JP2018147677A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery which enables the increase in battery capacity while suppressing the worsening of charge and discharge rate characteristics.SOLUTION: A lithium ion secondary battery 100 is arranged by sealing a laminate 110 in an outer packaging body 120. The laminate is arranged by laminating a plurality of positive electrodes 10 each having a positive electrode active material layer including a positive electrode active material and disposed on at least one face of a first current collector and a negative electrode 20 having a negative electrode active material layer including a negative electrode active material and disposed on at least one face of a second current collector through electrolyte layers. As to the plurality of positive electrodes, one or more center-side positive electrodes 10A disposed on a side of a center Z1 of the laminate in a lamination direction Z thereof are larger than, in the amount of the positive electrode active material per unit area of the first current collector, than one or more outer-side positive electrodes 10B disposed on a side Z2 farther from the center than the one or more center-side positive electrodes in the lamination direction.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a lithium ion secondary battery.

  The lithium ion secondary battery includes a laminate, and the laminate includes a positive electrode in which a positive electrode active material layer is disposed on at least one surface of the first current collector, and at least a second current collector. A negative electrode formed by disposing a negative electrode active material layer on one surface is laminated via an electrolyte layer (see Patent Document 1).

JP 2009-272048 A

  Lithium ion secondary batteries have recently been required to have higher capacities because of their use as power sources for driving electric vehicles. There is also a need for a lithium ion secondary battery with high charge / discharge rate characteristics, that is, a lithium ion secondary battery with a small decrease in charge / discharge amount even when the charge / discharge rate is increased.

  The capacity of the battery is mainly determined by the capacity of the entire active material contained in the battery. Therefore, as a method for increasing the capacity of the battery, a method for increasing the amount of the active material contained in each of the active material layers is conceivable.

  However, when the amount of the active material contained in each of the active material layers increases, the diffusion transfer distance of lithium ions in the active material layer increases, so the overvoltage due to the lithium ion diffusion transfer increases. Therefore, there is a problem that the internal resistance of the entire lithium ion secondary battery is increased and the charge / discharge rate characteristics are deteriorated.

  In recent years, by using a material having a relatively large capacity, such as silicon, as the negative electrode active material, it has become possible to increase the capacity of the entire negative electrode active material included in the battery without increasing the amount of the negative electrode active material. It is coming.

  On the other hand, there is no high-capacity material comparable to silicon among the materials that can be used as the positive electrode active material, and in order to increase the total capacity of the positive electrode active material, the amount of the positive electrode active material must be increased. There is no situation. Therefore, the above-described problem is remarkable when trying to increase the capacity of the entire positive electrode active material included in the lithium ion secondary battery.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a lithium ion secondary battery capable of increasing the capacity of the battery while suppressing a decrease in charge / discharge rate characteristics. .

  In order to achieve the above object, a lithium ion secondary battery of the present invention includes a plurality of positive electrodes each having a positive electrode active material layer including a positive electrode active material disposed on at least one surface of a first current collector, (2) A laminate formed by laminating a negative electrode formed by disposing a negative electrode active material layer containing a negative electrode active material on at least one surface of a current collector through an electrolyte layer is sealed inside the outer package. It becomes. And the quantity of the positive electrode active material per unit area of the 1st electrical power collector in the positive electrode of the one or some center side arrange | positioned at the center side of the lamination direction of a laminated body among several positive electrodes is from the positive electrode of a center side. Is larger than the amount of the positive electrode active material per unit area of the first current collector in the plurality of outer side positive electrodes arranged on the side far from the center in the stacking direction.

  The lithium ion secondary battery according to the present invention can provide a lithium ion secondary battery capable of increasing the capacity of the battery while suppressing a decrease in charge / discharge rate characteristics.

1 is a perspective view of a lithium ion secondary battery according to Embodiment 1. FIG. It is sectional drawing which follows the 2-2 line of FIG. It is a figure which expands and shows the broken-line part 3 of FIG. It is a figure which shows the relationship between the density of the positive electrode active material per unit volume of a positive electrode active material layer, and the internal resistance of the whole battery. FIG. 4 is an enlarged cross-sectional view corresponding to FIG. 3 of a lithium ion secondary battery according to Embodiment 2. It is a figure which shows the relationship between the thickness of a positive electrode active material layer, and the internal resistance of the whole battery. It is sectional drawing corresponding to FIG. 2 of the lithium ion secondary battery which concerns on a modification.

