A stress signal-based early warning method for thermal runaway of lithium battery

Abstract

The application discloses a kind of early warning methods of lithium battery thermal runaway based on stress signal, belong to lithium battery safety field.The method is by monitoring the surface stress of battery, proposes a new early warning method of thermal runaway.The film pressure sensor is arranged in advance on the surface of battery, the stress change in the process of thermal runaway is divided into four stages of exponential growth, linear growth, sudden drop and rebound, and by identifying the turning point of stress from exponential growth to linear growth, corresponding to the turning point of stress change rate from linear growth to platform, early thermal runaway 30 minutes can be warned.Compared with the traditional early warning method, the application greatly improves the warning time, and provides more time for personnel evacuation and rescue.In addition, the application provides guidance for the layout of the pressure sensor according to the stress distribution on the surface of the battery, which greatly reduces the cost.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of lithium ion battery safety, and particularly relates to a stress signal-based early warning method for thermal runaway of a lithium battery. BACKGROUND

[0002] With the increasing depletion of non-renewable resources such as oil, there is an urgent need for a new energy source to replace traditional fossil fuels. Lithium ion batteries have received increasing attention due to their high energy density, long life and ecological friendliness.

[0003] However, with the widespread use of lithium batteries, incidents of lithium battery thermal runaway have occurred, exposing the safety hazards of lithium batteries and restricting their further development. At the same time, the thermal runaway of lithium ion batteries is highly concealed and difficult to predict. Once it occurs, the consequences are serious and can pose a threat to people's life and property safety. Therefore, there is an urgent need for a convenient and effective method to identify and warn of battery thermal runaway in advance.

[0004] Traditional thermal runaway detection techniques mainly rely on voltage, current, temperature and gas production parameters, but these methods have obvious limitations. For example, the gas-based warning method is often not timely, because gas emission can only be detected after the battery safety valve is opened, and the warning at this time is too late. SUMMARY

[0005] To solve the above technical problems, the application provides a stress signal-based early warning method for thermal runaway of a lithium battery, which significantly improves the early warning time of thermal runaway 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 the sensor is optimized to reduce the monitoring cost.

[0006] To achieve the above purpose, the technical scheme adopted by the application is as follows:

[0007] A stress signal-based early warning method for thermal runaway of a lithium battery, comprising the following steps:

[0008] S01, a thin film pressure sensor is used 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 surface of the battery;

[0009] S02, the thin film pressure sensor is used to obtain real-time stress data and distribution of the battery surface, achieving high-precision stress monitoring;

[0010] S03, based on the detected stress data, an interpolation differential method is used to calculate the derivative of stress with respect to time, i.e. the stress change rate;

[0011] S04, based on the law of stress and stress rate of change, identify abnormal stress change trend, and then realize the early warning of lithium battery thermal runaway;

[0012] S05, analyze the stress distribution, and further optimize the layout of the sensor based on the analysis result.

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

[0014] Further, the thin film pressure sensor should be pressed on the battery using a relatively soft material and exert a pre-warning force to ensure that the thin film pressure sensor and the battery surface can be closely attached.

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

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

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

[0018] Further, the layout of the sensor should focus on the area where the stress of the battery surface is large.

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

[0020] 1. In the present application, the thin film pressure sensor is directly arranged on the battery surface, and only a certain pre-warning force needs to be exerted to accurately monitor the stress of the battery, thereby reducing the construction difficulty.

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

[0022] 3. The present application divides the stress change into four stages based on the law of stress and stress rate of change, each stage corresponds to a different development process of battery thermal runaway, so the current stress change law can be used to conveniently indicate the state of the battery.

[0023] 4、The stress distribution analysis can optimize the layout of the thin film pressure sensor, greatly reducing the coverage area and use cost of the sensor.

