start side and from which the negative electrode current collector 51 is exposed. In this embodiment, the first negative electrode current collector exposed portion 51a is provided on the outer winding surface of the negative electrode 12, and the negative electrode lead 21 is joined to the outer winding surface of the negative electrode 12. However, the first negative electrode current collector exposed portion may be provided on the inner winding surface of the negative electrode, and the negative electrode lead may be joined to the inner winding surface of the negative electrode.

[0032] It is preferable that the negative electrode mixture layer 52 is provided on at least one surface of the non-facing portion 61. It is also preferable that the non-facing portion 61 be wound 0.75 turns or more. In such cases, the rigidity of the inner peripheral side of the electrode body 14 can be increased, thereby suppressing blockage of the hollow portion 14a (see FIG. 1) of the electrode body 14 when the battery 10 abnormally heats up. As a result, gas is smoothly exhausted to the outside through the hollow portion 14a, improving the safety of the battery 10. It is also preferable that the non-facing portion 61 be wound 1.5 turns or less, in which case it is easier to increase the capacity of the battery 10.

[0033] Fig. 5 is an enlarged schematic plan view of the periphery of the positive electrode starting end in Fig. 4. Referring to Fig. 5, when the distance between the negative electrode current collector 51 of the first starting end facing portion 12a of the negative electrode 12 that faces the winding starting end of the positive electrode 11 on the outer side of the winding in the radial direction (the radial direction of the battery 10) and the negative electrode current collector 51 of the second starting end facing portion 12b of the negative electrode 12 that faces the winding starting end of the positive electrode 11 on the inner side of the winding in the radial direction is defined as x, and the thickness of the negative electrode mixture layer 52 in the first starting end facing portion 12a is defined as y, x / y>4.5 holds.

[0034] As will be described later, the present inventors have found that if x / y > 4.5 is satisfied, the resistance increase rate can be significantly suppressed, and a battery 10 that is less susceptible to deterioration can be produced. This is presumably because, when x / y > 4.5 is satisfied, the electrolyte is more likely to penetrate uniformly into the electrode assembly 14 regardless of the winding position of the electrode assembly 14, making it easier for the charge / discharge reaction to occur uniformly regardless of the winding position of the negative electrode 12. Note that it is preferable that x / y < 7.0 is satisfied. If x / y < 7.0 is satisfied, the negative electrode 12 can be prevented from becoming excessively thin relative to the positive electrode 11, allowing the electrode assembly 14 to be wound smoothly.

[0035] The conditions x / y > 4.5 and x / y < 7.0 can be achieved by adjusting the thickness of the positive electrode 11, the thickness of the negative electrode 12, the thickness of the separator 13, the inner diameter of the cylindrical portion 35 of the outer can 16 that faces the electrode assembly 14 in the radial direction, and the thickness of the negative electrode mixture layer 52. These conditions are easily achieved if the total thickness of the positive electrode 11 and the separator 13 between the negative electrodes 12 is 2.3 to 5 times the thickness of the negative electrode mixture. The conditions x / y > 4.5 and x / y < 7.0 only need to be satisfied at least one of the following periods: after shipment of the battery 10 and before use, and during use of the battery 10. Furthermore, the conditions x / y > 4.5 and x / y < 7.0 only need to be satisfied in a room temperature environment, more specifically, at least one temperature between 15°C and 25°C. x can be measured based on a CT (Computed Tomography) image of the battery 10 (a CT image of a cross section perpendicular to the axial direction of the battery 10, passing through the electrode assembly 14). The inner diameter of the cylindrical portion 35 (see FIG. 1 ) of the battery 10 that faces the electrode assembly 14 in the radial direction is known. Regarding y, the thickness of the negative electrode mixture layer 52 can be measured by disassembling the battery 10. Specifically, for example, the battery 10 is disassembled, the electrode assembly 14 is removed, and the thickness of the negative electrode 12 is measured. Then, the negative electrode mixture layers 52 disposed on both sides are peeled off, the thickness of the negative electrode current collector 51 is measured, and y is obtained by calculating (thickness of the negative electrode 12 - thickness of the negative electrode current collector 51) / 2. In this way, it is easy to determine whether the condition x / y > 4.5 or x / y < 7.0 is satisfied.

