Method and device for monitoring internal pressure of lithium ion battery

Abstract

The application discloses a kind of monitoring method and device of lithium ion battery internal pressure, wherein, monitoring method includes: step S1, by sending ultrasonic pulse transmission the lithium ion battery, acquisition different internal pressure state under ultrasonic transmission signal;Step S2, the waveform of ultrasonic transmission signal is acquired multiple times under the same internal pressure state is post-processed, and the waveform of ultrasonic after processing is obtained;Step S3, calculate the time of flight of ultrasonic after processing and characteristic amplitude, and with the time of flight of ultrasonic and characteristic amplitude of lithium ion battery initial state, lithium ion battery thickness variation amount jointly calculated to obtain the internal pressure increment of lithium ion battery.The application utilizes the time of flight of ultrasonic and amplitude response under different pressure states in lithium ion battery interior, can nondestructively obtain internal pressure state of lithium ion battery, without battery structure is reformed or installs built-in sensor, with nondestructive, low cost and the like advantages.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a method and device for monitoring the internal pressure of a lithium-ion battery. Background Technology

[0002] As an energy-containing system, a lithium-ion battery contains highly active positive and negative electrodes separated only by a polymer separator and immersed in a flammable organic electrolyte. When exposed to abuse conditions, the temperature may exceed the normal operating range, triggering internal material decomposition or reactions, releasing a large amount of heat, further increasing the temperature, intensifying internal chemical reactions, and ultimately causing thermal runaway. During the evolution from abuse to thermal runaway, the side reactions involved in lithium-ion batteries generally generate gaseous products that accumulate within the battery's sealed casing, causing the casing to bulge. When the gas accumulation reaches a certain threshold, the internal pressure becomes excessive, causing the casing to rupture or the explosion-proof valve to open, releasing large amounts of flammable gas or unstable highly active components, leading to more serious safety accidents. In practical applications, whether in new energy vehicles or large-scale energy storage batteries, the thermal runaway of a single battery can trigger thermal runaway in adjacent batteries. Once thermal runaway begins, the internal reactions will spontaneously accelerate and cannot be terminated by external means. Therefore, early warning of battery thermal runaway is crucial for lithium-ion batteries.

[0003] Improving the safety of lithium-ion batteries is a systematic project that requires an advanced battery management system to monitor, warn, regulate, and handle each cell. However, existing battery management systems cannot accurately sense the state of charge (SOC) and state of health (SOH) of all cells, thus failing to rationally control battery charging and discharging and provide early warnings of potential risks. The physical quantities collected by existing battery management systems are limited to voltage, current, and temperature at the module level, while faults in individual cells within the battery pack, such as overcharging, over-discharging, and short circuits, cannot be reflected in relevant parameter changes at the module level in a timely and effective manner. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method and device for monitoring the internal pressure of a lithium-ion battery, so as to effectively obtain the internal pressure state of the battery and prevent thermal runaway accidents.

[0005] To address the aforementioned technical problems, this invention provides a method for monitoring the internal pressure of a lithium-ion battery, comprising:

[0006] Step S1: By sending ultrasonic pulses through the lithium-ion battery, ultrasonic transmission signals under different internal pressure states are collected.

[0007] Step S2: Post-process the waveforms of the ultrasonic transmission signals acquired multiple times under the same internal pressure state to obtain the processed ultrasonic waveform.

[0008] Step S3: Calculate the processed ultrasonic flight time and characteristic amplitude, and calculate the internal pressure increment of the lithium-ion battery together with the ultrasonic flight time and characteristic amplitude of the lithium-ion battery in its initial state and the change in lithium-ion battery thickness.

[0009] Furthermore, in step S1, the ultrasonic transmitting transducer and the ultrasonic receiving transducer are respectively placed on the two working surfaces of the lithium-ion battery, and the centers of the ultrasonic transmitting transducer and the ultrasonic receiving transducer are kept coaxial.

[0010] Furthermore, in step S2, the waveform processing of the ultrasonic transmission signals acquired multiple times under the same internal pressure state specifically involves averaging and smoothing.

[0011] Further, in step S3, the internal pressure increment ΔP of the lithium-ion battery is calculated as follows:

[0012]

[0013] Where, τ n The time of flight of the processed ultrasonic wave is taken as the characteristic amplitude, denoted as A, which is 2 / 3 of the highest wave packet amplitude of the received ultrasonic wave. The characteristic amplitude of the lithium-ion battery after n cycles is A. n The corresponding ultrasonic flight time is τ n The battery thickness is d n The ultrasonic characteristic amplitude of the battery in its initial state is A0, and the corresponding ultrasonic flight time is denoted as τ0; k, ε, and b are all constants.

