A method for determining battery module packing pre-tension

Abstract

A kind of method for determining battery module packing pre-tightening force, belong to battery technical field, specifically include the following steps: step one, in theoretical design state, set the distance between the two end plates of battery module after packing as L, the distance between the two end plates within the maximum tolerance calculation is D, then the elongation of binding belt is 2 (D-L) ;Step two, if the circumferential length of battery module in theoretical design state is d, then the elongation rate of binding belt is 2 (D-L) / d;Step three, tension test is carried out to binding belt, the maximum tension corresponding to the above-mentioned elongation rate is T when binding belt reaches;Pressure test is carried out to buffer pad, and the pressure when compressed to the theoretical design state of battery module is P;The total friction force f=G (D-L) of battery module bottom is calculated, wherein G is the gravity of battery module;The final battery module packing pre-tightening force is F=T+P+f.The present application limits the thickness of battery cell expansion, prevents battery cell expansion from affecting battery performance, and reduces its service life.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a method for determining the pre-tightening force of battery module packaging. Background Technology

[0002] As a core component of new energy vehicles, the performance of lithium-ion batteries directly determines the development of these vehicles. Currently, the market and application of lithium-ion batteries are experiencing explosive growth. The application of lithium-ion batteries inevitably involves numerous charge-discharge cycles. During charging, lithium ions escape from the positive electrode and embed into the graphite of the negative electrode, causing the negative electrode to expand. During discharging, lithium ions escape from the negative electrode and embed into the layered positive electrode material, causing the positive electrode to expand. Simultaneously, during battery aging, the electrolyte produces gas, leading to an increase in battery thickness. This not only affects the battery's lifespan and cycle life but also significantly impacts the cell potential and size design of the module. Tests have shown that applying a certain pre-clamping force to lithium batteries significantly improves performance and cycle life compared to not using a clamping device. During use or operation, batteries undergo volume expansion, leading to performance changes. For example, in the later stages of their lifespan, batteries expand, increasing thickness, cell internal resistance, and capacity decay. Existing research has shown that applying a certain preload force to a battery during application slows down its expansion over its lifespan, thereby improving its performance (slower internal resistance growth and reduced capacity decay).

[0003] However, research on pre-tightening force in existing technologies is still in its early stages. Common methods involve clamping the module to its maximum pressure using pre-compression fixtures, or ensuring the module mounting holes meet requirements before packaging with steel straps. This inevitably leads to problems such as the battery being crushed, lacking expansion space and posing a safety hazard; or the module being difficult to install into the box after pre-compression packaging. Additionally, methods rely on manual control. While the battery modules are initially tight and secure after packaging, they gradually loosen over time after frequent use and repeated transport vibrations, leading to loosening of the welded busbars or increased internal resistance, potentially causing fires and other safety incidents. Many factors influence the pre-tightening force of battery module packaging, including the compression of the buffer pad and the strength of the rolling strip, as well as the dimensional tolerances of the module installation and the cell itself. Without a budget or standards, numerous experiments may be needed to reach a conclusion, significantly reducing production efficiency. This invention provides a precisely designed pre-tightening force for battery module packaging, which is of great significance for battery assembly. Summary of the Invention

[0004] The purpose of this invention is to solve the technical problems existing in the prior art and to provide a method for determining the pre-tightening force of battery module packaging.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for determining the pre-tightening force of a battery module, wherein the battery module comprises a plurality of batteries stacked side by side and end plates disposed at both ends of the plurality of batteries, a buffer pad is disposed between adjacent batteries, and the battery module is circumferentially packaged using straps, characterized in that the algorithm for the pre-tightening force includes the following steps:

[0007] Step 1: Under the theoretical design conditions, let the distance between the two end plates of the packaged battery module be L, and the distance between the two end plates including the maximum allowable tolerance be D. Then the elongation of the strap is 2 (DL).

[0008] Step 2: If the circumferential length of the battery module under theoretical design conditions is d, then the elongation of the strap is 2 (DL) / d;

[0009] Step 3: Perform a tensile test on the straps, determining the maximum tensile force (T) corresponding to the aforementioned elongation rate; perform a pressure test on the buffer pad, determining the pressure (P) required to compress it to the theoretical design state of the battery module; calculate the total frictional force at the bottom of the battery module: f = G. (DL), where G is the weight of the battery module; the final packing pre-tightening force of the battery module is F=T+P+f.

[0010] Furthermore, the theoretical design state of the battery module is that the compression rate of the buffer pad in the packaged battery module is 10%-30%.

[0011] Preferably, the theoretical design state of the battery module is that the compression rate of the packaged battery module buffer pad is 30%.

[0012] Preferably, the strap is a plastic-steel strap.

[0013] Preferably, the buffer pad is a silicone rubber pad.

