Thermal simulation method of thermal battery

Abstract

The invention discloses a thermal simulation method of a thermal battery, belongs to the technical field of thermal batteries, and aims to solve the problems existing in thermal battery simulation research. The method comprises the following steps: S1, establishing a thermal battery three-dimensional simulation model; s2, loading the thermal battery three-dimensional simulation model into COMSOL software; s3, designing a control equation of the thermal battery heat transfer physical model; s4, enabling the boundary of the thermal battery to reach a thermal balance design; s5, performing network division on the thermal battery three-dimensional model and setting boundary conditions; and S6, performing simulation calculation to obtain a temperature distribution cloud picture of the thermal battery activation process and a stress distribution cloud picture of the thermal battery.

Description

Technical Field

[0001] The invention relates to a thermal battery thermal simulation method based on COMSOL software, and belongs to the technical field of thermal batteries. Background Art

[0002] Thermal battery is a heat-activated primary reserve power source that uses the battery's own heating system to heat and melt non-conductive solid salt electrolytes into ionic conductors to enter the working state. Thermal batteries are ideal power sources for modern weapons and occupy a very important position in military power sources because of their high-power discharge, high specific energy, high specific power, wide operating temperature range, long storage time, rapid and reliable activation, and compact structure.

[0003] The basic structure of a thermal battery can be found in Figure 1 As shown, the battery cover 1, the upper insulation and heat preservation component 2, the side insulation and heat preservation layer 3, the battery stack 4, the battery shell 5, the lower insulation and heat preservation component 6, the battery bottom 7, the battery stack 4 is composed of a plurality of single cells 8 connected in series or in parallel, the single cell 8 is composed of a current collector 8-1, a diaphragm 8-2, a graphite paper 8-3, a heating plate 8-3, an anode 8-4 and a cathode 8-5, and the battery stack is formed by stacking and assembling, and the battery stack is the core of the thermal battery. The cathode of the thermal battery usually uses active metals such as lithium, magnesium, calcium, etc.; the anode uses some high-performance oxides or salts, such as vanadium pentoxide, iron disulfide, lead sulfate, calcium chromate, etc.; the electrolyte is a mixture of molten salt and fine clay, generally LiCl-KCl is used as the electrolyte. At room temperature, the electrolyte inside the thermal battery is a non-conductive solid, the electrode active material and the electrolyte do not react chemically with each other, and are in a non-working state, and the battery self-discharge is very small. When in use, electric current is used to ignite the electric ignition head, which ignites the pyrotechnic heat source inside the battery, causing the internal temperature of the battery to rise rapidly to about 500°C, melting the electrolyte and forming a high-conductivity ion conductor, thereby activating the battery and supplying the required DC voltage and current to the electrical components in a short time.

[0004] After the thermal battery is activated, the voltage rises rapidly from 0V to the peak voltage. As the heat from the internal pyrotechnic heating source dissipates and the active electrode material is exhausted, the voltage eventually drops to 0V after a period of time. Figure 2 .

[0005] The internal temperature of the thermal battery must be maintained within a certain range for the thermal battery to work properly. The time it maintains within a certain temperature range is called thermal life. The use of lightweight, porous, and efficient insulation materials can increase the thermal life of the thermal battery. t1 is the activation time, t2 is the time when the temperature reaches the highest point, t3 is the working time, and U1, U2, and U3 are the lower limit voltage, maximum voltage, and upper limit voltage for normal operation.

[0006] Since thermal design plays a vital role in the working life and performance of thermal batteries, thermal simulation of thermal batteries (including heat transfer process and heat distribution) has great scientific and practical value.

[0007] Research status of thermal batteries:

[0008] In 2008, Zhao Jinfeng and others used ANSYS software to simulate the transient heat distribution of the LiSi / FeS2 thermal battery during the discharge process. Based on the node temperature balance theory, they compared the temperature distribution of the upper, middle and lower parts of the battery stack with that of the actual discharge process of the thermal battery, and proved the practicality and feasibility of using ANSYS to simulate the LiSi / FeS2 thermal battery.

[0009] In 2012, Lan Wei and others briefly introduced the process of using ANSYS to perform thermal simulation on thermal batteries, and conducted a preliminary analysis on specific thermal batteries, proving that thermal simulation has guiding significance for battery thermal design.

