CN111459902A - Battery cell modeling method - Google Patents

Battery cell modeling method Download PDF

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CN111459902A
CN111459902A CN201910052324.2A CN201910052324A CN111459902A CN 111459902 A CN111459902 A CN 111459902A CN 201910052324 A CN201910052324 A CN 201910052324A CN 111459902 A CN111459902 A CN 111459902A
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cell
curve
battery cell
model
equivalent
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CN111459902B (en
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王艳龙
刘文峰
方伟峰
文娟·刘·麦蒂斯
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Microvast Power Systems Huzhou Co Ltd
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Microvast Power Systems Huzhou Co Ltd
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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    • Y02E60/10—Energy storage using batteries

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Abstract

The invention provides a cell modeling method, which comprises the following steps: s1: measuring the three-dimensional size of the battery cell; s2: extruding the battery cell along the thickness direction by adopting a first pressure head to obtain F of the battery cell1‑d1A curve; s3: calculating an equivalent sigma-curve of the battery cell; s4: selecting equivalent materials according to the equivalent sigma-curve, endowing parameters of the equivalent materials to the cell model, and carrying out simulation curve F on the cell model when the cell model is extruded by the first pressure head model1’‑d1Correcting the curve to establish an equivalent stiffness finite element model of the battery cell; s5: extruding the battery cell along the thickness direction by adopting a second pressure head to obtain F2‑d2A curve; s6: and on the basis of the step S4, replacing the first indenter model with the second indenter model to perform simulation and calibration correction, and establishing a final electrical core equivalent mechanical model. The cell equivalent mechanical model established by the method can improve the simulation precision of the battery pack, and the cell stress is carried out by utilizing a simulation meansMore accurate evaluation, and the evaluation capability of the CAE technology on the safety of the battery pack is expanded.

Description

Battery cell modeling method
Technical Field
The invention relates to a cell modeling method, in particular to a cell equivalent mechanical model modeling method based on a CAE (computer aided engineering) technology.
Background
The structure of the battery cell is complex, the interior of the battery cell is of a multilayer film layered structure, the thickness of the film is micron-scale, the length and the width of the battery cell are decimeter-scale, and the mechanical properties of the positive plate, the negative plate and the diaphragm in the film are different from each other. Therefore, the structure of the cell has the characteristics of span and containing a plurality of materials. For convenience of engineering calculation, the safety evaluation of the battery pack based on the CAE technology is limited to a part of important parts at present. When carrying out the structural simulation to the battery package, generally simplify into the module and gather materials point or quality piece, lack more accurate electric core parameter input, directly neglected the load state of electric core. In the extrusion working condition, the simulation evaluation index considers that the equivalent particles or mass blocks of the replacement module are judged to be safe when not extruded by the battery box body; in practice, however, the module can carry a certain load within a safe range, allowing a certain deformation.
Therefore, the problem that local precision is insufficient in the simulation modeling of the battery pack based on the CAE technology at present, an accurate cell equivalent mechanical model is lacked, and when the battery pack is subjected to mechanical abuse working conditions such as extrusion, the simulation model cannot make accurate reliability assessment on the safety problems of the module and the cell.
