A real-time temperature monitoring device for upconversion flexible fluorescent optical fiber and pouch battery

Abstract

This invention discloses an upconversion luminescent flexible fluorescent fiber and a real-time temperature monitoring device for a pouch cell. The upconversion luminescent material comprises an inorganic compound with the chemical formula NaLa. 1‑x‑ y Ti2O6:x%Yb 3+ / y%Er 3+ Where 0 ≤ x ≤ 10, 0 ≤ y ≤ 2. The upconversion luminescent material of this invention has multiple emission peaks with wavelengths of approximately 530, 550, and 660 nm, respectively. It can be excited by low-energy near-infrared light and exhibits good chemical and thermal stability. The intensity ratio of the emission peaks at 530 nm and 550 nm shows a specific response to temperature changes during temperature variations, possessing potential for use in fluorescence thermometry. The flexible optical fiber with the core-pack structure of this invention, when inserted into a pouch cell, will not affect the performance of the cell and can achieve real-time monitoring of the internal temperature of the pouch cell.

Description

Technical Field

[0001] This invention belongs to the field of luminescent materials technology, specifically relating to an upconversion flexible fluorescent optical fiber and a real-time temperature monitoring device for a pouch cell. Background Technology

[0002] Lithium-ion batteries have been widely used as power sources for electric vehicles, electronic products, and large-scale energy storage devices. To meet the growing demand for electric vehicles with long driving ranges and next-generation consumer electronics with long standby times, efforts are being made to develop lithium-ion batteries with high energy density and large capacity. However, the high temperatures caused by overheating during the electrochemical reaction process can lead to rapid performance degradation and even thermal runaway in lithium-ion batteries, causing significant damage. Therefore, real-time temperature monitoring of lithium-ion batteries is of paramount importance.

[0003] Recently, optical fibers have been used to monitor internal physical parameters of lithium-ion batteries. This temperature measurement strategy can monitor internal temperature and stress in real time during extensive cycling without affecting the charge-discharge performance of the lithium-ion battery. For example, Huang et al. used multiple fiber Bragg grating (FBG) sensors to monitor temperature and pressure in commercial sodium / lithium-ion batteries, contributing to the understanding of interface growth kinetics. Furthermore, Blanquer et al. embedded FBG sensors in coin cells and Swagelok batteries to detect chemimechanical stress at the electrodes and electrode / electrolyte interfaces during operation. Additionally, Mei et al. developed a compact, multifunctional fiber optic sensor and inserted it into a commercial 18650 battery to monitor temperature and pressure in real time during thermal runaway, demonstrating the feasibility of warning of impending thermal runaway before catastrophic safety venting. It is noteworthy that the FBG signal is an entangled convolution of temperature, pressure, and strain; decoupling multiple physical parameters is complex. