Lithium battery thermal runaway early warning method based on stress signal

Abstract

The invention discloses a lithium battery thermal runaway early warning method based on a stress signal, and belongs to the field of lithium battery safety. According to the method, the surface stress of the battery is monitored, and a novel thermal runaway early warning method is provided. A thin film pressure sensor is arranged on the surface of a battery in advance, the stress change in the thermal runaway process is divided into four stages of exponential growth, linear growth, sudden drop and rebound, and a turning point of stress from the exponential growth to the linear growth corresponds to a turning point of stress change rate from the linear growth to a platform. And early warning can be carried out 30 minutes in advance of thermal runaway. Compared with a traditional early warning method, the early warning time is greatly shortened, and more time is provided for personnel evacuation and rescue. Besides, according to the stress distribution condition of the surface of the battery, guidance is provided for the layout of the pressure sensors, and the cost is greatly reduced.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-ion battery safety, and in particular relates to a stress signal-based lithium battery thermal runaway early warning method. Background Art

[0002] With the increasing depletion of non-renewable resources such as oil, a new energy source is urgently needed to replace traditional fossil fuels. Lithium-ion batteries have attracted more and more attention due to their advantages such as high energy density, long life and eco-friendliness.

[0003] However, with the widespread use of lithium batteries, thermal runaway incidents of lithium batteries have emerged one after another, exposing the potential safety hazards of lithium batteries and restricting their further development. At the same time, thermal runaway of lithium-ion batteries is highly hidden and difficult to predict. Once it occurs, the consequences are serious and will threaten people's lives and property. Therefore, there is an urgent need for a convenient and effective method to identify and warn of thermal runaway of batteries in advance.

[0004] Traditional thermal runaway detection technologies mainly rely on parameters such as voltage, current, temperature and gas production, but these methods have obvious limitations. For example, the early warning method based on gas production is often not timely enough, because the gas emission can only be detected after the battery safety valve is opened, and it is too late to issue an early warning at this time. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a stress signal-based lithium battery thermal runaway early warning method, which significantly improves the thermal runaway early warning time by innovatively using a thin film pressure sensor, providing sufficient time for personnel evacuation and rescue. At the same time, according to the distribution of stress, the arrangement of sensors is optimized to reduce monitoring costs.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A stress signal-based lithium battery thermal runaway early warning method comprises the following steps:

[0008] S01. Use a thin film pressure sensor to cover the surface of the battery and apply a pre-tightening force to ensure close contact between the thin film pressure sensor and the battery surface;

[0009] S02. Use thin film pressure sensors to obtain real-time stress data and distribution on the battery surface to achieve high-precision stress monitoring;

[0010] S03. Based on the stress data obtained by the detection, the derivative of stress with respect to time, i.e., the stress change rate, is calculated by using the interpolation differential method;

[0011] S04. Based on the rules of stress and stress change rate, identify abnormal stress change trends, and then achieve early warning of thermal runaway of lithium batteries;

[0012] S05. Analyze the stress distribution and further optimize the layout of the sensors based on the analysis results.

[0013] Furthermore, the battery surface to which the thin film pressure sensor is attached should be the length and width of the battery, so as to more accurately obtain the stress data and distribution of the battery surface.

[0014] Furthermore, the thin film pressure sensor should be pressed on the battery using a relatively soft material and exert a warning force to ensure that the thin film pressure sensor and the battery surface can fit tightly.

[0015] Furthermore, the stress change trend is divided into four stages, namely exponential growth, linear growth, sudden drop and rebound. The exponential growth stage of stress is caused by the evaporation of the electrolyte, the linear growth of stress is the result of the coupling effect of electrolyte evaporation and gas production by side reactions, the sudden drop of stress is caused by the exhaust after the safety valve is opened, and the stress rebound is the result of thermal runaway of the battery.

[0016] Furthermore, the abnormal stress change trend should be the turning point from exponential growth to linear growth of stress, that is, the turning point from the linear growth stage to the platform stage of the stress change rate.

[0017] Furthermore, the stress distribution should focus on the stress distribution at the moment of maximum stress before the safety valve is opened.

[0018] Furthermore, the layout of the sensors should focus on areas with greater stress on the battery surface.

[0019] The beneficial effects of the present invention compared with the prior art are:

[0020] 1. In the present invention, the thin film pressure sensor is directly arranged on the surface of the battery, and the stress of the battery can be accurately monitored by applying a certain warning force, which reduces the difficulty of construction.

[0021] 2. In the present invention, compared with the traditional pressure sensor, the thin film pressure sensor can more conveniently divide the battery surface into different areas, making up for the deficiency that the traditional pressure sensor is difficult to obtain the distribution of battery surface stress.

[0022] 3. Based on the development law of stress and stress change rate, the present invention divides stress change into four stages. Each stage corresponds to a different development process of battery thermal runaway. Therefore, the state of the battery can be conveniently pointed out by the current stress change law.

