A battery cooling method based on phase change material

Abstract

The present invention provides a battery cooling method based on phase change materials, comprising: step S1, designating multiple equivalent thermal nodes on a lithium-ion battery structure coated with a phase change material layer at both ends of the battery cell, and modeling a three-dimensional thermal network model by combining air temperature nodes and cooling medium temperature nodes; step S2, establishing heat conduction paths between nodes within the three-dimensional thermal network model to simulate battery heat dissipation; step S3, collecting temperature material data during the battery heat dissipation simulation; step S4, obtaining multiple phase change material thickness optimization schemes as individuals to form a population cluster; step S5, extracting a preset number of individuals from the population cluster, and based on the temperature material data, continuously performing population iterative optimization on each individual using a pre-established weighted objective function to obtain the optimal individual, and then using the optimal individual to optimize the thickness of the phase change material layer. The present invention has the beneficial effect of improving temperature control accuracy and reducing material costs.

Description

Technical Field

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

[0002] Traditional, unoptimized thermal management systems struggle to precisely control the core temperature of lithium-ion batteries under complex operating conditions (such as rapid charging and discharging, high-temperature environments, and aging batteries), easily leading to the risk of thermal runaway. For example, during high-rate discharge, the internal heat generation rate of lithium-ion batteries can reach 3-5 times that of conventional conditions. The latent heat release rate of PCM (Phase Change Material) is limited by its thermal conductivity and thermal buffer delay. Therefore, if the thickness of the PCM is not optimized, effective temperature control cannot be achieved.

[0003] In addition, in the lithium-ion battery structure of the existing technology, the usage of phase change materials is not optimized, resulting in high thermal management costs of the thermal management system. Among them, the phase change material layer between the battery cells is usually 1-5mm thick, which is used to suppress the temperature difference between the battery cells and maintain stacking consistency; while the phase change material layer of the module shell covering the outside of the battery cell can usually be 5-10mm thick, which can delay the overall temperature rise of the module shell and improve thermal inertia.

[0004] However, the current production and manufacturing of lithium-ion battery structures lacks systematic parameter optimization below the phase change material layer. The thickness of the phase change material layer is designed and manufactured based on past design data or relying on manual experience, resulting in insufficient temperature control accuracy and excessively high material costs. Summary of the Invention

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

[0006] The present invention provides a battery cooling method based on phase change material, comprising the following steps:

[0007] Step S1, based on a lithium-ion battery structure with a phase change material layer covering both ends of the battery cell, a plurality of equivalent thermal nodes are proposed on the lithium-ion battery structure, and a three-dimensional thermal network model is obtained by combining air temperature nodes and cooling medium temperature nodes;

[0008] Step S2, establishing a heat conduction path between each of the equivalent heat nodes, the air temperature node, and the cooling medium temperature node in the three-dimensional thermal network model, and performing a battery heat dissipation simulation;

[0009] Step S3, collecting temperature material data of the three-dimensional thermal network model during the battery heat dissipation simulation process;

[0010] Step S4, obtaining a plurality of phase change material thickness optimization solutions, and including each phase change material thickness optimization solution as an individual into a population;

[0011] Step S5, using the Latin hypercube sampling method to extract a preset number of individuals in the population, based on the temperature material data, using a pre-constructed weighted objective function to continuously perform population iterative optimization on each individual to obtain the optimal individual, and then using the optimal individual to optimize the thickness of the phase change material layer.

[0012] Compared with the prior art, the battery cooling method based on phase change material of the present invention has the following advantages:

[0013] In the present invention, a three-dimensional thermal network model is constructed through step S1, a heat conduction path is established and a battery heat dissipation simulation is performed through step S2, temperature material data is collected through step S3, individual collection of phase change material thickness optimization schemes is performed through step S4, and population iterative optimization and phase change material layer thickness optimization are performed through step S5. Through the complete process of thermal network modeling-optimization scheme generation-intelligent population iteration, the blindness of relying on traditional empirical design is avoided, and the temperature control relationship and material usage relationship are balanced and controlled through the weighted objective function, thereby achieving multi-objective optimization of thermal performance and material cost, and reducing material cost while ensuring high temperature control accuracy.

