Instrument and method for evaluating expansion of battery pack

Abstract

The invention belongs to the technical field of batteries, and particularly relates to an instrument and method for evaluating expansion of a battery pack, and the method comprises the following steps: 1, placing a gas probe of a miniaturized gas pressure and temperature sensor into an internal gas cavity of the battery pack, and connecting the gas probe to an external gas pressure and temperature recorder; step 2, acquiring pressure and temperature of gas in the battery pack and gaps of the battery cell monomers through a gas pressure and temperature sensor, and acquiring and storing changes of the gas pressure and temperature by adopting a gas pressure and temperature recorder; 3, constructing a multi-environment coupling test system which comprises a charging and discharging module, a temperature control box, a vibration table and an impact testing machine; and 4, establishing a pressure-temperature-deformation coupling model, and separating an environmental interference signal based on wavelet transform. According to the invention, the pressure and temperature changes of the inner cavity of the battery pack in various environments can be accurately collected, and the expansion characteristics of the battery are obtained by using the pressure and temperature changes, so that the state of the battery pack is pre-warned and protected.

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 into 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 parallel to form modules, and then the modules are connected in series and parallel to form a battery pack. The outer shell of the lithium battery pack is a sealed cavity composed of rigid materials. In the gaps between the battery cell monomers / modules inside the sealed cavity, there are mainly gases mainly air, 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, the electrochemical reactions inside the battery cells will also generate gases and discharge them 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 with charging and discharging characteristics 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 warning and protection to the state of the battery pack.

[0007] The technical solutions adopted by the present invention are specifically as follows: A method for evaluating the expansion of a battery pack 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 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; Step 2: Obtain the pressure and temperature of the gas in the voids inside the battery pack and within 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; 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 relevant application environments, and synchronously extract characteristic parameters for three-level expansion threshold warning.

[0008] As a preferred solution, the connection between the gas pressure and temperature sensor and the battery pack housing adopts a sealing structure with a fluororubber O-ring nested with a metal flange.

[0009] 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; The specific mathematical expression of the temperature data compensation algorithm is: ; 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 over time.

[0010] 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; 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 relevant application environments are obtained.

[0011] As a preferred solution, the charge and discharge module test is carried out by charging at a constant current of 0.5C to 100% SOC, then standing for 30 minutes, and then discharging at a constant current of 1C to 20% SOC; Secondly, use 4C fast charging to quickly charge the battery from 0% to 80% SOC, then let it stand for 10 minutes, and then quickly discharge it at 3C to 10% SOC; And during the test, the battery capacity is calibrated in real time by the Coulomb integration method.

[0012] As a preferred solution, the temperature control box test includes a temperature gradient test and a thermal-mechanical coupling test; Among them, in the temperature gradient test, low-temperature cycling and high-temperature shock are adopted. The battery pack is kept at -40°C for 2 hours, then heated to 25°C, and the temperature rise rate is 5°C / min, and it 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 in the box is controlled by the PID algorithm to be ≤ ±1°C; 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 by an infrared thermal imager.

[0013] As a preferred solution, 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.

[0014] 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; Among them, in the first-level warning, the charge and discharge current is derated; in the second-level protection, the circuit is cut off and the pressure relief valve is activated; in the third-level fault, the fire aerosol injection is activated.

[0015] 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, and the two are connected by a wire harness; The gas pressure and temperature sensor includes a main body, and a gas probe, fixed terminals and a cable connector integrated on the main body. A gas-sensitive ceramic resistor and a thermosensitive ceramic resistor for detecting gas pressure and temperature changes 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.

[0016] As a preferred solution, it further includes a host computer, which includes: A processor; A memory for storing instructions executable by the processor; Wherein, the processor is configured to implement the method for evaluating the expansion of the battery pack when executing the instructions stored in the memory.

[0017] The technical effects achieved by the present invention are: The present invention adopts a composite gas pressure and temperature sensor. The cylindrical gas probe makes its installation with the battery pack simpler, and a fluororubber O-ring sealing structure is adopted to reduce the influence of the external environment. At the same time, the air in the battery pack is used as the medium to detect the expansion characteristics of the battery pack. 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.

