Lithium battery system thermal runaway propagation judgment method and evaluation method and device

Abstract

The present invention belongs to the field of lithium battery technology, and specifically relates to a method for judging the spread of thermal runaway in a lithium battery system and an evaluation method and device thereof. A method for judging the spread of thermal runaway in a lithium battery system, when the net heat absorption of the receptor battery is greater than the net heat absorption threshold of the battery thermal runaway, or when the net heat absorption of the receptor battery is greater than the net heat absorption threshold of the battery thermal runaway and the maximum temperature of the heating surface of the receptor battery is greater than the battery thermal runaway temperature threshold, it is judged that the receptor battery has thermal runaway; the net heat absorption of the receptor battery is calculated by the heat absorbed by the receptor battery from the thermal runaway battery and the heat exported to other batteries. This method uses the net heat absorption of the receptor battery for judgment, and the data is more accurate and effective, avoiding errors in the judgment conditions of the highest temperature or average temperature, and can more accurately reflect the spread of thermal runaway in the lithium battery system.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery safety performance detection, and specifically relates to a method for judging the spread of thermal runaway in a lithium battery system and an evaluation method and device thereof. Background Art

[0002] Lithium-ion batteries are widely used in the field of new energy technology. Due to the characteristics of lithium-ion batteries themselves, thermal runaway will cause a series of chain exothermic reactions, causing the temperature to rise rapidly in a short period of time and the lithium-ion battery structure to be irreversibly damaged. Therefore, it is of great significance to avoid thermal runaway of lithium-ion batteries.

[0003] In order to solve the above problems, the Chinese invention patent with the invention publication number CN 115828541A ​​proposes a lithium-ion battery protection design method based on thermal runaway propagation simulation. The thermal runaway protection design is improved through the proposed detection, modeling and simulation process, thereby avoiding the spread of battery thermal runaway. However, the current simulation software has a relatively simple way of determining whether a battery has thermal runaway. It often uses a single parameter such as average temperature or maximum temperature for determination. The parameter selection is not accurate enough, and the modeling calculation time of the simulation process is relatively long. In addition, when evaluating a lithium battery system under normal circumstances, thermal runaway is also an indicator for its evaluation. If this method is directly applied to the evaluation of a lithium battery system, technical problems such as inaccurate results and a time-consuming process will also occur. Summary of the invention

[0004] The purpose of the present invention is to provide a method and device for judging the spread of thermal runaway of a lithium battery system, so as to solve the problem that the judgment of the spread of thermal runaway of a lithium-ion battery system is not accurate enough and takes a long time; and also to provide a method and device for evaluating a lithium battery system, so as to solve the technical problem that the results of the protection evaluation method of a lithium-ion battery system are not accurate enough and take a long time.

[0005] In order to solve the above technical problems, the present invention provides a method for judging the spread of thermal runaway of a lithium battery system, comprising the following steps:

[0006] The net heat absorption of the acceptor battery is obtained. When the net heat absorption of the acceptor battery is greater than the net heat absorption threshold of the battery thermal runaway, or when the net heat absorption of the acceptor battery is greater than the net heat absorption threshold of the battery thermal runaway and the maximum temperature of the heated surface of the acceptor battery is greater than the battery thermal runaway temperature threshold, it is determined that the acceptor battery has thermal runaway. The net heat absorption of the acceptor battery is obtained by subtracting the heat absorbed by the acceptor battery from the thermal runaway battery from the heat extracted to other batteries.

[0007] Furthermore, the maximum temperature of the receiving battery heating surface is the maximum value of the receiving battery heating surface temperature, and the calculation method of the receiving battery heating surface temperature is:

[0008] In the formula, T 受 is the battery heating surface temperature at the current moment; T 0受 is the temperature of the battery heating surface at a certain time before the current time, k is the coefficient, θ is the thermal resistance in the thickness direction of the battery, Q 净 is the net heat absorption during the period between a certain moment and the current moment, C is the specific heat capacity of the battery, m is the battery weight.

[0009] Furthermore, the net heat absorption amount of the receptor battery and the net heat absorption threshold amount of the battery thermal runaway are both dynamic values, and change with time and heating power.