[0014] The advantages of this invention over the prior art are as follows:

[0015] 1. This invention limits the thickness of the battery cell expansion to prevent excessive cell expansion from affecting battery performance and reducing its service life;

[0016] 2. To prevent insufficient expansion space in the battery cell, which could cause the steel strip to break or the battery to explode;

[0017] 3. Prevent insufficient preload, module expansion, and excessive center distance of mounting holes from affecting assembly;

[0018] 4. To prevent insufficient battery clamping force, resulting in loose battery module packaging and affecting battery performance;

[0019] 5. To prevent uneven battery stress, misalignment of busbar mounting holes, and assembly difficulties, ensure precise busbar installation and welding;

[0020] 6. Prevent excessive preload, which could cause the buffer pad to become crushed and fail, affecting the performance of the battery system. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the packaged battery module structure;

[0022] In the diagram: 1. Battery; 2. End plate; 3. Buffer pad; 4. Strap; 5. Busbar. Detailed Implementation

[0023] The following is in conjunction with the appendix Figure 1 The present invention will be described in detail with reference to specific embodiments. Specific Implementation Method 1

[0025] A method for determining the pre-tightening force of a battery module packaging, wherein the battery module includes several batteries 1 stacked side by side and end plates 2 disposed at both ends of the batteries, a buffer pad 3 is disposed between two adjacent batteries 1, the battery module is packaged circumferentially with straps 4 to hold the batteries tightly, and then a busbar is welded to integrate the battery module. Since the pre-tightening force of the battery module packaging is related to the hardness and compression of the buffer pad, the strength and elongation of the plastic steel strap, the weight of the battery cell itself and the bottom friction force, and the magnitude of the force directly affects the battery module assembly and battery performance;

[0026] The method for determining the pre-tightening force for packaging battery modules includes the following steps:

[0027] Step 1: Under the theoretical design conditions, let the distance between the two end plates 2 of the packaged battery module be L, and the distance between the two end plates 2, including the maximum allowable tolerance, be D. Then the elongation of the strap 4 is 2 (DL).

[0028] Step 2: If the circumferential length of the battery module under theoretical design is d, then the elongation of the strap 4 is 2 (DL) / d;

[0029] Step 3: Perform a tensile test on the strap 4 using a tensile testing machine. The maximum tensile force corresponding to the aforementioned elongation rate of the strap 4 is T. Perform a pressure test on the buffer pad 3. The pressure when compressed to the theoretical design state of the battery module is P. Then, calculate the total frictional force f=G at the bottom of the battery module based on the working surface of the battery bottom. (DL), where G is the weight of the battery module; the final packing pre-tightening force of the battery module is F=T+P+f.

[0030] Furthermore, the theoretical design state of the battery module is that the compression rate of the buffer pad 3 in the packaged battery module is 10%-30%.

[0031] Preferably, the theoretical design state of the battery module is that the compression rate of the packaged battery module buffer pad 3 is 30%.

[0032] Preferably, the strap 4 is a plastic steel strap.

[0033] Preferably, the buffer pad 3 is a silicone rubber pad, which will not fail when compressed to within 30%, and the ideal compression is between 10% and 30%. Considering that the battery cell will expand during use, an upper limit is reserved, and the final calculated maximum tensile force of the plastic steel strip should meet its strength requirements.

[0034] Currently, when packaging battery modules, most manufacturers use tooling to hold them to a certain size and then tighten them. However, the pre-tightening force varies. Some are too tight, crushing the buffer pad 3, while others are not tight enough, making module assembly difficult and ultimately affecting the battery's performance.

[0035] This invention can determine the pre-tightening force of the plastic steel strapping through preliminary simulation calculations, and then seek steel strapping with sufficient strength. During packaging, the strapping machine is adjusted to a setting close to the calculated pre-tightening force, and packaging can be done directly without tooling. In this way, the center distance of the module mounting holes after packaging is basically within the tolerance range, and the compression of the buffer pad 3 is within the effective range, which can limit the expansion of the battery 1 without affecting the use of the battery 1.

[0036] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for determining the pre-tightening force of a battery module, wherein the battery module comprises a plurality of batteries (1) stacked side by side and end plates (2) disposed at both ends of the plurality of batteries, a buffer pad (3) is disposed between adjacent batteries (1), and the battery module is circumferentially packaged using straps (4), characterized in that, The algorithm for the packing preload includes the following steps: Step 1: Under the theoretical design state, let the distance between the two end plates (2) of the packaged battery module be L, and the distance between the two end plates (2) within the maximum allowable tolerance calculation be D. Then the elongation of the strap (4) is 2 (DL). Step 2: If the circumferential length of the battery module under the theoretical design state is d, then the elongation of the strap (4) is 2 (DL) / d; Step 3: Perform a tensile test on the strap (4), and determine the maximum tensile force T corresponding to the above elongation rate of the strap (4); perform a pressure test on the buffer pad (3), and determine the pressure P when compressed to the theoretical design state of the battery module; calculate the total frictional force f=G at the bottom of the battery module. (DL), where G is the weight of the battery module; the final packing pre-tightening force of the battery module is F=T+P+f.

2. The method for determining the pre-tightening force of battery module packaging according to claim 1, characterized in that: The theoretical design state of the battery module is that the compression rate of the buffer pad (3) in the packaged battery module is 10%-30%.

3. The method for determining the pre-tightening force of battery module packaging according to claim 2, characterized in that: The theoretical design state of the battery module is that the compression rate of the packaged battery module buffer pad (3) is 30%.

4. The method for determining the pre-tightening force of battery module packaging according to claim 1, characterized in that: The strap (4) is a plastic steel strap.

5. The method for determining the pre-tightening force of battery module packaging according to claim 1, characterized in that: The buffer pad (3) is a silicone rubber pad.

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