Secondary batteries

Abstract

The present invention provides a secondary battery that can appropriately suppress ion conduction through the electrolyte between the battery case and the electrode body without providing an insulating film between the electrode body and the excess electrolyte. [Solution] The secondary battery comprises a battery case having a bottom surface inside, an electrolyte, and an electrode body housed inside and impregnated with the electrolyte. The electrode body has a lower surface facing the bottom surface, spaced apart from the bottom surface. A void is formed in the electrode body. The amount of electrolyte is greater than or equal to the volume of the void, and less than the sum of the volume of the void and the volume of the part of the interior below the bottom surface.

Description

Technical Field

[0001] This disclosure relates to a secondary battery.

Background Art

[0002] For example, as disclosed in Japanese Unexamined Patent Application Publication No. 2020-057502 (Patent Document 1), there is disclosed a secondary battery capable of appropriately suppressing ion conduction through an electrolytic solution between a battery case and an electrode body.

[0003] Specifically, the secondary battery includes an electrode body, a battery case, and an insulating film. In the electrode body, a positive electrode and a negative electrode are laminated via a separator. The battery case has a bottomed box shape and houses the electrode body and the electrolytic solution. The insulating film is provided between the electrode body and the inner wall of the battery case to insulate the electrode body from the battery case. The insulating film includes a partition portion and an electrolytic solution passage portion. The partition portion prohibits the movement of the electrolytic solution between the electrode body side and the inner wall side in a range below a position higher than the liquid level of the excess electrolytic solution accumulated at the bottom of the battery case. The electrolytic solution passage portion is formed at a position higher than the liquid level of the excess electrolytic solution and allows the electrolytic solution to pass between the electrode body side and the inner wall side.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the secondary battery of Patent Document 1, it is necessary to provide a partition portion for isolating the electrode body from the excess electrolytic solution on the insulating film.

[0006] This disclosure provides a secondary battery capable of appropriately suppressing ion conduction through an electrolytic solution between a battery case and an electrode body without providing an insulating film between the electrode body and the excess electrolytic solution. [Means for solving the problem]

[0007] According to a certain aspect of this disclosure, a secondary battery comprises a battery case having a bottom surface inside, an electrolyte, and an electrode body housed inside and impregnated with the electrolyte. The electrode body has a lower surface facing the bottom surface, spaced apart from the bottom surface. A void is formed in the electrode body. The amount of electrolyte is greater than or equal to the volume of the void, and less than the sum of the volume of the void and the volume of the portion of the interior below the lower surface. [Effects of the Invention]

[0008] According to this disclosure, it becomes possible to appropriately suppress ion conduction through the electrolyte between the battery case and the electrode body without providing an insulating film between the electrode body and the excess electrolyte. [Brief explanation of the drawing]

[0009] [Figure 1] This is a cross-sectional view of a secondary battery for electric vehicles. [Figure 2] This diagram shows the relationship between the amount of electrolyte and the battery capacity retention rate. [Figure 3] This diagram shows the relationship between the amount of electrolyte and the rate of resistance increase. [Modes for carrying out the invention]

[0010] Embodiments of this disclosure will be described below with reference to the drawings. In the following description, the same reference numerals are used for identical components. Their names and functions are also the same. Therefore, detailed descriptions of them will not be repeated.

[0011] Figure 1 is a cross-sectional view of a secondary battery for electric vehicles. Note that an electric vehicle is a hybrid vehicle capable of running using power from at least one of a motor and an engine, or an electric vehicle that runs using driving force obtained from electrical energy.

[0012] As shown in Figure 1, the secondary battery 1 is a battery cell. The secondary battery 1 comprises an electrode body 10, a battery case 20, a positive electrode terminal 31, a negative electrode terminal 32, and an electrolyte. In Figure 1, a portion of the electrolyte is denoted by the reference numeral "80". In this example, the electrode body 10 is a laminated electrode body. However, the electrode body 10 is not limited to this and may be a wound electrode body.