[0018] By adopting a pressure-temperature-deformation coupling model, the present invention can predict dangerous expansion more efficiently, and sets a three-level expansion threshold mechanism to greatly improve the safety response speed, reduce the 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, thus ensuring the monitoring accuracy. Description of the Drawings

[0019] Figure 1 It is a schematic structural diagram of the process of the method for evaluating the expansion of the battery pack in the embodiment of the present invention; Figure 2 It is a schematic connection structure diagram of the instruments in the method for evaluating the expansion of the battery pack in the embodiment of the present invention; Figure 3 It is a schematic structural diagram of the gas pressure and temperature sensor in the instrument for evaluating the expansion of the battery pack in the embodiment of the present invention; Figure 4 It is a schematic assembly structure diagram of the gas pressure and temperature sensor in the instrument for evaluating the expansion of the battery pack in the embodiment of the present invention; Figure 5 It is a schematic structural diagram of the gas pressure and temperature recorder in the instrument for evaluating the expansion of the battery pack in the embodiment of the present invention.

[0020] In the accompanying drawings, the list of components represented by each reference numeral is as follows: 1. Gas pressure and temperature sensor; 11. Main body; 12. Gas probe; 13. Fixed terminal; 14. Cable connector; 2. Gas pressure and temperature recorder; 21. Physical channel; 22. BCPT interface; 23. Resistive touch screen. Detailed implementation manners

[0021] In order to make the objectives 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.

[0022] As Figures 1 - 5 shown, a method for evaluating the expansion of a battery pack includes the following steps: 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 of the explosion-proof valve, and connect it to the external gas pressure and temperature recorder 2.

[0023] Specifically refer to the attached Figure 3 , wherein, the gas pressure and 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, and 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 of the resistance into a voltage signal through circuit excitation, the gas pressure and temperature information can be obtained.

[0024] Specifically refer to the attached 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 gas filled in this part of the gap may be ordinary air, special gas or waste gas discharged 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 discharge 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; so as to achieve the purpose of monitoring the air pressure and temperature inside the battery pack.

[0025] It should be noted that the connection between the gas pressure and temperature sensor 1 and the battery pack housing adopts a sealing structure with a fluororubber O-ring nested with a metal flange, which can avoid detection errors caused by internal gas leakage and reduce the influence of the external environment on the detection process.

[0026] It should be noted that the sensor used in this embodiment is a sensor that can sense the pressure and temperature of gas, 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, automotive engine intake air, and void leakage gas in a lithium battery pack, so as to evaluate the physical state of the corresponding gaseous substances. It adopts a 4-wire design and can measure the air pressure and temperature simultaneously (2 wires for each of the air pressure and temperature). The specific technical specifications are as follows: Table 1. Technical Specification Table of Gas Pressure and Temperature Sensor 1 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 　 S2. 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 1, and use the gas pressure and temperature recorder 2 to collect and store the changes in gas pressure and temperature.

[0027] Specifically, refer to the appendix Figure 5 , the gas pressure and temperature recorder 2 has 2 physical channels 21, which can be connected to 2 gas pressure and temperature sensors 1 to compare data in real time and accurately capture abnormal data. It adopts a customized flip-top 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: Table 2. Performance Parameter Table of Gas Pressure and Temperature Recorder 2 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, 2 meters * 2 　 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 uses a temperature data compensation algorithm to compensate the original temperature values.

[0028] Furthermore, the specific mathematical expression of the temperature data compensation algorithm is: ; Among them, is the true value of the compensated temperature; is the original temperature value directly measured by the sensor; is the dynamic compensation coefficient; is the rate of change of temperature over time.

[0029] S3. Construct a multi - environment coupling test system, including a charge - discharge module, a temperature - control box, a vibration table, and a shock testing machine, and achieve millisecond - level timestamp alignment of environmental parameters and the data of the gas pressure and temperature sensor 1 through a synchronous control program.

