Method and system for in-situ measurement of strain of hard-shell lithium battery

Abstract

The invention discloses a method and a system for measuring the strain of a hard-shell lithium battery in situ, belongs to the technical field of lithium battery safety, and solves the problem of how to measure the strain of the hard-shell lithium battery in situ. After the surface of the battery is cleaned, the first stress-strain gauge is arranged at a monitoring point, the aluminum block with the second stress-strain gauge is arranged at a compensation point, and after the strain gauges are stabilized, the two stress-strain gauges are connected with an acquisition line in a half-bridge connection mode and then connected into an acquisition instrument to eliminate the influence caused by temperature. Fitting data on the upper computer to obtain a strain-time curve change to analyze the strain of the shell at the monitoring point; by arranging multiple groups of monitoring points and compensation points on the surface of the shell, multiple positions can be measured at the same time, and the strain difference of different positions of the same lithium battery can be compared and analyzed.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery safety, and relates to a method and system for in-situ measuring the strain of a hard-shell lithium battery. Background Art

[0002] A hard-shell lithium battery is a lithium-ion battery with a metal shell, and common metal shells are made of aluminum, steel, titanium, etc. Taking an aluminum-shell lithium battery as an example, its feature is that its shell is made of aluminum material. As a material with light weight, high strength, good thermal conductivity and strong corrosion resistance, the aluminum-shell lithium battery can have good battery performance and is widely used in various portable devices and energy storage systems.

[0003] During the normal charge and discharge process of a lithium battery, lithium ions will repeatedly intercalate and deintercalate between the positive and negative electrodes. This migration movement of lithium ions causes the crystal structures of the positive electrode material and the negative electrode graphite to undergo reversible deformation to a certain extent, resulting in reversible strain of the aluminum battery shell. The reversible strain is related to the stability of the battery material. Currently, there is a lack of research on the strain during the normal charge and discharge process of lithium ions.

[0004] Safety accidents caused by thermal runaway of lithium-ion batteries occur frequently. Currently, the existing early warning methods mainly rely on monitoring temperature, voltage, pressure and gas for early warning, and there is less research on using battery strain to warn of thermal runaway. In fact, under mechanical abuse, electrical abuse, and thermal abuse, various chemicals will be generated inside the lithium-ion battery, first causing irreversible strain of the shell, and then voltage drop, temperature rise, and gas ejection. Therefore, the magnitude of the strain of the aluminum-shell lithium battery will change with the evolution of thermal runaway. In-situ monitoring of the battery strain and using the strain situation of the aluminum-shell lithium battery as a signal to warn of thermal runaway can improve the timeliness and accuracy of early warning.

[0005] The prior art, such as the invention patent with the application publication number CN113410508A, discloses a method for in-situ measuring the strain of the electrode sheet of a lithium-ion battery, which uses common mechanical strain detection equipment and materials to measure the strain of the internal electrode of the lithium-ion battery, solves the drawback that the existing method can only measure the overall strain of the electrode sheet, can measure the strain in any direction on the electrode sheet, and does not require a complex conversion formula, reducing the measurement error. However, this prior art only focuses on the strain situation of the battery electrode sheet, and although it discloses that this prior art can be applied to common soft-pack type batteries and button batteries, it does not consider the phenomenon of irreversible strain of the aluminum-shell lithium battery shell during battery thermal runaway.

[0006] During the normal or abnormal use of aluminum-shell lithium batteries, various reactions occur inside the battery, resulting in strain on the external shell. The strain differences at different positions of the shell are relatively large, and the magnitude of the strain is related to the intensity and duration of the internal reactions. Therefore, in-situ measurement of different positions of aluminum-shell lithium batteries during charge and discharge helps to study the stability of lithium battery materials and the internal chemical reaction changes, providing a reference for the research and development of lithium batteries and thermal runaway warning. Summary of the Invention

[0007] The technical problem to be solved by the present invention is how to in-situ measure the strain of a hard-shell lithium battery.

[0008] The present invention solves the above technical problem through the following technical solutions:

[0009] A method for in-situ measuring the strain of a hard-shell lithium battery, comprising the following steps:

[0010] S1. Clean the surface of the battery shell, and select monitoring points and compensation points on the surface of the battery shell;

[0011] S2. Arrange the first stress-strain gauge at the monitoring point and collect the strain data of the monitoring point;

[0012] S3. Set a compensation element at the compensation point, attach the second stress-strain gauge to the compensation element, and collect the strain data of the compensation point;

[0013] S4. After the battery is stabilized, connect the first stress-strain gauge and the second stress-strain gauge and then connect them to the collector;

[0014] S5. Set the upper computer channel parameters and measurement types, fit the data transmitted by the collector, obtain the strain-time curve, and analyze the strain at the monitoring point.

