Method for measuring maximum expansion force of large face of square battery cell

Abstract

The application relates to a kind of square cell big face maximum expansion force measurement methods, using non-contact measurement principle, change the traditional direct constraint to big face to the constraint of area outside big face, make cell expansion force concentrated effect on specific measurement surface.The core technical innovation includes:1) through displacement sensor capture cell expansion displacement, replace traditional force sensor direct measurement mode;2) establish displacement-force value conversion model, utilize false cell inflation experiment to calibrate mechanical parameter;3) not limit the displacement of big face and concentrate gas to big face, establish experimental basis for the research between reversible expansion and irreversible expansion.The fixture can accurately quantify the maximum expansion force of square cell in charge-discharge cycle and the limit displacement of big face free expansion, provide key data support for battery safety design and performance evaluation, also provide data support for reserving gap in module lamination direction, avoid that gap is too small to cause expansion force accumulation or gap is too large to reduce space utilization.

Description

Technical Field

[0001] This invention relates to the field of battery performance evaluation technology, specifically a method for measuring the maximum expansion force of a square battery cell on its large surface. Background Technology

[0002] The expansion force of battery cells has always been one of the main concerns in the electric vehicle industry. Detailed research on the expansion force of battery cells can greatly improve driving safety. At present, research on the expansion force of battery cells is more focused on the particle level and the unit level, with less research on the cell level. At the cell level, we can divide the expansion force generated by the battery cell during charge and discharge cycles into four parts: lithium intercalation expansion force, thermal stress, force caused by the SEI film, and stress caused by gas generation.

[0003] In the experiment studying the effect of gas generation on the cell expansion force, we found that the gas generation stress was difficult to measure. The experiment used overcharging to achieve faster gas generation. The specific experimental scheme was as follows:

[0004] 1. A square LF253 battery cell was charged to full capacity with a constant current and constant voltage of 1C under a preload of 5000N, and then overcharged to 110% SOC with a small current of 0.33C. The gas generation effect was observed.

[0005] 2. A square LF253 battery cell was charged to full capacity with a constant current and constant voltage of 1C without preload, and then overcharged to 110% SOC with a small current of 0.33C. The gas generation effect was observed.

[0006] The results are as follows: When overcharged to 110% SOC under a preload of 5000N, the length increased from 173.9mm to 184.2mm (5.9%), and the height increased from 207.2mm to 207.5mm (0.1%). The width direction showed almost no displacement due to the preload. Without preload, the length increased from 173.4mm to 174.6mm (0.7%), the height decreased from 204mm to 201.9mm (1.2%), and the width decreased from 53.88mm to 99.88mm (85.4%).

[0007] Analysis reveals the following technical problems with the traditional method for measuring the maximum expansion force of a square battery cell's large surface area:

[0008] Traditional tooling fixtures cause the gas expansion force generated by the battery cell during charging and discharging to spread outwards rather than being concentrated on the large surface, resulting in a smaller measured expansion force that cannot accurately reflect the maximum expansion force actually experienced by the large surface.

[0009] Directly using force sensors to press down on the large surface poses a risk of crushing the battery cell, short circuit, and fire.

[0010] The inability to quantify the limit displacement of free expansion makes it difficult to provide accurate data for the design of module lamination gaps.

[0011] The lack of effective means to separate reversible expansion from irreversible (gas-generating) expansion restricts research on the safety mechanism of battery cells. Summary of the Invention

[0012] To address the problems existing in the prior art, the purpose of this invention is to provide a method for measuring the maximum expansion force of a square battery cell's large surface area. This method can accurately obtain the maximum expansion force of a square battery cell's large surface area under charging and discharging conditions caused by gas generation factors at the cell level. The measurement results are accurate, the experiment is safe, and reversible expansion and irreversible expansion can be separated.

[0013] To achieve the above objectives, the present invention adopts the following technical solution:

[0014] A method for measuring the maximum expansion force of a square battery cell on its large surface includes the following steps:

[0015] By using clamps to constrain the expansion of the square battery cell in directions other than the large surface area, only the displacement degree of freedom of the large surface area is released;

[0016] Charge and discharge the square battery cell and collect the maximum free expansion displacement of the large surface of the square battery cell during the charging and discharging process;

[0017] The expansion of the battery cell model in directions other than the large surface area is constrained by a clamp, while only the displacement degree of freedom of the large surface area is released. The battery cell model is a sealed shell with the same shape as a square battery cell.

[0018] Inflate the battery cell model and collect the expansion displacement of the large surface of the battery cell model in real time during the inflation process.

[0019] When the expansion displacement of the large surface of the battery cell model is equal to the maximum free expansion displacement of the large surface of the square battery cell, the gas pressure corresponding to the battery cell model and the area of ​​the large surface of the battery cell model after expansion are collected.

