An optical fiber embedded lithium battery for studying electrode phase change and its manufacturing method and application

Abstract

The present invention discloses an optical fiber embedded lithium battery for studying electrode phase change, and a manufacturing method and application thereof, belonging to the technical field of lithium batteries. The lithium battery comprises a battery cell, an internal sensing component and a battery package, wherein the battery cell is composed of a pole piece, a pole ear and a diaphragm, and the internal sensing component is located inside the battery cell. The present invention embeds the optical fiber sensor into different positions of the electrode through an optical fiber embedding device, and the combination of full embedding and partial embedding enables the optical fiber sensor to accurately and stably obtain strain, stress and temperature; at the same time, through the first-order derivative curves of strain-voltage, strain-state of charge (SOC) and strain-time, the actual phase change potential, actual phase change reaction stage distribution and actual phase change reaction duration of the positive and negative electrodes during the charging and discharging process are studied, so as to realize the research on the phase change stability of the lithium battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and in particular relates to an optical fiber embedded lithium battery for studying electrode phase change, and a manufacturing method and application thereof. Background Art

[0002] With the rapid development of electric vehicles, energy storage systems and portable electronic devices, the performance, safety and service life of batteries as core energy storage and power supply devices have become key concerns. Therefore, it is particularly important to monitor the working status of batteries in real time and accurately. Traditional battery monitoring methods are limited by sensitivity, anti-interference ability and distributed measurement capabilities, and it is difficult to meet the monitoring needs of modern high-performance batteries. Fiber optic sensors have become an ideal choice in the field of battery monitoring due to their high precision, anti-electromagnetic interference, long-distance transmission and distributed measurement capabilities.

[0003] In addition to the above-mentioned superior performance, optical fiber sensors are also small, light, and easy to integrate, making them very suitable for embedding inside batteries for in-situ, real-time monitoring. This embedded design not only reduces the interference between the monitoring system and the battery, improves the accuracy and reliability of monitoring data, but also provides important technical support for in-depth research on the dynamic behavior of the battery.

[0004] The existing Chinese patent CN113108955A discloses a stress monitoring device for electrode materials in batteries. It embeds a fiber Bragg grating (FBG) sensor into the electrode material, uses a spectrometer to collect the change of the Bragg wavelength, and converts it into a stress signal to achieve real-time monitoring of the internal stress of the battery. Chinese patent CN112014738A proposes a state of charge estimation method for lithium-ion batteries based on embedded optical fiber sensors. It collects strain data of internal electrodes by embedding FBG sensors, and realizes state of charge (SOC) estimation based on the internal state of the battery in combination with algorithms. These studies provide technical support for the accurate acquisition and application of battery internal state information. In addition, Chinese patent CN115377540A discloses a multi-feature detection device for thermal runaway of lithium batteries based on fiber Bragg gratings. By arranging the micro fiber Bragg grating assembly in a spiral manner between the positive electrode and the diaphragm or the negative electrode and the diaphragm of the battery, the device can detect the early characteristic values ​​of thermal runaway, including parameters such as hydrogen concentration, temperature and pressure, and provides an effective means for battery safety monitoring and early warning.

[0005] In summary, the current application of fiber optic sensors in lithium-ion battery research is mainly focused on battery internal temperature monitoring, battery internal stress monitoring, SOC estimation, health status assessment (SOH) and safety monitoring and early warning. There is a lack of monitoring research on the internal phase change behavior of lithium-ion batteries. The research on the phase change behavior of lithium-ion batteries has important scientific significance and practical application value. The phase change behavior is directly related to the energy storage mechanism and electrochemical reaction kinetics of the battery. For example, during the insertion and deinsertion of lithium ions, the lattice structure of the positive and negative electrode materials will change significantly, resulting in the volume expansion and contraction of the material. This phase change phenomenon not only affects the lithium ion diffusion path and rate, but also causes mechanical stress concentration of the electrode material, resulting in material shedding and damage, thereby affecting the cycle stability and service life of the battery.

[0006] Therefore, in-depth research on battery phase change behavior will help optimize the design and performance of battery materials. In addition, understanding phase change behavior can provide a theoretical basis for the development of new battery materials and structures, which will help achieve breakthroughs in battery energy density, power density and cycle life. Summary of the invention

[0007] The purpose of the present invention is to provide an optical fiber embedded lithium battery for studying electrode phase change and its manufacturing method and application, so as to study the phase change behavior of lithium batteries and fill the gap in the research on detecting the internal phase change behavior of lithium-ion batteries.

