A system and method for rapid identification of potential thermal runaway in lithium batteries

Abstract

A system and method for quickly identifying potential thermal runaway lithium battery cells, the battery module is composed of series-connected lithium battery cells, each lithium battery cell is built-in with a temperature sensor, including the steps: 1, measuring the terminal voltage of the lithium battery cell, calculating the voltage change rate Ei, finding the median value Em, then obtaining the voltage characteristic value Xi=Ei-Em of each lithium battery cell, when the absolute value |Xi| of the voltage characteristic value of any lithium battery cell >= threshold value, it is judged that the lithium battery cell will occur thermal runaway; 2, measuring the internal temperature of the lithium battery cell, calculating the temperature change rate Di, finding the median value Dm, then obtaining the temperature characteristic value Yi=Di-Dm of each lithium battery cell, when the absolute value |Yi| of the temperature characteristic value of any lithium battery cell >= threshold value, thermal runaway will occur; or 3, both the characteristic values of steps 1 and 2 are greater than the threshold value, it is determined that the lithium battery cell is a potential thermal runaway; step 4, determination of the threshold value, the threshold value is determined before the lithium battery leaves the factory. The application can timely early warning, avoid further property loss, and maximize the safety of the host operator and the surrounding personnel.

Description

Technical Field

[0001] This invention relates to the field of lithium batteries, specifically to a system and method for rapidly identifying potential thermal runaway lithium battery cells to prevent spontaneous combustion due to abnormal temperature rise. Here, lithium batteries refer to batteries whose positive electrode material contains lithium, therefore all-solid-state and semi-solid-state batteries are also included. Background Technology

[0002] With the increasing use of rechargeable lithium batteries, their safe use has naturally become a major concern. In reality, in addition to extreme cases of battery combustion caused by collisions, battery defects caused by manufacturing processes may also lead to spontaneous combustion. In the early stages of a battery's potential for spontaneous combustion or if it has already spontaneously combusted, effectively cooling or extinguishing it can greatly prevent the situation from escalating and protect the lives and property of consumers. Early judgment and warning of such lithium battery thermal runaway are of paramount importance. Summary of the Invention

[0003] This invention provides a system and method for rapidly identifying lithium-ion battery cells with potential thermal runaway.

[0004] This method for rapidly identifying lithium-ion battery cells with potential thermal runaway includes a battery module composed of several lithium-ion battery cells connected in series. Each lithium-ion battery cell contains a temperature sensor, which is placed in a cavity below the explosion-proof sheet on the top cover of the lithium-ion battery cell. The method for identifying lithium-ion battery cells with potential thermal runaway includes the following steps: Step 1: Measure the terminal voltage of each lithium cell in the battery module, calculate the voltage change rate Ei of each lithium cell, find the median value Em of the voltage change rate, and then the voltage characteristic value Xi of each lithium cell is Xi = Ei - Em. When the absolute value of the voltage characteristic value of any lithium cell in the module, |Xi| >= the threshold, it can be determined that this lithium cell has an internal short circuit and will experience thermal runaway.

[0005] Step 2: Measure the internal temperature of each lithium cell in the battery module, calculate the temperature change rate Di of each lithium cell (the temperature rise during discharge is generally called the temperature rise rate), find the median value Dm of the temperature change rate, and then the temperature characteristic value Yi of each lithium cell is Yi = Di - Dm. When the absolute value of the temperature characteristic value of any lithium cell in the module, |Yi|, is greater than or equal to the threshold, it can be determined that this lithium cell has an internal short circuit and will experience thermal runaway.

[0006] Step 3, threshold determination: The threshold is determined before the lithium battery leaves the factory by measuring the temperature change rate and voltage change rate of each lithium cell under different operating scenarios of the host system, and performing statistical analysis to obtain their respective standard deviations σ. The threshold is generally greater than 4σ. It is also determined by combining data analysis of the short-circuit current and charge / discharge curves within this type of lithium cell. Whether the threshold is related to voltage or temperature characteristics, it may be set to three different values ​​for the three operating states of the lithium battery (discharging / resting / charging). For thresholds related to voltage characteristics, adjustments can also be made based on where the voltage value falls within the charging or discharging curve.

[0007] Preferably, steps 1 and 2 are replaced by the following steps, where the absolute values ​​of the feature values ​​in steps 1 and 2 must be greater than the threshold to determine that the lithium battery cell is a lithium battery cell with potential thermal runaway.