[0010] Furthermore, the battery thermal runaway temperature threshold is the maximum temperature of the large surface of the battery when thermal runaway occurs under the input of an external heat source.

[0011] Furthermore, the heat absorbed by the acceptor battery from the thermal runaway battery includes the heat absorbed from the top, side, large surface and bottom of the acceptor battery, and the heat exported by the acceptor battery to other batteries includes the heat exported from the top, side, large surface and bottom of the acceptor battery.

[0012] The present invention is an improved invention creation, and its beneficial effects are: the method for judging the spread of thermal runaway of a lithium battery system of the present invention, scheme one uses the net heat absorption of the receptor battery as a condition for judging whether thermal runaway occurs in the lithium battery system, which can more accurately reflect the heat transfer of the lithium battery system and more accurately judge whether thermal runaway occurs in the lithium battery system compared to the maximum temperature or the average temperature. As another scheme of the present invention, the net heat absorption and the maximum temperature of the receptor battery are used as judgment conditions at the same time, avoiding the error of a single condition, making the judgment of the thermal runaway of the lithium battery more accurate, and further improving the judgment accuracy.

[0013] To solve the above technical problems, the present invention also provides a device for judging the spread of thermal runaway in a lithium battery system, comprising a processor and a memory, wherein the processor is used to execute a program in the memory to implement a judgment method as described in the method for judging the spread of thermal runaway in a lithium battery system, so as to achieve the same beneficial effects as the method for judging the spread of thermal runaway in a lithium battery system of the present invention.

[0014] In order to solve the above technical problems, the present invention also provides a lithium battery system evaluation method, comprising the following steps:

[0015] 1) Obtaining the net heat absorption of the acceptor battery. When the net heat absorption of the acceptor battery is greater than the net heat absorption threshold of the battery thermal runaway, or when the net heat absorption of the acceptor battery is greater than the net heat absorption threshold of the battery thermal runaway and the maximum temperature of the heated surface of the acceptor battery is greater than the battery thermal runaway temperature threshold, it is determined that the acceptor battery has thermal runaway. The net heat absorption of the acceptor battery is obtained by subtracting the heat absorbed by the acceptor battery from the thermal runaway battery from the heat extracted from other batteries.

[0016] 2) When the result of the judgment is that the receptor battery is in thermal runaway, the lithium battery system is adjusted.

[0017] Furthermore, the maximum temperature of the receiving battery heating surface is the maximum value of the receiving battery heating surface temperature, and the calculation method of the receiving battery heating surface temperature is:

[0018] In the formula, T 受 is the battery heating surface temperature at the current moment; T 0受 is the temperature of the battery heating surface at a certain time before the current time, k is the coefficient, θ is the thermal resistance in the thickness direction of the battery, Q 净 is the net heat absorption during the period between a certain moment and the current moment, C is the specific heat capacity of the battery, m is the battery weight.

[0019] Furthermore, the net heat absorption amount of the receptor battery and the net heat absorption threshold amount of the battery thermal runaway are both dynamic values, which change with time and heating power.

[0020] Furthermore, the battery thermal runaway temperature threshold is the maximum temperature of the large surface of the battery when thermal runaway occurs under the input of an external heat source.

[0021] Furthermore, the heat absorbed by the acceptor battery from the thermal runaway battery includes heat absorbed from the top, sides, large surface and bottom, and the heat exported by the acceptor battery to other batteries includes heat exported from the top, sides, large surface and bottom.

[0022] The present invention is an improved invention creation, and its beneficial effects are as follows: in the lithium battery system evaluation method of the present invention, scheme 1 uses the net heat absorption of the receptor battery as a condition for judging whether the lithium battery system has thermal runaway. Compared with the maximum temperature or the average temperature, it can more accurately reflect the heat transfer of the lithium battery system and more accurately judge whether the lithium battery system has thermal runaway. As another scheme of the present invention, the net heat absorption and the maximum temperature of the receptor battery are used as judgment conditions at the same time, avoiding the error of a single condition, making the judgment of the thermal runaway of the lithium battery more accurate, and further improving the judgment accuracy; then, according to the judgment result of the spread of thermal runaway, the battery system is optimized, so that the battery system can better meet the requirements of suppressing the spread of thermal runaway, and the result can be obtained by directly using relevant parameters for calculation, without the need to establish a three-dimensional model, eliminating the modeling step, shortening the design time, and improving efficiency.

