JP2001143671A - Gasket and flat battery using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flat battery having a high capacity and an improved discharge characteristic and preventing shortage of electrolyte in the latter half of discharging. SOLUTION: A plurality of flowing holes 11 is formed at an inner wall 12 of a gasket 10. If electrolyte lacks by an expansion of a positive electrode 21 in the latter half of discharging, electrolyte 26 stored in a space 25 flows into the positive electrode 21 through the flowing holes 11. Therefore, an amount of electrolyte lost by the expansion of the positive electrode 21 is supplied from an area (the space 25) not influencing the battery reaction. Since the plurality of flowing holes 11 are formed at the inner wall 12 at equal intervals, the electrolyte is evenly replenished throughout the positive electrode 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gasket for preventing electrolyte leakage and a flat battery using the same.

[0002]

2. Description of the Related Art In recent years, flat batteries have been increasingly demanded as portable power supplies for small electronic devices such as calculators, electronic watches, electronic organizers, and portable game machines. In addition, with the improvement in the performance of these small electronic devices, flat batteries are required to have high capacity and load characteristics capable of stably extracting a large current even at the end of discharge.

[0003]

In such a battery,
Depending on the material of the positive electrode and the type of battery reaction, the volume of the positive electrode pellet increases with discharge. Since the electrolyte is absorbed in the gap inside the positive electrode caused by the volume expansion, the electrolyte is insufficient at the end of discharge, and as a result, the internal resistance is greatly increased and a large current cannot be stably obtained. It is known. Therefore, it is necessary to supply a sufficient amount of the electrolytic solution in advance, but in order to add a larger amount of the electrolytic solution, it is necessary to reduce the amounts of the active materials of the positive electrode and the negative electrode.

Incidentally, for example, in a lead storage battery and a polymer battery which is currently under development, the discharge characteristics are deteriorated due to a decrease in the amount of the electrolyte or a decrease in the concentration of the electrolyte accompanying the electrode reaction. In other words, the decrease in the amount of the electrolytic solution and the change in the concentration of the electrolyte due to the electrode reaction occur regardless of the material of the electrode or the type of the reaction, and whether or not the positive electrode expands. This is a problem to be solved because the discharge characteristics are deteriorated.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a flat battery which can improve the shortage of the electrolyte in the latter half of discharge while having a high capacity and exhibit good discharge characteristics. An object of the present invention is to provide a gasket suitable for this.

[0006]

A gasket according to the present invention is used for a flat battery having a structure in which a positive electrode and a negative electrode are superimposed, and has a wall portion surrounding a side surface of the positive electrode. A circulation part for supplying the electrolytic solution to the positive electrode side is formed in the part. Note that, here, the substance passing through the flow part is expressed as an electrolyte, but it is assumed that not only the case where the liquid electrolyte passes but also the case where only the electrolyte contributing to ion conduction moves.

A flat battery according to the present invention has a structure in which a positive electrode and a negative electrode are overlapped, and includes a gasket having a wall formed so as to surround a side surface of the positive electrode. A flow hole for supplying the electrolyte to the positive electrode side is formed in the wall of the gasket.

In the flat battery according to the present invention, since the gasket of the present invention is provided, the electrolytic solution passes from one area partitioned by the wall of the gasket to the area where the positive electrode exists through the flow hole. Is moved and supplied. As a result, an increase in internal resistance due to lack of electrolyte in the latter half of discharge is suppressed, and good discharge characteristics are exhibited.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1A shows a plan configuration of a flat battery according to an embodiment of the present invention, in which a gasket is taken out. FIG. 1B shows a cross-sectional configuration along the line XX of FIG. The gasket 10 has an inner wall 12 and an outer wall 13 formed concentrically. Inside the inner wall 12, a positive electrode (not shown) formed in a pellet shape is housed. This inner wall 12 is slightly inclined inward,
Thereby, the expansion of the positive electrode in the horizontal direction is suppressed.