[0015] After cleaning the surface of the battery, the present invention arranges the first stress-strain gauge at the monitoring point and arranges an aluminum block with the second stress-strain gauge at the compensation point. After the strain gauges are stabilized, the two stress-strain gauges are connected to the acquisition line by a half-bridge connection method and then connected to the collector to eliminate the influence of temperature. The strain-time curve change is obtained by fitting the data on the upper computer to analyze the strain of the shell at the monitoring point; by setting multiple groups of monitoring points and compensation points on the surface of the shell, multiple positions can be measured simultaneously, and the strain differences at different positions of the same lithium battery can be compared and analyzed.

[0016] The present invention conducts in-situ monitoring of hard-shell lithium batteries, uses the irreversible strain of the shell as a signal for warning thermal runaway, and warns of the thermal runaway of lithium batteries. Compared with the existing warning methods (monitoring temperature, voltage, pressure, and gas changes), the speed and accuracy of lithium battery thermal runaway warning are effectively improved.

[0017] Further, it further includes: S6. Select multiple monitoring points and compensation points on the surface of the battery case, repeat steps S2 to S5, and analyze the strain at different positions of the battery.

[0018] In the present invention, monitoring points are set at different positions of the hard-shell lithium battery during the charge and discharge process, the strain conditions of multiple monitoring points are measured, and the position of the hard-shell lithium battery remains unchanged without affecting the original working conditions of the lithium battery (such as during normal charge and discharge), maintaining the original state of the lithium battery, and capturing the strain response of the case in real time, which helps to study the stability of the lithium battery material and the internal chemical reaction changes, and provides a reference for the research and development of lithium batteries and thermal runaway warning, having good guiding significance.

[0019] The present invention can not only measure the strain at any position of the battery, but also obtain the relationship between strain and time under various working conditions (such as battery charge and discharge, storage, transportation, cycle test, thermal runaway, etc.), truly reflecting the internal state of the battery; for example, when the present invention is used in the normal charge and discharge process of an aluminum-shell lithium battery, the stability of the battery material can be studied; when used in the thermal runaway process of an aluminum-shell lithium battery, thermal runaway warning can be studied.

[0020] Further, in S1, cleaning the surface of the battery case specifically includes: removing the insulating film, cross-grinding the monitoring points with sandpaper, and cleaning the monitoring points with alcohol.

[0021] Further, the temperature of the compensation point is close to that of the monitoring point, and the number of compensation points is the same as that of the monitoring points.

[0022] Further, in S2, arranging the first stress-strain gauge at the monitoring point specifically includes: thinly applying the colloid on the bottom of the first stress-strain gauge with a scraper and then sticking it on the monitoring point.

[0023] Further, in S3, arranging the compensation element at the compensation point and sticking the second stress-strain gauge on the compensation element specifically includes: thinly applying the colloid on the bottom of the second stress-strain gauge with a scraper and then sticking it on one end of the compensation element, and then thinly applying the colloid on the other end of the compensation element and sticking it on the compensation point.

[0024] Further, the compensation element includes but is not limited to an aluminum block.

[0025] Further, in S4, waiting for the battery to be stable specifically includes: naturally drying at room temperature and waiting for the colloid to cure.

[0026] Further, in S4, connecting the first stress-strain gauge and the second stress-strain gauge and then connecting them to the acquisition instrument specifically includes: using a soldering iron to connect the leads of the first stress-strain gauge and the second stress-strain gauge to the acquisition line of the acquisition instrument in a half-bridge manner by spot welding.

[0027] In the present invention, a compensation point with a temperature close to that of the monitoring point is selected near the monitoring point, and an aluminum block that is not prone to generating strain and has good heat transfer performance is selected as the compensation element. The two ends of the aluminum block are respectively connected to the second stress-strain gauge and the compensation point. Therefore, the change in the value of the second stress-strain gauge is due to the influence of temperature. Through the half-bridge connection method, the influence brought by temperature can be directly fitted and eliminated.

