Secondary battery
By incorporating recesses and protrusions on the surfaces of wound electrodes in secondary batteries, the positive electrode displacement is suppressed, maintaining electrode distance and preventing lithium deposition, enhancing battery performance.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO LTD
- Filing Date
- 2025-11-12
- Publication Date
- 2026-06-04
AI Technical Summary
Secondary batteries with wound electrodes experience positive electrode displacement during charging and discharging due to the expansion and contraction of the negative electrode mixture layer, leading to reduced distance between electrode layers and potential lithium metal deposition.
The positive and negative electrodes are designed with longitudinally extending recesses and protrusions on their surfaces, arranged alternately in the short direction, with these features facing each other through a separator to increase friction and prevent outward displacement of the positive electrode.
This design effectively suppresses positive electrode displacement in the winding axis direction, maintaining electrode layer distance and preventing lithium metal deposition, thus optimizing electrode utilization and battery performance.
Smart Images
Figure JP2025039704_04062026_PF_FP_ABST
Abstract
Description
secondary battery
[0001] This disclosure relates to secondary batteries.
[0002] Conventionally, there are secondary batteries that have an electrode body in which a positive electrode and a negative electrode are wound with a separator in between. For example, Patent Document 1 proposes a battery in which, in the cross-section in the width direction of the positive electrode, the amount of compound at the upper and lower ends is greater than the amount of compound in the central part, and in the width direction of the negative electrode, the amount of compound at both ends is smaller than the amount of compound in the central part. Furthermore, Patent Documents 2 and 3 propose batteries in which an uneven structure is formed on the positive electrode and the negative electrode, respectively.
[0003] Japanese Patent Publication No. 2001-015146, Japanese Patent Publication No. 2013-058427, Japanese Patent Publication No. 2011-070788
[0004] Incidentally, in secondary batteries with wound electrodes, the negative electrode is generally made slightly larger than the positive electrode to prevent lithium metal deposition during charging and discharging. Therefore, when the negative and positive electrodes are wound, the end of the positive electrode mixture layer in the width direction (short side direction) is located inward in the winding axis direction of the electrode body compared to the end of the negative electrode mixture layer in the width direction (short side direction). Hereafter, the width direction of electrodes and the components constituting the electrodes will all be referred to as the short side direction.
[0005] However, as secondary batteries are repeatedly charged and discharged, the expansion of the negative electrode mixture layer during charging can pull the positive electrode outward along the winding axis of the electrode body, causing the positive electrode to shift outward along the winding axis of the electrode body. Furthermore, if the positive electrode cannot keep up with the contraction of the negative electrode mixture layer during discharge, the shift of the positive electrode outward along the winding axis of the electrode body progresses. This reduces the distance along the winding axis of the electrode body between the short-side end of the positive electrode mixture layer and the short-side end of the negative electrode mixture layer. Moreover, the widthwise end of the positive electrode mixture layer is located further outward along the winding axis of the electrode body than the widthwise end of the negative electrode mixture layer, leading to the aforementioned problem of lithium metal deposition.
[0006] Therefore, the purpose of this disclosure is to provide a secondary battery that can suppress the displacement of the positive electrode outward in the winding axis direction of the electrode body during charging and discharging.
[0007] A secondary battery according to one aspect of the present disclosure comprises an electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound longitudinally with a separator in between, wherein the positive electrode comprises a positive electrode core and a positive electrode mixture layer disposed on the positive electrode core, and the surface of the positive electrode mixture layer has longitudinally extending recesses and protrusions arranged alternately in the short direction, the negative electrode comprises a negative electrode core and a negative electrode mixture layer disposed on the negative electrode core, and the surface of the negative electrode mixture layer has longitudinally extending recesses and protrusions arranged alternately in the short direction, the protrusions of the positive electrode mixture layer and the recesses of the negative electrode mixture layer face each other with the separator in between, and the recesses of the positive electrode mixture layer and the protrusions of the negative electrode mixture layer face each other with the separator in between.
[0008] According to this disclosure, it is possible to provide a secondary battery that can suppress the displacement of the positive electrode outward in the winding axis direction of the electrode body during charging and discharging.
[0009] This is a schematic cross-sectional view of a secondary battery 10, which is an example of an embodiment. This is a partial schematic cross-sectional view of the positive electrode 11 and negative electrode 12 in a wound state. This is a partial schematic cross-sectional view of the positive electrode 11 and negative electrode 12 in a wound state.
