Battery cooling method based on phase change material

Abstract

The invention provides a battery cooling method based on a phase change material, which comprises the following steps of: S1, drawing up a plurality of equivalent thermal nodes on a lithium ion battery structure of which two ends of a battery cell are covered with phase change material layers, and modeling by combining an air temperature node and a cooling medium temperature node to obtain a three-dimensional thermal network model; s2, establishing a heat conduction path between nodes in the three-dimensional thermal network model to carry out battery heat dissipation analogue simulation; s3, collecting temperature material data in the battery heat dissipation analogue simulation process; s4, obtaining a plurality of phase change material thickness optimization schemes as individuals to form a population; and S5, extracting a preset number of individuals from the population set, continuously performing population iteration optimization on each individual by adopting a pre-constructed weighted objective function based on the temperature material data to obtain an optimal individual, and then optimizing the thickness of the phase change material layer by utilizing the optimal individual. The method has the beneficial effects that the temperature control precision can be improved, and the material cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of battery cooling methods, and more particularly, to a battery cooling method based on phase change materials. Background Art

[0002] Traditional unoptimized thermal management systems are difficult to precisely control the core temperature of lithium-ion batteries under complex working conditions (such as rapid charging and discharging, high-temperature environments, aging batteries, etc.), which easily leads to the risk of thermal runaway. For example, during high-rate discharging, the internal heat generation rate of lithium-ion batteries can reach 3-5 times that of conventional working conditions. However, the latent heat release rate of PCM (Phase Change Material) is limited by the thermal conductivity and thermal buffering delay. If the thickness of the phase change material is not optimized, good temperature control effects cannot be achieved.

[0003] Moreover, in the lithium-ion battery structures of the prior art, the amount of phase change material used lacks optimization, resulting in high thermal management costs for the thermal management system. Among them, the thickness of the phase change material layer between the battery cells is usually 1-5 mm, which is used to suppress the temperature difference between the battery cells and maintain stacking consistency; while the thickness of the phase change material layer of the module housing covering the outside of the battery cells can usually reach 5-10 mm, which can delay the overall temperature rise of the module housing and improve the thermal inertia.

[0004] However, currently, during the production and manufacturing of lithium-ion battery structures, there is a lack of systematic parameter optimization for the phase change material layer. Design and manufacturing of the thickness of the phase change material layer are carried out according to past design data or relying on manual experience, resulting in problems such as insufficient temperature control accuracy and high material costs. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to improve the temperature control accuracy and reduce the material cost. To overcome the above defects of the prior art (or related technologies), the present invention provides a battery cooling method based on phase change materials.

[0006] The present invention provides a battery cooling method based on phase change materials, including the following steps: Step S1, based on a lithium-ion battery structure with phase change material layers covering both ends of the battery cells, a plurality of equivalent thermal nodes are determined on the lithium-ion battery structure, and combined with the air temperature node and the cooling medium temperature node, a three-dimensional thermal network model is established through modeling; Step S2, a heat conduction path is established among the equivalent thermal nodes, the air temperature node, and the cooling medium temperature node in the three-dimensional thermal network model, and battery heat dissipation simulation is carried out; Step S3, temperature material data of the three-dimensional thermal network model during the battery heat dissipation simulation is collected; Step S4: Obtain multiple optimized phase change material thickness schemes, and include each of the optimized phase change material thickness schemes as an individual in a population set; Step S5: Use the Latin hypercube sampling method to extract a preset number of the individuals from the population set. Based on the temperature material data, continuously perform population iteration optimization on each of the individuals using a pre-constructed weighted objective function to obtain an optimal individual, and then use the optimal individual to optimize the thickness of the phase change material layer.