[0023] In order to solve the above technical problems, the present invention also provides a lithium battery system evaluation device, wherein the processor is used to execute the program in the memory to implement the evaluation method as described in the lithium battery system evaluation method of the present invention, so as to achieve the same beneficial effects as the lithium battery system evaluation method of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of a lithium battery system evaluation method according to an embodiment of a method for judging the spread of thermal runaway of a lithium battery system of the present invention;

[0025] Figure 2 It is a schematic diagram of another lithium battery system evaluation method according to an embodiment of the method for judging the spread of thermal runaway of a lithium battery system of the present invention;

[0026] Figure 3 It is a schematic diagram of the distribution position of single cells in an embodiment of the method for judging the spread of thermal runaway of a lithium battery system of the present invention.

[0027] Figure numerals: 1. Heating plate; 2. Thermal insulation material; 3. Thermal runaway battery; 4. Acceptor battery; 5. Rear battery. DETAILED DESCRIPTION

[0028] The method for judging the spread of thermal runaway of a lithium battery system of the present invention uses the total absorbed heat of a receptor battery minus the total extracted heat to calculate the net heat absorbed by the receptor battery, compares the net heat absorbed by the receptor battery with the net heat absorbed threshold, or calculates the maximum temperature of the heating surface of the receptor battery based on the net heat absorbed by the receptor battery, compares the maximum temperature of the heating surface with the battery thermal runaway temperature threshold, and compares the net heat absorbed by the receptor battery with the net heat absorbed threshold to judge whether thermal runaway occurs in the receptor battery. The net heat absorbed by the battery can more intuitively reflect the temperature change of the receptor battery, and thus can more accurately reflect the spread of thermal runaway in the lithium battery system, thereby improving the accuracy of judging thermal runaway of the lithium-ion battery system. The second technical solution of the present invention combines the net heat absorbed with the maximum temperature of the heating surface to judge the thermal runaway of the receptor battery, thereby further improving the judgment accuracy of the thermal runaway of the receptor battery. At the same time, the method of the present invention does not need to use simulation software for simulation, but can directly judge based on the comparison results of relevant parameters, and does not need to establish a model, thereby saving time and improving the timeliness of the method. At the same time, the thermal runaway propagation judgment method of the lithium battery system of the present invention can also be applied to the design of the lithium battery system to realize an evaluation method of the lithium battery system. The evaluation method can better meet the requirements of suppressing the thermal runaway propagation of the lithium battery, and at the same time, does not require the establishment of a model, thereby shortening the design time.

[0029] Embodiment of a method for judging the spread of thermal runaway in a lithium battery system:

[0030] like Figure 1 and Figure 2 As shown, the method for judging the thermal runaway propagation of a lithium battery system of the present invention comprises the following steps:

[0031] 1) Calculate the net heat absorption of the acceptor cell and the maximum temperature of the heated surface.

[0032] When a battery in the lithium battery system (in this embodiment, all batteries in the lithium battery system are square-shell batteries) triggers thermal runaway, the thermal runaway battery 3 (which can be called the triggering battery) continuously transfers heat to the receptor battery 4, and the receptor battery transfers heat to the rear battery 5 (which can be called other batteries). The positional relationship of the three is as follows: Figure 3 As shown, the thermal runaway battery 3 is in contact with the heating plate 1, and two adjacent batteries are separated by the heat insulating material 2. At this time, the parameters of the heat absorption and heat dissipation of the acceptor battery 4 are obtained, wherein the heat absorption includes the heat introduced from the bottom, the heat introduced from the side, the heat introduced from the large surface, and the heat introduced from the top of the acceptor battery 4; the heat dissipation of the acceptor battery 4 includes the heat dissipation from the bottom, the heat dissipation from the side, the heat dissipation from the large surface, and the heat dissipation from the top.

