A winding method of a high-temperature-resistant battery cell

Abstract

The application belongs to the field of battery cell manufacturing, and provides a winding method of high-temperature-resistant battery cell, which comprises the following steps: obtaining the thermal stress distribution of a diaphragm through thermal simulation, and calculating the thermal film crack stress of the diaphragm according to the thermal stress distribution of the diaphragm; obtaining the finite element model of the wound diaphragm and performing thermal simulation to obtain the thermal film crack area of the wound diaphragm; performing crack edge analysis on the thermal film crack area to obtain a crack accumulation area; coating a high-temperature-resistant sealing coating material on the diaphragm to obtain a heat-resistant diaphragm, and covering the crack accumulation area with a ceramic modified coating material; winding the heat-resistant diaphragm and positive and negative electrode sheets to obtain a battery cell, and packaging the battery cell to obtain a battery. According to the winding method of the embodiment of the application, the battery cell can avoid the problem of explosion caused by the rupture of the diaphragm due to thermal expansion under high temperature and high load.

Description

Technical Field

[0001] This invention belongs to the field of battery cell manufacturing, and specifically relates to a winding method for high-temperature resistant battery cells. Background Technology

[0002] In battery technology, the thermal stability of separator materials is crucial. Traditional separators are prone to cracking or rupture under high temperature and high load conditions due to thermal expansion and thermal stress, leading to safety accidents such as short circuits, thermal runaway, and even explosions. Although finite element analysis (FEA) is widely used in the thermal stress analysis of materials and structures, there is a lack of effective analytical methods and models for specific applications of battery separators, making it impossible to accurately predict the thermal cracking region. Furthermore, while the phenomenon of thermal cracking is well studied in materials science, there are relatively few analytical methods for the accumulation and propagation of thermal cracks in battery separators caused by thermal stress, resulting in insufficient understanding of the failure mechanism. In the application of high-temperature resistant materials, existing technologies have failed to systematically solve the problem of separator rupture at high temperatures, and traditional encapsulation methods usually do not consider the thermal stress characteristics of the separator, affecting the encapsulation effect. Summary of the Invention

[0003] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, the objective of this invention is to provide a winding method for high-temperature resistant battery cells, which can prevent the battery cells from exploding due to thermal expansion caused by separator rupture under high temperature and high load conditions;

[0004] To achieve the above objectives, this invention provides a method for winding a high-temperature resistant battery cell, the method comprising the following steps:

[0005] S100, perform thermal simulation on the diaphragm to obtain the thermal stress distribution of the diaphragm, and calculate the thermal stress of the diaphragm based on the thermal stress distribution of the diaphragm.

[0006] S200 uses finite element simulation software to simulate the process of winding the electrode and diaphragm into a cylindrical shape by the winding machine, obtains the finite element model of the wound diaphragm and performs thermal simulation to obtain the thermal film cracking area of ​​the wound diaphragm.

[0007] S300, perform edge analysis of the hot film crack region to obtain the cumulative crack region;

[0008] S400 involves coating a separator with a high-temperature resistant sealing coating material to obtain a heat-resistant separator, and covering the areas where crazing accumulates with a ceramic-modified coating material. The heat-resistant separator and positive and negative electrode sheets are then wound together to obtain a battery cell, which is then encapsulated to obtain a battery.

[0009] The winding method according to embodiments of the present invention can prevent the battery cell from exploding due to thermal expansion caused by diaphragm rupture under high temperature and high load conditions.

[0010] Furthermore, in step S100, the separator is a battery separator proposed by Chinese Patent No. CN104823304B: a battery separator in which a modified porous layer is stacked on at least one side of a polyolefin microporous membrane, wherein the polyolefin microporous membrane contains a polyethylene resin, (a) has a shut-off temperature of 135°C or less, (b) has an air impermeability change rate of 1×104sec / 100cc / °C or more, and (c) has a lateral shrinkage rate of 20% or less at 130°C.

[0011] Furthermore, in step S100, the method for obtaining the thermal stress distribution of the diaphragm includes: using 3D scanning technology to perform high-precision digital acquisition of the diaphragm to obtain its three-dimensional point cloud data; using professional software to convert the point cloud data into an STL format model to obtain a diaphragm model; defining material properties, contact conditions, and boundary conditions for the diaphragm model; and importing the diaphragm model into finite element analysis software.

[0012] The diaphragm model was loaded into the finite element analysis software, and the diaphragm model was meshed using a mesh generation algorithm to obtain a tetrahedral mesh in the diaphragm finite element model.

[0013] Specifically, the diaphragm finite element model is subdivided 20 times using the loop subdivision algorithm, dividing the diaphragm finite element model into 20 sub-regions. Let PTE(i) represent the i-th sub-region, i∈[1,20]. The diaphragm finite element model is further meshed using the free mesh generation algorithm to obtain the subdivided diaphragm finite element model.

[0014] The thermal simulation software in the finite element analysis software simulates the high load state of the diaphragm at high temperature and obtains the thermal stress distribution of the diaphragm; the thermal stress value of each mesh in the divided finite element model of the diaphragm is obtained; where the thermal stress value of the mesh is the average value of the thermal stress value of all pixels in the mesh.

[0015] Specifically, the number of grids in PTE(i) is G, the maximum thermal stress value in each grid in PTE(i) is calculated and recorded as the vulnerable thermal stress value am(i), the median of the thermal stress values ​​in each grid in PTE(i) is ag(i), the average value of the thermal stress values ​​in each grid in PTE(i) is ak(i), and the thermal stress KU(i) of the thermal film cracking in PTE(i) is calculated.

