An in-situ monitoring system and method for the internal pressure of a lithium-ion battery

Abstract

The present invention discloses an in-situ monitoring system and method for the internal pressure of a lithium-ion battery. Specifically, two fiber optic F-P sensors with different sensitivity coefficients are used. The two fiber optic F-P sensors are installed at intervals on the lithium-ion battery to be monitored. The sensing probes of the fiber optic F-P sensors are located inside the lithium-ion battery to be monitored. The fiber optic F-P sensors are connected to a demodulation system. The fiber optic F-P sensors are used to obtain the temperature-pressure coupling data generated during the charging and discharging process of the lithium-ion battery to be monitored. The demodulation system decouples the temperature-pressure coupling data generated during the charging and discharging process of the lithium-ion battery to be monitored to obtain the temperature and pressure data generated during the charging and discharging process of the lithium-ion battery to be monitored. It can realize the in-situ simultaneous monitoring of the internal pressure and temperature changes of the lithium-ion battery. At the same time, it can establish the relationship between the internal temperature and pressure of the lithium-ion battery according to the temperature-pressure coupling data, providing strong support data for the safe life cycle of the lithium-ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery multi-parameter monitoring, and particularly relates to an in-situ monitoring system and method for the internal pressure of a lithium-ion battery. Background Art

[0002] With the large-scale application of lithium-ion batteries, battery safety accidents occur frequently, and their safety has received wide attention. There are various observable characteristics of battery failure forms, such as bulging, deformation, leakage, heating, etc. Among them, deformation and bulging are an important failure manifestation of battery performance degradation leading to potential safety hazards. The main reasons for battery bulging and deformation mainly include: overcharging causes excessive accumulation of lithium ions at the negative electrode, resulting in the growth of dendritic crystals of lithium atoms, or over-discharging causes the collapse of the negative electrode material after the SEI is damaged, as well as internal side reactions and the decomposition of electrolytes to generate gas. As the battery is used, the accumulation of gas generated by side reactions will inevitably cause an increase in internal pressure. The increase in pressure may cause the contact between the current collector and the electrode active material to break, resulting in battery capacity attenuation. Therefore, monitoring the internal pressure of a lithium-ion battery is also an important means to evaluate the degree of battery aging and safety warning.

[0003] Current monitoring methods are all indirect measurement methods, that is, the internal pressure change is indirectly reflected by monitoring the stress and strain outside the battery. For example, the battery is clamped by two flat plates, one side of the parallel plate is fixed, and a pressure sensor is installed on the other side to measure the pressure change during the charging and discharging process of the battery. There is also a similar measurement method, where multiple batteries are stacked together, and a strain gauge is used to monitor the volume change of the battery. Such sensing methods have the disadvantages of complex test systems, weak anti-electromagnetic interference ability of electronic sensors, and low sensitivity. In addition, although external parameters and internal parameters are related to each other, there must be certain differences, and the differences and correlations are uncertain. Therefore, it is difficult to accurately reflect the internal pressure state of the battery through external parameter monitoring. Therefore, the existing methods cannot meet the requirements of simultaneous monitoring of the internal temperature and pressure of the battery. To obtain the data of the internal temperature and pressure of the battery using the existing methods, at least two sensors need to be installed simultaneously to measure the temperature and pressure data respectively, resulting in a complex system structure and poor operability. Summary of the Invention

[0004] The purpose of the present invention is to provide an in-situ monitoring system and method for the internal pressure of a lithium-ion battery to overcome the problem that the prior art cannot simultaneously monitor the internal temperature and pressure of the battery, and provide strong support data for the safe life cycle of the battery.

[0005] A lithium-ion battery internal pressure in-situ monitoring system comprises a demodulation system and two optical fiber FP sensors with different sensitivity coefficients, wherein the two optical fiber FP sensors are installed at intervals on the lithium-ion battery to be monitored, the monitoring head of the optical fiber FP sensor is located inside the lithium-ion battery to be monitored, the optical fiber FP sensor is connected to the demodulation system, the optical fiber FP sensor is used to obtain temperature and pressure coupling data generated during the charging and discharging process of the lithium-ion battery to be monitored, and the demodulation system is used to decouple the temperature and pressure coupling data generated during the charging and discharging process of the lithium-ion battery to be monitored to obtain the temperature and pressure data generated during the charging and discharging process of the lithium-ion battery to be monitored.