Disclosure of Invention
The invention provides a modeling method of a cell equivalent mechanical model, which comprises the following steps:
s1: measuring three-dimensional dimensions of a battery cell, wherein the three-dimensional dimensions at least comprise the thickness H of the battery cell and the area S of a surface C perpendicular to the thickness direction;
s2: the cell was extruded in the thickness direction using a first ram (as shown in fig. 3), recording the extrusion processCompressive deformation d of battery cell in thickness direction1And contact load F1Obtaining F when the battery cell is in an elastic-plastic stage along with the change of time1-d1A curve;
s3: according to stress σ ═ F1(ii) S and bulk strain d1Obtaining an equivalent sigma-curve of the battery cell;
s4: selecting an equivalent material according to the equivalent sigma-curve, endowing parameters of the equivalent material to a cell model, and carrying out simulation curve F on the cell model when the cell model is extruded by a first pressure head model1’-d1' Curve by F1-d1Correcting the standard by taking the curve as a standard so as to establish an equivalent stiffness finite element model of the battery cell;
s5: the electric core is extruded along the thickness direction by a second pressure head (as shown in figure 4), and the compression deformation d of the electric core in the thickness direction in the extrusion process is recorded2And contact load F2Obtaining the load peak value F of the battery cell including the failure moment along with the change of timemaxF of (A)2-d2A curve;
s6: replacing the first pressure head model with a second pressure head model to carry out simulation on the basis of the equivalent stiffness finite element model in the step S4 to obtain a simulation curve F2’-d2' curves, and for simulation curve F2’-d2' Curve by F2-d2The curve is corrected to a standard value, and a simulated value F 'is obtained'maxAt peak test load FmaxWithin a range of + -5% and d2' and d2Same phase F2' at F2Setting the mechanical model within the range of +/-5% as a battery cell equivalent mechanical model;
the contact surface of the first pressure head is a plane and the size of the contact surface is larger than or equal to the C surface, and the contact surface of the second pressure head is a curved surface.
The cell model, the first pressure head model and the second pressure head model respectively refer to equivalent finite element models of the cell, the first pressure head and the second pressure head, which are established in finite element software. The first pressure head model and the second pressure head model are both rigid models.
The battery cell is a soft-package battery cell with a certain thickness, so that non-main body structures such as a tab and the like can be omitted in an extrusion test, the largest surface of the battery cell is a C surface, and the shape of the C surface comprises a regular or irregular geometric shape, such as any one of a circle, a rectangle (shown in fig. 2), a square or a polygon. And the second pressure head of the step S5 acts on the middle part of the battery cell and is more than 8mm away from the boundary of the C surface. The contact surface is the contact surface of the first pressure head or the second pressure head and the surface C. Testing the equivalent stiffness curve F of the cell by step S21-d1According to the curve (as shown in fig. 5), since the change of the contact area between the battery cell and the first indenter is negligible, the whole battery cell is in a stress state of bearing unidirectional compression, and is uniformly deformed. According to stress σ ═ F1(S) volume strain Δ V/V d1S/HS＝d1and/H, calculating to obtain an equivalent sigma-curve (shown in figure 6) of the battery core, wherein the equivalent sigma-curve is also called an equivalent constitutive curve, and the equivalent constitutive curve is a key basis for selecting equivalent materials in a modeling process. And selecting an equivalent material with the constitutive relation consistent with the equivalent sigma-curve, and giving a preset parameter of the equivalent material to the cell model to establish an equivalent stiffness finite element model of the cell. Obtaining the load peak value F of the battery cell failure moment through the step S5maxAnd the failure refers to the internal short circuit of the battery cell. Combining the equivalent stiffness model of the battery cell with the load peak F at the battery cell failure moment through the step S6maxAnd obtaining a final battery cell equivalent mechanical model.
The calibration refers to the difference of comparing simulation values by taking an actual value obtained by a test as a standard, and the correction is a process of adjusting simulation parameters by a pointer to a result of the calibration so as to enable the simulation values to be infinitely close to the actual value.
In one embodiment of the present invention, the step S2 further includes the step S21: monitoring voltage U of electric core in extrusion process1And/or temperature T1As a function of time, when the voltage U is1Decrease by more than 10% and/or temperature T1When the rise exceeds 10%, the extrusion is stopped. When voltage U1Fall within 10% or temperature T1When the rise is within 10%, the battery cell is considered to have no internal short circuit or thermal runaway, that is, the internal structure and materials of the battery cell are not failed, and the battery cell is in an elastoplastic stage. Thus, F of the cell in the elastoplastic phase1-d1The curve is the integral equivalent stiffness curve of the battery core. In the first pressure head extrusion test in the step S2, the battery cell cannot easily fail, and extrusion can be stopped when the extrusion force approaches the maximum allowable output load of the testing machine; monitoring the voltage U in the step S211And/or temperature T1Can monitor the safe state of electric core, if take place inside short circuit or thermal runaway, can in time stop the extrusion, raise the efficiency on the one hand, practice thrift the cost, on the other hand avoids dangerous the emergence.