[0016] Among them, the thermal stress KU(i) of the hot film crack is: ag(i) multiplied by the ratio between am(i) and ak(i);

[0017] Furthermore, the thermal stress of the hot film cracking in each sub-region is compared, and the maximum thermal stress of the hot film cracking in each sub-region is denoted as KUM.

[0018] Among them, thermal stress caused by thermal film cracking refers to the internal stress generated in the battery separator due to thermal expansion and temperature gradient under high temperature conditions. This stress can easily lead to cracks or ruptures in the material. The principle mainly includes: the material expands when heated, and the uneven temperature of different parts causes each region to expand at a different rate, thereby generating thermal stress; during the charging and discharging process of the battery, the thermal stress caused by temperature differences is further aggravated.

[0019] Furthermore, in step S200, the process of winding the electrode and diaphragm into a cylindrical shape is simulated using finite element simulation software. A finite element model of the wound diaphragm is obtained and thermal simulation is performed to obtain the thermal film crack region of the wound diaphragm.

[0020] Electrode and winding mandrel models were constructed using 3D modeling tools. These models were complete 3D models, using shell or solid element types. The diaphragm, electrode, and winding mandrel models were imported into the finite element simulation software CalculiX. Parameters such as elastic modulus, Poisson's ratio, density, thermal conductivity, and coefficient of thermal expansion were set for the electrode and diaphragm materials, respectively. Rotational boundary conditions were applied at the winding mandrel to simulate the winding action, while a certain initial tension was applied to the diaphragm and electrode. Surface-to-surface contact relationships were established between the multiple layers of materials, and friction coefficients were set to simulate interlayer friction. After setting the boundary conditions, transient structural simulation was run to obtain the thermal stress of the wound diaphragm finite element model.

[0021] The sub-regions in the finite element model of the wound diaphragm where the thermal stress is greater than the maximum thermal stress of the hot film crack are denoted as the hot film crack region.

[0022] In battery technology, the thermal stability of separator materials is crucial. Traditional separators are prone to cracking or rupture under high temperature and high load conditions due to thermal expansion and thermal stress, leading to safety accidents such as short circuits, thermal runaway, and even explosions. Although finite element analysis is widely used in the thermal stress analysis of materials and structures, there is a lack of effective analytical methods and models for specific applications of battery separators, making it impossible to accurately predict the thermal film cracking region. Furthermore, although the study of cracking phenomena in materials science is relatively in-depth, there are relatively few analytical methods for the accumulation and propagation of cracks in battery separators caused by thermal stress, resulting in insufficient understanding of the failure mechanism. In the application of high-temperature resistant materials, existing technologies have failed to systematically solve the problem of separator rupture at high temperatures, and traditional encapsulation methods usually do not consider the thermal stress characteristics of the separator, affecting the encapsulation effect. To solve the above problems, this invention proposes step S300.

[0023] Furthermore, in step S300, the step of performing crack edge analysis on the cracked area of ​​the thermal film to obtain the crack accumulation area is as follows:

[0024] S301, Obtain the cumulative amount of crimson cracks in the hot film cracked area.

[0025] Let the magnitude of the thermal stress of the t-th mesh be JLY(t), t=1,2,…,M, where M is the total number of meshes in the finite element model of the wound diaphragm. Let the M numbers JLY(1), JLY(2),…,JLY(M) form a thermal stress sequence denoted as JLYL. The cumulative amount of cracks includes the maximum cumulative amount of cracks and the minimum cumulative amount of cracks. Let the element with the largest value and the element with the smallest value in the thermal stress sequence be denoted as the maximum cumulative amount of cracks JLYT1 and the minimum cumulative amount of cracks JLYT2, respectively.

[0026] S302, Create a storage sequence for crimson crack edge analysis.

[0027] Specifically, initialize an integer variable j with an initial value of 1, and the range of j is [1, M]. Then, create two zero-valued variables KRT1 and KRT2, and two empty sequences PT.

[0028] S303 performs a crack edge analysis on the thermal stress values ​​of the mesh in the cracked region of the hot film, and imports the analyzed values ​​into the crack edge analysis storage sequence.

[0029] Specifically, calculate the value of KRTA, where KRTA is the value of JLYT1 minus the value of JLY(j), and simultaneously calculate the value of KRTB, where KRTB is the value of JLY(j) minus the value of JLYT2. Then, compare the values ​​of KRTA and KRTB; if KRTA is greater than KRTB, then add the value of the current variable j to the sequence PT.

[0030] The principle of stress collapse analysis is mainly based on the behavior of materials under thermal stress. When the internal thermal stress of a material exceeds its bearing capacity, it leads to the destruction of its microstructure, resulting in cracks or fissures. In this process, KRTA and KRTB represent the critical values ​​under different stress states. When KRTA is greater than KRTB, it means that under the high-load stress state of the battery, the bearing capacity of the separator material is close to its limit. The resulting microstructural damage leads to local stress concentration, which in turn triggers crack propagation. By using the difference comparison method, the mesh of high-risk areas is automatically identified. Compared with the traditional method that only compares absolute values, this strategy can more sensitively capture the stress concentration trend and has higher predictive ability.

[0031] S304, determine whether the analysis of the red crack edge is complete. If it is complete, extract the analyzed data and jump to S305. If it is not complete, return to S303.

