A three-dimensional electrochemical-thermal coupling modeling method for lithium-ion batteries containing composite current collectors

Abstract

The present invention provides a three-dimensional electrochemical-thermal coupling modeling method for a lithium-ion battery containing a composite current collector. First, an electrochemical model of a battery cell is established based on the geometric dimensions of the battery cell and the welding method of the conductive lugs. Secondly, the battery cells are stacked in an array to construct a battery cell geometric model and form an assembly, and then the continuity of the internal heat flux is achieved through the continuity boundary condition, and the thermal physical parameters and heat sources of the periodic pole lugs are analyzed using a periodic function. The three-dimensional thermal power of the battery cell is simplified by integral averaging and coupled to the battery cell thermal model, the average temperature of the battery cell is coupled to the battery cell, and finally, differentiated grid sizes are set in different areas of the battery cell thermal model to achieve three-dimensional electrochemical-thermal coupling. The present invention can predict the thermal characteristics of lithium-ion batteries containing composite current collectors with high precision, and improve the calculation efficiency through structural equivalence, heat source simplification and non-continuous grid setting.

Description

Technical Field

[0001] The invention relates to the technical field of batteries, and in particular to a three-dimensional electrochemical-thermal coupling modeling method for a lithium-ion battery containing a composite current collector. Background Art

[0002] Composite current collectors, which have the advantages of light weight and high safety, have attracted much attention due to their huge application potential in the field of batteries. Composite current collectors are composite materials with a "sandwich" structure, with an inner layer of polymer polymer layer (such as PET, PP or PI) and conductive metal layers (such as Al or Cu) on both sides. Due to the electrical insulation of the polymer layer, the tab area usually needs to weld conductive lugs on both sides of the metal layer to achieve electrical connection of the multi-layer composite current collector. However, this special tab welding method and the presence of the polymer layer increase the geometric complexity of the battery and weaken the heat dissipation performance. Compared with the metal current collector, the thinner conductive metal layer causes the voltage gradient of the composite current collector to increase, and the battery temperature rise and uneven temperature distribution are aggravated. Therefore, it is extremely important to develop an electrochemical-thermal coupling modeling method to accurately predict the electrochemical characteristics and thermal behavior of lithium-ion batteries containing composite current collectors.

[0003] Since the one-dimensional electrochemical-three-dimensional thermal coupling model or the two-dimensional electrochemical-three-dimensional thermal coupling model ignores or weakens the influence of the current collector, it is necessary to construct a three-dimensional electrochemical-thermal coupling model to study the influence of the composite current collector on the electrochemical characteristics and thermal behavior of the battery. At the same time, since the calculation of the three-dimensional coupling model is time-consuming, it is extremely important to develop an efficient three-dimensional electrochemical-thermal coupling modeling method. Summary of the invention

[0004] In view of this, the present invention uses the advantages of numerical simulation to provide an electrochemical-thermal coupling modeling method for lithium-ion batteries containing composite current collectors, which can accurately predict electrochemical characteristics and thermal behaviors and improve the calculation efficiency of the model.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] This embodiment provides a three-dimensional electrochemical-thermal coupling modeling method for a lithium-ion battery containing a composite current collector, the method comprising:

[0007] Step 1: According to the geometric dimensions of the battery cell and the welding method of the conductive lug, a battery cell geometric model is established to form a joint body, and then the corresponding welding conductivity, initial value and boundary conditions are set, and meshing is performed to obtain a three-dimensional electrochemical model of the battery cell;

[0008] Step 2: Consider the unit cells as the same area to obtain the unit cell domain, take the polymer layer of the single-layer composite current collector as the unit polymer layer domain, take the unit cell domain and the unit polymer layer domain as input objects, obtain the cell domain and the polymer layer domain by array stacking, the number of stacking layers is half the number of battery cells, and add aluminum-plastic film, periodic tabs and welding tabs, and then obtain the battery monomer geometric model by connecting the assembly;

[0009] Step 3: Equivalent the periodic tab to a homogenized rectangular parallelepiped structure, and use a periodic function with the Z-axis coordinate as a variable to represent its thermophysical property parameters and heat source;

[0010] Step 4: Based on the heat transfer principle, the corresponding initial values ​​and boundary conditions are set to construct a battery cell thermal model. The three-dimensional thermal power of the unit cell is reduced to a one-dimensional thermal power distributed along the Y axis through the integral averaging method and coupled to the cell domain of the battery cell thermal model. The volume average thermal power of the unit tab is coupled to the tab domain of the battery cell thermal model. At the same time, the average temperature of the cell domain and polymer layer domain of the battery cell is coupled to the battery cell, so as to realize the construction of a three-dimensional battery cell electrochemical-battery cell thermal cross-scale coupling model.

