Moire sheet and moire instrument for measuring warping degree of lithium battery

Abstract

The invention provides a moire sheet for measuring the warping degree of a lithium battery and a moire instrument, the moire sheet comprises a moire sheet film and optical glass, and the edge of the moire sheet film is adhered to the optical glass.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery performance testing, and relates to a moiré sheet and a moiré interferometer for measuring the warpage of a lithium battery. Background Art

[0002] With the wide application of lithium batteries in various fields, the quality and performance detection of lithium batteries have become crucial. Among them, the warpage of a lithium battery is an important factor affecting its performance and safety. At present, when measuring the warpage of a lithium battery, there is a lack of a measuring tool with high precision, convenient use and specifically for the characteristics of lithium batteries.

[0003] Traditional measuring tools have problems such as large errors and complex operations. As an effective measurement auxiliary tool, the existing manufacturing methods of moiré sheets are expensive and complex, and cannot well meet the requirements in the production and detection processes of lithium batteries. Summary of the Invention

[0004] The present invention provides a moiré sheet and a moiré interferometer for measuring the warpage of a lithium battery, which can effectively solve the above problems.

[0005] The present invention is implemented as follows:

[0006] On the one hand, the present invention provides a moiré sheet for measuring the warpage of a lithium battery, and the moiré sheet includes: a moiré sheet film and an optical glass, and the edge of the moiré sheet film is adhered to the optical glass.

[0007] On the other hand, the present invention provides a moiré interferometer for measuring the warpage of a lithium battery, and the moiré interferometer includes:

[0008] The above-mentioned moiré sheet, which is used to be horizontally placed on the surface of the lithium battery;

[0009] A camera, which is arranged above the moiré sheet and is used to photograph the moiré pattern formed on the moiré sheet;

[0010] A light source, which is arranged above the moiré sheet and is used to emit light and irradiate the moiré sheet;

[0011] The centers of the camera, the light source and the moiré sheet are located in the same plane.

[0012] On yet another aspect, the present invention provides a method for measuring the warpage of a lithium battery using the above-mentioned moiré interferometer, including:

[0013] Placing the lithium battery on a horizontal plane, and then placing the moiré sheet on the surface of the lithium battery;

[0014] Using the light source to irradiate the moiré sheet to form a stable moiré pattern on the moiré sheet;

[0015] Use a camera to capture the moiré pattern to obtain a picture;

[0016] Count the moiré fringes in the picture along the diagonal of the surface of the lithium battery to obtain the number of bright fringes m + n;

[0017] Obtain the warpage degree of the lithium battery according to the number of bright fringes m + n Wherein, the angle formed by the central connection line between the light source and the moiré sheet and the normal line at the center of the moiré sheet is α, and the angle formed by the central connection line between the camera and the moiré sheet and the normal line at the center of the moiré sheet is β.

[0018] The beneficial effects of the present invention are:

[0019] The present invention provides a moiré sheet for measuring the warpage degree of a lithium battery. The moiré sheet is prepared by attaching a moiré sheet film etched with a grating to an optical glass. The preparation method is simple, the cost is low, and it can meet the measurement accuracy requirements.

[0020] Furthermore, the moiré sheet film adopts a concentric circle grating structure, which has high regularity and repeatability, and is sensitive to minute deformations. It can clearly and sensitively reflect the warpage degree, facilitating the quantification of the warpage degree by observing the change of the moiré pattern.

[0021] Furthermore, the moiré sheet film adopts a material with a low coefficient of thermal expansion to avoid changes in optical properties or physical structures of the moiré sheet due to the high surface temperature of the battery during the test, so as to ensure the accuracy of the measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0023] Figure 1 is a schematic structural diagram of the moiré sheet provided by the embodiment of the present invention.

[0024] Figure 2 is a schematic diagram of the moiré sheet placed on the surface of the lithium battery.