[0030] Among them, the test process of the charge - discharge module is as follows: I. Test process 1. Cycling charge - discharge strategy 1.1. Charge at a constant current of 0.5C to 100% SOC, then stand still for 30 min, and then discharge at a constant current of 1C to 20% SOC; 1.2. Fast charge at 4C (0 - 80% SOC), then stand still for 10 min, and then fast discharge at 3C to 10% SOC; SOC accuracy control: Calibrate the capacity in real - time through the Coulomb integration method (error < ±5%); 2. Pulse test: Apply a current pulse of the 50 - ms level (such as a peak value of 200A) and synchronously record the pressure response.

[0031] II. Synchronous trigger mechanism Align the data of the charge - 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%.

[0032] Among them, the test process of the temperature - control box is as follows: I. Extreme temperature change test: 1.1. Low - temperature cycle: Keep in an environment of - 40°C for 2 h, then gradually heat up to 25°C (temperature - rise rate 5°C / min), and repeat this 3 times; 1.1. High - temperature shock: Gradually increase the environmental temperature from 25°C to 150°C (temperature - rise rate 10°C / min), and then keep in this temperature environment for 1 h; During the test process, precise temperature control is required: Control the temperature fluctuation in the box ≤ ±1°C through the PID algorithm (refer to GB / T 2423.22).

[0033] II. Thermal - mechanical coupling test Perform 4C fast charge at a high temperature of 85°C, synchronously start the vibration table (frequency 200 Hz), and at the same time verify the temperature distribution uniformity through an infrared thermal imager (temperature difference < 3°C).

[0034] Among them, in this embodiment, a vibration table (adjustable from 5 - 2000 Hz) is selected, and its specific parameters are as follows: I. Random vibration: Power spectral density (PSD): 0.04 g² / Hz (5 - 100 Hz) to 0.02 g² / Hz (100 - 2000 Hz), randomly selected; Duration: 3 hours for each axis (tested independently for X / Y / Z axes).

[0035] II. Sine sweep frequency: Sweep from 5 - 2000 Hz (rate 1 oct / min) to identify resonance frequencies (such as 120 Hz, 850 Hz).

[0036] Among them, the test process of the impact testing machine is as follows: I. Impact parameter setting 1.1. Impact waveform: Half - sine wave (peak acceleration 50g, pulse width 11ms); Trapezoidal wave (30g, 30ms) to simulate the transportation drop scenario.

[0037] 1.2. Multi - axial impact: Apply 3 impacts to each of the X / Y / Z axes (refer to ISTA 3A standard).

[0038] II. Impact damage assessment 2.1. Detect structural failure through sudden change in pressure fluctuation: If the instantaneous value of ΔP after impact > 40 kPa and does not fall back, it is determined that the sealing structure is damaged; Secondly, analyze local deformation using pressure - sensitive recording paper (deformation rate > 5% is judged as failure).

[0039] In this embodiment, the multi - environment coupling test process is as follows: S3.1: Complete 1 full charge - discharge cycle at 25°C (baseline data collection); S3.2: Perform 3C fast charging in an environment of - 20°C, and simultaneously start the vibration table (random vibration from 50 - 500 Hz); S3.3: Apply Y - axis impact (50g, half - sine wave) under high - temperature (60°C) working conditions; S3.4: Analyze the coupling coefficient of ΔP with temperature / vibration / impact (such as γ - value calibration).

[0040] 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 fluctuation; 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 current features and voltage features, and establishes a dynamic coupling analysis model.

[0041] The specific algorithm architecture is as follows: I. Time - series alignment module 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.

[0042] The sliding window method (window length 5 ms) is adopted to compensate for the transmission delays of different sensor signals, ensuring that the data synchronization error < 1 ms.

[0043] II. Feature Parameter Extraction 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 amount (Q = ∫I·dt).

[0044] Pressure features: Calculate the pressure fluctuation amplitude (ΔP), the pressure gradient (dP / dt), and the spectral energy distribution (obtain the main frequency component through FFT transformation).

[0045] III. Dynamic Coupling Analysis Model Establish the current-pressure transfer function: ; Among them, , , are fitting coefficients, which are optimized by the least squares method.

[0046] Introduce the electrochemistry-thermal expansion coupling equation: ; Among them, is the internal resistance of the battery, , , are experimental calibration parameters.

