Secondary battery

Abstract

A battery (10) comprises: an electrode body (14) that is formed by winding a positive electrode (11) and a negative electrode (12) with a separator (13) therebetween; and an electrolyte solution. The negative electrode (11) includes a negative electrode collector (51) and a negative electrode mixture layer (52) that is formed on the negative electrode collector (51) and includes a negative electrode active material. When the electrode body (14) has been discharged to 2.5 V at a discharge rate of 0.2 C, there is a gap G between the positive electrode (11) and the negative electrode (12) at a round of the positive electrode (11) where the entirety of both surfaces of the positive electrode (11) are opposite the negative electrode (12) within 1 / 2 of the number of rounds of the positive electrode (11) from a winding finish end of the positive electrode (11), the gap G being such that the ratio X of the maximum width of the gap G to the maximum thickness of the negative electrode (12) is at least 0.15.

Description

Secondary battery

[0001] The present disclosure relates to a secondary battery.

[0002] In a non-aqueous electrolyte secondary battery, for example, a material with a large volume change accompanying charge and discharge, such as a silicon material, may be used. In this case, the electrolyte becomes non-uniform during the charge-discharge cycle, the charge-discharge reaction becomes non-uniform, and the non-aqueous electrolyte secondary battery may deteriorate.

[0003] For example, Patent Document 1 discloses a technique of providing a gap between a positive electrode and a negative electrode in a non-aqueous electrolyte secondary battery using a negative electrode containing Si or Sn. In the non-aqueous electrolyte secondary battery disclosed in Patent Document 1, the non-uniformity of the electrolyte during the charge-discharge cycle can be eliminated.

[0004] Japanese Patent Application Laid-Open No. 2008-047303

[0005] However, in the non-aqueous electrolyte secondary battery disclosed in Patent Document 1, the gap between the positive electrode and the negative electrode results in a reduction in battery capacity. Therefore, it is desired to suppress the reduction in battery capacity while eliminating the non-uniformity of the electrolyte during the charge-discharge cycle.

[0006] Therefore, an object of the present disclosure is to provide a secondary battery that can suppress a reduction in battery capacity while eliminating the non-uniformity of the electrolyte during the charge-discharge cycle.

[0007] The secondary battery according to the present disclosure includes a positive electrode, an electrode body in which the positive electrode and the negative electrode are wound via a separator, and an electrolyte. The negative electrode has a negative electrode current collector and a negative electrode mixture layer containing a negative electrode active material formed on the negative electrode current collector. When the discharge rate is 0.2C and discharged to 2.5V, it is located in the range of 1 / 2 of the number of winding turns of the positive electrode from the end of the winding of the positive electrode of the electrode body, and a gap is provided between the positive electrode and the negative electrode around the positive electrode where the entire both surfaces of the positive electrode face the negative electrode. The gap is provided such that the ratio X of the maximum width of the gap to the maximum thickness of the negative electrode is at least 0.15 or more.

[0008] According to the secondary battery of the present disclosure, it is possible to suppress a reduction in battery capacity while eliminating the non-uniformity of the electrolyte during the charge-discharge cycle.

[0009] This is an axial cross-sectional view of a cylindrical battery, which is an example of an embodiment. This is a perspective view of the electrode body. This is a schematic diagram illustrating an example of the structure of the negative electrode mixture layer. This is a schematic cross-sectional view showing the gap in the electrode body.

[0010] Hereinafter, embodiments of the secondary battery according to this disclosure will be described in detail with reference to the drawings. The secondary battery of this disclosure may be a battery using an aqueous electrolyte or a battery using a non-aqueous electrolyte. In the following, a cylindrical secondary battery 10 which is a non-aqueous electrolyte secondary battery (lithium-ion battery) using a non-aqueous electrolyte will be given as an example, but the secondary battery of this disclosure is not limited to this. It is intended from the outset that new embodiments will be constructed by appropriately combining the characteristic features of the embodiments and modifications described below. In the following embodiments, the same components are denoted by the same reference numerals in the drawings, and redundant explanations will be omitted. In addition, multiple drawings include schematic diagrams, and the dimensional ratios such as length, width, and height of each component do not necessarily match between different drawings. Also, in this specification, the side of the sealing body 17 in the axial direction (height direction) of the cylindrical secondary battery 10 is referred to as "up," and the side of the bottom 68 of the outer casing 16 in the axial direction is referred to as "down." Among the components described below, components that are not described in the independent claim indicating the highest-level concept are optional components and are not essential components. Furthermore, this disclosure is not limited to the embodiments and their modifications described below, and various improvements and modifications are possible within the scope of the claims of this application and their equivalents.

