Non-aqueous electrolyte secondary battery
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO LTD
- Filing Date
- 2026-01-22
- Publication Date
- 2026-08-06
Smart Images
Figure JP2026002022_06082026_PF_FP_ABST
Abstract
Description
Nonaqueous electrolyte secondary battery
[0001] This disclosure relates to a non-aqueous electrolyte secondary battery.
[0002] Conventionally, non-aqueous electrolyte secondary batteries, which comprise an electrode body including a positive electrode and a negative electrode, and a non-aqueous electrolyte, and perform charging and discharging by moving lithium ions between the positive and negative electrodes, have been widely used. One end of a strip-shaped positive electrode tab and negative electrode tab is connected to each of the positive and negative electrodes, and the other end of the positive electrode tab and negative electrode tab is connected to the external terminals of the respective electrodes.
[0003] Patent Document 1 discloses a partially clad material for a positive electrode tab, which is configured such that the side connecting to the positive electrode is made of aluminum alone, while the surface of the side connecting to the external terminal has nickel or stainless steel on it, for the purpose of improving the connection strength between the positive electrode and the external terminal.
[0004] Japanese Patent Publication No. 2001-126709
[0005] Incidentally, in recent years, non-aqueous electrolyte secondary batteries have been steadily increasing in capacity and power output, and it is necessary to ensure the safety of such high-energy-density non-aqueous electrolyte secondary batteries even in the event of an external short circuit. If the positive electrode tab described in Reference 1 is used, the high-resistance metals such as nickel or stainless steel placed on the surface of the tab will generate heat and transfer that heat to the surrounding components, potentially causing the inside of the battery to become very hot.
[0006] The purpose of this disclosure is to provide a non-aqueous electrolyte secondary battery that suppresses the temperature rise of the battery in the event of an external short circuit.
[0007] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure comprises an electrode body in which a strip-shaped positive electrode and a negative electrode are wound longitudinally via a separator, an outer casing for housing the electrode body, and a sealing body for closing the opening of the outer casing. The positive electrode has a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector. A positive electrode tab is connected to the positive electrode current collector, and the positive electrode tab includes a first metal portion mainly composed of Al and a second metal portion mainly composed of a second metal different from Al. The second metal portion has a higher volume resistivity at 100°C than the first metal portion, and both surfaces in the thickness direction of the positive electrode tab are composed solely of the first metal portion.
[0008] The non-aqueous electrolyte secondary battery described herein can suppress the temperature rise of the battery in the event of an external short circuit, thereby improving the safety of the battery.
[0009] This is an axial cross-sectional view of a non-aqueous electrolyte secondary battery, which is an example of an embodiment. This is a perspective view of a positive electrode tab according to an example of an embodiment. This is a schematic diagram showing the top view, front view, and side view of a positive electrode tab according to an example of an embodiment. This is a diagram corresponding to Figure 3 in another example of an embodiment. This is a diagram corresponding to Figure 3 in another example of an embodiment. This is a diagram corresponding to Figure 3 in another example of an embodiment. This is a schematic diagram showing the top view, front view, and side view of a positive electrode tab in Comparative Example 2.
[0010] The following describes in detail an example of an embodiment of this disclosure. In the following description, specific shapes, materials, directions, and numerical values are illustrative examples to facilitate understanding of this disclosure and can be modified as appropriate to suit the application, purpose, and specifications. Furthermore, if the following description includes multiple embodiments and modifications, it is intended from the outset that their characteristic features may be combined as appropriate.
[0011] Figure 1 is an axial cross-sectional view of a non-aqueous electrolyte secondary battery 10, which is an example of an embodiment. In the following, a cylindrical secondary battery in which the electrode body is housed in a cylindrical outer casing is given as an example, but the outer casing is not limited to a cylindrical shape and may be, for example, rectangular, coin-shaped, etc.
[0012] As shown in Figure 1, the non-aqueous electrolyte secondary battery 10 consists of an electrode body 14, a non-aqueous electrolyte (not shown), an outer container 16 that houses the electrode body 14 and the non-aqueous electrolyte, and a sealing body 17 that closes the opening of the outer container 16. Hereafter, the side of the non-aqueous electrolyte secondary battery 10 with the sealing body 17 in the axial direction (height direction) will be referred to as "upper," and the bottom side of the outer container 16 in the axial direction will be referred to as "lower."