[0010] Figure 1 is a schematic cross-sectional view of a secondary battery 10, which is an example of an embodiment. The secondary battery 10 shown in Figure 1 comprises a wound electrode body 14 in which a strip-shaped positive electrode 11 and a strip-shaped negative electrode 12 are wound longitudinally via a separator 13, an electrolyte, insulating plates 18 and 19 arranged above and below the electrode body 14, respectively, and a battery case 15 that houses the above components. The battery case 15 is composed of a case body 16 and a sealing body 17 that closes the opening of the case body 16. Examples of battery cases 15 include cylindrical and rectangular metal cases, and resin cases (so-called pouch type) formed by laminating resin sheets.
[0011] The electrolyte may, for example, be ionic conductive (e.g., lithium ion conductive). The electrolyte may be a liquid electrolyte (electrolyte solution) or a solid electrolyte.
[0012] A liquid electrolyte (electrolyte solution) includes, for example, 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 in the solvent are replaced with halogen atoms such as fluorine. Examples of electrolyte salts include LiPF4. ６ Lithium salts such as these are used.
[0013] Furthermore, as the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, 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 the non-aqueous solvent and gels can be used. Examples of polymer materials include fluororesins, acrylic resins, and polyether resins. As the inorganic solid electrolyte, for example, materials known for all-solid-state secondary batteries, etc. (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. Although the electrolytes exemplified above are non-aqueous electrolytes, the electrolyte is not limited to non-aqueous electrolytes and may also be an aqueous electrolyte.
[0014] The case body 16 is, for example, a metal container in the shape of a bottomed cylinder. A gasket 28 is provided between the case body 16 and the sealing body 17 to ensure airtightness inside the battery. The case body 16 has, for example, a protruding portion 22 that supports the sealing body 17, which is a part of the side surface that protrudes inward. The protruding portion 22 is preferably formed in an annular shape along the circumferential direction of the case body 16, and its upper surface supports the sealing body 17.
[0015] The sealing body 17 has a structure in which a filter 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 to each other at their respective centers, with the insulating member 25 interposed between their respective peripheral edges. When the internal pressure of the secondary battery 10 rises due to heat generation caused by an internal short circuit or the like, for example, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 towards the 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 breaks, and gas is discharged from the opening of the cap 27.
[0016] In the secondary battery 10 shown in Figure 1, the positive electrode lead 20 attached to the positive electrode 11 extends through a through-hole in the insulating plate 18 towards the sealing body 17, and the negative electrode lead 21 attached to the negative electrode 12 extends outside the insulating plate 19 towards the bottom of the case body 16. The positive electrode lead 20 is connected by welding or the like to the lower surface of the filter 23, which is the bottom plate of the sealing body 17, and the cap 27, which is the top plate of the sealing body 17 and is electrically connected to the filter 23, becomes the positive electrode terminal. The negative electrode lead 21 is connected by welding or the like to the inner surface of the bottom of the case body 16, and the case body 16 becomes the negative electrode terminal.
[0017] Figure 2 is a schematic cross-sectional view of the positive electrode 11 and negative electrode 12 in their wound state. In Figure 2, the separator 13 is not shown. The direction of the arrow X in Figure 2 is the short-side direction of the electrode (width direction of the electrode) and is also the winding axis direction of the electrode body 14. The direction of the arrow Y in Figure 2 is the radial direction of the electrode body 14 and is also the method of stacking the electrodes. The positive electrode 11, the negative electrode 12, and the separator 13 (not shown) placed between the positive electrode 11 and the negative electrode 12 are all elongated strip-shaped bodies that are alternately stacked in the radial direction (direction of arrow Y) of the electrode body 14 by being wound in a spiral shape.
[0018] The positive electrode 11 comprises a positive electrode core 30 and a positive electrode mixture layer 32 disposed on the positive electrode core 30. The positive electrode mixture layer 32 may be provided on one side of the positive electrode core 30, or, as shown in Figure 2, on both sides of the positive electrode core 30. The positive electrode core 30 is a strip-shaped positive electrode core 30, and can be, for example, a foil of a metal that is stable in the potential range of the positive electrode 11, such as aluminum, or a film with the metal disposed on its surface. The positive electrode mixture layer 32 includes, for example, a positive electrode active material, a binder, a conductive agent, etc.
[0019] On the surface of the positive electrode mixture layer 32, recesses 32a and protrusions 32b are arranged alternately in the short direction of the positive electrode 11. Although not shown in the diagram, the recesses 32a and protrusions 32b extend along the longitudinal direction of the positive electrode 11. The longitudinal direction of the positive electrode 11 is the winding direction of the positive electrode 11. In Figure 2, three sets of recesses 32a and protrusions 32b are provided on the surface of the positive electrode mixture layer 32.
[0020] The negative electrode 12 comprises a negative electrode core 34 and a negative electrode mixture layer 36 disposed on the negative electrode core 34. The negative electrode mixture layer 36 may be provided on one side of the negative electrode core 34, or on both sides of the negative electrode core 34 as shown in Figure 2. The negative electrode core 34 is a strip-shaped negative electrode core 34, and can be, for example, a foil of a metal that is stable in the potential range of the negative electrode 12, such as copper, or a film with the metal disposed on its surface. The negative electrode mixture layer 36 includes, for example, a negative electrode active material, a binder, etc.