[0008] The present invention adopts the following technical solution:

[0009] An optical fiber embedded lithium battery for studying electrode phase change, comprising a battery core, an internal sensing component and a battery package, wherein the battery core comprises a positive electrode sheet, a diaphragm and a negative electrode sheet stacked in sequence, and pole ears welded on the positive electrode sheet and the negative electrode sheet; the internal sensing component comprises a first fiber Bragg grating sensor, a second fiber Bragg grating sensor, a third fiber Bragg grating sensor, a fourth fiber Bragg grating sensor and an optical fiber integrated protection device, wherein:

[0010] The first fiber Bragg grating sensor and the third fiber Bragg grating sensor are completely buried in the positive electrode sheet and the negative electrode sheet respectively, and both adopt an exposed Bragg grating structure;

[0011] The second fiber Bragg grating sensor and the fourth fiber Bragg grating sensor are partially buried in the positive electrode sheet and the negative electrode sheet respectively, and both are covered with quartz microtubes;

[0012] The first fiber Bragg grating sensor to the fourth fiber Bragg grating sensor all pass through the optical fiber integrated protection device and are sealed by a sealant;

[0013] The battery package is used to package the battery core and the internal sensor component.

[0014] In a further embodiment, the distance from one end of the first fiber Bragg grating sensor and the third fiber Bragg grating sensor to the surface of the positive electrode sheet and the negative electrode sheet respectively is 10%-20% of the total thickness of the electrode sheet, and the distance from the other end to the collector surface of the electrode sheet is 10%-20% of the total thickness of the electrode sheet.

[0015] Through the above technical solution, the two ends of the sensor are respectively separated from the surface of the electrode sheet and the surface of the current collector by a certain distance, ensuring that the sensor is completely wrapped by the electrode, preventing external interference and improving the reliability of the sensor.

[0016] In a further embodiment, one end of the quartz microtube is located outside the electrode sheet, and the distance to the surface of the electrode sheet is 10%-35% of the outer diameter of the quartz microtube, and the distance from the other end to the collector surface of the electrode sheet is 10%-35% of the total thickness of the electrode sheet.

[0017] Through the above technical solution, the two ends of the sensor are respectively separated from the electrode surface and the collector surface by a distance, ensuring that the core area of ​​the fiber grating of the sensor is completely wrapped by the electrode, thereby improving reliability.

[0018] The present invention also provides a method for manufacturing an optical fiber embedded lithium battery for studying electrode phase change, comprising the following steps:

[0019] Step 1: Determine the selection and formula ratio of active materials, conductive agents, and binders in positive electrode slurry and negative electrode slurry, and use a high-precision electronic scale to accurately weigh each raw material according to the predetermined formula ratio;

[0020] Step 2: Mix the binder and the solvent and stir them evenly, add the conductive agent and the active material in sequence and stir until they are evenly mixed to obtain positive electrode slurry and negative electrode slurry;

[0021] Step 3: placing two different current collectors in the optical fiber embedding device, and adjusting and determining the embedding position of the internal sensor component through the optical fiber embedding device;

[0022] Step 4: coating the positive electrode slurry and the negative electrode slurry on two different current collectors respectively by a doctor blade method, and placing the optical fiber embedding device together with the current collector and the slurry thereon into an oven for drying to obtain a positive electrode sheet and a negative electrode sheet;

[0023] Step 5: Determine the number of positive and negative electrodes according to the battery capacity, weld the aluminum tabs and nickel tabs to the collector surfaces of the positive and negative electrodes respectively, stack the positive electrodes, separators and negative electrodes in order, add electrolyte and use battery packaging materials to package the cells.

[0024] In a further embodiment, the optical fiber embedding device includes a horizontal base and an optical fiber fixing assembly, wherein: the horizontal base is used to place the collector, the optical fiber fixing assembly is used to simultaneously fix multiple different sensors, and the distance between the optical fiber fixing assembly and the horizontal base can be adjusted within an adjustment range of 10-2000um, which can be adjusted according to the required number of sensors and embedding depth.

[0025] In a further embodiment, the content of active material in the positive electrode slurry and the negative electrode slurry is 75%-85%, the content of binder is 10%-15%, the content of conductive agent is 5%-10%, the coating thickness of the slurry is 200-1000um, and the thickness of the positive electrode sheet and the negative electrode sheet obtained after drying is 110-200um.

[0026] In a further embodiment, the first to fourth fiber Bragg grating sensors are respectively fixed on the optical fiber fixing assembly, and by adjusting the height of the optical fiber fixing assembly, the distance from one end of the first fiber Bragg grating sensor and the third fiber Bragg grating sensor to the current collector is 10%-20% of the expected electrode sheet thickness, and the distance from one end of the second fiber Bragg grating sensor and the fourth fiber Bragg grating sensor to the current collector is 10%-35% of the expected electrode sheet thickness.