[0011] [Secondary Battery] Figure 1 is an axial cross-sectional view of a cylindrical secondary battery 10 according to one embodiment of the present disclosure, and Figure 2 is a perspective view of the electrode body 14 of the secondary battery 10. As shown in Figure 1, the secondary battery (hereinafter simply referred to as "battery") 10 comprises a wound electrode body 14, an electrolyte (not shown), a bottomed cylindrical metal outer casing 16 that houses the electrode body 14 and the electrolyte, and a sealing body 17 that closes the opening of the outer casing 16. As shown in Figure 2, the electrode body 14 has a wound structure in which a long positive electrode 11 and a long negative electrode 12 are wound around each other via two long separators 13. Examples of outer casings 16 include cylindrical, square, coin-shaped, button-shaped, and other metal outer casings.

[0012] 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 than the positive electrode 11 in both the longitudinal and widthwise (short-side) directions. The two separators 13 are also formed to be at least slightly larger than the positive electrode 11 and are arranged, for example, to sandwich the positive electrode 11. The negative electrode 12 may constitute the starting end of the winding of the electrode body 14. However, generally, the separator 13 extends beyond the starting end of the winding of the negative electrode 12, and the starting end of the winding of the separator 13 becomes the starting end of the winding of the electrode body 14.

[0013] Non-aqueous electrolytes are ionic conductive (e.g., lithium ion conductive). Non-aqueous electrolytes may be liquid electrolytes (electrolytes) or solid electrolytes. Liquid electrolytes (electrolytes) contain 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. Non-aqueous solvents may contain halogen-substituted compounds (e.g., fluoroethylene carbonate) in which at least some of the hydrogen atoms in these solvents are replaced with halogen atoms such as fluorine. Examples of electrolyte salts include LiPF4. ６ Lithium salts such as these are used.

[0014] The positive electrode 11 comprises a positive electrode current collector 41 (see Figure 4) and a positive electrode mixture layer 42 (see Figure 4) arranged on both sides of the positive electrode current collector 41. The positive electrode current collector 41 can be made of a metal foil that is stable within the potential range of the positive electrode 11, such as aluminum or an aluminum alloy, or a film with the metal arranged 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 manufactured, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder onto the positive electrode current collector 41, drying the coating, and then compressing it to arrange the positive electrode mixture layer 42 on both sides of the positive electrode current collector 41.

[0015] The positive electrode active material is mainly composed 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. A preferred example of a 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 has a layered rock salt structure because it makes it easier to produce a positive electrode with a large discharge capacity.

[0016] Examples of conductive agents included in the positive electrode mixture layer 42 include carbon materials such as carbon black, acetylene black, Ketjen black, and graphite. Examples of binders included 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 carboxymethylcellulose (CMC) or its salts, polyethylene oxide (PEO), etc.

[0017] The negative electrode 12 has a negative electrode current collector 51 (see Figure 4) and a negative electrode mixture layer 52 (see Figure 4) arranged on both sides of the negative electrode current collector 51. The negative electrode current collector 51 can be made of a metal foil that is stable in the potential range of the negative electrode 12, such as copper or a copper alloy, or a film with the metal arranged on its surface. The negative electrode mixture layer 52 contains a negative electrode active material and a binder. The negative electrode 12 can be manufactured, for example, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder onto the negative electrode current collector 51, drying the coating, and then compressing it to arrange the negative electrode mixture layer 52 on both sides of the negative electrode current collector 51.

[0018] Generally, carbon materials that reversibly intercept and release lithium ions are used as the negative electrode active material. Preferred carbon materials are graphite such as natural graphite such as flake graphite, lump graphite, and clay graphite, and artificial graphite such as lump 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. In order to effectively increase the discharge capacity per 1.0 g of the negative electrode mixture layer 52, it is preferable that the negative electrode mixture layer 52 contains a silicon-containing material containing silicon (Si) as the negative electrode active material.