[0024] 5、The early warning method of lithium battery thermal runaway based on stress signals realizes early warning of lithium battery thermal runaway, compared with the traditional thermal runaway detection method, greatly improves the early warning time of thermal runaway, provides sufficient time for personnel evacuation and rescue, and kills the lithium battery thermal runaway accident in the embryonic state. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The flowchart of the early warning method of lithium battery thermal runaway based on stress signals in the application.

[0026] Figure 2 The assembly scheme of the battery in the embodiment of the application.

[0027] Figure 3 The point distribution diagram of the thin film pressure sensor in the embodiment of the application.

[0028] Figure 4 The stress and stress change rate-time curve of the 280Ah lithium iron phosphate battery in the heating-induced thermal runaway process in the embodiment of the application.

[0029] Figure 5 The stress and stress change rate curve before the opening of the safety valve of the battery and the warning mark schematic diagram in the embodiment of the application.

[0030] Figure 6 The stress distribution diagram at the moment when the surface stress is maximum before the opening of the safety valve in the embodiment of the application, wherein (a) shows the specific stress value of each point, and (b) is a smooth diagram of (a). DETAILED DESCRIPTION

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

[0032] As shown in the figure, the early warning method of lithium battery thermal runaway based on stress signals in the embodiment of the application comprises the following steps: Figure 1 S01, a thin film pressure sensor is used to cover the length and width of the battery and a pre-tightening force is applied to ensure the close contact between the thin film pressure sensor and the surface of the battery, comprising:

[0033]

[0034] ​According to the size of the battery length and width, a thin film pressure sensor of the same size is customized, and the number of point positions is set according to the experimental requirements. In the embodiment of the present application, the thin film pressure sensor is evenly divided into 5*6, a total of 30 equal point positions, each of which can independently and synchronously detect the stress of the corresponding area, as shown in FIG. 1. Figure 2 As shown in FIG. 2, the battery, the heating plate, the thin film pressure sensor, the heat insulation cotton, the steel clamp and other equipment are assembled in the order shown in FIG. 2, and a pre-tightening force is applied to ensure the close contact between the thin film pressure sensor and the surface of the battery. Among them, the battery is arranged in the middle layer, and the thin film pressure sensor, the heat insulation cotton and the steel clamp are arranged from inside to outside on one side of the battery, and the heating plate, the heat insulation cotton and the steel clamp are arranged from inside to outside on the other side of the battery. Figure 3 As shown in FIG. 2, the battery, the heating plate, the thin film pressure sensor, the heat insulation cotton, the steel clamp and other equipment are assembled in the order shown in FIG. 2, and a pre-tightening force is applied to ensure the close contact between the thin film pressure sensor and the surface of the battery. Among them, the battery is arranged in the middle layer, and the thin film pressure sensor, the heat insulation cotton and the steel clamp are arranged from inside to outside on one side of the battery, and the heating plate, the heat insulation cotton and the steel clamp are arranged from inside to outside on the other side of the battery.

[0035] S02, using the thin film pressure sensor, real-time and accurate stress data and distribution of the battery surface are obtained, and high-precision stress monitoring is realized, including:

[0036] The thin film pressure sensor is connected to the computer using the pressure distribution measuring instrument, and the stress data and distribution are recorded in real time using the pressure distribution measuring software.

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

[0038] Using the stress data collected based on the thin film pressure sensor, a stress curve is drawn, and the stress data is interpolated and differentiated with respect to time, an image of the stress change rate is drawn, and the change law of the stress and the stress change rate is analyzed, as shown in FIG. 3, wherein Figure 4 represents the stress, represents the stress change rate.

[0039] S04, based on the law of stress and stress change rate, the abnormal stress change trend is identified, and early warning of lithium battery thermal runaway is realized, including:

[0040] Using the change law that the stress change rate changes from linear growth to platform before the safety valve is opened, the stress drops sharply after the safety valve is opened, and the stress rebounds when thermal runaway occurs, the stress evolution in the thermal runaway process is divided into four stages of exponential growth, linear growth, sudden drop and rebound, and the turning point of the stress from exponential growth to linear growth is determined as the starting point of the warning, which corresponds to the turning point of the stress change rate from linear growth to platform.

