CN109902372B

CN109902372B - Battery roll core simulation method based on finite element analysis

Info

Publication number: CN109902372B
Application number: CN201910127214.8A
Authority: CN
Inventors: 史方圆; 陈贤青; 李洁; 禹慧丽; 崔泰松; 赵会
Original assignee: Chongqing Changan Automobile Co Ltd
Current assignee: Chongqing Changan Automobile Co Ltd
Priority date: 2019-02-20
Filing date: 2019-02-20
Publication date: 2023-04-18
Anticipated expiration: 2039-02-20
Also published as: CN109902372A

Abstract

A battery roll core simulation method based on finite element analysis comprises the following steps: (1) According to the size of a battery winding core, establishing a volume ratio of 1: the battery roll core CAD model with the proportion of 1 is formed by winding a layer of cuboid with the thickness of b/2 n; (2) Establishing a finite element model of the battery roll core, wherein hexahedral units in the model are endowed with thick-shell unit types, the thickness direction of the hexahedral units is consistent with the thickness direction of the battery roll core, the number of integrating points of the thick-shell units in the thickness direction is 4m/n, and according to the actual structure of the roll core, from outside to inside, each integrating point respectively represents a diaphragm, an anode, a diaphragm and a cathode and is repeated for m/n times; and (3) giving the finite element model material properties. The thickness shell units of each layer wound by the invention can relatively slide, so that the layering phenomenon among layers can be simulated when the winding core is extruded, and the simulation is more accurate; and the number of layers of the actual anode, cathode and diaphragm is represented by only using the integral points, so that the number of finite element model units is reduced, and the calculation efficiency is saved.

Description

Battery roll core simulation method based on finite element analysis

Technical Field

The invention relates to the technical field of finite element analysis of automobiles, in particular to a finite element simulation method of a battery roll core of an electric automobile.

Background

Electric vehicles have become important products in the field of new energy vehicles as important components of new energy vehicles. The battery is one of the key parts of the electric automobile, and the safety performance of the battery directly influences the safety performance of the whole electric automobile. In order to meet the mileage requirement, and at the same time, limited by the structural arrangement, the battery pack of the electric vehicle is generally installed on the bottom of the vehicle. With the gradual increase of the keeping quantity of electric automobiles, the use working conditions of the electric automobiles are more and more complicated, and a plurality of accidents that the electric automobiles are ignited due to the impact from the bottom of the automobile have occurred. The main reason that the battery is on fire in the collision process is that when the battery pack is invaded by a foreign object, the diaphragm inside the battery is broken, so that the anode and cathode materials are in short circuit, and temperature rise is generated to cause fire.

Therefore, it is important to evaluate the collision safety performance of the electric vehicle in the design stage, so as to avoid the risk of short circuit of the battery due to the intrusion of the structure during the collision of the real vehicle. And the means that can be adopted in the design stage is to develop the finite element simulation of the battery roll core. The structure of a common battery roll core 1 is shown in fig. 1, and is mainly formed by winding four layers of materials including 2 layers of separators 1-1, 1 layer of anodes 1-2 and 1 layer of cathodes 1-3, wherein the winding is schematically shown as a view in fig. 1. For the winding core, modeling is generally performed by using pentahedral or hexahedral solid units with two coincident nodes, and the material of the winding core is isotropic in material property. As shown in FIG. 2, FIG. 2A and FIG. 2B, the node 2-1-1 on the side surface of the pentahedron unit 2-1 and the node 2-2-1 on the side surface of the hexahedron unit 2-2 are the same node, the node 2-1-2 on the unit 2-1 and the node 2-2-2 on the unit 2-2 are the same node, the node 2-1-3 on the unit 2-1 and the node 2-2-3 on the unit 2-2 are the same node, and the node 2-1-4 on the unit 2-1 and the node 2-2-4 on the unit 2-2 are the same node, i.e., two nodes coincide.

The battery roll core simulation mode has the following defects: (1) The method is relatively accurate in simulation in the thickness direction, but the layering phenomenon in the core extrusion process cannot be simulated in the height direction (the z direction of the core shown in figure 1) and the length direction (the y direction of the core shown in figure 1); (2) The material attribute is isotropy, and one model cannot simulate the mechanical properties in three directions simultaneously. If the battery winding core is extruded in the thickness direction (the x direction of the winding core shown in fig. 1), before simulation analysis, the material attribute in the thickness direction needs to be input; when the pressing is applied in the longitudinal direction (the y direction of the winding core shown in fig. 1), the material properties in the longitudinal direction need to be input, which makes the use complicated.