[0021] The negative electrode 12 is formed to be longer in both the longitudinal and transverse directions than the positive electrode 11 in order to prevent lithium deposition. Therefore, as shown in Figure 2, when the positive electrode 11 and the negative electrode 12 are wound, the transverse end of the positive electrode mixture layer 32 is located inward in the winding axis direction of the electrode body 14 compared to the transverse end of the negative electrode mixture layer 36. The region of the negative electrode mixture layer 36 that does not face the positive electrode mixture layer 32 becomes a surplus region that does not contribute to the charge-discharge reaction.
[0022] On the surface of the negative electrode mixture layer 36, recesses 36a and projections 36b are alternately arranged in the short side direction of the negative electrode 12. Although the description is omitted in the figure, the recesses 36a and projections 36b extend along the longitudinal direction of the negative electrode 12. The longitudinal direction of the negative electrode 12 is the winding direction of the negative electrode 12. In FIG. 2, three sets of combinations of recesses 36a and projections 36b are provided on the surface of the negative electrode mixture layer 36.
[0023] The projection 32b of the positive electrode mixture layer 32 and the recess 36a of the negative electrode mixture layer 36 face each other through the separator 13, and the recess 32a of the positive electrode mixture layer 32 and the projection 36b of the negative electrode mixture layer 36 face each other through the separator 13. At least a part of the projection 32b of the positive electrode mixture layer 32 and the recess 36a of the negative electrode mixture layer 36 only need to face each other through the separator 13, but it is preferable that the center of the projection 32b of the positive electrode mixture layer 32 in the short side direction faces the recess 36a of the negative electrode mixture layer 36 through the separator 13. The same applies to the recess 32a of the positive electrode mixture layer 32 and the projection 36b of the negative electrode mixture layer 36 facing each other through the separator 13, and it is preferable that the center of the projection 36b of the negative electrode mixture layer 36 in the short side direction faces the recess 32a of the positive electrode mixture layer 32 through the separator 13.
[0024] The convex portion 32b of the positive electrode mixture layer 32 and the concave portion 36a of the negative electrode mixture layer 36 face each other via the separator 13, and the concave portion 32a of the positive electrode mixture layer 32 and the convex portion 36b of the negative electrode mixture layer 36 face each other via the separator 13. As a result, the coefficient of friction in the short side direction between the positive and negative electrodes via the separator 13 increases, so that the displacement of the positive electrode 11 outward in the winding axis direction of the electrode body 14 accompanying charge and discharge is suppressed. That is, the distance in the winding axis direction of the electrode body 14 between the end portion in the short side direction of the positive electrode mixture layer 32 and the end portion in the short side direction of the negative electrode mixture layer 36 (the distance t shown in FIG. 2, hereinafter sometimes referred to as the phase difference distance t between the positive and negative electrodes in the winding axis direction) is suppressed from becoming small. Therefore, lithium metal precipitation due to charge and discharge is suppressed at the end portion in the width direction of the negative electrode mixture layer 36. Further, if the displacement of the positive electrode 11 outward in the winding axis direction of the electrode body 14 can be suppressed, it becomes possible to design the area of the surplus region of the negative electrode mixture layer 36 not facing the positive electrode mixture layer 32 to be small, and it becomes possible to effectively utilize the limited size of the electrode body 14.
[0025] In terms of further increasing the coefficient of friction in the short side direction between the positive and negative electrodes via the separator 13 and further suppressing the displacement of the positive electrode 11 outward in the winding axis direction of the electrode body 14 accompanying charge and discharge, it is preferable that the top of the convex portion 32b of the positive electrode mixture layer 32 faces the bottom of the concave portion 36a of the negative electrode mixture layer 36 via the separator 13, and the top of the convex portion 36b of the negative electrode mixture layer 36 faces the bottom of the concave portion 32a of the positive electrode mixture layer 32 via the separator 13. The top of the convex portions (32b, 36b) is the portion at the highest position of each convex portion (32b, 36b) in the thickness direction of the mixture layer. Further, the bottom of the concave portions (32a, 36a) is the portion at the lowest position of each concave portion (32a, 36a) in the thickness direction of the mixture layer.
