JP2014175164A - Wound type battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wound type battery which has excellent initial capacity and in which plastic deformation of an electrode body due to charging is suppressed.SOLUTION: A laminate battery 10 is a wound type battery which includes an electrode body 14 formed by winding a positive electrode 20 having a positive electrode active material layer 22 formed on a positive electrode current collector 21 and a negative electrode 30 therearound via a separator 40. The outermost peripheral part 14z of the electrode body 14 is constituted of at least the positive electrode 20, and the elongation percentage of a positive electrode outermost peripheral part 20z which is a portion consisting the outermost peripheral part 14z out of the positive electrode 20 is higher than that of the other portion of the positive electrode 20.

Description

  The present invention relates to a wound battery.

  As one form of a secondary battery such as a lithium ion battery, a wound battery including an electrode body in which a positive electrode and a negative electrode are wound via a separator is known. The positive electrode constituting such an electrode body includes, for example, a current collector made of a metal mainly composed of aluminum (hereinafter referred to as “aluminum current collector”), and a positive electrode active material layer formed on the surface thereof. Have

  By the way, although the said electrode body expand | swells somewhat by charge, since a general aluminum electrical power collector has low elongation rate and its flexibility is low, it cannot absorb the volume change by electrode plate expansion. For this reason, the electrode body may be plastically deformed, which causes, for example, uneven reaction and gas generation or the like easily occurs. Therefore, a method has been proposed in which the flexibility of the current collector is increased by annealing the aluminum current collector by heating the positive electrode at a predetermined temperature (see, for example, Patent Document 1).

JP 2011-60656 A

  However, annealing the entire positive electrode causes a decrease in initial capacity. This is considered due to the fact that the binder (binder resin) in the active material layer melts and covers the active material surface. Moreover, since the mechanical strength of the aluminum current collector is reduced, the current collector may be broken when the charge / discharge cycle is repeated.

  Although Patent Document 1 discloses a method of selectively annealing a portion where the curvature of the positive electrode is large, the plastic deformation of the electrode body cannot be sufficiently suppressed even by this method.

  A wound battery according to the present invention is a wound battery including an electrode body in which a positive electrode and a negative electrode each having a positive electrode active material layer formed on a positive electrode current collector are wound through a separator. The outermost peripheral portion is composed of at least a positive electrode, and the positive electrode outermost peripheral portion, which is the portion constituting the outermost peripheral portion of the positive electrode, has a higher elongation rate than other portions of the positive electrode.

  ADVANTAGE OF THE INVENTION According to this invention, the winding type battery which has a favorable initial capacity and the plastic deformation of the electrode body by charge can be suppressed can be provided.

It is a figure which shows the winding type battery which is an example of embodiment of this invention. It is sectional drawing of the electrode body which is an example of embodiment of this invention. It is the A section enlarged view of FIG. It is sectional drawing of the outermost periphery part of the electrode body which is an example of embodiment of this invention, and its vicinity. It is a figure which shows the cycling characteristics in the test cell of the comparative example 3.

Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.
The drawings referred to in the embodiments are schematically described, and the dimensional ratios of the components drawn in the drawings may be different from the actual products. Specific dimensional ratios and the like should be determined in consideration of the following description.

  In the present specification, “substantially **” is intended to include “substantially the same” as an example and includes what is recognized as substantially the same as the same.

  A laminated battery 10 described below is an example of an embodiment of the present invention. The present invention is not limited to the laminate battery 10 and can be applied to various battery forms such as a flat prismatic battery or a cylindrical battery. In particular, the configuration of the present invention is suitable for a battery including an electrode body that is wound so that the positive electrode is positioned outside the wound structure with respect to the negative electrode.

The configuration of the laminated battery 10 will be described in detail with reference to FIGS.
FIG. 1 is a view showing the appearance of a laminated battery 10. FIG. 2 is a cross-sectional view of the electrode body 14 constituting the laminated battery 10. 3 is an enlarged view of a portion A in FIG. 2, and FIG. 4 is a cross-sectional view showing the outermost peripheral portion 14z of the electrode body 14 and the vicinity thereof.

  As shown in FIG. 1, the laminate battery 10 includes an exterior body 11 composed of two laminate films 11a and 11b. The power generation elements (electrode body 14 and electrolyte) described later are accommodated in the internal space of the accommodating portion 12 formed between the laminate films 11a and 11b. A sealing portion 13 is formed on the exterior body 11 by bonding the laminate films 11a and 11b to each other, thereby sealing an internal space in which the power generation element is accommodated.