[0020] Based on the collected gas pressure and the area of ​​the large surface of the battery cell model after expansion, the maximum expansion force of the large surface of the square battery cell was calculated.

[0021] Furthermore, the method of using a clamp to constrain the expansion of a square battery cell or battery cell model in the non-major direction is as follows: a clamp frame for accommodating the square battery cell or battery cell model is composed of a bottom steel plate, two opposing side plates, and a top insulating cover plate; an adjustable preload is applied to the side plates and the top cover plate to limit the displacement of the sides and top and bottom surfaces of the square battery cell or battery cell model, while ensuring zero constraint in the major direction.

[0022] Furthermore, the height of the side plate shall not exceed the height of the square cell or cell model.

[0023] Furthermore, the top insulating cover is made of insulating wood and has pre-drilled holes for charging contacts to prevent short circuits during charging and discharging without interfering with normal wiring.

[0024] Furthermore, the method for collecting the expansion displacement of the square battery cell or battery cell model in the large-area direction is as follows: two opposing fixed steel plates are installed on the bottom steel plate, and the fixed steel plates are arranged corresponding to the large-area of ​​the square battery cell or battery cell model. Displacement sensors are installed on the two fixed steel plates respectively, and the displacement sensors directly contact the center of the large-area of ​​the square battery cell or battery cell model to collect the expansion displacement of the large-area in real time.

[0025] Furthermore, the displacement sensor is connected to the data display, and the fixture and the square battery cell are placed in the charging cabinet to charge and discharge according to the required charging and discharging strategy. The readings of the displacement sensor are recorded, and the sum of the readings of the two displacement sensors is the amount of expansion displacement of the large surface of the square battery cell.

[0026] Furthermore, the battery cell model has a vent hole on its side and is connected to an inflation tube.

[0027] Furthermore, the area of ​​the expanded battery cell model is collected by using a laser ring scanner to measure the area of ​​the expanded battery cell model.

[0028] Furthermore, the area of ​​the expanded battery cell model is collected by using a contact profilometer to measure the area of ​​the expanded battery cell model.

[0029] Furthermore, the method for collecting the area of ​​the expanded surface of the battery cell model is to use the original large surface area of ​​the battery cell model as the area of ​​the expanded large surface of the battery cell model.

[0030] In summary, the present invention has the following advantages:

[0031] 1) By capturing the expansion displacement of the battery cell through a displacement sensor, the traditional force sensor direct measurement method is replaced, eliminating the need to consider the strength of the large area and improving safety.

[0032] 2) It does not restrict the displacement of the large surface and concentrates the gas production to the large surface, thus establishing an experimental basis for the study of reversible and irreversible expansion.

[0033] 3) This fixture can accurately quantify the maximum expansion force and the limit displacement of the large surface free expansion of the square cell during the charge and discharge cycle, providing key data support for battery safety design and performance evaluation, as well as data support for reserving gaps in the module lamination direction, avoiding the accumulation of expansion force due to too small gaps or the reduction of space utilization due to too large gaps. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the overall structure of the tooling fixture.

[0035] Figure 2 This is a schematic diagram of the perforated side plate structure.

[0036] Figure 3 A schematic diagram of the mounting structure for the clamp side plate and the sensor mounting steel plate.

[0037] Figure 4 This is a schematic diagram of the displacement sensor installation.

[0038] Figure 5 This is a schematic diagram of the method flow of the present invention.

[0039] In the picture:

[0040] 1- Bottom steel plate; 2- Side plate; 3- Top insulating cover; 4- Fixing steel plate; 5- Displacement sensor; 6- Square battery cell. Detailed Implementation

[0041] The present invention will now be described in further detail.

[0042] like Figure 5 As shown, a method for measuring the maximum expansion force of a square battery cell includes the following steps:

[0043] 1) Fix the two side plates 2 to the bottom steel plate 1 with 6 M1O-L25 bolts respectively. Fix the two fixing steel plates 4 used to fix the displacement sensor 5 to the bottom steel plate 1 with four M1O-L25 bolts. Figures 1-3 As shown. In this embodiment, the width of the fixing holes of the side plate 2 and the bottom steel plate 1 is designed to be 21mm. If a certain margin is left for the constraint of battery cells of different widths (the LF253 battery cell model is used in the model), the width difference of the square battery cells 6 is small, and the width of the holes can be designed according to the specific battery cell width. If the width difference of the square battery cells 6 is large, the width design of the bottom steel plate 1 needs to be changed.

[0044] 2) Place the square battery cell 6 to be measured into the assembled fixture, adjust the position of the side plate 2 to ensure that both side plates 2 can fit the left and right sides of the square battery cell 6 to be measured.

