Rapid estimation method for thermal safety of lithium ion battery

Abstract

The invention discloses a lithium ion battery thermal safety rapid estimation method, and belongs to the technical field of lithium ion battery safety, and the method comprises the following steps: S1, obtaining basic thermal property data of a positive electrode, a negative electrode and an electrolyte material in a battery; s2, obtaining the weight ratio of a positive electrode, a negative electrode, an electrolyte and other materials in the designed or prepared battery, and performing normalization processing; s3, estimating the heat release performance of the battery through a formula; s4, the temperature change rate of the battery is obtained through conversion, and the thermal safety of the battery is estimated. According to the method, the problems of dangerousness of an existing lithium ion battery thermal safety analysis experiment and complexity of a modeling prediction method are solved, and the thermal safety of the lithium ion battery can be quickly estimated through simple formula conversion.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a method for quickly estimating the thermal safety of lithium ion batteries. Background Art

[0002] Lithium-ion batteries are widely used in electric vehicles, portable mobile devices, aerospace and other fields due to their high energy density, long cycle life, and no memory effect. However, lithium-ion batteries still have serious safety issues. Therefore, the safety prediction of lithium-ion batteries has received much attention in the field of battery design, preparation and application.

[0003] Traditional experimental methods mainly use thermal destruction experiments on lithium-ion batteries to characterize and measure the physical and chemical parameters of the battery during thermal explosion to study the thermal safety of lithium-ion batteries. These experimental devices are relatively complex and require a lot of lithium-ion battery preparation work. In addition, destructive experiments are prone to cause safety accidents and serious consequences.

[0004] CN2022106482708 is a three-dimensional modeling method for thermal runaway of lithium-ion batteries under different charge states based on differential scanning calorimeter experiments, including S1: obtaining battery active materials, performing differential scanning calorimeter experiments, and obtaining heat flow curves; S2: dividing the heat flow curve of the battery into multiple reaction peaks to obtain the reaction enthalpy of each peak of the battery; S3: analyzing the heat flow curve using the Kissinger equation to obtain activation energy and pre-exponential factor; S4: fitting the heat flow curve of the battery material using a genetic algorithm to obtain the reaction order of the active material of the lithium-ion battery; S5: establishing a battery thermal runaway model, comparing the simulation experiment results, and verifying the feasibility of the model; S6: changing the charge state of the lithium-ion battery, and studying the influence of different charge states on the thermal runaway of the lithium-ion battery. The thermal runaway model established based on the DSC experiment of the present invention can truly restore the thermal runaway reaction of the lithium-ion battery during the thermal runaway process and improve the accuracy of the model.

[0005] CN 2023106999013 A battery thermal runaway prediction method based on gradient-optimized multi-physics information neural network includes the following steps: establishing a multi-parameter coupling model for thermal runaway of a lithium-ion battery; constructing a multi-physics information neural network, the input of which is time, ambient temperature, and at least two spatially distributed variables of the lithium-ion battery, and the output is the temperature of the lithium-ion battery and the dimensionless concentration of lithium ions contained therein, and the loss function is determined based on the multi-parameter coupling model; using training data to train the multi-physics information neural network and optimizing the back propagation gradient during the training process; using the trained multi-physics information neural network to predict the thermal runaway process of the lithium-ion battery. The present application supervises and optimizes the training process of the neural network prediction model based on the multi-parameter physical mechanism of thermal runaway of lithium-ion batteries, which can effectively improve the prediction accuracy and robustness.

[0006] Existing thermal safety analysis of lithium-ion batteries involves a lot of preparation and testing work, as well as the dangers of battery safety tests. Although the method of using models to predict the safety of lithium-ion batteries can avoid safety tests, the model building requires a lot of data and the data processing method is relatively complicated. Therefore, a simple and fast method to predict battery safety is needed to help battery design and selection. Summary of the invention

[0007] In view of the above technical defects, the present invention provides a method for quickly estimating the thermal safety of lithium-ion batteries, which is used to solve the dangers of existing thermal safety analysis experiments of lithium-ion batteries and the complexity of modeling and prediction methods. Through simple formula conversion, the thermal safety of lithium-ion batteries can be quickly estimated.