In the present embodiment, a plurality of, for example, eight flow holes 11 are formed at equal intervals in the inner wall 12 of the gasket 10 so that the electrolyte can move through the flow holes 11. . A gasket having such a configuration is made of, for example, a synthetic resin such as polypropylene,
For example, it can be obtained by molding by injection molding or the like.

The gasket 10 is used by being incorporated in, for example, a so-called coin type flat battery shown in FIG.

FIG. 2 shows a sectional structure of the flat battery. The flat battery has a structure in which a disk-shaped negative electrode 23 housed in a negative electrode cup 22 and a disk-shaped positive electrode 21 housed in a positive electrode can 20 are overlapped with a separator 24 interposed therebetween. are doing. The separator 24 is impregnated with an electrolytic solution 26 which is a liquid organic electrolyte, and the periphery thereof is supported by the inner wall 12 of the gasket 10. The outer wall 13 of the gasket 10 has a negative electrode cup 22 and a positive electrode can 2.
The inside of the battery is sealed by being caulked together with the peripheral portion of the battery.

In this flat battery, a donut-shaped space 25 is formed by the inner wall 12 of the gasket 10, the negative electrode cup 22 and the side surface of the negative electrode pellet 23 which are in close contact with the inner periphery of the outer wall 13 and cover the inner wall. This space 25
A plurality of flow holes 1 formed in the inner wall 12 of the gasket 10
1 allows communication with the inside of the inner wall 12, that is, with the positive electrode 21 side. In this space 25, an electrolyte 26
Are stored, for example, from the separator 24 or by being pre-injected.

The positive electrode 21 is, for example, a positive electrode active material,
Transition metal chalcogen compounds such as FeS ₂ , TiS ₂ , MoS ₂ , NbSe ₂ or CuO, MnO ₂ , V ₂
It contains a transition metal oxide such as O ₅ or a composite compound of these and lithium. In addition, fluorinated graphite (C
F), carbon black, iodide and the like.

In particular, in a lithium ion secondary battery, it is preferable that the positive electrode contains a lithium composite oxide mainly composed of Li _x MO ₂ in order to increase the energy density. M is preferably one or more transition metals, and specifically, at least one of cobalt (Co), nickel (Ni), and manganese (Mn) is preferable. Also,
x is a value generally represented by 0.05 ≦ x ≦ 1.10. As specific examples, LiCoO ₂ , LiNiO ₂ , L
_{i x Ni y Co 1-y} O 2 ( where, the values of x and y vary according to charge and discharge state of the battery, usually, 0 <x <1, 0.
7 <y ≦ 1) or LiMn ₂ O ₄ . Incidentally, such a lithium composite oxide is, for example,
A carbonate, nitrate, oxide or hydroxide of lithium and a carbonate, nitrate, oxide or hydroxide of a transition metal are mixed so as to have a desired composition, pulverized, and then mixed in an oxygen atmosphere. It is prepared by firing at a temperature in the range of 〜1000 ° C.

The negative electrode 23 is made of, for example, metallic lithium (L
i) a lithium alloy such as LiAl, or a carbon material or oxide capable of inserting and extracting lithium ions,
Alternatively, it is configured to include any one or more of polymer materials. Carbon materials include, for example, graphites,
Examples include pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, carbon fibers and activated carbon. Among them, cokes include pitch coke, needle coke, petroleum coke, and the like. An organic polymer compound fired body is obtained by firing a polymer material such as a phenol resin or a furan resin at an appropriate temperature and carbonizing it. Say. Further, oxides include metal oxides, and particularly, oxides of transition metals such as Fe, Ru, Mo, W, Ti, Sn, and Si are preferable.

In addition, lithium is not necessarily all the positive electrode 21.
Alternatively, it is not necessary to be supplied from one of the negative electrodes 23, and it is sufficient that lithium is present in the battery system in an amount corresponding to the required charge / discharge capacity.

The separator 24 separates the positive electrode 21 from the negative electrode 23 and prevents a short circuit of current due to contact between the two electrodes,
It allows lithium ions to pass through, and is made of, for example, a porous film made of a synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene, or a ceramic.

