JP2011023249A - Secondary battery, battery pack - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a secondary battery capable of suppressing unevenness of heat generation of a current collector in an in-plane direction. <P>SOLUTION: A cathode current collector 11 is formed of cathode conductive layers 111 (conductive material) on both surfaces of a reinforcing layer 140. The cathode conductive layer 111 is formed to become thicker in thickness from a first end part 112 side toward a second end part 113 side opposite to the first end part 112. Then, a cathode terminal lead 20 connecting electrically a cathode current collector tab 18 is connected with the second end part 113 side. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a secondary battery and an assembled battery using the secondary battery.

  The secondary battery has a current collector for forming and holding an active material and collecting current. Conventionally, as this current collector, there is one in which a reinforcing portion is integrally formed on an electrolytic foil having a large number of mesh holes (Patent Document 1).

JP 2000-285926 A

  By the way, the current collector is connected to a current collecting tab for taking out current from the current collector. The thickness of the electrolytic foil used for the conventional current collector is uniform in the in-plane direction. Therefore, the resistance value is substantially the same from the end where the current collecting tab is connected to the opposite end side. For this reason, the current collected from the entire surface of the current collector is concentrated around the current collector tab connection portion. Then, current concentrates around the current collecting tab connection end, so that heat generation is relatively greater than the opposite end side. On the other hand, there is little heat generation on the opposite side of the current collecting tab connection end where there is no current concentration. Such a bias of heat generation in the surface of the current collector may lead to a decrease in battery performance and a decrease in durability.

  Accordingly, an object of the present invention is to provide a secondary battery that suppresses the bias of heat generation in the in-plane direction of the current collector.

  To achieve the above object, the present invention is configured as follows.

  The secondary battery according to the present invention includes a first current collector having a positive electrode active material layer formed thereon, and a negative electrode active material layer disposed at a position facing the positive electrode active material layer with an electrolyte layer interposed therebetween. A second current collector. The mass of at least one of the first current collector and the second current collector is such that the mass per unit area increases from the first end to the second end facing the current collector. A sloped conductive material is included, and a current collecting tab is electrically connected to the second end portion side.

  Further, the secondary battery of the present invention includes a first current collector on which a positive electrode active material layer is formed and a negative electrode active material layer disposed at a position facing the positive electrode active material layer with an electrolyte layer interposed therebetween. And a second current collector formed. At least one of the first current collector and the second current collector is provided with a conductive material whose sheet resistance decreases from the first end to the second end facing the current collector. A current collecting tab is electrically connected to the second end portion side.

  According to the present invention, in at least one of the positive electrode current collector and the negative electrode current collector, the mass is increased from the first end side to the second end direction opposite to the first end side, A current collecting tab is electrically connected to the second end side. Therefore, current easily flows on the second end side where current concentration occurs, and heat generation at that portion can be suppressed, so that uneven heat generation in the in-plane direction of the current collector can be suppressed.

  Further, according to the present invention, in at least one of the positive electrode current collector and the negative electrode current collector, the sheet resistance decreases from the first end side toward the second end portion on the opposite side. Thus, the current collecting tab is electrically connected to the second end portion side. Therefore, current on the second end side where current concentration occurs easily flows, and heat generation at that portion is suppressed, so that the bias of heat generation in the in-plane direction of the current collector can be suppressed.

It is an external view which shows the external appearance of the secondary battery of embodiment. FIG. 3 is a cross-sectional view for explaining the secondary battery according to the first embodiment. It is explanatory drawing for demonstrating the positive electrode electrical power collector of Embodiment 1, FIG. 3A is a top view, FIG. 3B is sectional drawing which follows the AA line in FIG. 3A. FIG. 4A is an external view of a typical embodiment of an assembled battery composed of secondary batteries, FIG. 4A is a plan view of the assembled battery, FIG. 4B is a front view of the assembled battery, and FIG. 4C is a side view of the assembled battery. It is. It is a figure for demonstrating the example of the vehicle carrying a secondary battery. 5 is a cross-sectional view of a main part for explaining a secondary battery according to Embodiment 2. FIG. 6 is an explanatory diagram for explaining a case where a conductor penetrates the secondary battery of Embodiment 2 from the outside. FIG. 5 is a cross-sectional view of a main part for explaining a secondary battery according to Embodiment 3. FIG. FIG. 6 is a cross-sectional view of a main part for explaining a secondary battery according to a fourth embodiment. It is explanatory drawing for demonstrating the positive electrode electrical power collector of Embodiment 4, FIG. 10A is a top view, FIG. 10B is sectional drawing which follows the AA line in FIG. 10A. It is sectional drawing. It is explanatory drawing for demonstrating the positive electrode electrical power collector of Embodiment 5, FIG. 11A is a top view, FIG. 11B is sectional drawing.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, elements having the same function are denoted by the same reference numerals, and redundant description is omitted. Further, since the drawings are only for explaining the embodiments of the present invention, the dimensions and ratios of the respective members are exaggerated or simplified for convenience of explanation, and are different from the actual dimensions and ratios.

[Embodiment 1]
Hereinafter, as a first embodiment to which the present invention is applied, a lithium ion secondary battery will be described as an example, but the technical scope of the present invention is not limited to only the following embodiments.

(Secondary battery)
FIG. 1 is an external view showing the external appearance of the secondary battery of the present embodiment, and FIG. 2 is a cross-sectional view for explaining the secondary battery of the present embodiment.

  As shown in FIGS. 1 and 2, the secondary battery 1 (lithium ion secondary battery) of the present embodiment is sealed by a battery exterior material 22 that houses a power generation element 17 (details will be described later). The battery exterior material 22 uses a polymer-metal composite laminate film, and the entire periphery thereof is joined by thermal fusion.

  Specific components of the power generation element 17 are as follows.