[0047] The specific correlation analysis model is as follows: I. Data Synchronization Unit 1.1. Adopt the millisecond-level timestamp alignment algorithm developed by LabVIEW, and realize the synchronous acquisition of the vibration spectrum and pressure fluctuation data through the sliding window compensation mechanism (window length 5 ms), with the synchronization error < 1 ms; 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).

[0048] II. Feature Parameter Extraction Unit 2.1. Vibration spectrum features: 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).

[0049] 2.2. Pressure fluctuation characteristics: Calculate the pressure gradient (dP / dt), the fluctuation amplitude (ΔP), and the main frequency of the spectrum (analyzed through the power spectral density PSD).

[0050] III. Core algorithms for correlation analysis 3.1 Cross-Correlation Function: ; where and represent two continuous-time signals to be analyzed; is the time delay (unit: second), representing the time interval by which the signal is shifted relative to ; is the time variable (unit: second), which is the independent variable of the integration 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.

[0051] 3.2 Wavelet Coherence Analysis: Adopt the Morlet wavelet transform to calculate the energy coherence between the vibration spectrum and the pressure fluctuation in the time-frequency domain, and locate the high-frequency resonance region.

[0052] 3.3 Transfer Function Modeling: Establish the frequency response function between the vibration acceleration (a) and the pressure fluctuation (ΔP): ; where is the cross-power spectrum, is the auto-power spectrum, which is used to quantify the transfer efficiency of the vibration energy to the pressure fluctuation.

[0053] By introducing the above dynamic coupling analysis model and correlation analysis model, the pressure fluctuation amplitude and the temperature gradient change rate of the battery pack in the relevant application environment can be obtained.

[0054] S4. Establish a pressure-temperature-deformation coupling model, and based on wavelet transform, separate the environmental interference signals, 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.

[0055] It should be noted that the specific mathematical expression of the pressure-temperature-deformation coupling model is: ; where is the change value of the internal gas pressure of the battery pack relative to the initial state; is the coefficient of thermal expansion of the gas; is the value of temperature change; is the coefficient of electrochemical gas production; is the state of charge; is the mechanical vibration influence factor; is the amplitude; is the vibration frequency; is the time.

[0056] The above coupling model comprehensively reflects the coupling effects of three factors, namely temperature change, electrochemical gas production, and mechanical vibration, on the expansion characteristics of the battery pack.

[0057] Furthermore, the specific physical meanings of each part are as follows: 1. Thermodynamic expansion component ( ) The thermal expansion and contraction effect of the gas caused by the temperature change ( ), is the coefficient of thermal expansion of the gas. In some embodiments, when the temperature of the battery pack increases by 1 °C, increases by approximately 0.5 - 1.2 kPa (the specific value depends on the type of gas).

[0058] 2. Electrochemical gas production component ( ) Caused by the gas production during the charge and discharge process of the battery due to the decomposition of the electrolyte, and the increase in SOC (state of charge) will exacerbate the gas production volume.

[0059] Experiments in some embodiments show that: when SOC increases from 50% to 100%, the contribution of gas production can reach 8 - 15 kPa.

[0060] 3. Mechanical vibration component ( ) External vibration (amplitude , frequency ) causes the deformation of the battery pack structure, triggering periodic pressure fluctuations in the gas cavity. In some embodiments, when the vibration frequency > 100 Hz, the amplitude can reach 3 - 5 times that of the static condition.

[0061] The characteristic parameters in S4 are the amplitude of pressure fluctuation and the rate of temperature gradient change, and 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. The specific warning process is as follows: First - level warning ( > 15 kPa): Trigger the derating of charge and discharge current; Second - level protection ( > 25 kPa): Cut off the circuit and activate the pressure relief valve; Third - level fault ( >40 kPa): Activate the fire aerosol injection.

[0062] Based on the above model, the prediction of dangerous expansion can be more efficient, and a three-level expansion threshold mechanism can be set to greatly improve the safety response speed, reduce the early 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, a breakthrough in multi-physical field coupling analysis can be achieved, thus ensuring the monitoring accuracy.

[0063] Such 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 shown).