[0026] Figure 3 is a schematic cross-sectional view of a portion of the positive electrode 11 and negative electrode 12 in a wound state. In Figure 3, the separator 13 is not shown. As shown in Figure 3, the convex portion 32b of the positive electrode mixture layer 32 and the concave portion 36a of the negative electrode mixture layer 36 face each other via the separator 13, and at least a portion of the convex portion 32b may be located in the groove of the concave portion 36a via the separator 13. Alternatively, the concave portion 32a of the positive electrode mixture layer 32 and the convex portion 36b of the negative electrode mixture layer 36 face each other via the separator 13, and at least a portion of the convex portion 36b may be located in the groove of the concave portion 32a via the separator 13. In other words, the structure is such that the convex portion 32b of the positive electrode mixture layer 32 and the concave portion 36a of the negative electrode mixture layer 36 are fitted together via the separator 13, or the structure may be such that the convex portion 36b of the negative electrode mixture layer 36 and the concave portion 32a of the positive electrode mixture layer 32 are fitted together via the separator 13. By making the concave portion (32a, 36a) and the convex portion (32b, 36b) fitted together in this way, the coefficient of friction in the short direction between the positive and negative electrodes via the separator 13 becomes larger, and the displacement of the positive electrode 11 outward in the winding axis direction of the electrode body 14 due to charging and discharging is further suppressed.
[0027] It is preferable to provide two or more sets of recesses (32a, 36a) and protrusions (32b, 36b) in the positive electrode mixture layer 32 and the negative electrode mixture layer 36, respectively, in order to increase the coefficient of friction in the short direction between the positive and negative electrodes via the separator 13 and to further suppress the displacement of the positive electrode 11 outward in the winding axis direction of the electrode body 14 during charging and discharging.
[0028] In order to increase the coefficient of friction in the short direction between the positive and negative electrodes via the separator 13 and to further suppress the displacement of the positive electrode 11 outward in the winding axis direction of the electrode body 14 due to charging and discharging, it is preferable that the height from the bottom of the recess (32a, 36a) to the top of the convex portion (32b, 36b) (heights h1, h2 shown in Figure 2) in the positive electrode mixture layer 32 and the negative electrode mixture layer 36 respectively be 3 μm or more and 20 μm or less, and more preferably 10 μm or more and 20 μm or less.
[0029] In the positive electrode 11, if the length in the short direction is c1 (length c1 shown in Figure 2) and the total length in the short direction of the region of the recesses 32a and protrusions 32b arranged alternately in the short direction is d1 (length d1 shown in Figure 2), then it is preferable that d1 / c1 is 0.5 or more. The total length in the short direction of the region of the recesses 32a and protrusions 32b arranged in the short direction is the length from the recess 32a located at one end in the short direction (or the protrusion 36b if the protrusion 32b is located at one end in the short direction) to the protrusion 32b located at the other end in the short direction (or the recess 32a if the recess 32a is located at the other end in the short direction). Furthermore, in the negative electrode 12, if the length in the short direction is c2 (length c2 shown in Figure 2) and the total length in the short direction of the region of the recesses 36a and protrusions 36b arranged in the short direction is d2 (length d2 shown in Figure 2), then it is preferable that d2 / c2 is 0.5 or more. The total length in the short direction of the region of the recesses 36a and protrusions 36b arranged in the short direction is the length from the protrusion 36b located at one end in the short direction (or the recess 36a if a recess 36a is located at one end in the short direction) to the recess 36a located at the other end in the short direction (or the protrusion 36b if a protrusion 36b is located at the other end in the short direction). When d1 / c1 and d2 / c2 satisfy the above range, the coefficient of friction in the short direction between the positive and negative electrodes via the separator becomes larger, and the displacement of the positive electrode 11 outward in the winding axis direction of the electrode body 14 due to charging and discharging is further suppressed.
[0030] From the viewpoint of suppressing burrs at the short-side ends due to slitting of the electrodes, the regions of recesses 32a and protrusions 32b arranged in the short-side direction of the positive electrode 11 may be positioned at a predetermined distance from one end and the other end of the positive electrode 11 in the short-side direction. For example, the distance E1 from one end of the region of recesses 32a and protrusions 32b in the short-side direction to one end of the positive electrode 11 in the short-side direction, and the distance E2 from the other end of the region of recesses 32a and protrusions 32b in the short-side direction to the other end of the positive electrode 11 in the short-side direction, may be 1% or more and 10% or less of the length C1 of the positive electrode 11 in the short-side direction, respectively.
[0031] Furthermore, from the viewpoint of suppressing burrs at the short-side ends due to slitting of the electrodes, the regions of the recesses 36a and protrusions 36b arranged in the short-side direction of the negative electrode 12 may be positioned at a predetermined distance from one end and the other end of the negative electrode 12 in the short-side direction. For example, the distance F1 from one end of the region of the recesses 36a and protrusions 36b in the short-side direction to one end of the negative electrode 12 in the short-side direction, and the distance F2 from the other end of the region of the recesses 36a and protrusions 36b in the short-side direction to the other end of the negative electrode 12 in the short-side direction, may be 1% or more and 10% or less of the length C2 of the negative electrode 12 in the short-side direction, respectively.