  The power generation element 17 has a configuration in which a plurality of unit cell layers 16 including the positive electrode active material layer 12, the electrolyte layer 13, and the negative electrode active material layer 15 are stacked. The positive electrode active material layer 12 is formed on both surfaces of a single positive electrode current collector 11 containing a conductive material (for example, a first current collector). A material in which the positive electrode active material layers 12 are formed on both surfaces of the positive electrode current collector 11 is referred to as a positive electrode 100 (for example, a first electrode). The negative electrode active material layer 15 is formed on both surfaces of a negative electrode current collector 14 (for example, a second current collector) containing a conductive material. A material in which the negative electrode active material layer 15 is formed on both surfaces of the negative electrode current collector 14 is referred to as a negative electrode 200 (for example, a second electrode).

  Here, the positive electrode 100, the electrolyte layer, and the positive electrode active material layer 12 on one side of the positive electrode current collector 11 and the negative electrode active material layer 15 on one side of the negative electrode current collector 14 adjacent to each other face each other through the electrolyte layer 13. 13 and the negative electrode 200 are stacked in this order, so that a plurality of single battery layers 16 are stacked and the single battery layers 16 are electrically connected in parallel.

  Outermost layer negative electrode current collectors 14 a are located in both outermost layers of the power generation element 17. Since the outermost negative electrode current collector 14a does not face the positive electrode and does not participate in the battery reaction, the negative electrode active material layer 15 is formed only on the inner surface of the power generation element. Depending on the number of stacked unit cell layers 16, the outermost layer having the positive electrode active material layer 12 formed on one surface of the positive electrode current collector may be used.

  One end of each of the positive electrode current collector 11 and the negative electrode current collector 14 is electrically joined to the positive electrode current collector tab 18 and the negative electrode current collector tab 19 via the positive electrode terminal lead 20 and the negative electrode terminal lead 21. The positive electrode current collector 11 and the negative electrode current collector 14 are partly exposed to the outside of the battery outer packaging material 22 through heat fusion with the laminate film, and the electric power from the power generation element 17 is taken out to the outside. It becomes a terminal for charging the power generation element 17. As will be described later, this terminal is also used when a plurality of secondary batteries 1 are connected to each other by a bus bar, a lead wire or the like (referred to as connecting terminal 25) to form an assembled battery 300.

  In addition, soldering, welding, ultrasonic bonding, etc. are used for the connection of the positive electrode terminal lead 20 and the negative electrode terminal lead 21 in the positive electrode current collector 11 and the negative electrode current collector 14. Similarly, soldering, welding, ultrasonic bonding, or the like is used to connect the positive terminal lead 20 and the negative terminal lead 21 to the positive current collecting tab 18 and the negative current collecting tab 19.

  3A and 3B are explanatory views for explaining the positive electrode current collector 11, FIG. 3A is a plan view, and FIG. 3B is a cross-sectional view taken along line AA in FIG. 3A.

  The positive electrode current collector 11 has a structure in which a positive electrode conductive layer 111 (conductive material) is formed on both surfaces of a reinforcing layer 110 (resin layer) made of a nonconductive material. That is, the reinforcing layer 110 is disposed along the positive electrode current collector 11. In the first embodiment, the negative electrode current collector 14 is not changed in thickness, and is a single plate having a uniform thickness (for example, a metal foil film such as aluminum or copper).

  Only the positive electrode conductive layer 111 (which means one of the two layers sandwiching the reinforcing layer 110 shown in FIG. 3 is hereinafter referred to as the positive electrode conductive layer 111 has the same meaning) as the positive electrode current collector 11. Mechanical strength may be weakened. By using the reinforcing layer 110, the mechanical strength of the positive electrode current collector 11 as a whole can be increased. Thereby, the tolerance with respect to the mechanical load at the time of the assembly | attachment of the electric power generation element 17 becomes high, for example, and manufacture becomes easy. In addition, resistance to mechanical stress accompanying expansion and contraction of the battery constituent member accompanying the thermal load during battery operation is increased, and durability as a secondary battery can be increased.

  The shape of the positive electrode conductive layer 111 is linearly inclined so as to increase the thickness of the positive electrode conductive layer 111 from the first end 112 to the second end 113 on the opposite side in the plane. Forming. Further, the positive electrode conductive layer 111 and the positive electrode current collecting tab 18 are electrically connected by connecting the positive electrode terminal lead 20 to the second end portion 112.

  On the other hand, in the first embodiment, the negative electrode current collector 14 is not changed in thickness, and is a single plate having a uniform thickness (for example, a metal foil film such as aluminum or copper).

  In this way, by changing the thickness of the positive electrode conductive layer 111, the mass per unit area on the active material forming surface of the positive electrode conductive layer 111 is made to be a gradient, and the electric resistance equivalent to that of the positive electrode active material layer 12 per unit area is obtained. It is trying to become. By doing in this way, in the active material formation surface of the electroconductive layer 111, sheet resistance becomes low from the 1st edge part 112 to the 2nd edge part 113 direction. In other words, the current flows more easily from the first end 112 to the second end 113.

  Therefore, if it cuts out so that it may become a fixed area in the position of the dotted lines af shown to FIG. 3A, the mass will be a> b> c> d> e> f. Similarly, if the sheet resistance of a certain area is measured at the positions of dotted lines a to f, a <b <c <d <e <f. In the present embodiment, the same mass and the same sheet on each of the dotted lines a to f, that is, in a direction orthogonal to the direction from the first end 112 to the second end 113 (directions of the dotted lines a to f). Resistance.

  Incidentally, the relationship between the sheet resistance and the thickness of the member is as shown in the following equations (1) and (2).

R = (ρL) / (tW) = Rs · (ρL) / W (1)
Therefore, Rs = ρ / t (2)
In each formula, R is a resistance value, Rs is a sheet resistance, t is a thickness, W is a width, and L is a length.

  From the equation (2), it can be seen that if the thickness t of the member changes, the sheet resistance changes, and the ease of current flow changes.