[0014] In a possible implementation, in step S1 , an equivalent thermal node is defined at the geometric center of the battery cell and on the surfaces of the six sides.

[0015] Compared with the existing technology, the above technical solution can formulate equivalent thermal nodes for the entire area of ​​the battery cell, thereby improving the accuracy and completeness of temperature material data at various locations in the battery cell during battery heat dissipation simulation.

[0016] In one possible embodiment, the phase change material layer includes a front surface phase change material layer and a rear surface phase change material layer. In step S1, an equivalent thermal node is respectively proposed 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 proposed on the contact surface between the front surface phase change material layer and the battery cell, and an equivalent thermal node is proposed on the contact surface between the rear surface phase change material layer and the battery cell.

[0017] Compared with the existing technology, the above technical solution can independently formulate 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 differentiated thickness design of the front surface phase change material layer and the rear surface phase change material layer.

[0018] In a possible implementation, in step S2, each of the equivalent heat nodes, the air temperature nodes, and the cooling medium temperature nodes are unified into a network node, and for any two of the network nodes, it is determined whether there is a heat exchange relationship between the two network nodes:

[0019] If so, connecting the two network nodes to establish an edge;

[0020] If not, exit.

[0021] Compared with the existing technology, the above technical solution can dynamically establish the thermal network topology layout between network nodes and adapt to different lithium-ion battery structures.

[0022] In a possible embodiment, in step S2, for each of the edges, the starting point position of the heat and the receiving point position of the heat in the heat exchange relationship of the edge are extracted, the starting point position, the receiving point position and the edge are associated and numbered, and then each edge, each starting point position and each receiving point position are sorted in sequence according to the numbering to construct an association matrix to describe the heat conduction path.

[0023] Compared with the existing technology, the above technical solution can replace the traditional differential equation solution with matrix operation, improve the simulation speed, and more intuitively reflect the heat conduction path through the correlation matrix.

[0024] 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 an admittance matrix is ​​constructed in the form of a diagonal matrix based on the column vector to describe the heat conduction path.

[0025] Compared with the existing technology, the above technical solution can quantify the change relationship of the thermal conductivity of the phase change material layer during the phase change process in real time by constructing an admittance matrix, and more intuitively reflect the heat conduction path.

[0026] In a possible embodiment, each of the phase change material thickness optimization schemes in step S4 includes a first thickness of the phase change material layer located at one end of the battery cell and a second thickness of the phase change material layer located at the other end of the battery cell, and the value range of the first thickness and the second thickness are both [1,10] mm.

[0027] In one 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, an ambient temperature, and a node temperature at each of the equivalent thermal nodes. In step S5, the weighted objective function is expressed as follows:

[0028] ;

[0029] in,

[0030] represents the weighted objective function;

[0031] represents a preset first weight coefficient;

[0032] represents the maximum value among the node temperatures;

[0033] represents the ambient temperature;

[0034] represents a preset second weight coefficient;

[0035] represents the first thickness;

[0036] represents the second thickness;

[0037] represents the first reference thickness;

[0038] represents the second reference thickness;

[0039] represents a preset third weight coefficient;

[0040] Indicates that the standard deviation of the temperature of each node is calculated;

[0041] represents the temperature of each node.

[0042] Compared with the existing technology, the above technical solution can rely on the peak temperature weight coefficient of the simulated thermal runaway risk, i.e. the first weight coefficient, the cost weight coefficient for reducing material cost, i.e. the second weight coefficient, and the uniformity weight coefficient for extending battery life, i.e. the third weight coefficient, to screen and optimize the phase change material thickness optimization scheme to obtain the optimal individual, ensuring that the first thickness and the second thickness reach the optimal value. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1is a flow chart of the steps of the present invention;

[0044] Figure 2 It is a structural schematic diagram of the three-dimensional thermal network model of the present invention;

[0045] Figure 3 Schematic diagram of the overall temperature of the phase change material layer before and after optimization of the present invention. DETAILED DESCRIPTION

[0046] First, those skilled in the art should understand that these embodiments are merely for explaining the technical principles of the embodiments of the present invention and are not intended to limit the scope of protection of the embodiments of the present invention. Those skilled in the art may make adjustments as needed to adapt to specific application scenarios.