[0036] The above description deals with a case in which the sealing body 17 has a laminated structure including two rupture plates (lower valve body 24 and upper valve body 26) and a convex terminal cap 27 that covers the rupture plate. However, the sealing body may be composed of only a rupture plate, or may have a structure in which an internal terminal plate, an insulating plate, and a rupture plate are laminated in this order from the electrode body side. Alternatively, the sealing body may not have a rupture plate, and the bottom of the outer can may have a thin, easily breakable portion that breaks when the battery generates abnormal heat.

[0037] In the cylindrical battery described above, the negative electrode discharge utilization rate (Ah / g), defined as the discharge capacity of the negative electrode mixture layer per 1.0 g of the negative electrode mixture layer, was 0.68 Ah, the silicon element weight ratio wt %, defined as the weight ratio of silicon element to the negative electrode mixture layer, was 15%, and no second negative electrode current collector exposed portion in contact with the inner peripheral surface of the outer can was provided. The x and y values ​​were 374 μm and 80 μm, respectively, and the x / y value was 4.7.

[0038] The negative electrode discharge utilization rate was measured as follows. First, the fabricated battery was disassembled, and the removed negative electrode was placed opposite lithium as a positive electrode. Then, the battery was discharged from a state in which the negative electrode was 5 mV higher than the lithium to a state in which the negative electrode was 1 V higher than the lithium. The negative electrode discharge utilization rate was calculated based on the charge released during the discharge.

[0039] The silicon element weight ratio was measured by disassembling the fabricated battery and using ICP (Inductively Coupled Plasma). ICP is a type of emission spectroscopy. When plasma energy is applied to an analysis sample from the outside, the contained component elements (atoms) are excited. In ICP, the emission lines (spectral lines) emitted when the excited atoms return to a lower energy level are measured, and the content of the component elements (atoms) is determined based on the measured emission lines. x was confirmed based on CT images. y was confirmed using the method described above.

[0040] Example 2 In the cylindrical battery described above, the discharge capacity per 1.0 g of the negative electrode mixture layer was 0.68 Ah, and the silicon weight ratio wt% was 15%. A second negative electrode current collector exposed portion was provided in contact with the inner peripheral surface of the outer can. x was 374 μm, y was 80 μm, and x / y was 4.7. The negative electrode discharge utilization rate, silicon weight ratio, x, and y were measured in the same manner as in Example 1.

[0041] Example 3 In the cylindrical battery described above, the discharge capacity per 1.0 g of the negative electrode mixture layer was 0.90 Ah, and the silicon weight ratio wt% was 25%. Furthermore, no second negative electrode current collector exposed portion in contact with the inner peripheral surface of the outer can was provided, and x was 345 μm, y was 65 μm, and x / y was 5.3. The negative electrode discharge utilization rate, silicon weight ratio, x, and y were measured in the same manner as in Example 1.

[0042] Example 4 In the cylindrical battery described above, the discharge capacity per 1.0 g of the negative electrode mixture layer was 1.13 Ah, and the silicon weight ratio wt% was 35%. Furthermore, no second negative electrode current collector exposed portion in contact with the inner peripheral surface of the outer can was provided, and x was 330 μm, y was 58 μm, and x / y was 5.7. The negative electrode discharge utilization rate, silicon weight ratio, x, and y were measured in the same manner as in Example 1.

[0043] Example 5 In the cylindrical battery described above, the discharge capacity per 1.0 g of the negative electrode mixture layer was 1.13 Ah, and the silicon weight ratio wt% was 35%. A second negative electrode current collector exposed portion was provided in contact with the inner peripheral surface of the outer can. x was 330 μm, y was 58 μm, and x / y was 5.7. The negative electrode discharge utilization rate, silicon weight ratio, x, and y were measured in the same manner as in Example 1.