[0006] Preferably, the lithium-ion battery to be monitored includes a battery casing and a top cover plate, the battery casing is an open structure, the top cover plate is assembled and fixed at the opening structure of the battery casing, the interior of the battery casing is used to place the battery core and electrolyte, two reserved holes are provided on the top cover plate, two optical fiber FP sensors with different sensitivity coefficients are respectively installed on a reserved hole, and the measuring part of the optical fiber FP sensor is placed in the lithium-ion battery through the reserved hole.

[0007] Preferably, the optical fiber FP sensor is fixed to the reserved hole on the top cover plate by threaded connection.

[0008] Preferably, the optical fiber FP sensor is welded and fixed in a reserved hole on the top cover plate.

[0009] Preferably, a pressure relief valve is also provided on the top cover plate.

[0010] Preferably, the fiber FP sensor includes a cylinder, an optical fiber, an optical fiber collimation head, a reflective membrane and a pressure sensitive unit. The cylinder is a centrally-through structure, the pressure sensitive unit is fixed to one end of the cylinder, the reflective membrane is arranged on the inner side of the pressure sensitive unit, the optical fiber is fixed to the other end of the cylinder through the optical fiber collimation head, and the other end of the optical fiber is spaced apart from the reflective membrane; the optical fiber and one end of the optical fiber collimation head are arranged flush, and an FP cavity is formed between one end of the optical fiber, one end of the optical fiber collimation head, the inner wall of the cylinder, and the pressure sensitive unit.

[0011] Preferably, the optical fiber FP sensor includes a cylinder, an inner hollow cylinder, an optical fiber, an optical fiber collimation head, a reflective membrane and a pressure sensitive unit, the cylinder is a centrally-through structure, the pressure sensitive unit is fixed to one end of the cylinder, the reflective membrane is arranged on the inner side of the pressure sensitive unit, the inner hollow cylinder is fixed to the other end of the cylinder, the inner hollow cylinder is a centrally-through structure, the optical fiber is fixed in the inner hollow cylinder through the optical fiber collimation head, and the other end of the optical fiber is spaced apart from the reflective membrane; the inner hollow cylinder, the optical fiber and one end of the optical fiber collimation head are arranged flush, and an FP cavity is formed between the inner hollow cylinder, the optical fiber and one end of the optical fiber collimation head and the inner wall of the cylinder, and the pressure sensitive unit.

[0012] Preferably, the optical fiber and the optical fiber collimation head are bonded and fixed by using optical fiber curing glue.

[0013] An in-situ monitoring method for the internal pressure of a lithium-ion battery, comprising the following steps:

[0014] Calibrate two fiber optic F-P sensors with different sensitivity coefficients on the lithium-ion battery to obtain the correlation coefficients between the change in the length of the fiber optic F-P sensing cavity and pressure and temperature;

[0015] Assemble the two fiber optic F-P sensing cavities with different sensitivity coefficients, for which the correlation coefficients between the change in the length of the fiber optic F-P sensing cavity and pressure and temperature have been obtained, on the lithium-ion battery to be monitored respectively;

[0016] Collect interference spectrum data in real time, and use a demodulation system to demodulate the change in the interference spectrum to obtain the information on the change in the internal pressure and temperature of the battery.

[0017] Preferably, the interference spectrum is demodulated by the following formula:

[0018]

[0019]

[0020] ΔL1 is the change in the length of the F-P cavity of fiber optic F-P sensor I, ΔL2 is the change in the length of the F-P cavity of fiber optic F-P sensor II, ΔP is the change in the internal pressure of the battery, ΔT is the change in the internal temperature of the battery, K p1 and K t1 are the correlation coefficients between the change in the length of the cavities of fiber optic F-P sensor I and fiber optic F-P sensor II and pressure and temperature respectively.