[0041] S05, the stress distribution is analyzed, and based on the analysis result, the layout of the sensor is further optimized, including:

[0042] ​The stress distribution collected by the thin film pressure sensor is used to extract the moment when the stress is the largest before the safety valve opens, analyze the stress distribution at this moment, determine the positions where the stress is the largest, and optimize the layout of the sensor.

[0043] Embodiments:

[0044] Taking a certain type of 280 Ah lithium iron phosphate battery monomer as an example, first, according to the formula Figure 3 , the experimental device is arranged. The heating plate is used to heat the lithium battery, the thin film pressure sensor is used to obtain the stress data and distribution of the battery surface, then the stress is interpolated and differentiated to obtain the stress change rate, and the abnormal stress change trend is identified to give an early warning of the battery thermal runaway, which specifically includes:

[0045] S01, the heating plate with the same size as the length and width of the battery and the maximum power of 500W is arranged on one side of the battery surface, and the thin film pressure sensor with the same size as the length and width of the battery and the number of points of 30 is arranged on the other side of the battery surface, as shown in Figure 2 , the thin film pressure sensor, the battery and the heating plate are surrounded by heat insulation cotton, and the fixture is used to fix them and apply pre-tightening force to ensure the close contact between the thin film pressure sensor and the battery surface;

[0046] S02, the thin film pressure sensor is connected to the computer through the pressure distribution measuring instrument, and the pressure distribution measuring software is used to record the stress data and distribution in real time;

[0047] S03, based on the stress data in the thermal runaway process of the lithium battery monomer, the stress change rate is obtained by interpolation and differentiation, and the images of stress and stress change rate are drawn, as shown in Figure 4 .

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

[0049] S05, the stress distribution at the moment when the stress is the largest before the safety valve opens is extracted, as shown in Figure 6 , wherein Figure 6 (a) shows the specific stress value of each point, Figure 6 (b) is the smooth graph of (a) of Figure 6 . By analyzing the stress distribution at this moment, it is found that the stress distribution on the surface of the battery presents a trend of weak around and strong in the middle, and Figure 6The stress in the area encircled by the middle black frame is relatively high, and therefore the layout of the thin film stress sensor can be optimized according to the above situation, and the area with high stress can be covered.

[0050] The specific embodiments of the present application are described in detail above, which are intended to help the skilled in the art to better understand. The accompanying drawings only show one embodiment of the present application, which is intended to illustrate its structure and principle. Therefore, the skilled in the art can make reasonable modifications or replacements to the present application on the basis of understanding the present application, without deviating from the creative spirit and technical scope of the present application, and design similar technical solutions and embodiments, which should all belong to the protection scope of the present application.

Claims

1. A method for early warning of thermal runaway in lithium batteries based on stress signals, characterized in that, Based on the development patterns of stress and stress change rates, stress changes are divided into four stages, each corresponding to a different development process of battery thermal runaway. By analyzing the current stress change patterns, the battery's current state is determined, including the following steps: S01. A thin-film pressure sensor is used to cover the surface of the battery, and a pre-tightening force is applied to ensure close contact between the thin-film pressure sensor and the battery surface. S02. Real-time stress data and distribution on the battery surface are obtained using a thin-film pressure sensor to achieve high-precision stress monitoring. S03. Based on the stress data obtained from the detection, the derivative of stress with respect to time, i.e. the rate of stress change, is calculated using the interpolation differential method. S04. Based on the laws of stress and stress change rate, identify abnormal stress change trends, thereby achieving early warning of lithium battery thermal runaway. S05. Analyze the stress distribution and, based on the analysis results, further optimize the sensor layout.

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

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

4. The method for early warning of lithium battery thermal runaway based on stress signals 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, while the rough surface is used to clearly display the distribution of sensor sites.

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

6. The method for early warning of lithium battery thermal runaway based on stress signals 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 synchronously and in real time monitor the stress in its own area.

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

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