  Hereinafter, embodiments of the present invention and modifications thereof will be described with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. The size and ratio of each member in the drawings are exaggerated for convenience of explanation and may be different from the actual size and ratio. In the figure, X indicates the short direction of the lithium ion secondary battery 100, Y indicates the longitudinal direction of the lithium ion secondary battery 100, and Z indicates the stacking direction of the stacked body 110. .

  A lithium ion secondary battery 100 according to this embodiment will be described with reference to FIGS.

  FIG. 1 is a perspective view of a lithium ion secondary battery 100 according to this embodiment. FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. FIG. 3 is an enlarged view of the broken line portion 3 of FIG. FIG. 4 is a diagram illustrating the relationship between the density ρ of the positive electrode active material per unit volume of the positive electrode active material layer 12 and the internal resistance R of the entire battery.

  With reference to FIGS. 1 to 3, the lithium ion secondary battery 100 according to the present embodiment can be summarized as follows: a positive electrode active material is placed on both surfaces 11 a and 11 b (see FIG. 3) of the first current collector 11. A negative electrode active material layer 22 containing a negative electrode active material is arranged on a plurality of positive electrodes 10 having a positive electrode active material layer 12 containing them and on both surfaces 21a and 21b (see FIG. 3) of the second current collector 21. The laminated body 110 formed by laminating the negative electrode 20 formed through the electrolyte layer 30 is sealed inside the exterior body 120 (see FIG. 2). And per unit area of the 1st electrical power collector 11 in the some positive electrode 10A of the center side (henceforth a center side positive electrode) arrange | positioned among the some positive electrodes 10 at the center side Z1 of the lamination direction Z of the laminated body 110. FIG. The amount Qa of the positive electrode active material is the first current collector in a plurality of outer positive electrodes (hereinafter referred to as outer positive electrodes) 10B disposed on the side Z2 farther from the center in the stacking direction Z than the central positive electrode 10A. 11 is larger than the amount Qb of the positive electrode active material per unit area. Hereinafter, the lithium ion secondary battery 100 according to the present embodiment will be described in detail.

<Laminate>
Referring to FIGS. 2 and 3, laminate 110 is formed by laminating positive electrode 10 and negative electrode 20 with electrolyte layer 30 interposed therebetween. In FIGS. 2 and 3, a part of the positive electrode 10, the negative electrode 20, and the electrolyte layer 30 is omitted, but the positive electrode 10, the negative electrode 20, and the electrolyte layer 30 are stacked over the entire stacking direction Z of the stacked body 110. Has been. The positive electrode 10 and the negative electrode 20 are laminated in a state of facing each other with the electrolyte layer 30 interposed therebetween. The laminate 110 is sealed inside the exterior body 120 together with the electrolytic solution.

<Electrolyte>
The kind of electrolyte solution is not specifically limited, A conventionally well-known thing can be utilized suitably. In the present embodiment, an electrolyte solution using a liquid electrolyte is used as the electrolyte solution, but an electrolyte solution using a gel electrolyte may be used.

  The liquid electrolyte is obtained by dissolving a lithium salt as a supporting salt in a solvent.

Type of lithium salt is not particularly limited, for _{example, Li (CF 3 SO 2)} 2 N, Li (C 2 F 5 SO 2) 2 N, LiPF 6, LiBF 4, LiAsF 6, LiTaF 6, LiClO 4, LiCF Conventionally known ones such as ₃ SO ₃ can be used as appropriate.

  The type of the solvent is not particularly limited. For example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate. Conventionally known materials such as (EMC) and methylpropyl carbonate (MPC) can be used as appropriate.

<Exterior body>
The exterior body 120 accommodates the stacked body 110 together with the electrolytic solution.

  The exterior body 120 is composed of a laminate sheet having a three-layer structure. The first layer corresponds to a heat-fusible resin and is formed using, for example, polyethylene (PE), ionomer, or ethylene vinyl acetate (EVA). The first layer material is adjacent to the negative electrode 20. The second layer corresponds to a metal foil formed, for example, an Al foil or Ni foil. The third layer corresponds to a resinous film and is formed using, for example, rigid polyethylene terephthalate (PET) or nylon. The third layer material is adjacent to the positive electrode 10.

