JP3419311B2 - Bipolar lithium-ion secondary battery - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of the structure of a bipolar lithium ion secondary battery.

[0002]

2. Description of the Related Art Conventionally, a bipolar type lithium ion secondary battery has been used in which a plurality of lithium ion secondary batteries connected in series is used as one battery. In such a bipolar lithium ion secondary battery, a battery assembly is formed by sandwiching a separator containing an electrolyte between a positive electrode and a negative electrode and having lithium ion conductivity, and the battery assembly is stacked in the electrode direction. It was formed by connecting the bodies in series. An example of such a bipolar lithium ion secondary battery is disclosed in Japanese Patent Laid-Open No. 59-90359.

FIG. 15 shows a sectional view of a bipolar type lithium ion secondary battery of this conventional example. 15, in the battery case 100, a positive electrode formed by applying the positive electrode active material 12 on the positive electrode current collector foil 10 and a negative electrode active material 16 applied on the negative electrode current collector foil 14 are formed. A bipolar type lithium ion secondary battery having a structure in which a separator 18 having lithium ion conductivity is sandwiched between the negative electrode and the negative electrode to form a battery structure, and the battery structure is stacked in a plurality of electrode directions is accommodated. . Both of the laminated end surfaces of the bipolar lithium-ion secondary battery configured in this way are the positive electrode current collector foil 10 and the negative electrode current collector foil 14, respectively, and the positive electrode terminal lead 20 and the negative electrode terminal lead 22 are attached to them. It is connected.

[0004]

However, in the above-mentioned conventional bipolar type lithium ion secondary battery, each battery component can be thinned in the stacking direction.
At the same time, in order to obtain a large capacity, it is necessary to increase the area of the positive electrode and the negative electrode. Therefore, there is a problem that it is difficult to make the positive electrode and the negative electrode compact in the area direction.

Further, the interval between the battery components is several tens to one.
Since it is as thin as 00 μm, there is also a problem that it is difficult to insulate the periphery of the battery structure.

The present invention has been made in view of the above conventional problems, and an object thereof is to provide a bipolar type lithium ion secondary battery having a large capacity, a compact size, and improved insulation. It is in.

[0007]

In order to achieve the above object, the present invention relates to a bipolar lithium ion secondary battery, which is wound with a separator sandwiched between a positive electrode and a negative electrode. A plurality of components are concentrically wound via an insulator, and are sequentially electrically connected in series from the inner battery component toward the outer battery component, and at each connection portion.
Is the positive or negative collector foil of the inner battery assembly and the outer
Is connected to the negative electrode or positive electrode current collector foil of the battery assembly of
Configures the connection between the inner battery structure and the outer battery structure
A structure in which the current collecting foil wraps around the entire outer periphery of the inner battery structure
It is characterized in that.

Further, in a bipolar type lithium ion secondary battery, a plurality of battery constituents wound in a state where a separator is sandwiched between a positive electrode and a negative electrode are concentrically wound through an insulator. Are sequentially and electrically connected in series from the inner battery structure toward the outer battery structure, and at each connection part, the positive electrode or negative electrode current collector foil of the inner battery structure and the outer battery structure are connected. The negative electrode or the positive electrode current collector foil is connected , and the electric capacities of the inner battery component and the outer battery component are
The same is also characterized in that the inner resistance of the inner battery structure is made higher .

[0009]

[0010]

[0011]

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention (hereinafter referred to as embodiments) will be described below with reference to the drawings.

Embodiment 1. FIG. 1 and FIG. 2 show an example of a battery structure that constitutes the bipolar lithium-ion secondary battery according to this embodiment. In FIG. 1, between the positive electrode formed by applying the positive electrode active material 12 on the positive electrode current collector foil 10 and the negative electrode formed by applying the negative electrode active material 16 on the negative electrode current collector foil 14. The battery structure 26 is configured with the lithium ion conductive separator 18 interposed therebetween. The battery structure 26 is wound as shown in FIG.
In this case, the insulating film 2 is provided outside the negative electrode current collector foil 14.
4 are stacked. Thereby, the battery structure 26
This prevents the positive electrode current collector foil 10 and the negative electrode current collector foil 14 from being short-circuited when being wound. A cross-sectional view of the battery structure 26 wound in this manner is shown in FIG. As shown in FIG. 2, the battery assembly 26 has the positive electrode current collector foil 10 exposed at the innermost part and the negative electrode current collector foil 14 exposed at the outermost part.

