An instrument and method for evaluating the swelling of a battery pack

Abstract

The present invention belongs to the technical field of batteries, and particularly relates to an instrument and method for evaluating the expansion of a battery pack, which includes the following steps: Step 1, place the gas probe of the miniaturized gas pressure and temperature sensor into the internal gas cavity of the battery pack and connect it to an external gas pressure and temperature recorder; Step 2, obtain the pressure and temperature of the gas in the voids inside the battery pack and the single battery cells through the gas pressure and temperature sensor, and use the gas pressure and temperature recorder to collect and store the changes in gas pressure and temperature; Step 3, construct a multi-environment coupling test system, including a charge and discharge module, a temperature control box, a vibration table, and a shock testing machine; Step 4, establish a pressure-temperature-deformation coupling model and separate the environmental interference signals based on wavelet transform. The present invention can accurately collect the changes in the internal cavity pressure and temperature of the battery pack under various environments, and use the changes in pressure and temperature to obtain the battery expansion characteristics, so as to give early warning and protection to the state of the battery pack.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and particularly relates to an instrument and method for evaluating the expansion of a battery pack. Background Art

[0002] The expansion of lithium batteries is one of the characteristics that have a significant impact on battery performance and safety. Regarding the causes, impacts, and testing methods of lithium battery expansion, it is still in the exploratory stage.

[0003] Battery packs come in a wide variety of shapes. For example, power battery packs need to be designed in different shapes to meet the requirements of the vehicle interior space, but their structural compositions and working principles are basically the same. Lithium batteries are first composed of small-volume battery cell monomers connected in series and in parallel to form modules, and then the modules are connected in series and in parallel to form a battery pack. The outer shell of the lithium battery pack is a closed cavity wrapped by rigid materials. In the gaps between the battery cell monomers / modules in this closed cavity, there are mainly air-based gases, which can undergo gas exchange and heat exchange with the external air under the thermal management system of the battery pack.

[0004] During the charging and discharging process of the battery pack, the battery cells will generate heat, causing the air around the battery cells to expand; at the same time, electrochemical reactions inside the battery cells will also produce gases that are discharged into the cavity of the battery pack. These two reasons will both cause changes in the gas pressure and temperature inside the battery pack and outside the battery cell monomers. Testing the changes in the gas pressure and temperature inside the battery pack and analyzing their correlation characteristics with charging and discharging are of great significance for analyzing battery performance characteristics.

[0005] Therefore, how to accurately obtain the changes in the internal gas pressure and temperature of the battery pack and use these changes in gas pressure and temperature to reflect the battery expansion characteristics is an urgent problem to be solved. Summary of the Invention

[0006] The purpose of the present invention is to provide an instrument and method for evaluating the expansion of a battery pack, which can accurately collect the changes in the internal cavity pressure and temperature of the battery pack in various environments, and use these changes in pressure and temperature to obtain the battery expansion characteristics, so as to give early warnings and protection for the state of the battery pack.

[0007] The technical solutions adopted by the present invention are specifically as follows:

[0008] A method for evaluating the expansion of a battery pack includes the following steps:

[0009] Step 1: Place the gas probe of the miniaturized gas pressure and temperature sensor into the internal gas cavity of the battery pack, and lead out the wire harness of the gas pressure and temperature sensor through the modified hole of the explosion-proof valve, and connect it to an external gas pressure and temperature recorder;

[0010] Step 2: Obtain the pressure and temperature of the gas in the voids inside the battery pack and inside the individual battery cells through a gas pressure and temperature sensor, and use a gas pressure and temperature recorder to collect and store the changes in gas pressure and temperature;

[0011] Step 3: Construct a multi-environment coupling test system, including a charge and discharge module, a temperature control box, a vibration table, and a shock testing machine, and achieve millisecond-level timestamp alignment of environmental parameters and gas pressure and temperature sensor data through a synchronous control program;

[0012] Step 4: Establish a pressure-temperature-deformation coupling model, and separate environmental interference signals based on wavelet transform, so as to obtain the expansion characteristics of the battery pack in relevant application environments, and synchronously extract characteristic parameters for three-level expansion threshold warning.

[0013] As a preferred solution, the connection between the gas pressure and temperature sensor and the battery pack housing adopts a sealing structure in which a fluororubber O-ring is nested with a metal flange.

[0014] As a preferred solution, the gas pressure and temperature recorder performs Butterworth low-pass filtering on the collected original pressure values, and compensates the original temperature values using a temperature data compensation algorithm;

[0015] The specific mathematical expression of the temperature data compensation algorithm is: ;

[0016] Where, is the true temperature value after compensation; is the original temperature value directly measured by the sensor; is the dynamic compensation coefficient; is the rate of change of temperature with time.