[0027] The present invention also provides an application of an optical fiber embedded lithium battery for studying electrode phase change, wherein the optical fiber embedded lithium battery is connected to an external receiving device, and the external receiving device includes a battery testing system, an electrochemical workstation and a fiber grating demodulator, wherein:

[0028] The battery testing system is connected to the lithium battery via a connecting line to study the phase change potential and stage distribution of the battery;

[0029] The electrochemical workstation is connected to the lithium battery via a connecting line for studying the electrochemical characteristics of the battery;

[0030] The fiber grating demodulator is connected to the lithium battery via a connecting line and is used to detect stress, strain and temperature changes caused by the battery phase change process.

[0031] The specific steps include:

[0032] Step 1: Assemble half-cells with positive and negative electrodes respectively, perform cyclic voltammetry test on the half-cells through an electrochemical workstation, determine the electrochemical phase change potentials of the positive and negative electrodes according to the positions of the oxidation / reduction peaks, perform charge and discharge test on the half-cells through a battery test system, and determine the distribution of the phase change reactions of the positive and negative electrodes according to the platform positions in the voltage-SOC curves;

[0033] Step 2: Use the battery test system to perform charge and discharge tests on the lithium battery embedded in the optical fiber, use the fiber grating demodulator to collect the Bragg wavelength changes, and convert them into strain, stress and temperature change values ​​through formula calculation.

[0034] The temperature of the positive electrode is: , the strain of the positive electrode is: ; The temperature of the negative electrode is: , the strain of the negative electrode is: ;

[0035] in: , , , are respectively the Bragg wavelength shifts from the first fiber Bragg grating sensor to the fourth fiber Bragg grating sensor, , , , are the temperature sensitivities of the first fiber Bragg grating sensor to the fourth fiber Bragg grating sensor, respectively, , is the strain sensitivity of the first fiber Bragg grating sensor and the third fiber Bragg grating sensor; and then through Hooke's law , converting strain into stress;

[0036] Step 3: Calculate the first-order derivative of strain-voltage, and analyze the actual phase change potential of the positive and negative electrodes during the charge and discharge process from the peak and valley voltages in the derivative curve;

[0037] Step 4: Calculate the first-order derivative of strain-SOC and distinguish the actual phase change reaction stage distribution according to the derivative curve;

[0038] Step 5: Calculate the first-order derivative of strain-time and determine the duration of the actual phase change reaction based on the derivative curve;

[0039] Step 6: The battery test system is set with different charge and discharge rates and different charge and discharge times, and steps 1 to 5 are repeated to study the phase change stability of the electrode at different charge and discharge rates and cycle processes.

[0040] Compared with the prior art, the present invention has the following significant effects:

[0041] (1) By embedding the fiber Bragg grating sensor in both the positive and negative electrodes, it is convenient to study the strain, temperature, stress and phase change process of the positive and negative electrodes simultaneously;

[0042] (2) By completely burying the first fiber Bragg grating sensor and the third fiber Bragg grating sensor inside the positive and negative electrodes, and partially burying the second fiber Bragg grating sensor and the fourth fiber Bragg grating sensor inside the positive and negative electrodes, high-precision monitoring of electrode strain, stress, and temperature is achieved. The "partial burial inside the electrode" method ensures that the sensor has a high sensitivity response to changes in electrode temperature and reduces intrusion into the electrode;

[0043] (3) The phase change potential and stage distribution are studied through an electrochemical workstation and a battery testing system. The Bragg wavelength change is collected using a fiber grating demodulator and further converted into strain, stress and temperature changes through formula calculations. The actual phase change potential, actual phase change reaction stage distribution and actual phase change reaction duration of the positive and negative electrodes during the charge and discharge process are studied through the strain-voltage first-order derivative, strain-SOC first-order derivative and strain-time first-order derivative curves, thereby realizing the study of the phase change stability of lithium batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a schematic diagram of the structure of the optical fiber embedded lithium battery used to study electrode phase change in the present invention;

[0045] Figure 2 for Figure 1 Enlarged cross-sectional view at point A;

[0046] Figure 3 is a schematic diagram of an internal sensing component in the present invention;

[0047] Figure 4 is a schematic diagram of the optical fiber embedding device of the present invention;

[0048] Figure 5 This is a schematic diagram of the connection between the optical fiber embedded lithium battery and the external receiving device in the present invention;

[0049] Figure 6 is a cross-sectional SEM image of the LFP electrode in the embodiment;

[0050] Figure 7 The evolution of the internal signal of the optical fiber embedded lithium battery at a rate of 0.1C in the embodiment;

[0051] Figure 8 It is the first-order derivative of strain-SOC during discharge at 0.1C rate in the embodiment.