[0025] Figure 3 is a schematic diagram of a moiré pattern formed by a moiré sheet with an overly large grating pitch.

[0026] Figure 4 is a schematic structural diagram of the moiré instrument provided by the embodiment of the present invention.

[0027] Figure 5 It is a schematic diagram of the warping on the surface of a lithium battery.

[0028] Figure 6 It is a result diagram of the moiré interferometer provided by an embodiment of the present invention for measuring the height of a spherical crown.

[0029] Figure 7 It is a result diagram of the moiré interferometer provided by an embodiment of the present invention for measuring the warping degree of the surface of a 280 Ah lithium battery. Detailed implementation manners

[0030] 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 with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some but not all of the embodiments of the present invention. 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. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. 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.

[0031] An embodiment of the present invention provides a moiré film 1 for measuring the warping degree of a lithium battery. Please refer to Figure 1 As shown, the moiré film 1 includes: a moiré film thin film 11 and an optical glass 12, and the edge of the moiré film thin film 11 is adhered to the optical glass 12.

[0032] The existing moiré films on the market are directly prepared by forming a grating structure on an optical glass through an etching technique. For the moiré films prepared by this process, as the size increases, the process difficulty increases significantly, and it is difficult to ensure the uniformity and accuracy of the grating on large-sized materials. To meet the accuracy requirements, only small-sized moiré films can be made to ensure the quality, and such moiré films can only be applied to electronic components. However, the warping on the surface of a lithium battery occurs at the micron level. If such a moiré film is increased to a size suitable for a lithium battery, its accuracy will be difficult to meet the requirements for measuring the warping degree of the lithium battery surface.

[0033] The embodiment of the present invention uses an optical glass as a substrate, and pastes a moiré film thin film etched with a grating structure on the optical glass to form the moiré film. The etching process of the moiré film thin film is simpler than that of the optical glass, and the trouble brought by the size can be overcome. Moreover, the size accuracy and pitch accuracy of the grating formed thereon can meet the high-precision measurement requirements for the warping degree of the lithium battery surface.

[0034] Furthermore, the moiré film has poor toughness and will bend when directly placed on the surface of the lithium battery, unable to maintain good flatness. Therefore, it is adhered to the optical glass.

[0035] Specifically, the moiré sheet can be used to measure the warpage of the surface of a large-sized 280Ah square battery.

[0036] Specifically, the preparation method of the moiré sheet includes:

[0037] S1. First, the optical glass substrate is cut and polished according to the (length, width) dimensions of the moiré film, and then cleaned in an ultrasonic cleaner with organic solvents (such as acetone, ethanol, etc.) to remove the oil stains and impurities on the surface. Then, it is rinsed clean with deionized water and dried in a clean environment.

[0038] S2. Apply or stick strong glue around the four edges of the optical glass, and then paste the moiré film on the optical glass substrate with strong glue attached, so that the two are horizontally adhered.

[0039] That is Figure 1 The moiré film 11 and the optical glass 12 shown are connected by strong glue around the four edges.

[0040] In some embodiments, heat is applied to further crosslink and cure the strong glue.

[0041] Specifically, the heating temperature is 100 - 150°C, and the heating time is 10 - 30 min.

[0042] In some embodiments, the dried substrate is surface-treated, and a uniform nano-scale adhesion layer is formed on the substrate surface by methods such as chemical coating or physical vapor deposition to enhance the adhesion between the glue and the substrate.

[0043] For example, the material of the adhesion layer is silica, and the thickness of the adhesion layer is 50 nm.

[0044] The size of the moiré sheet on the plane is adapted to the surface of the lithium battery to be measured. That is, the sizes of the optical glass substrate and the moiré film on the plane are both set according to the size of the surface of the lithium battery to be measured.

[0045] In some embodiments, a protective film is covered on the surface of the prepared moiré sheet by methods such as pasting or coating. The protective film material can be a transparent polymer film, and the protective layer is used to prevent the moiré sheet from being scratched or contaminated during use.

