JP5269296B2 - Secondary battery - Google Patents

Description

  The present invention relates to a secondary battery, and more particularly, to a technique for suppressing deterioration of a secondary battery using a plurality of electrode groups in which separators are folded.

  Generally, a thin lithium ion secondary battery has a configuration in which a laminated electrode group obtained by laminating a separator between a positive electrode and a negative electrode is housed in a laminate film exterior (see Patent Document 1).

  A configuration example of the electrode group in Patent Document 1 is shown in FIG. The laminated electrode group in FIG. 7 is pressed in the radial direction after being wound in a spiral shape with the separator 300 f interposed between the positive electrode 100 and the negative electrode 200.

  Moreover, the structural example of another electrode group in patent document 1 is shown in FIG. The stacked electrode group illustrated in FIG. 8 has a structure in which the separator 300g is sandwiched between the positive electrode 100 and the negative electrode 200 and is folded. The production of the electrode group can be simplified and the mechanical strength of the electrode group can be improved.

 In order to increase the capacity of such a thin lithium ion secondary battery, it is necessary to increase the number of stacked positive and negative electrodes, and the stacked electrode group becomes thick. Therefore, since the cooling of the central portion of the laminated electrode group thickened to increase the capacity is worsened, the temperature of the central portion becomes higher than the periphery of the laminated electrode group, and the deterioration of the central portion of the laminated electrode portion proceeds rapidly. was there.

Patent Document 2 discloses a secondary battery in which a heat medium portion is provided between stacked electrode groups in order to control the temperature of the stacked electrode group. However, the role of the heat mediating part in Patent Document 2 is mainly heating. By providing this heat medium part, it is possible to avoid a rise in internal resistance due to a low temperature and to ensure high output promptly even when a secondary battery is used in winter or cold regions.
JP 2004-47479 A JP 2003-17127 A

  However, when the electrode group having the configuration as shown in FIG. 7 is used, the convection of the electrolyte solution is unlikely to occur. Therefore, the central portion of the multilayer electrode group is not sufficiently cooled, and compared with the periphery of the multilayer electrode group. As the temperature increases, the deterioration proceeds faster.

  Further, when the electrode group having the configuration as shown in FIG. 8 is used, as in the configuration shown in FIG. 7, the convection of the electrolytic solution hardly occurs and the cooling is not sufficiently performed.

  On the other hand, as shown in FIG. 7 in Patent Document 1, when the separators and the electrodes are laminated one by one, there is no integrity after lamination, and there is a problem that the workability of the storing operation in the laminate film exterior is poor. .

  In the case of the thin lithium ion secondary battery in Patent Document 2, in order to ensure the cooling of the central portion of the laminated electrode group that has been thickened in order to increase the capacity, the density of the laminated electrode group can be increased by providing a heat-mediating portion in the central portion However, there is a problem that the output density and energy density as a secondary battery are lowered.

  Then, this invention makes it a subject to provide the secondary battery which can suppress deterioration of a battery, without reducing an output density and an energy density.

In order to solve the above problems, a secondary battery according to the present invention includes a plurality of flat electrode groups electrically connected in parallel, and a liquid nonaqueous electrolyte impregnated in the plurality of electrode groups, A plurality of electrode groups and an exterior material for accommodating the nonaqueous electrolyte, wherein each of the plurality of electrode groups is alternately laminated with one or more planar positive electrodes and one or more planar negative electrodes. The separator is provided between the positive electrode and the negative electrode and connected in a zigzag manner, and has a square opening in the fold portion of the separator, and the fold portion is arranged at substantially the center of the opening. It is characterized by that.

  According to the secondary battery of the present invention, since the electrode groups are not connected to each other including the separator, the electrolytic solution freely passes between the electrode groups without being inhibited by the separator. Therefore, convection of the electrolytic solution easily occurs, and the vicinity of the center of the multilayer electrode group is also cooled, so that it can be prevented from becoming high temperature, and the life is prolonged because deterioration of the battery is suppressed. In addition, since the separators in one electrode group are connected in a zigzag manner, the separators are integrated and the workability of the housing work in the exterior material is good.

  Furthermore, since a device such as a heat transfer unit and a complicated configuration are not required only for cooling, a thin electrode group can be configured. Therefore, it is possible to provide a secondary battery that can suppress the deterioration of the battery without reducing the output density and the energy density.

  Hereinafter, embodiments of the secondary battery of the present invention will be described in detail with reference to the drawings.