[0008] Preferably, 1) the formula for the voltage characteristic value is Xi=Ei-Em, which emphasizes that it is the difference between the voltage change rate Ei of a single lithium cell in the module and the median value Em of these change rates; 2) the formula for the temperature characteristic value is Yi=Di-Dm, which emphasizes that it is the difference between the temperature change rate Di of a single lithium cell in the module and the median value Dm of these change rates.

[0009] Preferably, the lithium battery has three states: discharge, rest, and charging. Voltage and temperature characteristic values ​​can be used in all three states to identify whether thermal runaway will occur in the series-connected lithium cells within the module. Because data acquisition is continuous 24 hours a day, year-round, data from the same state must be used to calculate the voltage and temperature change rates. Data spanning two states cannot be used for calculation and analysis. For example, data from 1 second before the end of discharge and data from the beginning of rest cannot be used to calculate the voltage and temperature change rates, or data from 1 second before the end of rest and data from the beginning of charging cannot be used to calculate the voltage and temperature change rates.

[0010] This application also provides a system for rapidly identifying lithium-ion battery cells with potential thermal runaway, including a battery module composed of several lithium-ion battery cells connected in series. Each lithium-ion battery cell contains a temperature sensor. The lithium-ion battery cell also includes a top cover with an explosion-proof valve. The explosion-proof valve has a through cylinder filled with sealing material. The temperature sensor passes through the cylinder and is located inside the battery module. The cavity below the explosion-proof valve of each lithium-ion battery cell is used to place the temperature sensor to prevent the temperature sensor from contacting the internal material of the lithium-ion battery cell.

[0011] Preferably, the external thread of the stud is tightened together with the internal thread of the cylinder to ensure a seal; or the stud can be replaced with a trapezoidal sealing ring, which can also provide a good seal when pressed into the cylinder.

[0012] The battery module provided in this application will promptly issue an early warning and activate the "thermal runaway suppression mechanism" of the host system when it detects that the absolute value of the characteristic value of a lithium battery cell exceeds the threshold, thus eliminating thermal runaway in its infancy, avoiding further property damage, and maximizing the safety of the host operator and surrounding personnel. Attached Figure Description

[0013] Figure 1 This is a system flowchart of the present invention.

[0014] Figure 2 This is a schematic diagram of the top cover structure of the battery module of the present invention.

[0015] Figure 3 This is a schematic diagram of the top cover structure according to the second embodiment of the present invention.

[0016] Figure 4 This is a schematic diagram of the top cover structure according to the third embodiment of the present invention. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0018] Noun: A battery module is a module or pack composed of one or more lithium battery cells; a pack is usually a system composed of multiple lithium battery cells that can perform overall functions such as discharging and charging. A pack usually also includes control components such as a BMS. A lithium battery cell refers to a single battery cell.

[0019] Units: All voltage data in this application are in volts, all temperature data are in °C, all temperature change rate data are in °C / min, and all voltage change rate data are in V / min.

[0020] The system and method for rapidly identifying lithium-ion battery cells with potential thermal runaway provided in this application are as follows: Figures 1 to 2 As shown, the device includes a battery module composed of several lithium-ion cells connected in series. Each lithium-ion cell has a built-in temperature sensor and a top cover 1. The top cover 1 includes a positive electrode 2, a negative electrode 3, and an explosion-proof valve 4. The explosion-proof valve 4 has a through-type cylindrical column 5, which is filled with sealing material, specifically a plastic stud 6. A temperature sensor 8 passes through the stud 6 and enters the cavity area of ​​the lithium-ion cell. In this example, the cylindrical column 5 has internal threads and an NTC thermistor with signal lines. Two thin signal lines 7 pass through the center of the plastic stud 6, screwing the plastic stud 6 into the inner cylindrical column 5 to achieve a sealing effect. The thermistor is placed in a space a few millimeters below the explosion-proof valve 4 inside the lithium-ion cell. Adhesive can be pre-applied to the internal threads of the cylindrical column or the threads of the plastic stud to enhance the sealing effect.

