Method for testing specific heat capacity of lithium battery cell

Abstract

The invention provides a method for testing the specific heat capacity of a lithium battery cell, which comprises the following steps of: testing the specific heat capacity of a cell sample by using a differential scanning calorimeter to obtain a specific heat capacity curve of the cell sample; calculating the specific heat capacity of the battery cell sample according to a formula; wherein Cp is the specific heat capacity of the battery cell sample and is the specific heat capacity value of the ith specific temperature read from the specific heat capacity curve of the battery cell sample, and n is the total number of the specific temperatures. According to the method, the specific heat capacity of the battery cell is rapidly measured through the sampling design of the battery cell and the differential scanning calorimeter method, and the problems that an existing battery specific heat capacity testing method is long in consumed time due to the fact that a heat balance process is included, and large testing deviation exists due to the fact that the method is greatly influenced by environmental conditions can be solved. Meanwhile, the specific heat capacity of the battery cell is directly measured, the method can be more directly used for temperature prediction and control strategies in the battery, and errors caused by the specific heat capacity of the battery are avoided.

Description

Technical Field

[0001] This invention relates to the field of specific heat capacity testing technology, and in particular to a method for testing the specific heat capacity of lithium battery cells. Background Technology

[0002] Lithium-ion batteries are widely used in electric vehicles, portable electronic devices, aerospace, and military fields due to their advantages such as high energy density, long cycle life, and no memory effect. However, lithium-ion batteries are prone to combustion or explosion due to thermal runaway during charging and discharging, posing serious safety hazards. Therefore, designing an efficient battery thermal management system (BMS) is crucial, requiring real-time monitoring of the battery's internal temperature and early warning of potential risks.

[0003] In battery thermal management systems, specific heat capacity is an extremely important thermophysical property parameter, serving as a quantitative indicator of the battery's thermal inertia. As a key parameter of battery thermal inertia, specific heat capacity (Cp) directly affects its temperature change rate. Accurate measurement of the specific heat capacity of batteries (especially cells) can provide core data support for thermal model construction, temperature prediction, and heat dissipation design.

[0004] Currently, common battery specific heat capacity testing methods mainly include constant temperature heating method, adiabatic method or natural cooling method, such as Chinese patents with publication numbers 2024113660041 and 2023110534470. However, these methods have the following problems: (1) long test cycle: it takes several hours or even longer to wait for the system to reach thermal equilibrium; (2) high environmental dependence: it is affected by the ambient temperature and other factors, resulting in data deviation; (3) limited test objects: most methods are for finished batteries (including shell, electrolyte, etc.), which cannot reflect the real thermal characteristics of the battery cell and do not match the internal temperature prediction requirements. Summary of the Invention

[0005] The purpose of this invention is to provide a method for testing the specific heat capacity of lithium battery cells, so as to solve the problems in the background art mentioned above.

[0006] The technical solution adopted in this invention includes: a method for testing the specific heat capacity of a lithium battery cell, comprising the following steps:

[0007] The specific heat capacity of the battery cell sample was tested using a differential scanning calorimeter, and the specific heat capacity curve of the battery cell sample was obtained.

[0008] According to the formula Calculate the specific heat capacity of the battery cell sample;

[0009] Where: C p The specific heat capacity of the battery cell sample. The value of the specific heat capacity at the i-th specific temperature is read from the specific heat capacity curve of the cell sample, and n is the total number of specific temperatures.

[0010] Preferred, T max <T 相变 T max T represents the maximum test temperature of the specific heat capacity curve of the battery cell sample. 相变 The solid-liquid phase transition temperature is the temperature of the system within the battery cell sample.

[0011] Preferred, T max <T 质变 T max T represents the maximum test temperature of the specific heat capacity curve of the battery cell sample. 质变 The temperature at which a chemical reaction occurs within the battery cell sample, resulting in a qualitative change.

[0012] Preferably, the sampling method for the battery cell sample includes:

[0013] Disassemble the lithium battery to obtain the target cell;

[0014] At least one repeating unit along the thickness direction of the target cell is selected as the cell sample.

[0015] Preferably, the lithium battery is the target battery, or a product battery or verification battery with the same cell manufacturing process as the target battery.

[0016] Preferably, the lithium battery is a lithium-ion battery, a lithium metal battery, a polymer lithium battery, a semi / quasi-solid-state lithium battery, a solid-state lithium battery, or a primary lithium battery.