[0032] The method for determining the edge of the crisscross is as follows: check if the value of the current variable j is less than M. If it is, increment the value of j and return to step S303. If the value of the current variable j is equal to M, create an empty array KOPT, import the elements of the sequence PT into the array KOPT, and continue to step S305.

[0033] S305, after rounding up each of the analyzed data, the cumulative sequence of the crisscross cracks is obtained, and the edge analysis of the crisscross cracks is completed.

[0034] Round up each element in the KOPT array to obtain the cumulative sequence of the crisscrossing, and denote the element with the smallest value in the cumulative sequence as e and the element with the largest value as f.

[0035] The beneficial effects of this step are as follows: It provides a quantitative identification mechanism based on thermal stress edge difference analysis, which can not only accurately locate high-risk crack areas in the three-dimensional mesh model, but also effectively reflect the asymmetry and local aggregation of thermal stress gradient through the bidirectional difference comparison mechanism of "JLYT1-JLY(j)" and "JLY(j)-JLYT2", thereby realizing early warning of the failure trend of the membrane structure and significantly improving the safety and thermal stability of battery design.

[0036] S306, traverse the crisscross cumulative sequence to filter out the crisscross cumulative grid, and obtain the crisscross cumulative line through the crisscross cumulative grid.

[0037] Let E be the mesh whose thermal stress value is closest to e in the finite element model of the wound diaphragm, and let N be the mesh whose thermal stress value is closest to n in the finite element model of the wound diaphragm.

[0038] The specific method for selecting the cumulative crimson crack mesh is as follows: Connect the center of E and the center of N to obtain the line segment EN. Let the center of E be P1 and the center of N be P2. Take the midpoint P3 of EN. Let the center point of the mesh in the finite element model of the wound diaphragm that is equidistant from P3, P2 and P1 be P4. Connect P3 and P4. Let the line segment between P1 and P3 be the first crimson crack edge line L1, the line segment between P3 and P4 be the second crimson crack edge line L2, and the line segment between P1 and P4 be the third crimson crack edge line. Let the mesh within the area enclosed by the first crimson crack edge line L1, the second crimson crack edge line L2 and the third crimson crack edge line L3 be the cumulative crimson crack mesh.

[0039] Specifically, the principle of the method for selecting the cumulative grid of the red crack is as follows: by connecting P1 and P2 to form a line segment EN, a baseline can be defined in space. By introducing the midpoint P3 of line segment EN, an equilibrium position is found between P1 and P2, representing the intermediate state between these two extreme grids. By using the center point P4 of all grids that are equidistant from P3, P2, and P1, the symmetry between the position of P4 and P1 and P2 is further ensured, thus forming a specific geometry that can reflect the uniformity of stress distribution from geometric features.

[0040] Furthermore, the difference between this step and the existing technology is that: existing battery simulation models are often limited to temperature field or overall thermal deformation rate analysis, lacking the ability to predict crack growth, direction and path. This method, by introducing structural geometric stress accumulation mapping, can refine the prediction of material failure and improve the spatial granularity of thermal failure path identification; it also improves the technical problems of uncertain direction and uncontrollable expansion in diaphragm crack analysis.

[0041] S307, the region formed by the cumulative grid of crimson cracks is denoted as the cumulative region of crimson cracks.

[0042] The beneficial effect of this step is that the principle of the connection method in step S306 is that, through geometric construction analysis, a complete crack accumulation region is formed by utilizing the relative positional relationship between the grids with the maximum and minimum amount of crack accumulation, thereby more effectively identifying and predicting potential crack paths.

[0043] Although published literature and patents have reported technical approaches to improve the thermal stability of diaphragms by using heat-resistant polymer materials or ceramic-modified coatings, these solutions usually only optimize the material formulation itself and do not consider the spatial distribution characteristics of thermal stress during the winding and operation of the diaphragm, nor do they establish a closed-loop control mechanism from structural stress identification to directional reinforcement. In order to solve the above problems, this invention proposes step S400.

[0044] Furthermore, in step S400, a high-temperature resistant sealing coating material is applied to the separator to obtain a heat-resistant separator, and a ceramic-modified coating material is selected to cover the area where the red cracks accumulate. The heat-resistant separator and the positive and negative electrode sheets are wound together to obtain a battery cell, and the battery cell is packaged to obtain a battery.

[0045] Specifically, the separator is first cleaned to remove dust and impurities. A heat-resistant polymer coating material is then applied and cured to obtain a preliminary heat-resistant separator. Next, a ceramic-modified coating material (such as an alumina-polymer composite coating) is applied evenly to the crack accumulation areas using spraying, brushing, or scraping methods, and then cured to obtain a double-layer heat-resistant reinforced separator. Finally, this separator is wound with positive and negative electrode sheets to form a battery cell, which is then packaged to obtain the battery.

[0046] Optionally, the proportion of the crack accumulation region on the diaphragm surface can be calculated, denoted as α = E / M, where α ∈ [0,1]. Here, E is the number of meshes in the crack accumulation region, and M is the total number of meshes in the finite element model of the wound diaphragm.

[0047] The membrane is coated with a composite polymer according to the proportion α, wherein the composite polymer includes a heat-resistant polymer and an adhesive polymer. The mass content range of the heat-resistant polymer in the composite polymer is set to R = 80% × 2α. When R > 100%, R is set to 99%.