[0014] Furthermore, k, ε, and b are calculated as follows:

[0015] The ultrasonic flight time τ and intensity A of lithium-ion batteries under different internal pressure conditions are measured, and the corresponding internal pressure increments are recorded. The values ​​of k and ε are obtained by fitting the linear relationship between the corresponding ultrasonic flight time and amplitude and the internal pressure increment. The value of constant b is obtained by summing the square roots of the absolute values ​​of the intercepts of the fitted curves.

[0016] The present invention also provides a device for monitoring the internal pressure of a lithium-ion battery, comprising:

[0017] An ultrasonic transducer is used to emit ultrasonic pulses that penetrate the lithium-ion battery.

[0018] An ultrasonic receiving transducer is used to receive the transmitted ultrasonic signal after transmission.

[0019] The signal acquisition module is used to acquire ultrasonic transmission signals under different internal pressure conditions;

[0020] The processing module is used to post-process the waveforms of ultrasonic transmission signals acquired multiple times under the same internal pressure state to obtain the processed ultrasonic waveforms.

[0021] The calculation module is used to calculate the processed ultrasonic flight time and characteristic amplitude, and together with the ultrasonic flight time and characteristic amplitude of the lithium-ion battery in its initial state and the change in lithium-ion battery thickness, calculate the internal pressure increment of the lithium-ion battery.

[0022] Furthermore, the ultrasonic transmitting transducer and the ultrasonic receiving transducer are respectively placed on two working surfaces of the lithium-ion battery, and their central axes coincide.

[0023] Furthermore, the processing module is specifically used to average and smooth the waveforms of ultrasonic transmission signals acquired multiple times under the same internal pressure state.

[0024] Furthermore, the calculation module specifically calculates the internal pressure increment ΔP of the lithium-ion battery in the following manner:

[0025]

[0026] Where, τ n The time of flight of the processed ultrasonic wave is taken as the characteristic amplitude, denoted as A, which is 2 / 3 of the highest wave packet amplitude of the received ultrasonic wave. The characteristic amplitude of the lithium-ion battery after n cycles is A. n The corresponding ultrasonic flight time is τ n The battery thickness is d n The ultrasonic characteristic amplitude of the battery in its initial state is A0, and the corresponding ultrasonic flight time is denoted as τ0; k, ε, and b are all constants.

[0027] Furthermore, k, ε, and b are calculated as follows:

[0028] The ultrasonic flight time τ and intensity A of lithium-ion batteries under different internal pressure conditions are measured, and the corresponding internal pressure increments are recorded. The values ​​of k and ε are obtained by fitting the linear relationship between the corresponding ultrasonic flight time and amplitude and the internal pressure increment. The value of constant b is obtained by summing the square roots of the absolute values ​​of the intercepts of the fitted curves.

[0029] The present invention has the following advantages: The present invention utilizes the ultrasonic flight time and amplitude response under different pressure states inside a lithium-ion battery to obtain the internal pressure state of the lithium-ion battery non-destructively. It does not require modification of the battery structure or installation of built-in sensors, and has the advantages of being non-destructive and low-cost. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a flowchart illustrating a method for monitoring the internal pressure of a lithium-ion battery according to Embodiment 1 of the present invention. Detailed Implementation

[0032] The following description of the embodiments is taken with reference to the accompanying drawings, which illustrate specific embodiments in which the invention can be implemented.

[0033] During thermal runaway in lithium-ion batteries, gas generation is often accompanied by gas accumulation. The continuous accumulation of gas increases the internal pressure of the battery. Among various characteristic parameters such as voltage, current, temperature, and internal resistance, internal pressure is the first and most significant to change in the early stages of thermal runaway. An abnormal increase in internal pressure is usually a common precursor to thermal runaway in lithium-ion batteries. Therefore, accurate measurement of the internal pressure of lithium-ion batteries can effectively prevent thermal runaway accidents. Thus, it is necessary to develop a non-destructive battery internal pressure monitoring technology to prevent thermal runaway accidents and ensure the safe operation of lithium-ion batteries throughout their entire lifecycle.