[0019] Figure 3 is a schematic diagram illustrating an example of the structure of the negative electrode mixture layer 52. As shown in Figure 3, it is preferable that the negative electrode mixture layer 52 contains graphite 60 and a silicon-containing material 70. The silicon-containing material 70 includes, for example, an ion-conducting phase 71 and a Si phase 72 dispersed in the ion-conducting phase 71. It is preferable that the weight ratio of the Si phase 72 in the silicon-containing material 70 is 30% or more, as this increases the discharge capacity and makes it easier for the battery 10 to achieve high output. Furthermore, it is preferable that the weight ratio of the Si phase 72 in the silicon-containing material 70 is 60% or less, as 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, and consequently making it easier for the battery 10 to have excellent durability. 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, etc. However, in order to suppress volume changes of the negative electrode active material during charging and discharging and to increase the charging and discharging efficiency, it is preferable that the ion conducting phase 71 contains an amorphous carbon phase.

[0020] From the viewpoint of the weight ratio of silicon element to the negative electrode mixture layer 52, it is preferable that the weight ratio of silicon element to the negative electrode mixture layer 52 be 3% by mass or more, and more preferably 12% by mass or more, in order to increase the discharge capacity and enable the battery 10 to have high output. Furthermore, it is preferable that the weight ratio of silicon element to the negative electrode mixture layer 52 be 50% by mass or less, in order to reduce 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, and thus improving the durability of the battery 10. When the negative electrode mixture layer 52 contains a silicon-containing material 70, the mass of the silicon element may be about the same as the mass of the Si phase 72. That is, the weight ratio of the Si phase 72 to the negative electrode mixture layer 52 may be 7% by mass or more and 50% by mass or less. The negative electrode active material may be a metal that alloys with lithium other than Si, an alloy containing the metal, a compound containing the metal, etc.

[0021] The binder contained in the negative electrode mixture layer 52 may be a fluororesin, PAN, polyimide resin, acrylic resin, polyolefin resin, etc., as in the case of the positive electrode 11, but preferably styrene-butadiene rubber (SBR) or a modified version thereof is used. In addition to SBR, 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, etc.

[0022] 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. The material of the separator 13 is preferably polyethylene, polyolefin resins such as polypropylene, or cellulose. The separator 13 may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be placed on the surface of the separator 13.

[0023] As shown again in Figure 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 on 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 extends towards the sealing body 17 through a through hole in the insulating plate 18, and the negative electrode lead 21 extends towards the bottom 68 of the outer casing 16 through a through hole in the insulating plate 19. The positive electrode lead 20 is connected to the lower surface of the sealing plate 23 of the sealing body 17 by welding or the like. The terminal cap 27 that constitutes the top plate of the sealing body 17 is electrically connected to the sealing plate 23, and the terminal cap 27 becomes the positive electrode terminal. The negative electrode lead 21 is connected to the inner surface of the bottom 68 of the metal outer casing 16 by welding or the like, and the outer casing 16 becomes the negative electrode terminal.

[0024] The positive electrode 11 has a positive electrode current collector exposed portion where the positive electrode current collector 41 is exposed in an intermediate part, such as the center in the winding direction, and the positive electrode lead 20 is electrically connected to this positive electrode current collector exposed portion. The negative electrode 12 has a first negative electrode current collector exposed portion where the negative electrode current collector 51 is exposed at the end on the winding start side in the winding direction, and a second negative electrode current collector exposed portion where the negative electrode current collector 51 is exposed at the end on the winding end side in the winding direction. The second negative electrode current collector exposed portion includes a part included in the outermost surface of the electrode body 14. The negative electrode lead 21 is electrically connected to the first negative electrode current collector exposed portion, and the second negative electrode current collector exposed portion includes a part that contacts the inner surface of the outer casing 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 current collection path is reduced and electrical resistance is reduced.

[0025] Alternatively, the negative electrode current collector may be configured such that the end of the winding in the winding direction of the negative electrode current collector does not come into contact with the inner surface of the outer casing, and only one negative electrode lead is electrically connected to the beginning of the winding in the winding direction of the negative electrode current collector. Or, two negative electrode leads may be joined to the electrode body, with one negative electrode lead electrically connected to the beginning of the winding in the winding direction of the negative electrode current collector and the other negative electrode lead electrically connected to the end of the winding in the winding direction of the negative electrode current collector.