[0052] Figure numerals: 1. battery cell; 2. battery package; 3. positive electrode sheet; 4. negative electrode sheet; 5. diaphragm; 6. tab; 7. first fiber Bragg grating sensor; 8. second fiber Bragg grating sensor; 9. third fiber Bragg grating sensor; 10. fourth fiber Bragg grating sensor; 11. optical fiber integrated protection device; 12. quartz microtube; 13. horizontal base; 14. optical fiber fixing assembly; 15. battery testing system; 16. electrochemical workstation; 17. fiber Bragg grating demodulator. DETAILED DESCRIPTION

[0053] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0054] like Figures 1 to 3 As shown, the present invention provides an optical fiber embedded lithium battery for studying electrode phase change, hereinafter referred to as "the lithium battery". The lithium battery includes a battery cell 1, an internal sensor component and a battery package 2. The battery cell 1 is composed of a positive electrode sheet 3, a negative electrode sheet 4, a separator 5 and a tab 6. The internal sensor is located inside the battery cell 1, and the battery package 2 is coated on the outside of the battery cell 1.

[0055] See also Figure 1 and Figure 2 The battery cell 1 includes a positive electrode sheet 3, a separator 5 and a negative electrode sheet 4 stacked in sequence, and a tab 6 welded on the positive electrode sheet 3 and the negative electrode sheet 4; Figure 1 and Figure 2 The internal sensing component includes a first fiber Bragg grating sensor 7, a second fiber Bragg grating sensor 8, a third fiber Bragg grating sensor 9, a fourth fiber Bragg grating sensor 10 and a fiber integrated protection device 11, wherein: the first fiber Bragg grating sensor 7 and the third fiber Bragg grating sensor 9 are completely buried in the positive electrode sheet 3 and the negative electrode sheet 4 respectively, and both adopt an exposed Bragg grating structure; the second fiber Bragg grating sensor 8 and the fourth fiber Bragg grating sensor 10 are partially buried in the positive electrode sheet 3 and the negative electrode sheet 4 respectively, and both are covered with a quartz microtube 12 on the outside, and the quartz microtube 12 is used to eliminate mechanical effects; the first fiber Bragg grating sensor 7 to the fourth fiber Bragg grating sensor 10 all pass through the fiber integrated protection device 11 and are sealed by a sealant, and the fiber integrated protection device 11 centrally protects the fiber Bragg grating sensors to prevent the sensors from breaking at the connection between the inside and outside of the battery.

[0056] Specifically, the Bragg wavelengths of the first fiber Bragg grating sensor 7 and the third fiber Bragg grating sensor 9 are affected by both temperature and strain, while the second fiber Bragg grating sensor 8 and the fourth fiber Bragg grating sensor 10 are only affected by temperature. By performing temperature compensation on the first fiber Bragg grating sensor 7 and the third fiber Bragg grating sensor 9 by the second fiber Bragg grating sensor 8 and the fourth fiber Bragg grating sensor 10, temperature and strain can be decoupled.

[0057] Continue reading Figure 1 , the distance from one end of the first fiber Bragg grating sensor 7 and the third fiber Bragg grating sensor 9 to the surface of the positive electrode sheet 3 and the negative electrode sheet 4 is 10%-20% of the total thickness of the electrode sheet, and the distance from the other end to the collector surface of the electrode sheet is 10%-20% of the total thickness of the electrode sheet, ensuring that the sensor is completely wrapped by the electrode to prevent external interference and improve the reliability of the sensor; one end of the quartz microtube 12 is located outside the electrode sheet, and the distance to the surface of the electrode sheet is 10%-35% of the outer diameter of the quartz microtube 12, and the distance from the other end to the collector surface of the electrode sheet is 10%-35% of the total thickness of the electrode sheet. In this embodiment, the optical fiber diameter of the fiber Bragg grating sensor is 80um, and the outer diameter of the quartz microtube 12 is 120um, ensuring that the core area where the sensor fiber grating is located is completely wrapped by the electrode to ensure the reliability of the sensor.

[0058] The present invention also provides a method for preparing an optical fiber embedded lithium battery for studying electrode phase change, comprising the following steps:

[0059] Step 1: Determine the selection and formula ratio of active materials, conductive agents, and binders in positive electrode slurry and negative electrode slurry, and use a high-precision electronic scale to accurately weigh each raw material according to the predetermined formula ratio;

[0060] Step 2: Mix the binder and the solvent and stir them evenly, add the conductive agent and the active material in sequence and stir until they are evenly mixed to obtain positive electrode slurry and negative electrode slurry;

[0061] Step 3: placing two different current collectors in the optical fiber embedding device, and adjusting and determining the embedding position of the internal sensor component through the optical fiber embedding device;

[0062] Step 4: coating the positive electrode slurry and the negative electrode slurry on two different current collectors respectively by a doctor blade method, and placing the optical fiber embedding device together with the current collector and the slurry thereon into an oven for drying to obtain a positive electrode sheet 3 and a negative electrode sheet 4;

[0063] Step 5: Determine the number of positive electrode sheets 3 and negative electrode sheets 4 according to the battery capacity, weld the aluminum tabs 6 and the nickel tabs 6 to the collector surfaces of the positive electrode sheets 3 and the negative electrode sheets 4 respectively, and stack the positive electrode sheets 3, the separators 5 and the negative electrode sheets 4 in order, add electrolyte to them, and use the battery packaging 2 material to package the battery cells 1.