[0007] Compared with the prior art, a battery cooling method based on a phase change material according to the present invention has the following advantages: In the present invention, a three-dimensional thermal network model is constructed through step S1, a heat conduction path is built and battery heat dissipation simulation is performed through step S2, temperature material data is collected through step S3, individuals of optimized phase change material thickness schemes are collected through step S4, population iteration optimization and phase change material layer thickness optimization are performed through step S5. Through the complete process of thermal network modeling - optimized scheme generation - intelligent population iteration, the blindness of relying on traditional experience design is avoided. The temperature control relationship and material usage relationship are balanced and controlled through a weighted objective function, realizing multi-objective optimization of thermal performance and material cost, and reducing material cost while ensuring a high temperature control accuracy.

[0008] In a possible implementation manner, in step S1, an equivalent thermal node is respectively defined at the geometric center of the battery cell and on the surfaces of six faces.

[0009] Compared with the prior art, adopting the above technical solution can define equivalent thermal nodes for the entire area of the battery cell, improving the accuracy and integrity of the temperature material data at each part of the battery cell during battery heat dissipation simulation.

[0010] In a possible implementation manner, the phase change material layer includes a front surface phase change material layer and a rear surface phase change material layer. Then, in step S1, an equivalent thermal node is respectively defined at the geometric centers of the front surface phase change material layer and the rear surface phase change material layer, an equivalent thermal node is defined on the contact surface between the front surface phase change material layer and the battery cell, and an equivalent thermal node is defined on the contact surface between the rear surface phase change material layer and the battery cell.

[0011] Compared with the prior art, adopting the above technical solution can separately define equivalent thermal nodes for the front surface phase change material layer and the rear surface phase change material layer, providing a data basis for the thickness differential design of the front surface phase change material layer and the rear surface phase change material layer.

[0012] In a possible implementation, in step S2, each of the equivalent thermal nodes, the air temperature node, and the cooling medium temperature node is unified into network nodes. For any two of the network nodes, it is determined whether there is a heat exchange relationship between the two network nodes: If so, connect the two network nodes to establish an edge; If not, exit.

[0013] Compared with the prior art, adopting the above technical solution can dynamically establish the thermal network topology layout between network nodes and adapt to different lithium-ion battery structures.

[0014] In a possible implementation, in step S2, for each edge, the starting position of the heat and the receiving position of the heat in the heat exchange relationship of the edge are extracted. The starting position, the receiving position, and the edge are associated and numbered, and then each edge, each starting position, and each receiving position are sorted in sequence according to the number to construct an association matrix to describe the heat conduction path.

[0015] Compared with the prior art, adopting the above technical solution can replace the solution of traditional differential equations through matrix operations, improve the simulation speed, and more intuitively reflect the heat conduction path through the association matrix.

[0016] In a possible implementation, in step S2, for each edge, the mutual admittance between the two network nodes on the edge is extracted, and then each mutual admittance is formed into a column vector and a conductance matrix is constructed in the form of a diagonal matrix based on the column vector to describe the heat conduction path.

[0017] Compared with the prior art, adopting the above technical solution can quantitatively describe the change relationship of the thermal conductivity of the phase change material layer during the phase change process in real time by constructing a conductance matrix, and more intuitively reflect the heat conduction path.

[0018] In a possible implementation, each of the phase change material thickness optimization schemes in step S4 includes a first thickness of the phase change material layer at one end of the battery cell and a second thickness of the phase change material layer at the other end of the battery cell. The value ranges of the first thickness and the second thickness are both [1, 10] mm.

[0019] In a possible implementation, the temperature material data includes a first reference thickness of the phase change material layer at one end of the battery cell, a second reference thickness of the phase change material layer at the other end of the battery cell, the ambient temperature, and the node temperatures at each of the equivalent thermal nodes. In step S5, the expression of the weighted objective function is as follows: ; Among them, represents the weighted objective function; represents a preset first weight coefficient; represents the maximum value among the node temperatures; represents the ambient temperature; represents a preset second weight coefficient; represents the first thickness; represents the second thickness; represents the first reference thickness; represents the second reference thickness; represents a preset third weight coefficient; represents calculating the standard deviation of each of the node temperatures; represents each of the node temperatures.