[0026] The battery 10 further includes a resin gasket 28 positioned between the outer casing 16 and the sealing body 17. The sealing body 17 is crimped and fixed to the opening of the outer casing 16 via the gasket 28. This seals the internal space of the battery 10. The gasket 28 is sandwiched between the outer casing 16 and the sealing body 17, insulating the sealing body 17 from the outer casing 16. The gasket 28 serves as a sealing material to maintain airtightness inside the battery and as an insulating material to insulate the outer casing 16 and the sealing body 17.

[0027] The outer can 16 contains the electrode body 14 and the electrolyte. The outer can 16 has a cylindrical portion 30 and a bottom portion 68, and 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 part of the side surface of the outer can 16 radially inward to create an annular recess on the radially inward side. The shoulder portion 38 is formed when the sealing body 17 is crimped and fixed to the outer can 16, by bending the upper end of the outer can 16 inward toward the peripheral edge 45 of the sealing body 17.

[0028] The sealing body 17 has a structure in which 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 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 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, and the insulating member 25 is interposed between their respective peripheral edges.

[0029] If the battery 10 overheats and its internal pressure rises, the lower valve body 24 deforms and ruptures, pushing the upper valve body 26 towards the terminal cap 27, thus 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 released from the through-hole 27a of the terminal cap 27. This release of gas prevents the battery 10 from rupturing due to an excessive rise in internal pressure, thereby increasing the safety of the battery 10.

[0030] The description above describes a case where the sealing body 17 has a laminated structure including two rupture plates (lower valve body 24 and upper valve body 26) and has a convex terminal cap 27 covering the rupture plates. However, the sealing body may consist only of rupture plates, or it may have a structure in which an internal terminal plate, an insulating plate, and a rupture plate are laminated in that order from the electrode body side. Alternatively, the sealing body may not have rupture plates, and the bottom of the outer casing may have a thin, easily breakable portion that breaks when the battery overheats abnormally.

[0031] [Gap between positive and negative electrodes] Figure 4 is a schematic cross-sectional view showing the winding structure on the inside of the electrode body 14. Note that the separator 13 is not shown in Figure 4. In the electrode body 14, a local gap G is provided between the positive electrode 11 and the negative electrode 12. As a result, although the details will be described later, it is possible to eliminate the non-uniformity of the electrolyte during the charge-discharge cycle of the battery 10 while suppressing the reduction in the battery capacity of the battery 10.

[0032] The following describes the position where the gap G is provided in the electrode body 14. It is assumed that the battery 10 is in a discharged state, and more specifically, that the battery 10 has been discharged to 2.5V when its discharge rate is 0.2C. A separator 13 is interposed in the gap G. Furthermore, the gap G is filled with an electrolyte.

[0033] The gap G is provided so as to be located within half the number of turns of the positive electrode 11 from the end of the winding of the positive electrode 11 of the electrode body 14. In other words, the gap G is provided in the radially outer portion (hereinafter referred to as the outer winding portion) when the radial length of the electrode body 14 is divided into two equal parts in the radial direction.

[0034] In this case, the outer side of the electrode body 14 has a higher degree of roundness than the inner side. In particular, in the electrode body 14 where the positive electrode lead 20 is provided on the inner side, the outer side has a significantly higher degree of roundness than the inner side. Also, a gap often occurs between the positive electrode 11 and the negative electrode 12 on the inner side where the degree of roundness is low, while a gap rarely occurs between the positive electrode 11 and the negative electrode 12 on the outer side where the degree of roundness is high. In this embodiment, by actively providing a localized gap G on the outer side of the electrode body 14 where a gap rarely occurs between the positive electrode 11 and the negative electrode 12, it is possible to eliminate the non-uniformity of the electrolyte during the battery cycle of the battery 10 while suppressing the reduction in the battery capacity of the battery 10 as described above.

[0035] Furthermore, the gap G is provided around the positive electrode 11 where both sides of the positive electrode 11 face the negative electrode 12. In other words, the gap G is provided everywhere except around the positive electrode 11 where the positive electrode lead 20 is attached. The circumference of the positive electrode 11 is counted from the end of the winding of the positive electrode 11, starting with the first turn, second turn, and so on. The gap G may also be provided on the inside or outside of the winding around the positive electrode 11 where both sides of the positive electrode 11 face the negative electrode 12.