[0017] Preferably, the battery cell sample is weighed, and the weighed battery cell sample is placed into a test container and sealed; the test container is an aluminum crucible, a stainless steel crucible, a copper crucible, or a ceramic crucible.

[0018] Preferably, when testing the specific heat capacity of the battery cell sample using a differential scanning calorimeter, either a direct method or an indirect method is employed.

[0019] The beneficial effects of this invention are as follows: By designing the cell sampling method and using differential scanning calorimetry to rapidly measure the specific heat capacity of the cell, it solves the problems of existing battery specific heat capacity testing methods being time-consuming due to the inclusion of a thermal equilibrium process and having significant testing deviations due to the large influence of environmental conditions. Furthermore, this invention directly measures the specific heat capacity of the cell, which can be more directly used for temperature prediction and control strategies within the battery, avoiding errors introduced by using the battery's specific heat capacity. Attached Figure Description

[0020] Figure 1 This is the specific heat capacity curve of the NCM523 / C cell sample measured in Example 1 of the present invention. Detailed Implementation

[0021] The embodiments of the present invention are described in detail below.

[0022] This invention provides a method for testing the specific heat capacity of a lithium battery cell, comprising the following steps:

[0023] (1) Sampling:

[0024] Disassemble the lithium battery to obtain the target cell;

[0025] At least one repeating unit along the thickness direction of the target cell is selected as the cell sample.

[0026] The proportions of each component in the aforementioned repeating unit are consistent with those of the target cell.

[0027] (2) Weighing and packaging:

[0028] Weigh the battery cell sample to ensure it meets the sample mass range requirements of the differential scanning calorimeter;

[0029] The weighed battery cell sample is placed in a sealed test container, which is made of a material that does not chemically react with the lithium battery cell, such as an aluminum crucible, stainless steel crucible, copper crucible, or ceramic crucible.

[0030] (3) Test to obtain the specific heat capacity curve of the cell sample:

[0031] The test container containing the battery cell sample is placed in a differential scanning calorimeter, and the specific heat capacity of the battery cell sample is tested using either a direct or indirect method to obtain the specific heat capacity curve of the battery cell sample.

[0032] The direct and indirect methods described above are standard test methods for determining the specific heat capacity of substances using differential scanning calorimetry, and are existing technologies. Therefore, the details will not be elaborated here.

[0033] (4) Calculate the specific heat capacity of the battery cell sample:

[0034] According to the formula Calculate the specific heat capacity of the battery cell sample;

[0035] Where: C p The specific heat capacity of the battery cell sample. The value of the specific heat capacity at the i-th specific temperature is read from the specific heat capacity curve of the cell sample, and n is the total number of specific temperatures.

[0036] It is worth noting that when obtaining the specific heat capacity curve of the battery cell sample using a differential scanning calorimeter in step (3), the test temperature should be controlled within a range where the physical and chemical properties of the battery cell sample are stable. A preferred design is: T max <T 相变 T max T represents the maximum test temperature of the specific heat capacity curve of the battery cell sample. 相变 Let T be the solid-liquid phase transition temperature of the system within the battery cell sample, and: max <T质变 T 质变 The temperature at which a chemical reaction occurs within the battery cell sample, resulting in a qualitative change.

[0037] Different lithium batteries have different cell system stability, as mentioned above (T). 相变 and T 质变 These parameters may vary, and researchers can determine the parameters themselves based on the composition system of the lithium battery cell to which this method is applicable.

[0038] This method is applicable to all chemical batteries characterized by changes in the valence state of lithium, including lithium-ion batteries, lithium metal batteries, polymer lithium batteries, semi / quasi-solid-state lithium batteries, solid-state lithium batteries, and primary lithium batteries.

[0039] When sampling in step (1), the disassembled lithium battery can be the target battery, or it can be a product battery or a verification battery from another batch or model with the same cell manufacturing process as the target battery.

[0040] This invention addresses the problems of existing battery specific heat capacity testing methods, which are time-consuming due to the inclusion of a thermal equilibrium process and suffer from significant testing deviations due to the influence of environmental conditions, by employing a cell sampling design and differential scanning calorimetry method for rapid measurement of cell specific heat capacity. Furthermore, this invention directly measures the cell's specific heat capacity, allowing for more direct application to battery internal temperature prediction and control strategies, thus avoiding errors introduced by relying solely on the battery's specific heat capacity.