<Positive electrode>
The positive electrode 10 is formed by disposing a positive electrode active material layer 12 on both surfaces 11 a and 11 b of a first current collector 11.

  The first current collector 11 has a thin film shape. The material which comprises the 1st electrical power collector 11 is not specifically limited, For example, it can be set as aluminum. A positive electrode tab 13 (see FIG. 1) for charging / discharging is connected to the first current collector 11.

The positive electrode active material layer 12 includes a positive electrode active material. Type of the positive electrode active material is not particularly limited, for example, be a LiNiCoAlO _2.

  The positive electrode active material layer 12 includes a conductive material. The kind of conductive material is not particularly limited, and can be, for example, acetylene black.

  Although the manufacturing method of the positive electrode 10 is not particularly limited, in the present embodiment, the positive electrode active material layer 12 is applied to the first current collector 11 by coating the positive electrode slurry on both surfaces 11a and 11b of the first current collector 11 and then drying. It is formed on both surfaces 11 a and 11 b of the electric body 11. The dried positive electrode active material layer 12 is pressed from both sides of the first current collector 11 while being bonded to both surfaces of the first current collector 11.

  The positive electrode slurry includes a positive electrode active material, a conductive material, a binder, and a viscosity adjusting solvent. PVDF may be used as a binder.

<Negative electrode>
The negative electrode 20 is formed by disposing a negative electrode active material layer 22 on both surfaces 21 a and 21 b of a second current collector 21.

  The second current collector 21 has a thin film shape. The material which comprises the 2nd electrical power collector 21 is not specifically limited, For example, it can be set as copper. A negative electrode tab 23 (see FIG. 1) for charging / discharging is connected to the second current collector 21.

  The area of the negative electrode active material layer 22 is larger than the area of the positive electrode active material layer 12.

  Thereby, even if the positions of the positive electrode active material layer 12 and the negative electrode active material layer 22 are relatively shifted, the facing area between the positive electrode active material layer 12 and the negative electrode active material layer 22 can be maintained constant. Therefore, it is possible to suppress a change in power generation capacity due to a change in the facing area between the positive electrode active material layer 12 and the negative electrode active material layer 22.

  The negative electrode active material layer 22 includes a negative electrode active material, and at least one of the negative electrode active materials is selected from the group consisting of silicon simple substance (Si), silicon alloy, and silicon oxide.

  Silicon has a higher lithium ion storage capacity per unit volume than graphite. Therefore, by using the above-described material for the negative electrode active material, the capacity of the entire negative electrode active material included in the lithium ion secondary battery 100 can be increased without increasing the amount of the negative electrode active material.

  The negative electrode active material layer 22 includes a conductive material. The kind of conductive material is not particularly limited, and can be, for example, acetylene black.

  Although the manufacturing method of the negative electrode 20 is not particularly limited, in the present embodiment, the negative electrode slurry is applied on both surfaces 21a and 21b of the second current collector 21 and then dried, whereby both surfaces of the second current collector 21 are dried. A negative electrode active material layer 22 is formed on 21a and 21b. The dried negative electrode active material layer 22 is pressed from both sides of the second current collector 21 while being bonded to both surfaces of the second current collector 21.

  The negative electrode slurry can include, for example, a negative electrode active material, a conductive material, a binder, and a viscosity adjusting solvent. As the negative electrode slurry, for example, a mixture of 80 wt% silicon alloy as a negative electrode active material, 5 wt% acetylene black as a conductive material, and 15 wt% polyimide as a binder can be used. NMP can be used as a solvent for adjusting the viscosity of the slurry.

<Electrolyte layer 30>
The electrolyte layer 30 has a separator.

  The separator holds the electrolyte contained in the electrolytic solution.

  The type of the separator is not particularly limited as long as the electrolyte contained in the electrolytic solution can be retained, and conventionally known separators can be appropriately used. As the separator, for example, a porous sheet separator or a nonwoven fabric separator made of a polymer or fiber that absorbs and holds the electrolyte contained in the electrolytic solution can be used.

<Positive electrode active material layer 12>
The positive electrode active material layer 12 will be further described in detail.

  The amount Qa of the positive electrode active material per unit area of the first current collector 11 in the plurality of center-side positive electrodes 10A arranged on the center side Z1 in the stacking direction Z of the stacked body 110 is larger than the center-side positive electrode 10A in the stacking direction Z. Larger than the amount Qb of the positive electrode active material per unit area of the first current collector 11 in the plurality of outer side positive electrodes 10B arranged on the side Z2 far from the center.