[0048] The beneficial effects of this step are: by reflecting the proportion of the crack accumulation area, we can identify the areas on the diaphragm that are more affected by thermal stress. By reasonably adjusting the proportion of heat-resistant polymer according to the size of these areas, we can ensure that these key areas have sufficient thermal stability and crack resistance under high temperature conditions. We can also avoid the decrease in the conductivity of the material due to an excessively high proportion of heat-resistant polymer in the coating.

[0049] The beneficial effects of this invention are as follows: As a key structure for electrolyte isolation and electronic insulation, the thermal stability of the battery separator directly determines the safety performance of the battery. During high temperatures or charging and discharging processes, the separator material may experience uneven expansion rates in different areas due to overall thermal expansion or uneven local temperature distribution, resulting in a non-uniform thermal stress field. Once the local thermal stress exceeds the material strength threshold, microcracks (called "crimson cracks") may be induced and gradually propagate into structural damage, leading to separator perforation, short circuits, or even thermal runaway. Compared to traditional methods that rely on homogeneous membrane design or simple thickness reinforcement, this invention uses a risk identification algorithm driven by thermal simulation to accurately quantify the critical value of thermal stress for cracking of the separator under winding and high-temperature operating conditions. Furthermore, it uses differential edge analysis to pinpoint the crack accumulation area where high thermal stress accumulates. By applying a silicone, polyimide, or ceramic-polymer composite sealing coating with excellent heat resistance and structural flexibility to this area, a triple-functional protective layer of thermal buffer, structural support, and crack suppression is formed in the microstructure. This significantly improves the thermal stress bearing capacity and high-temperature structural stability of the separator, and significantly reduces the safety hazards of perforation, short circuit, and thermal runaway induced by thermal expansion of the battery cell. Attached Figure Description

[0050] Figure 1 The diagram shows a flowchart of a method for winding a high-temperature resistant battery cell. Detailed Implementation

[0051] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0052] Figure 1 The diagram shows a flowchart of a method for winding a high-temperature resistant battery cell.

[0053] Reference Figure 1 This invention proposes a method for winding a high-temperature resistant battery cell, the method comprising the following steps:

[0054] S100, perform thermal simulation on the diaphragm to obtain the thermal stress distribution of the diaphragm, and calculate the thermal stress of the diaphragm based on the thermal stress distribution of the diaphragm.

[0055] S200 uses finite element simulation software to simulate the process of winding the electrode and diaphragm into a cylindrical shape by the winding machine, obtains the finite element model of the wound diaphragm and performs thermal simulation to obtain the thermal film cracking area of ​​the wound diaphragm.

[0056] S300, perform edge analysis of the hot film crack region to obtain the cumulative crack region;

[0057] S400 involves coating a separator with a high-temperature resistant sealing coating material to obtain a heat-resistant separator, and covering the areas where crazing accumulates with a ceramic-modified coating material. The heat-resistant separator and positive and negative electrode sheets are then wound together to obtain a battery cell, which is then encapsulated to obtain a battery.

[0058] According to the winding method of the present invention, the battery cell can avoid the problem of explosion caused by thermal expansion of the separator under high temperature and high load. The separator used in this embodiment is a PP / PE / PP three-layer composite microporous separator (Celgard2325, thickness 25μm, porosity about 39%, three-layer structure is PP-PE-PP).

[0059] Furthermore, in step S100, the method for obtaining the thermal stress distribution of the diaphragm includes: using 3D scanning technology to perform high-precision digital acquisition of the diaphragm to obtain its three-dimensional point cloud data; using professional software to convert the point cloud data into an STL format model to obtain a diaphragm model; defining material properties, contact conditions, and boundary conditions for the diaphragm model; and importing the diaphragm model into finite element analysis software.

[0060] The diaphragm model was loaded into the finite element analysis software FreeCAD, and the diaphragm model was meshed using a mesh generation algorithm to obtain a tetrahedral mesh in the diaphragm finite element model.

[0061] Specifically, the diaphragm finite element model is subdivided 20 times using the loop subdivision algorithm, dividing the diaphragm finite element model into 20 sub-regions. Let PTE(i) represent the i-th sub-region, i∈[1,20]. The diaphragm finite element model is further meshed using the free mesh generation algorithm to obtain the subdivided diaphragm finite element model.

[0062] The thermal stress distribution of the diaphragm was obtained by simulating the high-load state of the diaphragm at high temperature using thermal simulation software in finite element analysis software.

[0063] The thermal simulation software simulated the specific properties of the battery separator material under high temperature and high load conditions, identifying it as polyethylene (PE) with a density of 0.92 g / cm³. 3 Thermal conductivity: 0.3 W / (m·K); Specific heat capacity: 2.3 J / (g·K); Young's modulus: 800 MPa; Poisson's ratio: 0.35. Polypropylene (PP); Density: 0.90 g / cm³ 3 Thermal conductivity: 0.23 W / (m·K); Specific heat capacity: 1.8 J / (g·K); Young's modulus: 1500 MPa; Poisson's ratio: 0.3; Thickness: 0.01 mm; Width: 40 mm; Length: 200 mm.

[0064] Contact type: Use the "Contact" condition and set it to "Frictional contact"; set the coefficient of friction to 0.2, which is suitable for the contact between polyolefin and metal; set the contact stiffness to 1e6N / m to ensure true contact between the contact surfaces.

[0065] Temperature boundary conditions: Fixed temperature: The diaphragm boundary is set to 70℃ (simulating a high-temperature environment). Convection boundary: The convective heat transfer coefficient is set to 10W / (m²). 2 ·K), simulating the convection of the environment.

[0066] Fixed constraint: The bottom edge of the diaphragm is fixed to simulate the actual installation situation.