[0023] 4. In the present invention, by analyzing the distribution of stress, the layout of the thin film pressure sensor can be optimized, which greatly reduces the coverage area and use cost of the sensor.

[0024] 5. The present invention realizes the early warning of thermal runaway of lithium battery cells through the early warning method of thermal runaway of lithium battery based on stress signal. Compared with the traditional thermal runaway detection method, it greatly improves the early warning time of thermal runaway, provides sufficient time for personnel evacuation and rescue, and nip the thermal runaway accident of lithium battery in the bud. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The present invention is a flowchart of a lithium battery thermal runaway early warning method based on stress signals.

[0026] Figure 2 It is a schematic diagram of the assembly scheme of the battery in the embodiment of the present invention.

[0027] Figure 3 Schematic diagram of the point distribution of the thin film pressure sensor in the embodiment of the present invention.

[0028] Figure 4 It is a curve diagram of stress and stress change rate over time of a 280Ah lithium iron phosphate battery during heating-induced thermal runaway in an embodiment of the present invention.

[0029] Figure 5 It is a curve of stress and stress change rate before the battery safety valve is opened and a schematic diagram of a warning sign in an embodiment of the present invention.

[0030] Figure 6 1 is a stress distribution diagram of the moment when the surface stress is maximum before the safety valve is opened in an embodiment of the present invention, wherein (a) shows the specific stress value of each point, and (b) is a smoothed graph of (a). DETAILED DESCRIPTION

[0031] In order to make the purpose, features, technical methods and advantages of the present invention easier to understand, the specific implementation scheme of the present invention will be clearly and detailedly described below in conjunction with the preferred embodiments of the present invention. However, the protection scope of the present invention is not limited to the following embodiments.

[0032] like Figure 1 As shown, a stress signal-based early warning method for thermal runaway of a lithium battery according to an embodiment of the present invention comprises the following steps:

[0033] S01. Use a thin film pressure sensor to cover the length and width of the battery and apply a preload to ensure close contact between the thin film pressure sensor and the battery surface, including:

[0034] According to the length and width of the battery, a thin film pressure sensor of the same size is customized, and the number of points is set according to the experimental requirements. In the embodiment of the present invention, the thin film pressure sensor is evenly divided into 5×6, a total of 30 points of equal size, each point can independently and synchronously detect the stress of the corresponding area, such as Figure 2 As shown, they are numbered 1-1 to 6-5. Put the battery, heating plate, film pressure sensor, insulation cotton, steel fixture and other equipment in Figure 3 The assembly is performed in the order shown, and a pre-tightening force is applied to ensure close contact between the thin film pressure sensor and the battery surface. The battery is arranged in the middle layer, and a thin film pressure sensor, thermal insulation cotton, and a steel clamp are arranged on one side of the battery from the inside to the outside, and a heating plate, thermal insulation cotton, and a steel clamp are arranged on the other side of the battery from the inside to the outside.

[0035] S02. Use thin film pressure sensors to obtain real-time and accurate stress data and distribution on the battery surface to achieve high-precision stress monitoring, including:

[0036] Use the pressure distribution measuring instrument to connect the thin film pressure sensor to the computer, and use the pressure distribution measurement software to record the stress data and distribution in real time.

[0037] S03. Based on the stress data obtained by the test, the derivative of stress with respect to time, i.e., the stress change rate, is calculated by using the interpolation differential method, including:

[0038] The stress data collected by the thin film pressure sensor is used to draw the stress curve. At the same time, the stress data is interpolated and differentiated with respect to time to draw the image of the stress change rate, and the changing law of stress and stress change rate is analyzed, such as Figure 4 As shown, represents stress, Represents the rate of change of stress.

[0039] S04. Based on the rules of stress and stress change rate, identify abnormal stress change trends, and then achieve early warning of thermal runaway of lithium batteries, including:

[0040] By using the changing rules of the stress change rate from linear growth to platform before the safety valve is opened, the stress sudden drop after the safety valve is opened, and the stress recovery during thermal runaway, the stress evolution in the thermal runaway process is divided into four stages: exponential growth, linear growth, sudden drop and rebound. The turning point from exponential growth to linear growth is determined as the starting point of early warning, which corresponds to the turning point of the stress change rate from linear growth to platform.

[0041] S05. Analyze the stress distribution and further optimize the sensor layout based on the analysis results, including:

[0042] By using the stress distribution collected by the thin film pressure sensor, the moment when the stress is maximum before the safety valve is opened is extracted, the stress distribution at this moment is analyzed, the several locations with the maximum stress are determined, and the layout of the sensor is optimized.