[0013] The electrode body 14 has a strip-shaped positive electrode 11, a negative electrode 12, and a separator 13, and the positive electrode 11 and the negative electrode 12 are wound longitudinally via the separator 13. The positive electrode 11, the negative electrode 12, and the separator 13 are all elongated strips, and are alternately stacked in the radial direction of the electrode body 14 by being wound in a spiral. 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 width (short direction). The separator 13 is formed to be at least slightly larger than the positive electrode 11, and two separators are arranged so as to sandwich the positive electrode 11. The non-aqueous electrolyte secondary battery 10 includes insulating plates 18 and 19 arranged above and below the electrode body 14, respectively.
[0014] The positive electrode 11 comprises a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector. The positive electrode current collector 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 contains a positive electrode active material, a conductive agent, and a binder, and is preferably formed on both sides of the positive electrode current collector, excluding the exposed portion (not shown) of the positive electrode current collector to which the positive electrode tab 20 is welded. 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 to the surface of the positive electrode current collector, drying the coating, and then compressing it to form the positive electrode mixture layer on both sides of the positive electrode current collector.
[0015] The positive electrode composite layer contains particulate lithium metal composite oxide as the positive electrode active material. The lithium metal composite oxide is a composite oxide containing metal elements such as Co, Mn, Ni, and Al in addition to Li. The metal elements constituting the lithium metal composite oxide are, for example, at least one selected from Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Sn, Sb, W, Pb, and Bi. Among these, it is preferable to contain at least one selected from Co, Ni, and Mn. Examples of suitable composite oxides include lithium metal composite oxides containing Ni, Co, and Mn, and lithium metal composite oxides containing Ni, Co, and Al.
[0016] Examples of conductive agents included in the positive electrode mixture layer include carbon black such as acetylene black and Ketjenblack, graphite, carbon nanotubes (CNTs), carbon nanofibers, and graphene. Examples of binders included in the positive electrode mixture layer include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide, acrylic resins, and polyolefins. In addition, these resins may be used in combination with carboxymethylcellulose (CMC) or its salts, polyethylene oxide (PEO), etc.
[0017] The negative electrode 12 comprises a negative electrode current collector and a negative electrode mixture layer formed on the surface of the negative electrode current collector. The negative electrode current collector 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 contains a negative electrode active material, a binder, and optionally a conductive agent, and is preferably formed on both sides of the negative electrode current collector, excluding the exposed portion (not shown) of the negative electrode current collector to which the negative electrode tab 21 is welded. The negative electrode 12 can be manufactured by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the surface of the negative electrode current collector, drying the coating, and then compressing it to form the negative electrode mixture layer on both sides of the negative electrode current collector.
[0018] The negative electrode composite layer generally contains a carbon material that reversibly intercepts and releases lithium ions as the negative electrode active material. Suitable examples of carbon materials include natural graphite such as flake graphite, lumpy graphite, and clay-like graphite, as well as artificial graphite such as lumpy artificial graphite and graphitized mesophase carbon microbeads (MCMB). Furthermore, a material containing at least one of elements that alloy with Li, such as Si and Sn, and a material containing such elements may be used as the negative electrode active material. Among these, composite materials containing Si are preferred.
[0019] A preferred example of a composite material containing Si is SiO ２ Examples include materials in which Si nanoparticles are dispersed in a phase or a silicate phase such as lithium silicate, or materials in which Si nanoparticles are dispersed in an amorphous carbon phase. A conductive layer, such as a carbon film, is formed on the particle surface of the composite material.
[0020] The binder in the negative electrode mixture layer may be a fluororesin, PAN, polyimide, acrylic resin, polyolefin, etc., similar to the positive electrode mixture layer, but styrene-butadiene rubber (SBR) is preferred. Furthermore, the negative electrode mixture layer preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), etc. Among these, a combination of SBR and CMC or a salt thereof, PAA or a salt thereof is preferred. The negative electrode mixture layer may also contain a conductive agent such as CNT.
[0021] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator 13 include polyethylene, polyolefins such as polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. A heat-resistant resin layer, such as aramid resin, may be formed on the surface of the separator 13. A filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12.
[0022] A positive electrode tab 20 is connected to the exposed positive electrode current collector of the positive electrode 11, and a negative electrode tab 21 is connected to the exposed negative electrode current collector of the negative electrode 12. The positive electrode tab 20 extends towards the sealing body 17 through a through hole in the insulating plate 18, and the negative electrode tab 21 extends towards the bottom of the outer casing 16 through the outside of the insulating plate 19. The positive electrode tab 20 is connected to the lower surface of the sealing body 17 by welding or the like, so that the sealing body 17 becomes the positive electrode terminal. The negative electrode tab 21 is connected to the inner surface of the bottom of the metal outer casing 16 by welding or the like, so that the outer casing 16 becomes the negative electrode terminal.
[0023] Non-aqueous electrolytes include, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As the non-aqueous solvent (organic solvent), carbonates, lactones, ethers, ketones, and esters can be used, and two or more of these solvents can be used in mixture form. When using a mixture of two or more solvents, it is preferable to use a mixed solvent containing a cyclic carbonate and a linear carbonate. For example, ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC) can be used as cyclic carbonates, and dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) can be used as linear carbonates. As the electrolyte salt, LiPF ６ LiBF ４ , and LiCF ３ SO ３ These and mixtures thereof can be used. The solubility of the electrolyte salt in the non-aqueous solvent can be, for example, 0.5 mol / L or more and 2.0 mol / L or less. Note that the non-aqueous electrolyte is not limited to a liquid electrolyte, but may also be a solid electrolyte using a gel polymer or the like.
[0024] The outer container 16 is a cylindrical metal container with a bottom at one end and an opening at the other end. The body of the outer container 16 houses the electrode body 14 and the non-aqueous electrolyte. An annular groove 22 is formed between the body and the opening 24, the diameter of which is smaller than that of the body of the outer container 16.
[0025] The annular groove 22 is a portion of the outer can 16's side surface that is recessed radially inward, and is provided in an annular shape along the circumferential direction of the outer can 16. The annular groove 22 supports the sealing body 17 on its upper surface. The annular groove 22 can be formed, for example, by spinning a portion of the outer can 16's side surface radially inward to create an annular recess radially inward.
[0026] The opening is located on the side of the outer can 16, above the annular groove 22, and forms the opening of the outer can 16. The area near the opening end is bent radially inward, and the sealing body 17 is crimped and fixed to the outer can 16.
[0027] The sealing body 17 is a disc-shaped member equipped with a safety valve. The sealing body 17 is a metal plate having a thick portion 17a to which the positive electrode tab 20 is connected, an outer peripheral portion 17b, and a thin portion 17c that is thinner than the thick portion 17a and the outer peripheral portion 17b. The outer peripheral portion 17b is sandwiched between the open end of the outer can 16 and the annular groove 22 via a gasket 23.
[0028] If an abnormality occurs in the non-aqueous electrolyte secondary battery 10 and the internal pressure rises, the high-temperature gas generated pushes the sealing body 17 upward, causing it to bend at the thin-walled portion 17c and deform so that the thick-walled portion 17a protrudes outward from the battery. This deformation disconnects the connection between the sealing body 17 and the positive electrode tab 20, interrupting the current path in the sealing body 17. If the internal pressure of the non-aqueous electrolyte secondary battery 10 rises further after the current path is interrupted, the thin-walled portion 17c ruptures, forming a gas outlet in the sealing body 17.
[0029] The gasket 23 is a flexible insulating member that electrically isolates the sealing body 17, which is the positive terminal, from the outer can 16, which is the negative terminal, while ensuring airtightness inside the outer can 16 by being compressed vertically. The material of the gasket 23 is not particularly limited as long as it is a compressible insulating material, and for example, polypropylene (PP), polyphenylene sulfide (PPS), polyethylene (PE), polybutylene terephthalate (PBT), perfluoroalkoxyalkane (PFA), polytetrafluoroethylene (PTFE), polyamide (PA), etc. can be used.
[0030] Next, the positive electrode tab 20 will be described with reference to Figures 2 to 4D. Figure 2 is a perspective view of the positive electrode tab 20 according to one example of an embodiment.
[0031] As shown in Figure 2, the positive electrode tab 20 is a thin, strip-shaped metal plate. Hereafter, the X, Y, and Z directions will be referred to as the length direction, width direction, and thickness direction, respectively. The length, width, and thickness of the positive electrode tab 20 satisfy the relationship: length > width > thickness.
[0032] Figure 3 schematically shows a top view (XY plane), a front view (YZ plane), and a side view (XZ plane) of a positive electrode tab 20 according to one embodiment. In Figure 3, the actual length, width, and thickness of the positive electrode tab 20 are not accurately represented, and in particular, the thickness direction Z is shown in an enlarged view.
[0033] As shown in the front and side views, the positive electrode tab 20 includes a first metal portion 32 mainly composed of Al and a second metal portion 34 mainly composed of a second metal different from Al, and both surfaces of the positive electrode tab 20 in the thickness direction Z are composed only of the first metal portion 32. Furthermore, the second metal portion 34 has a higher volume resistivity at 100°C than the first metal portion 32. By having the high-resistivity metal exist only on the inside of the positive electrode tab 20 in this way, the surface of the positive electrode tab 20 can not become hot even when an external short circuit occurs, and the temperature rise inside the battery can be suppressed. In this specification, the main component means the component with the highest mass ratio among the constituent components. The proportion of Al in the first metal portion 32 is, for example, 80% by mass or more, and may be 90% by mass or more. The proportion of the second metal in the second metal portion 34 is, for example, 50% by mass or more, and may be 90% by mass or more. The first metal part 32 and the second metal part 34 may each be composed of Al only and the second metal only, respectively.
[0034] In the example shown in FIG. 3, the first metal part 32 is a strip-shaped metal plate mainly composed of Al with a thickness of (T1 - T2) / 2, and the second metal part 34 is a strip-shaped metal plate mainly composed of a second metal with a thickness of T2. Note that the first metal parts 32 arranged on both sides of the second metal part 34 in the thickness direction Z may have different thicknesses from each other. By arranging the first metal parts 32 on both sides of the second metal part 34 in the thickness direction Z, the positive electrode tab 20 becomes the mode shown in FIG. 3. Note that the first metal part 32 and the second metal part 34 are joined by pressure welding or the like.
[0035] The volume resistivity can be measured as follows, for example, using an electrode resistance measurement system manufactured by Hioki Electric Co., Ltd. (1) Prepare a sample cut out to a size of 20 mm × 50 mm. (2) Measure the thickness of the sample and input it as a measurement parameter into the measurement conditions. (3) Select an appropriate main current and voltage range. (4) Set the sample on a hot plate set at 100°C, bring the probe into contact, and measure the volume resistivity.
[0036] Examples of the second metal include Ni, Fe, Sn, Cr, etc. Ni or Fe is preferred, and Ni is more preferred. By using Ni or Fe, it is possible to suppress the temperature rise inside the battery while suppressing the resistance of the positive electrode tab 20 and improving the output of the battery.
[0037] When the maximum thickness of the positive electrode tab 20 is T1 and the maximum thickness of the second metal part 34 is T2, it is preferably satisfied that 0.1 ≦ T2 / T1 < 1, and more preferably satisfied that 0.15 ≦ T2 / T1 ≦ 0.75. T1 is, for example, 30 μm or more and 500 μm or less, and T2 is, for example, 3 μm or more and 250 μm or less.
[0038] In the example shown in FIG. 3, the cross-section (XY plane) perpendicular to the thickness direction Z of the positive electrode tab 20 is composed of only the first metal part 32 or only the second metal part 34. That is, when the positive electrode tab 20 is cut by a cross-section perpendicular to the thickness direction Z, the cut surface in the range from the surface to (T1 - T2) / 2 is composed of only the first metal part 32, and the cut surface in the range closer to the center in the thickness direction Z than the above is composed of only the second metal part 34. The positive electrode tab 20 in the aspect shown in FIG. 3 can be manufactured more easily than the positive electrode tab 20 in the aspects shown in FIGS. 4A to 4D described later.
[0039] The positive electrode tab 20 is connected to the sealing body 17 in the upper welding region 40 on the side of the sealing body 17, and is connected to the positive electrode current collector in the lower welding region 42 on the current collector side than the upper welding region 40. By connecting the positive electrode current collector and the sealing body 17 through the positive electrode tab 20, the sealing body 17 becomes the positive electrode terminal. The upper welding region 40 is, for example, located near the end on the side of the sealing body 17 of the positive electrode tab 20 in the length direction X, and is located near the center of the positive electrode tab 20 in the width direction Y. The position of the lower welding region 42 is not particularly limited as long as it is on the current collector side than the upper welding region 40. Also, in the example shown in FIG. 3, the lower welding region 42 is composed of one region, but as shown in FIGS. 4B to 4C described later, the lower welding region 42 may be composed of a plurality of regions. The lower welding region 42 is, for example, located near the center of the positive electrode tab 20 in the width direction Y, similar to the upper welding region 40.
[0040] All surfaces of the positive electrode tab 20 may be covered with an oxide film. In the example shown in FIG. 3, the upper and lower surfaces (XY plane) are covered with Al ２ O ３ which is an oxide of Al as the main component. Also, the two side surfaces (XZ plane), as well as the front and rear surfaces (YZ plane), are covered with Al ２ O ３ and an oxide of the second metal. When the second metal is Ni or Fe, the oxide film is NiO, or FeO or Fe ２ [[ID=十六]]O [[ID=十七]] ３ Thus, elution of the metal constituting the positive electrode tab 20 into the non-aqueous electrolyte can be suppressed.
[0041] Figures 4A to 4D all correspond to Figure 3 in another example of the embodiment. The positive electrode tab 20 shown in Figure 4A has a single section consisting only of the first metal section 32 on the current collector side from the boundary line B between the first metal section 32 and the second metal section 34 on the side surface, and a coexisting section 50 where the first metal section 32 and the second metal section 34 coexist on the sealing body 17 side from the boundary line B. Here, the single section is the part in the cross section perpendicular to the length direction X of the positive electrode tab 20 in which only the first metal section 32 exists, and the coexisting section 50 is the part in the cross section perpendicular to the length direction X of the positive electrode tab 20 in which the first metal section 32 and the second metal section 34 coexist.
[0042] The positive electrode tab 20 shown in Figure 4A can be manufactured, for example, as follows: (1) A portion corresponding to the second metal portion 34 is removed from a metal plate mainly composed of Al with length L1, width W1, and thickness T3, and the second metal portion 34 is bonded to this removed portion by vapor deposition. (2) Next, a metal plate mainly composed of Al with length L1, width W1, and thickness (T1-T3) is bonded to the upper surface where the first metal portion 32 and the second metal portion 34 are exposed by pressure welding, thereby manufacturing the positive electrode tab 20 shown in Figure 4A.
[0043] In the example shown in Figure 4A, the coexistence portion 50 is such that the first metal portion 32 covers the second metal portion 34 in the width direction Y and the thickness direction Z. That is, when the maximum width of the positive electrode tab 20 is W1 and the maximum width of the second metal portion 34 is W2, the condition W2 / W1 < 1 is satisfied. Al has better corrosion resistance compared to secondary metals such as Ni and Fe, and Figure 4A, in which the top, bottom, and side surfaces are covered with Al, has a remarkable effect in suppressing corrosion of the positive electrode tab 20. In the example shown in Figure 4A, the lower limit of W2 / W1 is preferably 0.5, more preferably 0.6, and even more preferably 0.65. This makes the above effect even more pronounced. The upper limit of W2 / W1 is, for example, 0.95. In the positive electrode tab 20 shown in Figure 4A, W1 is, for example, 1 mm or more and 10 mm or less, and W2 is, for example, 0.5 mm or more and less than 10 mm. In Figures 3 and 4B to 4D, W1 and W2 satisfy the condition W2 / W1 = 1.
[0044] When the length of the positive electrode tab 20 is L1 and the length of the coexisting portion 50 is L2, L2 / L1 is, for example, 0.3 or more and 1 or less, or 0.5 or more and 1 or less. For example, L1 is 15 mm or more and 140 mm or less, and L2 is 5 mm or more and 120 mm or less.
[0045] The positive electrode tab 20 shown in Figure 4B has a single section consisting only of the first metal part 32 on the current collector side, and a coexisting section 50 on the sealing body 17 side in which the first metal part 32 and the second metal part 34 coexist. In the example shown in Figure 4B, the coexisting section 50 is such that the first metal part 32 covers the second metal part 34 in the thickness direction Z, but does not cover the second metal part 34 in the width direction Y. The positive electrode tab 20 shown in Figure 4B can be manufactured, for example, by bonding the second metal part 34 to the first metal part 32, which is positioned on the current collector side of the second metal part 34 in the length direction X and thickness direction Z, by vapor deposition to create the coexisting section 50, and then bonding a single section of the first metal part having the same length and width as the coexisting section 50 by pressure welding and positioning it. After that, the first metal part is positioned. The positive electrode tabs 20 shown in Figures 4C and 4D, which will be described later, can also be manufactured in the same manner.
[0046] The positive electrode tab 20 shown in Figure 4B can be manufactured, for example, as follows. The positive electrode tabs 20 shown in Figures 4C and 4D, which will be described later, can also be manufactured in the same manner. (1) A portion corresponding to the second metal part 34 is cut off from a metal plate mainly composed of Al with length L1, width W1, and thickness T3, and the second metal part 34 is bonded to this cut-off portion by vapor deposition. (2) Next, the positive electrode tab 20 shown in Figure 4B is manufactured by joining a metal plate mainly composed of Al with length L1, width W1, and thickness (T1-T3) to the upper surface where the first metal part 32 and the second metal part 34 are exposed by pressure welding.
[0047] In the example shown in Figure 4B, the positive electrode tab 20 is connected to the current collector at two locations: the first region 42a closest to the sealing body and the second region 42b, which is the second region from the sealing body. That is, the lower welding region 42 has two regions: the first region 42a and the second region 42b. Note that the number of regions to which the positive electrode tab 20 is connected to the current collector is not limited to the above example and may be three or more.
[0048] In the example shown in Figure 4B, the second metal portion 34 exists between the upper welding region 40 and the first region 42a in the longitudinal direction X. Note that in Figures 3 and 4A, as well as in Figure 4C (described later), the second metal portion 34 also exists between the upper welding region 40 and the first region 42a in the longitudinal direction X.
[0049] In the example shown in Figure 4B, the first region 42a overlaps with the second metal portion 34 in the thickness direction of the positive electrode tab 20. Note that the position of the second region 42b is not limited to the example in Figure 4B; for example, the second region 42b may overlap with the second metal portion 34 in the thickness direction of the positive electrode tab 20. In Figures 3 and 4A, the second metal portion 34 is located between the upper welding region 40 and the first region 42a in the length direction X.
[0050] In the example shown in Figure 4C, the first region 42a does not overlap with the second metal portion 34 in the thickness direction of the positive electrode tab 20. Apart from the above, the positive electrode tab 20 shown in Figure 4C has the same configuration as the positive electrode tab 20 shown in Figure 4B.
[0051] The positive electrode tab 20 shown in Figure 4D has a single section consisting only of the first metal part 32 on the sealing body 17 side, and a coexisting section 50 on the current collector side in which the first metal part 32 and the second metal part 34 coexist. In the example shown in Figure 4D, the coexisting section 50 has the first metal part 32 covering the second metal part 34 in the thickness direction Z, but not covering the second metal part 34 in the width direction Y.
[0052] In the example shown in Figure 4D, in the length direction X, the second metal portion 34 does not exist between the upper welding region 40 and the first region 42a, and in the thickness direction of the positive electrode tab 20, the first region 42a does not overlap with the second metal portion 34.
[0053] In the examples shown in Figures 4B to 4D, the corrosion of the positive electrode tab 20 can be suppressed compared to the example shown in Figure 3. Furthermore, in the examples shown in Figures 4B to 4D, when the first region 42a of the positive electrode tab 20 overlaps with the second metal part 34 in the thickness direction Z, as in Figure 4B, the temperature rise suppression effect is also greater.
[0054] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited to these examples.
[0055] <Experimental Example 1> [Fabrication of the positive electrode] As the positive electrode active material, aluminum-containing lithium nickel cobalt oxide (LiNi ０．８８ Co ０．０９ Al ０．０３ O ２ A positive electrode slurry was prepared by mixing the positive electrode active material, acetylene black, and polyvinylidene fluoride in a mass ratio of 100:1:1, and then adding an appropriate amount of N-methyl-2-pyrrolidone (NMP). Next, the positive electrode slurry was applied to both sides of a positive electrode current collector made of aluminum foil, and after the coating film was dried, the coating film was rolled out with a rolling roller and cut to a predetermined electrode size to produce a positive electrode. An exposed portion was provided on a part of the positive electrode in which the surface of the positive electrode current collector was exposed.
[0056] [Fabrication of the negative electrode] Natural graphite was used as the negative electrode active material. The negative electrode active material, sodium carboxymethylcellulose (CMC-Na), styrene-butadiene rubber (SBR), and lithium methanesulfonate were mixed in an aqueous solution in a solid content mass ratio of 100:1:1:0.08 to prepare a negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both sides of a negative electrode core made of copper foil, and after the coating film was dried, the coating film was rolled using a rolling roller and cut to a predetermined electrode size to produce the negative electrode. An exposed portion was provided on a part of the negative electrode in which the surface of the negative electrode core body was exposed.
[0057] [Electrode Fabrication] A positive electrode tab in the configuration shown in Figure 3 was used. The upper and lower welding regions were also in the same positions as in the configuration shown in Figure 3. T1 was 100 μm, T2 was 50 μm, and T2 / T1 was 0.5. The length and width of the positive electrode tab were 72 mm and 3 mm, respectively. The first metal part was composed only of Al, and the second metal part was composed only of Ni. At 100°C, the volume resistivity of Al was 2.6 μΩcm, and the volume resistivity of Ni, the second metal, was 10.3 μΩcm. A nickel metal plate was used as the negative electrode tab. The positive electrode tab and negative electrode tab were connected to the exposed positive and negative electrodes, respectively. Next, a wound electrode body was fabricated by spirally winding the positive and negative electrodes via a polyolefin separator.
[0058] [Preparation of Non-Aqueous Electrolyte] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:3:4. Lithium hexafluoride phosphate (LiPF) was added to this mixed solvent. ６ A non-aqueous electrolyte was prepared by dissolving the substance to a concentration of 1.2 mol / liter.
[0059] [Fabrication of the secondary battery] Insulating plates were placed above and below the electrode assembly, the negative electrode tab was welded to the bottom of the outer casing, and the positive electrode tab was welded to the sealing body. The electrode assembly was then housed in a bottomed cylindrical metal outer casing. After that, a non-aqueous electrolyte was injected into the inside of the outer casing. Furthermore, the opening of the outer casing was sealed with a sealing body via a gasket to fabricate a cylindrical non-aqueous electrolyte secondary battery.