In the example shown in FIG. 1, the positive electrode current collector foil 10 and the negative electrode current collector foil 14 have positive electrode active material 1 on one side thereof.
2 and the negative electrode active material 16 are applied.
As shown in, the positive electrode active material 12 and the negative electrode active material 16 may be applied to both sides of each of the current collector foils 10 and 14, respectively. In this case, the separator 18a is sandwiched between the positive electrode active material 12 and the negative electrode active material 16 located inside the positive electrode current collector foil 10 and the negative electrode current collector foil 14 among the laminated layers. Further, the same separator 18b is also arranged on the outer side of the negative electrode active material 16 on the outer side of the negative electrode current collector foil 14. When this is wound in the direction of arrow A, the inner positive electrode active material 12 and the negative electrode active material 16 described above are arranged to face each other with the separator 18a interposed therebetween, and the outer positive electrode active material 12 and the negative electrode active material 16 are arranged.
The separator 18 disposed outside the negative electrode active material 16
It will be arranged facing each other via b. In this case, if the length of the portion of the negative electrode current collector foil 14 on which the negative electrode active material 16 is not applied is sufficiently secured, when the negative electrode current collector foil 14 is wound in the direction of arrow A in FIG. A battery structure 26 having a structure in which 10 is exposed and the negative electrode current collector foil 14 is exposed at the outermost part can be obtained.

The battery structure 26 shown in FIG. 2 is covered with an insulator, and the battery structure 2 shown in FIG.
6 is wound concentrically. In this way, the plurality of battery components 26 are concentrically wound with the insulator interposed therebetween, and are sequentially electrically connected in series from the inner battery component toward the outer battery component. A bipolar lithium-ion secondary battery according to the aspect is configured. in this way,
By winding the battery structure 26, the bipolar type lithium ion secondary battery can be made compact as compared with the case of stacking without winding, and has a large capacity and a compact size.

A cross-sectional view of the bipolar type lithium ion secondary battery as described above is shown in FIG. In FIG. 4, from the innermost battery structure 26a to the outermost battery structure 26d.
Up to the above, they are wound concentrically via the insulating container 28. These are housed in the battery case 100, and the battery components 26b, 26c, and 2 are sequentially arranged from the inner battery component 26a.
The lead wires 30 for serial connection are connected in series in the order of 6d. As described above, since the positive electrode current collector foil 10 is exposed at the innermost part of the battery structure 26, the positive electrode terminal lead 20 is connected to this, and the positive electrode current collector foil 10 is provided at the outermost part of the battery structure 26. Since the foil 14 is exposed, the negative terminal lead 22 is connected to it.

FIG. 5 shows a VV sectional view of the bipolar lithium ion secondary battery according to this embodiment shown in FIG. However, the battery case 100 is omitted. In this embodiment, four battery components 26a,
26b, 26c, and 26d are sequentially wound concentrically from the inner battery structure 26a to the outer side thereof, and are connected in series from the inner battery structure 26a toward the outer battery structure 26d. When using this bipolar type lithium ion secondary battery, the positive electrode terminal lead 20
Charge and discharge is performed via the negative electrode terminal lead 22 and the negative electrode terminal lead 22.

In this embodiment, the positive electrode is the innermost
Although the negative electrode is formed on the outermost part, the stacking order or the winding direction of the battery structure 26 may be reversed to reverse the arrangement of the positive electrode and the negative electrode.

A specific example of the bipolar type lithium ion secondary battery according to this embodiment will be described below as Example 1.

Example 1. LiMn as the positive electrode active material 12
₂ O ₄ was used and applied on an aluminum foil as the positive electrode current collector foil 10 to form a positive electrode. Further, graphite was used as the negative electrode active material 16, and this was applied onto a copper foil as the negative electrode current collector foil 14 to form a negative electrode. A nonwoven fabric was used as the separator 18. These were laminated as shown in FIG. 1 and wound to form a battery structure 26.
The battery structure 26 thus configured is put in a polypropylene (PP) bag as the insulating container 28, and the battery structure 26 similar to the one described above is further wound around the bag, and the whole structure is also made of polypropylene. I put it in the bag. In this way, the battery component is further wound around the outer periphery of the battery component placed in the polypropylene bag, and four batteries are inserted through the polypropylene bag as the insulating container 28 as shown in FIG. Constituent bodies 26a, 26b, 26c and 26d were wound concentrically.