[0011] Step 5: Divide the three-dimensional geometric model of the battery cell into regions and set the grid, regard the periodic pole ear including the composite current collector and the conductive support ear as the first region, regard the welded pole ear as the second region, regard the battery cell domain, the polymer layer domain and the aluminum-plastic film as the third region, set the first grid size in the first region, set the second grid size in the second region, and set the third grid size in the third region.

[0012] Preferably, the battery cell geometric model is a unit cell, a negative electrode unit tab and a positive electrode unit tab in the Z-axis direction, wherein the unit cell is composed of five parts: a negative electrode metal layer, a negative electrode active layer, a separator, a positive electrode active layer and a positive electrode metal layer, and the unit tab is composed of three parts: a metal layer, a welding area and a unit welding tab.

[0013] Preferably, a mapping swept gradient grid with different unit sizes is used in the Z-axis direction of the positive and negative electrode domains of the three-dimensional electrochemical model of the battery cell.

[0014] Preferably, the battery cell domain, polymer layer domain, aluminum-plastic film domain and tab domain are connected by an assembly to construct a three-dimensional geometric model of a battery cell; the geometric model constructed by the assembly is composed of multiple independent geometric parts, and the independent geometric parts are the basis for differentiated division of the grid. At the same time, consistent continuity boundary conditions need to be set to achieve the continuity of the internal heat flux.

[0015] Preferably, the periodic tabs are equivalent to homogenized rectangular parallelepiped structures, and their thermophysical property parameters and heat sources are represented by periodic functions with the Z-axis coordinate as a variable.

[0016] Preferably, the periodic function takes the Z-axis coordinate as a variable, and the thickness of the unit welding area and the polymer layer as a variable unit, to construct a periodic function that describes the distribution of the unit welding area and the polymer layer along the Z-axis; the thermophysical property parameters of the periodic pole ear are calculated by multiplying the periodic function of the unit welding area and the periodic function of the polymer layer with the thermophysical property parameters, and the heat source distribution of the periodic pole ear is represented by multiplying the periodic function of the unit welding area with the volume average thermal power of the metal layer and the welding area in the unit pole ear.

[0017] Preferably, the three-dimensional thermal power q(x,y,z,t) of the unit cell is simplified to a one-dimensional thermal power distributed along the Y axis by two integral averages. First, the three-dimensional thermal power q(x,y,z,t) is integrated along the X axis direction with the unit cell as the integral domain and the average value is obtained to simplify it to a two-dimensional thermal power q(y,z,t); then, the two-dimensional thermal power q(y,z,t) is integrated along the Z axis direction with the XY plane of the unit cell as the integral domain and the average value is obtained to simplify it to a one-dimensional thermal power q(y,t), and then the simplified one-dimensional thermal power of the unit cell is coupled to the cell domain of the thermal model of the battery cell. Then, the thermal power calculated by multiplying the volume average thermal power of the metal layer and the welding area in the unit tab with the periodic function is coupled to the periodic tab domain of the battery cell, and the volume average thermal power of the unit welding tab in the unit tab is coupled to the welding tab domain of the battery cell.

[0018] Preferably, the battery cell in step 5 can achieve discontinuous grid division, and a relatively thick mapping swept grid is used in the Z-axis direction of the battery cell domain, polymer layer domain, aluminum-plastic film domain and welding tab domain, and an extremely thin mapping swept grid is used in the periodic tab domain. The grid thickness of the periodic tab domain depends on the thickness of the unit welding area and the polymer layer. The grid thickness must be the greatest common divisor of the thickness of the unit welding area and the polymer layer to ensure accurate analysis of the periodic structure and periodic function.

[0019] The embodiment of the present application provides a method for modeling the electrochemical-thermal coupling of a lithium-ion battery containing a composite current collector. First, a battery cell electrochemical model is constructed; secondly, a battery cell geometric model is constructed by connecting the assembly, and the continuity of the internal heat flux is realized by using the boundary conditions of consistent continuity, and periodic thermophysical parameters and heat sources are set in the periodic pole ear domain, and then different grid sizes are set in different areas to complete the construction of the battery cell thermal model; finally, the integrated average simplified one-dimensional thermal power is coupled to the battery cell domain of the thermal model, and the heat source calculated by multiplying the volume average thermal power of the metal layer and the welding area in the unit pole ear with the periodic function of the unit welding area is coupled to the periodic pole ear domain of the thermal model, and the volume average thermal power of the unit welding pole ear is coupled to the welding pole ear domain of the thermal model, and the average temperature of the battery cell domain and the polymer layer domain in the thermal model is coupled to the battery cell, and the battery cell electrochemical-battery cell thermal cross-scale coupling model is constructed. The present invention can predict the electrochemical characteristics and behaviors of lithium-ion batteries containing composite current collectors with high precision, and improve the calculation efficiency through structural equivalence, heat source simplification and non-continuous grid setting.