[0046] In some embodiments, the length of the optical glass is 15 - 35 cm, the width is 15 - 35 cm, and the thickness is 1.5 - 2.5 mm.

[0047] The surface size of a 280Ah lithium battery is generally 15 - 25 cm.

[0048] The optical glass needs to have a certain thickness to provide strength for the moiré film connected to it, so that the moiré film remains as a flat surface placed on the surface of the lithium battery to ensure the optical performance of the moiré film, so that the formed moiré pattern can clearly and sensitively reflect the warping degree.

[0049] However, if the optical glass is too thick, on the one hand, it will cost, including material cost and processing cost for making the moiré film. On the other hand, it is inevitable that it will increase the propagation distance of light in the glass, resulting in more light being absorbed and scattered, thus reducing the light transmittance and the clarity of the moiré pattern obtained by camera shooting. On the third hand, the thickness of the glass will increase its thermal expansion coefficient, which will further affect the accuracy and stability of the optical system.

[0050] The selection of optical glass and moiré film is mainly based on the following criteria:

[0051] 1. High transparency:

[0052] It can allow light to pass through efficiently, minimize the absorption and scattering of light, and ensure the clarity and authenticity of imaging. This is crucial for the optical system and enables the observer to obtain accurate and clear images.

[0053] 2. High chemical stability:

[0054] It is not easy to react with other chemical substances and has strong corrosion resistance. During long-term use, it can maintain the stability of its optical performance and physical structure and will not deteriorate or be damaged due to contact with air, moisture, chemical reagents, etc.

[0055] In particular, the compatibility with the lithium battery test environment should be considered. There may be chemical substances such as electrolyte in the lithium battery.

[0056] 3. Good physical property uniformity:

[0057] Its internal structure and physical properties are very uniform in all directions, which means that when light passes through the optical glass, no matter from which direction it enters, its optical parameters such as refractive index and scattering rate are the same, thus ensuring the accuracy of the optical system and the quality of the images obtained by the camera.

[0058] 4. Specific and accurate optical constants:

[0059] It has definite and stable optical constants such as refractive index and dispersion coefficient, which are the basis for optical design and manufacturing.

[0060] 5. Good thermal stability:

[0061] It can maintain the stability of its optical properties and physical structure within a certain temperature range. When the temperature changes, the changes in parameters such as the refractive index and size of the optical glass are very small.

[0062] In particular, the thermal expansion coefficient of the material should be good. When the lithium battery is charged and discharged, the surface temperature is relatively high. It is necessary to avoid changes in the optical properties or physical structure of the moiré sheet due to the surface temperature of the lithium battery to ensure the accuracy of the measurement results.

[0063] Furthermore, materials with matching thermal expansion coefficients should be selected for the moiré sheet film and the optical glass respectively to reduce the stress caused by thermal expansion mismatch.

[0064] 6. High hardness:

[0065] Resistant to wear and scratches. During daily use and processing, it is not easily scratched or worn, and can maintain the optical properties of its surface, enabling the manufactured optical system to have a long service life.

[0066] 7. Good workability

[0067] It can be made into various shapes and sizes through various processing techniques such as cutting, grinding, and polishing to meet the tests of lithium batteries of different sizes. Moreover, during the processing, the optical glass can maintain high precision, surface quality, and the optical properties of its surface.

[0068] In some embodiments, the material of the moiré sheet film is PET or PC.

[0069] When the moiré sheet is placed on the surface of the lithium battery, the direct contact surface is the corresponding surface of the moiré sheet film. Both PET and PC have good chemical stability, which can reduce the possible corrosion of the moiré sheet by the electrolyte.

[0070] Moreover, the thermal expansion coefficients of PET and PC are relatively low, which can reduce the thermal expansion and contraction of the material caused by environmental temperature changes and prevent the moiré pattern and spacing accuracy from being affected.