Next, a liquid of EC: DEC = 1: 1 was added to Li.
PVDF-HF and a solution in which PF ₆ was dissolved at 1 mol / l
An electrolyte was prepared by mixing P and P in a weight ratio of 7: 1. Each of the battery components 26, 26 contained in the above-mentioned polypropylene bag is filled with the electrolytic solution.
b, 26c, and 26d were impregnated, heated to 120 ° C., and then returned to room temperature to cause the electrolytic solution to gel in the positive electrode, the negative electrode, and the separator 18. After that, the opening of the polypropylene bag was closed by hot pressing, and each battery structure 26, 26b, 26 was closed.
c and 26d were completely sealed and separated. Then, from the inner battery structure 26a toward the outer battery structure 26d, they were sequentially electrically connected in series by the series connection lead wire 30. Finally, these are enclosed in a battery case 100, and the innermost positive electrode current collector foil 10 and the outermost negative electrode current collector foil 14 are enclosed.
A positive electrode terminal lead 20 and a negative electrode terminal lead 22 were connected to and, respectively, to obtain a bipolar lithium ion secondary battery according to this example.

The bipolar lithium-ion secondary battery thus obtained was evaluated and found to have an average voltage of 1
It was possible to obtain 5.8V. Further, the voltage was kept at 15.6 V even after being left for 10 days in a charged state. As a comparative example, a bipolar lithium-ion secondary battery, in which the battery structure 26 shown in FIG. 1 was laminated without being wound, and the periphery of which was insulated was similarly evaluated. As a result, a voltage of 15.8V was initially obtained, but after leaving it for 10 days, it dropped to 10.8V. It is considered that this is because the thickness of each battery structure 26 is as thin as several tens to 100 μm, and it is difficult to insulate the surroundings, so that the leakage current is large.

Embodiment 2. FIG. 6 shows a cross-sectional view of the configuration of the bipolar lithium-ion secondary battery according to this embodiment. Further, FIG. 7 shows a cross-sectional view of the battery structure 26 that constitutes the bipolar lithium-ion secondary battery shown in FIG.

In FIG. 7, the positive electrode active material 12 is applied to both surfaces of the positive electrode current collector foil 10 to form a positive electrode. Further, the negative electrode active material 16 is applied to both surfaces of the negative electrode current collector foil 14 to form a negative electrode. Among the positive electrode active material 12 and the negative electrode active material 16, those arranged inside are opposed to each other via the separator 18a. Further, a separator 18b is further formed on the positive electrode active material 12 that is formed on the opposite side (outer side) of the positive electrode current collector foil 10 from the negative electrode. As a result, when the battery structure 26 is wound, the positive electrode active material 12 and the negative electrode active material 16 arranged outside are arranged to face each other with the separator 18b interposed therebetween. In such a battery structure 26, one positive electrode current collector foil 10 and the other negative electrode current collector foil 14 are connected at a connecting portion 32, and a plurality of battery structure members 26 are connected in series. In this way, by directly connecting the positive electrode current collector foil 10 and the other negative electrode current collector foil 14, the contact resistance can be reduced.

When the battery assembly thus constructed is wound in the direction of arrow A shown in FIG. 7, a bipolar lithium ion secondary battery having a structure as shown in FIG. 6 is obtained. You can In FIG. 6, a plurality of battery components 26 are wound in a concentric manner with the separators 18a and 18b sandwiched between the positive electrode and the negative electrode. Further, as shown in FIG. 7, since the battery components 26 are connected in series by the connecting portions 32, the battery components 26 in FIG. The structure is such that they are electrically connected in series.

At this time, the lengths in the winding direction of the positive electrode current collector foil 10 and the negative electrode current collector foil 14 that connect the one battery constituent member 26 and the other battery constituent member 26 are different from each other. In addition, the outer periphery of the inner battery structure 26 is set to have a length that allows one or more windings with only the current collecting foils 10 and 14. As a result, the entire outer periphery of the inner battery component 26 is wrapped with the current collector foil, and it is possible to prevent the positive electrode and the negative electrode of the inner battery component 26 and the outer battery component 26 from being short-circuited. At this time, it is desirable that the width of the connection portion 32 of the current collector foils 10 and 14 connecting the two battery components in the direction perpendicular to the winding direction is larger than that of the portion where the electrodes are formed. This is to prevent the electrolyte from moving from the upper and lower ends of the bipolar lithium-ion secondary battery having a cylindrical shape after winding the battery structure 26 to the adjacent battery structure and causing an electrolyte short circuit. .

The bipolar type lithium ion secondary battery shown in FIG. 6 constructed as described above has the positive electrode current collector foil 10 exposed at the innermost portion and the negative electrode current collector foil 14 exposed at the outermost portion. The positive electrode terminal lead 20 and the negative electrode terminal lead 22 are connected to each. Note that, also in this embodiment,
The innermost and outermost positive and negative electrodes can be configured in reverse. Further, in FIG. 6, the battery case 100 is omitted.

FIGS. 8A and 8B show a modified example of the battery structure 26 according to this embodiment. The characteristic point of this modified example is that the positive electrode current collector foil 1 of one of the battery components 26 is
This is because the connection current collector foil 34 made of stainless steel or the like was used to connect the negative electrode current collector foil 14 of the other battery assembly 26. This connection current collector foil 34 is used for the battery assembly 2
The width of 6 in the 90 ° direction with respect to the winding direction is larger than that of the electrode portion. Thereby, when the battery structure 26 is wound, it is possible to prevent the electrolyte from leaking out from the upper and lower ends of the cylindrical bipolar lithium-ion secondary battery and causing a short circuit.

Also in the bipolar type lithium ion secondary battery according to this embodiment, an aluminum foil is used as the positive electrode current collector foil 10 and the negative electrode current collector foil 14 is used as in the first embodiment.
Copper foil was used as. LiMn ₂ O ₄ was used as the positive electrode active material 12, and graphite was used as the negative electrode active material 16. These active materials are formed by coating the current collector foils 10 and 14 with a mixture with the binder PVDF. A non-woven fabric was used as the separator 18. The positive electrode, the negative electrode, and the separator 18 are impregnated with the same electrolytic solution as in Embodiment 1, heated to 120 ° C., and then returned to room temperature to be gelled.

Embodiment 3. FIG. 9 shows a cross-sectional view of the configuration of the bipolar lithium-ion secondary battery according to this embodiment. 10 (a) and 10 (b) are a cross-sectional view and a plan view of a battery structure 26 that constitutes the bipolar lithium-ion secondary battery shown in FIG.

As shown in FIG. 10 (a), in the battery assembly 26 of this embodiment, the positive electrode active material 12 is formed only on one surface of the positive electrode current collector foil 10, and the negative electrode current collector foil 14 is formed.
The negative electrode active material 16 is formed on only one surface of the. The positive electrode active material 12 and the negative electrode active material 16 are used in the separator 1
8 are arranged opposite to each other. Further, the positive electrode current collector foil 10 of one of the battery components 26 and the negative electrode current collector foil 14 of the other battery component 26 are connected by the connecting portion 32, and the battery components 26 are connected in series.

A feature of this embodiment is that each battery structure 26 is covered with an insulating film 36 made of polypropylene film or the like except the connecting portion 32. With such a configuration, as in the second embodiment,
When winding the outer battery component 26 around the outer periphery of the inner battery component 26, the inner battery component 26 and the inner battery component 26 need not be wound around the outer periphery of the inner battery component 26 for one or more rounds. The outer battery structure 26 is not short-circuited. Therefore, as shown in FIG. 9, in the bipolar lithium-ion secondary battery according to the present embodiment, the positive electrode current collector foil 10 and the negative electrode current collector foil 1 are provided at the connection portion 32.
When connecting with 4, the length of the current collector foil used can be shortened, and the electric capacity per volume can be increased accordingly.

Incidentally, in FIG. 9, three battery components are wound around the inside of the battery and the outside of the battery,
An example is shown in which each is connected in series from the inside to the outside. The number of battery components is not limited to three, and four or more can be wound in sequence.

A specific example of the bipolar type lithium ion secondary battery according to this embodiment will be described below as Example 2.

Example 2. An aluminum foil was used as the positive electrode current collector foil 10, and a copper foil was used as the negative electrode current collector foil 14. Further, LiMn ₂ O ₄ was used as the positive electrode active material 12, and graphite was used as the negative electrode active material 16. These active materials were mixed with a binder PVDF to form a paste, which was applied to only one surface of each current collector foil. A nonwoven fabric is used as the separator 18, and EC: DEC =
An electrolyte solution was prepared by impregnating a 1: 1 liquid solution of LiPF ₆ dissolved in 1 mol / l and PVDF-HFP in a weight ratio of 7: 1. This was heated to 120 ° C. and then returned to room temperature to gel the impregnated electrolytic solution. In addition to the separator 18, the electrolytic solution is impregnated into the positive electrode and the negative electrode.