  The positive electrode conductive layer 111 is preferably as thin as possible. The reason is as follows. Secondary batteries may cause internal short circuits for various reasons. The reason why the internal short circuit occurs is, for example, the inclusion of conductive foreign matter or the growth of dendrites on the positive electrode current collector or the negative electrode current collector. If an internal short circuit occurs in such a battery, if the positive electrode conductive layer 111 is made very thin, the current is heated and burned out due to current concentration due to the internal short circuit, and the current in the part is stopped. be able to. In order to have such an action, for example, aluminum is preferably 10 μm or less. The lower limit value (the first end 112 portion that is the thinnest) is not particularly limited, and may be a minimum thickness that allows current to flow. In particular, in the case of the first embodiment, since the reinforcing layer 110 is provided, there is no problem as long as the current can flow even if the metal thin film is thin enough that the shape cannot be maintained.

  Further, even when such a very thin metal film is used, the function necessary as a current collector, that is, the charge / discharge rate can be secured, as already described, the mass gradient and the sheet are formed on the conductive layer 111. A resistance gradient was added.

  The positive electrode current collector 11 is not particularly limited in the material constituting it, and a conductive resin can be adopted in addition to the above-described metals. In the case of using a metal, for example, copper or stainless steel can be used in addition to the above aluminum. Of these, aluminum is preferable from the viewpoint of electron conductivity and battery operating potential.

  On the other hand, in the case of a conductive resin, any of a conductive polymer in which the entire resin is conductive and a nonconductive material mixed with a conductive filler may be used. More specifically, it is as follows.

(Form in which the polymer material is a conductive polymer)
First, a mode in which the polymer material constituting the resin is a conductive polymer will be described. In this case, the entire positive electrode conductive layer 111 is made of a conductive polymer material.

  The conductive polymer is selected from materials that are conductive and that are not conductive with respect to the ions used as the charge transfer medium. These conductive polymers are considered to be conductive because the conjugated polyene system forms an energy band. As a typical example, a polyene-based conductive polymer that has been put into practical use in an electrolytic capacitor or the like can be used. Specifically, polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, polyoxadiazole, or a mixture thereof is preferable. Polyaniline, polypyrrole, polythiophene, and polyacetylene are more preferable from the viewpoints of electron conductivity and stable use in the battery.

(Form including non-conductive resin and conductive material (conductive filler))
Next, the form which contains a conductive filler in nonelectroconductive resin is demonstrated. In this case, the entire positive electrode conductive layer 111 is obtained by uniformly blending a non-conductive resin with a conductive filler and forming a conductive resin as a whole.

  The conductive filler is selected from materials having conductivity. Preferably, from the viewpoint of suppressing ion permeation in the resin layer having conductivity, it is desirable to use a material that does not have conductivity with respect to ions used as the charge transfer medium.

  Specific examples of the conductive filler include aluminum materials, stainless steel (SUS) materials, carbon materials such as graphite and carbon black, silver materials, gold materials, copper materials, and titanium materials, but are not limited thereto. is not. These conductive fillers may be used alone or in combination of two or more. Moreover, these alloy materials may be used. Silver material, gold material, aluminum material, stainless steel material, carbon material is preferable, and carbon material is more preferable. These conductive fillers may be those obtained by coating a conductive material (the above conductive filler) with a plating or the like around a particulate ceramic material or resin material.

  In addition, the shape (form) of the conductive filler may be used in the form of particles, but is not limited to the form of particles, but in a form other than the form of particles practically used as a so-called filler-based conductive resin composition such as carbon nanotube. There may be.

  The average particle diameter of the conductive filler is not particularly limited, but is preferably about 0.01 to 10 μm in consideration of the thickness when formed on the positive electrode conductive layer 111. That is, when the thickness of the positive electrode conductive layer 111 is set to a maximum value of 10 μm, if a conductive filler larger than this is used, the conductive filler exceeds the thickness of the positive electrode conductive layer 111, and the local This is not preferable because it causes variations in thickness. Of course, if the thickness of the positive electrode conductive layer 111 is increased, the conductive filler may be 10 μm or more.

  In the case where the resin layer includes a conductive filler, the resin forming the resin layer may include a non-conductive polymer material that binds the conductive filler in addition to the conductive filler. By using a polymer material as the constituent material of the resin layer, the binding property of the conductive filler can be improved and the reliability of the bipolar secondary battery can be improved. The polymer material is selected from materials that can withstand the applied positive electrode potential and negative electrode potential.

  Examples of polymer materials that are non-conductive resins are preferably polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide (PI), polyamide (PA). , Polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), An epoxy resin or a mixture thereof can be used. These materials have a very wide potential window and are stable to both positive and negative electrode potentials. In addition, since it is lightweight, it is possible to increase the output density of the secondary battery.

  The ratio of the conductive filler to the non-conductive resin is not particularly limited as long as sufficient conductivity is ensured. For example, 5 to 90 wt%, preferably 5 to 40 wt% of the conductive filler is uniformly blended with respect to the total of the polymer material (including the nonconductive resin and other additives) and the conductive filler. . If it is about 5-90 wt%, electroconductivity can be ensured.

  Moreover, when a binder is put in the resin component, the binding property can be improved by preferably setting the amount to about 5 to 40 wt%, and the form (shape) is stabilized.

  The binder polymer used as the binder is not particularly limited. For example, the following polymer materials can be used. Epoxy resin; styrene-ethylene-butylene-styrene block copolymer (SEBS); acrylonitrile-butadiene-styrene copolymer (ABS); synthetic rubber materials such as styrene butadiene rubber (SBR), polyethylene (PE), polypropylene Polyolefins such as (PP); Polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); Silicones, polyimides (PI); Polyamides (PA); Polyvinylidene fluoride (PVdF); Polytetrafluoroethylene (PTFE); Examples include polyacrylonitrile (PAN); polymethyl acrylate (PMA); polymethyl methacrylate (PMMA); polyvinyl chloride (PVC). These polymer materials may be used alone or in combination of two.