The electrolytic solution 26 is obtained by dissolving a lithium salt in an organic solvent, and ionizes the lithium salt to conduct ions. As the organic solvent, for example, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane , 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, anisole, acetate or propionate. Further, two or more of these may be used in combination.

As the lithium salt, for example, LiClO
_{4, LiAsF 6, LiPF 6,} LiBF 4, LiB
(C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ L
i, LiCl, and LiBr, of which 2
A mixture of more than one species may be used.

This flat battery is assembled as follows. That is, after the separator 24 is impregnated with the electrolytic solution 26, the positive electrode 21 and the negative electrode 23 are overlapped with each other via the separator 24, and this is placed in the positive electrode can 20. Next, the periphery of the positive electrode can 20 is caulked with the negative electrode cup 22 via the gasket 10 to seal the inside of the battery, thereby producing the flat battery shown in FIG. In this assembling process, generally, the electrolytic solution 26 may drop from the peripheral portion of the separator 24 and may be stored in the space 25 adjacent to the inner wall 12 of the gasket 10.

Next, the operation of the flat battery according to the present embodiment will be described.

In the flat battery according to the present embodiment, when discharging is performed, lithium is ionized and desorbed from the negative electrode active material contained in the negative electrode 23, and the separator 2 is separated via the electrolytic solution 26.
4 and is stored in the positive electrode 21. If the electrolyte is insufficient, the reaction will not be sufficiently performed, and the internal resistance of the battery will increase significantly, and a large current cannot be taken out. Incidentally, when used as a secondary battery, lithium is ionized and desorbed from the positive electrode 21 by further charging, passes through the separator 24 via the electrolytic solution 26, and returns to the negative electrode active material included in the negative electrode 23.

Here, in the present embodiment, the gasket 1
The electrolyte 26 stored in the space 25 is effectively supplied through the flow holes 11 provided in the inner wall 12 of the “0”. That is, in the discharge reaction, for example, when the positive electrode 21 is a compound having a layered or tunnel structure, as lithium ions are occluded, the crystal spacing increases and the volume increases. Then, the electrolytic solution 26 contained in the separator 24 becomes
It is gradually taken into the positive electrode 21 together with the lithium ions and is reduced. At this time, the positive electrode 21 expands in the direction of the arrow a as shown in FIG. Due to this pressure, the inner wall 12 compresses the space 25 as shown by the two-dot chain line, so that the electrolyte solution 26 stored in the space 25 passes through the flow hole 11 of the inner wall 12 as shown by the arrow b in the figure. Then, it flows into the positive electrode 21 side. Thus, the positive electrode 21
The amount of electrolyte solution lost due to the expansion of the positive electrode 21 is supplied from the space 25 as the positive electrode 21 expands. Since a plurality of flow holes 11 are provided at equal intervals in the inner wall 12, the positive electrode 21 is uniformly supplied to the whole.

As described above, in the gasket 10 according to the present embodiment, since the flow hole 11 is provided in the inner wall 12, in the flat battery using the same, the gasket 10 exists in the space 25 adjacent to the inner wall 12. The electrolytic solution is supplied to the positive electrode 21 through the flow hole 11 and can be effectively used for the electrode reaction. Therefore, it is possible to prevent the electrolyte solution from decreasing in the latter half of the discharge without impairing the discharge capacity. it can.

The space 25 has conventionally been present as an ineffective area adjacent to the inner wall 12 of the gasket 10 and not involved in the battery reaction, and the electrolyte present in this area has been dropped from the separator during the assembly process. It is stored. In the present embodiment, these regions and the electrolyte can be used effectively only by providing the flow holes 11 in the gasket having the conventional structure, without adding a new step to the conventional manufacturing process. , Can be easily realized. Of course, the electrolytic solution stored in the space 25 is not limited to the one dropped from the separator in the assembling process, and may be a separately injected solution.