[0021] Compared with the prior art, the present invention has the following beneficial technical effects:

[0022] The present invention provides an in-situ monitoring system for the internal pressure of a lithium-ion battery. Specifically, a demodulation system 5 and two fiber optic F-P sensors 3 with different sensitivity coefficients are used. The two fiber optic F-P sensors 3 are installed at intervals on the lithium-ion battery to be monitored. The monitoring heads of the fiber optic F-P sensors 3 are located inside the lithium-ion battery to be monitored. The fiber optic F-P sensors 3 are connected to the demodulation system 5. The fiber optic F-P sensors 3 are used to obtain the temperature-pressure coupling data generated during the charging and discharging process of the lithium-ion battery to be monitored. The demodulation system 5 is used to decouple the temperature-pressure coupling data generated during the charging and discharging process of the lithium-ion battery to be monitored to obtain the temperature and pressure data generated during the charging and discharging process of the lithium-ion battery to be monitored. Thus, in-situ simultaneous monitoring of the internal pressure and temperature changes of the lithium-ion battery can be achieved, ensuring the accuracy of the monitoring data. At the same time, the relationship between the internal temperature and pressure of the lithium-ion battery can be established based on the temperature-pressure coupling data, providing strong supporting data for the safe life cycle of the lithium-ion battery. Description of the Drawings

[0023] Figure 1 This is the integrated diagram of the pressure sensor and the lithium battery in the embodiment of the present invention.

[0024] Figure 2 In the embodiment of the present invention Figure 1 Partial sectional view.

[0025] Figure 3 This is the structural diagram of the fiber optic F-P pressure sensor in the embodiment of the present invention.

[0026] Figure 4 This is the diagram of the internal pressure monitoring system of the lithium ion battery based on the fiber optic sensor in the embodiment of the present invention.

[0027] Wherein, 1. Lithium ion battery housing; 2. Top cover plate; 3. Fiber optic F-P sensor; 4. Battery core; 5. Demodulation system; 6. Lithium ion battery to be monitored; 7. Computer; 8. Battery charging and discharging equipment; 21. Reserved hole; 22. Pressure relief valve; 23. Outer pole; 31. Outer U-shaped cylinder; 32. Inner hollow cylinder; 33. Optical fiber 33; 34. Fiber optic collimator; 35. Reflective film; 36. Pressure sensitive unit. Specific implementation manners

[0028] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0029] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0030] Such as Figures 1 to 4As shown in the figure, the present invention provides an in-situ monitoring system for the internal pressure of a lithium-ion battery, which specifically includes a demodulation system 5 and two fiber optic F-P sensors 3 with different sensitivity coefficients. The two fiber optic F-P sensors 3 are installed at intervals on the lithium-ion battery 6 to be monitored. The monitoring heads of the fiber optic F-P sensors 3 are located inside the lithium-ion battery to be monitored. The fiber optic F-P sensors 3 are connected to the demodulation system 5. The fiber optic F-P sensors 3 are used to obtain the temperature-pressure coupling data generated during the charge and discharge process of the lithium-ion battery to be monitored. The demodulation system 5 is used to decouple the temperature-pressure coupling data generated during the charge and discharge process of the lithium-ion battery to be monitored to obtain the temperature and pressure data generated during the charge and discharge process of the lithium-ion battery to be monitored, so as to be able to obtain the in-situ simultaneous monitoring of the internal pressure and temperature changes of the lithium-ion battery, ensuring the accuracy of the monitoring data. At the same time, the relationship between the internal temperature and pressure of the lithium-ion battery can be established based on the temperature-pressure coupling data, providing strong support data for the safe life cycle of the lithium-ion battery.

[0031] Specifically, this application conducts in-situ monitoring of the internal pressure of a lithium-ion battery. As Figure 1 、 Figure 2 shown, taking an assembled lithium-ion battery as an example, the lithium-ion battery includes a battery case 1 and a top cover plate 2. The battery case 1 is an open structure, and the top cover plate 2 is fixedly installed in an assembled manner at the open structure of the battery case 1. The inside of the battery case 1 is used to place a battery core 4 and electrolyte, and the electrolyte is filled around the battery core 4. There are two reserved holes 21 and two external pole columns 23 on the top cover plate 2. Two fiber optic F-P sensors 3 with different sensitivity coefficients are respectively installed on one reserved hole 21, and the measuring part of the fiber optic F-P sensor 3 is placed inside the lithium-ion battery through the reserved hole 21; the two external pole columns 23 are used as the output electrodes of the lithium-ion battery.