  In addition to the conductive filler and non-conductive resin, other additives may be included.

  The positive electrode conductive layer 111 made of these conductive resins can be manufactured by a conventionally known method (both forms in which the polymer material is a conductive polymer and forms in which a non-conductive resin includes a conductive filler). For example, the method of preparing the slurry of the nonelectroconductive polymer containing a conductive polymer material or a conductive filler, and apply | coating and hardening this is mentioned. Specifically, for example, the slurry adjusted by a spray method or a coating method is applied smoothly or stepwise by changing the thickness by changing the number of coatings or using nozzles having different opening diameters. It can also be manufactured by an ink jet method.

  Next, the reinforcing layer 110 has a minimum thickness or more according to the mechanical strength of the material to be used. However, since the volume of the power generation element 17 becomes larger than necessary even if it is too thick, for example, when a resin is used, it is preferable that the thickness of the reinforcing layer 110 is 10 to 30 μm.

  The reinforcing layer 110 is formed so that the thickness thereof is opposite to the thickness gradient of the positive electrode conductive layer 111. Thereby, the thickness as the positive electrode current collector 11 can be kept constant, and the thickness as the single battery layer 16 is also kept constant, and the single battery layer 16 is obliquely laminated when the power generation element 17 is assembled. Can be avoided.

  Examples of the material constituting the reinforcing layer 110 include an insulating material such as ceramic and a composite of ceramic and resin in addition to the resin. Among these, from the viewpoint of reducing the weight of the reinforcing layer, the constituent material of the reinforcing layer is preferably a resin. Although this resin is not particularly limited, for example, polyimide (PI), polyethylene terephthalate (PET), polyacrylonitrile (PAN), polypropylene (PP), polyethylene (PE) and the like can be used. Among these, from the viewpoint of heat resistance, polyimide or polyethylene terephthalate is preferable, and polyimide is particularly preferable. A specific name for polyimide is Kapton (registered trademark).

  In addition, about the positive electrode active material, negative electrode active material, and electrolyte which are used for the secondary battery of this embodiment, what is necessary is just to use the substance normally used for a lithium ion secondary battery, and description is abbreviate | omitted. Needless to say, when a secondary battery other than the lithium ion secondary battery is used as the secondary battery of this embodiment, a material matched to the secondary battery may be used.

(Battery)
Next, an assembled battery which is one of the usage forms of the secondary battery described above will be described.

  4A and 4B are external views of a typical embodiment of the assembled battery including the secondary battery described above. FIG. 4A is a plan view of the assembled battery, FIG. 4B is a front view of the assembled battery, and FIG. FIG. 3 is a side view of the assembled battery.

  As shown in FIG. 4, in the assembled battery 300, first, a plurality of the secondary batteries described above are connected in series and in parallel to form an assembled battery 250, and further, the plurality of assembled batteries 250 are connected in series and in parallel. ing. As a result, the assembled battery 300 is suitable for a vehicle driving power source and an auxiliary power source that require high volume energy density and high volume output density.

  The assembled batteries 250 are connected to each other using an electrical connection means such as a bus bar, and are stacked in multiple stages using a connection jig 310. The assembled battery 250 can be attached to and detached from the assembled battery 300 because the assembled battery 250 is attached by the connecting jig 310. The number of assembled batteries 250 to be incorporated into the assembled battery 300 and the connection form (in series or parallel) may be determined according to the battery capacity and output required by the vehicle (electric vehicle or the like) on which the battery is mounted.

  The same applies to the connection form (in series or parallel) of the individual secondary batteries 1 when configuring the assembled battery 250, and may be determined according to the desired output voltage and battery capacity.

(vehicle)
Next, mounting on a vehicle, which is one of the usage forms of the secondary battery described above, will be described.

  FIG. 5 is a diagram for explaining an example of a vehicle equipped with the above-described secondary battery.

  The secondary battery of this embodiment can be assembled in the form of the above-described assembled battery 300, for example, and mounted on a vehicle such as an electric vehicle 400 as shown in FIG. The secondary battery mounted on the electric vehicle 400 can be used as a power source for driving a vehicle motor, for example.

  In the example of the electric vehicle 400 shown in the figure, the assembled battery 300 is mounted under the seat at the center of the vehicle body of the electric vehicle 400. This is because if it is installed under the seat, the interior space and the trunk room can be widened. The place where the assembled battery 300 is mounted is not limited to the position under the seat, but may be a lower part of the rear trunk room or an engine room in front of the vehicle.

  According to the first embodiment described above, the following effects can be obtained.

  The positive electrode current collector 11 of this embodiment has a structure in which the positive electrode conductive layer 111 is bonded to one side or both sides of the reinforcing layer 110. The positive electrode conductive layer 111 was given a mass gradient so that the mass increased from the first end 112 toward the second end 113 opposite to the first end 112. Specifically, the thickness increases from the first end 112 toward the second end 113. Therefore, the positive electrode conductive layer 111 has a low sheet resistance from the first end 112 toward the second end 113, and current flows easily.

  As a result, the electrical resistance value becomes relatively smaller and the heat capacity can be kept large as it goes from the first end 112 side to the second end 113 side. Therefore, when the electric power is taken out from the secondary battery 1 and charged, the current can flow with a margin on the side where the positive current collecting tab 18 where the current is concentrated is connected. As a result, only the side where the positive current collecting tab 18 is connected and the current is concentrated does not generate heat relatively, and the battery as a whole is less likely to increase in temperature. Therefore, the secondary battery has little loss during charging / discharging due to heat generation.

  Further, with this configuration, a sufficient charge / discharge rate can be ensured, and charge / discharge characteristics are improved.