[0060] [Measurement of Internal Resistance] For cylindrical secondary batteries, constant current charging was performed at 0.3C until the battery voltage reached 4.2V in a 25°C environment, and then constant voltage charging was performed at 4.2V until the current value reached 0.02C. After that, the internal resistance of the batteries at 1kHz was measured using the AC four-terminal method with a digital low-resistance meter manufactured by Tsuruga Electric Co., Ltd. in a 25°C environment.
[0061] [Measurement of Maximum Temperature] For cylindrical secondary batteries, constant current charging was performed at 0.3C until the battery voltage reached 4.2V in a 25°C environment, and then constant voltage charging was performed at 4.2V until the current value reached 0.02C. After that, the outer casing and the sealing body were connected with a wire via a 10mΩ resistor and short-circuited externally for 10 minutes, and the maximum temperature reached near the axial center of the side of the secondary battery was measured using a thermocouple.
[0062] <Example 2> A secondary battery was prepared and measured in the same manner as in Example 1, except that T2 was changed to 75 μm.
[0063] <Example 3> A secondary battery was prepared and measured in the same manner as in Example 1, except that T2 was changed to 15 μm.
[0064] <Example 4> A secondary battery was prepared and measured in the same manner as in Example 1, except that T2 was changed to 5 μm.
[0065] <Example 5> A secondary battery was fabricated and measured in the same manner as in Example 1, except that the second metal part was made to consist only of Fe. The volume resistivity of Fe, the second metal, at 100°C was 14.7 μΩcm.
[0066] <Example 6> A secondary battery was fabricated and measured in the same manner as in Example 1, except that a positive electrode tab in the configuration shown in Figure 4A was used. W1 was 3 mm and W2 was 2 mm, and W2 / W1 was 0.67. L1 was 72 mm and L2 was 48 mm, and L2 / L1 was 0.67. The upper and lower welding regions were also in the same positions as in the configuration shown in Figure 4A.
[0067] <Example 7> A secondary battery was fabricated and measured in the same manner as in Example 1, except that a positive electrode tab in the configuration shown in Figure 4B was used. L1 was 72 mm, L2 was 36 mm, and L2 / L1 was 0.5. The upper and lower welding regions were also in the same positions as in the configuration shown in Figure 4B.
[0068] <Example 8> A secondary battery was fabricated and measured in the same manner as in Example 1, except that a positive electrode tab in the configuration shown in Figure 4C was used. L1 was 72 mm, L2 was 36 mm, and L2 / L1 was 0.5. The upper and lower welding regions were also in the same positions as in the configuration shown in Figure 4C.
[0069] <Example 9> A secondary battery was fabricated and measured in the same manner as in Example 1, except that a positive electrode tab in the configuration shown in Figure 4D was used. L1 was 72 mm, L2 was 36 mm, and L2 / L1 was 0.5. The upper and lower welding regions were also in the same positions as in the configuration shown in Figure 4D.
[0070] <Comparative Example 1> A secondary battery was fabricated and measured in the same manner as in Example 1, except that a positive electrode tab made solely of Al was used. The length, width, and thickness of the positive electrode tab were 72 mm, 3 mm, and 100 μm, respectively. The upper and lower welding regions were also positioned in the same locations as shown in Figure 3.
[0071] <Comparative Example 2> A secondary battery was manufactured and measured in the same manner as in Example 1, except that a positive electrode tab in the form shown in Figure 5 was used. L1 was 72 mm, L2 was 36 mm, and L2 / L1 was 0.5. The positive electrode tab 20 was manufactured by cutting off a portion corresponding to the second metal portion 34 from a metal plate mainly composed of Al with length L1, width W1, and thickness T1, and then bonding the second metal portion 34 to this cut-off portion by vapor deposition.
[0072] Table 1 shows the evaluation results for the examples and comparative examples.
[0073]
[0074] Comparative Example 1, which used a positive electrode tab made solely of Al, and Comparative Example 2, which used a positive electrode tab mimicking the embodiment described in Reference Document 1, both achieved higher maximum temperatures than the Examples. In other words, the secondary battery of the Examples achieved a lower maximum temperature than the secondary battery of the Comparative Examples, indicating improved battery safety. Furthermore, the positive electrode tab of the Examples has a smaller area of the second metal portion exposed on its surface compared to the positive electrode tab of the Comparative Examples, thus suppressing corrosion of the positive electrode tab. Among Examples 1 to 4, in which T2 was varied, Examples 1 and 2 were superior in achieving both low resistance and improved safety. In a comparison between Example 1 and Example 5, Ni was superior to Fe as the second metal in achieving both low resistance and improved safety. Also, among Examples 1 and 6 to 9, in which T1 / T2 was the same, Example 1 was superior in achieving both low resistance and improved safety. Furthermore, in Embodiment 7, where the first region 42a overlaps with the second metal portion 34 in the thickness direction Z of the positive electrode tab 20, the maximum temperature reached is lower compared to Embodiments 8 and 9, where the first region 42a does not overlap with the second metal portion 34, thus improving safety.