The battery structure 26 thus constructed was covered with a polypropylene film except the ends of the positive electrode current collector foil 10 and the negative electrode current collector foil 14, and thermocompression-bonded to seal. In this state, the battery characteristics were evaluated, and short circuits, variations in capacity, etc. were checked.

Next, each battery assembly 2 thus constructed
The positive electrode current collector foil 10 and the negative electrode current collector foil 14 of No. 6 are connected by spot welding and wound in the winding direction A shown in FIGS. 10 (a) and 10 (b), and the bipolar lithium ion 2 according to the present embodiment. The next battery was obtained. At this time, the positive electrode terminal lead 20 was attached to the positive electrode collector foil 10 exposed to the innermost portion, and the negative electrode terminal lead 22 was attached to the negative electrode collector foil 14 exposed to the outermost portion. The negative electrode terminal lead has a battery case 100 in which the outermost negative electrode current collector foil 14 is housed in the battery structure 26.
The negative electrode terminal lead 22 may be attached to the battery case 100 by contacting it (not shown). Also,
Also in this embodiment, the innermost part may be the negative electrode and the outermost part may be the positive electrode.

By the above method, four battery components 26
A bipolar lithium-ion secondary battery consisting of was constructed and its electrical characteristics were evaluated.

In the battery structure 26 according to this embodiment, the positive electrode active material 12 and the negative electrode active material 16 are formed on only one surface of the positive electrode current collector foil 10 and the negative electrode current collector foil 14, respectively. Since it was completed as a lithium-ion secondary battery before that, it is possible to check the capacity and short circuit of each battery constituent. The battery assembly 26 used in this example has a maximum capacity variation of 20%. However, as described above, since the capacity of each battery assembly 26 can be measured in advance, the battery assembly having a small capacity variation can be obtained. It is possible to form a bipolar lithium ion secondary battery with only the body. As a result, cycle characteristics can be improved.

Battery structure 26 having a capacity variation of 5% or less
Only four of them are connected in series and wound in the winding direction A shown in FIGS.
When the secondary battery was constructed and charged and discharged at a constant current of 1 C between 12V and 17V, the capacity retention ratio after 100 cycles was 87%, which was a good value.

Embodiment 4. FIG. 11 shows a cross-sectional view of the configuration of the bipolar lithium-ion secondary battery according to this embodiment. In addition, in FIGS. 12A and 12B, FIG.
A cross-sectional view and a plan view of a battery structure 26 that constitutes the bipolar lithium-ion secondary battery shown in FIG.

In FIG. 12A, the positive electrode active material 12 was formed on only one surface of the positive electrode current collector foil 10 to form a positive electrode. In addition, the negative electrode active material 16 is provided only on one surface of the negative electrode current collector foil 14.
To form a negative electrode. These positive and negative electrodes are
The active materials 12 and 16 are arranged so as to face each other with the separator 18 in between, and constitute a battery structure 26. The battery structure 26 according to the present embodiment has the positive electrode active material 1
Insulating members 38 are provided at both ends of the negative electrode active material 16, the negative electrode active material 16, and the separator 18, and thereby the positive electrode current collector foil 10 and the negative electrode current collector foil 14 of the battery structure 26 are brought into close contact with each other.
Thereby, the contents including the positive electrode active material 12 and the negative electrode active material 16 and the separator 18 can be sealed to prevent leakage of the electrolyte. Therefore, it is possible to prevent a voltage drop due to a short circuit of the electrolyte.

FIG. 12B shows collector foils 10 and 14 coated with active materials 12 and 16 and a separator 18 surrounded by an insulating member 38. When the battery structure 26 is formed by these, the active materials 12 and 16 are housed in the portion surrounded by the insulating member 38, and the positive electrode and the negative electrode are fitted to the insulating member 38 so as to be in contact with the separator 18. As a result, the battery structure 26 as shown in FIG. 12 (a) can be obtained.