  Further, when the thickness of the positive electrode conductive layer 111 is set to a thickness that can be burned out due to a rise in temperature when a short circuit occurs inside the secondary battery, durability during anomalous resistance can be improved. And by setting it as the structure of the above-mentioned positive electrode electroconductive layer 111, when it makes it so thin, sufficient charge / discharge rate is securable.

  In addition, since the reinforcing layer 110 is provided and the positive electrode conductive layer 111 is disposed along the reinforcing layer 110, the positive electrode current collector 11 as a whole can be obtained even when the positive electrode conductive layer 111 alone cannot obtain sufficient strength. As such, sufficient strength can be ensured. Moreover, the positive electrode current collector 11 can have a flat structure by making the thickness gradient of the reinforcing layer 110 opposite to the thickness gradient of the positive electrode conductive layer 111. For this reason, the secondary battery is not stacked obliquely when it is configured, and the assemblability is good.

  Further, since the mass gradient has the same mass per unit area in the direction perpendicular to the direction from the first end portion 112 to the second end portion 113, processing to change the thickness of the positive electrode conductive layer 111 is easy. is there.

  In addition, by using the assembled batteries 250 and 300 in which a plurality of the secondary batteries of the present embodiment are connected, various output voltages and battery capacities can be obtained. And since each battery is the secondary battery of this embodiment, since it has a good charge / discharge characteristic, it becomes a thing suitable for high-speed charge. For this reason, even during high-speed charging, there is little temperature rise and high durability.

  Furthermore, the electric vehicle 400 using the assembled battery 300 can provide a sufficient output even when used for a long period of time because the assembled battery 300 has little temperature rise even during high-speed charging and has high durability. Therefore, by mounting this in a vehicle, the number of times of replacement of the secondary battery can be reduced, and further, loss during charging / discharging due to heat generation is also small, so that it is possible to provide an electric vehicle and a hybrid vehicle with excellent fuel efficiency.

[Embodiment 2]
FIG. 6 is a cross-sectional view of a main part for explaining the secondary battery of the second embodiment.

  In the secondary battery 2 of Embodiment 2, a negative electrode current collector 14 in which a negative electrode conductive layer 141 is formed on both surfaces of a reinforcing layer 140 made of a nonconductive material is used. Since the configuration other than the negative electrode conductive layer 141 is the same as that of the first embodiment, the description thereof is omitted. Note that the negative electrode conductive layer 141 is one of two layers sandwiching the reinforcing layer 140 shown in FIG. Hereinafter, the negative electrode conductive layer 141 has the same meaning.

The negative electrode conductive layer 141 (conductive material) used here is formed so that the thickness decreases from the first end portion 142 side to the second end portion 143 side opposite to the first end portion 142 side. The negative electrode terminal lead 21 that electrically connects the negative electrode current collecting tab 19 (see FIG. 2) is connected. The mass of is heavy. Accordingly, the sheet resistance also decreases from the first end portion 142 toward the second end portion 143. That is, the current easily flows from the first end 142 toward the second end 143.

  The outermost negative electrode current collector 14 a has the negative electrode conductive layer 141 formed only on the side where the negative electrode conductive layer 141 facing the positive electrode active material layer 12 is formed with respect to the reinforcing layer 140.

  The negative electrode conductive layer 141 is not particularly limited in the material to be used, and for example, a metal or a conductive polymer can be adopted. Specifically, in the case of a metal, for example, a metal material such as nickel, copper, and stainless steel can be used. Among these, copper is preferable from the viewpoints of electron conductivity and battery operating potential.

  On the other hand, in the second embodiment, the positive electrode current collector 11 is not changed in thickness, and is a single plate having a uniform thickness (for example, a metal foil film such as aluminum or copper).

  The positive electrode current collector 11 can be made of, for example, aluminum that does not give any special consideration to the thickness, and the negative electrode conductive layer 141 can be made of a copper thin film with a gradient in thickness as described above. In this case, since the melting point of copper (1083 ° C.) is higher than the melting point of aluminum (660 ° C.), when an internal short circuit occurs, the aluminum is burned out first without considering the special thickness.

  In addition, as shown in FIG. 7, when the conductor 900 penetrates a plurality of batteries such as the secondary battery 2 of Embodiment 2 from the outside, the conductor 900 does not burn even if the positive electrode current collector 11 is burned. Since it is in contact with the positive electrode active material 15, it acts as a positive electrode current collector. Therefore, a short circuit is formed between the adjacent unit cells 16 through the negative electrode conductive layer 141 and the negative electrode current collecting tab 19 and the short circuit current I continues to flow. Since the negative electrode conductive layer 141 is the negative electrode current collector 14 in FIG. 2, the second end 143 side is electrically connected to each other by the negative electrode current collection tab 19.

  Therefore, if the negative electrode conductive layer 141 is thin, for example, if the maximum thickness is 3 μm or less, even copper is dissolved and burned out instantly due to heat generation. For this reason, when an internal short circuit occurs, the current can be interrupted before the temperature rise due to heat generation at the internal short circuit part reaches the periphery.

  In addition, the lower limit (especially 1st edge part side) of the thickness at the time of using copper is not specifically limited, The minimum thickness which can flow an electric current may be sufficient. Particularly in the present embodiment, since the reinforcing layer 140 is provided, there is no problem as long as the current can flow even if the metal thin film alone is thin enough that its shape cannot be maintained.

  On the other hand, the reinforcing layer 140 is formed with a thickness opposite to the thickness gradient of the negative electrode conductive layer 141. Since the reinforcing layer 140 may be the same as that described in the first embodiment, a detailed description thereof will be omitted.

  Moreover, also when using a conductive resin as a material of a negative electrode collector, the same conductive resin as Embodiment 1 can be used. Furthermore, the second embodiment can be applied to a battery other than the lithium ion battery as in the first embodiment.

  According to the second embodiment described above, the following effects can be obtained.