[0020] Compared with the prior art, it has the following beneficial effects:

[0021] 1. The present invention takes into account the contact resistance between the composite current collector and the conductive lug, and ensures the accuracy of the electrochemical model to the greatest extent. At the same time, the influence of the special welding method of the lug on the thermal distribution of the battery is considered, and the periodic lug composed of the polymer layer and the unit welding area is equivalent to a homogenized rectangular parallelepiped structure, and the layered structure is described by a periodic function, which can effectively improve the calculation efficiency compared with the refined structure of multi-layer stacking.

[0022] 2. The heat generation of lithium-ion batteries containing composite current collectors varies greatly along the length direction due to the thin thickness of the conductive metal layer. Therefore, the three-dimensional thermal power is taken as the integration object and simplified into one-dimensional thermal power distributed along the length direction through two integral averages, which reduces the number of coupled equations to be solved and further improves the calculation efficiency.

[0023] 3. Different from the common method of constructing a battery cell geometric model through a union and creating a continuous grid, the present invention constructs a battery cell geometric model through an assembly, divides it into different areas and sets a non-continuous grid. The geometric model constructed by the assembly can set a non-continuous grid at the interface of different geometric areas. Compared with the union, it can effectively reduce the model's degrees of freedom and improve calculation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the overall process of an embodiment of the present application.

[0025] Figure 2This is a schematic diagram of the composite current collector structure provided in an embodiment of the present application. This embodiment uses a composite current collector with a polymer layer of PET and a metal layer thickness of 1 μm for description.

[0026] Figure 3 A schematic diagram of the structure of the battery cell domain and the polymer layer domain provided in an embodiment of the present application.

[0027] Figure 4 A schematic diagram of the structure of the negative electrode periodic tab and the negative electrode welded tab provided in the embodiments of the present application.

[0028] Figure 5 A schematic diagram of the structure of the positive electrode periodic tab and the positive electrode welded tab provided in the embodiments of the present application.

[0029] Figure 6 A schematic diagram of the battery unit structure provided in an embodiment of the present application.

[0030] Figure 7 A schematic diagram of the battery cell structure provided in an embodiment of the present application.

[0031] Figure 8 A schematic diagram of a discontinuous grid of battery cells provided in an embodiment of the present application.

[0032] Fig. 9 A schematic diagram of a battery cell continuity grid provided in an embodiment of the present application.

[0033] Fig.10 A simplified schematic diagram of the three-dimensional thermal power of a unit cell provided in an embodiment of the present application.

[0034] The symbols of the accompanying drawings are as follows:

[0035] 1-PET layer, 2-unit battery cell domain, 3-negative electrode unit welding area (negative electrode conductive support ear + 2 layers of metal copper layer), 4-metal copper layer, 5-positive electrode unit welding area (positive electrode conductive support ear + 2 layers of metal aluminum layer), 6-positive electrode conductive support ear + 1 layer of metal aluminum layer, 7-negative electrode unit pole ear welding area, 8-negative electrode unit welding pole ear, 9-metal aluminum layer, 10-positive electrode unit pole ear welding area, 11-positive electrode unit welding pole ear, 12-positive electrode periodic pole ear, 13-positive electrode welding pole ear, 14-negative electrode periodic pole ear, 15-negative electrode welding pole ear. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but are not used to limit the present invention.

[0037] This embodiment is described by taking commercial finite element software as an example.

[0038] See also Figure 1 The embodiment of the present application provides a three-dimensional electrochemical-thermal coupling modeling method for a lithium-ion battery containing a composite current collector. The modeling process mainly includes four parts: construction of an electrochemical model of a battery cell, construction of a thermal model of a battery cell, cross-scale coupling setting of an electrochemical model and a thermal model, and discontinuous grid division.

[0039] Before further describing the present invention in detail, the nouns and terms involved in the embodiments of the present invention are explained. The nouns and terms involved in the embodiments of the present invention are subject to the following explanations.