[0045] The side plate 2 is connected to the fixing steel plate 4 of the displacement sensor 5 using eight M1O-L85 bolts. Simultaneously, a certain preload is applied to the left and right sides of the square battery cell 6 using these bolts to ensure it does not bulge. The height of the side plate 2 must be less than or equal to the height of the battery cell (excluding the aluminum foil). This fixture requires a certain preload to be applied to the top. If the rigidity of the side plate 2 is greater than the height of the battery cell, the preload of the top cover will act on the side plate 2, resulting in the top of the battery cell not being constrained, thus allowing some of the gas force to act on the top.

[0046] 3) Fix the two displacement sensors 5 to the fixing steel plate 4 of the displacement sensor 5 using two mounting brackets, ensuring that the contact point of the displacement sensor 5 is at the center of the large surface of the cell. Figure 4 As shown, this facilitates subsequent displacement acquisition. In this embodiment, the displacement sensor 5 has a range of ±5mm. Different range displacement sensors 5 can be selected based on the expansion measured by the square battery cell 6 under actual charging conditions without clamps. The positioning and installation of the contact displacement sensor 5 requires the use of a non-magnetic clamp with a low coefficient of thermal expansion. Using a metal block clamp would affect the displacement sensor 5.

[0047] 4) The top insulating cover plate 3 has bolt holes. The top insulating cover plate 3 is fixed to the side plate 2 using eight M8-L20 bolts passing through these holes. Simultaneously, ensure the battery pack is positioned within the openings in the top insulating cover plate 3 for easy subsequent charging. Secure the bolts and apply partial pre-tightening force to ensure the top of the battery cell does not expand or deform. If the position of the side plate 2 needs adjustment in step 2), the bolt hole positions in the top insulating cover plate 3 can be adjusted accordingly. This method is low-cost and convenient.

[0048] In this embodiment, the top insulating cover 3 is a wooden cover. Using a wooden cover for top constraint prevents short circuits during charging and discharging, avoiding safety issues. Simultaneously, the wooden cover provides sufficient space to ensure normal charging. The bottom steel plate 1 and the wooden cover ensure that the force of gas generation does not dissipate to the surrounding area, ensuring that all the force of gas generation acts on the large surface. To meet charging and discharging requirements, sufficient charging positions need to be reserved on the wooden cover according to the design of the aluminum bar to avoid the inability to install charging and discharging equipment. The wooden cover maximizes coverage area while ensuring no short circuits and reserving charging ports.

[0049] 5) Connect displacement sensor 5 to data display, place the fixture and the square battery cell 6 under test into the charging cabinet and charge and discharge according to the required charging and discharging strategy, record the reading of displacement sensor 5. Under the target working condition, the sum of the readings of the two displacement sensors 5 is the maximum free expansion displacement of the large surface of the square battery cell 6.

[0050] 6) Design a battery cell model (a sealed empty battery cell) with the same shape as the square battery cell 6. Make a hole on the side of the battery cell model, insert an air inlet tube, and apply glue around the hole to prevent air leakage. The area of ​​glue applied should be smaller than the area of ​​the hole.

[0051] 7) After removing the top insulating cover plate 3, take out the square battery cell 6 that has been tested, put the corresponding battery cell model into the fixture, and fix the battery cell model again according to step 4). The side plate 2 has a 30mm diameter round hole at 50mm from the bottom. Extend the inflation tube from the round hole of the side plate 2 and connect it to the inflation machine.

[0052] 8) Inflate the battery cell model with an air inflator until the maximum free expansion displacement measured in step 6) is reached, and record the gas pressure at this point.

[0053] 9) If a laser ring scanner or contact profilometer is available, the surface area of ​​the expanded cell model can be measured. According to F = P × A, the maximum expansion force on the surface can be calculated. If the surface area after expansion cannot be obtained, the surface area before expansion is used as A.

[0054] This method includes the following core technologies:

[0055] 1) The displacement sensor 5 captures the expansion displacement of the battery cell, replacing the traditional direct measurement method using a force sensor;

[0056] 2) Establish a displacement-force conversion model and calibrate the mechanical parameters using a cell model inflation experiment;

[0057] 3) This fixture does not restrict the displacement of the large surface area and concentrates gas generation there, establishing an experimental basis for research on reversible and irreversible expansion. It can accurately quantify the maximum expansion force and the limit displacement of the large surface area during charge-discharge cycles of the square cell 6, providing crucial data support for battery safety design and performance evaluation. It also provides data support for reserving gaps in the module lamination direction, avoiding the accumulation of expansion force due to excessively small gaps or reduced space utilization due to excessively large gaps.