[0010] In 2018, Wang Chao et al. simulated the activation process of electrically activated thermal batteries using ANSYS software, gave a simulation calculation method for the activation time of such thermal batteries, and gave the internal temperature distribution characteristics of the thermal battery activation process. They compared the electrolyte melting process of two different types of thermal batteries and explained that the temperature distribution change trend of the two thermal batteries during the electrolyte melting process is consistent, such as Figure 3 and Figure 4 The cloud graphs show the temperature distribution of two types of thermal batteries, battery No. 1 and battery No. 2, changing with time. After calculation, the simulation results of the activation time of the two thermal batteries are basically consistent with the measured values.

[0011] In 2020, Ran Ling and others used the ANSYS platform to decompose the entire working process of the thermal battery into appropriate working conditions and added each heat source according to the working stage, realizing a high-precision heat transfer simulation analysis of the entire process of thermal battery activation and discharge. By comparing the simulated and experimental values ​​of the temperature at two test points (1# and 2#) on the battery shell, the accuracy of the model was verified. The comparison curves are as follows: Figure 5 shown.

[0012] In the same year, Ye Danhong et al. used COMSOL to establish a two-dimensional axisymmetric thermal battery unit battery simulation model, simulated the activation time and surface temperature change process of the thermal battery at +60℃ and -30℃, and gave a comparison chart of the measured and simulated values ​​of the battery shell temperature before and after the model correction, such as Figure 6 and Figure 7 As shown in the figure, the high temperature corresponds to +60°C and the low temperature corresponds to -30°C. Compared with the three-dimensional model, the amount of calculation is greatly reduced while ensuring the simulation accuracy.

[0013] In summary, the research results on the simulation of thermal batteries are still not rich enough. However, based on the rapid development of numerical simulation technology and relying on mature numerical simulation platforms, a model for the simulation of the entire process of thermal batteries has been initially established, providing a basis for more comprehensive research. However, there are great deficiencies in the research on the comprehensive working mechanism of thermal batteries and the changing characteristics of the internal physical properties of thermal batteries during the working process of thermal batteries. Summary of the invention

[0014] In view of the problems existing in the existing thermal battery simulation research, the present invention provides a thermal simulation method for a thermal battery.

[0015] The thermal simulation method of the thermal battery of the present invention comprises the following steps:

[0016] S1. Establish a three-dimensional simulation model of a thermal battery;

[0017] S2, loading the thermal battery three-dimensional simulation model into COMSOL software;

[0018] S3. The heat transfer physical model of the thermal battery is designed according to the following control equations:

[0019]

[0020] Where ρ is the density of each material of the thermal battery, C p is the specific heat capacity of each material, T is the temperature inside the thermal battery, t is the time since the thermal battery was ignited, is the gradient operator, k is the thermal conductivity of each material, χ is the electrolyte mass fraction, Δ is the difference operator, H L is the latent heat of electrolyte phase change, w is the mass fraction of solidified electrolyte, i A is the surface current density inside the thermal battery, R is the internal resistance of the thermal battery, Q rh It is the heat of chemical reaction during the operation of thermal battery;

[0021] S4. The thermal battery boundary is designed to achieve thermal balance;

[0022] S5. Perform network division on the three-dimensional model of the thermal battery and set boundary conditions;

[0023] S6. Perform simulation calculations to obtain a temperature distribution cloud map of the thermal battery activation process and a stress distribution cloud map of the thermal battery.

[0024] Preferably, the chemical reaction heat Q during the operation of the thermal battery rh Calculate as follows:

[0025]

[0026] Where U is the potential when the electrochemical reaction reaches equilibrium.

[0027] i v is the current volume density in the thermal battery, i v Press the formula to obtain:

[0028]

[0029] Where d is the axial thickness of each component inside the thermal battery.

