A method for testing the expansion force of high cycle life battery cells

Abstract

The present invention relates to a device and method for testing the expansion force of a high-cycle-life battery cell. The device includes a first connecting member; a first pressure plate, a second pressure plate and a third pressure plate, which are sequentially arranged in series on the first connecting member at intervals, and the three are fastened to the first connecting member through a first pretightening member, a first support plate for supporting the battery cell is provided at the bottom of the first pressure plate, a support sleeve and a gasket are sleeved on the first connecting member located between the first pressure plate and the second pressure plate, and a pressure sensor is provided between the second pressure plate and the third pressure plate; a second connecting member; a fourth pressure plate, a fifth pressure plate and a sixth pressure plate, which are sequentially arranged in series on the second connecting member at intervals, the fourth pressure plate and the sixth pressure plate are fastened to the second connecting member through a second pretightening member, the fifth pressure plate is slidably provided on the second connecting member, a second support plate for supporting the battery cell is provided at the bottom of the fourth pressure plate, and an elastic member connecting the fifth pressure plate and the sixth pressure plate is provided between the two.

Description

Technical Field

[0001] The invention relates to a method for testing expansion force of a high cycle life battery core, belonging to the technical field of battery packs for electric vehicles. Background Art

[0002] Currently, most cell expansion tests utilize a constant-displacement expansion force test fixture. This fixture constrains the cell's two large surfaces with steel plates to limit expansion. However, the drawback is that the preload force exerted by the steel plates on the cell increases with the number of charge and discharge cycles. Research has shown that excessive preload can significantly reduce the cell's charge and discharge cycle life. Summary of the Invention

[0003] To address the above technical issues, the present invention provides a method for measuring the expansion force of high-cycle-life battery cells. This method effectively avoids the drawbacks of constant-displacement testing methods, such as excessive preload, which significantly reduces the cycle life of the battery cell and fails to capture the expansion force at the end of the battery cell's life. The advantage lies in accurately measuring the expansion force throughout the entire cycle while ensuring a high cycle life for the battery cell.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A device for testing the expansion force of a battery cell with a long cycle life, comprising:

[0006] a first connecting member;

[0007] The first pressing plate, the second pressing plate and the third pressing plate are sequentially arranged in series on the first connecting member and are fastened to the first connecting member by a first pre-tightening member. A first supporting plate for supporting the battery cell is provided at the bottom of the first pressing plate. A supporting sleeve and a gasket are sleeved on the first connecting member between the first pressing plate and the second pressing plate. A pressure sensor is provided between the second pressing plate and the third pressing plate.

[0008] a second connecting member;

[0009] The fourth pressure plate, the fifth pressure plate and the sixth pressure plate are arranged in series on the second connecting member at intervals in sequence. The fourth pressure plate and the sixth pressure plate are fastened to the second connecting member by a second preloaded member. The fifth pressure plate is slidably arranged on the second connecting member. A displacement monitoring sensor is provided on the fifth pressure plate. A second support plate for supporting the battery cell is provided at the bottom of the fourth pressure plate. An elastic member connecting the fifth pressure plate and the sixth pressure plate is provided between the two.

[0010] In the long cycle life battery cell expansion force testing device, preferably, the first connecting member is a first bolt, and the number of the first bolts is at least two.

[0011] In the long cycle life battery cell expansion force testing device, preferably, the first pre-tightening member is a first nut.

[0012] In the long cycle life battery cell expansion force testing device, preferably, the number of the first bolts is four, and the number of the first nuts is twelve.

[0013] In the long cycle life battery cell expansion force testing device, preferably, the second connecting member is a second bolt, and the number of the second bolts is at least two.

[0014] In the long cycle life battery cell expansion force testing device, preferably, the second pre-tightening member is a second nut.

[0015] In the long cycle life battery cell expansion force testing device, preferably, the number of the second bolts is four, and the number of the second nuts is eight.

[0016] In the device for testing expansion force of a battery cell with a long cycle life, preferably, the elastic member is a spring.