[0067] Obtain the thermal stress values ​​of each mesh within the divided finite element model of the diaphragm; where the thermal stress value of the mesh is the average of the thermal stress values ​​of all pixels in the mesh.

[0068] Specifically, the number of grids in PTE(i) is G, the maximum thermal stress value in each grid in PTE(i) is calculated and recorded as the vulnerable thermal stress value am(i), the median of the thermal stress values ​​in each grid in PTE(i) is ag(i), the average value of the thermal stress values ​​in each grid in PTE(i) is ak(i), and the thermal stress KU(i) of the thermal film cracking in PTE(i) is calculated.

[0069] Among them, the thermal stress KU(i) of the hot film crack is: ag(i) multiplied by the ratio between am(i) and ak(i);

[0070] Furthermore, the thermal stress of the hot film cracking in each sub-region is compared, and the maximum thermal stress of the hot film cracking in each sub-region is denoted as KUM.

[0071] Among them, thermal stress caused by thermal film cracking refers to the internal stress generated in the battery separator due to thermal expansion and temperature gradient under high temperature conditions. This stress can easily lead to cracks or ruptures in the material. The principle mainly includes: the material expands when heated, and the uneven temperature of different parts causes each region to expand at a different rate, thereby generating thermal stress; during the charging and discharging process of the battery, the thermal stress caused by temperature differences is further aggravated.

[0072] S200 uses finite element simulation software to simulate the process of winding the electrode and diaphragm into a cylindrical shape by the winding machine, obtains the finite element model of the wound diaphragm and performs thermal simulation to obtain the thermal film cracking area of ​​the wound diaphragm.

[0073] A complete 3D model was constructed using the 3D modeling tool FreeCAD, including: a central cylindrical mandrel;

[0074] A strip-shaped structure represents an electrode sheet with a thickness of 0.02 mm, a width of 40 mm, and a length of 200 mm.

[0075] The above model was meshed using solid tetrahedral elements for the winding mandrel, electrode sheet, and diaphragm sheet, ensuring at least two layers of elements in the thickness direction to improve the accuracy of contact analysis. Material parameters were defined for each structure: Electrode sheet material: elastic modulus 70 GPa, Poisson's ratio 0.33, density 2700 kg / m³ 3 The coefficient of thermal expansion is 2.3 × 10⁻⁶. -5 / K;

[0076] Diaphragm material: elastic modulus 1.5 GPa, coefficient of thermal expansion 1.0 × 10⁻⁶ -4 / K, density: 0.92 g / cm³ 3 Thermal conductivity: 0.3 W / (m·K); Specific heat capacity: 2.3 J / (g·K); Young's modulus: 800 MPa; Poisson's ratio: 0.35. Polypropylene (PP); Density: 0.90 g / cm³ 3 Thermal conductivity: 0.23 W / (m·K); Specific heat capacity: 1.8 J / (g·K); Young's modulus: 1500 MPa; Poisson's ratio: 0.3; Thickness: 0.01 mm; Width: 40 mm; Length: 200 mm.

[0077] The winding mandrel is set as a rigid body; a boundary condition of angular velocity about the Z-axis is applied to the winding mandrel, and the angular velocity is set to 10 rad / s; at the same time, an initial tension force along the length direction is applied to the free ends of the electrode sheet and the diaphragm sheet to simulate the tension state of the material during the winding process; the interlayer surface-to-surface contact relationship is set in the structural model, and the friction factor between the contact surfaces is set to 0.3 to simulate the friction force generated by sliding during the winding of multilayer materials.

[0078] After setting the boundary conditions and contact parameters as described above, a transient dynamic analysis was run using the CalculiX explicit solver. The total simulation duration was set to 1 second, with a time step of 0.001 seconds. During the analysis, the deformation behavior and contact stress changes of the diaphragm during the winding process were recorded in real time.

[0079] Finally, the structural state after the simulation is completed is extracted, and the output includes the residual equivalent stress distribution of the diaphragm and the geometry after winding.

[0080] The diaphragm under high temperature and high load conditions was simulated using the thermal simulation software ElmerFEM.

[0081] The thermal simulation software simulated the specific properties of the battery separator material under high temperature and high load conditions after winding. The material is polyethylene (PE); density: 0.92 g / cm³. 3 Thermal conductivity: 0.3 W / (m·K); Specific heat capacity: 2.3 J / (g·K); Young's modulus: 800 MPa; Poisson's ratio: 0.35. Polypropylene (PP); Density: 0.90 g / cm³ 3 Thermal conductivity: 0.23 W / (m·K); Specific heat capacity: 1.8 J / (g·K); Young's modulus: 1500 MPa; Poisson's ratio: 0.3.

[0082] Contact type: Use the "Contact" condition and set it to "Frictional contact"; set the coefficient of friction to 0.2, which is suitable for the contact between polyolefin and metal; set the contact stiffness to 1e6N / m to ensure true contact between the contact surfaces.

[0083] Temperature boundary conditions: Fixed temperature: The diaphragm boundary is set to 70℃ (simulating a high-temperature environment). Convection boundary: The convective heat transfer coefficient is set to 10W / (m²). 2 ·K), simulating the convection of the environment.

[0084] Force boundary conditions: Apply pressure, such as 0.5 MPa, to the contact surface between the electrode and the separator to simulate the pressure when the battery is working.

[0085] Fixed constraint: The bottom edge of the diaphragm is fixed to simulate the actual installation situation.