[0041] The following are specific embodiments of the present invention.

[0042] Example 1

[0043] (1) Sampling:

[0044] Disassemble the 3.8Ah NCM523 / C soft-pack lithium battery, remove the soft-pack outer shell and outer separator to obtain the target cell (system is NCM523 / C);

[0045] A repeating unit along the thickness direction of the target cell is selected, and a sampler is used to obtain multiple samples of different areas, which are used as cell samples.

[0046] (2) Weighing and packaging:

[0047] Weigh the battery cell sample, select a battery cell sample with the same mass as the comparison standard sample, and seal it in a stainless steel crucible.

[0048] (3) Test to obtain the specific heat capacity curve of the cell sample:

[0049] The test container containing the battery cell sample was placed in a differential scanning calorimeter. Using a sapphire standard as a reference, the specific heat capacity of the battery cell sample was tested indirectly. The test temperature range was -30 to 50℃, and the heating rate was 5℃ / min. The specific heat capacity curve of the battery cell sample was obtained (see attached figure). Figure 1 ).

[0050] (4) Calculate the specific heat capacity of the battery cell sample:

[0051] Specific temperature points were selected from the specific heat capacity curves of the battery cell samples, and their specific heat capacity values ​​were read. The data are shown in Table 1.

[0052] Table 1. Specific heat capacity values ​​at specific temperatures.

[0053] Serial Number Specific temperature / °C <![CDATA[Specific heat capacity value / J·K -1 ·g -1 > 1 -20 0.99916 2 -15 1.01486 3 -10 1.02769 4 -5 1.03738 5 0 1.04781 6 5 1.05511 7 10 1.06398 8 15 1.07305 9 20 1.07544 10 25 1.08683 11 30 1.09655 12 35 1.10541 13 40 1.11325

[0054] Substitute the data from Table 1 into the formula. In the calculation, the specific heat capacity of the NCM523 / C cell sample is 1061.27 J·K. -1 ·kg -1 .

[0055] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the claims, or equivalent forms of such scope and boundaries.

Claims

1. A method for testing the specific heat capacity of a lithium battery cell, characterized in that, Including the following steps: The specific heat capacity of the battery cell sample was tested using a differential scanning calorimeter, and the specific heat capacity curve of the battery cell sample was obtained. According to the formula Calculate the specific heat capacity of the battery cell sample; Where: C p The specific heat capacity of the battery cell sample. The value of the specific heat capacity at the i-th specific temperature is read from the specific heat capacity curve of the cell sample, and n is the total number of specific temperatures.

2. The method for testing the specific heat capacity of a lithium battery cell according to claim 1, characterized in that, T max <T 相变 T max T represents the maximum test temperature of the specific heat capacity curve of the battery cell sample. 相变 The solid-liquid phase transition temperature is the temperature of the system within the battery cell sample.

3. The method for testing the specific heat capacity of a lithium battery cell according to claim 1 or 2, characterized in that, T max <T 质变 T max T represents the maximum test temperature of the specific heat capacity curve of the battery cell sample. 质变 The temperature at which a chemical reaction occurs within the battery cell sample, resulting in a qualitative change.

4. The method for testing the specific heat capacity of a lithium battery cell according to claim 3, characterized in that, The sampling methods for battery cell samples include: Disassemble the lithium battery to obtain the target cell; At least one repeating unit along the thickness direction of the target cell is selected as the cell sample.

5. The method for testing the specific heat capacity of a lithium battery cell according to claim 4, characterized in that, The target battery is a lithium battery, or a product battery or verification battery with the same cell manufacturing process as the target battery.

6. The method for testing the specific heat capacity of a lithium battery cell according to claim 4 or 5, characterized in that, Lithium batteries include lithium-ion batteries, lithium metal batteries, polymer lithium batteries, semi / quasi-solid-state lithium batteries, solid-state lithium batteries, or primary lithium batteries.

7. The method for testing the specific heat capacity of a lithium battery cell according to claim 6, characterized in that, Weigh the battery cell sample and then place the weighed sample into a test container and seal it. The test container can be an aluminum crucible, a stainless steel crucible, a copper crucible, or a ceramic crucible.

8. The method for testing the specific heat capacity of a lithium battery cell according to any one of claims 1-2, 4-5, and 7, characterized in that, When testing the specific heat capacity of a battery cell sample using a differential scanning calorimeter, either the direct method or the indirect method can be used.

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