[0064] Specifically, the content of active material in the positive electrode slurry and the negative electrode slurry is 75%-85%, the content of binder is 10%-15%, the content of conductive agent is 5%-10%, the coating thickness of the slurry is 200-1000um, and the thickness of the positive electrode sheet 3 and the negative electrode sheet 4 obtained after drying is 110-200um.

[0065] like Figure 4 As shown, the optical fiber embedding device includes a horizontal base 13 and an optical fiber fixing assembly 14, wherein the horizontal base 13 is used to place the collector, and the optical fiber fixing assembly 14 is used to simultaneously fix multiple different sensors, and the distance between the optical fiber fixing assembly 14 and the horizontal base 13 can be adjusted within the range of 10-2000um.

[0066] Example 1

[0067] In this embodiment, the positive electrode material is lithium iron phosphate, and the negative electrode material is lithium titanate. The specific process is as follows:

[0068] Positive electrode preparation: lithium iron phosphate, binder, and conductive agent are sequentially added to N-dimethylpyrrolidone (NMP) in a mass ratio of 80:12:8 and stirred to obtain a positive electrode slurry. First, the binder and NMP are placed in a beaker and mixed on a stirrer for 2 hours, and then the conductive agent and lithium iron phosphate are sequentially added and stirred for 10 hours. In the process of burying the first fiber Bragg grating sensor 7 and the second fiber Bragg grating sensor 8 in the positive electrode, firstly, the aluminum foil is placed on the horizontal base 13 of the optical fiber embedding device, and then the first fiber Bragg grating sensor 7 and the second fiber Bragg grating sensor 8 are respectively fixed on the optical fiber fixing assembly 14, and the height of the optical fiber fixing assembly 14 is adjusted so that the distance between the lower end of the first fiber Bragg grating sensor 7 and the aluminum foil is 20um, and the distance between the lower end of the quartz microtube 12 of the second fiber Bragg grating sensor 8 and the aluminum foil is 30um, and then the positive electrode slurry is coated on the aluminum foil on the horizontal base 13 by a scraping method. The optical fiber embedding device, the aluminum foil thereon, and the positive electrode slurry were placed in an oven, and then placed in a forced air oven set at a temperature of 50° C. to dry for 7 hours to remove the solvent, thereby obtaining a positive electrode sheet 3.

[0069] Negative electrode preparation: lithium titanate, binder, and conductive agent are sequentially added to N-dimethylpyrrolidone (NMP) in a mass ratio of 85:10:5 and stirred to obtain a negative electrode slurry. First, the binder and NMP are placed in a beaker and mixed on a stirrer for 2 hours, and then the conductive agent and lithium titanate are sequentially added and stirred for 10 hours. In the process of burying the third fiber Bragg grating sensor 9 and the fourth fiber Bragg grating sensor 10 in the negative electrode, firstly, the copper foil is placed on the horizontal base 13 of the optical fiber embedding device, and then the third fiber Bragg grating sensor 9 and the fourth fiber Bragg grating sensor 10 are respectively fixed on the optical fiber fixing assembly 14, and the height of the optical fiber fixing assembly 14 is adjusted so that the distance between the lower end of the third fiber Bragg grating sensor 9 and the aluminum foil is 20um, and the distance between the lower end of the quartz microtube 12 of the fourth fiber Bragg grating sensor 10 and the aluminum foil is 30um, and then the negative electrode slurry is coated on the copper foil on the horizontal base 13 by a scraping method. The optical fiber embedding device, the copper foil thereon, and the negative electrode slurry were placed in a forced air oven set at 60° C. and dried for 7 hours to remove the solvent, thereby obtaining a negative electrode sheet 4 .

[0070] Battery preparation: Determine the number of positive electrode sheets 3 and negative electrode sheets 4 according to the battery capacity, weld the aluminum tabs 6 and the nickel tabs 6 to the surfaces of the aluminum foil and the copper foil respectively, stack the positive electrode sheets 3, the separators 5 and the negative electrode sheets 4 in order, then fill the electrolyte and use the battery package 2 to package the battery cells 1.

[0071] Example 2

[0072] The positive electrode material of this embodiment is a new type of NCM, and the negative electrode material is graphite. The manufacturing method refers to Example 1.