In one embodiment of the present invention, the calibration modification in step S4 includes adjusting the grid size and hourglass control, and adjusting the contact parameters to simulate curve F1’-d1' the curve is corrected for the norm.
The size of the grid refers to that in finite element calculation, a continuous body to be analyzed needs to be divided into a plurality of unit bodies, the size of the unit bodies is the size of the grid, the larger the number of the divided unit bodies is, the smaller the unit size is, and the smaller the grid is; the size of the grid can affect the contact search, the minimum time step and the number of cells in the simulation, and further affect the calculation time and the calculation accuracy. The hourglass control means that in the case of a reduced integral unit, the hourglass is controlled in a zero-energy mode of the hourglass, for example, a certain rigidity is artificially added to the unit.
In one embodiment of the present invention, the calibration correction in step S6 includes using a material failure mechanism and a unit life and death technique to simulate the curve F2’-d2' the curve is corrected for the norm. For simulation curve F2’-d2'correction of the standard curve mainly includes the correction of simulated value F'maxCan obtain different F 'when different failure criteria and failure threshold values are tried'max. When imitating value F'maxAt peak test load FmaxWithin a range of + -5% and d2' and d2Same phase F2' at F2Within the range of +/-5%, the material failure critical value adopted in the simulation can replace the equivalent failure value of the battery cell material, and the failure mode of the material can replace the failure mode of the battery cell equivalent material.
The material failure mechanism is also referred to as a strength criterion of the material, which is classified into a first, a second, a third and a fourth strength criterion according to classical material mechanics. The essence of the strength criterion is that the failure threshold of a material is characterized by a scalar quantity that is a combination of stress components or strain components. When the scalar corresponding to the stress state of the material reaches the strength threshold, the material fails. In the simulation of the invention, when the maximum hydrostatic pressure or the maximum equivalent strain borne by the battery cell reaches a set threshold, the unit stiffness is 0, and the unit with the stiffness of 0 no longer contributes to the stiffness of the whole structure. The unit life and death technology comprises the steps that a unit body does not participate in calculation any more, and the degree of freedom of an island node connected with the unit body does not participate in calculation of an integral structure any more; further, the failed cell is no longer displayed in post-processing.
In one embodiment of the present invention, the initial SOC of the battery cell is 10% or more.
In one embodiment of the present invention, the second pressing head in the step S5 includes at least one pressing head. If more than two pressure applying heads are adopted in the step S5, that is, multi-point contact is performed, the distances between the vertexes of all the pressure applying heads and the C surface of the battery cell are equal, so that the compression deformation d of the battery cell caused by each pressure applying head in the thickness direction is equal2Equal contact load F at this time2Is the sum of the contact loads between all the pressing heads and the cell.
In one embodiment of the present invention, the step S2 is performed in a quasi-static state, and the loading speed is 0.5-2 mm/min.
In one embodiment of the present invention, the step S5 is performed in a quasi-static state.
In one embodiment of the present invention, the contact surface of the second ram in step S5 is a spherical surface or an ellipsoidal surface.
In one embodiment of the invention, the battery cell is a rectangle including a short side with a length of L, the diameter of the spherical surface is greater than or equal to one tenth of L and less than or equal to one third of L, the length of the long axis of the ellipsoid is greater than or equal to one tenth of L and less than or equal to one third of L, and the ratio of the length of the short axis to the length of the long axis of the ellipsoid is greater than or equal to one third and less than 1.
In one embodiment of the invention, the diameter of the spherical surface is 10-40 mm; the major axis of the ellipsoid is 10-40mm, and the ratio of the minor axis length to the major axis length is greater than or equal to one third and less than 1. In another embodiment of the present invention, the diameter of the spherical surface is 12-32 mm; the major axis of the ellipsoid is 12-32 mm.