[0030] Preferably, the thermal battery boundary reaches thermal balance design process in step S4 as follows:

[0031] S41. Natural convection heat transfer is carried out between the thermal battery and the environment, and the heat transfer amount is calculated as follows:

[0032] Q h =h w (T w -T s )A s

[0033] In the formula, Q h is the heat exchange between the thermal battery and the environment, h w is the convective heat transfer coefficient between the thermal battery and the environment, T w is the ambient temperature, T s is the surface temperature of the thermal battery, A s is the effective area of ​​convective heat transfer between the thermal battery and the environment;

[0034] S42, the radial direction of the battery assembly is taken as the x direction, and the longitudinal direction of the battery assembly is taken as the y direction, and the effective thermal conductivity k in the x direction is calculated respectively. eff(x) and the effective thermal conductivity k in the y direction eff(y) :

[0035]

[0036] In the formula, l j is the radial thickness of the thermal battery assembly, k j is the radial thermal conductivity of the thermal battery assembly, l i is the axial thickness of the thermal battery assembly, k i is the axial thermal conductivity of the thermal battery assembly;

[0037] S43, according to step S41 and step S42, the relationship for achieving thermal equilibrium at the thermal battery boundary is designed as:

[0038]

[0039] In the formula, represents a radial unit vector.

[0040] Preferably, the boundary conditions in step S5 are set as follows:

[0041] Condition 1: Only heat conduction and contact thermal resistance between different components are considered inside the battery, and the contact thermal resistance is set to layer thermal resistance 0.001K·m 2 / W;

[0042] Condition 2: Initial temperature setting: There is natural convection heat exchange between the thermal battery and the environment. Set the ambient temperature T w =293.15K; the initial temperature of each part of the thermal battery is equal to the ambient temperature;

[0043] Condition 3: Ignore radiation heat transfer in the entire heat transfer process

[0044] Condition 4: Heat source setting during activation: The heating power is set to an internal heat source evenly distributed inside the heating plate, and the heating time is 0 to 0.5 s; according to the density of the heating plate 2.88 g / cm 3 And the calorific value is 1084J / g to obtain the average heat 6243840000W / m 3 , that is, the activation process heat source S h =6243840000W / m 3 ;

[0045] Condition 5: Symmetric boundary condition: The central axis should be set to a symmetric boundary condition, that is, when the thermal battery radius r = 0, it satisfies Relational.

[0046] Preferably, the insulating and heat-preserving layer in the thermal battery is composed of fiber felt, QNJ nano thermal insulation paper, mica tape and aerogel stacked in sequence; the shell material of the thermal battery is set to stainless steel.

[0047] Beneficial effects of the present invention: Compared with the prior art, the physical model adopted by the present invention for thermal battery simulation adds the second phase change latent heat, the third Joule heat and the fourth chemical reaction heat. The heat transfer model is more complete and comprehensive, making the simulation results more referenceable and providing support for the technical improvement of thermal batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 is a schematic diagram of the thermal battery geometry, where Figure 1 (a) is the overall diagram, Figure 1 (b) is a schematic diagram of the structure of a single cell;

[0049] Figure 2 This is a schematic diagram of the typical output voltage of a thermal battery;

[0050] Figure 3 It is the cloud diagram of the temperature distribution of thermal battery No. 1 changing with time, and the cloud diagrams at 0s, 0.1s and 0.6s are given respectively;

[0051] Figure 4It is the cloud diagram of the temperature distribution of thermal battery No. 2 changing with time, and the cloud diagrams at 0s, 0.1s and 0.6s are given respectively;

[0052] Figure 5 is a comparison chart between simulation results and measured data, where Figure 5 (a) is a cloud image, Figure 5 (b) is a curve graph;

[0053] Figure 6 It is the battery case temperature curve before +60℃ and -30℃ model correction;

[0054] Figure 7 It is the battery shell temperature curve after the +60℃ and -30℃ model correction;

[0055] Figure 8 is a flow chart of the thermal simulation method of the thermal battery of the present invention;

[0056] Fig. 9 The contact thermal resistance is 0.0001K·m 2 Temperature distribution cloud diagram of thermal battery activation process at 100 W;

[0057] Fig.10 The contact thermal resistance is 0.0001K·m 2 Temperature distribution cloud diagram of thermal battery activation process at 100 W;

[0058] Fig.11 is the minimum temperature of the electrolyte in the middle unit cell T emin Curve change comparison chart;

[0059] Fig.12 is the average temperature of the electrolyte in the middle unit cell T eave Curve comparison chart;

[0060] Fig.13 is the average anode temperature in the middle unit cell T pa Curve comparison chart;

[0061] Fig.14 is the average cathode temperature T in the middle unit cell na Curve comparison chart;