[0008] To achieve the above technical objectives, the present invention is implemented by the following technical solutions: A method for quickly estimating the thermal safety of a lithium-ion battery, comprising the following steps:

[0009] S1. Obtaining basic thermal property data of materials: Obtaining basic thermal property data of positive electrode, negative electrode and electrolyte materials at a certain state of charge in the battery;

[0010] S2. Obtaining the battery weight ratio and normalizing it: Obtain the weight or weight ratio of the positive electrode, negative electrode, electrolyte and other materials in the designed or prepared battery; assuming that the total weight of the battery is 1, normalize the ratio of the weight of the positive electrode, negative electrode, electrolyte and other materials in the battery to the total weight to obtain the normalized weight of each material;

[0011] S3. Estimate the heat release performance of the battery: Estimate the heat release data of the battery by summing the product of the weight of each material and the heat release rate or the amount of heat released;

[0012] S4. Estimate the thermal safety of the battery: Based on the ratio of the battery's heat release data to the battery's average specific heat capacity, obtain the battery's heating rate and temperature rise range, compare the commonly used lithium-ion battery thermal runaway stage temperature definitions, and estimate the battery's thermal safety.

[0013] Furthermore, in S1, basic thermal property data of battery materials are obtained through literature or other public data, historical data, data provided by material manufacturers and self-test data.

[0014] Furthermore, the self-test data is obtained through thermal property testing techniques such as TG, DSC, and calorimetry of materials in a certain charge state.

[0015] Furthermore, in S4, the average specific heat capacity of the battery is derived from self-test data, literature or other public data, and historical data.

[0016] Furthermore, in S3, the battery heat release rate and battery heat release estimation equation used are:

[0017] r cell =∑ i r i η i

[0018] q cell =∑ i q i η i

[0019] Among them, r cell is the heat release rate of the battery, r i is the heat release rate of the positive electrode, negative electrode and electrolyte material in the battery, η i is the normalized weight of the positive electrode, negative electrode, and electrolyte material in the battery, q cell is the heat released by the battery, q i The heat released by the positive electrode, negative electrode and electrolyte materials in the battery

[0020] Furthermore, in S4, the battery temperature rise rate and temperature rise amplitude estimation equation used is:

[0021] T t =r cell / C p

[0022] ΔT=q cell / C p

[0023] Among them, T t is the heating rate of the battery, r cell is the heat release rate of the battery, C pis the average specific heat capacity of the battery, ΔT is the temperature rise of the battery, q cell The heat released by the battery.

[0024] Furthermore, the positive electrode of the lithium-ion battery includes at least one of lithium iron phosphate material, nickel-cobalt-manganese ternary material, lithium cobalt oxygen material, lithium manganate material, and NCA material; the negative electrode of the lithium-ion battery includes at least one of carbon negative electrode, silicon negative electrode, and alloy negative electrode material; the electrolyte material includes at least one of electrolyte, polymer electrolyte, and inorganic solid electrolyte.

[0025] The advantages and technical effects of the present invention are as follows: the present invention estimates the thermal safety of the battery by using the basic thermal property data of the material and the weight ratio of each material in the battery through a simple formula calculation method, which can avoid the need for large-scale battery preparation and testing for battery safety tests, reduce the generation of uncontrollable factors, and reduce the danger. At the same time, it also avoids the large amount of data and complex data processing methods required to establish a battery thermal model. The thermal safety of the battery can be estimated simply and quickly. The present invention can simply and quickly estimate the thermal safety of lithium-ion batteries, and roughly analyze the impact of each component on the thermal safety of the battery, which has extremely high application value for thermal safety factors in battery design and application screening. At the same time, it can avoid a large number of dangerous experiments or data testing experiments, reducing experimental costs and the complexity of data processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the thermal property curve of NCM, carbon negative electrode and electrolyte in the NCM523 / C battery of the embodiment of the present invention.

[0027] Figure 2 The heat generation rate curve and temperature rise rate curve of the NCM523 / C battery in the embodiment of the present invention are shown. DETAILED DESCRIPTION

[0028] In order to make the above-mentioned purpose, control system and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] like Figure 1 and Figure 2 As shown, the method for rapid estimation of thermal safety of lithium-ion batteries of the present invention first obtains the thermal property data of each material in the battery and the weight ratio of each material in the battery, then calculates the heat release data and temperature and temperature change data of the battery through a formula, and finally estimates the thermal safety of the battery according to the temperature rise change rate of the battery. This technical solution can provide rapid data support for the safe design and screening of lithium-ion batteries.