[0020] Compared with the prior art, adopting the above technical solution can rely on the peak temperature weight coefficient for simulating the thermal runaway risk, i.e., the first weight coefficient, the cost weight coefficient for reducing material costs, i.e., the second weight coefficient, and the uniformity weight coefficient for extending the battery life, i.e., the third weight coefficient, to screen and optimize the phase change material thickness optimization scheme to obtain the optimal individual, and ensure that the first thickness and the second thickness reach the optimal values. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the flowchart of the steps of the present invention; Figure 2 is the structural schematic diagram of the three-dimensional thermal network model of the present invention; Figure 3 is the overall temperature schematic diagram of the phase change material layer before and after optimization of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] First of all, those skilled in the art should understand that these embodiments are only used to explain the technical principles of the embodiments of the present invention and are not intended to limit the protection scope of the embodiments of the present invention. Those skilled in the art can adjust them according to needs to adapt to specific application scenarios.

[0023] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0024] SeeFigure 1 , an embodiment of the present invention discloses a battery cooling method based on phase change materials, including the following steps: Step S1, based on the lithium-ion battery structure with phase change material layers covering both ends of the battery cells, a plurality of equivalent thermal nodes are defined on the lithium-ion battery structure. Combining the air temperature node and the cooling medium temperature node, a three-dimensional thermal network model is established through modeling; Step S2, establish the heat conduction paths between each equivalent thermal node, the air temperature node and the cooling medium temperature node in the three-dimensional thermal network model, and conduct battery heat dissipation simulation; Step S3, collect the temperature material data of the three-dimensional thermal network model during the battery heat dissipation simulation process; Step S4, obtain multiple phase change material thickness optimization schemes, and include each phase change material thickness optimization scheme as an individual in the population set; Step S5, use the Latin hypercube sampling method to extract a preset number of individuals from the population set. Based on the temperature material data, use the pre-constructed weighted objective function to continuously perform population iteration optimization on each individual to obtain the optimal individual, and then use the optimal individual to optimize the thickness of the phase change material layer.

[0025] See Figure 2 , the phase change material layer includes a front surface phase change material layer and a rear surface phase change material layer. Figure 2 From left to right in are the front surface phase change material layer, the battery cell, and the rear surface phase change material layer. In step S1, a three-dimensional thermal network model including the dynamic thermal characteristics of the phase change material layer is established. The three-dimensional thermal network model includes a seven-node battery thermal network, two two-node phase change material thermal networks, an air temperature node, and a cooling medium temperature node. The two two-node phase change material thermal networks correspond to the front surface phase change material layer and the rear surface phase change material layer respectively.

[0026] In the embodiment of the present invention, for the seven-node battery thermal network, an equivalent thermal node is defined respectively at the geometric center of the battery cell and on the surfaces of six faces; for the two two-node phase change material thermal networks, an equivalent thermal node is defined respectively at the geometric center of the front surface phase change material layer and the rear surface phase change material layer, an equivalent thermal node is defined on the contact surface between the front surface phase change material layer and the battery cell, and an equivalent thermal node is defined on the contact surface between the rear surface phase change material layer and the battery cell.

[0027] In the embodiment of the present invention, within step S2, all equivalent thermal nodes, air temperature nodes, and cooling medium temperature nodes are unified into network nodes. For any two network nodes, it is determined whether there is a heat exchange relationship between the two network nodes: if so, a connection is established between the two network nodes and an edge is proposed; if not, the process exits. Subsequently, for each edge, the starting position of the heat in the heat exchange relationship of the edge and the receiving position of the heat are extracted, and the starting position, the receiving position, and the edge are associated and numbered. Then, all edges, all starting positions, and all receiving positions are sorted in sequence according to the numbers to construct an incidence matrix; and for each edge, the mutual admittance between the two network nodes on the edge is extracted. Subsequently, all the mutual admittances are formed into a column vector and a conductance matrix is constructed in the form of a diagonal matrix based on the column vector. The heat conduction path is described by the incidence matrix and the conductance matrix.