[0017] A second aspect of the present invention provides a method for testing the expansion force of a long cycle life battery cell. The method is based on any one of the above-mentioned devices for testing the expansion force of a long cycle life battery cell, and comprises the following steps:

[0018] Placing the battery cell on the first support plate, placing the gasket between the support sleeve and the second pressure plate, and then tightening the other end of the second pressure plate with the first pretightening member, measuring the expansion force of the battery cell using the pressure sensor, and measuring the expansion force of the battery cell at different expansion thicknesses by continuously increasing the number of gaskets of equal thickness, thereby obtaining a curve of the battery cell expansion force versus expansion displacement;

[0019] The gap between the battery cell and the second pressure plate is ΔS. When the battery cell expands by ΔS, the expansion force release amount of the battery cell is ΔF=F1-F2, where F1 is the expansion force value in the initial state and F2 is the expansion force value after the battery cell expands by ΔS.

[0020] Placing the battery cell on the second support plate, with the fifth pressing plate in contact with the battery cell and the elastic member in a natural state, and measuring the displacement of the battery cell using the displacement monitoring sensor;

[0021] The displacement of the battery cell expansion is ΔS, and the spring support force of the elastic member on the battery cell is F3=K·ΔS, where K is the stiffness of the elastic member;

[0022] The expansion force F=ΔF+F3=F1-F2+K·ΔS at any time during the charge and discharge cycle of the battery cell.

[0023] The present invention has the following advantages due to the adoption of the above technical solution:

[0024] The expansion force testing method of this invention effectively avoids the drawbacks of constant displacement testing methods, such as excessive preload, which significantly reduces the cycle life of the battery cell and fails to capture the expansion force at the end of the battery cell's life. Its advantage lies in accurately measuring the expansion force throughout the entire cycle while ensuring a high cycle life for the battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of a device for measuring the expansion force of a battery cell provided by one embodiment of the present invention;

[0026] Figure 2 A view of the device for measuring the expansion force of a battery cell provided in this embodiment of the present invention;

[0027] Figure 3 A BB view of the device for measuring the expansion force of a battery cell provided by this embodiment of the present invention;

[0028] Figure 4 Schematic diagram of a device for measuring the spring support force applied to a battery cell provided by this embodiment of the present invention;

[0029] Figure 5 A C-direction view of the measuring cell provided in this embodiment of the present invention receiving a spring support force device;

[0030] Figure 6 A BB view of the measuring cell provided by this embodiment of the present invention receiving a spring support force device;

[0031] Figure 7 A flow chart of a method for testing the expansion force of a battery cell provided in this embodiment of the present invention;

[0032] Figure 8 A curve diagram showing the expansion force of the battery cell according to the embodiment of the present invention and its release curve as the expansion displacement is varied;

[0033] The marks in the figure are as follows:

[0034] 1-first pressure plate; 2-battery cell; 3-second pressure plate; 4-third pressure plate; 5-first nut; 6-first bolt; 7-pressure sensor; 8-gasket; 9-support sleeve; 10-first support plate; 11-fourth pressure plate; 12-fifth pressure plate; 13-displacement monitoring sensor; 14-sixth pressure plate; 15-second nut; 16-spring; 17-second bolt; 18-second support plate. DETAILED DESCRIPTION

[0035] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention are described clearly and completely below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by ordinary persons in this field based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0036] Unless otherwise defined, the technical or scientific terms used in the present invention shall have the usual meanings understood by persons of ordinary skill in the field to which the present invention belongs. The words "first", "second", "third", "fourth" and similar terms used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "include" or "comprise" mean that the elements or objects preceding the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect.

[0037] At present, most tests based on the expansion force of battery cells use a constant displacement expansion force test fixture. This fixture uses steel plates to constrain the two large surfaces of the battery cell to limit the expansion displacement of the battery cell. The disadvantage is that as the number of charge and discharge cycles of the battery cell increases, the pre-tightening force of the steel plate on the battery cell continues to increase. Studies have shown that excessive pre-tightening force will greatly reduce the charge and discharge cycle life of the battery cell. To address this problem, the present invention provides a high cycle life battery cell expansion force testing device and method. This testing method can effectively avoid the defect that the constant displacement test method has excessive pre-tightening force, which greatly reduces the cycle life of the battery cell and cannot capture the expansion force at the end of the battery cell life.

[0038] The technical solution of the present invention is described in detail below in conjunction with specific implementation methods.

[0039] like Figure 1-3 As shown, the device for measuring the expansion force value of a battery cell provided by the present invention includes:

[0040] The first pressure plate 1, the second pressure plate 3 and the third pressure plate 4 are arranged in series on the first bolt 6 at intervals, and all three are fastened to the first bolt 6 by the first nut 5. A first support plate 1 for supporting the battery cell 2 is provided at the bottom of the first pressure plate 1. A support sleeve 9 and a gasket 8 are sleeved on the first connecting piece between the first pressure plate 1 and the second pressure plate 3. A pressure sensor 7 is provided between the second pressure plate 3 and the third pressure plate 4.

