JP2010232011A - Secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a secondary battery capable of absorbing a pressure due to volume expansion following expansion of a power generation element accompanying charge and discharge of the secondary battery. <P>SOLUTION: The secondary battery 10 has a positive electrode and a negative electrode laminated through a separator 102 including an electrolyte in-between. Out of the electrode plates 101, 103 of the positive electrode or the negative electrode, the electrode layers 101b, c, 103b, c of one of the electrode plates are formed in lower density than the electrode layers 101b, c, 103b, c of the other electrode plate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

    The present invention relates to a secondary battery.

There is known a secondary battery in which a positive electrode plate and a negative electrode plate laminated via a separator are covered with a heat-shrinkable resin film to suppress loosening of the electrode plate due to expansion accompanying charge / discharge of the battery (Patent Document 1).
JP-A-11-204136

  However, in the configuration of the conventional secondary battery, in order to suppress expansion due to charging / discharging, the power generation element including the electrode plate and the separator is strongly pressed and covered with the heat-shrinkable resin film, so that excessive force is applied to the power generation element. There was a risk of joining.

  Therefore, the present invention provides a secondary battery that can absorb the pressure due to volume expansion following the expansion of the power generation element accompanying charging and discharging of the secondary battery.

This invention solves the said subject by forming the electrode layer of one electrode plate among the positive electrode plates or the negative electrode plates at a lower density than the electrode layers of the other electrode plates.

According to the present invention, when the power generation element expands as the secondary battery is charged / discharged, the low-density electrode layer absorbs the pressure due to the expansion, thereby reducing the influence of the expansion on the battery structure. can do.

1 is a plan view of a secondary battery according to an embodiment of the invention. It is sectional drawing which follows the AA line of the secondary battery of FIG. It is sectional drawing of the secondary battery which concerns on other embodiment of invention. It is a graph which shows the deterioration cycle number-surface pressure characteristic of the secondary battery of Example 1, and the battery of a comparative example.

Hereinafter, embodiments of the invention will be described with reference to the drawings.
<< First Embodiment >>
FIG. 1 is a plan view of a secondary battery 10 according to an embodiment of the invention. FIG. 2 is a cross-sectional view of the secondary battery of FIG. 1, taken along the line AA.

  The secondary battery 10 according to the present embodiment is a lithium-based, flat plate, and laminated type secondary battery. As shown in FIGS. 1 and 2, two positive plates 101, four separators 102, Three negative plates 103, a positive electrode tab 104 that is a positive electrode terminal, a negative electrode tab 105 that is a negative electrode terminal, an upper exterior member 106, a lower exterior member 107, and an electrolyte not shown It consists of and. The power generation element includes a positive electrode plate 101, a separator 102, a negative electrode plate 103, and an electrolytic solution.

  The positive electrode plate 101 constituting the power generation element includes a positive electrode side current collector 101a and positive electrode layers 101b and 101c formed on part of both main surfaces of the positive electrode side current collector 101a. The positive electrode side current collector 101a of the positive electrode plate 101 is made of an electrochemically stable metal foil such as an aluminum foil, an aluminum alloy foil, a copper foil, or a nickel foil.

  The positive electrode layers 101b and 101c of the positive electrode plate 101 are made of, for example, lithium composite oxide such as lithium nickelate (LiNiO2), lithium manganate (LiMnO2), or lithium cobaltate (LiCoO2), chalcogen (S, A positive electrode active material such as Se, Te), a conductive agent such as carbon black, an adhesive such as an aqueous dispersion of polytetrafluoroethylene or polyvinylidene fluoride, and a solvent such as N-methyl-2-pyrrolidone; The mixture is applied to a part of both main surfaces of the positive electrode side current collector 101a, dried and rolled.