Such a battery structure 26 is shown in FIG.
As shown in (a), a current collector foil, an active material, and a separator are laminated, and upper and lower laminated end faces of the laminated structure are a positive electrode current collector foil 10 and a negative electrode current collector foil 14. . Therefore, this is indicated by the arrow A shown in FIG.
In such a manner that the positive electrode current collector foil comes to the innermost part and the negative electrode current collector foil comes to the outermost part. The positive electrode current collector foil 10 can be wound outside so as to make electrical contact.
Thereafter, similarly, a predetermined number of battery components 26 are sequentially wound outward. As a result, as shown in FIG.
It is possible to obtain a bipolar lithium ion secondary battery in which the battery components 26 are connected in series from the inside to the outside. In the bipolar lithium-ion secondary battery thus assembled, the positive electrode terminal lead 20 is connected to the innermost positive electrode current collector foil, and the negative electrode terminal lead 22 is connected to the outermost negative electrode current collector foil. Also in this embodiment, the innermost part may be the negative electrode and the outermost part may be the positive electrode.

The battery assembly 26 according to the present embodiment.
A bipolar lithium-ion secondary battery can be obtained by stacking as in the prior art without winding.

A specific example of the bipolar type lithium ion secondary battery according to this embodiment will be described below as Example 3.

Example 3. An aluminum foil was used as the positive electrode current collector foil 10, and the active material was printed and dried to form a blank on the periphery of only one surface of the aluminum foil to obtain a positive electrode. LiMn ₂ O ₄ was used as the positive electrode active material 12, and natural graphite was mixed therein as a conductive agent. In addition, EC: DE is used as the gel electrolyte.
A solution in which 1 mol / l of LiPF ₆ was dissolved in a liquid of C = 1: 1 and PVDF-HFP in 3: 1 were used. Tetrahydrofuran (THF) was used as an organic solvent for forming a paste. These were mixed at a mixing ratio of LiMn ₂ O ₄ : natural graphite: gel electrolyte: organic solvent = 10: 1: 10: 30 to prepare a positive electrode paste, which was applied to the positive electrode current collector foil 10.

Further, a copper foil was used as the negative electrode current collector foil 14, and a margin was formed around the copper foil only on this one surface to print and dry the active material to obtain a negative electrode. Natural graphite was used as the negative electrode active material, and the same gel electrolyte and organic solvent as those used in the positive electrode were used. These were mixed at a mixing ratio of natural graphite: gel electrolyte: organic solvent = 1: 1: 4 to prepare a negative electrode paste, which was applied to the negative electrode current collector foil 14.

As the separator 18, a non-woven fabric impregnated with a gel electrolyte and an organic solvent and dried was used. As the gel electrolyte, a solution in which 1 mol / l of LiPF ₆ was dissolved in a liquid of EC: DEC = 1: 1 and PVD
Using a mixture of F-HFP at a ratio of 5: 1,
THF was used as the organic solvent. The mixing ratio of the gel electrolyte and the organic solvent was 1: 2. The separator 18 thus formed was surrounded by an insulating member 38 made of polypropylene film so that the gel electrolyte would not leak. Further, the positive electrode and the negative electrode active materials 12 and 14 described above are arranged so as to face each other with the separator 18 interposed therebetween, and hot pressed to collect the positive electrode current collector foil 10-insulating member 38-separator 18-insulating member 38-negative electrode. Collector foil 14
Was thermocompressed and the contents were sealed. By this hot pressing, the gel electrolyte in the positive electrode active material 12, the separator 18, and the negative electrode active material 16 is also re-gelled after being melted by heat, voids between gels are eliminated, and ionic conductivity is improved.

The battery assembly 26 constructed as described above
After checking its capacity and whether or not there is a short circuit, it is quadrupled in a battery case (not shown), and the inner battery assembly 2
Electrically connected in series from No. 6 to the outer battery structure 26 to obtain a bipolar lithium ion secondary battery.

As described above, the bipolar lithium-ion secondary battery according to this example had a voltage drop to 15.6V even after being left for 10 days while being initially charged to 16.4V. On the other hand, the periphery of the separator 18 is not covered with the insulating member 38 in advance, and
After winding 6 and insulating the exposed portion of the electrolyte with epoxy resin or the like, after leaving it for 10 days, 16.
The voltage of 4V had dropped to 3.8V. This allows
It can be seen that the bipolar lithium-ion secondary battery according to this example has extremely good insulating properties.