[0041] In some preferred embodiments of the present invention, the number of the first bolts 6 is at least two. More preferably, the number of the first bolts 6 is four, the number of the first nuts 5 is twelve, and the first pressing plate 1, the second pressing plate 3, and the third pressing plate 4 are all fastened to the second bolts 6 by four first nuts 5.

[0042] like Figure 4-6 As shown, the device for measuring the spring support force of a battery cell provided by the present invention includes:

[0043] The fourth pressure plate 11, the fifth pressure plate 12 and the sixth pressure plate 14 are arranged in series on the second bolt 17 at intervals. The fourth pressure plate 11 and the sixth pressure plate 14 are fastened to the second bolt 17 by the second nut 15. The fifth pressure plate 12 is slidably arranged on the second bolt 17. A displacement monitoring sensor 13 is provided on the fifth pressure plate 12. A second support plate 18 for supporting the battery cell 2 is provided at the bottom of the fourth pressure plate 11. A spring 16 connecting the fifth pressure plate 12 and the sixth pressure plate 14 is provided between the two.

[0044] In some preferred embodiments of the present invention, the number of the second bolts 17 is at least two. More preferably, the number of the second bolts 17 is four, the number of the second nuts 15 is eight, and the fourth pressing plate 11 and the sixth pressing plate 14 are each fastened to the second bolts 17 by four second nuts 15.

[0045] The present invention uses two measuring devices to comprehensively measure the true expansion force of the battery cell 2, specifically using the following two technical route measurement steps:

[0046] Step 1: Place the battery cell 2 on the first support plate 10, place the gasket 8 between the support sleeve 9 and the second pressure plate 3, and then tighten the other end 3 of the second pressure plate with the first nut 5. Use the pressure sensor 7 to measure the expansion force of the battery cell 2. By continuously increasing the number of gaskets 8 of equal thickness, measure the expansion force of the battery cell 2 at different expansion thicknesses, and obtain a curve of the expansion force of the battery cell 2 changing with expansion displacement;

[0047] Assuming that the gap between the battery cell 2 and the second pressure plate 3 is ΔS, when the battery cell 2 expands by ΔS, the expansion force released by the battery cell 2 is ΔF=F1-F2, where F1 is the expansion force value in the initial state and F2 is the expansion force value after the battery cell 2 expands by ΔS.

[0048] Step 2: Place the battery cell 2 on the second support plate 18, with the fifth pressure plate 12 in contact with the battery cell 2 and the spring in a natural state. Use the displacement monitoring sensor 13 to measure the displacement of the battery cell 2. Assuming that the displacement of the battery cell expansion is ΔS, the support force of the spring on the battery cell 2 is F3=K·ΔS, where K is the spring stiffness.

[0049] The expansion force F = ΔF + F3 = F1 - F2 + K·ΔS at any time during the charge and discharge cycle of battery cell 2.

[0050] The method for measuring the expansion force of a battery cell provided by the present invention first adopts technical route 1 to obtain the expansion force value of the battery cell at different expansion thicknesses, and then adopts the spring adaptive tooling structure in technical route 2 to measure the displacement value △S of the battery cell at the self-expansion thickness. In this state, combined with the force balance equation, it can be known that the spring support reaction force F3=K·ΔS, where K is the spring stiffness; in technical route 1, it can be known that after the battery cell expands by △S, the battery cell releases an expansion force of △F=F1-F2. Combining technical routes 1 and 2, it can be known that the battery cell expansion force F=△F+F3=F1-F2+K·ΔS. The expansion force testing method provided by the present invention can effectively avoid the defect that the constant displacement test method has excessive preload force, which greatly reduces the cycle life of the battery cell and cannot capture the expansion force at the end of the battery cell life. The advantage is that the expansion force of the entire cycle process can be accurately measured under the premise of ensuring a high cycle life of the battery cell.