[0032] In the positive electrode mixture layer 32 and the negative electrode mixture layer 36, the recesses (32a, 36a) and protrusions (32b, 36b) may be arranged at a predetermined distance apart in the short-side direction of the mixture layer. However, it is preferable that the recesses (32a, 36a) and protrusions (32b, 36b) are arranged adjacent to each other without any gap in the short-side direction of the mixture layer. Arranging the recesses (32a, 36a) and protrusions (32b, 36b) adjacent to each other in the short-side direction of the mixture layer allows for a larger coefficient of friction in the short-side direction between the positive and negative electrodes via the separator 13.
[0033] The longitudinal length of the recesses (32a, 36a) and protrusions (32b, 36b) is preferably 50% or more of the longitudinal length of the mixture layer, and more preferably 80% or more.
[0034] An example of a method for manufacturing electrodes (positive electrode 11, negative electrode 12) will be described. For example, an electrode mixture slurry containing an active material, a binder, a conductive agent, etc., is applied to a core body, and the coating film is dried. Then, the coating film is rolled using a rolling roller having recesses and protrusions with predetermined widths and lengths formed on its surface. In this way, an electrode having a mixture layer with the aforementioned recesses (32a, 36a) and protrusions (32b, 36b) can be manufactured on a core body.
[0035] Examples of positive electrode active materials included in the positive electrode mixture layer 32 include lithium transition metal oxides containing transition metal elements such as Co, Mn, and Ni. Lithium transition metal oxides include, for example, Li ｘ CoO ２ Li ｘ NiO ２ Liｘ MnO ２ , Li ｘ Co ｙ Ni １－ｙ O ２ , Li ｘ Co ｙ M １－ｙ O ｚ , Li ｘ Ni １－ｙ M ｙ O ｚ , Li ｘ Mn ２ O ４ , Li ｘ Mn ２－ｙ M ｙ O ４ , LiMPO ４ , Li ２ MPO ４ F(M; at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B, 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3). These may be used alone or in combination of multiple kinds. In terms of achieving high capacity of the non-aqueous electrolyte secondary battery, the positive electrode active material is Li ｘ NiO ２ , Li ｘ Co ｙ Ni １－ｙ O ２ , Li ｘ Ni １－ｙ M ｙ O ｚ (M; at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B, 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3), etc. lithium nickel composite oxides are preferably included.
[0036] As the conductive agent contained in the positive electrode mixture layer 32, for example, carbon black (CB) such as acetylene black (AB) and ketjen black, carbon nanotube (CNT), graphene, carbon-based particles such as graphite, etc. may be mentioned. These may be used alone or in combination of two or more kinds.
[0037] Examples of binders included in the positive electrode mixture layer 32 include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts (PAA-Na, PAA-K, etc., or partially neutralized salts), and polyvinyl alcohol (PVA). These may be used individually or in combination of two or more types.
[0038] The negative electrode active material contained in the negative electrode mixture layer 36 is not particularly limited as long as it can reversibly intercept and release lithium ions, for example, carbon materials, Si-based materials, etc.
[0039] The carbon material may be any conventionally known carbon material used as a negative electrode active material, such as natural graphite including flake graphite, lump graphite, and earthy graphite, or artificial graphite including lump graphite (MAG) and graphitized mesophase carbon microbeads (MCMB).
[0040] Si-based materials include, for example, a lithium ion conducting phase and Si particles dispersed within the lithium ion conducting phase. The lithium ion conducting phase includes, for example, at least one of a silicon oxide phase, a silicate phase, and a carbon phase.
[0041] The silicate phase preferably contains at least one element from Group 2 of the periodic table, which includes the alkali metal elements lithium, sodium, potassium, rubidium, cesium, and francium, and the elements beryllium, magnesium, calcium, strontium, barium, and radium, due to its high lithium ion conductivity, for example. Among these, the silicate phase containing lithium (hereinafter sometimes referred to as the lithium silicate phase) is preferred due to its high lithium ion conductivity.
[0042] The lithium silicate phase is, for example, given by formula: Li ２ｚ SiO ２＋ｚThis is expressed as (0 < z < 2). From the viewpoint of stability, ease of fabrication, lithium-ion conductivity, etc., it is preferable that z satisfies the relationship 0 < z < 1, and more preferably z = 1 / 2.
[0043] Si-based materials in which Si particles are dispersed in a silicon oxide phase include, for example, materials with the general formula SiO ｘ (The range 0 < x < 2 is preferred, and the range 0.5 ≤ x ≤ 1.6 is more preferred). A Si-based material in which Si particles are dispersed in a carbon phase is, for example, represented by the general formula Si ｘ C ｙ (Preferably in the ranges 0 < x ≤ 1 and 0 < y ≤ 1).