[0086] The sub-regions in the finite element model of the wound diaphragm where the thermal stress is greater than the maximum thermal stress of the hot film crack are denoted as the hot film crack region.

[0087] S300, perform edge analysis of the hot film crack region to obtain the cumulative crack region;

[0088] S301, Obtain the cumulative amount of crimson cracks in the hot film cracked area.

[0089] Let the magnitude of the thermal stress of the t-th mesh be JLY(t), t=1,2,…,M, where M is the total number of meshes in the finite element model of the wound diaphragm. Let the M numbers JLY(1), JLY(2),…,JLY(M) form a thermal stress sequence denoted as JLYL. The cumulative amount of cracks includes the maximum cumulative amount of cracks and the minimum cumulative amount of cracks. Let the element with the largest value and the element with the smallest value in the thermal stress sequence be denoted as the maximum cumulative amount of cracks JLYT1 and the minimum cumulative amount of cracks JLYT2, respectively.

[0090] S302, Create a storage sequence for crimson crack edge analysis.

[0091] Specifically, initialize an integer variable j with an initial value of 1, and the range of j is [1, M]. Then, create two zero-valued variables KRT1 and KRT2, and two empty sequences PT.

[0092] S303 performs a crack edge analysis on the thermal stress values ​​of the mesh in the cracked region of the hot film, and imports the analyzed values ​​into the crack edge analysis storage sequence.

[0093] Specifically, calculate the value of KRTA, where KRTA is the value of JLYT1 minus the value of JLY(j), and simultaneously calculate the value of KRTB, where KRTB is the value of JLY(j) minus the value of JLYT2. Then, compare the values ​​of KRTA and KRTB; if KRTA is greater than KRTB, then add the value of the current variable j to the sequence PT.

[0094] S304, determine whether the analysis of the red crack edge is complete. If it is complete, extract the analyzed data and jump to S305. If it is not complete, return to S303.

[0095] The method for determining the edge of the crisscross is as follows: check if the value of the current variable j is less than M. If it is, increment the value of j and return to step S303. If the value of the current variable j is equal to M, create an empty array KOPT, import the elements of the sequence PT into the array KOPT, and continue to step S305.

[0096] S305, after rounding up each of the analyzed data, the cumulative sequence of the crisscross cracks is obtained, and the edge analysis of the crisscross cracks is completed.

[0097] Round up each element in the KOPT array to obtain the cumulative sequence of the crisscrossing, and denote the element with the smallest value in the cumulative sequence as e and the element with the largest value as f.

[0098] S306, traverse the crisscross cumulative sequence to filter out the crisscross cumulative grid, and obtain the crisscross cumulative line through the crisscross cumulative grid.

[0099] Let E be the mesh whose thermal stress value is closest to e in the finite element model of the wound diaphragm, and let N be the mesh whose thermal stress value is closest to n in the finite element model of the wound diaphragm.

[0100] The specific method for selecting the cumulative crimson crack mesh is as follows: Connect the center of E and the center of N to obtain the line segment EN. Let the center of E be P1 and the center of N be P2. Take the midpoint P3 of EN. Let the center point of the mesh in the finite element model of the wound diaphragm that is equidistant from P3, P2 and P1 be P4. Connect P3 and P4. Let the line segment between P1 and P3 be the first crimson crack edge line L1, the line segment between P3 and P4 be the second crimson crack edge line L2, and the line segment between P1 and P4 be the third crimson crack edge line. Let the mesh within the area enclosed by the first crimson crack edge line L1, the second crimson crack edge line L2 and the third crimson crack edge line L3 be the cumulative crimson crack mesh.

[0101] S307, the region formed by the cumulative grid of crimson cracks is denoted as the cumulative region of crimson cracks.

[0102] S400 involves coating a separator with a high-temperature resistant sealing coating material to obtain a heat-resistant separator, and covering the areas where crazing accumulates with a ceramic-modified coating material. The heat-resistant separator and positive and negative electrode sheets are then wound together to obtain a battery cell, which is then encapsulated to obtain a battery.

[0103] Specifically, the proportion of the crisscross accumulation region on the diaphragm surface is calculated and denoted as α = E / M, where α ∈ [0,1], E is the number of meshes in the crisscross accumulation region, and M is the total number of meshes in the finite element model of the wound diaphragm.

[0104] A composite polymer is coated onto the separator according to a ratio α, wherein the composite polymer includes a heat-resistant polymer and an adhesive polymer. The mass content of the heat-resistant polymer in the composite polymer is set to R = 80% × 2α. When R > 100%, R is set to 99%. The separator is then wound with positive and negative electrode sheets to form a battery cell, which is then encapsulated to obtain a battery.

[0105] Example 1

[0106] Celgard 2325 PP / PE / PP three-layer composite microporous membrane was selected as the substrate, with a membrane thickness of 25 μm and a porosity of approximately 39%. Three-dimensional point cloud data of the membrane was acquired using 3D scanning technology and converted into an STL format model using MeshLab software. After assigning material properties to polyethylene and polypropylene in FreeCAD and setting boundary conditions, the data was imported into CalculiX finite element software for thermal simulation analysis.

[0107] The wound structure is designed as a cylinder with a diameter of 18 mm and a total length of 65 mm, consisting of 35 winding layers. In the model, the diaphragm is divided into 20 sub-regions PTE(i). For each sub-region, a loop subdivision algorithm and free mesh generation are used to obtain thermal stress distribution parameters. The simulation environment temperature is set to 70℃, the contact pressure to 0.5 MPa, and the convective heat transfer coefficient to 10 W / (m²). 2 ·K).