[0028] The present invention also provides a system for in-situ measurement of the strain of a hard-shell lithium battery, including:

[0029] A battery cleaning module for cleaning the surface of the battery case and selecting a monitoring point and a compensation point on the surface of the battery case;

[0030] A monitoring point acquisition module for arranging the first stress-strain gauge at the monitoring point and acquiring the strain data of the monitoring point;

[0031] A compensation point acquisition module for arranging a compensation element at the compensation point, attaching the second stress-strain gauge to the compensation element, and acquiring the strain data of the compensation point;

[0032] A data processing module for connecting the first stress-strain gauge and the second stress-strain gauge and then connecting them to the acquisition instrument after the battery is stabilized;

[0033] A data analysis module for setting the upper computer channel parameters and measurement types, fitting the data transmitted by the acquisition instrument, obtaining the strain-time curve, and analyzing the strain at the monitoring point.

[0034] The advantages of the present invention are as follows:

[0035] After cleaning the surface of the battery in the present invention, the first stress-strain gauge is arranged at the monitoring point, and the aluminum block with the second stress-strain gauge is arranged at the compensation point. After the strain gauges are stabilized, the two stress-strain gauges are connected to the acquisition line through the half-bridge connection method and then connected to the acquisition instrument to eliminate the influence brought by temperature. The strain-time curve change is obtained by fitting the data on the upper computer to analyze the strain of the case at the monitoring point; by setting multiple groups of monitoring points and compensation points on the surface of the case, multiple positions can be measured simultaneously to compare and analyze the strain differences at different positions of the same lithium battery.

[0036] By in-situ monitoring of the hard-shell lithium battery, the present invention uses the irreversible strain of the case as a signal for warning thermal runaway, and warns of the thermal runaway of the lithium battery. Compared with the existing warning methods (monitoring temperature, voltage, pressure, and gas changes), it effectively improves the speed and accuracy of warning the thermal runaway of the lithium battery. The present invention can be applied to different metal hard-shell lithium batteries and has good application prospects. Description of the Drawings

[0037] Figure 1 is a flowchart of a method for in-situ measurement of the strain of a hard-shell lithium battery according to Embodiment 1 of the present invention;

[0038] Figure 2 It is a schematic diagram of in-situ measurement of the strain of a hard-shell lithium battery in the first embodiment of the present invention;

[0039] Figure 3(a) is a strain-time trend diagram of the upper part of the aluminum-shell lithium battery in the first embodiment of the present invention;

[0040] Figure 3(b) is a strain-time trend diagram of the middle part of the aluminum-shell lithium battery in the first embodiment of the present invention;

[0041] Figure 3(c) is a strain-time trend diagram of the lower part of the aluminum-shell lithium battery in the first embodiment of the present invention;

[0042] Description of the drawings: 10. Housing; 11. First stress-strain gauge; 12. Second stress-strain gauge; 20. Acquisition instrument. Detailed implementation manners

[0043] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0044] The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings of the specification and specific embodiments:

[0045] Embodiment 1

[0046] As Figures 1-2 shown, specifically, a method for in-situ measurement of the strain of a hard-shell lithium battery is disclosed, including the following steps:

[0047] S1. Clean the surface of the battery housing 10, and select monitoring points and compensation points on the surface of the battery housing 10.

[0048] The specific cleaning of the surface of the battery housing 10 is to remove the insulating film, cross-grind the monitoring points with sandpaper, and clean the monitoring points with alcohol.

[0049] Furthermore, the compensation points are positions near the monitoring points. The distance between the compensation points and the monitoring points does not exceed 1 mm; the temperature of the compensation points is close to that of the monitoring points, and the temperature deviation does not exceed ±1°C; the number of compensation points is the same as that of the monitoring points.

[0050] Since the deformation of the battery will cause a gap between the insulating film and the battery housing, and the insulating film itself will also generate strain under the influence of the environment. If the insulating film is not removed, the actual measurement result will be the strain result of the insulating film, and there will be residual glue on the surface of the battery housing after the insulating film is removed. Therefore, in this embodiment, the outer insulating film of the battery needs to be removed, polished after cleaning, so that the strain gauge can be better pasted on the battery surface. At the same time, pay attention to the ignition problem during the operation. Do not contact the wire of the strain gauge with the negative electrode, and avoid contacting metal objects with the negative electrode of the battery to cause a short circuit.

[0051] S2. Arrange the first stress-strain gauge 11 at the monitoring point and collect the strain data of the monitoring point.