[0062] Fig.15 is the average temperature of the current collector in the middle unit cell T ca Curve comparison chart;

[0063] Fig.16 is the average temperature of the single heating plate in the middle unit battery T have Curve comparison chart;

[0064] Fig.17 is the average substrate temperature T in the middle unit cell baCurve comparison chart;

[0065] Fig.18 is the average temperature of the electrolyte in the middle unit cell T eave Curve comparison chart;

[0066] Fig.19 is the average substrate temperature T in the middle unit cell ba Curve comparison chart;

[0067] Fig. 20 is the average temperature of the current collector in the middle unit cell T ca Curve comparison chart;

[0068] Fig.21 is the average anode temperature in the middle unit cell T pa Curve comparison chart;

[0069] Fig. 22 is the average cathode temperature T in the middle unit cell na Curve comparison chart;

[0070] Fig.23 is the average temperature of the heating plate in the middle unit battery T have Curve comparison chart. DETAILED DESCRIPTION

[0071] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0072] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0073] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0074] Specific implementation method 1: The following is combined Figures 8 to 23 The present embodiment describes a thermal simulation method for a thermal battery in the present embodiment, the method comprising the following steps:

[0075] S1. Establish a three-dimensional simulation model of a thermal battery;

[0076] S2, loading the thermal battery three-dimensional simulation model into COMSOL software;

[0077] S3. The heat transfer physical model of the thermal battery is designed according to the following control equations:

[0078]

[0079] Where ρ is the density of each material of the thermal battery, C p is the specific heat capacity of each material, T is the temperature inside the thermal battery, and t is the time since the thermal battery was ignited. is the gradient operator, k is the thermal conductivity of each material, χ is the electrolyte mass fraction, Δ is the difference operator, H L is the latent heat of electrolyte phase change, w is the mass fraction of solidified electrolyte, i A is the surface current density inside the thermal battery, R is the internal resistance of the thermal battery, Q rh It is the heat of chemical reaction during the operation of thermal battery;

[0080] S4. The thermal battery boundary is designed to achieve thermal balance;

[0081] S5. Perform network division on the three-dimensional model of the thermal battery and set boundary conditions;

[0082] S6. Perform simulation calculations to obtain a temperature distribution cloud map of the thermal battery activation process and a stress distribution cloud map of the thermal battery.

[0083] First, the structure of the thermal battery can be seen in Figure 1 As shown, thermal batteries are generally divided into cup-type structures and sheet-type structures according to their structures. The main structure includes a battery cover 1, an upper insulating and heat-preserving component 2, a side insulating and heat-preserving layer 3, a battery stack 4, a battery shell 5, a lower insulating and heat-preserving component 6 and a battery bottom 7. The battery stack 4 is composed of a plurality of single cells 8 connected in series or in parallel, and the single cell 8 is composed of a current collector 8-1, a diaphragm 8-2, a graphite paper 8-3, a heating plate 8-3, an anode 8-4 and a cathode 8-5. The battery stack is constructed by stacking and assembling, and is the core of the thermal battery.

[0084] The specific embodiment of the thermal battery geometric structure parameters is shown in Table 1:

[0085] Table 1

[0086]

[0087]

[0088] The above-mentioned thermal battery three-dimensional model and specific geometric dimensions were imported into COMSOL software.

[0089] The present invention adopts an innovative thermal battery heat transfer physical model, and its control equation is:

[0090]

[0091] Compared with the existing technology, the second phase change latent heat, the third Joule heat and the fourth chemical reaction heat are added, and the heat transfer model is more complete and comprehensive. The definitions and units of the variables in the formula are shown in Table 2:

[0092] Table 2

[0093]

[0094] The left side of the equal sign in the control equation is the heat generated by the temperature change; the first term on the right side of the equal sign is the heat conduction term; the second term is the latent heat when the electrolyte changes phase, which only exists at the location where the electrolyte changes phase, and is zero everywhere else; the third term is the Joule heat generated during the operation of the thermal battery, which only exists at the location where the current passes, and is zero everywhere else; the fourth term is the chemical reaction heat generated by the electrochemical reaction when the thermal battery is working, and is non-zero only at the location where the electrochemical process occurs.