In one embodiment of the present invention, the step S5 further includes the step S51: monitoring voltage U of electric core in extrusion process2And/or temperature T2When a voltage U is applied2Decrease by more than 15% and/or temperature T2When the rise exceeds 15%, the extrusion is stopped. When the second pressure head extrudes the battery core, the battery core is in a local stress state, so that the battery core fails due to small extrusion force, and the structural nonlinearity and the reduction of the bearing capacity are caused due to material failure. When the cell has internal short circuit, the voltage U of the cell2Decrease of temperature T2And (4) rising. Thus, the temperature T can be monitored2Voltage U2And contact load F2The failure time of the battery cell can be judged by at least one numerical value, and the peak load F in failure is readmaxTo obtain a contact load F2F of the descending section2-d2Curve of said F2-d2The curve comprises the load peak value F at the time of the cell failuremax。
The cell equivalent mechanical model established by the method can improve the simulation precision of the battery pack, more accurately evaluate the cell stress by using a simulation means, and expand the evaluation capability of the CAE technology on the safety of the battery pack.
Drawings
FIG. 1: the invention discloses a flow chart of a cell modeling method;
FIG. 2: the invention discloses a structural schematic diagram of a rectangular battery cell;
FIG. 3: the invention discloses a structural schematic diagram of a first pressure head extruding a battery cell along the thickness direction;
FIG. 4: the invention discloses a structural schematic diagram of a second pressure head extruding a battery cell along the thickness direction;
FIG. 5: f of the cells described in example 11-d1A curve;
FIG. 6: the σ -curve of the cell described in example 1;
FIG. 7: a local schematic diagram of an equivalent stiffness finite element model of the cell in embodiment 1;
FIG. 8: simulation curve F in example 11’-d1' Curve and test F1-d1A comparison of the curves;
FIG. 9: a model diagram for simulation in example 4 using an equivalent strain failure criterion;
FIG. 10: f 'obtained by simulating different parameters according to equivalent strain failure criteria in embodiment 4'maxAnd the peak value of the test load FmaxA comparison graph of (A);
FIG. 11: a model diagram for simulation in example 5 using a maximum hydrostatic pressure failure criterion;
FIG. 12: f 'simulated in example 5 by maximum hydrostatic pressure failure criterion'maxAnd the peak value of the test load FmaxA comparative graph of (a).
Detailed Description
The following specific examples are intended to describe the present invention in detail, but the present invention is not limited to the following examples.
Example 1
As shown in fig. 1 except for the dashed line frame, the present embodiment provides a method for modeling an electrical core 10, including the following steps:
s1: measuring the three-dimensional size of the battery cell 10 by using a micrometer, wherein the three-dimensional size comprises the thickness H of the battery cell 10 and the thickness C perpendicular to the thickness directionThe battery core 10 is a cuboid structure with the length of 59.50mm, the width of 34.00mm and the thickness of 5.35mm, so that the area S is 59.5mm, × 34mm and 202.3mm2The thickness H is 5.35 mm; the initial SOC of the battery cell 10 is 10%.
S2: extruding the battery cell 10 (as shown in fig. 3) by using a first pressure head 11 at a rate of 1mm/min along the thickness direction, wherein a contact surface of the first pressure head 11 and a C surface is a plane and has a size larger than or equal to that of the C surface, and acquiring a compression deformation d of the battery cell 10 in the thickness direction in the extrusion process1And contact load F1Acquiring data changing along with time at a frequency of 1Hz to obtain an equivalent stiffness curve of the battery cell 10 in an elastoplastic stage, namely F1-d1Curve (as shown in fig. 5). Amount of compression set d1At the 0-1mm stage, contact load F1And amount of compression set d1In an exponential relationship, when the compression deformation d1The linear relationship is shown after being larger than 1 mm. When the first pressing head 11 is used for extrusion, the battery cell 10 is uniformly deformed in the thickness direction, and the battery cell 10 cannot fail under the general condition because the stressed area of the battery cell 10 is large. Therefore, the pressing is stopped when the pressing force approaches the maximum output load of the testing machine.