  First, Example 1 will be described with reference to FIGS. Fig.1 (a) is a figure which shows the basic composition of the secondary battery which concerns on Example 1 of this invention. This secondary battery includes an exterior 600, an electrolytic solution 400, and an electrode group 500. The exterior 600 corresponds to the exterior material of the present invention. The electrolytic solution 400 corresponds to the nonaqueous electrolyte of the present invention and is accommodated in the exterior material 600. A plurality of electrode groups 500 are electrically connected in parallel, immersed in the electrolytic solution 400, and stored in the exterior material 600.

  The electrode group 500 includes a positive electrode 100, a negative electrode 200, and a separator 300a, and is mainly flat. One or more planar positive electrodes 100 and one or more planar negative electrodes 200 are alternately stacked via separators 300a therebetween. Further, the separators 300a are all connected in a zigzag manner in one electrode group 500.

  FIG. 2 is a bird's-eye view showing an example of the secondary battery according to Example 1 of the present invention. The secondary battery includes a plurality of laminated electrode groups, that is, a laminated electrode group 520a, a laminated electrode group 520b, a laminated film exterior 600a that houses these laminated electrode groups, a laminated film exterior 600b, and a laminated electrode group. It is composed of a positive electrode terminal 150a for taking out power through the positive electrode current collector 120 to the outside of the film exterior and a negative electrode terminal 250b through the negative electrode current collector 220a.

  Further, as will be described in detail in Example 2, the configuration of the laminated electrode group is as shown in FIG. Here, the negative electrode current collector 220b and the negative electrode terminal 250b in FIG. 4B correspond to the negative electrode current collector 220a and the negative electrode terminal 250a in FIG. As shown in FIG. 4B, the laminated electrode group 520a and the laminated electrode group 520b are configured by laminating a plurality of electrodes with a separator 300c sandwiched between the positive electrode 100 and the negative electrode 200. It is immersed in the electrolytic solution in the film exterior 600b. The negative electrode 200 of the multilayer electrode group 520a and the multilayer electrode group 520b is connected to the negative electrode terminal 250a via the negative electrode current collector 220a, and the positive electrode 100 is connected to the positive electrode terminal 150a via the positive electrode current collector 120.

  In addition, various things can be considered about the material of each structural requirement. Hereinafter, the negative electrode, the positive electrode, the separator, the nonaqueous electrolyte, and the exterior material will be described.

(1) Negative electrode This negative electrode has a negative electrode current collector and a negative electrode layer that is supported on one or both sides of the negative electrode current collector and includes a negative electrode material and a binder.

  The negative electrode material is preferably a carbonaceous material that absorbs and releases lithium ions. Examples of carbonaceous materials include (I) graphite materials such as graphite, coke, carbon fiber, spherical carbon, and granular carbon, or carbonaceous materials, and (II) thermosetting resins, isotropic pitches, mesophase pitches, mesophase pitches. Examples thereof include graphite materials and carbonaceous materials obtained by heat-treating carbon-based carbon fibers, vapor-grown carbon fibers, mesophase spherules and the like at 500 to 3000 ° C. Among the carbonaceous materials subjected to the heat treatment, mesophase pitch-based carbon fiber graphite material or carbonaceous material, mesophase microsphere graphite material or carbonaceous material, or granular graphite material.

  As the current collector, a conductive substrate having a porous structure or a nonporous conductive substrate can be used. These conductive substrates can be formed from, for example, copper, stainless steel, or nickel.

  As the negative electrode material, a metal oxide, a metal sulfide, a metal nitride, lithium metal, or a lithium alloy can be used in addition to the above-described carbonaceous material that absorbs and releases lithium ions.

(2) Positive electrode The positive electrode includes a positive electrode current collector and a positive electrode layer that is supported on one or both surfaces of the positive electrode current collector and includes an active material and a binder.

  Examples of the positive electrode active material include various oxides such as manganese dioxide, lithium manganese composite oxide, lithium-containing nickel oxide, lithium-containing cobalt oxide, lithium-containing nickel cobalt oxide, lithium-containing iron oxide, and vanadium containing lithium. Examples thereof include oxides and chalcogen compounds such as titanium disulfide and molybdenum disulfide. Among these, when a lithium-containing cobalt oxide, a lithium-containing nickel cobalt oxide, or a lithium manganese composite oxide is used, it is preferable because a high voltage can be obtained.

  The positive electrode layer may further contain a conductive agent. Examples of the conductive agent include acetylene black, carbon black, and graphite.

(3) Separator A porous separator is used as the separator.

  Examples of the porous separator include a porous film containing polyethylene, polypropylene, cellulose, or polyvinylidene fluoride (PVdF), and a synthetic resin nonwoven fabric. Among these, a porous film made of polyethylene, polypropylene, or both is preferable because it can improve the safety of the secondary battery.