  The shape of the laminated battery 10, that is, the shape of the exterior body 11 is not particularly limited, and can be, for example, a substantially rectangular shape in plan view as shown in FIG. Here, “plan view” means a state viewed from a direction perpendicular to the main surfaces (surfaces having the largest areas) of the laminate films 11a and 11b. The sealing portion 13 can be formed in a frame shape with substantially the same width along the edge of the exterior body 11. A portion having a substantially rectangular shape in plan view surrounded by the sealing portion 13 is the accommodating portion 12. The accommodating portion 12 is preferably provided by forming a recess capable of accommodating the power generation element in at least one of the laminate films 11a and 11b. In the present embodiment, the depression is formed only in the laminate film 11a.

  In the laminated battery 10, the positive electrode lead 15 connected to the positive electrode 20 of the electrode body 14 and the negative electrode lead 16 connected to the negative electrode 30 are drawn out from the internal space of the housing portion 12. The leads are preferably drawn out from the same end side of the outer package 11 so as to be substantially parallel to each other. Each lead is made of a metal whose main component is, for example, nickel or copper.

  The laminate battery 10 includes an electrode body 14 and an electrolyte (not shown) as power generation elements. As described above, the power generation element is accommodated in the accommodating portion 12 sealed with the sealing portion 13. As the electrolyte, a nonaqueous electrolyte containing a nonaqueous solvent and an electrolyte salt such as a lithium salt dissolved in the nonaqueous solvent is used. The non-aqueous electrolyte is not limited to a liquid, and may be a solid electrolyte using a gel polymer.

  As shown in FIGS. 2 to 4, the electrode body 14 has a winding structure in which the positive electrode 20 and the negative electrode 30 are wound via a separator 40. Hereinafter, in the electrode body 14, the central axis direction of the winding structure and the direction parallel thereto are referred to as “axial direction”. The electrode body 14 has a flat shape in which a cylinder is crushed in one direction orthogonal to the axial direction. The electrode body 14 is preferably formed by laminating the separator 40, the negative electrode 30, the separator 40, and the positive electrode 20 in order from the inside, from the viewpoint of suppressing plastic deformation accompanying charging. That is, the electrode body 14 is formed so that the positive electrode 20 is positioned outside the wound structure with respect to the negative electrode 30.

In the electrode body 14, it is preferable that at least a part of the outermost peripheral portion 14 z of the wound structure is composed of only the positive electrode 20 or the positive electrode 20 and the separator 40. In the present embodiment, a part of the outermost peripheral portion 14z is composed of only the positive electrode 20. Here, the "outermost peripheral portion 14z 'portion located most outside in the winding structure of the electrode body 14, i.e. from one end P ₁ is a winding end portion of the winding structure of one turn length range Meaning (see FIG. 4). Details of the outermost peripheral portion 14z will be described later.

  The positive electrode 20 includes a positive electrode current collector 21 and a positive electrode active material layer 22 formed on the current collector. Specifically, the positive electrode active material layers 22 are formed on both surfaces of the positive electrode current collector 21 having a long sheet shape. Although described later in detail, it is preferable that the positive electrode 20 does not have the positive electrode active material layer 22 in the outermost peripheral portion 14z.

  As the positive electrode current collector 21, a conductive thin film sheet, particularly a metal foil or alloy foil that is stable in the potential range of the positive electrode 20, a film having a metal surface layer, or the like can be used. The metal constituting the positive electrode current collector 21 is preferably a metal containing aluminum as a main component, for example, aluminum or an aluminum alloy. Examples of the aluminum alloy include alloys containing aluminum and iron. The content of elements other than aluminum in the alloy is preferably 5% by weight or less. The thickness of the positive electrode current collector 21 is preferably about 5 μm to 40 μm, and more preferably about 10 μm to 20 μm, from the viewpoints of current collection and mechanical strength.