[0032] The demodulation system 5 specifically uses a fiber optic F-P demodulator. The demodulation system 5 is connected to a computer 7 for statistical storage of data. The computer 7 is connected to a battery charge and discharge device 8, and the battery charge and discharge device 8 is used to perform charge and discharge experiment operations on the lithium-ion battery to be monitored.

[0033] The fiber optic F-P sensor 3 is placed and installed through the reserved hole 21 on the top cover plate 2. The fiber optic F-P sensor 3 and the reserved hole 21 on the top cover plate 2 are fixed by screw connection. Threaded holes are prefabricated on the reserved hole 21, and connecting threads are provided on the outer ring of the fiber optic F-P sensor 3. The fiber optic F-P sensor 3 is threadedly connected to the reserved hole 21 on the top cover plate 2, and a sealing ring is provided at the connection or sealant is used for sealing.

[0034] In an embodiment of the present application, the fiber optic F-P sensor 3 is welded and fixed inside the reserved hole 21 on the top cover plate 2, and is specifically sealed by laser welding at the same time.

[0035] The top cover plate 2 is also provided with a pressure relief valve 22 to ensure the safety of the lithium-ion battery during the test.

[0036] The battery housing 1 and the top cover plate 2 are laser welded together. There is a gap between the battery core 4 and the top cover plate 2 at the upper end of the battery housing 1. The reserved hole 21 is opened on the top cover plate 2. The fiber optic F-P sensor 3 passes through the reserved hole 21 so that the measuring part of the fiber optic F-P sensor 3 is located in the gap between the battery core 4 and the top cover plate 2 at the upper end of the battery housing 1, which will not affect the layout of the battery core 4 inside the lithium-ion battery. After the battery core 4 is assembled into the battery housing 1, the electrolyte is injected through the reserved hole 21 on the top cover plate 2, and then two fiber optic F-P sensors 3 are installed and sealed; by installing two fiber optic F-P sensors 3 with different sensitivity coefficients, the decoupling of pressure and temperature information can be realized.

[0037] In an embodiment of the present application, the fiber optic F-P sensor 3 includes a cylinder body 31, an optical fiber 33, an optical fiber collimator 34, a reflective film 35, and a pressure sensitive unit 36. The cylinder body 31 has a through structure. The pressure sensitive unit 36 is fixed to one end of the cylinder body 31. The reflective film 35 is arranged inside the pressure sensitive unit 36. The optical fiber 33 is fixed to the other end of the cylinder body 31 through the optical fiber collimator 34. The other end of the optical fiber 33 is spaced from the reflective film 35; one end of the optical fiber 33 and the optical fiber collimator 34 are flush. An F-P cavity is formed between one end of the optical fiber 33, one end of the optical fiber collimator 34, the inner wall of the cylinder body 31, and the pressure sensitive unit 36. The thickness of the pressure sensitive unit 36 is adjusted according to the sensitivity requirement. The greater the thickness, the lower the sensitivity of the sensor.