[0017] As a preferred solution, the synchronous control program includes a dynamic matching algorithm for charge and discharge current and gas pressure and temperature sensor data, and a correlation analysis module for vibration spectrum and pressure fluctuation amplitude;

[0018] Among them, the dynamic matching algorithm realizes millisecond-level timestamp alignment of charge and discharge current parameters and gas pressure and temperature sensor data through a time series alignment module, extracts current characteristics and voltage characteristics, and establishes a dynamic coupling analysis model;

[0019] The correlation analysis module realizes synchronous acquisition of vibration spectrum and pressure fluctuation data through a sliding window compensation mechanism, extracts vibration spectrum and pressure fluctuation characteristics, and establishes a correlation analysis model;

[0020] Based on the dynamic coupling analysis model and the correlation analysis model, the pressure fluctuation amplitude and temperature gradient change rate of the battery pack in relevant application environments are obtained.

[0021] As a preferred solution, the charge and discharge module is tested by charging at a constant current of 0.5C to 100% SOC, then standing still for 30 minutes, and then discharging at a constant current of 1C to 20% SOC;

[0022] Secondly, the battery is fast charged from 0% to 80% SOC using 4C fast charging, then stands still for 10 minutes, and then quickly discharges at 3C to 10% SOC;

[0023] And during the test, the battery capacity is calibrated in real time through the Coulomb integration method.

[0024] As a preferred solution, the temperature control box test includes a temperature gradient test and a thermal-mechanical coupling test;

[0025] Among them, in the temperature gradient test, low-temperature cycling and high-temperature shock are used. The battery pack is kept at -40°C for 2 hours, then the temperature is raised to 25°C, and the temperature rise rate is 5°C / min, and this is repeated 3 - 5 times; then the ambient temperature is raised from 25°C to 150°C, and the temperature rise rate is 10°C / min, and it is kept for 1 hour; during the test, the temperature fluctuation inside the box is controlled by the PID algorithm to be ≤±1°C;

[0026] In the thermal-mechanical coupling test, the battery pack is placed at a high temperature of 85°C for 4C fast charging, the vibration table is started synchronously, and the temperature distribution uniformity is verified through an infrared thermal imager.

[0027] As a preferred solution, the specific mathematical expression of the pressure-temperature-deformation coupling model is:

[0028] ;

[0029] Among them, is the change value of the internal gas pressure of the battery pack relative to the initial state; is the gas thermal expansion coefficient; is the temperature change value; is the electrochemical gas generation coefficient; is the state of charge; is the mechanical vibration influence factor; is the amplitude; is the vibration frequency; is the time.

[0030] As a preferred solution, the characteristic parameters in step four are the pressure fluctuation amplitude and the temperature gradient change rate, and based on the pressure fluctuation amplitude, the three-level expansion threshold warning is divided into a first-level warning, a second-level protection, and a third-level fault;

[0031] Among them, under the first-level early warning, the charging and discharging current is derated; under the second-level protection, the circuit is cut off and the pressure relief valve is activated; under the third-level fault, the fire aerosol is ejected.

[0032] An instrument for evaluating the expansion of a battery pack, which is applied to the method for evaluating the expansion of a battery pack as described above, and is characterized in that it includes a pressure and temperature sensor and a gas pressure and temperature recorder, which are connected by a wire harness;

[0033] The gas pressure and temperature sensor includes a main body and a gas probe, a fixed terminal and a cable connector integrated on the main body. A gas-sensitive ceramic resistor and a thermosensitive ceramic resistor for detecting changes in gas pressure and temperature are integrated in the main body;

[0034] The gas pressure and temperature recorder has at least two channels and is used in combination with the gas pressure and temperature sensor to realize multi-channel intake pressure measurement and multi-channel intake temperature measurement. Each channel is provided with a flip-type BCPT interface.

[0035] As a preferred solution, it further includes a host computer, which includes:

[0036] A processor;

[0037] A memory for storing instructions executable by the processor;

[0038] Among them, the processor is configured to implement the method for evaluating the expansion of the battery pack as described above when executing the instructions stored in the memory.

[0039] The technical effects achieved by the present invention are:

[0040] The present invention adopts a composite gas pressure and temperature sensor. The cylindrical gas probe makes its installation with the battery pack simpler, and adopts a fluororubber O-ring sealing structure to reduce the influence of the external environment. At the same time, taking the air in the battery pack as the medium, the expansion characteristics of the battery pack are detected. Compared with the traditional deformation monitoring, the error is smaller and the monitoring accuracy is higher. At the same time, the multi-environment coupling test system greatly shortens the traditional test cycle and improves the test efficiency.