  In the present embodiment, the density ρ1 of the positive electrode active material per unit volume of the positive electrode active material layer 12 in the center-side positive electrode 10A is equal to the density ρ2 of the positive electrode active material per unit volume of the positive electrode active material layer 12 in the outer-side positive electrode 10B. Bigger than.

The values of the density ρ1 and the density ρ2 are not particularly limited as long as the density ρ1 is larger than the density ρ2, and can be set to be, for example, density ρ1 / density ρ2 = 1.67 to 5. The density ρ1 can be set to 3.2 to 3.9 g / cm ³ , for example. The density ρ2 can be, for example, 2.9 to 3.5 g / cm ³ .

  The method for adjusting the density ρ1 and the density ρ2 is not particularly limited. For example, when the positive electrode 10 is manufactured, by adjusting the amount of the positive electrode active material contained in the positive electrode slurry applied to the first current collector 11, The density ρ1 and the density ρ2 can be adjusted.

  In the present embodiment, the thickness h1 of the positive electrode active material layer 12 in the center-side positive electrode 10A is equal to the thickness h2 of the positive electrode active material layer 12 in the outer-side positive electrode 10B. Although the value of thickness h1 and thickness h2 is not specifically limited, For example, it may be 55-70 micrometers.

  In the present embodiment, the amount w1 of the conductive material contained in the positive electrode active material layer 12 in the center-side positive electrode 10A is smaller than the amount w2 of the conductive material contained in the positive electrode active material layer 12 in the outer-side positive electrode 10B.

  The values of the amounts w1 and w2 of the conductive material are not particularly limited as long as w1 is smaller than w2, but may be set so that, for example, w1 / w2 = 0.2 to 0.6. The amount w1 of the conductive material can be, for example, 0.5 to 3 wt%. The amount w2 of the conductive material may be 2 to 5 wt%, for example.

  The numbers of the center-side positive electrode 10A and the outer-side positive electrode 10B are not particularly limited, and can be appropriately set according to the performance required for the lithium ion secondary battery 100.

<Operation of lithium ion secondary battery>
The lithium ion secondary battery 100 is charged and discharged at a predetermined charge / discharge rate. The charge / discharge rate means the amount of electricity that is charged / discharged per unit time. Generally, when the charge / discharge rate is increased, the lithium ion secondary battery 100 has a characteristic (charge / discharge rate characteristic) in which the internal resistance increases and the amount of electricity that can be charged / discharged decreases.

  When the lithium ion secondary battery is charged and discharged, lithium ions diffuse and move in the positive electrode active material layer. As the amount of the positive electrode active material contained in the positive electrode active material layer increases, the capacity of the lithium ion secondary battery increases, while the diffusion transfer distance of lithium ions in the positive electrode active material layer increases, and the overvoltage increases. Resistance increases. For example, as shown in FIG. 4, when the amount of the positive electrode active material is increased by increasing the density of the positive electrode active material per unit volume of the positive electrode active material layer for all the positive electrodes, the internal resistance R of the entire battery increases. To do. When the internal resistance R of the entire battery increases, the charge / discharge rate characteristics deteriorate.

  Here, the heat generated inside the lithium ion secondary battery 100 is transferred from the center-side positive electrode 10A to the outer-side positive electrode 10B, and is radiated from the outer-side positive electrode 10B. For this reason, the temperature of the center-side positive electrode 10A tends to be higher than the temperature of the outer-side positive electrode 10B. When the temperature of the positive electrode 10 is high, the diffusion movement of lithium ions in the positive electrode active material layer 12 becomes easy, and thus an increase in overvoltage is suppressed.

  In the lithium ion secondary battery 100, the amount Qa of the positive electrode active material per unit area of the first current collector 11 in the center-side positive electrode 10A in which an increase in overvoltage is easily suppressed is the first current collector in the outer-side positive electrode 10B. 11 is larger than the amount Qb of the positive electrode active material per unit area. Thereby, the capacity | capacitance of a battery can be increased, suppressing the increase in the internal resistance R of the lithium ion secondary battery 100 whole. That is, the capacity of the battery can be increased while suppressing a decrease in discharge rate characteristics.