[0044] Comparative Example 1: In comparison with the cylindrical battery described above, the discharge capacity per 1.0 g of the negative electrode mixture layer was set to 0.43 Ah, which was less than 0.5, and x / y was set to 4.2, which was less than 4.5. Furthermore, x was set to 344 μm and y was set to 82 μm. The silicon element weight ratio wt % was set to 4%, and no exposed portion of the second negative electrode current collector contacting the inner circumferential surface of the outer can was provided. The negative electrode discharge utilization rate, silicon element weight ratio, x, and y were measured in the same manner as in Example 1.

[0045] <Comparative Example 2> In comparison with the cylindrical battery described above, x / y was set to 4.4, which did not satisfy x / y > 4.5. x was set to 396 μm and y was set to 91 μm. The discharge capacity per 1.0 g of the negative electrode mixture layer was set to 0.68 Ah, and the silicon weight ratio wt% was set to 15%. In addition, no second negative electrode current collector exposed portion contacting the inner peripheral surface of the outer can was provided. The negative electrode discharge utilization rate, silicon weight ratio, x, and y were measured in the same manner as in Example 1.

[0046] (Capacity Measurement) The capacity of each of the batteries of Examples 1-5 and Comparative Examples 1 and 2 was measured. Specifically, after each battery was fabricated, it was charged at a constant current of 0.3 C at 25°C until the battery voltage reached 4.2 V, and then it was charged at a constant voltage of 4.2 V until the current value reached 0.02 C. After a 20-minute rest, it was discharged at a constant current of 0.2 C until the battery voltage reached 2.5 V, and the capacity (discharge capacity) was measured. The capacity of each battery was calculated assuming that the capacity of the battery of Example 1 was 100.

[0047] (DC Resistance Measurement) Each of the batteries of Examples 1-5 and Comparative Examples 1 and 2 was subjected to constant-voltage charging at a constant current of 0.3 C in a 45°C air-cooled environment until the battery voltage reached 4.2 V, followed by constant-voltage charging at 4.2 V until the current value reached 0.02 C. After a 20-minute pause, the battery was discharged at a constant current of 0.5 C until the battery voltage reached 2.85 V, followed by a 20-minute pause. This charge-discharge cycle was repeated 100 times. Thereafter, the battery was again charged at a constant voltage of 4.2 V at a constant current of 0.3 C in a 25°C temperature environment until the capacity reached 50% of the initial capacity. The battery was then left to stand in an open circuit for 1 hour, after which it was discharged at a constant current of 0.5 C for 10 seconds. The direct current resistance (DCR) after cycling, (OCV-CCV) / I10s, was calculated using the open circuit voltage (OCV), the closed circuit voltage (CCV) 10 seconds after discharge, and the current value 10 seconds after discharge (I10s). Before conducting the 100-cycle test, the above-described charge / discharge cycle was performed once, and the initial direct current resistance (DCR) was measured using the method described above. The DCR increase rate was calculated by dividing the post-cycle direct current resistance (DCR) by the initial direct current resistance (DCR). The DCR increase rate for each battery was calculated by setting the DCR increase rate in Example 1 to 100.

[0048] (Test results)

[0049] The battery of Comparative Example 1, in which the negative electrode discharge utilization rate was less than 0.5, had a capacity of 94, which was significantly smaller by 6% than the capacity of the battery of Example 1, which was the smallest among the batteries of the Examples.

[0050] Furthermore, it was confirmed that the batteries of Comparative Examples 1 and 2, in which x / y was 4.5 or less, had DCR increase rates that were significantly greater by 2% or more than the battery of Example 1, which had the highest DCR increase rate among the batteries of Examples 1 to 5. In other words, it was confirmed that the batteries of Examples 1 to 5, in which x / y was greater than 4.5, had DCR increase rates that were significantly smaller by 1.98% or more than the battery of Comparative Example 1, which had the lowest DCR increase rate.