[0040] (1) The geometric model of the present invention is constructed based on a Cartesian coordinate system, where the X-axis direction is the battery width direction, the Y-axis direction is the battery length direction, and the Z-axis direction is the battery thickness direction.

[0041] (2) Conductive lug: Copper foil or aluminum foil welded to the conductive metal layer in the lug area.

[0042] (3) Unit cell: It consists of five parts: negative electrode metal layer, negative electrode active layer, separator, positive electrode active layer and positive electrode metal layer.

[0043] (4) Unit welding area: It is composed of the conductive lug and the adjacent conductive metal layer.

[0044] (5) Cell tab: The tab in the battery cell.

[0045] (6) Periodic tabs: They are composed of periodic stacking of unit welding areas and polymer layers.

[0046] (7) Welded pole lug: A metal pole lug welded to a periodic pole lug.

[0047] (8) Battery cell: A symmetrical geometric model consisting of a battery cell domain, a polymer domain, an aluminum-plastic film domain, and a tab domain.

[0048] (9) Similarly, the present invention describes the geometric structure of a battery cell as a unit structure, such as a unit tab and a unit cell, and the unit structure is stacked to form the corresponding geometric structure of a battery cell, such as the unit cells of a battery cell are stacked to form the cell domain of a battery cell.

[0049] Before building a coupled model, the corresponding relationship of the geometric structure is explained.

[0050] See also Figure 2 This embodiment uses a composite current collector with a polymer layer of PET and a metal layer thickness of 1 μm for description.

[0051] See also Figure 3The structural schematic diagram of the battery cell domain and the polymer layer domain provided in the embodiment of the present application is shown in the figure. The interior of the battery is composed of unit cells and PET layers stacked together, and the unit cells are composed of "negative electrode metal layer-negative electrode active material-diaphragm-positive electrode active material-positive electrode metal layer".

[0052] See also Figure 4 , Figure 5 , Figure 7 Due to the electrical insulation of the composite current collector, the pole ears need to be pre-welded with conductive support ears, and then the metal pole ears are welded. Therefore, one part of the pole ears is a periodic pole ear composed of alternating stacking of PET layers and unit welding areas, and the other part is a welded pole ear composed of metal pole ears.

[0053] See also Figure 6 The battery unit is composed of a unit cell and a unit tab. The unit cell is composed of five parts: a negative electrode metal layer, a negative electrode active layer, a separator, a positive electrode active layer and a positive electrode metal layer. The unit tab is composed of three parts: a metal layer, a unit welding area and a unit welding tab.

[0054] See also Figure 6 The geometric model of the three-dimensional battery unit takes into account the welding method of the composite current collector using the conductive lug. However, in order to reduce the thickness of the lug and reduce the difficulty of aluminum-plastic film packaging, the use of thinner metal copper foil or metal aluminum foil as the conductive lug during the welding process can effectively reduce the thickness of the lug. The conductive lug of this embodiment uses a copper foil with a thickness of 6μm and an aluminum foil with a thickness of 10μm. Since the conductive lug is welded in the middle seam of adjacent conductive metal layers, the thickness of the unit lug welding area is 6μm and 4μm respectively, and the thickness of the periodic lug unit welding area is twice that of the unit lug welding area.

[0055] See also Figure 6 The electrode tab welding of lithium-ion batteries containing composite current collectors does not involve the process of unit welding electrode tab stacking welding. The unit welding electrode tab is just the equivalent geometry of the welding electrode tab in the battery cell. This equivalent geometry can take into account the impact of the welding electrode tab on the electrochemical performance and heat generation. At the same time, in order to reduce the geometric complexity, this embodiment assumes that the thickness of the unit welding electrode tab is consistent with the welding area of ​​the unit electrode tab, and the two can achieve equal thickness welding.

[0056] See also Figure 4 , Figure 5 , Figure 6The metal layer, welding area and PET layer of the unit pole ear are alternately stacked to form the periodic pole ear of the battery cell. Although there is no welding of the conductive lug in the metal layer area of ​​the unit pole ear, this embodiment assumes that the conductive lug is welded to the entire metal layer area. This assumption can construct a regular geometric model. At the same time, this structural simplification will increase the coupling area of ​​the thermal power compared to the actual structure, but the equivalent coupled thermal power can be calculated by the volume weighted method; at the same time, this structural simplification will also lead to an increase in the thermal conductivity of the pole ear area, but due to the small length of the metal layer, the slightly increased thermal conductivity has a negligible effect on the battery temperature, but the convergence of the current causes the pole ear to generate more heat, so the size of the thermal power will significantly affect the battery behavior, so it is necessary to process the coupled thermal power by volume weighted average equivalent.