[0034] Therefore, please refer to Figure 1 As shown, Embodiment 1 of the present invention provides a method for monitoring the internal pressure of a lithium-ion battery, comprising:

[0035] Step S1: By transmitting ultrasonic pulses through the lithium-ion battery, ultrasonic transmission signals under different internal pressure states are collected.

[0036] Step S2: Post-process the waveforms of the ultrasonic transmission signals acquired multiple times under the same internal pressure state to obtain the processed ultrasonic waveform.

[0037] Step S3: Calculate the processed ultrasonic flight time and characteristic amplitude, and calculate the internal pressure increment of the lithium-ion battery together with the ultrasonic flight time and characteristic amplitude of the lithium-ion battery in its initial state and the change in lithium-ion battery thickness.

[0038] Specifically, firstly, the ultrasonic transmitting transducer and the ultrasonic receiving transducer are placed on the two working surfaces of the lithium-ion battery, respectively, and the centers of the ultrasonic transmitting transducer and the ultrasonic receiving transducer are kept coaxial. It can be understood that the largest surface area of ​​the lithium-ion battery is called the working surface; as an example, the lithium-ion battery in this embodiment is a square hard-shell lithium-ion battery (thickness between 10mm and 50mm), and the initial thickness d0 and the initial ultrasonic flight time τ0 of the lithium-ion battery are recorded.

[0039] After an ultrasonic pulse is emitted through an ultrasonic transmitting transducer and transmitted through a battery, the ultrasonic pulse is received by an ultrasonic receiving transducer, and ultrasonic transmission signals under different conditions are collected by a signal acquisition module.

[0040] Then, the waveforms of the ultrasonic transmission signals collected multiple times under the same internal pressure condition are averaged and smoothed to obtain the processed ultrasonic waveform W.

[0041] Calculate the flight time of the processed ultrasound wave, denoted as τ. n Calculate 2 / 3 of the highest wave packet amplitude of the received ultrasonic wave, and use it as the characteristic amplitude, denoted as A; the characteristic amplitude of the lithium-ion battery after n cycles is A. n The corresponding ultrasonic flight time is denoted as τ. n The battery thickness is d n The ultrasonic characteristic amplitude of the battery in its initial state is A0, and the corresponding ultrasonic flight time is denoted as τ0.

[0042] The internal pressure increment ΔP of a lithium-ion battery is calculated as follows:

[0043]

[0044] Among them, k, ε, and b are all constants, which can be obtained through multiple experiments and tests: First, measure the ultrasonic flight time τ and intensity A of the lithium-ion battery under different internal pressure conditions, and record the corresponding internal pressure increments. Then, fit the linear relationship between the corresponding ultrasonic flight time and amplitude and the internal pressure increment to obtain the values ​​of k and ε. Finally, calculate b based on the intercept (the value of constant b is obtained by summing the square roots of the absolute values ​​of the intercepts of the fitted curves).

[0045] Furthermore, in this embodiment of the invention, the ambient temperature range during the test is 10 to 50°C, and the ambient temperature is kept constant during the test.

[0046] The center frequencies of both the ultrasonic transmitting and receiving transducers are 1MHz to 5MHz, making it easy to acquire high signal-to-noise ratio transmitted ultrasonic signals. Both the ultrasonic transmitting and receiving transducers are focusing ultrasonic transducers with a focal length of 1cm to 4cm, which can be well matched to the thickness of lithium-ion batteries.

[0047] Based on the excellent directivity and penetrability of ultrasound, there is a potential correlation between the change in flight time and intensity of sound waves transmitted through a lithium-ion battery and the internal pressure of the battery. By establishing the relationship between the internal pressure of the battery and the flight time and transmission intensity, the internal pressure of the battery can be obtained. This invention does not require modification of the battery structure or installation of built-in sensors, and has the characteristics of being non-destructive and low-cost.

[0048] The invention will now be illustrated with specific examples.

[0049] An ultrasonic transducer with a center frequency of 2.5 MHz was used to measure a square hard-shell lithium-ion battery with a length of 30 mm, a height of 40 mm, and a thickness of 25 mm. The ultrasonic transmitting transducer and the ultrasonic receiving transducer were fixed at the center of the working surface of the square hard-shell lithium-ion battery, ensuring that their central axes coincided. The change in battery thickness Δd under different internal pressure conditions was measured, as were the ultrasonic flight time τ0 and the change in ultrasonic flight time Δτ under the initial state.