[0051] In particular, when the battery of Example 1 and Comparative Example 2, which differ only in x / y under the same conditions as the negative electrode discharge utilization rate, silicon element weight ratio, and presence or absence of a second negative electrode current collector exposed portion, are compared, the battery of Example 1 has a DCR increase rate of 100 and a capacity of 100, while the battery of Comparative Example 2 has a DCR increase rate of 102 and a capacity of 98. That is, compared to the battery of Example 1, the battery of Comparative Example 2 has a DCR increase rate that is abruptly increased by 2% and a capacity that is significantly reduced by 2%. This confirms that the value of x / y has a decisive effect on the DCR increase rate and capacity.

[0052] Through the above-mentioned tests and numerous other tests, the present inventors have found that when x / y is greater than 4.5, the DCR increase rate can be suppressed and the capacity can be increased, as long as the negative electrode discharge utilization rate is not less than 0.5. As shown in Example 1-5, when the value of x / y is 4.7 or more and 5.7 or less, the DCR increase rate can be effectively suppressed and the capacity can be effectively increased.

[0053] The batteries of Examples 1 to 5 all had a silicon element weight ratio in the range of 7% to 50%. Through the above-mentioned tests and numerous other tests, the inventors confirmed that when the silicon element weight ratio is in the range of 7% to 50%, the DCR increase rate is easily suppressed and the capacity is easily increased. Furthermore, a silicon element weight ratio of 12% or more tends to result in high output from battery 10, and a silicon element weight ratio of 25% or more significantly increases the output of battery 10.

[0054] Furthermore, among the batteries of Examples 1 to 5, the batteries of Examples 2 and 5 in which the second negative electrode current collector exposed portion was in contact with the inner circumferential surface of the outer can both had the lowest DCR increase rate of 94. Therefore, it was confirmed that by bringing the second negative electrode current collector exposed portion into contact with the inner circumferential surface of the outer can, the current collection path can be shortened and the DCR increase rate can be effectively suppressed.

[0055] In order to facilitate the establishment of 4.5<x / y<7.0, it is preferable to satisfy 300≦x≦400, and it is more preferable to satisfy 320≦x≦380. In addition, in order to facilitate the establishment of 4.5<x / y<7.0, it is preferable to satisfy 45≦y≦100, and it is more preferable to satisfy 50≦y≦90.

[0056] The cylindrical battery of the present disclosure may also have the following configuration: Configuration 1: An electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a non-aqueous electrolyte, and a bottomed cylindrical outer can accommodating the electrode assembly and the non-aqueous electrolyte, wherein the positive electrode has a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector, the negative electrode has a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector, the positive electrode mixture layer contains a lithium-containing composite oxide as a positive electrode active material, and the negative electrode mixture layer contains a silicon-containing material as a negative electrode active material, and the discharge capacity per 1.0 g of the negative electrode mixture layer is 0.5 Ah or more, and a negative electrode lead is connected to the end of the negative electrode on the winding start side. a first negative electrode current collector exposed portion at which the negative electrode current collector is exposed, the negative electrode has a non-facing portion at a winding start side of the electrode assembly that does not face the positive electrode, the negative electrode mixture layer is provided on at least a portion of at least one surface of the non-facing portion, and when x is the distance between the negative electrode current collector in a first starting end facing portion that faces the winding start end of the positive electrode on the outer side of the winding of the negative electrode in the negative electrode, and the negative electrode current collector in a second starting end facing portion that faces the winding start end of the positive electrode on the inner side of the winding of the negative electrode in the negative electrode, and y is the thickness of the negative electrode mixture layer in the first starting end facing portion, the relationship x / y > 4.5 is satisfied. Configuration 3: The non-aqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the non-facing portion is wound 0.75 turns or more.Configuration 4: The non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the non-facing portion is wound 1.5 turns or less.Configuration 5: The non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the silicon-containing material includes an ion-conducting phase and a Si phase dispersed in the ion-conducting phase.Configuration 6: The non-aqueous electrolyte secondary battery according to Configuration 5, wherein the ion-conducting phase includes an amorphous carbon phase.Configuration 7: The non-aqueous electrolyte secondary battery according to Configuration 5 or 6, wherein the weight ratio of the Si phase in the silicon-containing material is 30% or more and 60% or less.Configuration 8: The non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 7, wherein the weight ratio of elemental silicon in the negative electrode mixture layer is 7% by mass or more.Configuration 9: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 8, wherein the weight ratio of silicon element in the negative electrode mixture layer is 50 mass % or less.Configuration 10: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 9, wherein x / y<7.0 is satisfied.Configuration 11: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 10, wherein the lithium-containing composite oxide has a layered rock salt structure.