S3: according to stress σ ═ F1(ii) S and bulk strain d1and/H, obtaining an equivalent sigma-curve of the battery cell 10 (as shown in FIG. 6). The inside of the battery cell 10 is of a porous structure, and when the first pressure head 11 is adopted for extruding along the thickness direction, the deformation of the C surface is very small and can be ignored, so that the poisson ratio of the battery cell 10 equivalent material is very small, and the stress state of the battery cell 10 is a unidirectional stress state. Therefore, the three-dimensional size and stress σ of the battery cell 10 can be used as F1(ii) S and bulk strain d1And calculating an equivalent sigma-curve of the battery cell 10, namely an equivalent constitutive curve.
S4: selecting an equivalent material according to the equivalent sigma-curve, endowing parameters of the equivalent material to the cell model 10a, and carrying out simulation curve F on the cell model 10a when the cell model is extruded by the first pressure head model 11a1’-d1' Curve by F1-d1And (4) performing calibration correction by taking the curve as a standard so as to establish an equivalent stiffness finite element model of the battery cell 10. A cross-sectional junction as shown in fig. 7The structure, the top sheet is a rigid first indenter model 11a, the middle portion is a cell model 10a, the bottom dotted line frame is a rigid basal plane model 13a supporting the cell model 10a from the equivalent constitutive curve obtained in step S3, it can be seen that, in the initial elastic stage, σ and σ are in a nonlinear relationship, the compressible foam material is a porous material, the constitutive curve has the property of initial non-linear elasticity, so Mat63 compressible foam material in L S _ dyna is selected to establish the equivalent finite element model of the cell 101’-d1' curves and test values F1-d1A comparison of the curves is shown in FIG. 8, which shows good agreement between the two.
S5: extruding the battery cell 10 along the thickness direction by using a second pressing head 12 (as shown in fig. 4), wherein a contact surface between the second pressing head 12 and the C surface is a curved surface, and recording a compression deformation d of the battery cell 10 in the thickness direction during the extrusion process2And contact load F2Obtaining the load peak value F of the battery cell 10 including the failure moment along with the change of timemaxF of (A)2-d2Curve line. The middle part of the cell 10 is pressed with a second ram 12 having a diameter of 12.7 mm. The second pressing head 12 has a smooth surface so as not to scratch the surface of the battery cell 10. The test is a quasi-static test, and the loading rate is 1 mm/min. When being pressed by the second pressing head 12, the battery cell 10 is in a local stress state. Under the same extrusion force, because the stress area is smaller, the local stress of the battery cell 10 is larger, the battery cell 10 can generate the failure of materials or structures, so that local collapse is caused, and the contact load F2It will suddenly decrease. So by monitoring the contact load F2The failure time of the battery cell 10 can be judged and the load peak can be obtainedValue Fmax。
S6: on the basis of the equivalent stiffness finite element model in the step S4, replacing the first indenter model 11a with the second indenter model 12a to perform simulation to obtain a simulation curve F2’-d2' curves, and for simulation curve F2’-d2' Curve by F2-d2The curve is corrected to a standard value, and a simulated value F 'is obtained'maxAt peak test load FmaxWithin a range of + -5% and d2' and d2Same phase F2' at F2And setting the mechanical model within the range of +/-5% as a cell equivalent mechanical model. On the basis of the equivalent stiffness finite element model of the battery cell 10, the first indenter model 11a is replaced by a second indenter model 12a for simulation. Contact load F 'without adding any failure criteria'2Will not drop. To simulate the contact load F 'at the time of breakage of the cell model 10 a'2The reduction of (2) is to introduce a material failure criterion and a unit life and death technology, in finite element calculation, a corresponding unit is deleted after the material fails, the corresponding rigidity is reduced to 0, and the bearing capacity is lost, which is close to the actual condition.