[0038] As Figure 3 shown, the fiber optic F-P sensor 3 includes a cylinder body 31, an inner hollow cylinder 32, an optical fiber 33, an optical fiber collimator 34, a reflective film 35, and a pressure sensitive unit 36. The cylinder body 31 has a through structure. The pressure sensitive unit 36 is fixed to one end of the cylinder body 31. The reflective film 35 is arranged inside the pressure sensitive unit 36. The inner hollow cylinder 32 is fixed to the other end of the cylinder body 31. The inner hollow cylinder 32 has a through structure. The optical fiber 33 is fixed inside the inner hollow cylinder 32 through the optical fiber collimator 34. The other end of the optical fiber 33 is spaced from the reflective film 35; one end of the inner hollow cylinder 32, the optical fiber 33, and the optical fiber collimator 34 are flush. An F-P cavity is formed between one end of the inner hollow cylinder 32, the optical fiber 33, the optical fiber collimator 34, the inner wall of the cylinder body 31, and the pressure sensitive unit 36. The optical fiber 33 and the optical fiber collimator 34 are adhesively fixed with an optical fiber curing adhesive 353ND. The cylinder body 31 and the pressure sensitive unit 36 are integrally processed and formed; a reflective film 35 with a high reflectivity is arranged inside the pressure sensitive unit 36; the cavity between the reflective film 35 and the optical fiber collimator 34 forms an F-P cavity, and the length of the F-P cavity can be adjusted by rotating the inner hollow cylinder 32.

[0039] An inner hollow cylinder 32 is used as a transition structure for installing the cylinder body 31 and the optical fiber 33. The inner hollow cylinder 32 is threadedly connected to the inner wall of the cylinder body 31, and the relative height of the connection between the inner hollow cylinder 32 and the cylinder body 31 can be adjusted, so as to obtain an optical fiber F-P sensor structure with different sensitivities.

[0040] As the lithium-ion battery ages, the internal pressure of the lithium-ion battery increases and directly acts on the bottom of the sensor sensitive unit 36, causing the distance between the reflection film 35 and the optical fiber collimator 32 to become shorter, that is, the length of the F-P cavity changes, and the corresponding interference spectrum will also change. By demodulating the wavelength change or intensity change of the spectrum, the in-situ online monitoring of the internal pressure of the battery can be realized.

[0041] Since heat is generated during the operation of the lithium-ion battery and the temperature rises, due to the thermal expansion and contraction of materials, the length of the F-P cavity of the optical fiber F-P sensor 3 will also change. In this application, two optical fiber F-P sensors 3 with different sensitivity coefficients are installed in two reserved holes to solve this problem. Using two sensors with different sensitivity coefficients can achieve the mutual decoupling of temperature and pressure.

[0042] The pressure-sensitive unit 6 of the optical fiber F-P sensor 3 is a thin-walled metal disc. When it is under pressure, within the elastic deformation range, the relationship between the deformation amount w at the center of the inner disc and the pressure P can be expressed as: From this, the deformation of the pressure-sensitive unit can be obtained, that is, the change in the length of the F-P cavity shows a linear relationship with the pressure. When the internal pressure of the lithium-ion battery increases and the pressure acts on the pressure-sensitive unit 6 of the F-P sensor, it causes the pressure-sensitive unit 6 to deform inward, thereby causing a change in the length of the F-P cavity, and finally causing a change in the interference spectrum of the optical fiber F-P sensor 3. The change information of the internal pressure of the battery can be obtained by using the demodulation system.

[0043] During the operation of the lithium-ion battery, a series of endothermic and exothermic reactions will occur inside, which will cause temperature changes. Due to the thermal expansion and contraction of the material of the optical fiber F-P sensor 3, the temperature will also cause a change in the length of the F-P cavity. To solve this problem of temperature-pressure cross-coupling, two optical fiber F-P pressure sensing probes with different sensitivity coefficients are implanted in the battery. This method can achieve the mutual decoupling of internal pressure and temperature. The performance parameters of the measurement parts of the two optical fiber F-P sensors 3 are different, mainly reflected in different pressure-temperature sensitivity coefficients. Different sensing parameters are adjusted by the length of the F-P cavity and the thickness of the pressure-sensitive element. Let the relationship between the length of the F-P cavity of the optical fiber F-P sensor I and the optical fiber F-P sensor II and temperature and pressure satisfy the following:

[0044] ΔL1=K p1 ΔP+K t1 ΔT (1)

[0045] ΔL2 = K p2 ΔP + K t2 ΔT (2)