[0071] In addition, PET and PC have good light transmittance.

[0072] In some embodiments, the thermal expansion coefficient α of the optical glass 100 / 300℃ is 1×10 -5 / K - 1×10 -6 / K.

[0073] The thermal expansion coefficient of the optical glass is lower than that of the moiré sheet film. Therefore, optical glass with a thermal expansion coefficient matching (10 -5 level) with the moiré sheet film should be selected as much as possible.

[0074] In some embodiments, the grating pitch on the moiré film is 120 - 180 μm.

[0075] Please refer to Figure 2 As shown, the left figure is a schematic diagram of a lithium battery, where the gray surface represents the surface of the lithium battery for warpage measurement. The blue part on the gray surface in the right figure represents the moiré film placed on the surface of the lithium battery.

[0076] It should be noted that the size of the moiré film may be larger than, equal to, or smaller than the size of the surface of the lithium battery on which it is placed.

[0077] For example, in the embodiments of the present invention, the size of the moiré film is 32 cm × 32 cm. The size of the surface of the lithium battery is 20.7 cm × 17.3 cm.

[0078] First, for the same warpage, as the grating pitch increases, the number of bright and dark fringes in the moiré pattern formed during the test decreases correspondingly, or in other words, the spacing between the fringes increases.

[0079] Please refer to Figure 3 As shown, if the grating pitch is too large, it will result in the lack of regularity of the bright and dark fringes in the moiré pattern formed during the test, making it difficult to quantify the warpage by observing the change of the moiré pattern.

[0080] If the grating pitch is too small, on the one hand, it will increase the manufacturing cost of the moiré film, and on the other hand, it will cause the spacing between the fringes in the formed moiré pattern to be too small, making it difficult to distinguish the fringes.

[0081] In some embodiments, the gratings on the moiré film are arranged in concentric circles.

[0082] Specifically, the center of the concentric circles is set at the center of the moiré film.

[0083] The moiré film adopts a concentric circle grating structure, which has a high degree of regularity and repeatability, and is sensitive to small deformations, can clearly and sensitively reflect the warpage degree, and is convenient to quantify the warpage by observing the change of the moiré pattern.

[0084] Furthermore, the embodiments of the present invention provide a moiré instrument for measuring the warpage of a lithium battery, and the moiré instrument includes:

[0085] The moiré film, which is used to be horizontally placed on the surface of the lithium battery.

[0086] A camera, which is arranged above the moiré film and is used to photograph the moiré pattern formed on the moiré film.

[0087] In some embodiments, please refer to Figure 4As shown, the angle formed by the central connection line between the camera and the moiré pattern and the normal line at the center of the moiré pattern is β, and β = 0°.

[0088] When the camera is in the vertical position (i.e., consistent with the normal direction of the object surface), the propagation path of light is symmetric, and it can capture the light reflected or diffracted from the entire object surface, thereby capturing a complete moiré pattern. Observing the moiré pattern in the vertical position can minimize perspective distortion, ensure the integrity and accuracy of the moiré pattern. At the same time, the light intensity distribution on the observed object surface is relatively uniform, and the contrast of the moiré can be clearly captured.

[0089] A light source, which is arranged above the moiré pattern and is used to emit light and irradiate the moiré pattern.

[0090] In some embodiments, please refer to Figure 4 As shown, the angle formed by the central connection line between the light source and the moiré pattern and the normal line at the center of the moiré pattern is α, and α = 45°.

[0091] When the incident light irradiates at an angle of 45°, the periodic structure of the grating projects a shadow on the object surface. If there is a height change Δh on the object surface, the shadow will have a displacement Δx in the horizontal direction. Since the incident angle θ = 45° and tanθ = 1, so Δx = Δh. That is, the height difference is directly converted into a horizontal displacement.

[0092] In some embodiments, the light source is a spotlight with a brightness of 500 - 1100LM.