[0057] See also Figure 4 , Figure 5 , Figure 6 , Figure 6 The periodic stacking of the metal layer and welding area of ​​the middle unit tab constitutes Figure 4 , Figure 5 The periodic pole lugs shown, Figure 6 The periodic stacking of the welded tabs in the middle unit constitutes Figure 4 , Figure 5 Welding lugs shown.

[0058] The modeling process of this embodiment mainly includes four parts: construction of the electrochemical model of the battery unit, construction of the thermal model of the battery unit, cross-scale coupling setting of the electrochemical model and the thermal model, and discontinuous meshing.

[0059] Step 1: Obtain the parameters required to construct a three-dimensional electrochemical-thermal coupling model of lithium-ion batteries containing composite current collectors.

[0060] Since the present invention involves many physical parameters in the description of the implementation process, in order to facilitate the understanding of the technical solution of the present invention, some physical parameters that may be used later are first presented in the form of a list, and when each physical parameter appears later, it will not be described separately one by one.

[0061]

[0062]

[0063] Table 1

[0064] Among them, some parameters required for the electrochemical-thermal coupling model are shown in Table 1.

[0065] Step 2: According to the geometric dimensions of the battery cell and the welding method of the conductive lug, a geometric model of the battery cell is established to form a joint body, and then the corresponding welding conductivity, initial value and boundary conditions are set, and the three-dimensional electrochemical model of the battery cell is obtained after meshing.

[0066] See also Figure 6 Since only the metal layer of the composite current collector can conduct current, only the metal layer of the composite current collector is selected as the design input of the model when constructing the three-dimensional electrochemical model, and the PET layer is not considered. The specific steps are as follows:

[0067] (1) First, construct a unit cell geometric model, set the length of the unit cell to 8 cm and the width to 5 cm, and stack a metal copper layer with a thickness of 1 μm, a negative electrode active layer of 85 μm, a separator of 20 μm, a positive electrode active layer of 67 μm, and a metal aluminum layer of 1 μm in the Z-axis direction. Then add a unit tab, the width of the unit tab is 0.5 cm, the length of the metal layer is 0.3 cm, the thickness is 1 μm, the length of the welding area is 0.6 cm, and the thickness is 4 μm or 6 μm. Finally, add a unit welding tab with a length of 0.6 cm and a thickness of 3 μm or 5 μm.

[0068] (2) Set the corresponding electrode materials in the geometric model. First, set the positive electrode active layer material to NMC811, the negative electrode active layer material to graphite, the electrolyte of the active layer and the separator to LiPF6, the positive electrode unit tab to aluminum, and the negative electrode unit tab to copper. Then set the initial lithium ion concentration and initial temperature. Finally, set the charge and discharge conditions, boundary flux conditions, and negative electrode grounding conditions. In addition, set the welding resistance in the welding area of ​​the unit tab.

[0069] (3) The meshing method is a combination of mapping and sweeping. Due to the large difference in thickness between the metal layer and the positive and negative active layers, a gradient mesh is used in the Z direction of the positive and negative regions, and a uniform mesh is used in the remaining regions. The battery side is selected as the mapping source surface, and the number of meshes along the X direction of all mapping source surfaces is set to 15, the number of meshes along the Y direction is set to 10, the number of meshes along the Z direction of the positive and negative metal layer regions is set to 1, the number of meshes in the Z direction of the positive and negative regions is set to 15, and it gradually decreases from the diaphragm end to both sides. The unit size ratio is 4, and the number of meshes in the Z direction of the diaphragm region is 4.

[0070] Step 3: Construct a battery cell geometric model based on the geometric model of the battery cell and the equivalent design of the tab and form an assembly.

[0071] See also Figure 2 In order to reduce the computational complexity, the battery cell thermal model of this embodiment uses a symmetrical geometric model. The specific steps are as follows:

[0072] (1) Taking the unit cell domain and the single-layer PET as input objects, the array is stacked 15 times in the Z direction to obtain the cell domain and PET domain of the battery monomer, and an aluminum-plastic film with a thickness of 152 μm is added around them.

[0073] (2) See Figure 4According to the stacking order of the positive and negative electrodes in the battery, the negative electrode periodic tab of the battery cell is composed of 15 layers of unit welding area, 16 layers of PET layer, and 2 layers of copper metal layer, and its thickness is 0.0218cm. Figure 5 From the stacking order of the positive and negative electrodes inside the battery, it can be inferred that the positive electrode periodic tab of the battery cell consists of 14 layers of unit welding area, 15 layers of PET layer, 2 layers of metal aluminum layer and 2 layers of metal aluminum foil, and its thickness is 0.028cm. From the consistency of the thickness of the unit welding tab and the thickness of the welding area of ​​the unit tab, it can be inferred that the thickness of the positive electrode welding tab in the battery cell is 0.019cm, and the thickness of the negative electrode welding tab is 0.0122cm.