[0041] The present invention adopts a pressure-temperature-deformation coupling model, which can more efficiently predict dangerous expansion, and sets a three-level expansion threshold mechanism to greatly improve the safety response speed, reduce the early warning trigger delay, improve the safety of the battery pack, and at the same time, by quantifying and distinguishing the contribution degrees of thermal expansion and electrochemical gas production, a breakthrough in multi-physical field coupling analysis can be achieved, thereby ensuring the monitoring accuracy. Description of the Drawings

[0042] Figure 1 It is a schematic flow structure diagram of the method for evaluating the expansion of a battery pack in an embodiment of the present invention;

[0043] Figure 2 It is a schematic diagram of the connection structure of the instrument in the method for evaluating the expansion of the battery pack according to the embodiment of the present invention;

[0044] Figure 3 It is a schematic diagram of the structure of the gas pressure and temperature sensor in the instrument for evaluating the expansion of the battery pack according to the embodiment of the present invention;

[0045] Figure 4 It is a schematic diagram of the assembly structure of the gas pressure and temperature sensor in the instrument for evaluating the expansion of the battery pack according to the embodiment of the present invention;

[0046] Figure 5 It is a schematic diagram of the structure of the gas pressure and temperature recorder in the instrument for evaluating the expansion of the battery pack according to the embodiment of the present invention.

[0047] In the attached drawings, the list of components represented by each reference numeral is as follows:

[0048] 1. Gas pressure and temperature sensor;

[0049] 11. Main body; 12. Gas probe; 13. Fixed terminal; 14. Cable connector;

[0050] 2. Gas pressure and temperature recorder;

[0051] 21. Physical channel; 22. BCPT interface; 23. Resistive touch screen. Detailed implementation manners

[0052] In order to make the purpose and advantages of the present invention clearer, the present invention will be specifically described below in conjunction with embodiments. It should be understood that the following text is only used to describe one or several specific implementation manners of the present invention, and does not strictly limit the scope of protection specifically claimed by the present invention.

[0053] As Figures 1 - 5 shown, a method for evaluating the expansion of a battery pack includes the following steps:

[0054] S1. Place the miniaturized gas pressure and temperature sensor 1 into the internal air cavity of the battery pack, lead out the wire harness of the gas pressure and temperature sensor 1 through the modified hole position of the explosion-proof valve, and connect it to the external gas pressure and temperature recorder 2.

[0055] Specifically refer to the attached Figure 3, wherein, the gas pressure and temperature sensor 1 includes a main body 11, a gas probe 12, a fixed terminal 13 and a cable connector 14 integrated on the main body 11. A gas-sensitive ceramic resistor and a thermosensitive ceramic resistor for detecting gas pressure and temperature changes are integrated in the main body 11. As the gas vacuum degree and temperature at the gas probe 12 end fluctuate, the resistance values of the gas-sensitive ceramic resistor and the thermosensitive ceramic resistor inside the main body 11 will also change accordingly. By converting the change in resistance into a voltage signal through circuit excitation, the information on its gas pressure and temperature can be obtained.

[0056] Specifically refer to the appendix Figure 4 , a large number of battery cell monomers, wire harnesses, battery management system controllers, etc. are placed inside the battery pack, and there are also certain gaps. The gaps may be filled with ordinary air, special gas or waste gas emitted by the battery cell monomers. The pressure and temperature of this part of the gas will change due to thermal expansion and contraction or because the battery cell monomers emit more waste gas. Place the gas pressure and temperature sensor 1 inside the battery pack, insert the gas probe 12 deep into the battery pack but not in contact with gas components such as battery cell monomers, only in contact with the internal gas, fix the sensor to the battery pack through the fixed terminal 13, and at the same time connect the tail of the sensor to the outside of the battery pack and connect it to the recorder; in order to achieve the purpose of monitoring the air pressure and temperature inside the battery pack.

[0057] It should be noted that the connection between the gas pressure and temperature sensor 1 and the battery pack housing adopts a sealing structure of a fluororubber O-ring nested with a metal flange, which can avoid detection errors caused by internal gas leakage and at the same time reduce the influence of the external environment on the detection process.

[0058] It should be noted that the sensor used in this embodiment is a sensor that can sense the gas pressure and temperature, can measure the pressure and temperature of gaseous substances, and can be used to test the pressure and temperature of various gaseous substances such as ordinary air, intake air of automobile engines, and leakage gas in the gaps of lithium battery packs, so as to evaluate the physical state of the corresponding gaseous substances. It adopts a 4-wire system design and can measure the gas pressure and temperature simultaneously (2 wires for each of the gas pressure and temperature). The specific technical specifications are as follows:

[0059] Table 1. Technical Specification Table of Gas Pressure and Temperature Sensor 1

[0060] Serial Number Name Parameter Description 1 Power Supply Voltage Range 4.5V - 5.5V 　 2 Rated Voltage 5V 　 3 Rated Current 8mA, maximum 10mA 　 4 Air Pressure Range 10 - 250kpa 　 5 Temperature Range -40~130℃, NTC 　 6 Pin Description GND, Power Supply, Temperature Output, Air Pressure Output 　 7 Maximum Current 0.3A (operation at 0.3A should not exceed 5 minutes) 　 8 Operating Temperature -40~130℃, NTC 　 9 Overall Precision Error 3.4kpa 　 10 Overall Dimensions 52.4 * 35.2 * 17.7mm 　 11 Outer Diameter of Air Outlet 11.85 ± 0.07mm Inner Diameter of Corresponding Air Duct 12 Inner Diameter of Air Outlet 4mm 　 13 Thickness of Sealing Ring 2.5 ± 0.1mm 　 14 Installation Angle 0~±60° Angle with the Vertical Direction 15 Material PBT - GF30 Housing Material 16 Cable Interface BC2W 4pin

[0061] S2. Obtain the pressure and temperature of the gas in the gaps inside the battery pack and the battery cell monomers through the gas pressure and temperature sensor 1, and use the gas pressure and temperature recorder 2 to collect and store the changes in gas pressure and temperature.