[0044] A conductive layer coated with conductive carbon may be formed on the surface of the Si-based material. The conductive layer can be formed by, for example, a CVD method using acetylene, methane, etc., or by mixing coal pitch, petroleum pitch, phenolic resin, etc. with a silicon-based active material and performing heat treatment. Examples of heat treatment equipment that can be used include a hot air furnace, hot press, lamp, sheath heater, ceramic heater, rotary kiln, etc. Alternatively, a conductive layer may be formed by fixing a conductive filler such as carbon black to the particle surface of the Si-based material using a binder.
[0045] The negative electrode active material preferably contains a Si-based material in terms of increasing the battery capacity, and the Si-based material content is preferably 3% by mass or more, and more preferably 5% by mass or more, relative to the total mass of the negative electrode active material. Generally, the inclusion of a Si-based material in the negative electrode active material increases the expansion rate of the negative electrode mixture layer 36 during charging, which makes it easier for the positive electrode 11 to shift outward in the winding axis direction of the electrode body 14 during charging and discharging. However, by using an electrode body 14 in which the aforementioned recesses (32a, 36a) and protrusions (32b, 36b) are formed in the negative electrode mixture layer 36 and the positive electrode mixture layer 32, the shift of the positive electrode 11 outward in the winding axis direction of the electrode body 14 during charging and discharging is suppressed, even if the negative electrode active material contains a Si-based material.
[0046] The binder contained in the negative electrode mixture layer 36 is, for example, the same as that used in the positive electrode 11. The negative electrode mixture layer 36 may also contain a conductive agent. The conductive agent is, for example, the same as that used in the positive electrode 11.
[0047] For example, a porous sheet having ion permeability and insulating properties can be 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 either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be formed on the surface of the separator.
[0048] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited to these examples.
[0049] <Example 1> [Preparation of the positive electrode] A lithium transition metal oxide, carbon black, and polyvinylidene fluoride (PVDF) were mixed in a solid content mass ratio of 98:1:1, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added. The mixture was then kneaded to prepare a positive electrode mixture slurry. This slurry was applied to both sides of a positive electrode core made of aluminum foil. After the coating film was dried, the coating film was rolled using a rolling roller having recesses and protrusions of a predetermined width and length formed on its surface. In this way, a positive electrode was obtained in which a positive electrode mixture layer with recesses and protrusions formed on its surface was arranged on both sides of the positive electrode core. The recesses and protrusions on the surface of the positive electrode mixture layer have a shape that extends in the longitudinal direction. As shown in Figure 2, three sets of recesses and protrusions are arranged along the short direction.
[0050] The dimensions of the recesses and protrusions in the positive electrode mixture layer are as follows. The height h1 from the bottom of the recess to the top of the protrusion in the positive electrode mixture layer was 10 μm. The thickness of the positive electrode mixture layer from the positive electrode current collector to the bottom of the recess was 60 μm, and the thickness of the positive electrode mixture layer from the positive electrode current collector to the top of the protrusion was 70 μm. The length c1 in the short direction of the positive electrode was 66.5 mm. The length in the short direction of one pair of recesses and protrusions was 18 mm, and the total length d1 in the short direction of the region of recesses and protrusions arranged in the short direction was 54 mm. Therefore, d1 / c1 is 0.81. The length in the longitudinal direction of the recesses and protrusions is approximately the same as the length in the longitudinal direction of the positive electrode mixture layer.
[0051] [Fabrication of the Negative Electrode] A negative electrode active material was prepared by mixing graphite powder and Si-based material in a mass ratio of 92:8. This mixture was then mixed with carboxymethylcellulose and styrene-butadiene rubber in an aqueous solution in a solid content mass ratio of 100:1:1 to prepare a negative electrode mixture slurry. This slurry was applied to both sides of a negative electrode core made of copper foil. After drying the coating, the coating was rolled using a rolling roller with recesses and protrusions of a predetermined width and length formed on its surface. In this way, a negative electrode was obtained in which a negative electrode mixture layer with recesses and protrusions formed on its surface was arranged on both sides of the negative electrode core. The recesses and protrusions formed on the surface of the negative electrode mixture layer have a shape that extends in the longitudinal direction. As shown in Figure 2, three sets of recesses and protrusions are arranged along the short direction.
[0052] The dimensions of the recesses and protrusions in the negative electrode mixture layer are as follows. The height h2 from the bottom of the recess to the top of the protrusion in the negative electrode mixture layer was 10 μm. The thickness of the negative electrode mixture layer from the negative electrode current collector to the bottom of the recess was 80 μm, and the thickness of the negative electrode mixture layer from the negative electrode current collector to the top of the protrusion was 90 μm. The length c2 in the short direction of the negative electrode was 68 mm. The length in the short direction of one pair of recesses and protrusions was 18 mm, and the total length d2 in the short direction of the region of recesses and protrusions arranged in the short direction was 54 mm. Therefore, d2 / c2 is 0.79. The length in the longitudinal direction of the recesses and protrusions is approximately the same as the length in the longitudinal direction of the negative electrode mixture layer.