Example 2
The embodiment 1 is similar to that of the embodiment 1, except that the initial SOC of the battery cell 10 is 20%, and the step S2 further includes the step S21: monitoring voltage U of cell 10 during extrusion1And/or temperature T1As the thickness of the tab is smaller than that of the battery cell 10, the two ends of the voltage sensor are respectively connected to the two tabs of the battery cell 10, the thermocouple is connected to any one of the two tabs, and when the voltage U is applied, the voltage U is applied1Decrease by more than 10% and/or temperature T1When the rise exceeds 10%, the extrusion is stopped. When voltage U1Fall within 10% or temperature T1When the rise is within 10%, it is considered that the internal short circuit or thermal runaway of the battery cell 10 does not occur, that is, the internal structure and material of the battery cell 10 do not fail, and the battery cell is in an elastoplastic stage. Thus, F of the cell 10 in the elastoplastic phase1-d1The curve is an equivalent stiffness curve of the entire battery cell 10. By monitoring the voltage U in said step S211And/or temperature T1Can monitorThe safety state of the battery cell 10 is controlled, and if an internal short circuit occurs, extrusion can be stopped in time, so that the efficiency is improved, the cost is saved, and the danger is avoided.
Example 3
Unlike embodiment 1, the difference is that the step S5 further includes a step S51: monitoring voltage U of cell 10 during extrusion2And/or temperature T2When a voltage U is applied2Decrease by more than 15% and/or temperature T2When the rise exceeds 15%, the extrusion is stopped. When the second pressing head 12 presses the battery cell 10, the battery cell 10 is in a local stress state, so that the battery cell 10 fails due to a small pressing force, and the structural nonlinearity and the bearing capacity decrease due to material failure. When the internal short circuit occurs in the battery cell 10, the voltage U of the battery cell 102Decrease of temperature T2And (4) rising. Thus, the temperature T can be monitored2Voltage U2And contact load F2The failure time of the battery cell 10 can be judged by at least one value, and the peak load F in failure is readmaxTo obtain a contact load F2F of the descending section2-d2Curve of said F2-d2The curve includes the load peak F at the time of failure of the cell 10max. Two ends of the voltmeter are respectively connected with two tabs of the battery cell 10, and the thermocouple is adhered to the position near the extrusion position by glue.
Example 4
Unlike embodiment 1, the calibration correction in step S6 includes correction using an equivalent strain failure criterion. The corresponding key is MAT _ ADD _ error, EFFEPS. Due to the compression deformation d 'of the pressed region of the cell model 10 a'2Maximum, strain is also maximum. When the equivalent strain is greater than the set critical equivalent strain, the cell model 10a fails, and the corresponding units lose the bearing capacity and the contact load F'2It will drop. Different contact loads F 'when different failure thresholds are set are given in FIG. 10'2And (4) changing. It can be seen that the failure threshold only affects peak load F'maxNo change in peak load value F'maxThe mechanical response of the previous cell model 10 a. Tong (Chinese character of 'tong')By contrast, when the equivalent strain is set to 0.7525, the simulation results are more consistent with the test results. It can be seen that the deformation mode of the cell model 10a is also reasonable (as shown in fig. 9) at the time of failure, and when the equivalent strain of the foam material reaches the set value 0.7525, the cell model 10a begins to fail, and the corresponding load reaches the peak load value F'maxAnd then begins to fall.
Example 5
Unlike embodiment 1, the correction of the calibration in step S6 includes correction using the maximum hydrostatic pressure failure criterion. The corresponding key is MAT _ ADD _ error, MXPRES. The hydrostatic pressure is positive for the compressive stress and negative for the tensile stress. When the second indenter pattern 12a presses the cell pattern 10a, the contact portion is subjected to a compressive stress, and a portion away from the contact portion is subjected to a smaller tensile stress. Hydrostatic pressure guidelines state that failure occurs when the compressive stress is greater than a given critical compressive stress. By contrast, when the failure threshold was set at 52.5MPa, the simulation results were more consistent with the test results (shown in fig. 12). It can be seen that the deformation mode of the cell model 10a at the time of failure is also reasonable (shown in fig. 11).
Example 6
The same as example 1, except that the second indenter 12 in step S5 has an ellipsoidal top shape, a major axis of which is 28mm in length and a minor axis of which is 20mm in length.
Example 7
The difference from the embodiment 1 is that the second pressing head 12 in the step S5 includes four pressing heads, the top of the pressing head is a spherical surface, and the diameter of the spherical surface is 15 mm.