  The negative electrode plate 103 constituting the power generation element includes a negative electrode side current collector 103a and negative electrode layers 103b and 103c formed on both main surfaces of a part of the negative electrode side current collector 103a. The negative electrode side current collector 103a of the negative electrode plate 103 is made of an electrochemically stable metal foil such as a nickel foil, a copper foil, a stainless steel foil, or an iron foil.

  Further, the negative electrode layers 103b and 103c of the negative electrode plate 103 occlude and release lithium ions of the positive electrode active material such as amorphous carbon, non-graphitizable carbon, graphitizable carbon, or graphite. An aqueous dispersion of a styrene butadiene rubber resin powder as a precursor material of an organic fired body is mixed with the negative electrode active material, and dried and pulverized to support carbonized styrene butadiene rubber on the carbon particle surfaces. Is mixed with a binder such as an acrylic resin emulsion or polyvinylidene fluoride and a solvent such as N-methyl-2-pyrrolidone, and this mixture is mixed with both main electrodes of the negative electrode side current collector 103a. It is formed by applying to a part of the surface, drying and rolling.

  In particular, when amorphous carbon or non-graphitizable carbon is used as the negative electrode active material, the flatness of the potential during charge / discharge is poor and the output voltage decreases with the amount of discharge. This is advantageous because there is no reduction in output. The configuration of the negative electrode layers 103b and 103c will be described later.

  The separator 102 of the power generation element prevents a short circuit between the positive electrode plate 101 and the negative electrode plate 103 described above, and has a function of holding an electrolyte. This separator 102 is a microporous film made of polyolefin such as polyethylene (PE) or polypropylene (PP), for example. When an overcurrent flows, the pores of the layer are blocked by the heat generation and the current is cut off. It also has a function to

  The separator 102 according to the present embodiment is not limited to a single-layer film such as polyolefin, but may be a three-layer structure in which a polypropylene film is sandwiched between polyethylene films, or a laminate of a polyolefin microporous film and an organic nonwoven fabric. Thus, by making the separator 102 into multiple layers, various functions such as an overcurrent preventing function, an electrolyte holding function, and a separator shape maintaining (stiffness improving) function can be provided.

  The above power generation element has a configuration in which positive plates 101 and negative plates 103 are alternately stacked with separators 102 interposed therebetween. The two positive plates 101 are respectively connected to the positive electrode tab 104 made of metal foil through the positive current collector 101a. On the other hand, the three negative electrode plates 103 are similarly connected to the negative electrode tab 105 made of metal foil through the negative electrode side current collector 103a.

  In addition, the positive electrode plate 101, the separator 102, and the negative electrode plate 103 of the power generation element according to the present embodiment are not limited to the above number. For example, one positive plate 101, three separators 102, and one negative plate 103 can constitute a power generation element, and the number of positive plates 101, separators 102 and negative plates 103 can be selected as necessary. Can be configured.

Although the positive electrode tab 104 and the negative electrode tab 105 are not particularly limited as long as they are electrochemically stable metal materials, as the positive electrode tab 104, for example, an aluminum foil, Aluminum alloy foil, copper foil, nickel foil, or the like can be used. In addition, as the negative electrode tab 105, for example, a nickel foil, a copper foil, a stainless steel foil, an iron foil, or the like can be used in the same manner as the negative electrode side current collector 103a.

  By the way, in this embodiment, the electrode plates 101 and 103 are connected to the electrode terminals 104 and 105 by extending the metal foil itself constituting the current collectors 101 a and 103 a of the electrode plates 101 and 103 to the electrode terminals 104 and 105. ing. However, the metal foil constituting the current collectors 101a and 103a located between the positive electrode layers 101b and 101c and the negative electrode layers 103b and 103c and the metal foil constituting the connecting member are connected by different materials and parts. You can also.

  The power generation element is housed and sealed in the upper exterior member 106 and the lower exterior member 107. Both the upper exterior member 106 and the lower exterior member 107 in this embodiment are composed of a plurality of layers.