[0095] The chemical reaction heat Q during the operation of the thermal battery rh Calculate as follows:

[0096]

[0097] Where U is the potential when the electrochemical reaction reaches equilibrium, V,

[0098] i v is the current volume density in the thermal battery, A / m 3 ,i v Get it by pressing:

[0099]

[0100] Where d is the axial thickness of each component inside the thermal battery, m.

[0101] The design process of achieving thermal balance at the thermal battery boundary in step S4 is as follows:

[0102] S41. Natural convection heat transfer is carried out between the thermal battery and the environment, and the heat transfer amount is calculated as follows:

[0103] Q h =h w (T w -T s )A s

[0104] In the formula, Q h is the heat exchange between the thermal battery and the environment, W, h w is the convection heat transfer coefficient between the thermal battery and the environment, W / (m2·K), T w is the ambient temperature, K, T s is the surface temperature of the thermal battery, K, A sis the effective area of ​​convective heat transfer between the thermal battery and the environment, m 2 ;

[0105] S42, the radial direction of the battery assembly is taken as the x direction, and the longitudinal direction of the battery assembly is taken as the y direction, and the effective thermal conductivity k in the x direction is calculated respectively. eff(x) and the effective thermal conductivity k in the y direction eff(y) :

[0106]

[0107] In the formula, l j is the radial thickness of the thermal battery assembly, m, k j is the radial thermal conductivity of the thermal battery assembly, W / (m·K), l i is the axial thickness of the thermal battery assembly, m, k i is the axial thermal conductivity of the thermal battery assembly, W / (m·K);

[0108] S43, according to step S41 and step S42, the relationship for achieving thermal equilibrium at the thermal battery boundary is designed as:

[0109]

[0110] In the formula, represents a radial unit vector.

[0111] The combustion process of the "single heating sheet" is completely released at constant power within 0 to 0.5 seconds after the battery starts working. After the electrode is heated to the specified temperature (436°C), the "diaphragm sheet" begins to absorb heat and melt. After the battery stack (including: positive electrode, diaphragm, negative electrode, current collector and single heating sheet) reaches the maximum temperature, the battery begins to slowly dissipate heat and cool down the surrounding environment. After the electrode cools to the specified temperature, the "diaphragm sheet" begins to solidify and release heat, and the battery ends. The material settings of each part of the thermal battery are shown in Table 3, and the physical properties of each part of the material are shown in Table 4. The insulating and thermal insulation layer in the thermal battery is composed of fiber felt, QNJ nano insulation paper, mica tape and aerogel stacked in sequence; the shell material of the thermal battery is set to stainless steel.

[0112] Table 3

[0113]

[0114] Table 4

[0115]

[0116] Based on the above settings, the boundary conditions are set in step S5 as follows:

[0117] Condition 1: Only heat conduction and contact thermal resistance between different components are considered inside the battery, and the contact thermal resistance is set to layer thermal resistance 0.001K·m2 / W;

[0118] Condition 2: Initial temperature setting: There is natural convection heat exchange between the thermal battery and the environment. Set the ambient temperature T w =293.15K; the initial temperature of each part of the thermal battery is equal to the ambient temperature;

[0119] Condition 3: Ignore radiation heat transfer in the entire heat transfer process

[0120] Condition 4: Heat source setting during activation: The heating power is set to an internal heat source evenly distributed inside the heating plate, and the heating time is 0 to 0.5 s; according to the density of the heating plate 2.88 g / cm 3 And the calorific value is 1084J / g to obtain the average heat 6243840000W / m 3 , that is, the activation process heat source S h =6243840000W / m 3 ;

[0121] Condition 5: Symmetric boundary condition: The central axis should be set to a symmetric boundary condition, that is, when the thermal battery radius r = 0, it satisfies Relational.

[0122] The first boundary condition is the setting of contact thermal resistance, which shows the importance of contact thermal resistance.

[0123] The internal structures of the sheet-type single cells of the thermal battery will generate contact thermal resistance when they are in contact. Contact thermal resistance refers to the phenomenon that the heat conduction efficiency is reduced due to imperfections in the contact surface (such as microscopic unevenness, air gaps, etc.). In a thermal battery, the contact thermal resistance between the anode sheet, electrolyte sheet and cathode sheet may affect the overall thermal efficiency of the battery.