[0052] The specific operation of arranging the first stress-strain gauge 11 at the monitoring point is as follows: thinly apply the colloid on the bottom of the first stress-strain gauge 11 with a scraper and then paste it on the monitoring point.

[0053] S3. Set the compensation element at the compensation point, paste the second stress-strain gauge 12 on the compensation element, and collect the strain data of the compensation point.

[0054] The specific operation of setting the compensation element at the compensation point and pasting the second stress-strain gauge 12 on the compensation element is as follows: thinly apply the colloid on the bottom of the second stress-strain gauge 12 with a scraper and paste it on one end of the compensation element, and then thinly apply the colloid on the other end of the compensation element and paste it on the compensation point.

[0055] Further, the compensation element is used to conduct temperature so that the second stress-strain gauge 12 can collect the strain data only affected by temperature. Specifically, the compensation element includes but is not limited to an aluminum block or other materials with good thermal conductivity and not easy to generate strain. The cross-sectional area formed by cutting the compensation element with a cutting machine is larger than the area of the second stress-strain gauge 12. The two ends of the compensation element are first polished crosswise with sandpaper and then cleaned with alcohol.

[0056] Further, the first stress-strain gauge 11 and the second stress-strain gauge 12 are made of a combination of polyimide and constantan foil; among them, polyimide is used as the base and constantan foil is used as the sensing material.

[0057] Further, the colloid is an oily glue, and the stress-strain gauge is fixed by using the oily glue for pasting.

[0058] In this embodiment, the stress-strain gauge is made of a polyimide base and constantan foil, which can ensure its excellent performance in terms of high temperature, stress, and electrical stability. Polyimide provides excellent heat resistance and mechanical stability, while constantan foil has good electrical conductivity and can accurately detect the resistance change caused by strain. Using an oil-based adhesive to fix the strain gauge can ensure that the strain gauge is firmly bonded to the test surface, providing stable adhesion, and at the same time having good temperature resistance, moisture resistance, and flexibility, thus ensuring the reliability and accuracy of the strain data.

[0059] S4. After the battery is stabilized, connect the first stress-strain gauge 11 and the second stress-strain gauge 12 and then connect them to the collector 20.

[0060] The specific step of stabilizing the battery is: naturally dry at room temperature for 3 to 4 hours until the colloid solidifies.

[0061] Further, the specific operation of connecting the first stress-strain gauge 11 and the second stress-strain gauge 12 and then connecting them to the collector 20 is: use a soldering iron to connect the leads of the first stress-strain gauge 11 and the second stress-strain gauge 12 to the collector line of the collector 20 in a half-bridge manner by spot welding.

[0062] In this embodiment, the principle of setting the strain gauge to collect strain data lies in measuring the resistance change before and after strain occurs at this point. During the charging and discharging process of the aluminum shell lithium battery, not only strain will be generated, but the temperature will also change. The change in the strain data of the monitoring point collected by the first stress-strain gauge 11 set at the monitoring point is affected by both the battery strain and the temperature. To eliminate the temperature influence, in this embodiment, a compensation point with a temperature close to that of the monitoring point is selected near the monitoring point, and an aluminum block that is not prone to strain and has good heat transfer is selected as the compensation element. The two ends of the aluminum block are respectively connected to the second stress-strain gauge 12 and the compensation point. Therefore, the change in the value of the second stress-strain gauge 12 is due to the temperature influence. Through the half-bridge connection method, the influence brought by the temperature can be directly fitted and eliminated. When the two strain gauges are connected into a half-bridge structure, their resistance changes are symmetric with each other. Since the temperature of the monitoring point and the compensation point is similar, the resistance changes caused by temperature are the same, and the voltage signals caused by this part of the temperature change will cancel each other out in the half-bridge circuit, thereby eliminating the interference of temperature change on the strain data. Therefore, the strain data obtained after conversion through the half-bridge connection method is the strain magnitude of the monitoring point.

[0063] S5. Set the upper computer channel parameters and measurement types, fit the data transmitted by the collector, obtain the strain-time curve, and analyze the strain at the monitoring point.

[0064] The specific channel parameters are selected with the measured quantity being strain, and the measurement type being stress-strain.

[0065] The data transmitted by the fitting collector is specifically as follows: The upper computer sets the angles of the second stress-strain gauge 12 to the temperature compensation of the corresponding angles of the first stress-strain gauge 11.