[Embodiment] Next, a specific embodiment of the present invention will be described.

A gasket 10 having eight flow holes 11 in the inner wall 12 shown in FIG. 1 was obtained by injection molding polypropylene.

The positive electrode 21 was manufactured as follows. 9
Heat treated manganese dioxide as 0 wt% active material, 8w
A positive electrode pellet having a diameter of 16 mm and a thickness of 2.0 mm was produced by press-molding a mixture comprising t% of graphite as a conductive agent and 2 wt% of a fluororesin as a binder.

The negative electrode 23 was produced by punching metallic lithium and molding it into a coin shape having a diameter of 16 mm and a thickness of 0.6 mm.

The electrolytic solution 26 was prepared by dissolving LiClO _{4 in} a mixed solvent of propylene carbonate and 1,2-dimethoxyethane having a volume ratio of 1: 1 so as to have a concentration of 0.5 mol / l. The electrolytic solution 26 is applied to a thickness of 0.15
The separator 24 made of polypropylene non-woven fabric having a thickness of 2 mm was sufficiently impregnated.

The positive electrode can 20 and the negative electrode cup 22 are both made of stainless steel plated with nickel, and also serve as positive and negative electrode terminals, respectively. A positive electrode 21, a separator 24, and a negative electrode 23 were sealed inside the positive electrode can 20 and the negative electrode cup 22 in this order from the positive electrode can side, and the periphery was crimped through the gasket 10. Thus, the outer diameter is 20.0 mm and the height is 3.
A 2 mm flat battery was manufactured.

Comparative Example As a comparative example of the present example, a flat battery was produced in the same manner as in the example, using the same gasket as that of the example except that the through hole 11 was not provided.

Next, the characteristics of each flat battery were evaluated as described below.

First, at room temperature (23 ° C.), a load resistance of 15 k
Discharge was performed under the conditions of Ω and a final voltage of 2.5 V, and the initial capacity was measured. The number of samples was 10 in both the examples and comparative examples.
It was made into pieces. Table 1 shows the average value and standard deviation of these initial volumes.

[0037]

[Table 1]

From Table 1, it can be seen that the standard deviation of the example is smaller than that of the comparative example and the discharge capacity is larger. That is,
The example has a larger and more stable discharge capacity than the comparative example.

Next, the closing voltage after 15 seconds at a temperature of -10 ° C. and a load resistance of 500Ω was set to 0% and 80% of the depth of discharge.
Was measured for each case. For a sample having a discharge depth of 80%, 80% of the discharge capacity shown in Table 1 was used at room temperature (23
(° C.) at 15 ° C. for discharging. The number of samples in each of the examples and comparative examples was 20. Table 2 shows the average value of the low-temperature closing voltage for each discharge depth.

[0040]

[Table 2]

From Table 2, it can be seen that the closed circuit voltage of the example is not as low as that of the comparative example even at the end of discharge at the depth of 80% with respect to the discharge depth of 0%. Even when only the closed circuit voltage at a depth of 80% is compared, the example shows a higher value than the comparative example, and it can be seen that a large current can be taken out.

Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above-described embodiments and examples, and can be variously modified. For example, in the above-described embodiments and examples, a lithium battery is described as an example. However, the present invention can be similarly applied to other batteries that can be processed into a flat shape. In the above-described embodiment and each example, the number of the flow holes is eight. However, the number of the flow holes, the shape and size thereof, the position on the inner wall of the gasket, and the like are arbitrary.

In the above embodiments and examples, the passage of the electrolyte is described as a hole. However, the present invention is not limited to the hole, but may be a groove (or cut) obtained by dividing the inner wall portion of the gasket into a plurality. There may be.