[0124] The magnitude of the thermal contact resistance depends on factors such as the nature of the contact surface, pressure, surface roughness, and thermal conductivity of the contact material. During the operation of the thermal battery, the thermal contact resistance may change due to factors such as temperature changes, differences in material expansion coefficients, or creep caused by long-term use. The magnitude of the thermal contact resistance is difficult to determine because it is affected by many factors. During the design and manufacturing process, the thermal contact resistance should be minimized, for example by optimizing the flatness of the contact surface, using materials with high thermal conductivity, or adopting special contact structure designs.

[0125] In actual situations, the influence of the contact thermal resistance between the components in the thermal battery on the thermal battery needs to be considered. Fig. 9 , Fig.10 The contact thermal resistance is 0.0001K·m 2 / W thermal battery activation process temperature distribution cloud diagram and contact thermal resistance is 0.0001K·m 2 / W temperature distribution cloud diagram of the electrochemical reaction process of the thermal battery. Fig. 9 (a) to (d) are the cloud diagrams at t = 0.1s, 0.5s, 0.6s and 0.9s respectively. Fig.10 (a) to (d) are the cloud diagrams at t = 32s, 100s, 500s and 700s respectively.

[0126] See also Fig. 9 When the thermal battery starts working after being activated, the heat from the heating plate in the thermal battery is quickly transferred to the battery stack over time. Fig.10 As shown in the figure, it can be seen that the temperature of the thermal battery end and the temperature inside the thermal battery stack tend to be consistent at a faster rate, indicating that the contact thermal resistance is 0.0001K·m 2 / W, the heat transfer performance of the thermal battery is less affected.

[0127] It can be seen that when the contact thermal resistance is 0.0001K·m2 / W, the temperature of the battery stack inside the thermal battery quickly converges to the same level within 1s.

[0128] The influence of contact thermal resistance on heat transfer is analyzed below.

[0129] The first is the influence of contact thermal resistance on the activation process of single cells, such as Fig.11 , Fig.12 The following are the curves showing the change of the minimum and average electrolyte temperatures in the unit cell in the middle of the stack with time when the contact thermal resistance is 0.01 K·m 2 / W and the ideal state with no thermal resistance.

[0130] Whether it is the average temperature or the minimum temperature, the contact thermal resistance greatly prolongs the activation time of the thermal battery, indicating that when the contact thermal resistance reaches a certain value, its influence on the performance of the thermal battery cannot be ignored. On the one hand, the heat transfer is weakened, the temperature drop of each component slows down, and the thermal insulation performance becomes stronger. On the other hand, the heat cannot be quickly transferred to the electrolyte, which prolongs the activation time. Therefore, the influence of the contact thermal resistance on the performance of the thermal battery needs further discussion.

[0131] like Fig.13 , Fig.14 , Fig.15 , Fig.16 and Fig.17 Shown are comparisons of the time variation curves of the average temperature of each component of a unit cell in a thermal battery with and without thermal resistance.

[0132] During the activation process, when there is contact thermal resistance between the components of the unit cell and when there is no thermal resistance, the temperature change curve is smoother when there is contact thermal resistance. This is because when there is contact thermal resistance, the heat transfer process is hindered, so the temperature changes more slowly.

[0133] The contact thermal resistance not only hinders the heat transfer of the heater during the activation process, but also affects the heat transfer performance of the thermal battery during the electrochemical reaction, and further affects the thermal life of the thermal battery. Therefore, the influence of the contact thermal resistance on the entire working process of the unit battery is analyzed.

[0134] like Fig.18 , Fig.19 , Fig. 20 , Fig.21 , Fig. 22 , Fig.23 The thermal battery contact thermal resistance is shown as 0.01K·m 2 / W and thermal batteries without thermal resistance, the temperature change curves of the electrolyte, substrate, current collector, anode, cathode and heater are compared.

[0135] Similar to the activation process, when contact thermal resistance exists, the temperature change curve in the electrochemical reaction process will have an inflection point later, especially for the electrolyte, which will extend the thermal life of the thermal battery to a certain extent. This is because the heat transfer is slower, which weakens the heat transfer between the components inside the battery stack, so the thermal life of the thermal battery is extended. At the same time, the activation time is also extended accordingly. That is, when contact thermal resistance exists, it has both positive and negative effects on the thermal battery.