[0062] Specifically refer to the appendix Figure 5, the gas pressure and temperature recorder 2 has two physical channels 21, which can be connected to two gas pressure and temperature sensors 1 to compare data in real time and accurately capture abnormal data. It adopts a customized flip-sealed BCPT interface 22, which can effectively ensure the safe and reliable operation of the instrument in harsh environments such as dust and water mist. It is equipped with an industrial-grade resistive touch screen 23, with a simple and intuitive interface design, supporting pressure and temperature viewing, historical data viewing, and pressure alarm setting. The device is built-in with a high-speed memory card, which can achieve long-term data storage; at the same time, it has an open 485 communication interface, which is convenient for users to remotely read the channel data through the host computer in real time. The specific performance parameters are as follows:

[0063] Table 2. Performance Parameter Table of Gas Pressure and Temperature Recorder 2

[0064] Serial Number Name Parameter Description 1 Power Supply Voltage 220AC 　 2 Acquisition Channels 2CH 　 3 Signal Channels 2 air pressures, 2 temperatures 1CH Physical Channel = 1CH Air Pressure + 1CH Temperature 4 Air Pressure Type Absolute Air Pressure Relative to Vacuum Air Pressure 5 Air Pressure Range Depending on the sensor 　 6 Air Pressure Precision 1%。 　 7 Sampling Rate 2 S / s / CH 　 8 Operating Temperature -20~55°C 　 9 Storage TF Card / 16G / txt Document Can be replaced by oneself 10 Communication Interface RS 485 　 11 Screen 7 - inch Touch Screen 12 Product Dimensions 200mm * 130mm * 55mm 　 13 Weight Approximately 1.15kg 　 14 Main Functions Real - time pressure display, historical waveform display, pressure alarm, data storage, remote communication, etc. 15 Interface Type BCPT 16 Wiring BCPT to BC2W4pin, 2m * 2

[0065] It should be noted that the gas pressure and temperature recorder 2 performs Butterworth low-pass filtering (cutoff frequency 50Hz) on the collected original pressure values, and compensates the original temperature values using a temperature data compensation algorithm.

[0066] Furthermore, the specific mathematical expression of the temperature data compensation algorithm is: ;

[0067] Among them, is the true temperature value after compensation; is the original temperature value directly measured by the sensor; is the dynamic compensation coefficient; is the rate of change of temperature over time.

[0068] S3. Build a multi-environment coupling test system, including a charge and discharge module, a temperature control box, a vibration table, and a shock testing machine, and achieve millisecond-level timestamp alignment of environmental parameters and data of the gas pressure and temperature sensor 1 through a synchronous control program.

[0069] Among them, the test process of the charge and discharge module is as follows:

[0070] I. Test Process

[0071] 1. Cyclic charge and discharge strategy

[0072] 1.1. Constant current charge at 0.5C to 100% SOC, then stand for 30 minutes, and then immediately discharge at 1C constant current to 20% SOC;

[0073] 1.2. Fast charge at 4C (0 - 80% SOC), then stand for 10 minutes, and then immediately discharge at 3C fast to 10% SOC;

[0074] SOC accuracy control: Calibrate the capacity in real time through the Coulomb integration method (error < ±5%);

[0075] 2. Pulse Test: Apply a current pulse of the order of 50 ms (such as a peak value of 200 A), and synchronously record the pressure response.

[0076] II. Synchronous Trigger Mechanism

[0077] Align the data of the charge and discharge current and the pressure sensor through the LabVIEW timestamp (error < 1 ms); at the same time, start the vibration table sweep frequency test when the SOC reaches 80%.

[0078] Among them, the test process of the temperature control box is as follows:

[0079] I. Extreme Temperature Change Test:

[0080] 1.1 Low-temperature cycle: Maintain at -40°C for 2 h, and then gradually heat up to 25°C (temperature rise rate 5°C / min), and repeat 3 times;

[0081] 1.2 High-temperature shock: Gradually increase the ambient temperature from 25°C to 150°C (temperature rise rate 10°C / min), and then maintain at this temperature for 1 h;

[0082] During the test, precise temperature control is required: Control the temperature fluctuation in the box ≤ ±1°C through the PID algorithm (refer to GB / T 2423.22).