[0053] [Preparation of Non-Aqueous Electrolyte] A mixed solvent prepared by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:3 is prepared, to which lithium hexafluoride phosphate (LiPF) is added. ６ A non-aqueous electrolyte was prepared by dissolving ) at a concentration of 1.0 mol / liter.
[0054] [Fabrication of a secondary battery] A positive electrode lead was connected to the positive electrode, and a negative electrode lead was connected to the negative electrode. The positive and negative electrodes were then placed opposite each other via a polyolefin separator. At this time, the recesses of the positive electrode mixture layer and the protrusions of the negative electrode mixture layer, and the protrusions of the positive electrode mixture layer and the recesses of the negative electrode mixture layer were facing each other. While maintaining the opposing state of the recesses and protrusions, the positive electrode, negative electrode, and separator were wound in a spiral shape to fabricate a wound electrode body.
[0055] After placing insulating plates above and below the electrode assembly, the negative electrode lead was welded to the inner surface of the bottom of a cylindrical outer casing with a closed bottom, and the positive electrode lead was welded to a sealing body, thereby housing the electrode assembly inside the casing. Subsequently, a non-aqueous electrolyte was injected into the casing, and the opening of the casing was sealed with a sealing body via a gasket to create a secondary battery.
[0056] <Example 2> A secondary battery was manufactured in the same manner as in Example 1, except that in the positive electrode mixture layer, two sets of recessed and convex portions were arranged along the short direction, the short-direction length d1 of the region of recessed and convex portions arranged along the short direction was set to 36 mm and d1 / c1 was set to 0.54, and in the negative electrode mixture layer, two sets of recessed and convex portions were arranged along the short direction, the short-direction length d2 of the region of recessed and convex portions arranged along the short direction was set to 36 mm and d2 / c2 was set to 0.53.
[0057] <Example 3> A secondary battery was manufactured in the same manner as in Example 1, except that in the positive electrode mixture layer, the thickness of the positive electrode mixture layer from the positive electrode current collector to the bottom of the recess in the positive electrode mixture layer was 63.5 μm, the thickness of the positive electrode mixture layer from the positive electrode current collector to the top of the convex portion of the positive electrode mixture layer was 66.5 μm, and the height h1 from the bottom of the recess to the top of the convex portion was 3 μm; and in the negative electrode mixture layer, the thickness of the negative electrode mixture layer from the negative electrode current collector to the bottom of the recess in the negative electrode mixture layer was 83.5 μm, the thickness of the negative electrode mixture layer from the negative electrode current collector to the top of the convex portion of the negative electrode mixture layer was 86.5 μm, and the height h2 from the bottom of the recess to the top of the convex portion was 3 μm.
[0058] <Example 4> A secondary battery was manufactured in the same manner as in Example 1, except that in the positive electrode mixture layer, the thickness of the positive electrode mixture layer from the positive electrode current collector to the bottom of the recess in the positive electrode mixture layer was 50 μm, the thickness of the positive electrode mixture layer from the positive electrode current collector to the top of the convex portion of the positive electrode mixture layer was 70 μm, and the height h1 from the bottom of the recess to the top of the convex portion was 20 μm; and in the negative electrode mixture layer, the thickness of the negative electrode mixture layer from the negative electrode current collector to the bottom of the recess in the negative electrode mixture layer was 75 μm, the thickness of the negative electrode mixture layer from the negative electrode current collector to the top of the convex portion of the negative electrode mixture layer was 95 μm, and the height h2 from the bottom of the recess to the top of the convex portion was 20 μm.
[0059] <Comparative Example> A secondary battery was manufactured in the same manner as in Example 1, except that no recesses or protrusions were formed in either the positive electrode mixture layer or the negative electrode mixture layer.
[0060] [Charge-Discharge Cycle Test] The secondary batteries of each example and comparative example were charged at a constant current of 0.2C in a temperature environment of 25°C. When the battery voltage reached 4.2V, constant voltage charging was performed until the charging current was 0.01C or less. Next, constant current discharge at 0.2C was performed until the battery voltage reached 2.5V. This charge-discharge cycle was repeated 100 times.
[0061] After the charge-discharge test, the electrode bodies were removed from the secondary battery, and the removed electrode bodies were observed using an X-ray CT scanner to measure the phase difference distance t between the positive and negative electrodes in the winding axis direction (distance t shown in Figure 2). The results are shown in Table 1 as relative values with the phase difference distance t between the positive and negative electrodes in Example 1 set to 100.