  The negative electrode current collector 14 of the present embodiment has a structure in which the negative electrode conductive layer 141 is bonded to one side or both sides of the reinforcing layer 140. The negative electrode conductive layer 141 has a gradient so that the mass increases from the first end portion 142 toward the second end portion 143 opposite to the first end portion 142, and the negative electrode current collecting tab 19 is formed on the second end portion 143 side. Are electrically connected. Specifically, the thickness is increased from the first end 142 toward the second end 143. Therefore, the negative electrode conductive layer 141 has a sheet resistance that decreases from the first end 142 toward the second end 143.

  Thereby, the electrical resistance value becomes relatively smaller and the heat capacity can be kept large as it goes from the first end 142 side to the second end 143 side. Therefore, when the electric power is taken out from the secondary battery 2 and charged, the current can flow with a margin on the side where the negative electrode current collecting tab 19 where the current is concentrated is connected. As a result, only the side of connecting the negative electrode current collecting tab 19 where current is concentrated does not generate heat relatively, and the battery as a whole is less likely to increase in temperature. Therefore, the secondary battery has little loss during charging / discharging due to heat generation.

  Further, with this configuration, a sufficient charge / discharge rate can be ensured, and charge / discharge characteristics are improved.

  In addition, when the thickness of the negative electrode conductive layer 141 is set to a thickness that can be burned out due to a rise in temperature when a short circuit occurs inside the secondary battery, durability during abnormal resistance can be improved. And by setting it as the structure of the above negative electrode electroconductive layers 141, even when it makes it so thin, sufficient charge / discharge rate is securable.

  In addition, by providing the reinforcing layer 140 and disposing the negative electrode conductive layer 141 along the reinforcing layer 140, the entire positive electrode current collector 11 can be obtained even when the negative electrode conductive layer 141 alone cannot obtain sufficient strength. As such, sufficient strength can be ensured. In addition, the reinforcing layer 140 can have a flat structure as the negative electrode current collector 14 by setting the thickness gradient to be opposite to the thickness gradient of the negative electrode conductive layer 141. For this reason, the secondary battery is not stacked obliquely, and deterioration of assemblability can be suppressed.

  Further, since the mass gradient has the same mass per unit area in the direction perpendicular to the direction from the first end 142 to the second end 143, processing to change the thickness of the negative electrode conductive layer 141 is easy. is there.

  Furthermore, the secondary battery 2 of the second embodiment can be configured as an assembled battery as in the first embodiment. Moreover, this assembled battery can also be mounted in a vehicle. In this case, the functions and effects of the assembled battery and the vehicle can be obtained as in the first embodiment.

[Embodiment 3]
FIG. 8 is a cross-sectional view of a main part for explaining the secondary battery of the third embodiment.

  The secondary battery 3 of Embodiment 3 is a form in which Embodiment 1 and Embodiment 2 described above are integrated. That is, the positive electrode current collector 11 uses a positive electrode conductive layer 111 (conductive material) formed on both surfaces of a reinforcing layer 140 made of a nonconductive material. The positive electrode conductive layer 111 is formed so as to increase in thickness from the first end portion 112 side to the second end portion 113 side opposite to the first end portion 112 side. The positive terminal lead 20 for electrically connecting the positive current collecting tab 18 (see FIG. 2) is connected to the second end 113 side. Note that the positive electrode conductive layer 111 is one of two layers sandwiching the reinforcing layer 110 shown in FIG. Hereinafter, the positive electrode conductive layer 111 has the same meaning.

  On the other hand, the negative electrode current collector 14 is formed by forming a negative electrode conductive layer 141 (conductive material) on both surfaces of a reinforcing layer 140 made of a nonconductive material. The negative electrode conductive layer 141 is formed so as to increase in thickness from the first end 142 side to the second end 143 side opposite to the first end 142 side. And the negative electrode terminal lead 21 which electrically connects the negative electrode current collection tab 19 (refer FIG. 2) is connected to the 2nd end part 143 side. Note that the negative electrode conductive layer 141 is one of two layers sandwiching the reinforcing layer 140 shown in FIG. Hereinafter, the negative electrode conductive layer 141 has the same meaning.

  Therefore, the configuration of the positive electrode conductive layer 111 is the same as that of the first embodiment, and the configuration of the negative electrode conductive layer 141 is the same as that of the second embodiment. Therefore, detailed description thereof is omitted. Since the configuration other than these is the same as that of the first or second embodiment, the description thereof is omitted.

  According to the third embodiment, the following effects can be obtained.

  By using the positive electrode conductive layer 111 and the negative electrode conductive layer 141 each having a mass gradient for both the positive electrode current collector 11 and the negative electrode current collector 14, it is possible to further suppress the bias of heat. Further, the charge / discharge rate is further maintained, and high battery performance can be extracted. Further, in order to improve the dissolution and burn-out properties of both the positive electrode conductive layer 111 and the negative electrode conductive layer 141, both thicknesses can be made as thin as possible. Therefore, in the case of an internal short circuit due to foreign matter contamination or dendritic growth inside the battery, or in the case of a short circuit where a conductor penetrates multiple batteries from the outside, no matter where the short circuit occurs in the surface, the short circuit will occur immediately. The current flow can be cut off. In addition, the battery performance can be improved while maintaining a sufficient charge / discharge rate.

  In the third embodiment, the positive and negative current collecting tabs 18 and 19 are arranged at positions facing the secondary battery. Thereby, the positive electrode conductive layer 111 is laminated so that the negative electrode conductive layer 141 changes from the thin direction to the thick direction with respect to the thin direction from the thick direction. Therefore, the positive electrode current collector 11 and the negative electrode current collector 14 are opposite in the direction of the gradient of the electric resistance value.

  As a result, if the conductive member penetrates from the outside of the battery and a short circuit occurs inside the battery, the thinner one of the positive and negative electrodes is baked first regardless of where the conductive member penetrates in the surface. As a result, the short circuit current can be improved. Therefore, the safety resulting from the internal short circuit of the battery can be further improved.