[0036] Here, in the positive electrode 11 of the electrode body 14, a gap may occur between the positive electrode 11 and the negative electrode 12 on both sides in the circumferential direction of the portion where the positive electrode lead 20 is provided. In this embodiment, by actively providing a localized gap G in areas other than the circumferential direction of the positive electrode 11 where the positive electrode lead 20 is provided, where a gap between the positive electrode 11 and the negative electrode 12 is less likely to occur, it is possible to eliminate the non-uniformity of the electrolyte during the battery cycle of the battery 10 while suppressing the reduction in the battery capacity of the battery 10 as described above.

[0037] The gap G is provided such that the ratio X of the maximum width (maximum radial dimension) of the gap G to the maximum thickness (maximum radial dimension) of the negative electrode 12 is at least 0.15. In other words, within the above range of the electrode body 14, there exists a portion where the ratio X of the maximum width of the gap G to the maximum thickness of the negative electrode 12 is 0.15 or greater. Here, "maximum thickness of the negative electrode 12" refers to the maximum thickness of the portion of the negative electrode mixture layer 52 that has layers on both sides around the circumference of the negative electrode 12 adjacent to the gap G. Also, "circumference of the negative electrode 12 adjacent to the gap G" refers to the circumference centered on the portion of the negative electrode 12 adjacent to the gap G. Furthermore, the gap G is provided such that the ratio X is 0.5 or less. In other words, there is no portion of the electrode body 14 where the ratio X of the maximum width of the gap G to the maximum thickness of the negative electrode 12 is greater than 0.5.

[0038] Furthermore, the gap G is provided such that the ratio Y of the minimum width (minimum radial dimension) of the gap G between the positive electrode 11 and the negative electrode 12 to the maximum thickness of the negative electrode 12 is 0.03 or less. In other words, there are parts of the electrode body 14 where the gap G is not provided locally. That is, this disclosure does not include an electrode body in which a predetermined gap is provided around the entire circumference between the positive electrode and the negative electrode. Note that "maximum thickness of the negative electrode 12" refers to the maximum thickness of the portion of the negative electrode mixture layer 52 that has layers on both sides around the circumference of the negative electrode 12 adjacent to the gap G, as described above.

[0039] Providing a gap G in the electrode body 14 can be achieved, for example, in the manufacturing process of the battery 10 by pre-providing a gap G1 between the electrode body 14 and the outer casing 16 and then housing the electrode body 14 in the outer casing 16. More specifically, by pre-providing a gap G1 between the electrode body 14 and the outer casing 16 and then housing the electrode body 14 in the outer casing 16, the negative electrode 12 in the electrode body 14 repeatedly expands and contracts, and the pre-provided gap G1 is locally distributed to provide the aforementioned gap G. Normally, in the manufacturing process of the battery 10, a gap G2 is provided between the electrode body 14 and the outer casing 16 to absorb the variation between the inner diameter of the outer casing 16 and the outer diameter of the electrode body 15. Therefore, it is preferable that the aforementioned gap G1 is larger than the gap G2. The gap G1 is preferably, for example, 0.3 mm.

[0040] Furthermore, providing a gap G in the electrode body 14 can be achieved by locally providing a protrusion along the height direction (axial direction) on the separator 13, positive electrode 11, or negative electrode 12. More specifically, by locally providing a protrusion along the height direction (axial direction) on the separator 13, positive electrode 11, or negative electrode 12, a gap G is provided on both sides of the protrusion in the circumferential direction. The material of the protrusion is not particularly limited, but examples include polyethylene, polypropylene, polyolefins such as copolymers of polyethylene and α-olefin, acrylic resin, polystyrene, polyester, cellulose, polyimide, polyphenylene sulfide, polyether ether ketone, fluororesin, etc.

[0041] In this embodiment, by actively providing a localized gap G between the positive electrode 11 and the negative electrode 12 in the electrode body 14, it is possible to eliminate non-uniformity of the electrolyte during the charge-discharge cycle of the battery 10 while suppressing a reduction in the battery capacity of the battery 10.