[0046] Where: ΔL1 is the change in the F - P cavity length of the fiber optic F - P sensor I, ΔL2 is the change in the F - P cavity length of the fiber optic F - P sensor II, ΔP is the change in the internal pressure of the battery, ΔT is the change in the internal temperature of the battery, and K p1 is the correlation coefficient between the change in the F - P cavity length of the fiber optic F - P sensor I and the pressure, and K t1 is the correlation coefficient between the change in the F - P cavity length of the fiber optic F - P sensor I and the temperature, and K p2 is the correlation coefficient between the change in the F - P cavity length of the fiber optic F - P sensor II and the pressure, and K t2 is the correlation coefficient between the change in the F - P cavity length of the fiber optic F - P sensor II and the temperature. The correlation coefficient between the change in the F - P cavity length of the fiber optic F - P sensor and the temperature, as well as the correlation coefficient between the change in the F - P cavity length of the fiber optic F - P sensor and the pressure, are obtained through experimental calibration.

[0047] By combining the equations, the demodulated interference spectrum can be obtained through the following formula:

[0048]

[0049]

[0050] When the sensor structure remains unchanged, its temperature and pressure sensitivity performance parameters are constants. From the above formula, it can be seen that the changes in pressure and temperature are only related to the changes in the cavity lengths of the two sensors. The change in the F - P cavity length is obtained by demodulating the change in the interference spectrum, thereby realizing the mutual decoupling of pressure and temperature.

[0051] The above embodiments are only a preferred implementation manner of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. Any equivalent transformation of the technical solution of the present invention adopted by reading the specification of the present invention is covered by the claims of the present invention.

Claims

1. An in-situ monitoring system for the internal pressure of a lithium-ion battery, characterized in that It includes two fiber optic F-P sensors (3) with different sensitivity coefficients. The two fiber optic F-P sensors (3) are installed at intervals on the lithium-ion battery to be monitored. The monitoring heads of the fiber optic F-P sensors (3) are located inside the lithium-ion battery to be monitored. The two fiber optic F-P sensors (3) are connected to a demodulation system (5). The fiber optic F-P sensors (3) are used to obtain the temperature-pressure coupling data generated during the charge and discharge process of the lithium-ion battery to be monitored, and the demodulation system (5) is used to decouple the temperature-pressure coupling data generated during the charge and discharge process of the lithium-ion battery to be monitored to obtain the temperature and pressure data generated during the charge and discharge process of the lithium-ion battery to be monitored; The demodulated interference spectrum is obtained by the following formula: ΔL1 is the change in the F-P cavity length of fiber optic F-P sensor I, ΔL2 is the change in the F-P cavity length of fiber optic F-P sensor II, ΔP is the change in the internal pressure of the battery, ΔT is the change in the internal temperature of the battery, K p1 is the correlation coefficient between the change in the F-P cavity length of fiber optic F-P sensor I and the pressure, K t1 is the correlation coefficient between the change in the F-P cavity length of fiber optic F-P sensor I and the temperature, K p2 is the correlation coefficient between the change in the F-P cavity length of fiber optic F-P sensor II and the pressure, K t2 is the correlation coefficient between the change in the F-P cavity length of fiber optic F-P sensor II and the temperature.

2. The in-situ internal pressure monitoring system for a lithium-ion battery according to claim 1, characterized in that The lithium-ion battery to be monitored includes a battery case (1) and a top cover plate (2). The battery case (1) is an open structure, and the top cover plate (2) is fixedly assembled at the open structure of the battery case (1). The inside of the battery case (1) is used to place the battery core (4) and the electrolyte. Two reserved holes (21) are provided on the top cover plate (2). The two fiber optic F-P sensors (3) with different sensitivity coefficients are respectively installed on one reserved hole (21), and the measuring part of the fiber optic F-P sensor (3) is placed inside the lithium-ion battery through the reserved hole (21).

3. The in-situ internal pressure monitoring system for a lithium-ion battery according to claim 2, wherein The fiber optic F-P sensor (3) is fixedly connected to the reserved hole (21) on the top cover plate (2) by a threaded connection.

4. The in-situ internal pressure monitoring system for a lithium-ion battery according to claim 2, characterized in that The fiber optic F-P sensor (3) is fixedly welded in the reserved hole (21) on the top cover plate (2).