[0064] 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. A gas-sensitive ceramic resistor and a thermosensitive ceramic resistor for detecting gas pressure and temperature changes are integrated in the main body 11; the gas probe 12 can be inserted into the battery pack without contacting the gas components such as the battery cells, only contacting the internal gas, and the fixed terminal 13 is used to fix it to the battery pack as a whole. At the same time, the cable connector 14 at the tail is connected to the outside of the battery pack through a cable and connected to the gas pressure temperature recorder 2 to monitor the gas temperature and pressure inside the battery pack.

[0065] Furthermore, the gas pressure temperature recorder 2 has at least two channels 21 and is used in combination with the gas pressure temperature sensor 1 to realize multi-channel intake pressure measurement and multi-channel intake temperature measurement. A flip-type BCPT interface 22 is provided on each channel 21; it 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 realize long-term data storage; at the same time, a 485 communication interface is opened to facilitate users to remotely read the channel data through the host computer in real time.

[0066] It should be noted that it also includes a host computer, which is a computer device (PC) in this implementation and is presented in the form of a general computing device.

[0067] 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).

[0068] The bus represents one or more of several types of bus architectures, including a memory bus or memory controller, a peripheral bus, an Accelerated Graphics Port, a processor, or a local bus using any of the various bus architectures. By way of example, these architectures include, but are not limited to, Industry Standard Architecture (ISA) bus, Micro Channel Architecture (MAC) bus, Enhanced ISA bus, Video Electronics Standards Association (VESA) local bus, and Peripheral Component Interconnect (PCI) bus.

[0069] A 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 nonvolatile media, removable and non-removable media.

[0070] System memory can include computer system readable media in the form of volatile memory, such as random access memory (RAM) and / or cache memory. The computer device can further include other removable / non-removable, volatile / nonvolatile computer system storage media. By way of example only, a storage system can be used for reading from and writing to a non-removable, nonvolatile magnetic medium (commonly referred to as a "hard disk drive"). A disk drive can be provided for reading from and writing to a removable nonvolatile disk (such as a "floppy disk"), and an optical disk drive for reading from and writing to a removable nonvolatile optical disk (such as a CD-ROM, DVD-ROM, or other optical medium). In these instances, each drive can be connected to the bus by one or more data media interfaces. The memory can include at least one program product having a set (e.g., at least one) of program modules that are configured to carry out the functions of the embodiments of the present invention.

[0071] A program / utility having a set (at least one) of program modules can 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, and an implementation of a network environment may be included in each or some combination of these examples. The program modules typically carry out the functions and / or methods of the embodiments described in the present invention.

[0072] The computer device can also communicate with one or more external devices (such as a keyboard, a pointing device, a display, etc.), and can 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 can be carried out through an input / output (I / O) interface. Moreover, the computer device can 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 a bus. It should be understood that other hardware and / or software modules can be used in combination 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.

[0073] 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 the battery pack provided by the embodiments of the present invention.

[0074] 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 refinements can be made, and these improvements and refinements 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, unless otherwise specified and limited, are implemented according to the conventional means in the art.

Claims

1. A method for evaluating battery pack expansion, characterized in that: The following steps are involved: Step 1: Place the gas probe of the miniaturized gas pressure and temperature sensor into the internal air cavity of the battery pack, and lead the gas pressure and temperature sensor harness through the modified hole of the explosion-proof valve to connect it to an external gas pressure and temperature recorder; Step 2: Obtain the pressure and temperature of the gas inside the battery pack and in the gaps of the battery cells through a gas pressure and temperature sensor, and use a gas pressure and temperature recorder to collect and store changes in gas pressure and temperature; Step 3: Build a multi-environment coupling test system, including a charging and discharging module, a temperature control box, a vibration table, and an impact tester, and use a synchronous control program to achieve millisecond-level timestamp alignment between environmental parameters and gas pressure and temperature sensor data; Step 4: Establish a pressure-temperature-deformation coupling model and separate the environmental interference signal based on wavelet transform to obtain the expansion characteristics of the battery pack in the relevant application environment, and simultaneously extract characteristic parameters for three-level expansion threshold warning.