[0042] <Example 1> In the cylindrical battery described above, the mass ratio of silicon element to the mass of the negative electrode mixture layer was set to 3%. Also, when the thickness of the negative electrode was 181.7 μm, the maximum width of the gap G was set to 29.1 μm and the minimum width of the gap G was set to 2.40 μm. At this time, X was 0.160 and Y was 0.013. <Example 2> In the cylindrical battery described above, the mass ratio of silicon element to the mass of the negative electrode mixture layer was set to 3%. Also, when the thickness of the negative electrode was 181.7 μm, the maximum width of the gap G was set to 31.3 μm and the minimum width of the gap G was set to 6.20 μm. At this time, X was 0.172 and Y was 0.034.

[0043] <Example 3>In the above cylindrical battery, the mass ratio of the silicon element to the mass of the negative electrode mixture layer was set to 17%. Further, when the thickness of the negative electrode was 144.7 μm, the maximum width of the gap G was set to 52.5 μm, and the minimum width of the gap G was set to 0.30 μm. At this time, X described above was 0.363, and Y described above was 0.002.<Example 4>In the above cylindrical battery, the mass ratio of the silicon element to the mass of the negative electrode mixture layer was set to 17%. Further, when the thickness of the negative electrode was 144.7 μm, the maximum width of the gap G was set to 60.8 μm, and the minimum width of the gap G was set to 6.2 μm. At this time, X described above was 0.420, and Y described above was 0.043.

[0044] <Comparative Example 1> In the above cylindrical battery, the mass ratio of the silicon element to the mass of the negative electrode mixture layer was set to 3%. Further, when the thickness of the negative electrode was 181.7 μm, the maximum width of the gap G was set to 22.9 μm, and the minimum width of the gap G was set to 0.60 μm. At this time, X described above was 0.126, and Y described above was 0.003. <Comparative Example 2> In the above cylindrical battery, the mass ratio of the silicon element to the mass of the negative electrode mixture layer was set to 3%. Further, when the thickness of the negative electrode was 181.7 μm, the maximum width of the gap G was set to 12.7 μm, and the minimum width of the gap G was set to 0.40 μm. At this time, X described above was 0.070, and Y described above was 0.002.

[0045] <Comparative Example 3>In the above cylindrical battery, the mass ratio of silicon element to the mass of the negative electrode mixture layer was set to 17%. Further, when the thickness of the negative electrode was 144.7 μm, the maximum width of the gap G was set to 17.4 μm, and the minimum width of the gap G was set to 0.40 μm. At this time, X described above was 0.120, and Y described above was 0.003. [Capacity measurement] The capacities of the batteries of Examples 1-4 and Comparative Examples 1-3 were measured. Specifically, after each battery was fabricated, each battery was charged at a constant current of 0.3 C until the battery voltage reached 4.2 V under the condition of 25 °C, and then charged at a constant voltage until the current value reached 0.02 C at a voltage of 4.2 V. After a 20-minute rest, the battery was discharged at a constant current of 0.2 C until the battery voltage reached 2.85 V, and the capacity (discharge capacity) was measured. The capacity of each battery was calculated when the capacity of the battery of Example 1 was set to 100.

[0046] [Measurement of battery capacity retention rate] For the batteries of Examples 1-4 and Comparative Examples 1-3, after the measurement of the above battery capacity, they were charged at a constant current of 0.3 C until the battery voltage reached 4.2 V under the temperature condition of 25 °C, and then charged at a constant voltage until the current value reached 0.02 C at a voltage of 4.2 V. This charge-discharge cycle was repeated 100 times, and the ratio (battery capacity retention rate) of the discharge capacity of the 100th cycle to the discharge capacity of the first cycle was calculated.

[0047] [Test results]

[0048] It was confirmed that the battery capacity retention rates of all the batteries of Examples 1-4 were 100 or more. That is, it was confirmed that when the ratio X was at least 0.15 or more, the non-uniformity of the electrolytic solution during the cycle could be eliminated.

[0049] It was confirmed that the capacities of all the batteries of Examples 1 and 3 were 100 or more. That is, it was confirmed that when the ratio X was 0.15 or more and the ratio Y was 0.03 or less, the non-uniformity of the electrolytic solution during the cycle could be eliminated, and furthermore, the reduction of the battery capacity could be suppressed.

[0050] All batteries in Examples 1-4 have a silicon element weight ratio within the range of 3% to 50%. In particular, the tests described above and numerous other tests confirmed that when the silicon element weight ratio falls within the range of 3% to 17%, it is possible to eliminate electrolyte non-uniformity during the battery cycle while suppressing the reduction in battery capacity.