[0083] II. Thermal-Mechanical Coupling Test

[0084] Perform 4C fast charging at a high temperature of 85°C, start the vibration table (frequency 200 Hz) synchronously, and at the same time verify the temperature distribution uniformity through an infrared thermal imager (temperature difference < 3°C).

[0085] Among them, in this embodiment, a vibration table (adjustable from 5 - 2000 Hz) is selected, and its specific parameters are as follows:

[0086] I. Random Vibration:

[0087] Power Spectral Density (PSD): 0.04 g² / Hz (5 - 100 Hz) to 0.02 g² / Hz (100 - 2000 Hz), randomly selected;

[0088] Duration: 3 hours per axis (independent test for X / Y / Z axes).

[0089] II. Sine Sweep:

[0090] Sweep from 5 - 2000 Hz (rate 1 oct / min) to identify the resonance frequencies (such as 120 Hz, 850 Hz).

[0091] Among them, the test process of the impact testing machine is as follows:

[0092] I. Impact Parameter Settings

[0093] 1.1 Impact Waveform:

[0094] Half - sine wave (peak acceleration 50g, pulse width 11ms);

[0095] Trapezoidal wave (30g, 30ms) to simulate the transportation drop scenario.

[0096] 1.2 Multi - axial Impact: Apply 3 impacts on each of the X / Y / Z axes (refer to the ISTA 3A standard).

[0097] II. Impact Damage Assessment

[0098] 2.1 Detecting Structural Failure through Sudden Changes in Pressure Fluctuations:

[0099] If the instantaneous value of ΔP after impact > 40 kPa and does not fall back, it is determined that the sealing structure is damaged;

[0100] Secondly, analyze local deformation using pressure - sensitive recording paper (deformation rate > 5% is judged as failure).

[0101] In this embodiment, the multi - environment coupling test process is as follows:

[0102] S3.1: Complete 1 full charge - discharge cycle at 25°C (baseline data collection);

[0103] S3.2: Perform 3C fast charging in an environment of - 20°C, and simultaneously start the vibration table (random vibration from 50 - 500 Hz);

[0104] S3.3: Apply Y - axis impact (50g, half - sine wave) under high - temperature (60°C) conditions;

[0105] S3.4: Analyze the coupling coefficient of ΔP with temperature / vibration / impact (such as γ - value calibration).

[0106] Among them, the synchronous control program includes a dynamic matching algorithm for the charge - discharge current and the data of gas pressure and temperature sensor 1, as well as a correlation analysis module for the vibration spectrum and the amplitude of pressure fluctuations;

[0107] In S3, the dynamic matching algorithm realizes the millisecond - level timestamp alignment of the charge - discharge current parameters and the data of gas pressure and temperature sensor 1 through the time - series alignment module, extracts the current characteristics and voltage characteristics, and establishes a dynamic coupling analysis model.

[0108] The specific algorithm architecture is as follows:

[0109] I. Time - series Alignment Module

[0110] The synchronization program developed by LabVIEW realizes the alignment of the millisecond-level timestamps of the charge and discharge current parameters (such as the rate and SOC value) with the data of the pressure sensor.

[0111] The sliding window method (window length 5 ms) is used to compensate for the transmission delays of different sensor signals, ensuring that the data synchronization error < 1 ms.

[0112] II. Feature Parameter Extraction

[0113] Current Features: Extract the instantaneous value of the charge and discharge current (such as 4C fast charging), the current change rate (dI / dt), and the cumulative charge (Q = ∫I·dt).

[0114] Pressure Features: Calculate the pressure fluctuation amplitude (ΔP), the pressure gradient (dP / dt), and the spectral energy distribution (obtain the main frequency components through FFT transformation).

[0115] III. Dynamic Coupling Analysis Model

[0116] Establish the current-pressure transfer function:

[0117] ;

[0118] where , , are fitting coefficients, optimized by the least squares method.

[0119] Introduce the electrochemistry-thermal expansion coupling equation:

[0120] ;

[0121] where is the internal resistance of the battery, , , are experimentally calibrated parameters.

[0122] The specific correlation analysis model is as follows:

[0123] I. Data Synchronization Unit

[0124] 1.1. The millisecond-level timestamp alignment algorithm developed by LabVIEW is used to realize the synchronous acquisition of the vibration spectrum and the pressure fluctuation data through the sliding window compensation mechanism (window length 5 ms), with the synchronization error < 1 ms;

[0125] 1.2. The data interface supports multi-channel input, including signals such as vibration acceleration (0 - 10 kHz), pressure fluctuation (0 - 50 kPa), and temperature (-40~150°C).

[0126] II. Feature Parameter Extraction Unit

[0127] 2.1. Vibration spectrum characteristics:

[0128] Extract the main frequency components (such as 1X rotation frequency, meshing frequency), harmonic amplitudes (2X, 3X), and sideband frequency intervals (such as gear fault characteristics); at the same time, calculate the vibration energy distribution (obtain the energy ratio of the 0 - 1 kHz frequency band through FFT spectrum integration).