[0028] In the embodiment of the present invention, if there is a heat exchange relationship between two network nodes, an edge is established between the two network nodes. In the incidence matrix, for the edge numbered i, the starting position of the heat is denoted as nout, and the receiving position of the heat is denoted as nin. Then, it is recorded that the incidence matrix A(nout, i)=-1 and A(nin, i)=1; all the mutual admittances of the edges are written in sequence as a column vector Ye_value, and a diagonal matrix is constructed using it to obtain the conductance matrix Ye: Ye = diag(Ye_value).

[0029] In the embodiment of the present invention, each phase change material thickness optimization scheme in step S4 includes a first thickness of the phase change material layer at one end of the battery cell, i.e., the front surface phase change material layer, and a second thickness of the phase change material layer at the other end of the battery cell, i.e., the rear surface phase change material layer. The first thickness is defined as the geometric thickness of the front surface phase change material layer of the battery cell in the normal direction, which characterizes the heat buffering ability of the phase change material on the front side of the battery cell. Its physical meaning is that it directly determines the thermal resistance characteristics of the front surface of the battery cell facing the environment. Increasing the thickness can improve the thermal inertia but increase the system weight. The second thickness is defined as the geometric thickness of the rear surface phase change material layer of the battery cell in the normal direction, which characterizes the thermal management ability of the phase change material on the rear side of the battery cell. Its physical meaning is that it affects the thermal coupling effect between the rear surface phase change material layer and the adjacent battery module, and needs to be optimized in coordination with the first thickness to avoid asymmetric heat distribution.

[0030] In the embodiment of the present invention, within step S4, the population set is initialized. Each individual represents a set of phase change material thickness optimization schemes, and the individual includes a first thickness and a second thickness.

[0031] In the embodiment of the present invention, within step S5, 20 individuals are generated within the population set by Latin hypercube sampling to ensure uniform coverage of the parameter space. Then, a weighted objective function is used to continuously perform population iteration optimization on each individual until the preset number of iterations or the change rate <0.01% is reached.

[0032] In the embodiment of the present invention, the temperature material data includes the first reference thickness of the phase change material layer at one end of the battery cell, the second reference thickness of the phase change material layer at the other end of the battery cell, the ambient temperature, and the node temperatures at each equivalent thermal node. In step S5, the expression of the weighted objective function is as follows: ; Wherein, represents the weighted objective function; represents a preset first weight coefficient; represents the maximum value among the node temperatures; represents the ambient temperature; represents a preset second weight coefficient; represents the first thickness; represents the second thickness; represents the first reference thickness; represents the second reference thickness; represents a preset third weight coefficient; represents calculating the standard deviation of each node temperature; represents each node temperature.

[0033] In the embodiment of the present invention, the thermophysical parameters of the phase change material layer at different real-time temperatures are calculated in real time through liquid fraction interpolation, and its calculation formula is as follows: ; Wherein, represents the thermophysical parameter, represents the real-time temperature, represents the phase change starting temperature, represents the phase change interval; Then, the equivalent thermal conductivity is calculated through the thermophysical parameters calculated by liquid fraction interpolation, and its calculation formula is as follows: ; Wherein, represents the equivalent thermal conductivity, represents the solid-phase thermal conductivity of the phase change, represents the equivalent coefficient, represents the liquid thermal conductivity of the phase change material. The heat conduction path can be better represented through the equivalent thermal conductivity.

[0034] In the embodiments of the present invention, the method of the present invention is applied to a 120 Ah battery. The discharge rate is set to 5C. The material of the phase change material layer is paraffin. The simulation platform is MATLAB R2023a. Through simulation, the first thickness of the front surface phase change material layer before optimization is 5 mm, and the second thickness of the rear surface phase change material layer before optimization is 5 mm. The first thickness of the front surface phase change material layer after optimization is 3.3 mm, and the second thickness of the rear surface phase change material layer after optimization is 3.3 mm. As Figure 3 shown, when the overall temperature is almost the same, the thickness of the phase change material layer becomes 66% of the original, which can greatly reduce the material cost.