[0030] The specific implementation process of the present invention is as follows:

[0031] 1. Obtain basic thermal property data of battery materials through literature or other public data, historical data, data provided by material manufacturers and self-test data. In the self-test data, the battery material is firstly controlled to obtain a certain state of charge by controlling the charge and discharge amount, and then the basic exothermic reaction property test method such as TG, DSC or calorimetry is used to obtain the thermal property data of the material.

[0032] 2. According to the battery design or preparation process, the weight of the positive electrode, negative electrode, electrolyte and other materials of the battery and the total weight of the battery are obtained. Assuming that the total weight of the battery is 1, the weight of the positive electrode, negative electrode, electrolyte and other materials in the battery is normalized to the ratio of the total weight to obtain the normalized weight of each material. The calculation formula for the normalized weight of each material is:

[0033] η i =G i / G cell

[0034] where η i is the normalized weight of the positive electrode, negative electrode, and electrolyte material in the battery, G i is the weight of the positive electrode, negative electrode, and electrolyte material in the battery, G cell is the weight of the battery.

[0035] 3. Estimate the heat release data of the battery based on the weights of the weight ratios of each material and the basic thermal properties data obtained in the above two steps. The heat release data of the battery is the sum of the weights of each material and the product of the heat release rate or heat release amount. The battery heat release rate and battery heat release estimation equation is:

[0036] r cell =∑ i r i η i

[0037] q cell =∑ i q i η i

[0038] Among them, r cell is the heat release rate of the battery, r i is the heat release rate of the positive electrode, negative electrode and electrolyte material in the battery, η i is the normalized weight of the positive electrode, negative electrode, and electrolyte material in the battery, q cell is the heat released by the battery, q i It is the heat released by the positive electrode, negative electrode and electrolyte materials in the battery.

[0039] 4. According to the ratio of the heat release data of the battery to the average specific heat capacity of the battery (self-test data, literature or other public data, historical data, etc.), the heating rate and temperature rise range of the battery are obtained, and the temperature definition of the stage of thermal runaway of commonly used lithium-ion batteries is compared to estimate the thermal safety of the battery. The battery heating rate and temperature rise range estimation equation is:

[0040] T t =r cell / C p

[0041] ΔT=q cell / C p

[0042] Among them, T t is the heating rate of the battery, r cell is the heat release rate of the battery, C p is the average specific heat capacity of the battery, ΔT is the temperature rise of the battery, q cell The heat released by the battery.

[0043] The positive electrode of the lithium-ion battery includes at least one of lithium iron phosphate material, nickel-cobalt-manganese ternary material, lithium cobalt oxygen material, lithium manganate material, and NCA material; the negative electrode of the lithium-ion battery includes at least one of carbon negative electrode, silicon negative electrode, and alloy negative electrode material; the electrolyte material includes at least one of electrolyte, polymer electrolyte, and inorganic solid electrolyte.

[0044] Example: Thermal safety prediction of NCM523 / C lithium-ion battery

[0045] Step 1: Perform DSC tests on the fully charged NCM523 (charged to 4.2V), fully charged carbon anode (discharged to 0.01V) and electrolyte, respectively. Figure 1 .

[0046] Step 2: Normalize the weight of each material in the NCM523 / C lithium-ion battery. The results are shown in Table 1.

[0047] Table 1 shows the weight and weight ratio of NCM, carbon negative electrode, electrolyte and other components in NCM523 / C battery

[0048] Battery components Weight(g) Weight Ratio NCM523 62.50 0.46 Carbon negative electrode 36.36 0.27 Electrolyte 21.10 0.16 other 15.32 0.11 Battery Total 135.28 1.00

[0049] Step 3: Calculate the heat release rate curve of the battery based on the weight ratio of each material and the DSC test data. Figure 2 .