[0073] Based on the above embodiments, the present invention also applies for an application of an optical fiber embedded lithium battery for studying electrode phase change, which needs to be connected to an external receiving device, such as Figure 5 As shown, the external receiving device includes a battery testing system 15, an electrochemical workstation 16 and a fiber Bragg grating demodulator 17, wherein the battery testing system 15 and the electrochemical workstation 16 are used to study the phase change potential and stage distribution, and the fiber Bragg grating demodulator 17 is used to study the stress, strain and temperature caused by the phase change; specifically, the electrochemical workstation 16 and the battery testing system 15 respectively perform cyclic voltammetry test and charge and discharge test on the battery, and study the phase change potential and stage distribution through the oxidation / reduction voltage and the first-order derivative of voltage-SOC; the fiber Bragg grating demodulator 17 collects the Bragg wavelength change of the fiber Bragg grating sensor, and converts it into strain, stress and temperature change values ​​through formula calculation.

[0074] Its specific research application includes the following steps:

[0075] Step 1: assemble a half-cell using positive and negative electrodes respectively, perform cyclic voltammetry test on the half-cell through an electrochemical workstation 16, determine the electrochemical phase change potential of the positive and negative electrodes according to the position of the oxidation / reduction peak, perform charge and discharge test on the half-cell through a battery testing system 15, and determine the distribution of the phase change reaction stages of the positive and negative electrodes according to the platform position in the voltage-SOC curve;

[0076] Step 2: Perform charge and discharge tests on the lithium battery embedded in the optical fiber through the battery testing system 15, collect the Bragg wavelength change using the fiber grating demodulator 17, and convert it into strain, stress and temperature change values ​​through formula calculation.

[0077] The temperature of the positive electrode is: , the strain of the positive electrode is: ; The temperature of the negative electrode is: , the strain of the negative electrode is: ;

[0078] in: , , , are the Bragg wavelength shifts of the first fiber Bragg grating sensor 7 to the fourth fiber Bragg grating sensor 10, , , , are the temperature sensitivities of the first fiber Bragg grating sensor 7 to the fourth fiber Bragg grating sensor 10, respectively, , is the strain sensitivity of the first fiber Bragg grating sensor 7 and the third fiber Bragg grating sensor 9; and then according to Hooke's law , converting strain into stress;

[0079] Step 3: Calculate the first-order derivative of strain-voltage, and analyze the actual phase change potential of the positive and negative electrodes during the charge and discharge process from the peak and valley voltages in the derivative curve;

[0080] Step 4: Calculate the first-order derivative of strain-SOC and distinguish the actual phase change reaction stage distribution according to the derivative curve;

[0081] Step 5: Calculate the first-order derivative of strain-time and determine the duration of the actual phase change reaction based on the derivative curve;

[0082] Step 6: The battery testing system 15 is set with different charge and discharge rates and different charge and discharge times, and steps 1 to 5 are repeated to study the phase change stability of the electrode at different charge and discharge rates and cycle processes.

[0083] The research on the electrode phase change is applied to Example 1, comprising the following steps:

[0084] A half-cell was assembled using a lithium iron phosphate electrode, and a cyclic voltammetry test was performed on the half-cell using an electrochemical workstation 16. According to the positions of the oxidation / reduction peaks, the charging and discharging phase transition voltages of the lithium iron phosphate were determined to be 3.48 V and 3.38 V, respectively. A charge and discharge test was performed on the half-cell using a battery testing system 15. According to the platform position in the voltage-SOC curve, it was determined that the phase transition reaction stage of the lithium iron phosphate was 10%-98% SOC.

[0085] The battery test system 15 is used to test the charge and discharge of the fiber-embedded lithium battery. The fiber Bragg grating demodulator 17 is used to collect the Bragg wavelength change and convert it into strain, stress and temperature change values ​​through formula calculation. The actual phase change voltage of lithium iron phosphate is determined to be 3.4V through the first-order derivative of strain-voltage; the actual phase change reaction stage distribution of lithium iron phosphate is determined to be 9%-98% SOC through the first-order derivative of strain-SOC. At a rate of 0.1C, the strain of lithium iron phosphate in the phase change stage is 25 ; At 0.5C rate, the strain of lithium iron phosphate in the phase change stage is 20 ; After 1000 cycles at 0.5C, the strain of lithium iron phosphate in the phase change stage is 14 .

[0086] like Figure 6 As shown, it is a cross-sectional SEM image of the LFP electrode in Example 1. The electrode has a thickness of 120 um, the diameter of the first fiber Bragg grating sensor is 80 um, and the sensor is completely buried inside the electrode.

[0087] like Figure 7 As shown, the evolution of the internal signal of the optical fiber embedded lithium battery at a rate of 0.1C in Example 1, where Figure 7 (a) is the voltage-current curve. Figure 7 (b) is the temperature change curve. Figure 7 (c) in the figure is the strain change curve. The middle of the two dotted lines is the lithium iron phosphate phase change reaction stage during the charging process, and the middle of the two solid lines is the lithium iron phosphate phase change reaction stage during the discharging process.