Furthermore, in the above-described embodiment, an example has been described in which the electrolyte stored in the space is pushed out to the positive electrode side by the pressure due to the expansion of the positive electrode in order to compensate for the decrease in the electrolyte due to the discharge reaction. What accelerates the movement of the positive electrode need not be the expansion of the positive electrode. For example, the present invention can be applied not only to a decrease in the electrolytic solution but also to a decrease in the electrolyte, that is, a decrease in the concentration. The driving force for the movement of the electrolyte at this time may be at least the osmotic pressure due to the concentration difference between the positive electrode side and the space. As long as the electrolyte can move to the positive electrode side through the flow hole 11 provided in the gasket 10 as described above, the present invention can be applied regardless of the mechanism.

[0045]

As described above, according to the gasket of the present invention, since the flow portion is formed on the wall, the region (space) where the electrolyte is partitioned by the wall and does not participate in the battery reaction is formed. Part) to the region where the positive electrode is present, and by using this to produce a flat battery, the electrolytic solution in the battery can be effectively used for the battery reaction, so that good discharge characteristics can be obtained. It has the effect of being able to.

Further, according to the flat battery of the present invention, since the gasket of the present invention is used, the electrolyte can be supplied without exchanging the amount of the electrode, so that a high battery capacity can be maintained and the latter half of the discharge can be maintained. Prevents the internal resistance from increasing due to the shortage of the electrolytic solution, and obtains good discharge characteristics.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a gasket according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a configuration of a flat battery using the gasket of FIG.

FIG. 3 is a cross-sectional view of a main part for describing a mechanism of supplying an electrolytic solution to a positive electrode side of the flat battery illustrated in FIG. 2;

[Description of Signs] 10: insulating gasket, 11: flow hole, 12: inner wall, 1
3 outer wall, 20 positive electrode can, 21 positive electrode, 22 negative electrode cup, 23 negative electrode, 24 separator

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H011 AA09 CC06 DD15 FF03 GG02 HH02 JJ04 5H029 AJ02 AJ15 AK01 AK02 AK03 AK05 AK07 AL02 AL06 AL07 AL08 AL12 AL16 AL18 AM02 AM03 AM04 AM05 AM07 BJ03 DJ03 DJ14 HJ12

Claims (10)

[Claims] 1. A gasket for use in a flat battery having a structure in which a positive electrode and a negative electrode are overlapped, the gasket having a wall surrounding a side surface of the positive electrode, wherein the wall is provided with an electrolyte and the positive electrode pellet. A gasket, characterized in that a flow part for supplying to the side is formed. 2. The gasket according to claim 1, wherein said flow portion is a flow hole formed near a lower end portion of said wall portion. 3. A flat battery having a structure in which a positive electrode and a negative electrode are overlapped with each other, comprising a first wall surrounding a side surface of the positive electrode, wherein an electrolyte is provided on the first wall. A flat battery comprising a gasket provided with a flow portion for supplying the gas to the side. And a separator impregnated with an electrolytic solution interposed between the positive electrode and the negative electrode, a positive electrode can containing the positive electrode, and a negative electrode cup covering the negative electrode. 4. The flat battery according to claim 3, wherein a wall portion forms a space portion for storing an electrolyte solution between the wall portion and a peripheral portion of the negative electrode cup. 5. The flat battery according to claim 4, wherein a peripheral portion of the separator extends to the space. 6. The flat battery according to claim 5, wherein the electrolyte stored in the space is supplied from a peripheral portion of the separator. 7. The gasket further comprises a second wall integrally formed with the first wall so as to surround the first wall.
5. The device according to claim 4, wherein the second wall portion is interposed between the positive electrode can and the negative electrode cup.
The flat battery according to any one of the preceding claims. 8. The flat battery according to claim 4, wherein the gasket is provided with a plurality of flow portions uniformly on the first wall portion. 9. The gasket is formed of a material having elasticity, and the first wall is inclined toward the positive electrode, and the first wall is displaced by expansion of the positive electrode. 5. The flat battery according to claim 4, wherein the electrolyte stored in the space portion is supplied to the positive electrode side through the flow portion. 10. The negative electrode is lithium, a lithium alloy,
5. The flat battery according to claim 4, comprising at least one of a material capable of being alloyed with lithium and a material capable of inserting and extracting lithium.