Disclosure of Invention

The invention aims to provide a battery roll core simulation method based on finite element analysis, which is used for establishing an anisotropic battery roll core model, so that the simulation is more accurate and the calculation efficiency is higher.

The technical scheme of the invention is as follows:

a battery roll core simulation method based on finite element analysis comprises the following steps:

firstly, according to the contour dimension length a of the battery winding core, the thickness b, the height h and the actual winding number m, the simplified winding number n of the finite element model of the battery winding core is determined, and then the number of finite element units distributed in the thickness is 2n.

Further, according to the size of the battery winding core, 1: a battery roll core CAD model with the size of 1 proportion;

the built battery roll core CAD model is close to a real object and is formed by only winding a layer of cuboid with the thickness of b/2 n.

And secondly, importing the established battery roll core CAD model into finite element preprocessing software, setting the unit size as b/2n, and establishing a finite element model of the battery roll core by adopting a hexahedral unit.

The cell size b/2n here means the length, width and height of the cell. The preprocessing software will divide the elements according to the set size, because the part to be divided is not a regular cuboid (or the size of the part is not an integral multiple of the set size of the element), but has some characteristics, such as radian, non-right angle, etc., so the size of the element actually divided at last is not the absolute initially set size of the element, but is the optimal quality element obtained through optimization calculation inside the finite element preprocessing software, and the size may be larger or smaller than the set size of the element, and the shape is not an absolute cuboid.

Hexahedron units in the battery roll core finite element model are endowed with thick shell unit types, and the thickness direction of the hexahedron units is consistent with the thickness direction of the battery roll core.

In finite element modeling, the three very common element types are shell element, thick shell element and solid element. The specific form of the shell unit is a three-node triangular unit, a four-node quadrilateral unit and the like; the specific form of the thick-shell unit is an eight-node hexahedron-shaped unit; the concrete form of the solid unit is an eight-node hexahedron-shaped unit, a four-node tetrahedron-shaped unit and the like. Although the hexahedral unit may be a thick-shell unit type or a solid unit type, only the thick-shell unit type having the same shape as the solid unit type and the same simulation method as the shell unit may set a plurality of integration points in the thickness direction thereof as needed, and each integration point may be given a different thickness and a different material. Thus in the present invention, although not in terms of the actual structure of the cell jelly roll, a 1:1, but each layer of the positive electrode, the negative electrode, and the separator can be simulated by the set integration points in the thickness direction every 1 turn. The final simplified finite element model only differs from the real object in the layer number, but the attribute and the overall size of each corresponding material (positive electrode, negative electrode and diaphragm) can be in one-to-one correspondence with the real object.

The number of the integral points of the thick-shell unit in the thickness direction is 4m/n, and each integral point respectively represents a diaphragm, an anode, a diaphragm and a cathode from outside to inside according to the actual structure of the winding core, and the process is repeated for m/n times.

Thirdly, giving the material attribute to the finite element model of the built battery winding core;

the material properties of the positive electrode are converted from force-displacement data obtained by performing extrusion tests on a plurality of layers of positive electrodes in three directions in a superposition mode, and the material property obtaining modes of the negative electrode and the diaphragm are consistent with those of the positive electrode.

The material properties of the positive electrode, the negative electrode and the separator have a uniform local coordinate system.

The invention has the advantages that:

1. by adopting the method, the wound thick shell units of each layer can slide relatively, the layering phenomenon among layers can be simulated when the winding core is extruded, and the simulation is more accurate.

In the traditional simulation method, nodes between one unit and adjacent units (4 or 5 units) around the unit are superposed, while in the simulation method of the invention, one unit is superposed with only nodes between 2 units on the same layer, and is not superposed with nodes between units on adjacent layers, and the superposition of the nodes of the units between the layers can slide relatively. Or in a more vivid way, a strip-shaped paper tape with certain thickness is wound and flattened to form a battery winding core, the traditional simulation method is similar to brushing a layer of glue among the wound paper tapes, the layers are fixedly connected, and the simulation method is similar to brushing no glue and is more consistent with the reality.