[0043] Example:

[0044] Take a 280Ah lithium iron phosphate battery cell as an example. First, follow Figure 3 Arrange the experimental device. Use a heating plate to heat the lithium battery, use a thin film pressure sensor to obtain the stress data and distribution on the battery surface, then interpolate and differentiate the stress to obtain the stress change rate, identify abnormal stress change trends, and issue an early warning for battery thermal runaway, including:

[0045] S01. Arrange a heating plate with a maximum power of 500W and the same size of the battery length and width on the surface of one side of the battery, and arrange a thin film pressure sensor with the same size of the battery length and width and 30 points on the surface of the other side, such as Figure 2 As shown, the thin film pressure sensor, the battery and the heating plate are surrounded by heat insulating cotton, and fixed by a clamp, and a pre-tightening force is applied to ensure close contact between the thin film pressure sensor and the battery surface;

[0046] S02. Connect the thin film pressure sensor to the computer through the pressure distribution measuring instrument, and use the pressure distribution measurement software to record the stress data and distribution in real time;

[0047] S03. Perform interpolation differentiation based on the stress data during the thermal runaway process of the lithium battery cell to obtain the stress change rate, and draw images of stress and stress change rate, such as Figure 4 shown.

[0048] S04. Analysis found that the stress changes in the thermal runaway process can be divided into four stages: exponential growth, linear growth, sudden drop and rebound. The turning point from exponential growth to linear growth of stress is determined as the starting point of the warning, which corresponds to the turning point from linear growth to platform of stress change rate. The starting point of the warning can be 30 minutes in advance of thermal runaway. Figure 5 As shown, "Stage 1" is the stress exponential growth stage, and "Stage 2" is the stress linear growth stage;

[0049] S05. Extract the stress distribution at the moment when the stress is maximum before the safety valve is opened, such as Figure 6 As shown, Figure 6 (a) shows the specific stress value at each point. Figure 6 (b) is Figure 6 Analyzing the stress distribution at this moment, it is found that the stress distribution on the battery surface shows a trend of being weak around the edges and strong in the middle, and Figure 6The stress in the area circled by the black frame is relatively high. Therefore, the layout of the thin film stress sensor can be optimized according to the above situation, focusing on covering the area with higher stress.

[0050] The above detailed description of the specific implementation of the present invention is intended to help those skilled in the art to better understand. The accompanying drawings only show one implementation of the present invention, which is intended to illustrate its structure and principle. Therefore, those skilled in the art can reasonably modify or replace the present invention without departing from the creative spirit and technical scope of the present invention on the basis of understanding the present invention, and design technical solutions and embodiments similar to the present invention, which should all fall within the protection scope of the present invention.

Claims

1. A stress signal-based lithium battery thermal runaway early warning method, characterized in that: The steps include: S01. Use a thin film pressure sensor to cover the surface of the battery and apply a pre-tightening force to ensure close contact between the thin film pressure sensor and the battery surface; S02. Use thin film pressure sensors to obtain real-time stress data and distribution on the battery surface to achieve high-precision stress monitoring; S03. Based on the stress data obtained by the detection, the derivative of stress with respect to time, i.e., the stress change rate, is calculated by using the interpolation differential method; S04. Based on the rules of stress and stress change rate, identify abnormal stress change trends, and then achieve early warning of thermal runaway of lithium batteries; S05. Analyze the stress distribution and further optimize the layout of the sensors based on the analysis results.

2. The early warning method for thermal runaway of a lithium battery based on a stress signal according to claim 1, characterized in that: By identifying the turning point of the stress change rate, a warning of thermal runaway can be given 30 minutes in advance.

3. The early warning method for thermal runaway of a lithium battery based on a stress signal according to claim 1, characterized in that: The thin film pressure sensor comprises two layers of flexible thin film materials, the upper layer is a pressure-sensitive functional film, and the lower layer is an electrode film.

4. The early warning method for thermal runaway of a lithium battery based on a stress signal according to claim 1, characterized in that: The surface of the thin film pressure sensor is divided into a smooth surface and a rough surface. The smooth surface is attached to the battery surface to improve the accuracy of stress readings, and the rough surface is used to clearly display the distribution of sensor sites.

5. The early warning method for thermal runaway of a lithium battery based on a stress signal according to claim 3, characterized in that: A thin film pressure sensor is installed on the surface of the battery to monitor the stress changes of the battery in real time during thermal runaway.

6. The early warning method for thermal runaway of a lithium battery based on a stress signal according to claim 1, characterized in that: The battery surface is divided into multiple small units according to the specifications of the thin film pressure sensor, and each unit can monitor the stress in its respective area synchronously and in real time.

7. The early warning method for thermal runaway of a lithium battery based on a stress signal according to claim 1, characterized in that: In S05, the moment when the surface stress reaches the maximum before the safety valve is opened is extracted, the stress distribution at this moment is analyzed, and the layout of the sensors is optimized accordingly.

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