The positive electrode active material layer 22 preferably contains a conductive material and a binder in addition to the positive electrode active material. Examples of the positive electrode active material include lithium-containing transition metal oxides containing transition metal elements such as Co, Mn, and Ni. Examples of the lithium-containing transition metal oxide include Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _x Co _y Ni _{1 -y} O ₂ , Li _x Co _y M _{1 -y} O _z , and 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; Na, Mg, Sc, Y, Mn, Fe, Co, At least one of Ni, Cu, Zn, Al, Cr, Pb, Sb, and B). Here, 0 <x ≦ 1.2 (value immediately after the production of the active material, which increases or decreases due to charge / discharge), 0 <y ≦ 0.9, and 2.0 ≦ z ≦ 2.3.

  The conductive agent is used to increase the electrical conductivity of the positive electrode active material layer. Examples of the conductive agent include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. These may be used alone or in combination of two or more. The binder is used for maintaining a good contact state between the positive electrode active material and the conductive agent and enhancing the binding property of the positive electrode active material and the like to the surface of the positive electrode current collector. As the binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), or a modified product thereof is used. The binder may be used in combination with a thickener such as carboxymethyl cellulose (CMC) or polyethylene oxide (PEO).

  The negative electrode 30 includes a negative electrode current collector 31 and a negative electrode active material layer 32 formed on the current collector. Specifically, negative electrode active material layers 32 are formed on both surfaces of a negative electrode current collector 31 having a long sheet shape. As will be described in detail later, it is preferable that the negative electrode 30 does not have the negative electrode active material layer 32 in the outermost peripheral portion 14z.

  As the negative electrode current collector 31, a conductive thin film sheet, particularly a metal foil or alloy foil that is stable in the potential range of the negative electrode 30, a film having a metal surface layer, or the like can be used. The metal constituting the negative electrode current collector 31 is preferably a metal mainly composed of copper. The thickness of the negative electrode current collector 31 is preferably about 5 μm to 40 μm, more preferably about 10 μm to 20 μm, like the positive electrode current collector 21.

  For example, the negative electrode active material layer 32 preferably contains a binder in addition to the negative electrode active material capable of inserting and extracting lithium ions. Examples of the negative electrode active material include natural graphite, artificial graphite, lithium, silicon, carbon, tin, germanium, aluminum, lead, indium, gallium, lithium titanate, and alloys and mixtures thereof. As the binder, PTFE or the like can be used as in the case of the positive electrode, but styrene-butadiene copolymer (SBR) or a modified body thereof is preferably used. The binder may be used in combination with a thickener such as CMC.

  As the separator 40, a porous sheet having ion permeability and insulating properties is used. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a non-woven fabric. As a material of the separator 40, an olefin resin such as cellulose, polyethylene, or polypropylene is preferable.

  Hereinafter, the outermost peripheral portion 14z of the electrode body 14 and the configuration in the vicinity thereof will be described in more detail.

The outermost peripheral portion 14z, as described above, in the range from one end P ₁ is a winding end portion of the winding structure of the electrode body 14 length of one round. Hereinafter, the portion overlapping the end P ₁ and 1 lap from one end P _1, that the other end P ₂ of the outermost peripheral portion 14z. In the example shown in FIG. 4, a part on the other end P ₂ side of the outermost peripheral part 14 z is composed of the negative electrode 30, the two separators 40, and the positive electrode 20, and the other part is composed of only the positive electrode 20. Yes. It is preferable that at least half of the outermost peripheral portion 14 z does not include the negative electrode 30, and only the positive electrode 20 or the positive electrode 20 and the separator 40 are configured. The entire region of the outermost peripheral portion 14z may be composed of only the positive electrode 20. Note that one end P ₁ of the outermost peripheral portion 14z is attached in the vicinity of the other end P ₂ by, for example, an insulating tape.

The positive electrode outermost peripheral part 20z, which is a part constituting the outermost peripheral part 14z of the positive electrode 20, preferably does not have the positive electrode active material layer 22 and is constituted only by the positive electrode current collector 21. In the example shown in FIG. 4, the positive electrode active material layer 22 is not provided over a length range of approximately 1.5 turns from the one end P ₁ beyond the positive electrode outermost peripheral portion 20 z. Hereinafter, in the positive electrode outermost peripheral part 20z and a region continuous therewith, a part in which the positive electrode 20 is composed only of the positive electrode current collector 21 is referred to as an exposed part 21z. Range exposed portion 21z is provided, from the viewpoint of suppression and battery capacity ensure plastic deformation of the electrode assembly 14, starting from one end P _1, 0.5 laps (i.e., about half of Seikyokusai outer peripheral portion 20z) ~ 2 rounds are preferable, and 1 round (that is, substantially the entire region of the positive electrode outermost peripheral portion 20z) to 1.5 rounds is more preferable.