Embodiment 5. In the bipolar lithium-ion secondary battery according to each of the embodiments described above, when the charging / discharging current becomes large, the inner battery structure 2
The temperature rises by about 6. Therefore, the inner battery assembly 2
6, the lithium ion conductivity is better, and the internal resistance is lower than that of the outer battery component 26. Each battery structure 2
Since 6 is connected in series and the same amount of current flows, the voltage is higher in the outer battery component 26 having the higher internal resistance. Therefore, when a high voltage is applied, there is a possibility that the battery may deteriorate due to deterioration of the electrolytic solution of the outer battery structure 26 or elution of the current collector foil. Therefore, it is preferable to adjust the internal resistances of the individual battery components 26 so that they are equal in use.

FIG. 13 shows each of such battery components 26.
A cross-sectional view of the structure of a bipolar lithium-ion secondary battery in which the internal resistances of the two are equal in use is shown. Also, FIG.
4 shows a sectional view of a battery structure 26 for forming the bipolar lithium ion secondary battery shown in FIG. In FIG. 14, when the bipolar lithium ion secondary battery shown in FIG. 13 is formed, the battery structure 26 is wound in the direction of arrow A in the drawing. Is the battery assembly 26 on the right side of the figure.
Will be more inside. Therefore, the battery assembly 2 on the left side of the figure
If the internal resistance of 6 is increased in advance, the temperature of the inner battery assembly 26 becomes high during use, and even if the internal resistance becomes low, the battery assembly 26 on the right side in the figure that comes to the outside
Can be equal to the internal resistance of. Thereafter, similarly, the battery components 26 arranged on the outer side are configured such that the internal resistance thereof is lowered in advance.

As a method of adjusting the internal resistance, the total amount of the active material and the porosity of each electrode are kept constant, the thickness of the active material is adjusted, and as a result, the effective area, that is, the separator 18 is opposed. There is a method of controlling the area of the active material layer. That is, if the thickness is increased, the effective area is reduced accordingly and the resistance is increased.

On the other hand, the internal resistance can also be adjusted by keeping the weight per unit area, that is, the weight of the active material per unit area and the effective area constant, adjusting the thickness of the active material, and changing the porosity. . That is, as the thickness of the active material is changed by pressing to reduce the porosity, the electrolyte existing between the active materials decreases, the ionic conductivity decreases, and the resistance increases.

As described above, the resistance is adjusted by the effective area by changing the thickness while keeping the total amount of active material and the porosity constant, or the porosity of the active material is adjusted by making the basis weight and effective area constant. A method of adjusting the internal resistance is considered to be suitable.

Specific examples of the method of adjusting the internal resistance as described above will be described as Examples 4 and 5.

Example 4. In this embodiment, four battery components 26 are used and the internal resistance of each is varied. The four battery components 26 are I, II, III, in this order from the innermost wound one to the outer one.
Table 1 shows the values of the effective areas of the positive electrode and the negative electrode, respectively. In this example, the effective area was changed by keeping the total active material amount and porosity of each electrode constant and changing the basis weight.

[0059]

[Table 1] The porosity of each active material was 45% for both the positive electrode and the negative electrode.

Example 5. Four battery assemblies 26I, I
The weight of the positive and negative electrodes of I, III, and IV is 2 each.
0.4mg / cm ^2, a constant of 10.2mg / cm ^2,
The effective area was also fixed at 100 cm ² . The positive electrode and negative electrode active materials were pressed to have the thicknesses shown below, and the porosity thereof was adjusted.

[0061]

[Table 2] In the case of the battery structure IV, the porosity is 50%, and if the porosity is further increased, the contact resistance between the active materials increases and the resistance increases with the increase in the film thickness, so this thickness is considered to be the limit. . Below the film thickness of the battery structure IV, the porosity decreases as the film thickness decreases, the electrolytic mass between the active materials decreases, the ionic conductivity decreases, and the resistance increases. That is, the higher the pressing pressure of the active material, the higher the resistance.

With respect to the above two embodiments, all the four battery components I, II, III, IV have a positive electrode basis weight of 2
0.4 mg / cm ² , negative electrode basis weight 10.2 mg / c
Those having m ² and porosity of 45% were prepared and evaluated together with the above two examples.

When the bipolar type lithium ion secondary battery obtained as described above was charged and discharged at a constant current of 1 C at a voltage of 12-17 V, the capacity retention rate after 100 cycles was 90% in Example 4. %, Example 5 was 91%, and Comparative Example was 87%. Therefore, like Example 4 and Example 5, the cycle characteristics could be improved by increasing the internal resistance of the inner battery components.