  About this structure, although not particularly illustrated, from a resin film excellent in electrolytic solution resistance and heat fusion properties such as polyethylene, modified polyethylene, polypropylene, modified polypropylene, or ionomer from the inside to the outside of the secondary battery 10. It has a three-layer structure consisting of an inner layer, an intermediate layer made of a metal foil such as aluminum, and an outer layer made of a resin film with excellent electrical insulation, such as a polyamide resin or a polyester resin. Yes.

  Therefore, both the upper exterior member 106 and the lower exterior member 107 are made of resin such as polyethylene, modified polyethylene, polypropylene, modified polypropylene, or ionomer on one surface of the metal foil such as aluminum foil (inner surface of the secondary battery 10). And the other surface (the outer surface of the secondary battery 10) is laminated with a polyamide resin or a polyester resin, and is formed of a flexible material such as a resin-metal thin film laminating agent.

  As described above, when the exterior members 106 and 107 include the metal layer in addition to the resin layer, the strength of the exterior member itself can be improved. Further, the inner layer of the exterior members 106 and 107 is made of a resin such as polyethylene, modified polyethylene, polypropylene, modified polypropylene, or ionomer, so that the exterior members 106 and 107 and the exterior members 106 and 107 are described later. It is possible to ensure good fusing properties with the sealing members 110 and 111 to be performed.

  As shown in FIGS. 1 and 2, the positive electrode tab 104 is led out from one end portion of the sealed exterior members 106 and 107, and the negative electrode tab 105 is led out from the other end portion. , 105, a gap is formed in the heat-sealed portion between the upper exterior member 106 and the lower exterior member 107. Sealing members 110 and 111 made of polyethylene, polypropylene, or the like are interposed at portions where the electrode tabs 104 and 105 and the exterior members 106 and 107 are in contact with each other to maintain the sealing performance inside the secondary battery 10. .

  The sealing members 110 and 111 are preferably made of the same type of resin as that constituting the exterior members 106 and 107 in both the positive electrode tab 104 and the negative electrode tab 105 from the viewpoint of thermal fusion.

  These exterior members 106 and 107 enclose the above-described power generation element, a part of the positive electrode tab 104 and a part of the negative electrode tab 105, and an organic liquid solvent is added to the space formed by the exterior members 106 and 107. While injecting a liquid electrolyte having a lithium salt such as lithium chlorate, lithium borofluoride or lithium hexafluorophosphate as a solute, the space formed by the exterior members 106 and 107 is sucked into a vacuum state, The outer peripheral ends of the members 106 and 107 are heat-sealed by hot pressing and sealed.

  The organic liquid solvent of the present embodiment uses an ester solvent such as propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC) or methyl ethyl carbonate, but is not limited to this, and is an ester solvent. In addition, an organic liquid solvent prepared by mixing and preparing an ether solvent or the like such as γ-butylactone (γ-BL) or dietoschiethane (DEE) can also be used.

  By the way, the lithium ion secondary battery which laminates | stacks a thin cell battery deteriorates by repeating charging / discharging, and an electrode layer expand | swells. This expansion of the electrode layer increases the thickness of the plurality of stacked cell batteries, and may affect the structure of the pack of lithium ion secondary batteries. In particular, when the lithium ion secondary battery is mounted as an assembled battery for a vehicle, the assembled battery is stored in a sturdy case or the like in order to withstand vibrations and the like associated with the operation of the vehicle. Therefore, since the arrangement space of the assembled battery is limited, the expanded secondary battery cannot release pressure to the outside, the internal pressure increases, and a load is applied to the internal structure of the battery.

  The secondary battery 10 of the present example has an electrode layer having a lower density than other electrode layers in the positive electrode plate or the negative electrode plate. Hereinafter, a description will be given with reference to FIG.

  In the secondary battery 10 of this example, the negative electrode plate 103 disposed in the outermost layer, that is, the negative electrode layers 103b and 103c of the upper negative electrode plate 103 and the lower negative electrode plate 103 shown in FIG. The negative electrode layers 103b and 103c have a density lower than that of the negative electrode layers 103b and 103c.