  The negative electrode outermost peripheral part 30z which is a part constituting the outermost peripheral part 14z of the negative electrode 30 also has a part (exposed part 33z) which does not have the negative electrode active material layer 32 and is constituted only by the negative electrode current collector 31. Is preferred. The exposed portion 31z is preferably provided corresponding to the exposed portion 21z. However, from the viewpoint of suppressing lithium precipitation, the area of the negative electrode active material layer 32 is generally slightly larger than the area of the positive electrode active material layer 22.

  The positive electrode 20 is characterized in that the positive electrode outermost peripheral portion 20z has higher flexibility than other portions. Specifically, the elongation rate of the positive electrode outermost periphery 20z is higher than the elongation rate of the other part of the positive electrode 20. Thereby, the plastic deformation of the electrode body 14 by charge is suppressed. The reason why the effect is obtained is not clear, but by increasing the elongation rate of the positive electrode outermost peripheral portion 20z, it is possible to absorb the electrode plate expansion to some extent as in the structure formed by gently winding. It is assumed that When the positive electrode or the like is gently wound, plastic deformation is easily suppressed, but the capacity density is lowered. In contrast, the electrode body 14 can suppress plastic deformation even when the electrode body 14 is strongly tightened.

Here, “elongation” means the elongation at break (%) measured by a tensile test, and can be determined by the following equation.
Elongation at break (%) = 100 × (L−L ₀ ) / L ₀
L: Length of the test sample at the time of breakage (Gage distance at break)
L ₀ : Length of test sample before test (original mark distance)
The tensile test for obtaining the elongation at break can be performed based on JIS Z2241 (corresponding international standard ISO 6892).

  In the present embodiment, since the positive electrode outermost peripheral portion 20z has the exposed portion 21z composed of only the positive electrode current collector 21, the elongation ratio of the exposed portion 21z is higher than the elongation ratio of other portions of the positive electrode current collector 21. It can be said. Even if the positive electrode outermost peripheral portion 20z has the positive electrode active material layer 22, the positive electrode active material layer 22 hardly affects the elongation rate of the positive electrode current collector 21, and the positive electrode outermost periphery portion 20z has an elongation rate of It is substantially equivalent to the elongation rate of the exposed part 21z.

That is, the positive electrode 20 has a structure in which the elongation rate is selectively increased in the positive electrode outermost peripheral portion 20z. Thereby, as will be described in detail in Examples described later, plastic deformation of the electrode body 14 due to charging can be suppressed while maintaining good initial capacity and cycle characteristics. In addition, even if the elongation rate of the part other than the positive electrode outermost peripheral part 20z, for example, the inner peripheral side part is selectively increased, the plastic deformation of the electrode body 14 cannot be suppressed. The range in which the elongation rate is selectively increased is preferably from 0.5 to 2 laps from one end P ₁ from the viewpoint of suppressing plastic deformation of the electrode body 14, and preferably from 1 to 1.5 laps. A circumference is more preferable. That is, a part of Seikyokusai outer peripheral portion 20z, for example, it may be increased selectively elongation only approximately half of the end P ₁ positive outermost portion 20z, and more preferably Seikyokusai outer periphery whole of 20z (exposed portion Elongation rate is increased in the entire area of 21z.

  As a method for selectively increasing the elongation percentage of the positive electrode outermost peripheral portion 20z, a method of annealing by locally heating only the positive electrode outermost peripheral portion 20z is suitable. The elongation percentage of the positive electrode outermost peripheral portion 20z can be changed as appropriate by adjusting the heating temperature and the heating time. The elongation ratio of the positive electrode outermost peripheral portion 20z is better as it is higher, and is preferably 1.4 times or more, more preferably 1.7 times or more, particularly preferably 2.0 times or more with respect to other portions. For example, it is preferable that the elongation ratio of the positive electrode outermost peripheral portion 20z is 2.2% or more or 3.0% or more, and the elongation ratio of other portions is 1.5% or less.

  Hereinafter, the manufacturing process of the laminated battery 10 having the above configuration, particularly the manufacturing process of the electrode body 14 will be described in detail.