[0033] The calculation method for the heat input and output of a certain side of the lithium battery is as follows:

[0034] Q = λ*A*dT / dx;

[0035] In the formula, Q is the heat imported / exported from a certain surface of the lithium battery per unit time, T is the temperature difference between the heat conduction part (bottom / side / large surface / top) and the adjacent surface at the starting moment, λ is the thermal conductivity, A is the area of ​​the heat conduction part, and x is time. The steady-state heat transfer calculation is performed per unit time and the time period is accumulated, with a unit time range of 0.001s~1s. If the temperature of the heat transfer part is greater than the temperature of the adjacent surface, T is a positive value, and the corresponding Q is a positive value and represents the exported heat; if the temperature of the heat transfer part is less than the temperature of the adjacent surface, T is a negative value, and the corresponding Q is a negative value, which means that the heat transfer part imports heat, and the value of the imported heat is the absolute value of Q.

[0036] The total heat input of the acceptor battery 4 (square shell battery) is calculated based on the heat input from the top, the heat input from the side, the heat input from the large surface and the heat input from the bottom; the total heat output of the acceptor battery 4 is calculated based on the heat output from the top, the heat output from the side, the heat output from the large surface and the heat output from the bottom, and the net heat input of the acceptor battery 4 is obtained by subtracting the total heat output from the total heat input. The curve of the change of the heat input of the acceptor battery 4 over time and the maximum temperature of the heating surface of the battery are obtained based on the net heat input. The heating surface is the surface closest to the thermal runaway battery 3, and the back heat surface is the surface closest to the rear battery 5.

[0037] The maximum temperature of the heating surface is calculated by calculating the temperature distribution in the heat transfer direction of the battery based on parameters such as net heat absorption and thermal resistance. The specific calculation method of the heating surface temperature is as follows:

[0038]

[0039]

[0040] In the formula, T 受 is the battery heating surface temperature at the current moment; T 0受 is the temperature of the battery heating surface at a certain time before the current time, k is the coefficient, θ is the thermal resistance in the thickness direction of the battery, Q 净 is the net heat absorption during the period between a certain moment and the current moment, C is the specific heat capacity of the battery, m is the battery weight. is the heat introduced by the acceptor battery 4 per unit time, that is, the sum of the heat introduced by all heat-conducting parts per unit time, The heat outputted by the acceptor battery 4 per unit time is the sum of the heat outputted by all heat conducting parts per unit time. In this embodiment, the time interval between the current moment and a previous moment is the unit time. As other embodiments, the time interval between the current moment and a previous moment can be set arbitrarily.

[0041] 2) Test the thermal runaway net heat absorption threshold and temperature threshold of single battery.

[0042] Use different heating powers to perform heating tests on the single cells in the lithium battery system, obtain the relationship between the heat absorption and trigger time at the moment of thermal runaway of the lithium battery under different heating powers, and use this relationship curve as the curve of the net heat absorption threshold of the battery thermal runaway under the corresponding heating power over time; at the same time, obtain the large surface temperature at the moment of thermal runaway under different heating powers as the battery thermal runaway temperature threshold. The above heating test can be performed using an actual single cell for heating test experiments, or a simulation method can be used to perform heating tests on a battery model.

[0043] 3) Compare the calculated net heat absorption curve of the acceptor battery 4 with the battery thermal runaway net heat absorption threshold curve; compare the maximum temperature of the battery heating surface with the battery thermal runaway temperature threshold, and determine whether the acceptor battery 4 has thermal runaway based on the comparison results.

[0044] If the net heat absorption curve of the acceptor battery 4 is higher than the battery thermal runaway net heat absorption threshold curve; and the maximum temperature of the battery heating surface is higher than the battery thermal runaway temperature threshold, it is determined that the acceptor battery 4 is thermally runaway.

[0045] In this embodiment, the two parameters of net heat absorption and maximum temperature of the heated surface are used simultaneously. When both parameters are greater than the corresponding thresholds, the receiver battery 4 is judged to be in thermal runaway, and the thermal runaway judgment accuracy is higher. As another embodiment, only the net heat absorption parameter of the receiver battery 4 may be used. When the net heat absorption is higher than the corresponding threshold, the receiver battery 4 is judged to be in thermal runaway.

[0046] This method can be applied to actual lithium battery systems. When a single battery in the system triggers thermal runaway, the spread of thermal runaway can be predicted to determine whether the thermal runaway will spread from the triggering battery to the receptor battery 4. It can also be applied to lithium battery system evaluation methods to modify and optimize the design scheme based on the prediction results of the thermal runaway spread of the lithium battery system.