[0108] Simulation results show:

[0109] The maximum thermal stress am(i) in each sub-region ranges from 15 to 25 MPa;

[0110] The median thermal stress ag(i) is between 9.8 and 13.5 MPa;

[0111] The average thermal stress ak(i) is approximately 8.5–12.2 MPa;

[0112] The maximum thermal stress KU(i) for thermal film cracking was calculated to be 15.78 MPa, corresponding to the sub-region PTE(13).

[0113] In step S300, the edge mesh of the hot film crack region is identified by the KRTA-KRTB difference comparison method, and a total of 382 meshes with KRTA greater than KRTB are obtained. After further screening, 73 cumulative crack meshes are obtained, with a total area of ​​approximately 6.3 mm². 2 A triangular structure is constructed based on the edge points P1, P2, and P4 of the crisscross, and the target is identified within the region enclosed by the edge lines L1, L2, and L3.

[0114] In step S400, the proportion of the crack accumulation region on the separator surface is calculated. Based on the proportion α, a composite polymer is coated onto the separator. The composite polymer includes a heat-resistant polymer and an adhesive polymer, with the mass content of the heat-resistant polymer in the composite polymer set to R = 80% × 2α. The separator is then wound with positive and negative electrode sheets to form a battery cell, which is then encapsulated to obtain the battery. Subsequently, thermal stress simulation is performed again. The results show that the thermal stress of the original high-stress propagation path is reduced by about 21%, the crack evolution trend is significantly delayed, and no new high-stress concentration areas are formed in the simulation.

[0115] The simulation results of this embodiment show that by identifying and processing the hot film cracked region and the crack accumulation region, the thermal stability and structural integrity of the separator can be improved under simulation conditions, providing technical support for the thermal safety design of battery structure.

[0116] The specific test subjects are as follows:

[0117] Comparative Example Cell 1: Traditional PE Separator Cell; Cell Design: This cell uses a traditional polyethylene (PE) separator, commonly found in ordinary lithium-ion batteries. PE separators have good electrochemical stability, but under high-temperature conditions, thermal expansion can lead to a decrease in the mechanical strength of the separator.

[0118] Comparative Example Cell 2: Traditional PP membrane cell; Cell Design: This cell uses a polypropylene (PP) membrane. PP material has good insulation performance at room temperature, but its thermal expansion characteristics at high temperatures make it unsuitable for long-term high-temperature environments.

[0119] Comparative Example Cell 3: Traditional Composite Membrane Cell; Cell Design: This cell uses a composite material membrane, typically made of layers of PE and PP. This design enhances the membrane's strength to some extent, but its adaptability to high temperatures is insufficient.

[0120] Comparative cell 4: Traditional thick separator cell; Cell design: This cell uses a thicker separator design in an attempt to increase mechanical strength by increasing the thickness of the separator and prevent cracking caused by thermal expansion.

[0121] High-temperature cycle life test conditions:

[0122] Ambient temperature: The test was conducted at a high temperature of 70°C. This temperature was chosen to simulate the battery's operating conditions under high load and high temperature.

[0123] Charging and discharging process: Charging rate: 1C charging rate, meaning the battery capacity is fully charged in 1 hour. Discharging rate: 3C discharging rate, meaning the battery capacity is completely discharged in 20 minutes, simulating high-load discharge conditions.

[0124] Charge-discharge cycles: A 0.5C charge cycle test is performed after every 50 charge-discharge cycles to evaluate the battery's stability during long-term use. A 1C fast charge test is performed after every 100 charge-discharge cycles to simulate the impact of fast charging on battery performance.

[0125] Test equipment and configuration:

[0126] Battery testing system: Using standard battery testing equipment, it can accurately control the current, voltage and temperature during charging and discharging.

[0127] Test objectives: To test the battery's cycle life, capacity retention, thermal stability, crack propagation, and overall safety under high-temperature conditions. To observe whether thermal stress causes material cracking, deformation, or failure, and its overall performance under high-temperature load conditions.

[0128] Performance degradation standard: The end standard for cycle life test is when the battery capacity drops to 80%, that is, when the battery capacity fails to maintain 80% of its original capacity, the test is stopped, indicating that the battery has reached the end of its life.

[0129] The test results are as follows:

[0130]

[0131]

[0132] The test results show that the embodiments of the present invention significantly improve the high-temperature cycle life of the diaphragm by using high-temperature resistant materials and precise thermal stress control.

[0133] The following are the ACIR / DCIR (Alternating Current Resistance / Direct Current Resistance) tests performed on the examples and comparative examples according to typical battery performance testing standards and methods:

[0134] Specifically, AC internal resistance (ACIR) and DC internal resistance (DCIR) are used to evaluate the battery's internal resistance. AC and DC internal resistances are closely related to the battery's charge / discharge efficiency, heat generation, and performance stability. ACIR is measured at 1 kHz, while DCIR is measured at 1 Hz.

[0135]

[0136]

[0137] In summary, Example 1 exhibits low ACIR and DCIR, demonstrating good conductivity and suitability for high-load applications; conventional cells have higher internal resistance, affecting their charging efficiency and discharge stability.

[0138] It should be noted that the logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include: an electrical connection having one or more wires (electronic device), a portable computer disk drive (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Alternatively, the computer-readable medium may be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in a computer memory.