[0093] Since the brightness of the moiré in the moiré pattern shows a decreasing trend as the order increases, the light source needs to provide sufficient light intensity to ensure the clarity of the formed moiré pattern and the further captured moiré pattern.

[0094] The centers of the camera, the light source, and the moiré pattern are located in the same plane.

[0095] Furthermore, please refer to Figure 4 As shown, an embodiment of the present invention provides a method for measuring the warpage of a lithium battery, including:

[0096] Place the lithium battery on a horizontal plane, and then place the moiré pattern on the surface of the lithium battery.

[0097] Use the light source to irradiate the moiré pattern to form a stable moiré pattern on the moiré pattern.

[0098] Use a camera to capture the moiré pattern to obtain a picture.

[0099] Count the moiré fringes in the picture to obtain the number of bright fringes m + n.

[0100] The center of the moiré pattern is a formed bright spot (the center of the moiré pattern is a circular bright line). Light and dark moiré stripes are formed around the bright spot.

[0101] In some embodiments, m and n are respectively the number of bright stripe patterns on two rays in opposite directions starting from the center of the surface of the lithium battery, and the two rays are located on the same straight line.

[0102] In some embodiments, m and n are respectively the number of bright stripe patterns on two rays in opposite directions starting from the center of the bright spot of the moiré pattern, and the two rays are located on the same straight line.

[0103] Specifically, moiré stripe counting is performed along the diagonal direction passing through the center of the surface of the lithium battery.

[0104] Please refer to Figure 5 As shown, according to the number of bright stripe patterns m + n, the warpage degree of the lithium battery is obtained Wherein, the angle formed by the central connection line between the light source and the moiré sheet and the normal line at the center of the moiré sheet is α, and the angle formed by the central connection line between the camera and the moiré sheet and the normal line at the center of the moiré sheet is β.

[0105] The principle of the moiré sheet and the moiré instrument for measuring the warpage degree of the lithium battery surface is the shadow moiré method. This method converts the height change of the object surface into a visible moiré pattern by using the projection and occlusion effects of the grating under the geometric optics framework. When the reference grating is superposed with the shadow grating after the deformation of the object surface, if their periods are similar but there is a small displacement, Moiré fringes (moiré) will be formed. The pitch of the moiré is much larger than the grating period, thereby magnifying the small displacement and making it easy to observe.

[0106] The camera can capture the fringes in the shadow moiré method because it can collect and record the light reflected from the object surface. These lights contain the information of the grating shadow, and through the imaging system of the camera, the fringe pattern of the object surface can be clearly presented.

[0107] In some embodiments, α = 45°.

[0108] In some embodiments, β = 0°.

[0109] In some embodiments, the method further includes:

[0110] Measuring the first warpage degree of one surface of the lithium battery at room temperature;

[0111] Measuring the second warpage degree of the surface after the lithium battery is charged / discharged;

[0112] Determine whether there are defects in the internal structure of the lithium battery based on the difference between the first warpage degree and the second warpage degree.

[0113] The warping deformation on the surface of the lithium battery may be caused by the deformation of the internal structure or the leakage of the electrolyte under high-temperature environment.

[0114] For example, when the battery cells are laminated or wound, the lamination between layers is not tight, and displacement occurs after each layer expands at high temperature.

[0115] Another example is that the leaked electrolyte decomposes to generate gas (such as carbon dioxide), and the internal pressure increases, resulting in the expansion of the housing.

[0116] Therefore, a threshold value can be preset to determine whether the cause of the warping deformation can be attributed to the internal structure.

[0117] The threshold value can be measured by the same product without defects.

[0118] Alternatively, the threshold value can be set as the average value of the differences measured for the products of the same batch.

[0119] Specifically, the warpage degree at different temperatures can also be corrected to eliminate the interference of temperature.