[0047] Embodiment of the device for judging the spread of thermal runaway in a lithium battery system:

[0048] The device for judging the thermal runaway propagation of a lithium battery system of the present invention comprises a processor and a memory, and the processor is used to execute a program in the memory to implement the method for judging the thermal runaway propagation of a lithium battery system as in the judgment method embodiment. The specific steps, principles and beneficial effects of the method have been described in detail in the system evaluation method embodiment, and will not be repeated in this embodiment.

[0049] The processor may be a microprocessor MCU, a programmable logic device FPGA or other processing device. The memory may be RAM, ROM or the like.

[0050] Lithium battery system evaluation method example:

[0051] The system evaluation method of this embodiment is as follows Figure 1 As shown, the judgment method of the judgment method embodiment of the lithium battery system is judged, and the parameters of the lithium battery system are optimized according to the judgment result. After the parameter optimization, the heat imported / exported at the top, the heat imported / exported at the side, the heat imported / exported on the large surface, and the heat imported / exported at the bottom of the acceptor battery 4 change accordingly; when the net heat absorption of the acceptor battery 4 is less than or equal to the thermal runaway net heat absorption threshold or / and the maximum temperature of the heated surface is less than or equal to the thermal runaway temperature threshold, it is determined that the battery system meets the requirements for suppressing the spread of thermal runaway.

[0052] The evaluation method of this embodiment can be applied to a physical battery system, and the above-mentioned lithium battery system evaluation method is used to evaluate the import / export status of the physical battery system, that is, to evaluate the thermal runaway propagation suppression capability of the lithium battery system.

[0053] The evaluation method of this embodiment can also be applied to battery system models or design schemes. According to the relevant parameters of the model and design scheme, the imported / exported heat can be predicted and the battery system can be evaluated. If the lithium battery model / design scheme is found to be unqualified, the design parameters of the battery system can be adjusted to ensure that the thermal runaway propagation suppression capability of the lithium battery model / design scheme meets the standards.

[0054] In this embodiment, the two parameters of net heat absorption and maximum temperature of the heated surface are used simultaneously. When both parameters are greater than the corresponding thresholds, the receiver battery 4 is judged to be in thermal runaway, and the accuracy of thermal runaway judgment is higher. As other implementations, only the net heat absorption parameter of the receiver battery 4 can be used. When the net heat absorption is higher than the corresponding threshold, the receiver battery 4 can be judged to be in thermal runaway. Correspondingly, when the net heat absorption of the receiver battery 4 is less than or equal to the net heat absorption threshold of thermal runaway, the final design solution can be obtained.

[0055] The lithium battery system evaluation method of the present invention does not require modeling, can save design time, and uses the net heat absorption to judge the spread of thermal runaway, which makes the judgment more accurate and makes the final design result meet the requirements of thermal runaway spread suppression.

[0056] Lithium battery system evaluation device example:

[0057] The evaluation device for the lithium battery system of the present invention includes a processor and a memory, and the processor is used to execute the program in the memory to implement the lithium battery system evaluation method in the system evaluation method embodiment. The specific steps, principles and beneficial effects of the method have been described in detail in the system evaluation method embodiment, and will not be repeated in this embodiment.

[0058] The processor may be a microprocessor MCU, a programmable logic device FPGA or other processing device. The memory may be RAM, ROM or the like.

Claims

1. A method for judging the spread of thermal runaway in a lithium battery system, characterized in that: The following steps are involved: Obtaining the net heat absorption of the acceptor battery per unit time, when the net heat absorption of the acceptor battery per unit time is greater than the battery thermal runaway net heat absorption threshold, or when the net heat absorption of the acceptor battery per unit time is greater than the battery thermal runaway net heat absorption threshold and the maximum temperature of the heated surface of the acceptor battery is greater than the battery thermal runaway temperature threshold, it is determined that the acceptor battery has thermal runaway; The net heat absorption of the receptor battery per unit time is obtained by subtracting the heat absorbed from the thermal runaway battery per unit time from the heat extracted from other batteries per unit time; the heated surface of the receptor battery is the surface closest to the thermal runaway battery among all surfaces of the receptor battery; the relationship curve between the net heat absorption and trigger time of the lithium battery at the moment of thermal runaway under different heating powers is used as the curve of the change of the net heat absorption threshold of the battery thermal runaway under the corresponding heating power over time, and the net heat absorption of the receptor battery per unit time and the net heat absorption threshold of the battery thermal runaway are both dynamic values, and change with time and heating power; The maximum temperature of the receiving battery heating surface is the maximum value of the receiving battery heating surface temperature. The calculation method of the receiving battery heating surface temperature is: In the formula, T 受 is the battery heating surface temperature at the current moment; T 0受 is the temperature of the battery heating surface at a certain time before the current time, k is the coefficient, θ is the thermal resistance in the thickness direction of the battery, Q 净 is the net heat absorbed during the period between a certain moment and the current moment, C is the specific heat capacity of the battery, and m is the weight of the battery.