  The density of the electrode layer can be adjusted by changing the pressing pressure in the pressing step, which is the manufacturing process of the cell battery. In this example, the upper negative electrode plate 103 and the lower negative electrode plate 103 are not pressed, and the intermediate negative electrode plate 103 and the positive electrode plate 101 are respectively pressed.

  In this example, the conductive material contained in the low-density negative electrode layers 103b and 103c is made larger than the conductive material of the other non-low-density negative electrode layers 103b and 103c. The conductive material of the electrode layer has a composition that forms a conductive path by being formed at a certain high density. For this reason, the electrode layer is pressed to form a conductive path for deriving an electric charge, and the performance as a battery is maintained. On the other hand, in this example, the low-density negative electrode layers 103b and 103c are not subjected to a pressing step, but a conductive path can be secured by increasing the content of the conductive material as compared with the other negative electrode layers 103b and 103c. .

  When the secondary battery 10 of this example repeats charging and discharging, and the positive electrode layers 101b and 101c of the positive electrode plate 101 or the negative electrode layers 103b and 103c of the negative electrode plate 103 expands, the volume of the cell battery increases, especially the lamination of the electrode plates. The thickness in the direction increases. However, in the secondary battery 10 of this example, the low-density electrode layers 103b and 103c absorb the increase in the volume, so that the internal pressure of the battery can be properly maintained, and the internal structure has battery performance. Can be kept long in condition.

  In addition, when the electrode layer expands due to repeated charge and discharge, the pressure accompanying the increase in volume is transmitted from the inside of the battery to the outside, so that the pressure on the outside is higher than the inside of the battery. And the sensitivity which absorbs pressure with respect to the transmission direction of pressure is higher outside the battery than inside the battery. In this example, since the low-density negative electrode layers 103b and 103c are arranged on the outer electrode plate, the pressure due to the expansion can be absorbed more and the battery life can be extended.

  Further, in this example, the outermost electrode layer in the stacking direction of the electrode plates, that is, the negative electrode layer 103b of the upper negative electrode plate 103 and the negative electrode layer 103c of the lower negative electrode plate 103 shown in FIG. Place. When the positive electrode plate 101 and the negative electrode plate 103 of this example are laminated via a separator, the outermost electrode layer becomes a layer that does not affect the battery performance, and thus low-density negative electrode layers 103b and 103c are arranged in this layer. Thereby, even if other electrode layers expand | swell by repetition of charging / discharging and a pressure is applied to the said electrode layer of the outermost layer, it is hard to influence battery performance. Further, since the outermost electrode layer is a layer that does not affect the battery performance, the conductive path does not need to be formed and can be formed at a lower density.

  Further, in a general lithium ion battery, the conductivity of the negative electrode plate 103 is lower than the conductivity of the positive electrode plate 101. Therefore, in this example, the low density negative electrode layers 103b and 103c are disposed on the negative conductivity negative electrode plate 103, thereby minimizing the decrease in conductivity due to the low density, and the entire battery. As the capacity can be kept high.

  In this example, in order to change the density of the electrode layer, the pressure of the pressing process is adjusted while using the same material for the electrode layers 103b and 103c of the negative electrode plate 103. The density may be changed by using a material different from the material of the electrode layer. Further, the density may be changed by changing the average particle diameter of the material contained in each electrode layer or changing the particle shape.

  In the secondary battery of this example, when the plurality of negative electrode plates 103 have at least two electrode layers 103b and 103c having different densities, the electrode having the lowest density among the electrode layers 103b and 103c. The layer may be disposed on the outermost electrode plate. Thus, this example can easily absorb the expansion of the volume of the power generation element due to repeated charging and discharging of the battery.

  In addition, the low-density electrode layer is not necessarily provided on both sides of the negative electrode plate 103, and may be provided only on one side or on the positive electrode plate 101.