[0051] Conventional constant-displacement fixtures restrict the breathing space of the battery cell (the second pressure plate 3 is in a fixed position, with no displacement). As the number of charge and discharge cycles increases, lithium ions embed into the negative electrode and deposit lithium on the negative electrode surface, thickening the negative electrode. This prevents the cell surface from releasing excess pressure. Excessive pressure reduces the cell's activity and significantly reduces its cycle life. The expansion force testing method provided by the present invention accurately measures the cell's expansion force while ensuring a normal, high cycle life for the battery cell 2. Furthermore, the present application requires two fixtures because ensuring the normal cycle life of the battery cell requires an adaptive spring fixture (a functional requirement that conventional constant-displacement fixtures cannot meet). The cell's expansion stiffness, specifically the amount of expansion force released by the cell under different release spaces (breathing spaces, i.e., when the fifth pressure plate 12 is set to movable mode), needs to be measured. The cell's actual expansion force is the sum of these two factors, necessitating a fixture that measures the cell's expansion stiffness.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for testing the expansion force of a high cycle life battery cell, the method being based on a device for testing the expansion force of a high cycle life battery cell, the device comprising: a first connecting member; A first pressing plate (1), a second pressing plate (3) and a third pressing plate (4) are sequentially arranged in series on the first connecting member at intervals, and the three are fastened to the first connecting member via a first pre-tightening member; a first supporting plate (10) for supporting the battery cell (2) is provided at the bottom of the first pressing plate (1); a supporting sleeve (9) and a gasket (8) are sleeved on the first connecting member located between the first pressing plate (1) and the second pressing plate (3); and a pressure sensor (7) is provided between the second pressing plate (3) and the third pressing plate (4); a second connecting member; The fourth pressing plate (11), the fifth pressing plate (12) and the sixth pressing plate (14) are sequentially arranged in series at intervals on the second connecting member, the fourth pressing plate (11) and the sixth pressing plate (14) are fastened to the second connecting member via a second pre-tightening member, the fifth pressing plate (12) is slidably arranged on the second connecting member, a displacement monitoring sensor (13) is provided on the fifth pressing plate (12), a second supporting plate (18) for supporting the battery cell (2) is provided at the bottom of the fourth pressing plate (11), and an elastic member connecting the fifth pressing plate (12) and the sixth pressing plate (14) is provided between the two. The method is characterized in that the method comprises the following steps: The battery cell (2) is placed on the first support plate (10), the gasket (8) is placed between the support sleeve (9) and the second pressure plate (3), and then the other end (3) of the second pressure plate (3) is fastened with the first pre-tightening member. The expansion force value of the battery cell (2) is measured using the pressure sensor (7), and the expansion force values ​​of the battery cell (2) at different expansion thicknesses are measured by continuously increasing the number of gaskets (8) of equal thickness, thereby obtaining a curve showing a change in the expansion force of the battery cell (2) with respect to expansion displacement. The gap between the battery cell (2) and the second pressure plate (3) is ΔS, and when the battery cell (2) expands by ΔS, the expansion force release amount of the battery cell (2) is ΔF=F1-F2, wherein F1 is the expansion force value in the initial state, and F2 is the expansion force value of the battery cell (2) after the expansion by ΔS; The battery cell (2) is placed on the second support plate (18), the fifth pressing plate (12) is in contact with the battery cell (2) and the elastic member is in a natural state, and the displacement monitoring sensor (13) is used to measure the displacement of the battery cell (2); The displacement of the battery core (2) when expanded is ΔS, and the support force exerted on the battery core (2) by the elastic member is F3=K·ΔS, where K is the stiffness of the elastic member; The expansion force F=ΔF+F3=F1-F2+K·ΔS at any time during the charge and discharge cycle of the battery cell (2).

2. The method for testing the expansion force of a long cycle life battery cell according to claim 1, wherein: The first connecting member is a first bolt (6), and the number of the first bolts (6) is at least two.

3. The method for testing the expansion force of a long cycle life battery cell according to claim 2, wherein: The first pre-tightening member is a first nut (5).

4. The method for testing expansion force of a long cycle life battery cell according to claim 3, wherein: The number of the first bolts (6) is four, and the number of the first nuts (5) is twelve.

5. The method for testing expansion force of a long cycle life battery cell according to claim 1, wherein: The second connecting member is a second bolt (17), and the number of the second bolts (17) is at least two.

6. The method for testing expansion force of a long cycle life battery cell according to claim 5, characterized in that: The second pre-tightening member is a second nut (15).

7. The method for testing expansion force of a long cycle life battery cell according to claim 6, wherein: The number of the second bolts (17) is four, and the number of the second nuts (15) is eight.

8. The method for testing expansion force of a long cycle life battery cell according to claim 1, wherein: The elastic member is a spring (16).

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