[0129] 2.2. Pressure fluctuation characteristics:

[0130] Calculate the pressure gradient (dP / dt), fluctuation amplitude (ΔP), and the main frequency of the spectrum (through power spectral density PSD analysis).

[0131] III. Core algorithms for correlation analysis

[0132] 3.1. Cross - Correlation Function:

[0133] ;

[0134] Among them, , represent two continuous - time signals to be analyzed; is the time delay (unit: second), indicating the time interval by which the signal is translated relative to ; is the time variable (unit: second), the independent variable of the integral operation; is the cross - correlation value of the two signals at the delay . A positive value indicates positive correlation, a negative value indicates negative correlation, and a zero value indicates no correlation.

[0135] 3.2. Wavelet Coherence Analysis:

[0136] Adopt the Morlet wavelet transform to calculate the energy coherence of the vibration spectrum and pressure fluctuation in the time - frequency domain, and locate the high - frequency resonance region.

[0137] 3.3. Transfer Function Modeling:

[0138] Establish the frequency response function between vibration acceleration (a) and pressure fluctuation (ΔP):

[0139] ;

[0140] Among them, is the cross - power spectrum, is the auto - power spectrum, used to quantify the transfer efficiency of vibration energy to pressure fluctuation.

[0141] By introducing the above - mentioned dynamic coupling analysis model and correlation analysis model, the pressure fluctuation amplitude and temperature gradient change rate of the battery pack in the relevant application environment can be obtained.

[0142] S4. Establish a pressure-temperature-deformation coupling model, and separate environmental interference signals based on wavelet transform, so as to obtain the expansion characteristics of the battery pack in the relevant application environment, and synchronously extract characteristic parameters for three-level expansion threshold warning.

[0143] It should be noted that the specific mathematical expression of the pressure-temperature-deformation coupling model is:

[0144] ;

[0145] Wherein, is the change value of the internal gas pressure of the battery pack relative to the initial state; is the gas thermal expansion coefficient; is the temperature change value; is the electrochemical gas generation coefficient; is the state of charge; is the mechanical vibration influence factor; is the amplitude; is the vibration frequency; is the time.

[0146] The above coupling model comprehensively reflects the coupling effects of three factors, namely temperature change, electrochemical gas generation, and mechanical vibration, on the expansion characteristics of the battery pack.

[0147] Furthermore, the specific physical meanings of each part:

[0148] 1. Thermodynamic expansion component ( )

[0149] The thermal expansion and contraction effect of the gas caused by the temperature change ( ), is the gas thermal expansion coefficient. In some embodiments, when the temperature of the battery pack increases by 1 °C, increases by about 0.5 - 1.2 kPa (the specific value depends on the gas type).

[0150] 2. Electrochemical gas generation component ( )

[0151] Caused by the gas generation during the electrolyte decomposition in the battery charging and discharging process, and the increase in SOC (state of charge) will exacerbate the gas generation amount.

[0152] Experiments in some embodiments show that: when SOC increases from 50% to 100%, the contributed by gas generation can reach 8 - 15 kPa.

[0153] 3. Mechanical vibration component ( )

[0154] External vibration (amplitude 、 Frequency ) causes the deformation of the battery pack structure, resulting in periodic pressure fluctuations in the gas chamber. In some embodiments, when the vibration frequency > 100 Hz, the amplitude can reach 3 - 5 times that of the static condition.

[0155] The characteristic parameters in S4 are the amplitude of pressure fluctuation and the change rate of temperature gradient. Based on the amplitude of pressure fluctuation, the three - level expansion threshold warning is divided into primary warning, secondary protection, and tertiary fault. The specific warning process is as follows:

[0156] Primary warning ( > 15 kPa): Trigger the derating of charge - discharge current;

[0157] Secondary protection ( > 25 kPa): Cut off the circuit and activate the pressure relief valve;

[0158] Tertiary fault ( > 40 kPa): Activate the fire aerosol injection.

[0159] Based on the above - mentioned model, the dangerous expansion can be predicted more efficiently, and the three - level expansion threshold mechanism is set to greatly improve the safety response speed, reduce the warning trigger delay, improve the safety of the battery pack. At the same time, by quantifying and distinguishing the contribution degrees of thermal expansion and electrochemical gas generation, the breakthrough of multi - physical - field coupling analysis can be achieved, thus ensuring the monitoring accuracy.

[0160] As Figures 1 - 5 shown, an instrument for evaluating the expansion of a battery pack, which is applied to the method for evaluating the expansion of a battery pack in this embodiment, includes a pressure - temperature sensor and a gas pressure - temperature recorder 2, and the two are connected by a wire harness (as shown in the appendix Figure 2 ).