<< Second Embodiment >>
FIG. 3 is a secondary battery 10 according to another embodiment of the invention, and shows a cross-sectional view of the internal structure of the secondary battery as a schematic diagram. This example is the same as the first embodiment described above in that it has a low-density electrode layer, but is different in that no electrode layer is disposed on the outermost layer in the stacking direction of the electrode plates. Since the other configuration is the same as that of the first embodiment described above, the description thereof is incorporated.

  As shown in FIG. 3, in the upper negative electrode plate 201, the negative electrode layer 201c is formed only on one lower surface of the negative electrode side current collector 201a, and in the lower negative electrode plate 203, the negative electrode layer 203b is the negative electrode side current collector. It is formed only on the upper surface of 203a.

  The upper negative electrode plate 201 and the lower negative electrode plate 203 are dried without forming a negative electrode layer 201c and a negative electrode layer 203b on one side of the negative electrode side current collector 201a and the negative electrode side current collector 203a, respectively, It is formed. On the other hand, the negative electrode plate 202 in the middle stage is formed by forming the negative electrode layer 202b and the negative electrode layer 202c on both surfaces of the negative electrode side current collector 202a, and drying after the pressing step.

  Thus, the negative electrode layer 201c and the negative electrode layer 203b of the negative electrode plate 201 and the negative electrode plate 203 are formed at a lower density than the negative electrode layer 202b and the negative electrode layer 202c of the intermediate negative electrode plate 202.

  In the secondary battery 10 of this example, when the battery expands repeatedly by charging and discharging, the low-density negative electrode layer 201c and the negative electrode layer 203b absorb the pressure due to expansion, and thus the volume expansion of the entire secondary battery is suppressed, Moreover, the pressure applied to the electrode layer and the current collector inside the battery can be relaxed.

  Also, in the secondary battery, different from this example, when an electrode layer that is not low density and is formed through a pressing process by applying an electrode layer to one side of the current collector is disposed on the outermost electrode plate, the outermost layer The electrode plate is bent during the pressing process, affecting the laminate of the secondary battery. That is, when the electrode layer is applied on both sides of the current collector, the pressure applied by the pressing step is evenly applied on both sides during the pressing step, but the electrode layer is applied only on one side of the current collector like the outermost layer. In the case of application, the pressure applied by the pressing process is different between the main surface of the current collector and the main surface of the electrode layer, so that the electrode plate is curved. In particular, the edge portion of the electrode plate is curled because it does not have an electrode layer.

In this example, in the secondary battery 10 in which the electrode plates are stacked, the negative electrode plate 201 and the negative electrode plate 203 each having a low-density electrode layer are arranged in the outermost layer, so that the negative electrode plate 201 and the negative electrode plate 203 are prevented from being bent. it can. Further, in this example, since the negative electrode plate 201 and the negative electrode plate 203 having low-density electrode layers are formed in the outermost layer and are not pressed, curling of the negative electrode plate 201 and the negative electrode plate 203 or curl generated at the edge portion of the electrode plate Can be prevented.

  In this example, the electrode plate disposed in the outermost layer forms an electrode layer only on one side of the current collector, and one side of the current collector that does not contribute to the battery reaction has an electrode layer. The thickness of the battery can be reduced, and the weight and cost of the battery as a whole can be reduced.

  In the secondary battery of this example, when the plurality of negative electrode plates 103 have at least two electrode layers 103b and 103c having different densities, the electrode having the lowest density among the electrode layers 103b and 103c. The layer may be disposed on the outermost electrode plate. Thus, this example can easily absorb the expansion of the volume of the power generation element due to repeated charging and discharging of the battery.

  In the secondary battery 10 of this example, the low-density negative electrode plate 201 and the negative electrode plate 203 are disposed in the outermost layer, but the positive electrode plate may be disposed in the outermost layer to form a low-density electrode layer.