  In other words, the lithium ion secondary battery 100 is particularly effective for suppressing a decrease in charge / discharge rate characteristics in a low temperature environment.

  Specifically, as shown in FIG. 4, the increase in the internal resistance R of the entire battery when the density of the positive electrode active material contained in the positive electrode active material layer is increased for all positive electrodes is significant in a low temperature environment. Further, in a low temperature environment, the temperature difference between the center-side positive electrode 10A and the outer-side positive electrode 10B is significant, and the overvoltage of the outer-side positive electrode 10B is particularly likely to increase as compared with the center-side positive electrode 10A.

  According to the lithium ion secondary battery 100, the amount Qa of the positive electrode active material in the center-side positive electrode 10A is larger than the amount Qb of the positive electrode active material in the outer-side positive electrode 10B where the overvoltage is particularly likely to increase in a low temperature environment. Moreover, according to the lithium ion secondary battery 100, the resistance in the center-side positive electrode 10A increases due to the large amount of the positive electrode active material, and the amount of heat generated by Joule heat generation increases. And since the heat which generate | occur | produced in 10 A of center side positive electrodes is transmitted to the outer side positive electrode 10B, the temperature of the outer side positive electrode 10B becomes easy to rise, and the increase in the overvoltage of the outer side positive electrode 10B can be suppressed.

  As a result, the lithium ion secondary battery 100 is particularly effective for suppressing a decrease in charge / discharge rate characteristics in a low temperature environment in which the internal resistance R of the entire battery tends to decrease.

  Further, according to the lithium ion secondary battery 100, the amount w1 of the conductive material contained in the positive electrode active material layer 12 in the center-side positive electrode 10A is the amount of the conductive material contained in the positive electrode active material layer 12 in the outer-side positive electrode 10B. It is smaller than w2. When the amount w1 of the conductive material contained in the center-side positive electrode 10A decreases, the resistance of the center-side positive electrode 10A increases and the amount of heat generated by Joule heat generation of the center-side positive electrode 10A increases. Therefore, more heat is transferred from the center-side positive electrode 10A to the outer-side positive electrode 10B, and the temperature of the outer-side positive electrode 10B becomes higher, so that the overvoltage of the outer-side positive electrode 10B further decreases. Therefore, the lithium ion secondary battery 100 can further suppress a decrease in charge / discharge rate characteristics, particularly a decrease in charge / discharge rate characteristics in a low-temperature environment.

  Note that the amount of heat generated in the outer positive electrode 10B itself can be increased by reducing the amount w2 of the conductive material contained in the outer positive electrode 10B, so that the temperature of the outer positive electrode 10B can be increased. However, since the outer-side positive electrode 10B is in a state of being easily cooled, the temperature does not easily rise, and the overvoltage of the outer-side positive electrode 10B is hardly lowered. Therefore, from the viewpoint of improving the charge / discharge rate characteristics, the configuration of the lithium ion secondary battery 100 in which the amount w1 of the conductive material in the center-side positive electrode 10A is smaller than the amount w2 of the conductive material in the outer-side positive electrode 10B. Is advantageous.

  Further, as described above, the configuration of the lithium ion secondary battery 100 has an effect of lowering the internal resistance R, and the amount of heat generated by Joule heat generation of the entire lithium ion secondary battery 100 does not increase so much. Moreover, since the overvoltage of the positive electrode 10 decreases as the temperature of the positive electrode 10 increases, the internal resistance R decreases and the amount of heat generated by Joule heat generation decreases. That is, in the center-side positive electrode 10A, the heat generation amount decreases as the temperature increases to some extent. Therefore, the temperature of the center-side positive electrode 10A does not rise excessively.

(Action / Effect)
The lithium ion secondary battery 100 according to the present embodiment includes a plurality of positive electrodes 10 in which a positive electrode active material layer 12 including a positive electrode active material is disposed on both surfaces 11a and 11b of a first current collector 11, and a second A laminate 110 formed by laminating a negative electrode 20 in which a negative electrode active material layer 22 including a negative electrode active material is disposed on both surfaces 21 a and 21 b of a current collector 21 with an electrolyte layer 30 interposed therebetween is used as an outer package 120. Sealed inside. The amount Qa of the positive electrode active material per unit area of the first current collector 11 in the plurality of center-side positive electrodes 10A arranged on the center side Z1 in the stacking direction Z of the stack 110 among the plurality of positive electrodes 10 is the center. The amount Qb of the positive electrode active material per unit area of the first current collector 11 in the plurality of outer side positive electrodes 10B arranged on the side Z2 farther from the center in the stacking direction Z than the side positive electrode 10A is larger.