[0074] According to the structural dimensions of the above-mentioned tabs, first add the homogenized positive and negative periodic tabs of rectangular structure, the length and width of the two tabs are equal, the length is 0.9cm, the width is 0.5cm, and the thickness is 0.028cm and 0.0218cm respectively. Then add the positive and negative electrode welding tabs, the length and width of the two tabs are equal, the length is 0.6cm, the width is 0.5cm, and the thickness is 0.019cm and 0.0122cm respectively.

[0075] (3) The connection relationship between the various geometric parts of the battery cell domain, PET layer domain, periodic tab domain and welded tab domain is established through the connection method of the assembly to obtain a battery cell with an assembly structure.

[0076] Step 4: See Figure 4 , Figure 5 and Figure 7 In order to reduce the coupling complexity, the periodic tab described in step 3 is equivalent to a homogenized structure. Therefore, a periodic function is needed to describe the structural distribution of the unit welding area and the PET layer.

[0077] (1) Define the basic parameters required for the periodic function. The parameters are shown in Table 2. For ease of writing, the parameters used in the periodic function are represented by abbreviations in brackets.

[0078] name value describe N_cell_tot(Nct) 30 Total number of battery cells N_PET_tot(Npt) 31 Total number of PET layers H_batt(Hba) 0.5408 cm Cell thickness H_ptab_unit(Hpu) 12μm Positive electrode welding area thickness H_ntab_unit(Hnu) 8μm Negative electrode welding area thickness H_ptab_cycl(Hpc) 0.028 cm Positive electrode periodic lug thickness H_ntab_cycl(Hnc) 0.0218 cm Negative electrode periodic lug thickness H_ptab_weld(Hpw) 0.019 cm Positive electrode welding lug thickness H_ntab_weld(Hnw) 0.0122 cm Negative electrode welding lug thickness H_ntab_ini(Hni) 0.2595 cm The starting position of the negative electrode periodic lug H_ptab_ini(Hpi) 0.2564 cm The starting position of the positive electrode periodic lug L_neg_Cu(Lnc) 1μm Thickness of copper layer L_pos_Al(Lpa) 1μm Aluminum layer thickness L_PET(Lpe) 6μm PET layer thickness L_Al(Lal) 10μm Aluminum foil thickness

[0079] Table 2

[0080] (2) With the Z-axis coordinate as a variable, a periodic function of the negative electrode unit welding area is constructed, denoted as An1(Z). This function indicates that the value of the negative electrode unit welding area is 1, and the value of other areas is 0.

[0081]

[0082] (3) Taking the Z-axis coordinate as the variable, a periodic function of the PET layer in the negative electrode periodic lug is constructed, denoted as An2(Z). This function indicates that the value of the PET layer is 1 and the value of other regions is 0.

[0083]

[0084] (4) With the Z-axis coordinate as a variable, a periodic function of the positive electrode unit welding area is constructed, denoted as An3(Z). This function indicates that the value of the positive electrode unit welding area is 1, and the value of other areas is 0.

[0085]

[0086] (5) Taking the Z-axis coordinate as the variable, a periodic function of the PET layer in the positive electrode periodic lug is constructed, denoted as An4(Z). This function indicates that the value of the PET layer is 1 and the value of other regions is 0.

[0087]

[0088] The thermophysical parameters of the homogenized periodic tab are calculated by multiplying the above periodic function with the thermophysical parameters of the unit welding area and the PET layer. The heat source distribution of the homogenized periodic tab is obtained by multiplying the periodic function of the unit welding area with the volume average heat power of the metal layer and the welding area in the unit tab.

[0089] Step 5: Set up the coupling relationship between the electrochemical model and the thermal model. The specific steps are as follows:

[0090] (1) The thermophysical parameters of the material are input into the geometric model of the battery cell, the thermal insulation conditions are set for the symmetry plane, the natural convection heat dissipation conditions are set for the battery boundaries other than the symmetry plane, and the consistent continuity boundary conditions are set inside the battery to achieve the continuity of the internal heat flux.