5. The in-situ internal pressure monitoring system for a lithium-ion battery according to claim 2, wherein A pressure relief valve (22) is also provided on the top cover plate (2).

6. The in-situ internal pressure monitoring system for a lithium-ion battery according to claim 1, characterized in that, The fiber optic F-P sensor (3) includes a cylinder body (31), an optical fiber (33), an optical fiber collimator head (34), a reflective film (35) and a pressure sensitive unit (36). The cylinder body (31) is a through structure. The pressure sensitive unit (36) is fixed at one end of the cylinder body (31). The reflective film (35) is arranged inside the pressure sensitive unit (36). The optical fiber (33) is fixed at the other end of the cylinder body (31) through the optical fiber collimator head (34). The other end of the optical fiber (33) is arranged at an interval from the reflective film (35); One end of the optical fiber (33) and the optical fiber collimator head (34) are flush. An F-P cavity is formed between one end of the optical fiber (33), one end of the optical fiber collimator head (34), the inner wall of the cylinder body (31), and the pressure sensitive unit (36).

7. The in-situ internal pressure monitoring system for a lithium-ion battery according to claim 1, characterized in that, The fiber optic F-P sensor (3) includes a cylinder body (31), an inner hollow cylinder (32), an optical fiber (33), an optical fiber collimator head (34), a reflective film (35) and a pressure sensitive unit (36). The cylinder body (31) is a through structure. The pressure sensitive unit (36) is fixed at one end of the cylinder body (31). The reflective film (35) is arranged inside the pressure sensitive unit (36). The inner hollow cylinder (32) is fixed at the other end of the cylinder body (31). The inner hollow cylinder (32) is a through structure. The optical fiber (33) is fixed inside the inner hollow cylinder (32) through the optical fiber collimator head (34). The other end of the optical fiber (33) is arranged at an interval from the reflective film (35); One end of the inner hollow cylinder (32), the optical fiber (33), and the optical fiber collimator (34) is flushly arranged, and an F-P cavity is formed between one end of the inner hollow cylinder (32), the optical fiber (33), and the optical fiber collimator (34) and the inner wall of the cylinder body (31) and the pressure sensitive unit (36).

8. An in-situ internal pressure monitoring system for a lithium-ion battery according to claim 6 or 7, characterized in that The optical fiber (33) and the optical fiber collimator (34) are fixedly glued with optical fiber curing glue.

9. An in-situ monitoring method for the internal pressure of a lithium-ion battery based on the in-situ monitoring system for the internal pressure of a lithium-ion battery described in claim 1, characterized in that, It includes the following steps: Calibrate two fiber optic F-P sensors with different sensitivity coefficients on a lithium-ion battery to obtain the correlation coefficients between the change in the length of the fiber optic F-P sensing cavity and pressure and temperature; Assemble the two fiber optic F-P sensing cavities with different sensitivity coefficients, for which the correlation coefficients between the change in the length of the fiber optic F-P sensing cavity and pressure and temperature have been obtained, on the lithium-ion battery to be monitored respectively; Collect interference spectrum data in real time, and use a demodulation system to demodulate the change in the interference spectrum to obtain the information on the change in the internal pressure and temperature of the battery.

10. The in-situ internal pressure monitoring method of a lithium-ion battery for the in-situ internal pressure monitoring system of a lithium-ion battery according to claim 9, characterized in that, The demodulated interference spectrum is obtained through the following formula: ΔL1 is the change in the F-P cavity length of fiber optic F-P sensor I, ΔL2 is the change in the F-P cavity length of fiber optic F-P sensor II, ΔP is the change in the internal pressure of the battery, ΔT is the change in the internal temperature of the battery, K p1 is the correlation coefficient between the change in the F-P cavity length of fiber optic F-P sensor I and the pressure, K t1 is the correlation coefficient between the change in the F-P cavity length of fiber optic F-P sensor I and the temperature, K p2 is the correlation coefficient between the change in the F-P cavity length of fiber optic F-P sensor II and the pressure, K t2 is the correlation coefficient between the change in the F-P cavity length of fiber optic F-P sensor II and the temperature.

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