[0136] In order to avoid adverse effects, the present invention imposes corresponding limitations on the contact thermal resistance.

[0137] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that the features described in conjunction with a single embodiment may be used in other described embodiments.

Claims

1. A thermal simulation method for a thermal battery, characterized in that: The method comprises the following steps: S1. Establish a three-dimensional simulation model of a thermal battery; S2, loading the thermal battery three-dimensional simulation model into COMSOL software; S3. The heat transfer physical model of the thermal battery is designed according to the following control equations: Where ρ is the density of each material of the thermal battery, C p is the specific heat capacity of each material, T is the temperature inside the thermal battery, t is the time since the thermal battery was ignited, is the gradient operator, k is the thermal conductivity of each material, χ is the electrolyte mass fraction, Δ is the difference operator, H L is the latent heat of electrolyte phase change, w is the mass fraction of solidified electrolyte, i A is the surface current density inside the thermal battery, R is the internal resistance of the thermal battery, Q rh It is the heat of chemical reaction during the operation of thermal battery; S4. The thermal battery boundary is designed to achieve thermal balance; S5. Perform network division on the three-dimensional model of the thermal battery and set boundary conditions; S6. Perform simulation calculations to obtain a temperature distribution cloud map of the thermal battery activation process and a stress distribution cloud map of the thermal battery.

2. The thermal simulation method of a thermal battery according to claim 1, characterized in that: The chemical reaction heat Q during the operation of the thermal battery rh Calculate as follows: Where U is the potential when the electrochemical reaction reaches equilibrium. i v is the current volume density in the thermal battery, i v Get it by pressing: Where d is the axial thickness of each component inside the thermal battery.

3. The thermal simulation method of a thermal battery according to claim 2, characterized in that: The design process of achieving thermal balance at the thermal battery boundary in step S4 is as follows: S41. Natural convection heat transfer is carried out between the thermal battery and the environment, and the heat transfer amount is calculated as follows: Q h =h w (T w -T s )A s In the formula, Q h is the heat exchange between the thermal battery and the environment, h w is the convective heat transfer coefficient between the thermal battery and the environment, T w is the ambient temperature, T s is the surface temperature of the thermal battery, A s is the effective area of ​​convective heat transfer between the thermal battery and the environment; S42, the radial direction of the battery assembly is taken as the x direction, and the longitudinal direction of the battery assembly is taken as the y direction, and the effective thermal conductivity k in the x direction is calculated respectively. eff(x) and the effective thermal conductivity k in the y direction eff(y) : In the formula, l j is the radial thickness of the thermal battery assembly, k j is the radial thermal conductivity of the thermal battery assembly, l i is the axial thickness of the thermal battery assembly, k i is the axial thermal conductivity of the thermal battery assembly; S43, according to step S41 and step S42, the relationship for achieving thermal equilibrium at the thermal battery boundary is designed as: In the formula, represents a radial unit vector.

4. The thermal simulation method of a thermal battery according to claim 1, characterized in that: In step S5, the boundary conditions are set as follows: Condition 1: Only heat conduction and contact thermal resistance between different components are considered inside the battery, and the contact thermal resistance is set to layer thermal resistance 0.001K·m 2 / W; Condition 2: Initial temperature setting: There is natural convection heat exchange between the thermal battery and the environment. Set the ambient temperature T w =293.15K; the initial temperature of each part of the thermal battery is equal to the ambient temperature; Condition 3: Ignore radiation heat transfer in the entire heat transfer process Condition 4: Heat source setting during activation: The heating power is set to an internal heat source evenly distributed inside the heating plate, and the heating time is 0 to 0.5 s; according to the density of the heating plate 2.88 g / cm 3 And the calorific value is 1084J / g to obtain the average heat 6243840000W / m 3 , that is, the activation process heat source S h =6243840000W / m 3 ; Condition 5: Symmetric boundary condition: The central axis should be set to a symmetric boundary condition, that is, when the thermal battery radius r = 0, it satisfies Relational.

5. The thermal simulation method of a thermal battery according to claim 1, characterized in that: The insulating layer in the thermal battery is composed of fiber felt, QNJ nano thermal insulation paper, mica tape and aerogel stacked in sequence; the shell material of the thermal battery is set to stainless steel.

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