[0058] This invention has the following technical advantages:

[0059] 1. Improve safety by replacing traditional measurement methods: The displacement sensor 5 is used for indirect measurement instead of the traditional force sensor for direct measurement. This eliminates the need to consider the influence of large surface strength on the sensor, avoids sensor damage or measurement failure caused by excessive cell expansion force, and improves experimental safety.

[0060] 2. Concentrate expansion force to ensure measurement accuracy: By constraining the expansion of the left and right sides, bottom and top of the battery cell, the force generated by gas production and structural expansion is concentrated on the large surface, which solves the problem of the expansion force spreading in all directions in traditional fixtures, resulting in smaller measured values, and ensures the measurement accuracy of the maximum expansion force of the large surface.

[0061] 3. Supports research on reversible and irreversible expansion: The design does not restrict large-area displacement, providing an experimental basis for distinguishing between reversible expansion (such as caused by lithium intercalation) and irreversible expansion (such as caused by SEI film or gas generation) during the charging and discharging process of the battery cell, and helping to conduct in-depth research on the expansion mechanism of the battery cell.

[0062] 4. Provides key data for battery design: Precisely quantified maximum expansion force and limit displacement of the large surface area can provide direct data support for the design of the 6-shell strength of square cells and the optimization of the reserved gap in the module lamination direction (avoiding the accumulation of force due to too small gaps or the reduction of space utilization due to too large gaps), thereby improving battery safety performance and structural rationality.

[0063] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for measuring the maximum expansion force of a square battery cell on its large surface, characterized in that, Includes the following steps: The expansion of the square battery cell in directions other than the large surface area is constrained by a clamp, releasing only the displacement degree of freedom of the large surface area; Charge and discharge the square battery cell and collect the maximum free expansion displacement of the large surface of the square battery cell during the charging and discharging process; The expansion of the battery cell model in directions other than the large surface area is constrained by a clamp, while only the displacement degree of freedom of the large surface area is released. The battery cell model is a sealed shell with the same shape as a square battery cell. Inflate the battery cell model and collect the expansion displacement of the large surface of the battery cell model in real time during the inflation process. When the expansion displacement of the large surface of the battery cell model is equal to the maximum free expansion displacement of the large surface of the square battery cell, the gas pressure corresponding to the battery cell model and the area of ​​the large surface of the battery cell model after expansion are collected. Based on the collected gas pressure and the area of ​​the large surface of the battery cell model after expansion, the maximum expansion force of the large surface of the square battery cell is calculated. The battery cell model has a vent hole on its side, which is connected to an inflation tube.

2. The method according to claim 1, characterized in that: The method of using a clamp to constrain the expansion of a square battery cell or battery cell model in the non-major direction is as follows: a clamp frame for accommodating the square battery cell or battery cell model is composed of a bottom steel plate, two opposing side plates, and a top insulating cover plate; an adjustable preload is applied to the side plates and the top cover plate to limit the displacement of the sides and top and bottom surfaces of the square battery cell or battery cell model, while ensuring zero constraint in the major direction.

3. The method according to claim 2, characterized in that: The height of the side plate shall not exceed the height of the square battery cell or the battery cell model.

4. The method according to claim 2, characterized in that: The top insulating cover is made of insulating wood and has a pre-drilled hole for the charging pad to prevent short circuits during charging and discharging without interfering with normal wiring.

5. The method according to claim 2, characterized in that: The method for collecting the expansion displacement of a square battery cell or battery cell model in the large-area direction is as follows: two opposing fixed steel plates are installed on the bottom steel plate, and the fixed steel plates are arranged corresponding to the large-area of ​​the square battery cell or battery cell model. Displacement sensors are installed on the two fixed steel plates respectively, and the displacement sensors directly contact the center of the large-area of ​​the square battery cell or battery cell model to collect the expansion displacement of the large-area in real time.

6. The method according to claim 5, characterized in that: Connect the displacement sensor to the data display, place the fixture and the square battery cell into the charging cabinet and charge and discharge according to the required charging and discharging strategy, record the readings of the displacement sensor, and the sum of the readings of the two displacement sensors is the amount of expansion displacement of the large surface of the square battery cell.

7. The method according to claim 1, characterized in that: The method for acquiring the area of ​​the expanded battery cell model is to use a laser ring scanner to measure the area of ​​the expanded battery cell model.

8. The method according to claim 1, characterized in that: The method for collecting the area of ​​the expanded surface of the battery cell model is to use a contact profilometer to measure the area of ​​the expanded surface of the battery cell model.

9. The method according to claim 1, characterized in that: The method for collecting the area of ​​the expanded surface of the battery cell model is to use the original large surface area of ​​the battery cell model as the area of ​​the expanded large surface of the battery cell model.

Images