  According to such a configuration, the amount Qa of the positive electrode active material per unit area of the first current collector 11 in the center-side positive electrode 10A in which an increase in overvoltage is easily suppressed is the first current collector in the outer-side positive electrode 10B. 11 is larger than the amount Qb of the positive electrode active material per unit area. Thereby, the capacity | capacitance of a battery can be increased, suppressing the increase in the resistance of the lithium ion secondary battery 100 whole. Therefore, it is possible to provide a lithium ion secondary battery capable of increasing the capacity of the battery while suppressing a decrease in charge / discharge rate characteristics.

  In the lithium ion secondary battery 100 according to the present embodiment, the density ρ1 of the positive electrode active material per unit volume of the positive electrode active material layer 12 in the center-side positive electrode 10A is equal to that of the positive electrode active material layer 12 in the outer-side positive electrode 10B. It is larger than the density ρ2 of the positive electrode active material per unit volume.

  According to such a configuration, the amount Qa of the positive electrode active material contained in the center-side positive electrode 10A can be made larger than the amount Qb of the positive electrode active material contained in the outer-side positive electrode 10B by a simple method of changing the density. . Therefore, it becomes easy to manufacture a lithium ion secondary battery.

  Further, in the lithium ion secondary battery 100 according to this embodiment, the positive electrode active material layer 12 includes a conductive material, and the amount w1 of the conductive material included in the positive electrode active material layer 12 in the central positive electrode 10A is the outer side. It is smaller than the amount w2 of the conductive material contained in the positive electrode active material layer 12 in the positive electrode 10B.

  According to such a configuration, the amount of heat generated by Joule heat generation of the center-side positive electrode 10A increases. Therefore, more heat is transferred from the center-side positive electrode 10A to the outer-side positive electrode 10B, and the temperature of the outer-side positive electrode 10B becomes higher, so that the overvoltage of the outer-side positive electrode 10B further decreases. Accordingly, it is possible to further suppress a decrease in charge / discharge rate characteristics, particularly a decrease in charge / discharge rate characteristics in a low temperature environment.

(Embodiment 2)
In Embodiment 1 described above, the density ρ1 of the positive electrode active material per unit volume of the positive electrode active material layer 12 in the center-side positive electrode 10A is set as the positive electrode active material per unit volume of the positive electrode active material layer 12 in the outer side positive electrode 10B. By making it larger than the density ρ2, the amount Qa of the positive electrode active material in the center-side positive electrode 10A was made larger than the amount Qb of the positive electrode active material in the outer-side positive electrode 10B. However, the method of making the amount Qa of the positive electrode active material in the center-side positive electrode 10A larger than the amount Qb of the positive electrode active material in the outer-side positive electrode 10B is not particularly limited.

  For example, by making the thickness h1 of the positive electrode active material layer 12 in the center-side positive electrode 10A larger than the thickness h2 of the positive electrode active material layer 12 in the outer-side positive electrode 10B, the first current collector in the center-side positive electrode 10A. The amount Qa of the positive electrode active material per unit area of 11 may be larger than the amount Qb of the positive electrode active material per unit area of the first current collector 11 in the outer-side positive electrode 10B.

  FIG. 5 is an enlarged cross-sectional view corresponding to FIG. 3 of the lithium ion secondary battery 200 according to the present embodiment. FIG. 6 is a diagram showing the relationship between the thickness h of the positive electrode active material layer and the internal resistance R of the entire battery.

  The configuration of the lithium ion secondary battery 200 according to the present embodiment is such that the density ρ1 of the positive electrode active material per unit volume of the positive electrode active material layer 12 in the center-side positive electrode 10A is equal to that of the positive electrode active material layer 12 in the outer-side positive electrode 10B. It is equal to the density ρ2 of the positive electrode active material per unit volume, and the thickness h1 of the positive electrode active material layer 12 in the central positive electrode 10A is larger than the thickness h2 of the positive electrode active material layer 12 in the outer positive electrode 10B. The configuration is the same as that of the lithium ion secondary battery 100 according to Embodiment 1 described above. The same components as those of the lithium ion secondary battery 100 according to the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. Only the components related to the differences will be described below.