[0013] The battery case 20 houses the electrode body 10 inside. The electrolyte is housed in the battery case 20. By housing the electrode body 10 in the battery case 20, a gap S is formed inside. Specifically, the battery case 20 has a case body 21 and a lid 22. The case body 21 is a bottomed box shape. The battery case 20 has a bottom surface 26 inside. The bottom surface 26 is the inner bottom surface of the case body 21.

[0014] The electrode body 10 comprises a positive electrode current collector foil 11, a negative electrode current collector foil 12, a positive electrode current collector plate 13, and a negative electrode current collector plate 14. The electrode body 10 is impregnated with an electrolyte. The electrode body 10 has voids (not shown). The electrolyte is impregnated into these voids. The electrolyte is held in the electrode body 10 by these voids.

[0015] The current collector foil 11 is connected to the current collector plate 13 by welding. The current collector plate 13 is electrically connected to the positive terminal 31. The current collector foil 12 is connected to the current collector plate 14 by welding. The current collector plate 14 is electrically connected to the negative terminal 32.

[0016] The electrode body 10 further comprises a lower surface 15, an upper surface 16, a first main surface 17, and a second main surface 18. The second main surface 18 is located on the positive side of the Y-axis direction compared to the first main surface 17. The first and second main surfaces 17 and 18 extend in the X-axis direction and the Z-axis (vertical direction). The Y-axis direction is the thickness direction of the secondary battery 1.

[0017] An insulating film (not shown) is provided between the first main surface 17 and the inner side surface of the battery case 20 facing the first main surface 17. Similarly, an insulating film (not shown) is also provided between the second main surface 18 and the inner side surface of the battery case 20 facing the second main surface 18.

[0018] The lower surface 15 faces the bottom surface 26 in a state of being separated from the bottom surface 26 of the battery case 20. The lower region Sa is a region of the gap S that is below the lower surface 15 (on the side of the bottom surface 26). The lower region Sa is the bottom part inside the battery case 20. Excess electrolyte 80 has accumulated in a part of the lower region Sa (the lower side portion). The excess electrolyte 80 is the electrolyte remaining after excluding the electrolyte impregnated in the electrode body 10 from the electrolyte injected into the battery case 20.

[0019] Next, the amount of electrolyte in the battery case 20 will be described. A part of the electrolyte injected into the battery case 20 impregnates the voids of the electrode body 10. As a result, the electrode body 10 is in a state of being impregnated with the electrolyte. The rest accumulates as excess electrolyte 80 at the bottom of the battery case 20.

[0020] In the secondary battery 1, the electrode body 10 is sufficiently impregnated with the electrolyte. The reason for this is to ensure the performance of the secondary battery 1 by sufficiently impregnating the electrolyte into the electrode body 10.

[0021] By the way, when the electrode body 10 is immersed in the excess electrolyte 80, the battery case 20 and the electrode body 10 (specifically, the negative electrode of the electrode body 10 (not shown)) are electrically connected through the excess electrolyte 80. When such electrical conduction (ion conduction) through the excess electrolyte 80 occurs, the alloy reaction progresses, and there is a risk of holes forming in the battery case 20. Therefore, it is necessary to prevent a short circuit in the battery case 20. Thus, in the secondary battery 1, the injection amount of the electrolyte is set so that the electrode body 10 is not immersed in the excess electrolyte 80.

[0022] As described above, in the secondary battery 1, the amount of the electrolytic solution is defined as follows. The amount of the electrolytic solution is set to be not less than the volume of the voids in the electrode body 10. Further, the amount of the electrolytic solution is set to be less than the sum of the volume of the voids and the volume of the portion below the lower surface 15 (i.e., the lower region Sa) inside the battery case 20. That is, when the amount of the electrolytic solution is V, the volume of the voids in the electrode body 10 is V1, and the volume of the portion below the lower surface 15 inside the battery case 20 is V2, the amount of the electrolytic solution (V) is expressed by the following formula (1).