[0139] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0140] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0141] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0142] Furthermore, the terms "first," "second," etc., used in the embodiments of this invention are for descriptive purposes only and should not be construed as indicating or implying relative importance, or implicitly specifying the number of technical features indicated in this embodiment. Therefore, features defined with terms such as "first" and "second" in the embodiments of this invention can explicitly or implicitly indicate that the embodiment includes at least one of those features. In the description of this invention, the word "multiple" means at least two or more, such as two, three, four, etc., unless otherwise explicitly specified in the embodiments.

[0143] In this invention, unless otherwise explicitly specified or limited in the embodiments, the terms "installation," "connection," "joining," and "fixing" appearing in the embodiments should be interpreted broadly. For example, a connection can be a fixed connection, a detachable connection, or an integral part; it can also be a mechanical connection, an electrical connection, etc. Of course, it can also be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two components, or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific implementation.

[0144] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0145] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for winding a high-temperature resistant battery cell, characterized in that, The method includes the following steps: S100, perform thermal simulation on the diaphragm to obtain the thermal stress distribution of the diaphragm, and calculate the thermal stress of the diaphragm's thermal cracking based on the thermal stress distribution; the methods for calculating the thermal stress of the diaphragm's thermal cracking based on the thermal stress distribution include: The diaphragm finite element model is subdivided 20 times using the loop subdivision algorithm, dividing it into 20 sub-regions. Let PTE(i) represent the i-th sub-region, where i∈[1,20]. The number of meshes in PTE(i) is G. The maximum thermal stress value in each mesh of PTE(i) is calculated and denoted as the vulnerable thermal stress value am(i). The median thermal stress value ag(i) and the average thermal stress value ak(i) in each mesh of PTE(i) are also obtained. The thermal stress KU(i) of the hot film cracking in PTE(i) is calculated. The thermal stress KU(i) is ag(i) multiplied by the ratio between am(i) and ak(i). The thermal stress of the hot film cracking in each sub-region is compared, and the maximum thermal stress among all sub-regions is denoted as KUM. S200 uses finite element simulation software to simulate the process of winding the electrode and diaphragm into a cylindrical shape by the winding machine, obtains the finite element model of the wound diaphragm and performs thermal simulation to obtain the thermal film cracking area of ​​the wound diaphragm. S300, perform edge analysis of the hot film crack region to obtain the cumulative crack region; S400 involves coating a separator with a high-temperature resistant sealing coating material to obtain a heat-resistant separator, and covering the areas where crazing accumulates with a ceramic-modified coating material. The heat-resistant separator and positive and negative electrode sheets are then wound together to obtain a battery cell, which is then encapsulated to obtain a battery.

2. The method for winding a high-temperature resistant battery cell according to claim 1, characterized in that, The method for obtaining the thermal stress distribution of the diaphragm includes: using 3D scanning technology to perform high-precision digital acquisition of the diaphragm to obtain its three-dimensional point cloud data; using professional software to convert the point cloud data into an STL format model to obtain the diaphragm model; defining the material properties, contact conditions, and boundary conditions of the diaphragm model; and importing the diaphragm model into finite element analysis software.

3. The method for winding a high-temperature resistant battery cell according to claim 1, characterized in that, Step S200 includes: The sub-regions in the finite element model of the wound diaphragm where the thermal stress is greater than the maximum thermal stress of the hot film crack are denoted as the hot film crack region.

4. The method for winding a high-temperature resistant battery cell according to claim 1, characterized in that, Step S300 includes: S301, Obtain the cumulative amount of crest cracks in the hot film crest crack region; S302, Create a storage sequence for crimson crack edge analysis; S303, perform crack edge analysis on the thermal stress value of the mesh in the cracked region of the hot film, and import the analyzed values ​​into the crack edge analysis storage sequence; S304, determine whether the analysis of the red crack edge is complete. If it is complete, extract the analyzed data and jump to S305. If it is not complete, return to S303. S305, Round up each of the analyzed data to obtain the cumulative sequence of the crimson cracks, and complete the crimson crack edge analysis; S306, traverse the cumulative sequence of crimson cracks to filter out the cumulative grid of crimson cracks, and obtain the cumulative line of crimson cracks through the cumulative grid of crimson cracks; S307, the region formed by the cumulative grid of crimson cracks is denoted as the cumulative region of crimson cracks.

5. The method for winding a high-temperature resistant battery cell according to claim 1, characterized in that, Step S400 includes: first, cleaning the separator to remove dust and impurities; then, applying and curing a heat-resistant polymer coating material to the separator to obtain a preliminary heat-resistant separator; next, applying a ceramic-modified coating material to the areas where cracks accumulate, uniformly coating the area using spraying, brushing, or scraping methods, and curing it to obtain a double-layer heat-resistant reinforced separator; and finally, winding the separator with positive and negative electrode sheets to form a battery cell, and encapsulating it to obtain a battery.

6. The method for winding a high-temperature resistant battery cell according to claim 1, characterized in that, Step S400 further includes: calculating the proportion of the crack accumulation region on the surface of the separator, denoted as α = E / M, α ∈ [0,1], where E is the number of grids in the crack accumulation region and M is the total number of grids in the finite element model of the wound separator; coating the separator with a composite polymer according to the proportion α, wherein the composite polymer includes a heat-resistant polymer and an adhesive polymer, wherein the mass content range of the heat-resistant polymer in the composite polymer is set to R = 80% × 2α, and when R > 100%, R is set to 99%; and forming a battery cell by winding the separator with positive and negative electrode sheets, and encapsulating it to obtain a battery.

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