[0075] This disclosure is further illustrated by the following embodiments. Configuration 1: A non-aqueous electrolyte secondary battery comprising an electrode body in which strip-shaped positive and negative electrodes are wound longitudinally via a separator, an outer casing for housing the electrode body, and a sealing body for closing the opening of the outer casing, wherein the positive electrode has a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector, a positive electrode tab is connected to the positive electrode current collector, the positive electrode tab includes a first metal portion mainly composed of Al and a second metal portion mainly composed of a second metal different from Al, the second metal portion has a higher volume resistivity at 100°C than the first metal portion, and both surfaces in the thickness direction of the positive electrode tab are composed only of the first metal portion. Configuration 2: The non-aqueous electrolyte secondary battery according to Configuration 1, wherein when the maximum thickness of the positive electrode tab is T1 and the maximum thickness of the second metal portion is T2, the condition 0.1 ≤ T2 / T1 < 1 is satisfied. Configuration 3: A non-aqueous electrolyte secondary battery according to Configuration 1 or 2, wherein when the maximum width of the positive electrode tab is W1 and the maximum width of the second metal part is W2, W2 / W1 < 1. Configuration 4: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the positive electrode tab has an upper welded region connected to the sealing body and one or more lower welded regions connected to the positive electrode current collector, and the second metal part exists between the upper welded region and the first region of the lower welded region that is closest to the sealing body. Configuration 5: A non-aqueous electrolyte secondary battery according to Configuration 4, wherein in the thickness direction of the positive electrode tab, the first region overlaps with the second metal part. Configuration 6: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein all surfaces of the positive electrode tab are covered with an oxide film. Configuration 7: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 6, wherein the second metal is Ni. Configuration 8: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 7, wherein the cross section perpendicular to the thickness direction of the positive electrode tab is composed of only the first metal part or only the second metal part.
[0076] 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer casing, 17 Sealing body, 17a Thick-walled section, 17b Outer periphery, 17c Thin-walled section, 18, 19 Insulating plate, 20 Positive electrode tab, 21 Negative electrode tab, 22 Annular groove, 23 Gasket, 32 First metal section, 34 Second metal section, 40 Upper welding area, 42 Lower welding area, 42a First area, 42b Second area, 50 Coexistence section
Claims
1. A non-aqueous electrolyte secondary battery comprising an electrode body in which strip-shaped positive and negative electrodes are wound longitudinally via a separator, an outer container for housing the electrode body, and a sealing body for closing the opening of the outer container, wherein the positive electrode has a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector, a positive electrode tab is connected to the positive electrode current collector, the positive electrode tab includes a first metal portion mainly composed of Al and a second metal portion mainly composed of a second metal different from Al, the second metal portion has a higher volume resistivity at 100°C than the first metal portion, and both surfaces in the thickness direction of the positive electrode tab are composed only of the first metal portion.
2. The non-aqueous electrolyte secondary battery according to claim 1, wherein when the maximum thickness of the positive electrode tab is T1 and the maximum thickness of the second metal part is T2, 0.1 ≤ T2 / T1 < 1.
3. The non-aqueous electrolyte secondary battery according to claim 1, wherein when the maximum width of the positive electrode tab is W1 and the maximum width of the second metal part is W2, W2 / W1 < 1.
4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode tab has an upper welded region connected to the sealing body and one or more lower welded regions connected to the positive electrode current collector, and the second metal portion exists between the upper welded region and the first region of the lower welded region that is closest to the sealing body.
5. The non-aqueous electrolyte secondary battery according to claim 4, wherein in the thickness direction of the positive electrode tab, the first region overlaps with the second metal portion.
6. The non-aqueous electrolyte secondary battery according to claim 1, wherein all surfaces of the positive electrode tab are covered with an oxide film.
7. The non-aqueous electrolyte secondary battery according to claim 1, wherein the second metal is Ni.
8. The non-aqueous electrolyte secondary battery according to claim 1, wherein the cross section perpendicular to the thickness direction of the positive electrode tab is composed of only the first metal portion or only the second metal portion.