[0047] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0048] See also Figure 1 , an embodiment of the present invention discloses a battery cooling method based on phase change material, comprising the following steps:

[0049] Step S1, based on a lithium-ion battery structure with a phase change material layer covering both ends of the battery cell, multiple equivalent thermal nodes are proposed on the lithium-ion battery structure, and a three-dimensional thermal network model is obtained by combining air temperature nodes and cooling medium temperature nodes;

[0050] Step S2, establishing heat conduction paths between equivalent heat nodes, air temperature nodes, and cooling medium temperature nodes in a three-dimensional thermal network model to perform battery heat dissipation simulation;

[0051] Step S3, collecting temperature material data of the three-dimensional thermal network model during the battery heat dissipation simulation process;

[0052] Step S4, obtaining multiple phase change material thickness optimization solutions, and including each phase change material thickness optimization solution as an individual into a population;

[0053] In step S5, a Latin hypercube sampling method is used to extract a preset number of individuals from the population. Based on the temperature material data, a pre-constructed weighted objective function is used to continuously perform population iterative optimization on each individual to obtain the optimal individual. The optimal individual is then used to optimize the thickness of the phase change material layer.

[0054] See also Figure 2 , the phase change material layer includes a front surface phase change material layer and a rear surface phase change material layer, Figure 2From left to right in the figure 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.

[0055] In an embodiment of the present invention, for a seven-node battery thermal network, an equivalent thermal node is respectively proposed at the geometric center of the battery cell and on the surfaces of the six sides; for two two-node phase change material thermal networks, an equivalent thermal node is respectively proposed 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 proposed on the contact surface between the front surface phase change material layer and the battery cell, and an equivalent thermal node is proposed on the contact surface between the rear surface phase change material layer and the battery cell.

[0056] In an embodiment of the present invention, in step S2, each equivalent heat node, air temperature node, and cooling medium temperature node are unified into a network node. For any two network nodes, it is determined whether there is a heat exchange relationship between the two network nodes: if so, the two network nodes are connected and an edge is suggested; if not, the method exits; then, for each edge, the starting point position of the heat and the receiving point position of the heat in the heat exchange relationship of the edge are extracted, the starting point position, the receiving point position, and the edge are associated and numbered, and then each edge, each starting point position, and each receiving point position are sorted in sequence according to the numbering to construct an association matrix; and 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 an admittance matrix is ​​constructed based on the column vector in the form of a diagonal matrix to describe the heat conduction path.

[0057] In an embodiment of the present invention, if a heat exchange relationship exists between two network nodes, an edge is established between the two network nodes. In the association matrix, for the edge numbered i, the starting point of the heat is recorded as nout, and the receiving point of the heat is recorded as nin, then the association matrix A(nout, i)=-1, A(nin, i)=1; the mutual admittances of all edges are written in order as a column vector Ye_value, and the diagonal matrix is ​​constructed using it to obtain the admittance matrix Ye: Ye=diag(Ye_value).

[0058] In an 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 located 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 located 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 thermal buffering capacity of the phase change material on the front side of the battery cell. The physical meaning is to directly determine 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 weight of the system. 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. The physical meaning is to affect 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.

[0059] In the embodiment of the present invention, in step S4, the population is initialized, each individual represents a set of phase change material thickness optimization solutions, and the individual includes a first thickness and a second thickness.

[0060] In the embodiment of the present invention, in step S5, Latin hypercube sampling is used to generate 20 individuals in the population to ensure uniform coverage of the parameter space, and then a weighted objective function is used to continuously perform population iterative optimization on each individual until a preset number of iterations is reached or the rate of change is <0.01%.

[0061] In the embodiment of the present invention, 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 temperature at each equivalent thermal node. In step S5, the expression of the weighted objective function is as follows:

[0062] ;

[0063] in,

[0064] represents the weighted objective function;

[0065] represents a preset first weight coefficient;

[0066] Indicates the maximum value of each node temperature;

[0067] Indicates the ambient temperature;

[0068] represents a preset second weight coefficient;

[0069] represents the first thickness;

[0070] Indicates the second thickness;

[0071] represents the first reference thickness;

[0072] represents the second reference thickness;

[0073] represents a preset third weight coefficient;

[0074] Indicates the calculation of the standard deviation of each node temperature;

[0075] Indicates the temperature of each node.