[0066] Stress-strain gauges are divided into three types: uniaxial, biaxial, and triaxial according to different measurement directions. In this embodiment, a triaxial stress-strain gauge with three measurement angles (0°, 45°, and 90°) is used to analyze the complete complex stress state at the monitoring point.

[0067] In this embodiment, the 0°, 45°, and 90° directions of the first stress-strain gauge 11 are respectively welded to the corresponding directions of the second stress-strain gauge 12 through a half-bridge circuit to form three independent half-bridge circuits (for example, the 0° direction of the first stress-strain gauge 11 and the 0° direction of the second stress-strain gauge 12 form a half-bridge and are connected to the first channel of the collector), and the 0°, 45°, and 90° directions of the second stress-strain gauge 12 are respectively specified as the temperature compensation sources of the corresponding directions of the first stress-strain gauge 11 in the upper computer software.

[0068] The upper computer fits the output signals of the second stress-strain gauge 12 at different angles to simulate and compensate the temperature influence of the first stress-strain gauge 11 at different angles, which can eliminate the influence of temperature fluctuations on the measurement data and thus obtain more accurate strain data.

[0069] S6. Select multiple monitoring points and compensation points on the surface of the battery case 10, and repeat steps S2 to S5 to analyze the strain at different positions of the battery.

[0070] In this embodiment, the monitoring points can be arranged at any position on the surface of the battery case 10 except the safety valve for in-situ strain measurement, and multiple monitoring points can be set.

[0071] Furthermore, in this embodiment, by setting multiple groups of monitoring points and compensation points on the surface of the case 10, multiple positions can be measured simultaneously to compare and analyze the strain differences at different positions of the same aluminum-shell lithium battery. This embodiment can not only measure the strain at any position of the battery, but also obtain the relationship between strain and time under various working conditions (such as battery charging and discharging, storage, transportation, cycle testing, thermal runaway, etc.), and truly reflect the internal state of the battery; for example, when the present invention is used in the normal charging and discharging process of an aluminum-shell lithium battery, the stability of the battery material can be studied; when used in the thermal runaway process of an aluminum-shell lithium battery, thermal runaway warning can be studied.

[0072] Such as Figures 3(a)-3(c)As shown in the figure, this embodiment takes the study of thermal runaway warning of aluminum shell lithium batteries using the above test method as an example. After the battery is cleaned, the first and second stress-strain gauges are respectively arranged at the monitoring points and compensation points at the upper, middle, and lower parts of the aluminum shell lithium battery, and the strain-time trend changes are significantly observed. The strain magnitudes at different positions of the same battery are different. After connecting the first and second stress-strain gauges in a half-bridge manner by spot welding and then connecting them to the acquisition instrument, matching parameters are set on the upper computer. When thermal runaway trigger conditions such as heating, overcharging, and pinpricking are applied to the battery, the measurement is started to obtain the relationship between strain and time.

[0073] Before thermal runaway, the strain shows a trend of increasing first and then decreasing with time; the change in strain can reflect the degree of thermal runaway inside the battery. At the beginning, the internal reaction is slow and the strain does not change significantly. Then the internal reaction intensifies and the strain also increases sharply. When approaching thermal runaway, the strain begins to decrease. When it is completely out of control, there will be a sudden drop. According to the above strain-time relationship, it can provide an effective reference basis for the early warning of lithium batteries.

[0074] The present invention conducts in-situ monitoring of aluminum shell lithium batteries and uses the irreversible strain of the battery shell as a signal for warning thermal runaway, so as to warn of the thermal runaway of lithium batteries. Compared with the existing warning methods (monitoring temperature, voltage, pressure, and gas changes), it effectively improves the speed and accuracy of lithium battery thermal runaway warning.

[0075] The present invention sets monitoring points at different positions of the aluminum shell lithium battery during the charging and discharging process, measures the strain conditions of multiple monitoring points, keeps the position of the aluminum shell lithium battery unchanged, does not affect the original working condition of the lithium battery (such as during normal charging and discharging), maintains the original state of the lithium battery, and captures the strain response of the battery shell in real time, which helps to study the stability of lithium battery materials and the internal chemical reaction changes, and provides a reference for the research and development of lithium batteries and thermal runaway warning, and has good guiding significance.

[0076] In addition, the in-situ measurement method provided by the present invention can be applied to different metal hard shell lithium batteries, including but not limited to metal shells made of materials such as aluminum, steel, and titanium, and has good application prospects.