[0050] Step 4: Calculate the battery heating rate curve based on the battery heat release rate data and specific heat capacity, and mark its characteristic temperature according to the stage temperature definition of thermal runaway of common lithium-ion batteries. The results are shown in Figure 2

[0051] By using the calculation method described in the embodiment, the thermal safety of NCM523 / C lithium-ion battery can be estimated, such as Figure 2 As shown. According to the stage temperature definition of thermal runaway of commonly used lithium-ion batteries, when the heating rate reaches 1℃ / s, the NCM523 / C lithium-ion battery is in a thermal runaway state. The thermal runaway temperature of the NCM523 / C lithium-ion battery is 262℃, which is consistent with the results of the actual thermal safety test. Therefore, when the battery operating or storage temperature reaches or exceeds the predicted temperature point, serious safety hazards will arise.

[0052] Also preferably, the thermal safety of different lithium-ion battery systems can be quickly estimated by changing the types and charge states of the positive electrode materials, negative electrode materials and electrolytes tested.

[0053] In summary, the lithium-ion battery thermal safety prediction method disclosed in the present invention can simply and quickly predict the safety of lithium-ion batteries, and has high application value for the safety design and screening of lithium-ion batteries.

[0054] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for rapid estimation of thermal safety of lithium-ion batteries, characterized in that: The following steps are involved: S1. Obtaining basic thermal property data of materials: Obtaining basic thermal property data of positive electrode, negative electrode and electrolyte materials at a certain state of charge in the battery; S2. Obtaining the battery weight ratio and normalizing it: Obtain the weight or weight ratio of the positive electrode, negative electrode, electrolyte and other materials in the designed or prepared battery; assuming that the total weight of the battery is 1, normalize the ratio of the weight of the positive electrode, negative electrode, electrolyte and other materials in the battery to the total weight to obtain the normalized weight of each material; S3. Estimate the heat release performance of the battery: Estimate the heat release data of the battery by summing the product of the weight of each material and the heat release rate or the amount of heat released; S4. Estimate the thermal safety of the battery: Based on the ratio of the battery's heat release data to the battery's average specific heat capacity, obtain the battery's heating rate and temperature rise range, compare the commonly used lithium-ion battery thermal runaway stage temperature definitions, and estimate the battery's thermal safety.

2. The method for rapid estimation of thermal safety of lithium-ion batteries according to claim 1, characterized in that: In S1, basic thermal property data of battery materials are obtained through literature or other public data, historical data, data provided by material manufacturers and test data.

3. The method for rapid estimation of thermal safety of lithium-ion batteries according to claim 2, characterized in that: The test data are obtained through TG, DSC and calorimetry thermal property testing techniques of materials in a certain charge state.

4. The method for rapid estimation of thermal safety of lithium-ion batteries according to claim 1, characterized in that: In S4, the average specific heat capacity of the battery is derived from test data, literature or other public data, and historical data.

5. The method for rapid estimation of thermal safety of lithium-ion batteries according to claim 1, characterized in that: In S3, the battery heat release rate and battery heat release estimation equation used are: r cell =∑ i r i or i what cell =∑ i what i the i Among them, r cell is the heat release rate of the battery, r i is the heat release rate of the positive electrode, negative electrode and electrolyte material in the battery, η i is the normalized weight of the positive electrode, negative electrode, and electrolyte material in the battery, q cell is the heat released by the battery, q i It is the heat released by the positive electrode, negative electrode and electrolyte materials in the battery.

6. The method for rapid estimation of thermal safety of lithium-ion batteries according to claim 1, characterized in that: In S4, the battery temperature rise rate and temperature rise amplitude estimation equation used are: T t =r cell / C p ΔT=q cell / C p Among them, T t is the heating rate of the battery, r cell is the heat release rate of the battery, C p is the average specific heat capacity of the battery, ΔT is the temperature rise of the battery, q cell The heat released by the battery.

7. The method for rapid estimation of thermal safety of lithium-ion batteries according to claim 1, characterized in that: The positive electrode of the lithium-ion battery includes at least one of lithium iron phosphate material, nickel-cobalt-manganese ternary material, lithium cobalt oxygen material, lithium manganate material, and NCA material; the negative electrode of the lithium-ion battery includes at least one of carbon negative electrode, silicon negative electrode, and alloy negative electrode material; the electrolyte material includes at least one of electrolyte, polymer electrolyte, and inorganic solid electrolyte.

Images