  In the manufacturing process of the electrode body 14 (hereinafter referred to as “this process”), first, the positive electrode 20, the negative electrode 30, and the separator 40 are prepared. Each of the positive electrode 20 and the like has a long sheet shape, and can be manufactured by a conventionally known method (detailed description of the method is omitted). The electrode body 14 is formed by laminating the positive electrode 20, the negative electrode 30, and the two separators 40, and winding them as described later.

  In this process, before forming the winding structure of the electrode body 14, the part which becomes the positive electrode outermost peripheral part 20z is locally heated. Thereby, the positive electrode outermost peripheral part 20z is selectively annealed, and the elongation rate is higher than that of other parts. The heat treatment is performed in the process of forming a wound structure of the electrode body 14, for example. Alternatively, it is performed after the positive electrode active material layer 22 is applied on the positive electrode current collector 21, for example, on the positive electrode current collector 21. It is preferable that the positive electrode active material layer 22 is not applied to a portion that becomes the positive electrode outermost peripheral portion 20z, and an exposed portion 21z is provided in the portion.

  As a specific example, in the process of laminating and winding the positive electrode 20, the negative electrode 30, and the separator 40, the respective parts that become the positive electrode outermost peripheral portion 20 z are locally heated by sandwiching them with a heat bar before each component member is laminated. A method is mentioned. When the positive electrode current collector 21 is made of a metal whose main component is aluminum, the heating temperature is preferably 150 ° C to 300 ° C, more preferably 170 ° C to 250 ° C, and particularly preferably 180 ° C to 200 ° C. The heating time varies depending on the heating temperature, and is preferably about 0.5 to 10 seconds, for example. The heating method is not limited to contact heating using a heat bar or the like, and may be non-contact heating using a laser or the like.

  The electrode body 14 is manufactured by laminating the first separator 40, the negative electrode 30, the second separator 40, and the positive electrode 20 in this order, and winding the first separator 40 so as to be inside. The electrode body 14 may be wound so as to have a flat shape, or may be wound in one direction orthogonal to the axial direction after being wound into a cylindrical shape to form a flat shape. Subsequently, the positive electrode lead 15 is fixed to the positive electrode current collector 21 and the negative electrode lead 16 is fixed to the negative electrode current collector 31 by spot welding or the like. In this embodiment, each lead is fixed to the exposed portions 21z and 31z located slightly inside the outermost peripheral portion 14z.

  Finally, the electrode body 14 to which each lead is welded is accommodated in the accommodating portion 12 of the laminate film 11a together with the electrolyte. Then, the laminated film 11b is stacked on the laminate film 11a to form the sealing portion 13, whereby the internal space of the housing portion 12 is sealed, and the laminated battery 10 in which each lead is drawn out from the housing portion 12 is manufactured.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

<Example 1>
[Production of positive electrode]
100 parts by weight of LiCoO ₂ as a positive electrode active material, ₂ parts by weight of acetylene black as a conductive material, 3 parts by weight of PVdF as a binder, and an appropriate amount of N-methyl-2-pyrrolidone are mixed to form a slurry-like positive electrode composition. An agent was prepared. Subsequently, this positive electrode mixture was applied to both surfaces of the positive electrode current collector. As the positive electrode current collector, an aluminum alloy foil (Alloy No. 8021; Al 98.5 wt%, Fe 1.5 wt%) having a thickness of 15 μm was used. An exposed portion (hereinafter referred to as a “positive electrode exposed portion”) composed only of the positive electrode current collector was provided on the portion that became the outermost peripheral portion of the positive electrode without applying the positive electrode mixture. The coated positive electrode mixture was dried at 110 ° C. for 5 minutes and then rolled three times to form a positive electrode active material layer (positive electrode mixture layer). The thickness of each positive electrode active material layer was about 60 μm.

  Next, only the positive electrode exposed part was heated for 1 second using a heat bar heated to 190 ° C. so that the elongation ratio of the positive electrode exposed part was 2.2%. As described above, the elongation was measured by a tensile test based on JIS Z2241 (corresponding international standard ISO 6892), and the relationship between the heating condition and the elongation was obtained in advance by experiments. The elongation rate of the other parts other than the positive electrode exposed part is 1.5% (elongation rate of exposed part / elongation rate of other parts = 1.47).