[0057] REFERENCE SIGNS LIST 10 nonaqueous electrolyte secondary battery, 11 positive electrode, 11a starting end of positive electrode, 12 negative electrode, 12a first starting end facing portion of negative electrode, 12b second starting end facing portion of negative electrode, 13 separator, 14 electrode body, 14a hollow portion, 16 outer can, 17 sealing body, 18, 19 insulating plate, 20 positive electrode lead, 21 negative electrode lead, 23 sealing plate, 23a through hole, 24 lower valve body, 25 insulating member, 26 upper valve body, 27 terminal cap, 27a through hole, 28 gasket, 30 cylindrical portion, 34 grooved portion, 35 cylindrical portion, 38 shoulder portion, 41 positive electrode current collector, 42 positive electrode mixture layer, 45 peripheral portion, 51 negative electrode current collector, 51a first negative electrode current collector exposed portion, 51b second negative electrode current collector exposed portion, 52 negative electrode mixture layer, 60 graphite, 61 non-facing portion, 68 bottom portion, 70 silicon-containing material, 71 ion-conducting phase, 72 Si phase.

Claims

1. An electrochemical cell comprising an electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a non-aqueous electrolyte, and a bottomed cylindrical exterior can for accommodating the electrode body and the non-aqueous electrolyte, wherein the positive electrode has a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector, the negative electrode has a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector, the positive electrode mixture layer contains a lithium-containing composite oxide as a positive electrode active material, and the negative electrode mixture layer contains a silicon-containing material as a negative electrode active material, the discharge capacity per 1.0 g of the negative electrode mixture layer is 0.5 Ah or more, a negative electrode lead is connected to an end of the negative electrode on the winding start side, and a first negative electrode current collector exposed portion is provided where the negative electrode current collector is exposed, and the negative electrode has a non-facing portion that does not face the positive electrode on the winding start side of the electrode body, a negative electrode mixture layer is provided on at least a portion of at least one surface of the non-facing portion, and wherein, when a distance between the negative electrode current collector of a first starting end facing portion that faces the winding starting end of the positive electrode on the outside of winding in the negative electrode and the negative electrode current collector of a second starting end facing portion that faces the winding starting end of the positive electrode on the inside of winding in the negative electrode is defined as x, and a thickness of the negative electrode mixture layer at the first starting end facing portion is defined as y, x / y>4.5 is satisfied.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein a second negative electrode current collector exposed portion is provided at the winding end of the negative electrode, the second negative electrode current collector exposed portion being in contact with the inner peripheral surface of the outer can and exposing the negative electrode current collector.

3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-facing portion is wound by 0.75 turns or more.

4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-facing portion is wound 1.5 times or less.

5. The nonaqueous electrolyte secondary battery according to claim 1, wherein the silicon-containing material includes an ion-conducting phase and a Si phase dispersed in the ion-conducting phase.

6. The nonaqueous electrolyte secondary battery according to claim 5, wherein the ion-conducting phase includes an amorphous carbon phase.

7. The nonaqueous electrolyte secondary battery according to claim 5, wherein the weight ratio of the Si phase in the silicon-containing material is 30% or more and 60% or less.

8. The nonaqueous electrolyte secondary battery according to claim 1, wherein the weight ratio of silicon in the negative electrode mixture layer is 7 mass % or more.

9. The nonaqueous electrolyte secondary battery according to claim 1, wherein the weight ratio of silicon in the negative electrode mixture layer is 50 mass % or less.

10. The nonaqueous electrolyte secondary battery according to claim 1, wherein x / y<7.

0.

11. The nonaqueous electrolyte secondary battery according to claim 1, wherein the lithium-containing composite oxide has a layered rock salt structure.

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