[0120] Embodiment 1

[0121] Preparation of the moiré pattern sheet:

[0122] Prepared according to the above-mentioned preparation method of the moiré pattern sheet.

[0123] The size of the optical glass substrate is 20 cm × 20 cm, and the thickness is 2 mm.

[0124] The optical glass is purchased from Qingyong Glass Cutting Shop, Jimei District, Xiamen City.

[0125] Measure the thickness in each direction with a vernier caliper to reduce the deformation of the moiré pattern and the uneven spacing of the moiré fringes caused by the uneven thickness of the substrate.

[0126] The moiré pattern sheet film is purchased from Jiudi Microelectronics Technology (Hubei) Co., Ltd. The thickness is 0.5 mm. The gratings on the moiré pattern sheet film are arranged in concentric circles. The grating pitch ε is 150 μm. The width of the light-transmitting area is equal to that of the light-blocking area (duty cycle 50%).

[0127] The moiré pattern sheet includes an adhesion layer.

[0128] Specifically, a uniform silica adhesion layer with a thickness of 50 nm is formed on the surface of the optical glass substrate of the moiré pattern sheet close to the moiré pattern sheet film by physical vapor deposition.

[0129] Apply a hot-melt adhesive tape to the four peripheral edges of the surface of the optical glass with an adhesion layer, and then paste the moiré film on the optical glass substrate with the tape, so that the two are horizontally bonded. Heat at 120 °C for 20 min to further crosslink and cure the tape.

[0130] Specifically, after heating, the width of the adhesive layer is 1 cm and the thickness is 0.05 mm.

[0131] The moiré sheet includes a protective layer.

[0132] Specifically, a uniform transparent polymer protective film with a thickness of 0.1 mm is formed on the surface of the moiré film away from the optical glass substrate side in the moiré sheet by a bonding method.

[0133] Construction of the moiré interferometer:

[0134] Place a sphere with a radius R of 5 cm on a horizontal plane, and then place the moiré sheet horizontally on the sphere. Among them, the moiré film in the moiré sheet faces down and is in direct contact with the sphere.

[0135] Specifically, by setting support structures at both sides of the sphere with the same height as the top of the sphere, the moiré sheet is horizontally placed on the sphere.

[0136] Irradiate the moiré sheet with a light source to form a stable moiré pattern on the moiré sheet. Among them, the angle formed by the central connection line between the light source and the moiré sheet and the normal line at the center of the moiré sheet is 45°. The light source is a spotlight with a brightness of 1000 LM.

[0137] Use a camera to photograph the moiré pattern to obtain a picture. Among them, the central connection line between the camera and the moiré sheet coincides with the normal line at the center of the moiré sheet.

[0138] Please refer to Figure 6 As shown, at the bottom radius x of 15 cm corresponding to the top of the sphere in the picture, it is exactly a dark fringe. Count the dark fringes in this spherical cap part, and the number of dark fringe stripes is 15 (excluding the central dark spot).

[0139] The reason for the central dark spot may be that the curvature of the sphere is much larger than that of the plane, resulting in a half-period misalignment of the grating. Therefore, calculations are made using the dark fringes, but it does not affect the accuracy of the optical system.

[0140] The height of this spherical cap:

[0141] Calculate according to the sphere radius R:

[0142] Measured by the moiré interferometer:

[0143] The spherical crown height value detected by using the moiré interferometer is the same as the actual value, indicating that the moiré interferometer has almost no error in micron-level measurement, and its accuracy can meet the measurement requirements of the surface warpage of lithium batteries.

[0144] Example 2

[0145] Please refer to Figure 4 As shown, replace the sphere in Example 1 with a 280 Ah lithium battery, and use the moiré interferometer in Example 1 to measure the surface warpage of the lithium battery after charging for 1 h.

[0146] Specifically, the brand of this lithium battery is CATL.

[0147] Please refer to the measurement results Figure 7 as shown.