"Example"
Hereinafter, although this invention is demonstrated based on a more detailed Example, this invention is not limited to these Examples. Also, in this example, an example of confirming the effect of the secondary battery 10 according to the first embodiment will be described.

(Positive electrode plate)
Anhydrous NMP (N-methyl-2-pyrrolidone) having a purity of 99.9% was put into a dispersing mixer, and then polyvinylidene fluoride (PVdF) was put into the mixer, which was sufficiently dissolved in NMP. Then, after adding a positive electrode active material and a conductive support agent little by little and fully disperse-mixing, NMP was added and the viscosity was adjusted and the slurry A was obtained. The compounding material at this time uses lithium manganese composite oxide (average particle diameter 10 μm) as the positive electrode active material, acetylene black as the conductive auxiliary agent, and polyvinylidene fluoride (PVdF) as the binder component, and the compounding ratio is the positive electrode active material. : Conductive aid: Binder = 84: 10: 6. The positive electrode active material coating slurry A prepared above was applied to both surfaces of an aluminum foil (thickness: 20 μm) as a positive electrode current collector by a doctor blade method and dried on a hot plate to obtain a positive electrode plate. . Next, the positive electrode plate was pressed with a load of 10 t or less using a roll press machine to obtain a positive electrode plate 101. The density g / cm 3 of the positive electrode plate 101 is 1.55 g / cm 3.

(Negative electrode plate)
85% by mass of hard carbon having an average particle size of 9 μm as a negative electrode active material, 5% by mass of vapor grown carbon fiber (VGCF: registered trademark) as a conductive additive, and 10% by mass of polyvinylidene fluoride (PVDF) as a binder An appropriate amount of N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, was added to the solid content consisting of to prepare slurry B for negative electrode active material coating. The negative electrode active material coating slurry B prepared above was applied onto a copper foil (thickness: 15 μm) as a negative electrode current collector by a doctor blade method and dried on a hot plate to obtain a negative electrode plate 101. It was. Next, the negative electrode plate 101 was pressed with a load of 10 t or less using a roll press machine to obtain a negative electrode plate 103. Here, the negative electrode plate 103 that has not been subjected to the pressing step becomes the low-density negative electrode plate 103. The density of the low density negative electrode plate 103 was 1.05 g / cm 3, and the density of the non-low density negative electrode plate 103 was 1.55 g / cm 3.

(Electrolyte)
Ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate were mixed at a volume ratio of 2: 2: 6 to obtain a plasticizer (organic solvent) of the electrolytic solution. Next, lithium hexafluorophosphate (LiPF ₆ ), which is a lithium salt, was added to the plasticizer so as to have a concentration of 1 mol / liter to prepare an electrolytic solution.

(Secondary battery of Example 1)
The unit cell A in which the lithium ion battery separator 102 is sandwiched between the positive electrode plate 101 and the low density negative electrode plate 103 that are produced as described above, and the lithium ion battery separator is opposed to the positive electrode plate 101 and the negative electrode plate 103. A unit cell B was formed so as to be sandwiched between them. Next, a laminated body in which one single cell A and 14 single cells B were laminated was formed. Further, a lithium ion battery separator 102 was sandwiched between the positive electrode layer 101 b and the negative electrode plate 103 which are the outermost layers of the laminate, thereby forming a laminate. Thereafter, the obtained laminate was covered with a laminate pack and sealed by heat welding, and the secondary battery 10 of Example 1 was produced.

(Secondary battery of Comparative Example 1)
A laminate in which 15 unit cells B were laminated was formed. Further, a lithium ion battery separator 102 was sandwiched between the positive electrode layer 101 b and the negative electrode plate 103 which are the outermost layers of the laminate, thereby forming a laminate. Thereafter, the obtained laminate was covered with a laminate pack and sealed by heat welding, and a secondary battery of Comparative Example 1 was produced.