(4) Non-aqueous electrolyte This non-aqueous electrolyte is held by at least the separator. In particular, the nonaqueous electrolyte is preferably dispersed throughout the electrode group. As this non-aqueous electrolyte, a liquid non-aqueous electrolyte composed of a non-aqueous solvent in which the electrolyte is dissolved (hereinafter referred to as a non-aqueous solution), a polymer material holding the non-aqueous solution, or a solid non-aqueous electrolyte can be used. . As the polymer material in which the non-aqueous solution is retained, a gel-like non-aqueous electrolyte in which the non-aqueous solution is gelled, a part of the non-aqueous solution is gelled, and the rest remains liquid, and the non-aqueous solution is liquid What is held as it is can be mentioned. Among these, it is preferable to use a liquid nonaqueous electrolyte. Since the liquid non-aqueous electrolyte can increase the ionic conductivity of the electrode group, the interface resistance between the positive electrode and the separator and the interface resistance between the negative electrode and the separator can be reduced.

(5) Exterior material As this exterior material, for example, a metal can or a sheet having a function of blocking moisture can be used. The metal can can be formed from, for example, iron, stainless steel, or aluminum. As the sheet, for example, a multilayer sheet formed of two or more types of resin layers, one or both surfaces being a thermoplastic resin, or a multilayer formed by forming a protective layer on one or both surfaces of a flexible metal layer. A sheet can be mentioned.

  An exterior material including a resin layer can also be used. The resin layer can be formed from, for example, a thermoplastic resin. Examples of the thermoplastic resin include polyethylene and polypropylene.

  As an exterior material containing a resin layer, the multilayer sheet which consists of a metal layer and the resin layer formed in both surfaces of a metal layer can be mentioned, for example. The resin layer serving as the inner surface of the exterior material has a function as a heat seal surface and a function of preventing the metal layer from being corroded by the nonaqueous electrolyte. Moreover, the resin layer used as the outer surface of an exterior material plays the role which prevents damage to a metal layer. Each resin layer may be formed from one type of resin, or may be formed from two or more types of resins. Each resin layer is preferably formed from a thermoplastic resin.

  Next, the effect | action of the secondary battery of this Embodiment is demonstrated. In the present embodiment, the plurality of electrode groups 500 are housed in the exterior 600, but the separator 300a is not connected between each electrode group. Therefore, as shown by the flow 50a of the electrolytic solution that is an arrow in FIG. 1A, the electrolytic solution 400 can freely flow between the electrode groups. That is, as shown in FIG. 1B, the electrolytic solution 400 can circulate so as to pass through the central portions of the electrode group 500a and the electrode group 500b. Therefore, as shown in the flow 50b of the electrolytic solution, convection due to the electrolytic solution 400 is easily generated, and the central portion of the electrode groups 500a and 500b can be prevented from being cooled to a high temperature. In FIG. 1B, two electrode groups are shown, but the number is not limited to two, and a plurality of electrode groups can be accommodated.

  On the other hand, the separators 300a can be stacked one by one between the positive electrode 100 and the negative electrode 200 without being folded, but the resulting stacked electrode group tends to be disjointed and difficult to assemble. .

  As described above, according to the secondary battery according to the first embodiment of the present invention, the separator 300a is not connected between each electrode group, so that convection of the electrolyte 400 is likely to occur, and the laminated electrode group 500a and The vicinity of the center of the 500b is also cooled, so that it can be prevented from becoming a high temperature, and the life is prolonged in order to suppress the deterioration of the battery.

  That is, by storing a plurality of thin electrode groups instead of one thick electrode group, the cooling effect can be enhanced while maintaining the same energy density and output density as when one thick electrode group is used.

  In addition, the structure in the electrode group is also open except for the fold portions of the separator that is folded in a zigzag manner so that the electrolyte can pass therethrough. Since the structure is open in three directions in this way, it is structurally more likely to cause convection than the structure in which the separator is open only in two directions as shown in FIGS. Therefore, the cooling effect can be enhanced, and as a result, the deterioration of the battery can be avoided and the life can be extended.

  In addition, since it has a simple structure in which a plurality of electrode groups are housed, it is not necessary to install a heat-mediating unit between the electrode groups for temperature adjustment as in Patent Document 2. Therefore, the central portion of the stacked electrode groups 500a and 500b can be cooled without increasing the thickness of the battery, and deterioration of the battery can be suppressed without causing a decrease in output density or energy density.