[0021] like Figure 1As shown, when the battery is activated, the host computer powers on, performs safety component checks (such as temperature sensor checks), collects temperature and voltage data, calculates the rate of temperature and voltage change, and then determines the working state of the lithium battery module (including discharge, rest, and charging states). It then calculates voltage and temperature characteristic values, comparing the absolute values ​​of both the voltage and temperature characteristics with thresholds. If the absolute value of the characteristic value is less than the threshold, it indicates normal operation, and the system continues data collection for the next round of analysis. If the absolute value of the characteristic value is greater than or equal to the threshold, it is considered thermal runaway, and the host computer activates the thermal runaway suppression system (the two judgment methods can be used independently or together, depending on the needs of the host system). The threshold is determined before the lithium battery leaves the factory by measuring the rate of temperature and voltage change of each lithium cell under different operating scenarios, statistically analyzing their respective standard deviations σ. The threshold is generally greater than 4σ, and is also determined by combining data analysis of the short-circuit current and charge / discharge curves within this type of lithium battery cell. Whether the threshold is related to voltage characteristics or temperature characteristics, it can be set to three different values ​​for the three operating states of a lithium battery (discharging / resting / charging). The threshold related to voltage characteristics can also be modified based on where the voltage value falls on the charging or discharging curve. The following uses measured data to further illustrate this embodiment: Taking the discharge phase of a battery module as an example: A lithium battery consists of 10 lithium cells connected in series. The internal temperature and terminal voltage data of each of the 10 cells are collected every second (or longer). The system immediately calculates the voltage and temperature change rates for each lithium cell. The table below shows the data collected at a certain moment in three different states of the battery module: I. Discharge Stage Assuming ten 100Ah lithium-ion cells are connected in series in one module, the following data are collected at two time points one minute apart: voltage change rate in V / min, temperature change rate in °C / min. lithium battery cell number B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 Voltage Vt0 3.811 3.812 3.811 3.810 3.814 3.809 3.812 3.808 3.813 3.809 Voltage Vt1 3.808 3.810 3.808 3.807 3.812 3.804 3.809 3.804 3.811 3.806 Ei 0.003 0.002 0.004 0.003 0.002 0.005 0.003 0.004 0.002 0.003 Sorted by Ei: 0.002, 0.002, 0.002, 0.003, 0.003, 0.003, 0.003, 0.004, 0.004, 0.005 The median is 0.003, therefore Em = 0.003. Therefore, according to the formula Xi = Ei - Em, the characteristic value of each lithium battery cell at this moment is as follows: lithium battery cell number B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 Xi 0 -0.001 0.001 0 -0.001 0.002 0 0.001 -0.001 0 The rate of temperature change is the change in temperature every minute. Temperature data is omitted below; the characteristic value of temperature, Yi = Di - Dm, is directly used as the rate of temperature change. If the voltage threshold is 0.02V / minute, then the absolute value of the voltage characteristic value of each lithium battery cell, |Xi|, is less than the threshold.

[0022] If the temperature threshold is 0.5℃ / minute, then the absolute value of the temperature characteristic value of each lithium battery cell, |Yi|, is less than the threshold.

[0023] II. Settling Stage When the battery module is not working, i.e. when the discharge current is 0, the method for calculating the characteristic value is the same as that in the discharge stage, i.e.: Xi=Ei-Em, Yi=Di-Dm. However, the threshold may be different from that in the discharge stage, which will not be illustrated here.

[0024] III. Charging Stage During the charging phase, since each OEM has different charging standards and methods in the real world, we will only list the calculation of temperature characteristic values ​​here. The algorithm is the same as that for the discharging phase, as follows: Assuming that there are 10 lithium battery cells connected in series in a module, the following calculation is based on real-time data before and after 1 minute in the discharging phase.

[0025] The formula for calculating the temperature characteristic value is the same as that for the discharge stage: Temperature characteristic value Yi = Di - Dm, where Di is the temperature change rate of each lithium cell in the module, and Dm is the median value of these temperature change rates.

[0026] Example: Suppose 10 100Ah lithium battery cells are connected in series in a module. At two moments 1 minute apart, the following data is collected: temperature change rate ℃ / min.

[0027] lithium battery cell number B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 Rate of temperature change 1.1 2.11 1.15 1.05 1.14 1.14 1.13 1.08 1.1 1.13 Yi -0.02 0.98 0.02 -0.08 0.01 0.01 0 -0.05 -0.03 0 Di sorting: 1.05, 1.08, 1.1, 1.1, 1.13, 1.13, 1.14, 1.14, 1.15, 2.11 Therefore, Dm = 1.13, and then calculate Yi = Di - Dm, as shown in the table above.

[0028] If the temperature threshold is 0.5℃ / minute, then the absolute value of the temperature characteristic value Yi of each lithium battery cell is less than the threshold.

[0029] The method for calculating voltage characteristic values ​​during the charging phase is the same as that during the discharging phase, but determining the threshold is more complex.

[0030] In another embodiment, such as Figure 3 As shown, the sealing material is a plug 9 made of elastic material, and the cylinder 5 has a smooth structure.

[0031] Or, such as Figure 4 As shown, the plug body 10 can also include several annular sealing rings, and such a structure can achieve the same purpose.