[0051] Furthermore, the cylindrical battery of this disclosure may have the following configurations: Configuration 1: A secondary battery comprising an electrode body in which a positive electrode and a negative electrode are wound with a separator in between, and an electrolyte, wherein the negative electrode has a negative electrode current collector and a negative electrode mixture layer containing a negative electrode active material formed on the negative electrode current collector, and when discharged to 2.5V at a discharge rate of 0.2C, a gap is provided between the positive electrode and the negative electrode in the circumference of the positive electrode, located within half the number of windings of the positive electrode from the end of the winding of the positive electrode of the electrode body, and both sides of the positive electrode facing the negative electrode, wherein the gap is provided such that the ratio X of the maximum width of the gap to the maximum thickness of the negative electrode is at least 0.15 or more. Configuration 2: The secondary battery according to Configuration 1, wherein the ratio X is 0.5 or less. Configuration 3: The secondary battery according to Configuration 1 or 2, wherein the gap is provided such that the ratio Y of the minimum width of the gap to the maximum thickness of the negative electrode is 0.03 or less. Configuration 4: The secondary battery according to Configuration 1 or 2, wherein the negative electrode active material includes a silicon-containing material. Configuration 5: The secondary battery according to Configuration 4, wherein the mass ratio of silicon element to the mass of the negative electrode mixture layer is 3% by mass or more. Configuration 6: The secondary battery according to Configuration 4, wherein the mass ratio of silicon element to the mass of the negative electrode mixture layer is 50% by mass or less. Configuration 7: The secondary battery according to Configuration 4, wherein the silicon-containing material includes an ionic conduction phase and a Si phase dispersed in the ionic conduction phase. Configuration 8: The secondary battery according to claim 7, wherein the ionic conduction phase includes particles in which the amorphous carbon phase is present. Configuration 9: The secondary battery according to Configuration 7, wherein the ratio of the total mass of the Si phase to the total mass of the silicon-containing material is 30% by mass or more and 60% by mass or less. Configuration 10: A secondary battery according to configuration 1 or 2, wherein the electrode body is wound in a cylindrical shape.

[0052] 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer casing, 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 part, 34 Grooved part, 38 Shoulder part, 41 Positive electrode current collector, 42 Positive electrode mixture layer, 45 Peripheral part, 51 Negative electrode current collector, 52 Negative electrode mixture layer, 60 Graphite, 68 Bottom part, 70 Silicon-containing material, 71 Ion conducting phase, 72 Si phase.

Claims

1. A secondary battery comprising an electrode body in which a positive electrode and a negative electrode are wound with a separator in between, and an electrolyte, wherein the negative electrode comprises a negative electrode current collector and a negative electrode mixture layer containing a negative electrode active material formed on the negative electrode current collector, and a gap is provided between the positive electrode and the negative electrode in the circumference of the positive electrode, located within half the number of windings of the positive electrode from the end of the winding of the positive electrode of the electrode body, and where both sides of the positive electrode face the negative electrode, when the discharge rate is 0.2C and the battery is discharged to 2.5V, wherein the gap is provided such that the ratio X of the maximum width of the gap to the maximum thickness of the negative electrode is at least 0.

15.

2. The secondary battery according to claim 1, wherein the ratio X is 0.5 or less.

3. The secondary battery according to claim 1 or 2, wherein the gap is provided such that the ratio Y of the minimum width of the gap to the maximum thickness of the negative electrode is 0.03 or less.

4. The secondary battery according to claim 1 or 2, wherein the negative electrode active material includes a silicon-containing material.

5. The secondary battery according to claim 4, wherein the mass ratio of silicon element to the mass of the negative electrode mixture layer is 3% by mass or more.

6. The secondary battery according to claim 4, wherein the mass ratio of silicon element to the mass of the negative electrode mixture layer is 50% by mass or less.

7. The secondary battery according to claim 4, wherein the silicon-containing material comprises an ionic conductive phase and a Si phase dispersed in the ionic conductive phase.

8. The secondary battery according to claim 7, comprising particles in which the ion-conducting phase is an amorphous carbon phase.

9. The secondary battery according to claim 7, wherein the ratio of the total mass of the Si phase to the total mass of the silicon-containing material is 30% by mass or more and 60% by mass or less.

10. The secondary battery according to claim 1 or 2, wherein the electrode body is wound in a cylindrical shape.

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