  Furthermore, since the separators 300a are connected in a zigzag manner, the separators 300a are integrated after stacking, and the workability of the storing work in the exterior material is good.

  Further, when the electrode group configured as shown in FIG. 8 is used, since the negative electrodes 200 are in contact with each other, even if a negative electrode active material is applied to the portion, the active material hardly functions as a battery. However, when only the separator has a zigzag folded structure, there is no portion where the positive electrodes or the negative electrodes are in contact with each other, and the active materials on both sides of the electrode can be used for charging and discharging. That is, the ratio of the active material can be increased, and the energy density of the battery can be increased.

  FIG. 3A is a diagram showing a basic configuration of a secondary battery according to Example 2 of the present invention. The difference from the first embodiment is only that the electrode group 500c is not a plurality but one. Therefore, duplicate description is omitted.

  Fig.4 (a) is a bird's-eye view which shows one example of the secondary battery which concerns on Example 2 of this invention. Moreover, FIG.4 (b) is the figure which expanded the A section of Fig.4 (a). The secondary battery includes a laminated electrode group 520c, a laminated film outer package 600c that houses the laminated electrode group 520c, a positive electrode terminal 150b that extracts power from the laminated electrode group 520c to the outside of the laminated film outer package 600c, It is composed of

  As shown in FIG. 4B, the laminated electrode group 520c is formed by laminating a plurality of electrodes with a separator 300c sandwiched between a positive electrode 100 and a negative electrode 200, and is immersed in an electrolyte solution in a laminate film exterior 600c. ing. In addition, the negative electrode 200 of the stacked electrode group 520c is connected to the negative electrode terminal 250b via the negative electrode current collector 220b, and the positive electrode 100 is connected to the positive electrode terminal 150b via a positive electrode current collector that is also not shown. .

  Next, the effect | action of the secondary battery of this Embodiment is demonstrated. As shown in FIG. 3A, each of the positive electrode 100 and the negative electrode 200 has a structure in which a separator 300b at one end is opened, and has a structure in which three directions are opened. Therefore, convection of the electrolytic solution 400 is more likely to occur than a wound electrode group or an electrode group that is open only in two directions, such as a positive electrode and a negative electrode group.

  However, since there is only one electrode group in this embodiment, it is easy for the electrolyte 400 to flow around the outer periphery of the electrode group 500d as shown in the flow 50d of the electrolyte in FIG. However, it is difficult to flow through the central portion of the electrode group 500d.

  On the other hand, when the separators 300b are stacked one by one between the positive electrode 100 and the negative electrode 200 without being folded, the resulting stacked electrode group is likely to be disjointed and difficult to assemble.

  As described above, according to the secondary battery according to Example 2 of the present invention, since the separator 300b is connected by zigzag folding, there is integrity after stacking, and workability of storing work in the exterior material is good. .

  In addition, the three directions are open, and the structure is more susceptible to convection than the conventional structure shown in FIGS. 7 and 8, so that the cooling effect can be enhanced and the battery is deteriorated. It is possible to extend the life by avoiding the above.

  Furthermore, since a device such as a heat transfer unit and a complicated configuration are not required only for cooling, the thin electrode group 500c can be configured. Therefore, battery deterioration can be suppressed without lowering the output density or energy density.

  Further, when the electrode group having the configuration as shown in FIG. 8 in Patent Document 1 is used, the negative electrodes 200 are in contact with each other. Although there is a problem, by forming only the separator in a zigzag folded structure, there is no portion where the positive electrodes or the negative electrodes are in contact with each other, and the active materials on both sides of the electrode can be used for charging and discharging. That is, the ratio of the active material can be increased, and the energy density of the battery can be increased. This means that the maximum energy density can be obtained with a minimum number of electrodes, which can contribute to cost reduction.

  FIG. 5 is a diagram showing the structure of the electrode group of the secondary battery according to Example 3 of the invention. The difference from the first and second embodiments is only that the opening 700a is provided in the fold portion of the separator 300d. Other configurations are the same as those in the first and second embodiments.

  The width of the opening 700a is shorter than that of the negative electrode and the positive electrode. By doing in this way, it can prevent that a negative electrode and a positive electrode protrude outside from the opening part of this separator 300d.

  Next, the effect | action of the secondary battery of this Embodiment is demonstrated. Since the electrolytic solution 400 can pass through the opening 700a provided in the fold portion of the separator 300d without resistance, the central portion of the stacked electrode group can be cooled.