2. A method for evaluating battery pack expansion according to claim 1, characterized in that: The connection between the gas pressure and temperature sensor and the battery pack housing adopts a sealing structure in which a fluororubber O-ring and a metal flange are nested.

3. The method for evaluating battery pack expansion according to claim 1, characterized in that: The gas pressure and temperature recorder performs Butterworth low-pass filtering on the collected original pressure values, and uses a temperature data compensation algorithm to compensate the original temperature values; The specific mathematical expression of the temperature data compensation algorithm is: ; in, is the actual value of temperature after compensation; It 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. A method for evaluating battery pack expansion according to claim 1, characterized in that: The synchronous control program includes a dynamic matching algorithm between charge and discharge current and gas pressure and temperature sensor data and a correlation analysis module between vibration spectrum and pressure fluctuation amplitude; The dynamic matching algorithm realizes the millisecond timestamp alignment of the charge and discharge current parameters and the gas pressure and temperature sensor data through the time series alignment module, extracts the current characteristics and voltage characteristics, and establishes a dynamic coupling analysis model; The correlation analysis module realizes the synchronous acquisition of vibration spectrum and pressure fluctuation data through a sliding window compensation mechanism, extracts the 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 the temperature gradient change rate of the battery pack in the relevant application environment are obtained.

5. The method for evaluating battery pack expansion according to claim 1, characterized in that: The charge and discharge module test uses 0.5C constant current charging to 100% SOC, then standing for 30 minutes, and then 1C constant current discharge to 20% SOC; Secondly, use 4C fast charging to charge the battery from 0% to 80% SOC, then let it sit for 10 minutes, and then discharge it to 10% SOC at 3C. During the test, the battery capacity is calibrated in real time using the Coulomb integration method.

6. A method for evaluating battery pack expansion according to claim 1, characterized in that: The temperature control box test includes a temperature gradient test and a thermal-mechanical coupling test; The temperature gradient test uses low temperature cycle and high temperature shock. The battery pack is kept at -40℃ for 2 hours, then heated to 25℃ at a rate of 5℃ / min, and repeated 3-5 times. Then the ambient temperature is raised from 25℃ to 150℃ at a rate of 10℃ / min and kept for 1 hour. During the test, the temperature fluctuation in the box is controlled by the PID algorithm to be ≤±1℃. The thermal-mechanical coupling test places the battery pack at a high temperature of 85°C for 4C fast charging, simultaneously starts the vibration table, and verifies the uniformity of temperature distribution with an infrared thermal imager.

7. A method for evaluating battery pack expansion according to claim 1, characterized in that: The specific mathematical expression of the pressure-temperature-deformation coupling model is: ； in, is the change in gas pressure inside the battery pack relative to the initial state; is the thermal expansion coefficient of gas; is the temperature change value; is the electrochemical gas production coefficient; is the state of charge; is the mechanical vibration influence factor; is the amplitude; is the vibration frequency; For time.

8. The method for evaluating battery pack expansion according to claim 1, characterized in that: The characteristic parameters in step 4 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; Among them, under the first-level warning, the charging and discharging current derating is triggered; under the second-level protection, the circuit is cut off and the pressure relief valve is started; under the third-level fault, the fire aerosol spray is activated.

9. An instrument for evaluating battery pack expansion, applied to the method for evaluating battery pack expansion according to any one of claims 1 to 8, characterized in that: It includes a pressure temperature sensor and a gas pressure temperature recorder, which are connected by a wiring harness; The gas pressure and temperature sensor comprises a main body and a gas probe, a fixed terminal and a cable connector integrated on the main body, wherein a gas-sensitive ceramic resistor and a thermistor ceramic resistor for detecting 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 conjunction with the gas pressure and temperature sensor to achieve multi-channel intake pressure measurement and multi-channel intake temperature measurement. A flip-top BCPT interface is provided on each of the channels.

10. The apparatus for evaluating battery pack expansion according to claim 9, characterized in that: It also includes a host computer, which includes: processor; a memory for storing processor-executable instructions; Wherein, the processor is configured to implement the method for evaluating battery pack expansion when executing instructions stored in the memory.

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