In the present embodiment, the density ρ1 of the positive electrode active material in the center-side positive electrode 10A is equal to the density ρ2 of the positive electrode active material in the outer-side positive electrode 10B. The values of the density ρ1 and ρ2 are not particularly limited, but may be, for example, 2.9 to 3.5 g / cm ³ .

  In the present embodiment, the thickness h1 of the positive electrode active material layer 12 in the center-side positive electrode 10A is larger than the thickness h2 of the positive electrode active material layer 12 in the outer-side positive electrode 10B. The values of the thickness h1 and the thickness h2 are not particularly limited as long as the thickness h1 is larger than the thickness h2, but may be set to be, for example, h1 / h2 = 1.15 to 1.45. The thickness h1 can be set to 65 to 80 μm, for example. The thickness h2 can be set to 55 to 70 μm, for example.

  Although the method in particular of controlling the thickness of the positive electrode active material layer 12 is not restrict | limited, A doctor blade method etc. are mentioned. Various methods are conceivable as a method for quantitatively obtaining the thickness of the positive electrode active material layer 12. For example, the thickness can be obtained by measurement with a micrometer or measurement of film thickness using radiation.

  Similarly to the lithium ion secondary battery 100 according to the first embodiment described above, the lithium ion secondary battery 200 according to the present embodiment can increase the capacity of the battery while suppressing a decrease in charge / discharge rate characteristics. A lithium ion secondary battery can be provided.

  As shown in FIG. 6, even when the amount of the positive electrode active material is increased by increasing the thickness h of the positive electrode active material layer for all the positive electrodes, the same as in the case of FIG. 4 described above in the first embodiment. In particular, the internal resistance R of the entire battery increases particularly in a low temperature environment. Therefore, the lithium ion secondary battery 200 according to the present embodiment has an effect that it is possible to suppress a decrease in charge / discharge rate characteristics, particularly in a low temperature environment, similarly to the lithium ion secondary battery 100 according to the first embodiment described above. is there.

  Further, according to the lithium ion secondary battery 200 according to the present embodiment, the amount Qa of the positive electrode active material included in the center-side positive electrode 10A is included in the outer-side positive electrode 10B by a simple method of changing the thickness. The amount can be larger than the amount Qb of the positive electrode active material. Therefore, it becomes easy to manufacture a lithium ion secondary battery.

(Modification example)
In the above-described embodiment, the change in the amount of the positive electrode active material is in two stages, Qa and Qb. However, the change in the amount of the positive electrode active material may be multistage.

  Specifically, as shown in FIG. 7, for the plurality of positive electrodes 10, the first positive electrode P <b> 1, the second positive electrode P <b> 2, the second positive electrode P <b> 2, and the second positive electrode P <b> 2 are arranged from the center side Z <b> 1 in the stacking direction Z toward the side Z2 far from the center in the stacking direction Z. 3 positive electrodes P3,..., N positive electrode Pn, and Qk is the amount of positive electrode active material of the k positive electrode, Q1 ≧ Q2 ≧ Q3 ≧ ... ≧ Qn, and at least one first It is only necessary that Qm> Qm + 1 for the m positive electrode.

  When the amount of the positive electrode active material is changed in three stages, Q1 = Q2 = ... = Qm> Qm + 1 = Qm + 2 = ... = Qm + k> Qm + k + 1 = Qm + k + 2 = ... = Qn.

  Further, the amount of the positive electrode active material may be varied for all the positive electrodes 10. That is, it is good also as Q1> Q2> Q3> ...> Qn.

  The method of varying the amount of the positive electrode active material may be either the method of varying the density described in Embodiment 1 or the method of varying the thickness described in Embodiment 2 or both.

  Also with the lithium ion secondary battery according to this modified example, as in the lithium ion secondary battery according to the first and second embodiments described above, the capacity of the battery is increased while suppressing a decrease in charge / discharge rate characteristics. Can be provided.

  As described above, the lithium ion secondary battery has been described through the embodiment and the modified example thereof, but the present invention is not limited to the configuration described in the embodiment and the modified example, and is based on the description of the scope of claims. It can be changed as appropriate.