2. By adopting the method, 1 layer of grid is used for representing multiple layers of the anode, the cathode and the diaphragm, and only the integral points are used for representing the number of layers of the actual anode, the actual cathode and the actual diaphragm, so that the number of finite element model units is reduced, and the calculation efficiency is saved.

3. By adopting the method, the material attribute has anisotropic characteristic and has a local coordinate system, when the roll core model is used, the roll core model can be moved and rotated randomly according to the requirement without manually adjusting the material attribute according to the stress direction, and the use is convenient.

Drawings

FIG. 1 is a schematic view of a winding structure of a prior art battery roll core;

FIG. 1A is a view from the direction A of FIG. 1;

FIG. 2 is a core finite element model for the winding structure shown in FIG. 1;

FIG. 2A is a block diagram of the pentahedron unit 2-1 of FIG. 2;

fig. 2B is a structural view of the hexahedral unit 2-2 in fig. 2;

fig. 3 is a schematic view of a winding structure of a battery winding core related to the method of the invention;

FIG. 4 is a diagram illustrating a method for establishing a battery roll core finite element model 4 by using hexahedral units;

FIG. 4A is a block diagram of the thick shell unit 4-1 of FIG. 4;

FIG. 4B is a block diagram of the thick shell unit 4-2 of FIG. 4;

FIG. 5 is a schematic view of nodes of a battery roll core distributed in sequence in the thickness direction;

FIG. 6 is a schematic view of a crush test to obtain crush test data.

Detailed Description

The following describes the implementation steps of the method of the present invention, taking a winding core formed by winding 25 turns of 1 layer of positive electrode, 1 layer of negative electrode and 2 layers of separators as an example, with reference to the accompanying drawings:

1. CAD model for establishing battery roll core

Firstly, the number of winding turns of the simplified battery winding core 3 is determined to be 5, and the length 3-1, the thickness 3-2 and the height 3-3 of the simplified battery winding core 3 are determined according to the actual size of the winding core.

Further in this embodiment, a CAD model corresponding to the simplified battery roll core 3 is built in three-dimensional drawing software according to the length 3-1, the thickness 3-2 and the height 3-3 of the simplified battery roll core 3, as shown in FIG. 3.

In this embodiment, the simplified battery jelly roll 3 is built to have a single layer thickness of 3-1-1. The single layer thickness is determined when the number of turns is reduced (e.g., 5 in this example), then the cell core model has 5 x 2=10 layers in the thickness direction, and the cell core thickness dimension 3-2 can be measured, and the single layer thickness can be obtained by dividing the cell core thickness dimension by 10.

2. Establishing a finite element model

And importing the established CAD model of the simplified battery roll core 3 into finite element pretreatment software, and establishing a battery roll core finite element model 4 by adopting a hexahedral unit, as shown in fig. 4, 4A and 4B.

In this embodiment, the finite element model 4 of the battery roll core is composed of thick-shell units (i.e. hexahedral units), such as the thick-shell unit 4-1 and the thick-shell unit 4-2 between adjacent layers, one on the 4 th layer and one on the 5 th layer, which have the same appearance and different sizes, i.e. the sizes of the two are not absolutely set but have different sizes. The reason is that the part to be divided is not a regular cuboid (or the size of the part is not an integral multiple of the set unit size), but has some characteristics, such as radian, non-right angle and the like, so that the size of the unit to be divided actually finally is not the absolute unit size set at the beginning, but is a unit with the optimal quality obtained through optimization calculation in the finite element preprocessing software, the size of the unit may be larger or smaller than the set unit size, and the shape of the unit is not an absolute cuboid. 4-1 and 4-2 are positioned in different layers, the radian between the two layers is different, and the final size is also different.

Taking a thick shell unit 4-1 as an example, each thick shell unit is a hexahedron and is provided with 4 nodes which are respectively 4-1-1, 4-1-2, 4-1-3, 4-1-4, 4-1-5, 4-1-6, 4-1-7 and 4-1-8 in one-to-one correspondence from top to bottom, the normal direction of the thick shell unit is formed by the nodes 4-1-1, 4-1-2, 4-1-3 and 4-1-4, and the surface formed by the nodes 4-1-5, 4-1-6, 4-1-7 and 4-1-8 points to the surface formed by the nodes 4-1-1, 4-1-6, 4-1-7 and 4-1-8, and the distance between the two surfaces is the thickness of the thick shell unit.