[0064]

As described above, according to the present invention,
Since the battery structure is wound to form a bipolar lithium-ion secondary battery, a compact and large-capacity battery can be obtained.

Further, since the inner battery structure and the outer battery structure are electrically connected by directly connecting the current collectors to each other, the contact resistance can be reduced.

Further, since the current collector foil is wound around the outer periphery of the inner battery structure for one or more turns, the electrolyte short circuit can be prevented and the insulating property can be improved, and the short circuit can be prevented only by the current collector foil. Since it is not necessary to use an insulating film, the size can be reduced accordingly.

Further, since the outermost current collecting foil of the inner battery component and the outermost current collecting foil of the outer battery component are directly contacted and electrically connected, the contact area becomes large, The internal resistance can be reduced.

In addition, since the internal resistance of the battery components located closer to the inside is made higher, the internal resistances of all the battery components become substantially equal during use, and the voltages applied to the respective battery components can be made approximately equal. Deterioration can be suppressed.

[Brief description of drawings]

FIG. 1 is a bipolar lithium ion 2 according to the present invention.
1 is a cross-sectional view of a battery structure used in a first battery of Embodiment 1.

FIG. 2 is an explanatory diagram when the battery structure shown in FIG. 1 is wound.

FIG. 3 is a cross-sectional view showing a modified example of the battery structure used in the first embodiment.

FIG. 4 is a cross-sectional view of the configuration of the bipolar lithium-ion secondary battery according to the first embodiment.

5 is a VV cross-sectional view of the bipolar lithium-ion secondary battery shown in FIG.

FIG. 6 is a bipolar lithium ion 2 according to the present invention.
It is sectional drawing of Embodiment 2 of the following battery.

FIG. 7 is a cross-sectional view of a battery structure that constitutes the bipolar lithium-ion secondary battery shown in FIG.

FIG. 8 is a diagram showing a modified example of the battery structure that constitutes the bipolar lithium-ion secondary battery shown in FIG.

FIG. 9: Bipolar lithium ion 2 according to the present invention
It is sectional drawing of Embodiment 3 of the following battery.

FIG. 10 is a cross-sectional view and a plan view of a battery structure that constitutes the bipolar lithium-ion secondary battery shown in FIG.

FIG. 11 is a cross-sectional view of Embodiment 4 of a bipolar lithium-ion secondary battery according to the present invention.

12 is a cross-sectional view and a plan view of a battery constituent body that constitutes the bipolar lithium-ion secondary battery shown in FIG.

FIG. 13 is a cross-sectional view of Embodiment 4 of a bipolar lithium-ion secondary battery according to the present invention.

FIG. 14 is a cross-sectional view of a battery structure that constitutes the bipolar lithium-ion secondary battery shown in FIG.

FIG. 15 is a cross-sectional view of a conventional bipolar lithium-ion secondary battery.

[Explanation of symbols]

10 positive electrode current collector foil, 12 positive electrode active material, 14 negative electrode current collector foil, 16 negative electrode active material, 18 separator, 20 positive electrode terminal lead, 22 negative electrode terminal lead, 24 insulating film, 26 battery component, 28 insulating container, 30 series Connection lead wire, 32 connection part, 34 connection current collector foil, 3
6 insulating film, 38 insulating member, 100 battery case.

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 10/40 H01M 2/20-2/34 H01M 10/04

Claims (2)

(57) [Claims] 1. A plurality of battery constituents wound in a state where a separator is sandwiched between a positive electrode and a negative electrode are concentrically wound through an insulator, and a battery outside the inner battery constituent. To the structure, they are sequentially electrically connected in series and each connection
In the sequel, the positive or negative current collector foil of the inner battery assembly
Connected to the negative electrode or positive electrode current collector foil of the outer battery structure
Contact between the inner battery structure and the outer battery structure.
The current collector foil that forms the connecting part is the entire outer circumference of the battery structure inside.
A bipolar lithium-ion secondary battery having a structure that encloses 2. A plurality of battery constituents wound in a state where a separator is sandwiched between a positive electrode and a negative electrode are concentrically wound with an insulator interposed therebetween, and the battery constituents from the inner constituent to the outer constituent. Towards the structure, connected in series electrically in sequence ,
The inner battery structure and the outer battery structure have the same electrical capacity
Then, a bipolar lithium-ion secondary battery characterized in that the internal resistance is made higher toward the inner battery structure .