[0088] like Figure 8 As shown, it is the first-order derivative of strain-voltage during the discharge process at 0.1C rate in Example 1. It can be seen from the figure that the strain signal remains unchanged at 100%-98% SOC, the strain signal rises steadily and slowly at 98%-9% SOC, and the strain signal drops rapidly at 9%-0% SOC. The middle of the two solid lines is the lithium iron phosphate phase change reaction stage during the discharge process.

[0089] The study of electrode phase change was applied to Example 2, and the following results were obtained:

[0090] After testing, the actual phase change voltage of the new NCM is 3.8V, and the actual phase change reaction stage distribution is 10%-85% SOC. At a rate of 0.1C, the strain of the new NCM in the phase change stage is 18 ; At 0.5C rate, the strain of the new NCM during the phase transition stage is 14 ; Cycled 1000 times at 0.5C, the strain of the new NCM in the phase transition stage is 10 .

[0091] In the present application, the type of lithium battery can be selected from soft-pack lithium batteries, cylindrical lithium batteries or square lithium batteries.

[0092] As a preferred solution, the optical fiber integrated protection device 11 is made of high temperature resistant and chemical corrosion resistant materials to improve the stability and durability of the optical fiber Bragg grating sensor inside the battery.

[0093] In summary, this application applies optical fiber sensors to the study of lithium-ion battery phase change behavior, and combines the high sensitivity and real-time monitoring capabilities of optical fiber sensors to provide more accurate data support for the optimization of battery materials and structures. Research in this field will open up new directions for improving battery performance, safety and service life, and promote the development of new energy storage technologies.

[0094] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the present invention itself. Various changes may be made to it in form and detail without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims

1. An optical fiber embedded lithium battery for studying electrode phase change, comprising a battery cell (1), an internal sensor component and a battery package (2), characterized in that: The battery cell (1) comprises a positive electrode sheet (3), a diaphragm (5) and a negative electrode sheet (4) stacked in sequence, and a pole ear (6) welded on the positive electrode sheet (3) and the negative electrode sheet (4); the internal sensing component comprises a first fiber Bragg grating sensor (7), a second fiber Bragg grating sensor (8), a third fiber Bragg grating sensor (9), a fourth fiber Bragg grating sensor (10) and an optical fiber integrated protection device (11), wherein: The first fiber Bragg grating sensor (7) and the third fiber Bragg grating sensor (9) are completely buried inside the positive electrode sheet (3) and the negative electrode sheet (4), respectively, and both adopt an exposed Bragg grating structure; The second fiber Bragg grating sensor (8) and the fourth fiber Bragg grating sensor (10) are partially embedded in the positive electrode sheet (3) and the negative electrode sheet (4), respectively, and both are covered with a quartz microtube (12); The first fiber Bragg grating sensor (7) to the fourth fiber Bragg grating sensor (10) all pass through the optical fiber integrated protection device (11) and are sealed by a sealant; The battery package (2) is used to package the battery core (1) and the internal sensor component; The distance between one end of the first fiber Bragg grating sensor (7) and the third fiber Bragg grating sensor (9) and the surface of the positive electrode sheet (3) and the surface of the negative electrode sheet (4) is 10%-20% of the total thickness of the electrode sheet, and the distance between the other end and the current collector surface of the electrode sheet is 10%-20% of the total thickness of the electrode sheet; One end of the quartz microtube (12) is located outside the electrode sheet, and the distance to the surface of the electrode sheet is 10%-35% of the outer diameter of the quartz microtube (12), and the distance from the other end to the current collector surface of the electrode sheet is 10%-35% of the total thickness of the electrode sheet.

2. The method for manufacturing a fiber-embedded lithium battery for studying electrode phase change according to claim 1, characterized in that it comprises the following steps: S1: Determine the selection and formula ratio of active materials, conductive agents, and binders in positive electrode slurry and negative electrode slurry, and use a high-precision electronic scale to accurately weigh each raw material according to the predetermined formula ratio; S2: Mix the binder and the solvent and stir them evenly, add the conductive agent and the active material in sequence and stir until they are evenly mixed to obtain positive electrode slurry and negative electrode slurry; S3: placing two different current collectors in the optical fiber embedding device, and adjusting and determining the embedding position of the internal sensing component through the optical fiber embedding device; S4: coating the positive electrode slurry and the negative electrode slurry on two different current collectors respectively by a doctor blade method, and placing the optical fiber embedding device together with the current collector and the slurry thereon into an oven for drying to obtain a positive electrode sheet (3) and a negative electrode sheet (4); S5: Determine the number of positive electrode sheets (3) and negative electrode sheets (4) according to the battery capacity, weld the aluminum electrode tab (6) and the nickel electrode tab (6) to the current collector surfaces of the positive electrode sheet (3) and the negative electrode sheet (4), respectively, and stack the positive electrode sheet (3), the separator (5) and the negative electrode sheet (4) in order, add electrolyte to them, and use the battery packaging (2) material to package the battery cell (1).

