Secondary batteries

Abstract

To provide a secondary battery that can secure a load for pressurizing the electrode body. [Solution] A secondary battery 1 in which an electrode body 3 is housed inside a case 2, comprising an insulating sheet 4 placed between the electrode body 3 and the inner surface of the case 2 inside the case 2 and wrapped around the electrode body 3, wherein the insulating sheet 4 is a sheet containing a liquid material.

Description

Technical Field

[0001] The present invention relates to a secondary battery.

Background Art

[0002] Patent Document 1 discloses a secondary battery in which an electrode body and a porous elastic body are housed inside a case. When the electrode body expands and presses the porous elastic body, the electrolyte contained in the porous elastic body flows out from the porous elastic body and is supplied to the electrode body.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the configuration described in Patent Document 1, sufficient pressure cannot be applied when it is desired to pressurize the electrode body in a battery activation process or the like. If the pressure applied to the electrode body is not sufficient, there is a risk that the battery performance will deteriorate.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide a secondary battery capable of ensuring a load for pressurizing an electrode body.

Means for Solving the Problems

[0006] The present invention is a secondary battery in which an electrode body is housed inside a case, and includes an insulating sheet disposed between the electrode body and the inner surface of the case inside the case and wound around the electrode body, and the insulating sheet is a sheet that encloses a liquid material.

Effects of the Invention

[0007] In this invention, it is possible to secure a load for pressurizing the electrode body. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram showing a secondary battery in an embodiment. [Figure 2] This is a diagram illustrating the structure of a secondary battery. [Figure 3] This diagram schematically shows a secondary battery under pressure. [Figure 4] This is a diagram illustrating the insulating sheet under pressure. [Figure 5] This is a diagram illustrating how to wrap an insulating sheet. [Figure 6] This graph shows the relationship between the external restraining load and the load applied to the electrode body. [Figure 7] This graph shows the change in load applied to the electrode over time. [Modes for carrying out the invention]

[0009] The secondary battery in the embodiments of the present invention will be described in detail below. However, the present invention is not limited to the embodiments described below.

[0010] Figure 1 is a schematic diagram showing a secondary battery in an embodiment. The secondary battery 1 is configured as a battery cell. The secondary battery 1 comprises a case 2, an electrode body 3, and an insulating sheet 4. The secondary battery 1 is a battery cell in which the electrode body 3 and the insulating sheet 4 are housed inside the case 2. The secondary battery 1 in this embodiment is a lithium-ion secondary battery.

[0011] Case 2 is formed in the shape of a flat rectangular parallelepiped with an opening on its upper side. The secondary battery 1 is equipped with a lid that seals the opening of Case 2. Case 2 and the lid are made of aluminum or an aluminum alloy. The secondary battery 1 is sealed by attaching the lid to Case 2. The case 2 is filled with electrolyte. The lid is provided with a positive electrode terminal and a negative electrode terminal. As shown in Figure 2, the secondary battery 1 is equipped with a positive electrode current collector 5 and a negative electrode current collector 6. The positive electrode terminal is connected to the electrode body 3 via the positive electrode current collector 5. The negative electrode terminal is connected to the electrode body 3 via the negative electrode current collector 6.

[0012] The electrode body 3 comprises a strip-shaped positive electrode sheet, a strip-shaped negative electrode sheet, and a strip-shaped separator. The electrode body 3 is a flat wound body formed by winding a laminate in which the positive electrode sheet and the negative electrode sheet are stacked with the separator in between.

[0013] The positive electrode sheet of electrode body 3 comprises a positive electrode current collector foil and a positive electrode composite layer. The positive electrode current collector foil is an electrode substrate formed in a long length and is made of aluminum foil. The positive electrode composite layer is provided on both sides of the positive electrode current collector foil. The positive electrode composite layer is a positive electrode active material layer containing positive electrode active material. The positive electrode active material is composed of lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium nickel oxide (LiNiO2), etc. The positive electrode current collector foil has an uncoated positive electrode side at one end in the width direction where the positive electrode active material layer is not formed and the positive electrode current collector foil is exposed. The uncoated positive electrode side functions as a positive electrode side connection part to which the positive electrode current collector body 5 is connected, and as a current collector part that extracts electricity from the positive electrode composite layer of the positive electrode sheet.