[0076] 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 by liquid fraction interpolation, and the calculation formula is as follows:

[0077] ;

[0078] in, represents the thermophysical parameters, Indicates the real-time temperature. represents the phase transition starting temperature, represents the phase change interval;

[0079] Then, the equivalent thermal conductivity is calculated by interpolating the thermophysical parameters obtained by the liquid fraction, and the calculation formula is as follows:

[0080] ;

[0081] in, represents the equivalent thermal conductivity, represents the phase change solid phase thermal conductivity, represents the equivalent coefficient, It represents the thermal conductivity of phase change material liquid. The equivalent thermal conductivity can better represent the heat conduction path.

[0082] In the embodiment of the present invention, the method of the present invention is applied to a 120Ah On the battery, the discharge rate is set to 5C, the material of the phase change material layer is paraffin, and the simulation platform is MATLAB R2023a. Through simulation, it is found that the first thickness of the front surface phase change material layer before optimization is 5mm, the second thickness of the rear surface phase change material layer before optimization is 5mm, the first thickness of the front surface phase change material layer after optimization is 3.3mm, and the second thickness of the rear surface phase change material layer after optimization is 3.3mm. Figure 3 As shown in the figure, 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.

[0083] In the description of the present invention, the reference terms "one embodiment", "some embodiments", "in the present embodiment", "specific examples", or "some examples" mean that the specific features, mechanisms, materials or characteristics described in conjunction 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 any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0084] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A battery cooling method based on phase change material, characterized in that: The following steps are involved: Step S1, based on a lithium-ion battery structure with a phase change material layer covering both ends of the battery cell, a plurality of equivalent thermal nodes are proposed on the lithium-ion battery structure, and a three-dimensional thermal network model is obtained by combining air temperature nodes and cooling medium temperature nodes; Step S2, establishing a heat conduction path between each of the equivalent heat nodes, the air temperature node, and the cooling medium temperature node in the three-dimensional thermal network model, and performing a battery heat dissipation simulation; Step S3, collecting temperature material data of the three-dimensional thermal network model during the battery heat dissipation simulation process; Step S4, obtaining a plurality of phase change material thickness optimization solutions, and including each phase change material thickness optimization solution as an individual into a population; Step S5, using a Latin hypercube sampling method to extract a preset number of individuals from the population, and based on the temperature material data, using a pre-established weighted objective function to continuously perform population iterative optimization on each of the individuals to obtain an optimal individual, and then using the optimal individual to optimize the thickness of the phase change material layer; 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, and the value range of the first thickness and the second thickness are both [1, 10] mm; 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, an ambient temperature, and a node temperature at each equivalent thermal node. In step S5, the weighted objective function is expressed as follows: ； in, 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; Indicates that the standard deviation of the temperature of each node is calculated; Represents the temperature of each node.

2. A battery cooling method based on phase change material according to claim 1, characterized in that: In the step S1 , an equivalent thermal node is defined at the geometric center of the battery cell and on the surfaces of the six sides.

3. The battery cooling method based on phase change material according to claim 1, characterized in that: The phase change material layer includes a front surface phase change material layer and a rear surface phase change material layer. In step S1, an equivalent thermal node is respectively proposed 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 proposed on the contact surface between the front surface phase change material layer and the battery cell, and an equivalent thermal node is proposed on the contact surface between the rear surface phase change material layer and the battery cell.

4. The battery cooling method based on phase change material according to claim 1, characterized in that: In step S2, each of the equivalent heat nodes, the air temperature nodes, and the cooling medium temperature nodes are unified into a network node, and for any two of the network nodes, it is determined whether there is a heat exchange relationship between the two network nodes: If so, connecting 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, the starting point position and the receiving point position of the heat in the heat exchange relationship of the edge are extracted, the starting point position, the receiving point position and the edge are associated and numbered, and then the edges, the starting point positions and the receiving point positions are sorted in sequence according to the numbers to construct an association matrix to describe the heat conduction path.

6. The battery cooling method based on phase change material according to claim 4, characterized in that: 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 an admittance matrix is ​​constructed in the form of a diagonal matrix based on the column vector to describe the heat conduction path.

Images