[0091] (2) See Fig.10 The three-dimensional thermal power q(x,y,z,t) of the unit cell is simplified by two integral averagings. First, the unit cell is used as the integral domain, the three-dimensional thermal power q(x,y,z,t) is integrated along the X-axis direction and the average value is obtained to simplify it into the two-dimensional thermal power q(y,z,t). Then, the XY plane of the unit cell is used as the integral domain, the two-dimensional thermal power q(y,z,t) is integrated along the Z-axis direction and the average value is obtained to simplify it into the one-dimensional thermal power q(y,t).

[0092] (3) The simplified one-dimensional thermal power q(y, t) is coupled to the battery cell domain of the thermal model; the thermal power calculated by multiplying the volume average thermal power of the metal layer and the welding area in the above-mentioned unit tab with the periodic function of the unit welding area is coupled to the periodic tab domain of the thermal model, and the coupled heat source is corrected based on the volume weighted method; finally, the volume average thermal power of the unit welded tab is coupled to the welding tab domain of the thermal model.

[0093] (4) The temperature volume average of the cell domain and the PET layer in the battery cell is coupled to the electrochemical model to affect the electrochemical reaction process of the battery cell in real time, thereby constructing a three-dimensional battery cell electrochemical-battery cell thermal cross-scale coupling model.

[0094] Step 6: See Figure 8 , use the mapped swept mesh to mesh the battery cells constructed by the assembly. For the first region, the number of grids in the X direction of the positive and negative periodic tabs is set to 1, and the number of grids in the Y direction is set to 4. Because the greatest common divisor of the thickness of the unit welding area and the PET layer is 1μm, the number of grids in the Z direction of the positive periodic tab is set to 140, and the number of grids in the Z direction of the negative periodic tab is set to 109. For the second region, the number of grids in the X direction of the welding tab is set to 1, the number of grids in the Y direction is set to 4, and the number of grids in the Z direction is 3. For the battery cell domain and PET layer in the third region, the number of grids in the X direction is set to 10, the number of grids in the Y direction is set to 10, the number of grids in the Z-axis direction of the PET layer is set to 1, and the number of grids in the Z-axis direction of the unit battery cell is set to 2. By using different grid sizes for the three regions, the meshing of the battery cell is achieved.

[0095] See also Fig. 9 When using the mapped swept mesh to mesh the battery cell constructed by the consortium, the meshes of the adjacent cell domain and the welded tab domain are relatively dense because the meshes of the adjacent interfaces must be continuous and the periodic tabs must be resolved using very thin meshes. Figure 7 When building a mesh based on an assembly, the meshes in the cell domain and the welding tab domain are relatively sparse, which can greatly reduce the coupling complexity.

[0096] Step 7: Based on the coupling model, output the electrochemical characteristics of the battery unit and the thermal behavior of the battery unit.

[0097] See Table 3. Taking a 5Ah battery as the modeling object, the three-dimensional electrochemical-thermal coupling model uses different dimensions of heat source coupling to compare the calculation time and calculation process of the coupling model. The calculation uses a 384G, 256-core AMD server. The model grid is shown in Figure 8 , Fig. 9 .

[0098] Heat source coupling method Analysis of periodic tabs Geometric connection method Computation time (computation process) q(x,y,z,t) Homogenized structure + periodic function Assembly 100h(0％) q(x,y,z,t) Homogenized structure + periodic function Consortium 100h(0％) q(y,t) Homogenized structure + periodic function Assembly 22h(100％) q(y,t) Homogenized structure + periodic function Consortium 113h(100％)

[0099] Table 3

[0100] See Table 4 for a comparison of the calculation time and process of the three-dimensional electrochemical-thermal coupling model when using different analytical methods to describe the periodic tab. The calculation was performed using a 384G, 256-core AMD server. The model grid is shown in Figure 8 , Fig. 9 .

[0101] The first method is to analyze the hierarchical structure of the periodic tab by combining the homogenized structure with the periodic function; the second method is to Figure 4 , Figure 5 The refined structure shown represents the layered structure of the periodic tab. The mesh used for the layered structure is given in Figure 8 .

[0102]

[0103]

[0104] Table 4

[0105] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement and improvement made within the spirit and scope of the present invention are included in the protection scope of the present invention.