[0077] The present invention also provides a system for in-situ measuring the strain of a hard shell lithium battery, including:

[0078] A battery cleaning module for cleaning the surface of the battery shell and selecting monitoring points and compensation points on the surface of the battery shell;

[0079] A monitoring point acquisition module for arranging the first stress-strain gauge at the monitoring point and acquiring the strain data of the monitoring point;

[0080] A compensation point acquisition module for setting a compensation element at the compensation point, attaching the second stress-strain gauge to the compensation element, and acquiring the strain data of the compensation point;

[0081] A data processing module, after the battery is stabilized, is used to connect the first stress-strain gauge and the second stress-strain gauge and then connect them to the collector.

[0082] A data analysis module is used to set the upper computer channel parameters and measurement types, fit the data transmitted by the collector, obtain the strain-time curve, and analyze the strain at the monitoring point.

[0083] 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 foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for in-situ measurement of strain of a hard-shell lithium battery, characterized in that: The following steps are involved: S1. Clean the surface of the battery shell and select monitoring points and compensation points on the surface of the battery shell; S2, arranging the first stress strain gauge at the monitoring point and collecting strain data of the monitoring point; S3, setting a compensation element at the compensation point, attaching a second stress strain gauge to the compensation element, and collecting strain data of the compensation point; S4. After the battery is stable, connect the first stress strain gauge to the second stress strain gauge and then connect them to the data collector; S5. Set the host computer channel parameters and measurement type, fit the data transmitted by the acquisition instrument, obtain the strain-time curve, and analyze the strain at the monitoring point.

2. The method for in-situ measuring strain of a hard-shell lithium battery according to claim 1, characterized in that: Also includes: S6. Select multiple monitoring points and compensation points on the surface of the battery casing, repeat steps S2 to S5, and analyze the strains at different positions of the battery.

3. The method for in-situ measuring strain of a hard-shell lithium battery according to claim 1, characterized in that: The cleaning of the battery shell surface in S1 specifically includes: removing the insulating film, cross-grinding the monitoring points with sandpaper, and cleaning the monitoring points with alcohol.

4. The method for in-situ measuring strain of a hard-shell lithium battery according to claim 3, characterized in that: The number of the compensation points is the same as the number of the monitoring points.

5. The method for in-situ measuring strain of a hard-shell lithium battery according to claim 1, characterized in that: The step of arranging the first stress strain gauge at the monitoring point in S2 specifically includes: using a scraper to apply a thin layer of colloid to the bottom of the first stress strain gauge and then attaching the gauge to the monitoring point.

6. The method for in-situ measuring strain of a hard-shell lithium battery according to claim 1, characterized in that: In the S3, the compensation element is arranged at the compensation point, and the second stress strain gauge is attached to the compensation element by applying a thin layer of colloid to the bottom of the second stress strain gauge with a scraper and then attaching it to one end of the compensation element, and then applying a thin layer of glue to the other end of the compensation element and then attaching it to the compensation point.

7. The method for in-situ measuring strain of a hard-shell lithium battery according to claim 6, characterized in that: The compensation element includes but is not limited to an aluminum block.

8. The method for in-situ measuring strain of a hard-shell lithium battery according to claim 1, characterized in that: Waiting for the battery to be stable in S4 specifically includes: drying naturally at room temperature and waiting for the colloid to solidify.

9. The method for in-situ measuring strain of a hard-shell lithium battery according to claim 8, characterized in that: In S4, the first stress strain gauge and the second stress strain gauge are connected and then connected to the acquisition instrument. Specifically, the leads of the first stress strain gauge and the second stress strain gauge are connected to the acquisition line of the acquisition instrument in a half-bridge manner by spot welding using an electric soldering iron.

10. A system for in-situ measurement of strain of hard-shell lithium batteries, characterized in that: include: A battery cleaning module is used to clean the surface of the battery shell and select monitoring points and compensation points on the surface of the battery shell; A monitoring point acquisition module, used to arrange the first stress strain gauge at the monitoring point and collect strain data of the monitoring point; A compensation point acquisition module is used to arrange the compensation element at the compensation point, attach the second stress strain gauge to the compensation element, and collect strain data of the compensation point; A data processing module is used to connect the first stress strain gauge with the second stress strain gauge and then connect it to the data acquisition instrument after the battery is stabilized; The data analysis module is used to set the host computer channel parameters and measurement type, fit the data transmitted by the acquisition instrument, obtain the strain-time curve, and analyze the strain at the monitoring point.

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