(Evaluation methods)
The secondary battery 10 of Example 1 and the secondary battery of Comparative Example 1 are sandwiched using jigs for fixing the thickness, and the secondary battery is repeatedly charged and discharged, and the external surface of the secondary battery due to deterioration swelling The pressure of was measured.

  The evaluation results are shown in Table 1 and FIG. The number of deterioration cycles indicates the number of times the battery is charged / discharged. FIG. 4 is a graph showing characteristics of the generated surface pressure with respect to the number of deterioration cycles of the secondary batteries of Example 1 and Comparative Example 1.

（考察）
表１及び図４より、本例に係る二次電池１０は比較例１に係る二次電池と比較すると、電池の充放電の繰り返しにより電池内部の膨れにより生じる圧力が小さい。特に、劣化サイクルが１０００回以上では、実施例１と比較例１の間で、発生面圧の差が大きくなる。これにより本例は、充放電による電極層の膨張を抑制し、電池内部へ加わる圧力を軽減し、電池を延命できることが確認された。

(Discussion)
From Table 1 and FIG. 4, when compared with the secondary battery according to Comparative Example 1, the secondary battery 10 according to this example has a smaller pressure generated due to swelling inside the battery due to repeated charging and discharging of the battery. In particular, when the deterioration cycle is 1000 times or more, the difference in generated surface pressure between Example 1 and Comparative Example 1 increases. Thereby, it was confirmed that this example can suppress the expansion | swelling of the electrode layer by charging / discharging, reduce the pressure added to the inside of a battery, and can extend a battery life.

DESCRIPTION OF SYMBOLS 10 ... Secondary battery 101 ... Positive electrode plate 101a ... Positive electrode side collector 101b, c ... Positive electrode layer 102 ... Separator 103 ... Negative electrode plate 103a ... Negative electrode side collector 103b, c ... Negative electrode layer 104 ... Negative electrode tab 105 ... Negative electrode Electrode tab 106 ... Upper exterior member 107 ... Lower exterior member 110 ... Seal member 111 ... Seal members 201, 202, 203 ... Negative electrode plate 201a, 202a, 202a ... Negative electrode side current collector 201b, c ... Negative electrode layer 202b, c ... Negative electrode Layer 203b, c ... negative electrode layer

Claims (10)

In a secondary battery in which these are laminated via a separator containing an electrolytic solution between a positive electrode and a negative electrode,
Of the positive electrode plate or the negative electrode plate, an electrode layer of one electrode plate is formed at a lower density than an electrode layer of another electrode plate. The positive or negative electrode plate has the electrode layer mainly composed of an electrode active material on both sides of a current collector,
The secondary battery according to claim 1, wherein the electrode layer formed on one surface of the current collector is formed at a density lower than that of the electrode layer formed on the other surface of the current collector. The secondary battery according to claim 1, wherein the low-density electrode layer is disposed on the outermost side with respect to the stacking direction of the electrode plates. 2. The secondary according to claim 1, wherein the electrode plate disposed on the outermost side with respect to the stacking direction of the electrode plates has the low-density electrode layer only on one surface of the current collector. battery. 5. The secondary battery according to claim 1, wherein the conductive material contained in the low-density electrode layer is contained in a larger amount than the conductive material contained in the other electrode layer. The secondary battery according to claim 1, wherein the material included in the low-density electrode layer is formed of a material different from a material included in the other electrode layer. The secondary battery according to claim 1, wherein the low-density electrode layer is formed on a negative electrode plate. The secondary battery according to any one of claims 1 to 7,
Having one electrode plate of the plurality of positive electrodes or negative electrodes,
The low-density electrode layer is an electrode layer having the lowest density among the electrode layers of one of the plurality of positive and negative electrode plates, and is disposed on the outermost electrode plate. Secondary battery. An assembled battery using the battery according to any one of claims 1 to 8. A vehicle equipped with the battery according to any one of claims 1 to 9 as a motor driving power source.

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