  In addition, the third embodiment has the same effects as the first and second embodiments with respect to the thickness and the reinforcing layer for providing the mass gradient.

  Of course, also in the third embodiment, the battery can be an assembled battery or can be mounted on a vehicle, and the same effects as the assembled battery and the vehicle described in the first embodiment can be obtained.

[Embodiment 4]
9 is a cross-sectional view of a main part for explaining the secondary battery of Embodiment 4, FIG. 10 is an explanatory view for explaining the positive electrode current collector of Embodiment 4, and FIG. 10A is a plan view. 10B is a cross-sectional view taken along line AA in FIG. 10A. It is sectional drawing.

  In the fourth embodiment, the positive electrode current collector 11 has a structure in which a positive electrode conductive layer 161 having a porous structure is provided on one side or both sides of a reinforcing layer 110. The positive electrode conductive layer 161 is configured so that the porosity of the porous body per unit area gradually decreases from the first end portion 162 toward the second end portion 163 opposite to the first end portion 162. And the positive electrode lead 20 which electrically connects the positive electrode current collection tab 18 is connected to the 2nd end part 163 side.

  That is, in the positive electrode conductive layer 161, as shown in FIG. 10, for example, the number of gap portions 168 decreases from the first end portion 162 toward the second end portion 163. As a result, the area of the conductive element portion 167 increases from the first end portion 162 toward the second end portion 163, and the mass per unit area of the conductive material increases. As a result, the sheet resistance also decreases from the first end portion 162 toward the second end portion 163, so that a current easily flows from the first end portion 162 toward the second end portion 163.

  The size of the gap portion 168 is not particularly limited, but it is necessary to receive a current from the positive electrode active material and to ensure that the current flows from the first end portion 162 toward the second end portion 163. There is. From this viewpoint, for example, a size of about 0.1 to several hundred μm is preferable. This is because if the size of the gap portion 168 is too large, the conductive element portion 167 may be interrupted or the gap may become too large to reduce the current collecting action.

  Since other configurations are the same as those of the first embodiment, description thereof is omitted.

  According to the fourth embodiment, the following effects can be obtained.

  In the fourth embodiment, the sheet resistance is changed by changing the porosity to change the sheet resistance, so that the thickness of the positive electrode conductive layer 161 need not be changed. Therefore, since it is not necessary to give a gradient to the thickness of the reinforcing layer 110, the workability of the positive electrode conductive layer 161 and the reinforcing layer 110 is improved. Of course, it is possible to improve the dissolution / burn-out property of the positive electrode conductive layer 161 while maintaining the battery charge / discharge rate and ensuring the battery performance.

  In addition, the fourth embodiment has the same effects as those of the first and second embodiments.

  The configuration of the fourth embodiment can also be applied to the negative electrode conductive layer 14. Further, the present invention can be applied to both the positive electrode current collector 11 and the negative electrode current collector 14. Furthermore, it is the same as that described in the first embodiment that the secondary battery of these forms can be used as an assembled battery and can be mounted on a vehicle, and the effects thereof can be obtained in the same manner.

  In addition, the porous structure has a hexagonal shape similar to the honeycomb structure as the void portion 168, but in addition to such a shape, a circular shape (including an elliptical shape), other polygonal shapes, and an irregular shape are also shown. It may be. In order to change the void ratio, the number of the gap portions 168 per unit area may not be changed, but the size of the gap portions 168 per unit area may be changed. Further, the void portion 168 of the porous structure may be a structure embedded with a non-conductive material (for example, resin) instead of being a space. In other words, the positive electrode conductive layer 161, which is a conductive material, has a ratio of non-conductive portions made of voids or non-conductive materials (volume of non-conductive portions / volume of the entire conductive material) from the first end to the second end. What is necessary is just to be comprised so that it may become small in a direction.

  Further, in the drawing, the gap portion 168 is shown to exist in a plane, but this may be present in the thickness direction or may be a porous structure. Of course, in these cases, the ratio of the non-conductive portion (the volume of the non-conductive portion / the volume of the entire conductive material) only needs to be reduced in the direction from the first end portion 162 to the second end portion 163. is there.

  Further, as an application of the fourth embodiment, the sheet resistance can be reduced by using a conductive resin in which a non-conductive resin is mixed with a conductive filler as the positive electrode conductive layer 161 and changing the mixing ratio of the conductive filler per unit area. You can make a difference.

  That is, the blending amount of the conductive filler with respect to the non-conductive resin is increased stepwise or smoothly from the first end portion 162 toward the second end portion 163. As a result, the sheet resistance as the conductive material of the positive electrode conductive layer 161 decreases from the first end portion 162 toward the second end portion 163, and current easily flows in this direction. Also in this case, the sheet resistance can be changed without changing the thickness of the positive electrode conductive layer 161.

[Embodiment 5]
FIG. 11 is an explanatory diagram for explaining a positive electrode current collector of Embodiment 5, FIG. 11A is a plan view, and FIG. 11B is a cross-sectional view.

  In the fifth embodiment, the thickness of the positive electrode conductive layer 111 in the first embodiment described above is as follows. The thickness is the same on a concentric circular arc (shown by dotted line) centered on the portion where the positive terminal lead 20 is connected, and is in a direction orthogonal to the circular arc (shown by an arrow) and from the first end 112 to the second end. The thickness is increased in the 113 direction. The positive terminal lead 20 is connected to the second end 113 side. Accordingly, when the cross sections in the directions of the arrows are viewed, a gradient can be formed in the thickness of the positive electrode conductive layer 111 as shown in FIG. 11B. Accordingly, a mass gradient is created in a direction perpendicular to the arc from a substantially center that is an electrical connection point with the positive electrode current collecting tab 18 including the direction from the first end 112 to the second end 113, and the sheet resistance is also increased. Lower in the direction. Here, the “substantially center” is because there is a range of mechanical attachment errors.