  As described above, according to the secondary battery according to Example 3 of the present invention, the electrolytic solution 400 can freely pass through the opening 700a by having the opening 700a in the fold portion of the separator 300d. Therefore, convection of the electrolytic solution 400 easily occurs, and heat generation due to current in the central portion of the electrode group is suppressed and cooled, so that deterioration of the battery can be suppressed and the life can be extended. In addition, since a heat transfer unit for cooling and a complicated configuration are not required, cooling can be performed without causing a decrease in the power density and energy density of the battery as in the first and second embodiments.

  Moreover, since the electrolytic solution 400 can circulate through the central portion of the laminated electrode group without being divided into a plurality of electrode groups as in the first embodiment, the number of laminated electrode groups may be one. Therefore, since the separator 300d is connected in a zigzag manner to the entire electrode group, there is integrity after stacking, and workability of storing work in the exterior material is good.

  Further, since the width of the opening 700a is shorter than the width of the positive electrode 100 and the negative electrode 200, the positive electrode 100 and the negative electrode 200 are prevented from protruding outside the opening 700a. Accordingly, it is possible to maintain the integrity, improve the workability of the housing operation into the exterior material, and prevent a short circuit between the positive electrode and the negative electrode.

  FIG. 6 is a view showing the structure of the electrode group of the secondary battery according to Example 4 of the present invention. The difference from the third embodiment is only that a plurality of openings 700b are provided in one side of at least one fold portion of the separator 300e. Other configurations are the same as those of the third embodiment.

  Next, the effect | action of the secondary battery of this Embodiment is demonstrated. As in the case of Example 3, the electrolytic solution 400 can pass through the opening 700b provided in the fold portion of the separator 300e without resistance. Therefore, convection of the electrolytic solution 400 easily occurs, and the central portion of the stacked electrode group Can be cooled.

  As described above, according to the secondary battery according to the fourth embodiment of the present invention, the same effects as in the third embodiment can be obtained.

  Further, by providing a plurality of openings 700b in one side of the fold portion, it is possible to contribute to the cooling effect of the entire electrode group as in the third embodiment. In addition, since the plurality of openings 700b having a small width are provided on one side, the positive electrode 100 and the negative electrode 200 do not protrude outside, and can contribute to maintenance of integrity and prevention of a short circuit.

  Furthermore, in Example 3 and Example 4, by forming openings in all the crease portions of the separator, the entire electrode group can be cooled more effectively and uniformly.

  The present invention is applicable to lithium ion secondary batteries.

It is a figure which shows the basic composition of the secondary battery which concerns on Example 1 of this invention. It is a bird's-eye view which shows one example of the secondary battery which concerns on Example 1 of this invention. It is a figure which shows the basic composition of the secondary battery which concerns on Example 2 of this invention. It is a bird's-eye view which shows one example of the secondary battery which concerns on Example 2 of this invention. It is a block diagram of the electrode group of the secondary battery which concerns on Example 3 of this invention. It is a block diagram of the electrode group of the secondary battery which concerns on Example 4 of this invention. It is a block diagram of the winding type electrode group of the conventional secondary battery. It is a block diagram of the zigzag folded electrode group of the conventional secondary battery.

Explanation of symbols

50a, 50b, 50c, 50d Electrolyte flow 100 Positive electrode 120 Positive electrode current collector 150a, 150b Positive electrode terminal 200 Negative electrode 220a, 220b Negative electrode current collector 250, 250a, 250b Negative electrode terminal 300a, 300b, 300c, 300d, 300e, 300f , 300 g Separator 400 Electrolyte 500 Electrode group 500a Laminated electrode group 500b, 500c Electrode group 500d, 500e Laminated electrode group 600 Exterior 600a, 600b, 600c Laminated film exterior 700a, 700b Opening

Claims (4)

A plurality of flat electrode groups;
A liquid non-aqueous electrolyte impregnated in the plurality of electrode groups;
A plurality of electrode groups and an exterior material in which the nonaqueous electrolyte is accommodated,
Each of the plurality of electrode groups is
One or more planar positive electrodes;
One or more planar negative electrodes;
A separator provided between the positive electrode and the negative electrode, which are alternately stacked, and connected in a zigzag manner;
Have
A secondary battery having a square opening in a fold portion of the separator, wherein the fold portion is disposed at a substantially center of the opening. The width of the opening is shorter than the width of the positive electrode and the negative electrode, and the positive electrode terminal connected to the positive electrode and the negative electrode terminal connected to the negative electrode are output from approximately 180 degrees opposite to each other. The secondary battery according to claim 1. 2. The secondary battery according to claim 1, wherein a plurality of the square openings are formed in one side of at least one fold portion of the separator. The secondary battery according to any one of claims 1 to 3, wherein the opening is formed in all folds of the separator.

Images