  Next, the positive electrode lead made of aluminum was fixed to the positive electrode exposed part located slightly inside the outermost peripheral part of the positive electrode by spot welding. In order to prevent an internal short circuit, an insulating tape made of polypropylene was attached to the positive electrode current collector so as to cover the positive electrode lead. Thus, a positive electrode having a width of 35 mm, a length of 460 mm, and a thickness of 0.14 mm was produced.

[Production of negative electrode]
100 parts by weight of scaly graphite as a negative electrode active material, 1 part by weight (in terms of solid content) of an aqueous dispersion of a styrene-butadiene copolymer as a binder, 1% by weight of CMC as a thickener, and an appropriate amount of water Were mixed to prepare a slurry-like negative electrode mixture. Subsequently, this negative electrode mixture was applied to both surfaces of the negative electrode current collector. A copper foil having a thickness of 10 μm was used for the negative electrode current collector. An exposed portion (hereinafter referred to as “negative electrode exposed portion”) composed only of the negative electrode current collector was provided on the portion that became the outermost peripheral portion of the negative electrode without applying the negative electrode mixture. The coated negative electrode mixture was dried at 110 ° C. for 30 minutes and then rolled to form a negative electrode active material layer (negative electrode mixture layer). The thickness of each negative electrode active material layer was about 60 μm.

  Next, the negative electrode lead made of nickel was fixed to the negative electrode exposed part located slightly inside the outermost peripheral part of the negative electrode by spot welding. In order to prevent an internal short circuit, an insulating adhesive made of polypropylene was attached to the negative electrode current collector so as to cover the negative electrode lead. In this way, a negative electrode having a width of 36 mm, a length of 450 mm, and a thickness of 0.14 mm was produced.

[Production of electrode body]
As a constituent material of the electrode body, the positive electrode, the negative electrode, and two separators were used. As the separator, a polyethylene microporous film having a thickness of 16 μm was used. Each constituent material was laminated in the order of the first separator, the negative electrode, the second separator, and the positive electrode, and was wound so that the first separator was on the inside to produce a cylindrical electrode body. Subsequently, the cylindrical winding structure was crushed in one direction orthogonal to the axial direction by pressing to produce an electrode body having a flat shape.

[Preparation of square lithium ion secondary battery (test cell A1)]
For the battery case (exterior body), a packaging material made of a laminate film in which a polypropylene film (thickness 10 μm) was laminated on both surfaces of an aluminum foil (thickness 100 μm) was used. After housing the electrode body in the battery case, it was vacuum dried at 85 ° C. for 2 hours. Thereafter, the amount of water contained in the electrode body was measured with a Karl Fischer moisture meter and confirmed to be 100 ppm or less.

  For the non-aqueous electrolyte, a mixed solvent containing ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1: 2 was used as the non-aqueous solvent, and LiPF 6 was used as the electrolyte. The concentration of the electrolyte was 1.0 mol / L. After injecting this non-aqueous electrolyte into the battery case, the opening was heat sealed to prepare a test cell A1 which is a prismatic lithium ion secondary battery having a battery capacity (design value) of 800 mAh.

[Evaluation of electrode body shape]
The thickness of the test cell A1 was measured before and after charging to evaluate the degree of plastic deformation. The greater the increase in thickness after charging, the greater the amount of plastic deformation.
The thickness of the test cell A1 was measured at the center of the battery using a thickness gauge. The thickness before charging was 4.8 mm (the same applies to other examples and comparative examples).
The charging conditions are as follows.
Under an environment of 20 ° C., the battery was charged at a constant current of 800 mA (1.0 CmA) until the battery voltage reached 4.2 V, and further charged at a constant voltage until the current was attenuated to 40 mA (0.05 CmA). The charging time was about 2 hours.

[Evaluation of initial capacity]
The capacity when the battery charged under the above charging conditions was discharged at a constant current of 160 mA (0.2 CmA) until the battery voltage reached 2.5 V was defined as the initial capacity.

[Evaluation of cycle characteristics]
The charge / discharge was repeated (300 cycles), and the capacity retention rate (discharge capacity ratio) was calculated by multiplying the value obtained by dividing the discharge capacity of each cycle by the discharge capacity of the first cycle by 100.

<Example 2>
Test cell A2 was produced in the same manner as in Example 1 except that only the positive electrode exposed portion was heated for 5 seconds using a heat bar heated to 190 ° C. so that the elongation ratio of the positive electrode exposed portion was 3.0%.