[0050] The changes in ultrasonic flight time, thickness, and sound intensity of a square hard-shell lithium-ion battery under different internal pressure conditions are measured. The corresponding relationships are fitted, the correlation coefficient is solved, and the internal pressure of the battery under different conditions can be calculated based on the fitted equation.

[0051] First, under conditions of 25℃, the battery was charged at a 1C rate, and ultrasonic signals were collected every 10 minutes. Simultaneously, the battery thickness and internal pressure increment were measured. The test results are shown in the table below:

[0052]

[0053]

[0054] With ΔP The fitting process yielded a curve with a slope of 17065 and an intercept of -1597, corresponding to k = 17065 in the model equation.

[0055] With ΔP The fitting process yielded a curve with a slope of -47075 and an intercept of 10017, corresponding to ε = 10017 in the model equation.

[0056] Among them, the results obtained from the fitting relationship are:

[0057] Under this temperature condition, the model equation is:

[0058] The internal pressure of the battery was measured using this model after charging at 1C rate for 30 minutes at 40℃ and 50℃. The test results are as follows:

[0059]

[0060] After charging the battery for 30 minutes at 40℃, the internal pressure was calculated to be 58613 Pa by substituting various parameters into the model equation, while the actual measured pressure was 56245 Pa. At 50℃, the internal pressure calculated by the model equation was 66310 Pa, while the actual measured pressure was 65247 Pa. The model calculations and actual measurements are quite close, indicating that the model equation has high accuracy.

[0061] Corresponding to the method for monitoring the internal pressure of a lithium-ion battery in Embodiment 1 of the present invention, Embodiment 2 of the present invention also provides a device for monitoring the internal pressure of a lithium-ion battery, comprising:

[0062] An ultrasonic transducer is used to emit ultrasonic pulses that penetrate the lithium-ion battery.

[0063] An ultrasonic receiving transducer is used to receive the transmitted ultrasonic signal after transmission.

[0064] The signal acquisition module is used to acquire ultrasonic transmission signals under different internal pressure conditions;

[0065] The processing module is used to post-process the waveforms of ultrasonic transmission signals acquired multiple times under the same internal pressure state to obtain the processed ultrasonic waveforms.

[0066] The calculation module is used to calculate the processed ultrasonic flight time and characteristic amplitude, and together with the ultrasonic flight time and characteristic amplitude of the lithium-ion battery in its initial state and the change in lithium-ion battery thickness, calculate the internal pressure increment of the lithium-ion battery.

[0067] Furthermore, the ultrasonic transmitting transducer and the ultrasonic receiving transducer are respectively placed on two working surfaces of the lithium-ion battery, and their central axes coincide.

[0068] Furthermore, the processing module is specifically used to average and smooth the waveforms of ultrasonic transmission signals acquired multiple times under the same internal pressure state.

[0069] Furthermore, the calculation module specifically calculates the internal pressure increment ΔP of the lithium-ion battery in the following manner:

[0070]

[0071] Where, τ n The time of flight of the processed ultrasonic wave is taken as the characteristic amplitude, denoted as A, which is 2 / 3 of the highest wave packet amplitude of the received ultrasonic wave. The characteristic amplitude of the lithium-ion battery after n cycles is A. n The corresponding ultrasonic flight time is τ nThe battery thickness is d n The ultrasonic characteristic amplitude of the battery in its initial state is A0, and the corresponding ultrasonic flight time is denoted as τ0; k, ε, and b are all constants.

[0072] Furthermore, k, ε, and b are calculated as follows:

[0073] The ultrasonic flight time τ and intensity A of lithium-ion batteries under different internal pressure conditions are measured, and the corresponding internal pressure increments are recorded. The values ​​of k and ε are obtained by fitting the linear relationship between the corresponding ultrasonic flight time and amplitude and the internal pressure increment. The value of constant b is obtained by summing the square roots of the absolute values ​​of the intercepts of the fitted curves.

[0074] For the working principle and process of this embodiment, please refer to the description of Embodiment 1 of the present invention, which will not be repeated here.

[0075] As can be seen from the above description, compared with the prior art, the beneficial effects of the present invention are as follows: The present invention utilizes the ultrasonic flight time and amplitude response under different pressure states inside the lithium-ion battery to obtain the internal pressure state of the lithium-ion battery non-destructively, without the need to modify the battery structure or install built-in sensors, and has the advantages of being non-destructive and low-cost.