  For example, in Embodiment 1 and Embodiment 2 described above, by varying either the density of the positive electrode active material or the thickness of the positive electrode active material layer 12 between the center-side positive electrode 10A and the outer-side positive electrode 10B, The amount Qa of the positive electrode active material contained in the center-side positive electrode 10A was made larger than the amount Qb of the positive electrode active material contained in the outer-side positive electrode 10B. However, the density ρ1 of the positive electrode active material per unit volume of the positive electrode active material layer 12 in the central positive electrode 10A is larger than the density ρ2 of the positive electrode active material per unit volume of the positive electrode active material layer 12 in the outer positive electrode 10B. In addition, by making the thickness h1 of the positive electrode active material layer 12 in the central positive electrode 10A larger than the thickness h2 of the positive electrode active material layer 12 in the outer positive electrode 10B, the positive electrode included in the central positive electrode 10A The amount Qa of the active material may be larger than the amount Qb of the positive electrode active material included in the outer-side positive electrode 10B.

  Moreover, in Embodiment 1 and Embodiment 2 mentioned above and its modification, the some positive electrode 10 formed by arrange | positioning the positive electrode active material layer 12 containing a positive electrode active material on both surfaces 11a and 11b of the 1st electrical power collector 11. FIG. And a negative electrode 20 in which a negative electrode active material layer 22 including a negative electrode active material is disposed on both surfaces 21a and 21b of the second current collector 21, a so-called non-hyperbolic secondary battery is taken as an example. Explained. However, the present invention provides a positive electrode in which the positive electrode active material layer 12 is disposed on the one surface 11a of the first current collector 11 and the one surface 21a of the second current collector 21, and the first current collector. 11 and a negative electrode in which a negative electrode active material layer 22 is disposed on the other surface 21b of the second current collector 21 and the so-called hyperbolic secondary battery. Is also possible.

  Furthermore, in Embodiment 1 and Embodiment 2 described above and the modifications thereof, the description has been given of the laminated secondary battery as an example. However, the present invention can also be applied to a wound secondary battery.

10 positive electrode,
10A center-side positive electrode (center-side positive electrode),
10B outer side positive electrode (outer side positive electrode),
11 First current collector,
11a, 11b surface,
12 positive electrode active material layer,
20 negative electrode,
21 Second current collector,
21a, 21b surface,
22 negative electrode active material layer,
30 electrolyte layer,
100, 200 lithium ion secondary battery,
110 laminate,
120 exterior body,
Qa The amount of the positive electrode active material of the central positive electrode,
Qb Amount of positive electrode active material on the outer side positive electrode,
Z stacking direction,
Z1 is the center in the stacking direction,
Z2 The side far from the center in the stacking direction,
w1 The amount of the conductive material of the center positive electrode,
w2 Amount of conductive material of the outer positive electrode,
ρ1 The density of the positive electrode active material of the central positive electrode,
ρ2 The density of the positive electrode active material of the outer positive electrode.

Claims (4)

A plurality of positive electrodes in which a positive electrode active material layer containing a positive electrode active material is disposed on at least one surface of the first current collector, and a negative electrode active material is included on at least one surface of the second current collector A laminate formed by laminating a negative electrode formed by arranging a negative electrode active material layer via an electrolyte layer is sealed inside the exterior body,
Among the plurality of positive electrodes, the amount of the positive electrode active material per unit area of the first current collector in one or a plurality of central positive electrodes arranged on the center side in the stacking direction is the center. Lithium ions larger than the amount of the positive electrode active material per unit area of the first current collector in the plurality of outer positive electrodes arranged on the side farther from the center in the stacking direction than the positive electrode on the side Secondary battery.   The density of the positive electrode active material per unit volume of the positive electrode active material layer in the positive electrode on the center side is higher than the density of the positive electrode active material per unit volume of the positive electrode active material layer in the positive electrode on the outer side. The lithium ion secondary battery according to claim 1, which is larger.   3. The lithium ion secondary according to claim 1, wherein a thickness of the positive electrode active material layer in the positive electrode on the center side is larger than a thickness of the positive electrode active material layer in the positive electrode on the outer side. battery. The positive electrode active material layer includes a conductive material,
The amount of the conductive material contained in the positive electrode active material layer in the positive electrode on the center side is smaller than the amount of the conductive material contained in the positive electrode active material layer in the positive electrode on the outer side. The lithium ion secondary battery of any one of -3.