[0161] Among them, the gas pressure - temperature sensor 1 includes a main body 11 and a gas probe 12, a fixed terminal 13, and a cable connector 14 integrated on the main body 11. The main body 11 integrates a gas - sensitive ceramic resistor and a thermistor ceramic resistor for detecting gas pressure and temperature changes; the gas probe 12 can be inserted into the battery pack without contacting the gas components such as the cell modules, only contacting the internal gas, and is fixed to the battery pack by using the fixed terminal 13. At the same time, the cable connector 14 at the tail is connected to the outside of the battery pack through a cable and then connected to the gas pressure - temperature recorder 2 to monitor the gas temperature and pressure inside the battery pack.

[0162] Furthermore, the gas pressure and temperature recorder 2 has at least two channels 21 and is used in conjunction with the gas pressure and temperature sensor 1 to achieve multi-channel intake pressure measurement and multi-channel intake temperature measurement. Each channel 21 is provided with a flip-type BCPT interface 22, which can effectively ensure the safe and reliable operation of the instrument in harsh environments such as dust and water mist. An industrial-grade resistive touch screen 23 is configured, and the interface design is simple and intuitive, supporting pressure and temperature viewing, historical data viewing, and pressure alarm setting. The device is built-in with a high-speed memory card to achieve long-term data storage. At the same time, a 485 communication interface is opened, which is convenient for users to remotely read the channel data through the host computer in real time.

[0163] It should be noted that a host computer is also included, which is a computer device (PC) in this implementation and is presented in the form of a general computing device.

[0164] The components of the computer device may include, but are not limited to: one or more processors or processing units, a system memory, and a bus connecting different system components (including the system memory and the processing unit).

[0165] The bus represents one or more of several bus architectures, including a memory bus or a memory controller, a peripheral bus, a graphics acceleration port, a processor, or a local bus using any of the various bus architectures. For example, these architectures include, but are not limited to, the Industry Standard Architecture (ISA) bus, the Micro Channel Architecture (MAC) bus, the Enhanced ISA bus, the Video Electronics Standards Association (VESA) local bus, and the Peripheral Component Interconnect (PCI) bus.

[0166] The computer device typically includes a variety of computer system-readable media. These media can be any available media that can be accessed by the computer device, including volatile and non-volatile media, removable and non-removable media.

[0167] The system memory may include computer system readable media in the form of volatile memory, such as random access memory (RAM) and / or cache memory. The computer device may further include other removable / non-removable, volatile / non-volatile computer system storage media. By way of example only, a storage system may be used for reading and writing on a non-removable, non-volatile magnetic medium (commonly referred to as a "hard disk drive"). A disk drive may be provided for reading and writing on a removable non-volatile disk (such as a "floppy disk"), and an optical disk drive for reading and writing on a removable non-volatile optical disk (such as a CD-ROM, DVD-ROM or other optical medium). In these cases, each drive may be connected to the bus through one or more data media interfaces. The memory may include at least one program product having a set (e.g., at least one) of program modules configured to perform the functions of the embodiments of the present invention.

[0168] A program / utility with a set (at least one) of program modules may be stored, for example, in the memory. Such program modules include, but are not limited to, an operating system, one or more application programs, other program modules, and program data. An implementation of a network environment may be included in each or some combination of these examples. The program modules generally perform the functions and / or methods in the embodiments described in the present invention.

[0169] The computer device may also communicate with one or more external devices (such as a keyboard, a pointing device, a display, etc.), and may also communicate with one or more devices that enable a user to interact with the computer device, and / or communicate with any device that enables the computer device to communicate with one or more other computing devices (such as a network card, a modem, etc.). Such communication may be carried out through an input / output (I / O) interface. Moreover, the computer device may also communicate with one or more networks (such as a local area network (LAN), a wide area network (WAN), and / or a public network, such as the Internet) through a network adapter. The network adapter communicates with other modules of the computer device through the bus. It should be understood that other hardware and / or software modules may be used in conjunction with the computer device, including but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup storage systems, etc.

[0170] The processing unit executes various functional applications and data processing by running programs stored in the system memory, such as implementing the method for evaluating the swelling of a battery pack provided by the embodiments of the present invention.

[0171] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention. The structures, devices, and operation methods not specifically described and explained in the present invention are implemented according to the conventional means in the art without special explanation and limitation.

Claims

1. A method for evaluating the swelling of a battery pack, characterized in that, It includes the following steps: Step 1: Place the gas probe of the miniaturized gas pressure and temperature sensor into the internal gas cavity of the battery pack, lead out the wire harness of the gas pressure and temperature sensor through the modified hole of the explosion-proof valve, and connect it to the external gas pressure and temperature recorder; Step 2: Obtain the pressure and temperature of the gas in the voids inside the battery pack and the single cells through the gas pressure and temperature sensor, and use the gas pressure and temperature recorder to collect and store the changes in gas pressure and temperature; Step 3: Construct a multi-environment coupling test system, including a charge and discharge module, a temperature control box, a vibration table, and a shock testing machine, and achieve millisecond-level timestamp alignment of environmental parameters and gas pressure and temperature sensor data through a synchronous control program; Step 4: Establish a pressure-temperature-deformation coupling model, and separate environmental interference signals based on wavelet transform, so as to obtain the expansion characteristics of the battery pack in the relevant application environment, and synchronously extract characteristic parameters for three-level expansion threshold warning; The specific mathematical expression of the pressure-temperature-deformation coupling model is: ； Among them, is the change value of the internal gas pressure of the battery pack relative to the initial state; is the gas thermal expansion coefficient; is the temperature change value; is the electrochemical gas generation coefficient; is the state of charge; is the mechanical vibration influence factor; is the amplitude; is the vibration frequency; is the time.