[0035] In the description of the present invention, the descriptions referring to terms such as "one embodiment", "some embodiments", "in this embodiment", "specific examples", or "some examples", etc. mean that the specific features, mechanisms, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, mechanisms, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0036] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A battery cooling method based on phase change materials, characterized in that, It includes the following steps: Step S1: Based on the lithium-ion battery structure with phase change material layers covering both ends of the battery cell, a plurality of equivalent thermal nodes are determined on the lithium-ion battery structure. Combining the air temperature node and the cooling medium temperature node, a three-dimensional thermal network model is established through modeling; Step S2: In the three-dimensional thermal network model, heat conduction paths are established among the equivalent thermal nodes, the air temperature node, and the cooling medium temperature node, and battery heat dissipation simulation is carried out; Step S3: Temperature material data of the three-dimensional thermal network model during the battery heat dissipation simulation is collected; Step S4: Obtain multiple phase change material thickness optimization schemes, and include each phase change material thickness optimization scheme as an individual in the population set; Step S5: Use the Latin hypercube sampling method to extract a preset number of individuals from the population set. Based on the temperature material data, use the pre-constructed weighted objective function to continuously perform population iteration optimization on each individual to obtain the optimal individual, and then use the optimal individual to optimize the thickness of the phase change material layer.

2. The battery cooling method based on phase change material according to claim 1, wherein In step S1, one equivalent thermal node is determined respectively at the geometric center of the battery cell and on the surfaces of its six faces.

3. The battery cooling method based on phase change material according to claim 1, characterized in that If the phase change material layer includes a front surface phase change material layer and a rear surface phase change material layer, then in step S1, one equivalent thermal node is determined respectively at the geometric centers of the front surface phase change material layer and the rear surface phase change material layer, one equivalent thermal node is determined on the contact surface between the front surface phase change material layer and the battery cell, and one equivalent thermal node is determined on the contact surface between the rear surface phase change material layer and the battery cell.

4. A battery cooling method based on phase change materials according to claim 1, characterized in that In step S2, the equivalent thermal nodes, the air temperature node, and the cooling medium temperature node are unified into network nodes. For any two network nodes, it is judged whether there is a heat exchange relationship between the two network nodes: If so, connect the two network nodes to establish an edge; If not, exit.

5. The battery cooling method based on phase change material according to claim 4, characterized in that, In step S2, for each edge, extract the heat departure position and the heat receiving position in the heat exchange relationship of the edge, associate and number the departure position, the receiving position, and the edge, and then sort the edges, the departure positions, and the receiving positions in sequence according to the number to construct an incidence matrix to describe the heat conduction path.

6. The battery cooling method based on phase change material according to claim 4, wherein In step S2, for each edge, extract the mutual admittance between the two network nodes on the edge, and then form a column vector with each mutual admittance and construct a conductance matrix in the form of a diagonal matrix based on the column vector to describe the heat conduction path.

7. A battery cooling method based on phase change materials according to claim 1, characterized in that, Each phase change material thickness optimization scheme in step S4 includes a first thickness of the phase change material layer at one end of the battery cell and a second thickness of the phase change material layer at the other end of the battery cell, and the value ranges of the first thickness and the second thickness are both [1, 10] mm.

8. A battery cooling method based on phase change materials according to claim 7, characterized in that, The temperature material data includes a first reference thickness of the phase change material layer at one end of the battery cell, a second reference thickness of the phase change material layer at the other end of the battery cell, the ambient temperature, and the node temperatures at each of the equivalent thermal nodes. In step S5, the expression of the weighted objective function is as follows: ； wherein, denote the weighted objective function; represent a preset first weight coefficient; represents the maximum value among the temperatures of each of the said nodes; Indicates the ambient temperature; denote a preset second weight coefficient; represent the first thickness; representing the second thickness; represent the first reference thickness; representing the second reference thickness; Indicates a preset third weight coefficient; Indicates to calculate the standard deviation of each of the node temperatures; Indicates the temperature of each of the said nodes.

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