[0032] Although the algorithm for the relevant feature values ​​in this application is: voltage feature value Xi = Ei - Em, where Ei is the voltage change rate of a single lithium-ion cell in the module, and Em is the median value of these voltage change rates, any application using the same approach, such as replacing Em with "the minimum value, average value, values ​​several digits apart from Em, and values ​​several digits apart from the minimum value," falls under the category of using the same feature value algorithm approach as in this application and is also within the scope of protection of this application. Similarly, the algorithm for the temperature feature values ​​in this application is: temperature feature value Yi = Di - Dm, where Di is the temperature change rate of a single lithium-ion cell in the module, and Dm is the median value of these temperature change rates. However, any application using the same approach, such as replacing Dm with "the minimum value, average value, values ​​several digits apart from Dm, and values ​​several digits apart from the minimum value," falls under the category of using the same feature value algorithm approach as in this application.

[0033] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for rapidly identifying lithium-ion battery cells with potential thermal runaway, comprising a battery module, the battery module being composed of several lithium-ion battery cells connected in series, each lithium-ion battery cell containing a temperature sensor, characterized in that, A method for identifying lithium-ion cells with potential thermal runaway by placing a temperature sensor inside the cavity below the explosion-proof vent of the top cover of the lithium-ion cell includes the following steps: Step 1: Measure the terminal voltage of each lithium cell in the battery module, calculate the voltage change rate Ei of each lithium cell, find the median value Em of the voltage change rate, and then the voltage characteristic value Xi of each lithium cell is Xi = Ei - Em. When the absolute value of the voltage characteristic value of any lithium cell in the module, |Xi| >= the threshold, it is determined that this lithium cell has an internal short circuit and will experience thermal runaway. Step 2: Measure the internal temperature of each lithium cell in the battery module, calculate the temperature change rate Di of each lithium cell, find the median value Dm of the temperature change rate, and then the temperature characteristic value Yi of each lithium cell is Yi = Di - Dm. When the absolute value of the temperature characteristic value of any lithium cell in the module, |Yi| >= the threshold, it is determined that this lithium cell has an internal short circuit and will experience thermal runaway. Step 3, Determining the threshold: The threshold is determined before the lithium battery leaves the factory by measuring the temperature change rate and voltage change rate of each lithium cell under different working scenarios of the host system, and statistically analyzing their respective standard deviations σ. The threshold is greater than 4σ. At the same time, it is determined by combining the data analysis of the short circuit current and charge-discharge curve of this type of lithium cell.

2. The method for rapidly identifying lithium-ion cells with potential thermal runaway according to claim 1, characterized in that, Replace steps 1 and 2 with the following steps. The absolute values ​​of the feature values ​​in steps 1 and 2 must be greater than the threshold to determine that the lithium battery cell is a potential thermal runaway lithium battery cell.

3. The method for rapidly identifying lithium-ion cells with potential thermal runaway according to claim 1 or 2, characterized in that, 1) The formula for voltage characteristic value is Xi=Ei-Em, which emphasizes that it is the difference between the voltage change rate Ei of a single lithium cell in the module and the median value Em of these change rates; 2) The formula for temperature characteristic value is Yi=Di-Dm, which emphasizes that it is the difference between the temperature change rate Di of a single lithium cell in the module and the median value Dm of these change rates.

4. The method for rapidly identifying lithium-ion cells with potential thermal runaway according to claim 3, characterized in that, Lithium batteries have three states: discharge, rest, and charging. Voltage and temperature characteristics can be used to identify whether the lithium battery cells connected in series in the module will experience thermal runaway.

5. A system for rapidly identifying lithium-ion battery cells with potential thermal runaway, comprising a battery module consisting of several lithium-ion battery cells connected in series, each lithium-ion battery cell having a built-in temperature sensor, and each lithium-ion battery cell also including a top cover, the top cover being equipped with an explosion-proof valve, characterized in that... The explosion-proof valve has a through cylinder filled with sealing material. It also includes a temperature sensor that passes through the cylinder and is placed inside the lithium battery cell. At the same time, the lower part of the explosion-proof valve plate of the lithium battery cell is a cavity, in which the temperature sensor is placed. The purpose is to measure the gas temperature inside the lithium battery cell, especially in the early stage of thermal runaway.

6. The system for rapidly identifying lithium-ion cells with potential thermal runaway according to claim 5, characterized in that, Tighten the external thread of the stud to the internal thread of the cylinder to ensure a seal; or replace the stud with a trapezoidal sealing ring, which can be pressed into the cylinder for a good seal.

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