[0076] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for monitoring the internal pressure of a lithium-ion battery, characterized in that, include: Step S1: By sending ultrasonic pulses through the lithium-ion battery, ultrasonic transmission signals under different internal pressure states are collected. Step S2: Post-process the waveforms of the ultrasonic transmission signals acquired multiple times under the same internal pressure state to obtain the processed ultrasonic waveform. Step S3: Calculate the processed ultrasonic flight time and characteristic amplitude, and calculate the internal pressure increment of the lithium-ion battery together with the ultrasonic flight time and characteristic amplitude of the lithium-ion battery in the initial state and the change in the thickness of the lithium-ion battery. In step S2, the waveform of the ultrasonic transmission signal collected multiple times under the same internal pressure state is specifically processed by averaging and smoothing. In step S3, the internal pressure increment of the lithium-ion battery is calculated as follows: : in, The time of flight of the processed ultrasonic wave is taken as the characteristic amplitude, denoted as A, which is 2 / 3 of the highest wave packet amplitude of the received ultrasonic wave. The characteristic amplitude of the lithium-ion battery after n cycles is... The corresponding ultrasonic flight time is The battery thickness is The characteristic amplitude of the ultrasonic waves in the initial state of the battery is The corresponding ultrasonic flight time is denoted as The initial thickness of the lithium-ion battery is ; All are constants.

2. The monitoring method according to claim 1, characterized in that, In step S1, the ultrasonic transmitting transducer and the ultrasonic receiving transducer are placed on the two working surfaces of the lithium-ion battery, respectively, and the centers of the ultrasonic transmitting transducer and the ultrasonic receiving transducer are kept coaxial.

3. The monitoring method according to claim 1, characterized in that, The calculation method is as follows: Measuring the ultrasonic time of flight of lithium-ion batteries under different internal pressure conditions and intensity Simultaneously, the corresponding internal pressure increments are recorded, and the linear relationship between the corresponding ultrasonic flight time and amplitude and the internal pressure increment is fitted to obtain the solution. The value of is then used to calculate the sum of the square roots of the absolute values ​​of the intercepts of the fitted curves to obtain the constant. The value of .

4. A device for monitoring the internal pressure of a lithium-ion battery, characterized in that, include: An ultrasonic transducer is used to emit ultrasonic pulses that penetrate the lithium-ion battery. An ultrasonic receiving transducer is used to receive the transmitted ultrasonic signal after transmission. The signal acquisition module is used to acquire ultrasonic transmission signals under different internal pressure conditions; The processing module is used to post-process the waveforms of ultrasonic transmission signals acquired multiple times under the same internal pressure state to obtain the processed ultrasonic waveforms. The calculation module is used to calculate the processed ultrasonic flight time and characteristic amplitude, and together with the ultrasonic flight time and characteristic amplitude of the lithium-ion battery in the initial state and the change in the thickness of the lithium-ion battery, calculates the internal pressure increment of the lithium-ion battery. The processing module is specifically used to average and smooth the waveforms of ultrasonic transmission signals acquired multiple times under the same internal pressure state. The calculation module specifically calculates the internal pressure increment of the lithium-ion battery in the following manner. : in, The time of flight of the processed ultrasonic wave is taken as the characteristic amplitude, denoted as A, which is 2 / 3 of the highest wave packet amplitude of the received ultrasonic wave. The characteristic amplitude of the lithium-ion battery after n cycles is... The corresponding ultrasonic flight time is The battery thickness is The characteristic amplitude of the ultrasonic waves in the initial state of the battery is The corresponding ultrasonic flight time is denoted as The initial thickness of the lithium-ion battery is ; All are constants.

5. The monitoring device according to claim 4, characterized in that, The ultrasonic transmitting transducer and the ultrasonic receiving transducer are respectively placed on two working surfaces of the lithium-ion battery, and their central axes coincide.

6. The monitoring device according to claim 4, characterized in that, The calculation method is as follows: Measuring the ultrasonic time of flight of lithium-ion batteries under different internal pressure conditions and intensity Simultaneously, the corresponding internal pressure increments are recorded, and the linear relationship between the corresponding ultrasonic flight time and amplitude and the internal pressure increment is fitted to obtain the solution. The value of is then used to calculate the sum of the square roots of the absolute values ​​of the intercepts of the fitted curves to obtain the constant. The value of .

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