3. The method for manufacturing an optical fiber embedded lithium battery for studying electrode phase change according to claim 2, characterized in that: The optical fiber embedding device comprises a horizontal base (13) and an optical fiber fixing assembly (14), wherein: the horizontal base (13) is used to place a current collector, the optical fiber fixing assembly (14) is used to simultaneously fix a plurality of different sensors, and the distance between the optical fiber fixing assembly (14) and the horizontal base (13) can be adjusted within a range of 10-2000 um.

4. The method for manufacturing a fiber-embedded lithium battery for studying electrode phase change according to claim 2, characterized in that: The content of active material in the positive electrode slurry and the negative electrode slurry is 75%-85%, the content of binder is 10%-15%, the content of conductive agent is 5%-10%, the coating thickness of the slurry is 200-1000um, and the thickness of the positive electrode sheet (3) and the negative electrode sheet (4) obtained after drying is 110-200um.

5. The method for manufacturing an optical fiber embedded lithium battery for studying electrode phase change according to claim 3, characterized in that: The first fiber Bragg grating sensor (7) to the fourth fiber Bragg grating sensor (10) are respectively fixed on the optical fiber fixing assembly (14), and by adjusting the height of the optical fiber fixing assembly (14), the distance from one end of the first fiber Bragg grating sensor (7) and the third fiber Bragg grating sensor (9) to the current collector is 10%-20% of the expected electrode sheet thickness, and the distance from one end of the second fiber Bragg grating sensor (8) and the fourth fiber Bragg grating sensor (10) to the current collector is 10%-35% of the expected electrode sheet thickness.

6. The use of the optical fiber embedded lithium battery for studying electrode phase change according to claim 1, characterized in that: The optical fiber embedded lithium battery is connected to an external receiving device, and the external receiving device includes a battery testing system (15), an electrochemical workstation (16) and a fiber grating demodulator (17), wherein: The battery testing system (15) is connected to the lithium battery via a connecting line and is used to study the phase change potential and stage distribution of the battery; The electrochemical workstation (16) is connected to the lithium battery via a connecting line and is used to study the electrochemical characteristics of the battery; The fiber grating demodulator (17) is connected to the lithium battery via a connecting line and is used to detect stress, strain and temperature changes caused during the phase change of the battery.

7. The use of the optical fiber embedded lithium battery for studying electrode phase transition according to claim 6, Its characteristics include the following steps: S10: assembling a half-cell using positive and negative electrodes respectively, performing a cyclic voltammetry test on the half-cell using an electrochemical workstation (16), determining the electrochemical phase change potentials of the positive and negative electrodes according to the positions of the oxidation / reduction peaks, performing a charge and discharge test on the half-cell using a battery testing system (15), and determining the distribution of the phase change reactions of the positive and negative electrodes according to the platform positions in the voltage-SOC curve; S20: Performing a charge and discharge test on the optical fiber embedded lithium battery through a battery testing system (15), collecting Bragg wavelength changes using a fiber grating demodulator (17), and converting them into strain, stress and temperature change values ​​through formula calculation. The temperature of the positive electrode is: The strain at the positive electrode is: The temperature of the negative electrode is: The strain at the negative electrode is: Where: Δλ FBG1 , Δλ FBG2 , Δλ FBG3 , Δλ FBG4 are the Bragg wavelength shifts of the first fiber Bragg grating sensor (7) to the fourth fiber Bragg grating sensor (10), k T1 , k T2 , k T3 , k T4 are the temperature sensitivities of the first fiber Bragg grating sensor (7) to the fourth fiber Bragg grating sensor (10), k ε1 , k ε3 is the strain sensitivity of the first fiber Bragg grating sensor (7) and the third fiber Bragg grating sensor (9); and the strain is converted into stress through Hooke's law σ=Εε; S30: Calculate the first-order derivative of strain-voltage, and analyze the actual phase change potential of the positive and negative electrodes during the charge and discharge process from the voltages at the peak and valley in the derivative curve; S40: Calculate the first-order derivative of strain-SOC and distinguish the actual phase change reaction stage distribution according to the derivative curve; S50: calculating the first-order derivative of strain-time, and determining the duration of the actual phase change reaction according to the derivative curve; S60: The battery testing system (15) is set with different charge and discharge rates and different charge and discharge times, and the method of S20-S50 is repeated to study the phase change stability of the electrode under different charge and discharge rates and cycle processes.

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