<Comparative Example 1>
As in Example 1, except that an aluminum alloy foil (Alloy No. 3003; Al 98 wt%, Fe 0.6 wt%, Mn 1.4%, elongation 0.3%) was used as the positive electrode current collector. A test cell X1 was prepared.

<Comparative example 2>
Test cell X2 in the same manner as in Example 1, except that the entire positive electrode current collector was heated (190 ° C. × 1 second) so that the elongation was 2.2% before coating the positive electrode mixture. Was made.

<Comparative Example 3>
After coating and rolling the positive electrode mixture, the test cell X3 was prepared in the same manner as in Example 1 except that the entire positive electrode was heated (190 ° C. × 1 second) so that the elongation was 2.2%. did.

  Table 1 shows the evaluation results and the like. In Table 1, “elongation” means the elongation of the annealed portion. “Battery thickness” is the thickness after charging. “Plastic deformation” is a result of evaluation based on the thickness, and means that the smaller the thickness, the smaller the deformation amount. “Cyclic characteristics” was evaluated as “◯” when the sudden decrease in capacity retention rate could not be confirmed by 300 cycles, and “×” when the capacity retention rate decreased rapidly.

  As shown in Table 1, the test cells A1 and A2 of the examples had a small amount of plastic deformation after charging, and had good initial capacity and cycle characteristics. In particular, the higher the elongation percentage of the outermost peripheral portion, the more remarkable the effect of suppressing plastic deformation. On the other hand, when the elongation percentage of the outermost peripheral portion is low (test cells X1, X2), plastic deformation due to charging is large. When the entire positive electrode current collector is annealed (test cell X3), as shown in FIG. 5 (a diagram showing the relationship between the number of cycles and the capacity retention ratio), the capacity retention ratio exceeds 200 cycles. A sharp decline was confirmed. This is because the positive electrode current collector is broken at the inner peripheral side portion of the winding structure. In addition, when the entire positive electrode was annealed (test cell X4), the capacity retention rate decreased rapidly in less than 300 cycles, and the initial capacity decreased by about 2%. The decrease in the initial capacity is considered to be caused by the binder melting and covering the active material surface.

  As described above, it is possible to maintain good initial capacity and cycle characteristics by selectively heating only the outermost peripheral portion of the positive electrode to increase the elongation rate, and to suppress plastic deformation of the electrode body due to charging. Is possible.

DESCRIPTION OF SYMBOLS 10 Laminated battery, 11 Exterior body, 11a, 11b Laminated film, 12 Housing | casing part, 13 Sealing part, 14 Electrode body, 14z Outermost periphery part, 15 Positive electrode lead, 16 Negative electrode lead, 20 Positive electrode, 20z Positive electrode outermost periphery part, 21 cathode current collector, 22 electrode active material layer, 30 negative electrode, 30z Fukyokusai outer peripheral portion, 31 the anode current collector, 32 electrode active material layer, 40 separators, one end of the P ₁ outermost periphery, the other P ₂ outermost periphery end

Claims (7)

In a wound battery comprising an electrode body in which a positive electrode having a positive electrode active material layer formed on a positive electrode current collector and a negative electrode are wound through a separator,
The outermost peripheral part of the electrode body is composed of at least the positive electrode,
A wound battery in which the positive electrode outermost peripheral portion, which is the portion constituting the outermost peripheral portion of the positive electrode, has a higher elongation rate than other portions of the positive electrode. The wound battery according to claim 1,
The positive electrode outermost periphery part does not have the said positive electrode active material layer, The winding type battery comprised only with the said positive electrode electrical power collector. The wound battery according to claim 1 or 2,
The wound battery in which the elongation rate of the outermost peripheral portion is 2.2% or more and the elongation rate of the other portion is 1.5% or less. The wound battery according to claim 1 or 2,
The winding type battery in which an elongation rate of the outermost peripheral portion of the positive electrode is 1.4 times or more that of the other portion. The wound battery according to any one of claims 1 to 4,
At least a part of the outermost peripheral part of the positive electrode is a wound type battery including only the positive electrode or the positive electrode and the separator. The wound battery according to any one of claims 1 to 5,
The positive electrode current collector is a wound battery made of a metal mainly composed of aluminum. The wound battery according to any one of claims 1 to 6,
The electrode body is a wound battery having a flat shape.

Images