2. The method for determining the spread of thermal runaway in a lithium battery system according to claim 1, characterized in that: The battery thermal runaway temperature threshold is the maximum temperature of the large surface of the battery when thermal runaway occurs under the input of an external heat source.

3. The method for judging the spread of thermal runaway in a lithium battery system according to claim 1 or 2, characterized in that: The heat absorbed by the acceptor battery from the thermal runaway battery includes the heat absorbed from the top, side, large surface and bottom of the acceptor battery, and the heat exported by the acceptor battery to other batteries includes the heat exported from the top, side, large surface and bottom of the acceptor battery.

4. A device for judging the spread of thermal runaway in a lithium battery system, characterized in that: It comprises a processor and a memory, wherein the processor is used to execute a program in the memory to implement the method for judging the spread of thermal runaway of a lithium battery system as claimed in any one of claims 1 to 3.

5. A lithium battery system evaluation method, characterized in that: The steps include: 1) Obtain the net heat absorption of the acceptor battery per unit time. When the net heat absorption of the acceptor battery per unit time is greater than the net heat absorption threshold of the battery thermal runaway, or when the net heat absorption of the acceptor battery per unit time is greater than the net heat absorption threshold of the battery thermal runaway and the maximum temperature of the heated surface of the acceptor battery is greater than the battery thermal runaway temperature threshold, it is determined that the acceptor battery has thermal runaway; The net heat absorption of the receptor battery per unit time is obtained by subtracting the heat absorbed from the thermal runaway battery per unit time from the heat extracted from other batteries per unit time; the heated surface of the receptor battery is the surface closest to the thermal runaway battery among all surfaces of the receptor battery; the relationship curve between the net heat absorption and trigger time of the lithium battery at the moment of thermal runaway under different heating powers is used as the curve of the change of the net heat absorption threshold of the battery thermal runaway under the corresponding heating power over time, and the net heat absorption of the receptor battery per unit time and the net heat absorption threshold of the battery thermal runaway are both dynamic values, and change with time and heating power; 2) When the result of the judgment is that the receptor battery is in thermal runaway, the ability of the lithium battery system to suppress the spread of thermal runaway is assessed to be not up to standard, and the lithium battery system is adjusted; The maximum temperature of the receiving battery heating surface is the maximum value of the receiving battery heating surface temperature. The calculation method of the receiving battery heating surface temperature is: In the formula, T 受 is the battery heating surface temperature at the current moment; T 0受 is the temperature of the battery heating surface at a certain time before the current time, k is the coefficient, θ is the thermal resistance in the thickness direction of the battery, Q 净 is the net heat absorbed during the period between a certain moment and the current moment, C is the specific heat capacity of the battery, and m is the weight of the battery.

6. The lithium battery system evaluation method according to claim 5, characterized in that: The battery thermal runaway temperature threshold is the maximum temperature of the large surface of the battery when thermal runaway occurs under the input of an external heat source.

7. The lithium battery system evaluation method according to claim 5 or 6, characterized in that: The heat absorbed by the acceptor battery from the thermal runaway battery includes heat absorbed from the top, sides, large surface and bottom, and the heat exported by the acceptor battery to other batteries includes heat exported from the top, sides, large surface and bottom.

8. A lithium battery system evaluation device, characterized in that: It comprises a processor and a memory, wherein the processor is used to execute a program in the memory to implement the lithium battery system evaluation method as described in any one of claims 5 to 7.

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