  At this time, the reinforcing layer 110 is formed with a gradient opposite to that of the positive electrode conductive layer 111 as in the first embodiment. Other configurations are the same as those in the first embodiment, and thus description thereof is omitted.

  According to the fifth embodiment, the following effects can be obtained.

  When the width W 2 of the positive electrode conductive layer 111 is larger than the width W 1 of the positive electrode terminal lead 20, the current flows from the entire peripheral direction of the positive electrode terminal lead 20. For this reason, compared with the case where a gradient is given in one direction from the first end 112 to the second end 113, the thickness in the vicinity of the sides 114 and 115 perpendicular to the side of the first end 112 is reduced. Can do. Thereby, the flow of current from the side 114 or 115 orthogonal to the side of the first end 112 to the electrical connection point with the positive electrode current collecting tab 18 in the direction of the second end 113 is also improved. For this reason, the dissolution / burn-out property of the positive electrode conductive layer 111 can be further improved while maintaining the charge / discharge rate of the battery and ensuring the battery performance.

  The fifth embodiment can be applied to the negative electrode conductive layer 14, and can be applied to both the positive electrode current collector 11 and the negative electrode current collector 14, and the same effect is obtained in those cases. be able to.

  In the figure, a portion where the positive terminal lead 20 is connected (electrical connection point with the current collecting tab) is provided in the middle of one side of the positive current collector (side of the second end 113). However, this electrical connection point may be the end of one side of the positive electrode current collector. Also in this case, the thickness of the positive electrode conductive layer 111 is set to the same thickness on the concentric arc with the center of the portion where the positive electrode terminal lead 20 is connected, and the first end 112 is in a direction perpendicular to the arc. To the second end 113 direction. Thereby, the same effect as the said effect can be acquired. In addition, this embodiment can be implemented in the same manner regardless of where the positive electrode terminal lead 20 is connected to the positive electrode current collector. Of course, the same can be applied to the negative electrode current collector.

  As mentioned above, although embodiment which applied this invention was described, this invention is not limited to these embodiment.

  For example, in the above-described embodiment, the thickness gradient (Embodiments 1 to 3 and 5) has been described with a smooth gradient in the drawing, but may be a step gradient.

  Moreover, although the above-described embodiment has been described by using a stacked flat secondary battery, a cylindrical secondary battery (including an elliptical shape) or a square-shaped secondary battery is also available. It may be a thing. In the case of a cylindrical shape or a square shape, there is no particular limitation such that a laminate film may be used for the exterior material, and a conventional cylindrical can (metal can) may be used.

  Moreover, embodiment mentioned above demonstrated the lithium ion secondary battery as an example. This is because the lithium ion secondary battery has a large voltage per unit cell (one cell), can achieve high energy density and high output density, and is excellent as a vehicle driving power source or an auxiliary power source. However, the present invention is not limited to this, and can be applied to, for example, a nickel metal hydride secondary battery.

  Further, the secondary battery and the assembled battery of the present embodiment can be used as a mounting power source (fixed power source) such as an uninterruptible power supply, in addition to being mounted on a vehicle.

  In addition, it goes without saying that various embodiments of the present invention are possible within the scope of the technical idea of the present invention.

1, 2, 3, 4 secondary battery,
11 positive electrode current collector,
14 negative electrode current collector,
18 Positive current collecting tab,
19 Negative electrode current collecting tab,
20 positive terminal lead,
21 negative terminal lead,
110, 140 reinforcement layer,
111, 161 positive electrode conductive layer 112, 142, 162 first end,
113, 143, 163 second end,
141 negative electrode conductive layer,
167 conductive element portion,
168 Void portion.

Claims (10)

A first current collector on which a positive electrode active material layer is formed;
A second current collector formed with a negative electrode active material layer disposed at a position facing the positive electrode active material layer with an electrolyte layer interposed therebetween;
It is included in at least one of the first current collector and the second current collector, so that the mass per unit area becomes heavier in the direction from the first end to the second end facing the first current collector. A conductive material with a mass gradient;
A current collecting tab electrically connected to the second end side;
A secondary battery comprising: A first current collector on which a positive electrode active material layer is formed;
A second current collector formed with a negative electrode active material layer disposed at a position facing the positive electrode active material layer with an electrolyte layer interposed therebetween;
A conductive material that is included in at least one of the first current collector and the second current collector and has a low sheet resistance in the direction from the first end to the second end facing the first current collector; ,
A current collecting tab electrically connected to the second end side;
A secondary battery comprising:   The secondary battery according to claim 1, wherein the conductive material has a thickness that increases from the first end toward the second end. The current collector includes a reinforcing layer disposed along the conductive material,
The secondary battery according to claim 3, wherein the thickness of the reinforcing layer changes in reverse to the thickness of the conductive material.   The conductive material includes a conductive portion and a non-conductive portion, and a ratio of the non-conductive portion per unit area in the conductive material (volume of the non-conductive portion / volume of the entire conductive material) is the first end. The secondary battery according to claim 1, wherein the secondary battery decreases in the direction from the portion toward the second end portion.   6. The conductive material according to claim 1, wherein the mass per unit area is the same in a direction perpendicular to the direction from the first end to the second end. Secondary battery described in 1.   The mass per unit area of the conductive material is the same in the arc direction of a concentric circle centering on a portion where the current collecting tab is electrically connected. Secondary battery described in 1.   Using the current collector containing the conductive material for both the first current collector and the second current collector, a first end of the first current collector and a second end of the second current collector The positive electrode active material layer in the first current collector, the electrolyte layer, and the negative electrode active material layer in the second current collector are laminated so that the portions face each other. The secondary battery according to claim 1, wherein the secondary battery is disposed at a position facing each other.   The secondary battery according to claim 1, wherein the positive electrode active material layer contains lithium and becomes a lithium ion secondary battery.   A battery pack comprising a plurality of the batteries according to claim 1 electrically connected.

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