[0062]
[0063] In Example 1, the phase difference distance t between the positive and negative electrodes in the winding axis direction remained almost unchanged when comparing the state before charging and discharging with the state after 100 charge-discharging cycles. Therefore, it can be said that the displacement of the positive electrode in the short direction due to charging and discharging of the secondary battery is sufficiently suppressed.
[0064] In Examples 2 to 4, the phase difference distance t between the positive and negative electrodes in the winding axis direction after 100 charge-discharge cycles was almost the same as in Example 1. Therefore, it can be said that in all of Examples 2 to 4, the displacement of the positive electrode in the short direction due to charging and discharging of the secondary battery is suppressed.
[0065] On the other hand, in the comparative example, the phase difference distance t between the positive and negative electrodes in the winding axis direction after 100 charge-discharge cycles was halved compared to Example 1. Therefore, it can be said that the comparative example exhibits a greater displacement of the positive electrode in the short-axis direction due to the charging and discharging of the secondary battery compared to Example 1.
[0066] The present disclosure will be further described by the following embodiments. Configuration 1: A secondary battery comprising an electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound longitudinally with a separator, wherein the positive electrode comprises a positive electrode core and a positive electrode mixture layer disposed on the positive electrode core, and the surface of the positive electrode mixture layer has longitudinally extending recesses and protrusions arranged alternately in the short direction, the negative electrode comprises a negative electrode core and a negative electrode mixture layer disposed on the negative electrode core, and the surface of the negative electrode mixture layer has longitudinally extending recesses and protrusions arranged alternately in the short direction, the protrusions of the positive electrode mixture layer and the recesses of the negative electrode mixture layer face each other with the separator, and the recesses of the positive electrode mixture layer and the protrusions of the negative electrode mixture layer face each other with the separator. Configuration 2: The secondary battery according to Configuration 1, wherein two or more sets of the recess and the protrusion are provided in the positive electrode mixture layer and the negative electrode mixture layer, with each set comprising one recess and one protrusion. Configuration 3: The secondary battery according to Configuration 1 or 2, wherein in each of the positive electrode mixture layer and the negative electrode mixture layer, the height from the bottom of the recess to the top of the protrusion is 3 μm or more and 20 μm or less. Configuration 4: The secondary battery according to any one of Configurations 1 to 3, wherein in each of the positive electrode and the negative electrode, when the length of the electrode in the short direction is c and the total length in the short direction of the region of the recess and protrusion arranged in the short direction is d, d / c is 0.5 or more. Configuration 5: The secondary battery according to any one of Configurations 1 to 4, wherein the negative electrode mixture layer contains a Si-based material as a negative electrode active material, and the content of the Si-based material is 3% by mass or more with respect to the total mass of the negative electrode active material.
[0067] 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Battery case, 16 Case body, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Protruding part, 23 Filter, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket, 30 Positive electrode core body, 32 Positive electrode mixture layer, 32a, 36a Recessed part, 32b, 36b Protruding part, 34 Negative electrode core body, 36 Negative electrode mixture layer.
Claims
1. A secondary battery comprising an electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound longitudinally via a separator, wherein the positive electrode comprises a positive electrode core and a positive electrode mixture layer disposed on the positive electrode core, and the surface of the positive electrode mixture layer has longitudinally extending recesses and protrusions arranged alternately in the short direction, the negative electrode comprises a negative electrode core and a negative electrode mixture layer disposed on the negative electrode core, and the surface of the negative electrode mixture layer has longitudinally extending recesses and protrusions arranged alternately in the short direction, the protrusions of the positive electrode mixture layer and the recesses of the negative electrode mixture layer face each other via the separator, and the recesses of the positive electrode mixture layer and the protrusions of the negative electrode mixture layer face each other via the separator.
2. The secondary battery according to claim 1, wherein two or more sets of the recess and the protrusion are provided in the positive electrode mixture layer and the negative electrode mixture layer, with each set comprising one recess and one protrusion.
3. The secondary battery according to claim 1 or 2, wherein in each of the positive electrode mixture layer and the negative electrode mixture layer, the height from the bottom of the recess to the top of the convex portion is 3 μm or more and 20 μm or less.
4. The secondary battery according to claim 1 or 2, wherein, in each of the positive electrode and the negative electrode, when c is the length of the electrode in the short direction and d is the total length in the short direction of the regions of recesses and protrusions arranged in the short direction, d / c is 0.5 or more.
5. The secondary battery according to claim 1 or 2, wherein the negative electrode mixture layer contains a Si-based material as a negative electrode active material, and the content of the Si-based material is 3% by mass or more relative to the total mass of the negative electrode active material.