The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are merely illustrative of the principles of the invention, but that various changes and modifications may be made without departing from the spirit and scope of the invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims (10)

1. A cell modeling method is characterized in that: the method comprises the following steps:
s1: measuring three-dimensional dimensions of the battery cell (10), wherein the three-dimensional dimensions at least comprise the thickness H of the battery cell (10) and the area S of the surface C perpendicular to the thickness direction;
s2: extruding the battery cell (10) along the thickness direction by adopting a first pressure head (11), and recording the compression deformation d of the battery cell (10) in the thickness direction in the extrusion process1And contact load F1Obtaining F of the battery core (10) in the elastic-plastic stage along with the change of time1-d1A curve;
s3: according to stress σ ═ F1(ii) S and bulk strain d1Obtaining an equivalent sigma-curve of the battery cell (10);
s4: selecting an equivalent material according to the equivalent sigma-curve, endowing parameters of the equivalent material to a cell model (10a), and carrying out simulation curve F when the cell model (10a) is extruded by a first pressure head model (11a)1’-d1' Curve by F1-d1Correcting the standard by taking the curve as a standard so as to establish an equivalent stiffness finite element model of the battery cell (10);
s5: extruding the battery cell (10) along the thickness direction by adopting a second pressure head (12), and recording the compression deformation d of the battery cell (10) in the thickness direction in the extrusion process2And contact load F2Obtaining a load peak value F of the battery cell (10) including a failure moment along with the change of timemaxF of (A)2-d2A curve;
s6: replacing the first pressure head model (11a) with the second pressure head model (12a) to carry out simulation on the basis of the equivalent stiffness finite element model in the step S4 to obtain a simulation curve F2’-d2' curves, and for simulation curve F2’-d2' Curve by F2-d2The curve is corrected to a standard value, and a simulated value F 'is obtained'maxAt peak test load FmaxWithin a range of + -5% and d2' and d2Same phase F2' at F2Is set as electricityAn equivalent mechanical model of the core (10);
the contact surface of the first pressure head (11) is a plane and the size of the contact surface is larger than or equal to that of the C surface, and the contact surface of the second pressure head (12) is a curved surface.
2. The cell modeling method of claim 1, wherein: the step S2 further includes a step S21: monitoring the voltage U of the cell (10) during the extrusion process1And/or temperature T1As a function of time, when the voltage U is1Decrease by more than 10% and/or temperature T1When the rise exceeds 10%, the extrusion is stopped.
3. The cell modeling method of claim 1, wherein: the calibration modification in step S4 includes adjusting the grid size and hourglass control, and adjusting the contact parameters to simulate curve F1’-d1' the curve is corrected for the norm.
4. The cell modeling method of claim 1, wherein: the calibration correction in the step S6 includes using a material failure mechanism and a unit life and death technique to simulate the curve F2’-d2' the curve is corrected for the norm.
5. The cell modeling method of claim 1, wherein: the initial SOC of the battery core (10) is more than 10%.
6. The cell modeling method of claim 1, wherein: the second ram (12) in said step S5 includes at least one pressure ram.
7. The cell modeling method of claim 1, wherein: the contact surface of the second pressure head (12) in the step S5 is a spherical surface or an ellipsoidal surface.
8. The cell modeling method of claim 7, wherein the cell (10) is rectangular and includes a short side with a length of L, the diameter of the spherical surface is greater than or equal to one-tenth of L and less than or equal to one-third of L, the length of the major axis of the ellipsoid is greater than or equal to one-tenth of L and less than or equal to one-third of L, and the ratio of the length of the minor axis to the length of the major axis of the ellipsoid is greater than or equal to one-third and less than 1.
9. The cell modeling method of claim 7, wherein: the diameter of the spherical surface is 10-40 mm; the major axis of the ellipsoid is 10-40mm, and the ratio of the minor axis length to the major axis length is greater than or equal to one third and less than 1.
10. The cell modeling method of claim 1, wherein: the step S5 further includes a step S51: monitoring the voltage U of the cell (10) during the extrusion process2And/or temperature T2When a voltage U is applied2Decrease by more than 15% and/or temperature T2When the rise exceeds 15%, the extrusion is stopped.
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