Claims

1. A three-dimensional electrochemical-thermal coupling modeling method for lithium-ion batteries containing composite current collectors, characterized in that: The method comprises: Step 1: According to the geometric dimensions of the battery cell and the welding method of the conductive lug, a battery cell geometric model is established to form a joint body, and then the corresponding welding conductivity, initial value and boundary conditions are set, and meshing is performed to obtain a three-dimensional electrochemical model of the battery cell; Step 2: Consider the unit cell as a homogenized region to obtain the unit cell domain, take the polymer layer of the single-layer composite current collector as the unit polymer layer domain, take the unit cell domain and the unit polymer layer domain as input objects, obtain the cell domain and the polymer layer domain by array stacking, the number of stacking layers is half the number of battery cells, and add aluminum-plastic film, periodic tabs and welded tabs to obtain aluminum-plastic film domain and tab domain, and then obtain the battery monomer geometric model by connecting the assembly; Step 3: The periodic tab composed of the unit welding area and the polymer layer stack is used to calculate its thermal physical parameters and thermal power using a periodic function with the Z axis as a variable; Step 4: Based on the heat transfer principle, the corresponding initial values ​​and boundary conditions are set to construct a battery cell thermal model. The three-dimensional thermal power of the unit cell is reduced to a one-dimensional thermal power distributed along the Y axis through the integral averaging method and coupled to the cell domain of the battery cell thermal model. The volume average thermal power of the negative electrode unit tab and the positive electrode unit tab is coupled to the tab domain of the battery cell thermal model. At the same time, the average temperature of the cell domain and the polymer layer domain of the battery cell is coupled to the battery cell to construct a battery cell electrochemical-battery cell thermal cross-scale coupling model; the unit cell The three-dimensional thermal power q(x,y,z,t) is equivalently simplified by two integral averagings. First, the unit cell is used as the integral domain, the three-dimensional thermal power q(x,y,z,t) is integrated along the X-axis direction and the average value is obtained to simplify it into the two-dimensional thermal power q(y,z,t); then, the XY plane of the unit cell is used as the integral domain, the two-dimensional thermal power q(y,z,t) is integrated along the Z-axis direction and the average value is obtained to simplify it into the one-dimensional thermal power q(y,t); finally, the simplified one-dimensional thermal power of the unit cell is coupled to the cell domain of the battery monomer thermal model; Step 5: performing regional division and grid setting on the three-dimensional geometric model of the battery cell, wherein the periodic pole ear including the composite current collector and the conductive support ear is regarded as the first area, the welded pole ear is regarded as the second area, the battery cell area, the polymer layer area and the aluminum-plastic film are regarded as the third area, the first area is set with a first grid size, the second area is set with a second grid size, and the third area is set with a third grid size; Step 6: Based on the battery cell electrochemical-battery cell thermal cross-scale coupling model, output the electrochemical characteristics of the battery cell and the thermal behavior of the battery cell.

2. A three-dimensional electrochemical-thermal coupling modeling method for a lithium-ion battery containing a composite current collector according to claim 1, characterized in that: The battery cell geometric model of step 1 is a unit battery cell, a negative electrode unit tab, and a positive electrode unit tab in sequence in the Z-axis direction.

3. A three-dimensional electrochemical-thermal coupling modeling method for a lithium-ion battery containing a composite current collector according to claim 1, characterized in that: The periodic tabs in step 3 are equivalent to a homogenized rectangular parallelepiped structure.

4. A three-dimensional electrochemical-thermal coupling modeling method for a lithium-ion battery containing a composite current collector according to claim 1, characterized in that: In step 3, a periodic function is constructed with the thickness of the unit welding area and the polymer layer as the variable unit, and the thermophysical parameters of the periodic pole ear are calculated by multiplying the periodic function with the thermophysical parameters, and the periodic heat source of the periodic pole ear is calculated by multiplying the periodic function with the volume average thermal power of the metal layer and the welding area in the unit pole ear.

5. A three-dimensional electrochemical-thermal coupling modeling method for a lithium-ion battery containing a composite current collector according to claim 1, characterized in that: In step 4, the periodic thermal power calculated by multiplying the volume average thermal power of the metal layer and the welding area in the unit tab by the periodic function is coupled to the periodic tab domain of the battery cell, and the volume average thermal power of the unit welding tab in the unit tab is coupled to the welding tab domain of the battery cell.

6. A three-dimensional electrochemical-thermal coupling modeling method for a lithium-ion battery containing a composite current collector according to claim 1, characterized in that: The battery cell in step 2 may adopt the non-continuous mesh analytical geometry in step 5, and a relatively thick mapping swept mesh is used in the Z-axis direction of the battery cell domain, polymer layer domain, aluminum-plastic film domain and welding tab domain; an extremely thin mapping swept mesh is used in the periodic tab domain, and the mesh thickness of the periodic tab domain depends on the thickness of the unit welding area and the polymer layer, and the mesh thickness must be the greatest common divisor of the thickness of the unit welding area and the polymer layer.

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