[0023] V1≦V<V1+V2 … (1) In this example, the volume (V1) of the voids is measured in advance by the mercury intrusion method. The volume (V2) of the portion below the lower surface 15 can also be expressed as the volume from the bottom surface 26 of the battery case 20 to the lower surface 15 of the electrode body 10.

[0024] [[ID=,10]]According to such a configuration, as described above, sufficient battery performance can be ensured. Further, ionic conduction through the electrolytic solution between the battery case 20 and the electrode body 10 can be appropriately suppressed. Specifically, a short circuit of the battery case 20 can be prevented. Further, since the lower surface 15 of the electrode body 10 is not immersed in the excess electrolytic solution 80, according to the secondary battery 1, an insulating film covering the lower surface 15 becomes unnecessary. That is, there is no need to provide an insulating film between the electrode body 10 and the excess electrolytic solution 80.

[0025] Further, in this example, since the volume of the voids in the electrode body 10 is used, the injection amount of the electrolytic solution can be set accurately. Thereby, it is possible to prevent the electrode body 10 from being immersed in the excess electrolytic solution 80.

[0026] Hereinafter, the amount of the electrolytic solution will be described by taking a specific secondary battery 1 with a nominal capacity of 4.3 Ah as an example. The volume of the voids in the electrode body 10 of the secondary battery 1 in this example was 27.3 cm 3 The volume of the portion below the lower surface 15 (lower region Sa) inside the battery case 20 was 1.94 cm 3 The volume of the lower region Sa was not more than 1 / 13 of the volume of the voids. The density of the electrolytic solution was 1.25 g / cm 3Therefore, the amount of electrolyte should be 34.0g (=1.25 × 27.3) or more, and less than 36.4g (=1.25g × (27.3 + 1.94)).

[0027] Figure 2 shows the relationship between the amount of electrolyte and the battery capacity retention rate. Figure 3 shows the relationship between the amount of electrolyte and the resistance increase rate. As shown in Figure 2, even if the amount of excess electrolyte 80 increases by increasing the amount of electrolyte, the capacity does not change significantly. As shown in Figure 3, even if the excess electrolyte 80 increases, the resistance increase rate does not change significantly.

[0028] <Note> (1) A step of measuring the volume of the void in the electrode body 10 housed inside the battery case 20 using the mercury intrusion method, A method comprising the step of setting the amount of electrolyte to be injected into the battery case 20 to be greater than or equal to the volume of the measured void, and less than the sum of the volume of the void and the volume of the portion of the battery case 20 below the lower surface of the electrode body 10.

[0029] (2) The step of measuring the volume of the void in the electrode body 10 housed inside the battery case 20 by the mercury intrusion method, The process includes the step of injecting an electrolyte solution into the battery case 20 containing the electrode body 10, in an amount greater than or equal to a first capacity and less than a second capacity greater than the first capacity. The first volume is the volume of the void, The second capacity is less than the sum of the volume of the void and the volume of the portion of the battery case 20 below the lower surface of the electrode body 10.

[0030] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims, and all modifications within the meaning and scope of equivalents of the claims are intended. [Explanation of Symbols]

[0031] 1 Secondary battery, 10 Electrode body, 11,12 Current collector foil, 13,14 Current collector plate, 15 Bottom surface, 16 Top surface, 17 First main surface, 18 Second main surface, 20 Battery case, 21 Case body, 22 Lid, 26 Bottom surface, 31 Positive electrode terminal, 32 Negative electrode terminal, 80 Excess electrolyte, S Gap, Sa Lower region.

Claims

[Claim 1] A battery case with a bottom inside, Electrolyte and The device comprises an electrode body housed inside the aforementioned and impregnated with the aforementioned electrolyte, The electrode body has a lower surface that is separated from the bottom surface and faces the bottom surface, The electrode body has a gap formed in it. A secondary battery in which the amount of the electrolyte is equal to or greater than the volume of the void, and less than the sum of the volume of the void and the volume of the interior portion below the bottom surface.

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