[0014] The negative electrode sheet of electrode body 3 comprises a negative electrode current collector foil and a negative electrode composite layer. The negative electrode current collector foil is an electrode substrate formed in a long length and is made of copper foil. The negative electrode composite layer is provided on both sides of the negative electrode current collector foil. The negative electrode composite layer is a negative electrode active material layer containing a negative electrode active material. The negative electrode active material contains a powdered carbon material such as graphite. The negative electrode current collector foil has an uncoated negative electrode side at one end in the width direction where the negative electrode composite layer is not formed and the negative electrode current collector foil is exposed. The uncoated negative electrode side functions as a negative electrode connection part to which the negative electrode current collector body 6 is connected, and as a current collection part that extracts electricity from the negative electrode composite layer of the negative electrode sheet.

[0015] The separator of electrode body 3 is a porous resin material for holding the electrolyte between the positive electrode sheet and the negative electrode sheet. The separator is a highly insulating nonwoven fabric. The separator is composed of a porous polymer membrane such as a porous polyethylene membrane, a porous polyolefin membrane, or a porous polyvinyl chloride membrane. When electrode body 3 is immersed in the electrolyte, the electrolyte permeates from the edges of the separator toward the center of the separator.

[0016] In electrode body 3, the positive electrode sheet, negative electrode sheet, and separator are stacked so that their respective longitudinal directions coincide. Before winding, the stacked material is arranged in the thickness direction in the order of positive electrode sheet, separator, negative electrode sheet, and separator. Electrode body 3 has a flattened structure in which the positive electrode sheet and negative electrode sheet, stacked with a separator in between, are wound around an axis extending in the width direction of their strip.

[0017] Case 2 has a pair of side walls 11 facing the thickness direction of the secondary battery 1. The side walls 11 are walls that receive a restraining load (pressure) from outside the secondary battery 1. The side walls 11 have an outer surface that is pressed from the outside and an inner surface that faces the flat surface of the electrode body 3.

[0018] The insulating sheet 4 is a stretchable sheet wound around the electrode body 3. The insulating sheet 4 is disposed between the inner surface of the case 2 and the electrode body 3 inside the case 2. The insulating sheet 4 is a sheet made of a resin material and contains a non-aqueous liquid material. The resin material constituting the insulating sheet 4 is polypropylene, polyethylene, polyurethane, etc. The liquid material encapsulated in the insulating sheet 4 is a non-aqueous material such as Fluorinert (registered trademark), components derived from an electrolytic solution, etc.

[0019] The insulating sheet 4 is formed in dimensions that can be wound around the electrode body 3. The insulating sheet 4 can be wound around the electrode body 3 without a step. Since the electrode body 3 is wrapped by the insulating sheet 4, it does not contact the inner surface of the case 2. The thickness of the insulating sheet 4 is 0.1 mm to 1.0 mm. Since the insulating sheet 4 has stretchability, its shape can be flexibly changed according to the thickness of the electrode body 3, the insertion state into the case 2, the pressurized state during the use of the secondary battery 1, etc. As shown in FIGS. 3 and 4, when pressurized, the insulating sheet 4 can be deformed by applying pressure. By pressurizing the electrode body 3, the liquid material is dispersed vertically, horizontally, and fills the gaps on the bottom and side surfaces of the case 2, holding the electrode body 3 in an appropriate position. That is, the insulating sheet 4 functions as a holding member for holding the electrode body 3. The insulating sheet 4 suppresses damage to the electrode body 3 due to defects during battery activation and vibrations and impacts during actual use.