Each thick shell cell thickness is 5 (single layer positive thickness + single layer negative thickness +2 layers separator thickness).

The nodes 4-1-1, 4-1-2, 4-1-3 and 4-1-4 on the thick shell unit 4-1 on the 4 th ring on the battery winding core finite element model 4 are not overlapped with the nodes 4-2-1, 4-2-2, 4-2-3 and 4-2-4 on the thick shell unit 4-2 on the 5 th ring, so that the two units 4-1 and 4-2 can slide relatively, and the deformation condition of the winding core during extrusion can be simulated more accurately.

As shown in fig. 5, each thick-shell unit of the battery roll core finite element model 4 has 20 integration points in the thickness direction, taking the thick-shell unit 4-2 as an example, the thickness direction thereof is sequentially distributed with nodes 4-2-9-4-2-28, and each integration point represents a diaphragm, an anode, a diaphragm and a cathode respectively according to the actual structure of the roll core, and the repetition is repeated for 5 times;

3. imparting properties to materials

The material properties are assigned to the finite element model 4 of the battery roll core and are converted from force-displacement data obtained from the extrusion test data.

The extrusion test is schematically shown in fig. 6, the material properties of the positive electrode are superposed by a plurality of layers of positive electrodes 5-1 which are cut from a roll core and have the same size, the three-direction extrusion test of x, y and z is respectively carried out, and if the material properties of the x direction are to be obtained, a pair of Fx loads are applied to a sample along the x direction; applying a pair of Fy loads to the sample in the y-direction if material data is to be obtained in the y-direction; if material data is to be obtained in the z-direction, a pair of Fz loads is applied to the sample in the y-direction. The material properties of the negative electrode and the separator are obtained in the same manner as those of the positive electrode.

In this embodiment, the material properties of the positive electrode, the negative electrode, and the separator have a uniform local coordinate system 5-2.

Claims

1. A battery roll core simulation method based on finite element analysis is characterized by comprising the following steps:

(1) CAD model for establishing battery roll core

According to the contour dimension length a of the battery winding core, the thickness b, the height h and the actual winding number m, the simplified winding number n of the finite element model of the battery winding core is determined, and the number of finite element units distributed in the thickness is 2n;

according to the size of a battery winding core, establishing a volume ratio of 1: the battery roll core CAD model with the proportion of 1 is formed by winding a layer of cuboid with the thickness of b/2 n;

establishing finite element model of battery roll core

Importing a battery roll core CAD model into finite element preprocessing software, setting the unit size as b/2n, and establishing a finite element model of the battery roll core by adopting a hexahedral unit;

the hexahedral unit in the battery roll core finite element model is endowed with a thick shell unit type, and the thickness direction of the hexahedral unit is consistent with the thickness direction of the battery roll core;

the number of the integration points of the thick shell unit in the thickness direction is 4m/n, and according to the actual structure of the winding core, from outside to inside, each integration point represents a diaphragm, a positive electrode, a diaphragm and a negative electrode respectively and repeats for m/n times;

(3) Endowing built battery roll core finite element model material attribute

The material properties of the positive electrode are converted from force-displacement data obtained by performing extrusion test on a plurality of layers of positive electrodes in three directions in a stacking manner, and the material properties of the negative electrode and the diaphragm are obtained in the same manner as that of the positive electrode;

the compression test is as follows: the material attribute of the positive electrode is formed by superposing a plurality of layers of positive electrodes which are cut from a roll core and have the same size, respectively carrying out extrusion tests in three directions of x, y and z, and applying a pair of Fx loads to a sample along the x direction to obtain the material attribute in the x direction; applying a pair of Fy loads to the sample along the y direction to obtain material data in the y direction; applying a pair of Fz loads to the sample along the y-direction to obtain material data in the z-direction; the material properties of the negative electrode and the diaphragm are obtained in the same way as the positive electrode;

2. The finite element analysis-based battery roll core simulation method of claim 1, wherein the simplified winding turns n are minimum turn numbers determined to meet engineering accuracy requirements and computational efficiency after repeated simulation analysis and calculation.

3. The finite element analysis-based battery core simulation method of claim 2, wherein the simplified number of winding turns n is 5.