2. The method for evaluating the swelling of a battery pack according to claim 1, wherein, A sealing structure in which a fluororubber O-ring is nested with a metal flange is adopted at the connection between the gas pressure and temperature sensor and the battery pack housing.

3. A method for evaluating the swelling of a battery pack according to claim 1, characterized in that, The gas pressure and temperature recorder performs Butterworth low-pass filtering on the collected original pressure value, and compensates the original temperature value using a temperature data compensation algorithm; The specific mathematical expression of the temperature data compensation algorithm is as follows: ; Among them, is the true temperature value after compensation; is the original temperature value directly measured by the sensor; is the dynamic compensation coefficient; is the rate of change of temperature with time.

4. The method for evaluating the swelling of a battery pack according to claim 1, wherein The synchronous control program includes a dynamic matching algorithm for charge and discharge current and gas pressure and temperature sensor data and a correlation analysis module for vibration spectrum and pressure fluctuation amplitude; Among them, the dynamic matching algorithm realizes millisecond-level timestamp alignment of charge and discharge current parameters and gas pressure and temperature sensor data through a time series alignment module, extracts current characteristics and voltage characteristics, and establishes a dynamic coupling analysis model; The correlation analysis module realizes synchronous acquisition of vibration spectrum and pressure fluctuation data through a sliding window compensation mechanism, extracts vibration spectrum and pressure fluctuation characteristics, and establishes a correlation analysis model; Based on the dynamic coupling analysis model and the correlation analysis model, the pressure fluctuation amplitude and temperature gradient change rate of the battery pack in the relevant application environment are obtained.

5. A method for evaluating the swelling of a battery pack according to claim 1, characterized in that, For the charge and discharge module test, charge at a constant current of 0.5C to 100% SOC, then stand still for 30 minutes, and then discharge at a constant current of 1C to 20% SOC; Secondly, quickly charge the battery from 0% to 80% SOC with 4C fast charging, then stand still for 10 minutes, and then quickly discharge at 3C to 10% SOC; And the battery capacity is calibrated in real time through the Coulomb integration method during the test.

6. The method for evaluating the swelling of a battery pack according to claim 1, wherein The temperature control box test includes temperature gradient test and thermal-mechanical coupling test; Among them, for the temperature gradient test, low-temperature cycle and high-temperature shock are adopted. Keep the battery pack at -40°C for 2 hours, then raise the temperature to 25°C, and the temperature rise rate is 5°C / min, and repeat 3-5 times; then raise the ambient temperature from 25°C to 150°C, and the temperature rise rate is 10°C / min, and keep it for 1 hour; during the test, control the temperature fluctuation in the box ≤±1°C through the PID algorithm; For the thermal-mechanical coupling test, the battery pack is placed at a high temperature of 85°C for 4C fast charging. The vibration table is started synchronously, and the infrared thermal imager is used to verify the uniformity of the temperature distribution.

7. A method for evaluating the swelling of a battery pack according to claim 1, wherein The characteristic parameters in step 4 are the amplitude of pressure fluctuation and the change rate of temperature gradient. Based on the amplitude of pressure fluctuation, the three-level expansion threshold warning is divided into first-level warning, second-level protection, and third-level fault. Among them, under the first-level warning, the charging and discharging current is derated; under the second-level protection, the circuit is cut off and the pressure relief valve is started; under the third-level fault, the fire-fighting aerosol is activated for spraying.

8. An instrument for evaluating the swelling of a battery pack, which is applied to the method for evaluating the swelling of a battery pack according to any one of claims 1-7, characterized in that, It includes a gas pressure and temperature sensor and a gas pressure and temperature recorder, which are connected by a wire harness. The gas pressure and temperature sensor includes a main body, a gas probe, a fixed terminal, and a cable connector integrated on the main body. A gas-sensitive ceramic resistor and a thermosensitive ceramic resistor for detecting the changes in gas pressure and temperature are integrated in the main body. The gas pressure and temperature recorder has at least two channels and is used in combination with the gas pressure and temperature sensor to achieve multi-channel intake pressure measurement and multi-channel intake temperature measurement. A flip-type BCPT interface is provided on each channel. It further includes a host computer, which includes: a processor; a memory for storing instructions executable by the processor; Among them, the processor is configured to implement the method for evaluating the expansion of the battery pack according to any one of claims 1-7 when executing the instructions stored in the memory.

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