[0020] As shown in FIG. 5, the insulating sheet 4 includes an encapsulating portion 21 that encapsulates a liquid material and a non-encapsulating portion 22 that does not encapsulate a liquid material. The thickness of the encapsulating portion 21 is 0.1 mm to 1.0 mm. The non-encapsulating portion 22 is provided on both end sides of the encapsulating portion 21. The non-encapsulating portion 22 has an appropriate length according to the size of the electrode body 3. The insulating sheet 4 is wound around the electrode body 3 such that the encapsulating portion 21 covers the entire electrode body 3. The non-encapsulating portion 22 on one end side with respect to the encapsulating portion 21 becomes the starting side part of the winding, and the non-encapsulating portion 22 on the other end side with respect to the encapsulating portion 21 becomes the ending side part of the winding. The non-encapsulating portion 22 on the ending side of the winding is joined to the outer surface of the encapsulating portion 21 by adhesion or welding.

[0021] In the initial state of the secondary battery 1, as shown in Figures 1 and 2, the insulating sheet 4 maintains a uniform thickness when the electrode body 3 is inserted into the case 2, thus not hindering insertion into the case 2. Furthermore, because the insulating sheet 4 contains a liquid material, it can effectively transmit the load when pressurizing the electrode body 3 in the initial state. For example, during the manufacturing of the secondary battery 1, the insulating sheet 4 can maintain the pressurizing force during battery activation. Similarly, because the insulating sheet 4 contains a liquid material, the liquid material that flows up, down, left, and right due to pressurization performs the function of holding the electrode body 3 inside the case 2.

[0022] As shown in Figure 6, the secondary battery 1 with the insulating sheet 4 allows for the effective application of external constraint loads to the electrode body 3. In Figure 6, line L1 shows the load relationship in the secondary battery 1 with the insulating sheet 4, and L2 shows the load relationship in the comparative example without the insulating sheet 4. As shown by lines L1 and L2, when the secondary battery 1 receives an external constraint load of the same magnitude as the comparative example, the load applied to the electrode body 3 becomes larger than in the comparative example due to the action of the insulating sheet 4 containing the liquid material. Therefore, the secondary battery 1 can obtain the load necessary for activation even with a smaller external constraint load than in the conventional example. In Figure 6, the horizontal axis represents the constraint load input to the secondary battery 1 from the outside, and the vertical axis represents the load applied to the electrode body 3.

[0023] When the secondary battery 1 is used for an extended period, if the applied pressure decreases due to creep in the electrode body 3, the liquid material that flowed during pressurization is pushed back, preventing an extreme decrease in the load acting on the electrode body 3. The insulating sheet 4 helps to suppress this load reduction. As shown in Figure 7, with the secondary battery 1 having the insulating sheet 4, the load on the electrode body 3 is less likely to decrease due to the return of the liquid material. In Figure 7, line L3 shows the change in load over time in the secondary battery 1 with the insulating sheet 4, and L4 shows the change in load over time in a comparative example without the insulating sheet 4. As shown by lines L3 and L4, the secondary battery 1, due to the action of the insulating sheet 4 containing the liquid material, has a longer period during which the load on the electrode body 3 is greater than the load required to maintain the battery compared to the comparative example. In other words, with the secondary battery 1, battery performance can be ensured over a long period of time.

[0024] As described above, according to the embodiment, when pressure is applied from the outer surface of the case 2, the insulating sheet 4 deforms, thereby appropriately pressurizing the electrode body 3 and suppressing a decrease in battery performance. [Explanation of Symbols]

[0025] 1 Secondary battery 2 cases 3 Electrode body 4. Insulating sheet 5 Positive electrode current collector 6 Negative electrode current collector

Claims

1. A secondary battery in which electrodes are housed inside a case, The case is provided with an insulating sheet that is placed between the electrode body and the inner surface of the case and is wrapped around the electrode body, The insulating sheet is a sheet containing a liquid material. A secondary battery characterized by the following features.

2. The aforementioned insulating sheet is an elastic sheet made of a resin material. The aforementioned liquid material is a non-aqueous material. The secondary battery according to claim 1.

Images