[0148] Along the diagonal direction passing through the center of the lithium battery surface, count the moiré fringes in the picture, and obtain the number of bright fringes m = 13, n = 10.

[0149] Calculate the warpage ω of the lithium battery according to the above formula: ω = 1725 μm.

[0150] This warpage value is a relatively large deformation amount. Combining with the warpage value of the same surface of the lithium battery at room temperature, it is determined that the lithium battery may have internal structural defects.

[0151] The moiré sheet and moiré interferometer provided by the present invention can detect minute displacement changes and can accurately measure the subtle warpage of the lithium battery surface. This is very important for lithium batteries with high flatness requirements, helps to discover minute deformation problems, provides accurate measurement data for the production process, and ensures the quality and performance of lithium batteries.

[0152] The moiré interferometer can measure the entire surface of the lithium battery to obtain all warpage information, which helps to discover local warpage problems and the overall deformation trend, and provides more comprehensive information for the quality control of lithium batteries.

[0153] The measurement method can obtain a large amount of measurement data in a short time, improving the measurement efficiency. For lithium batteries in large-scale production, it can quickly detect a large number of products, timely discover quality problems, improve production efficiency and product quality. At the same time, the measurement method is simple to operate, reduces the technical requirements for operators, and improves the operability and efficiency of measurement.

[0154] Furthermore, the measurement method can be equipped with corresponding data analysis software, which can quickly process and analyze the obtained moiré pattern and extract the deformation information of the object surface.

[0155] The measurement method may not be limited to the measurement of the warpage of the surface of a lithium battery, and can also be applied to the measurement of the warpage of the surface of other objects, especially objects with relatively large sizes.

[0156] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, various modifications and variations can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A moiré sheet for measuring the warpage of a lithium battery, characterized in that: The moiré sheet comprises a moiré sheet film and an optical glass, and the edge of the moiré sheet film is adhered to the optical glass.

2. The moiré sheet according to claim 1, characterized in that: The material of the moiré film is PET or PC.

3. The moiré sheet according to claim 1, characterized in that: The thermal expansion coefficient of the optical glass is α 100 / 300℃ 1×10 -5 / K-1×10 -6 / K.

4. The moiré sheet according to claim 1, characterized in that: The optical glass has a length of 15-35 cm, a width of 15-35 cm, and a thickness of 1.5-2.5 mm.

5. The moiré sheet according to claim 1, characterized in that: The grating spacing ε on the moiré film is 120-180 μm.

6. The moiré sheet according to claim 1, characterized in that: The gratings on the moiré sheet are arranged in concentric circles.

7. A moiré instrument for measuring the warpage of lithium batteries, characterized in that: The moiré instrument comprises: The moiré sheet according to any one of claims 1 to 6, wherein the moiré sheet is used to be placed horizontally on the surface of a lithium battery; A camera, the camera being disposed above the moiré sheet and being used for photographing the moiré pattern formed on the moiré sheet; A light source, the light source is disposed above the moiré sheet and is used to emit light to illuminate the moiré sheet; The centers of the camera, the light source and the moiré sheet are located in the same plane.

8. A method for measuring the warpage of a lithium battery, characterized in that: include: Place a lithium battery on a horizontal surface, and then place the cloud pattern sheet according to claim 6 on the surface of the lithium battery; irradiating the moiré sheet with the light source to form a stable moiré pattern on the moiré sheet; Using a camera to photograph the moiré pattern to obtain a picture; Count the moire fringes in the image to obtain the number of bright fringes m+n; According to the number of bright fringe stripes m+n, the warpage of the lithium battery is obtained. The angle formed by the center line connecting the light source and the moiré sheet and the normal at the center of the moiré sheet is α, and the angle formed by the center line connecting the camera and the moiré sheet and the normal at the center of the moiré sheet is β.

9. The method according to claim 8, characterized in that α＝45°。 10. The method according to claim 8, characterized in that β＝0°。

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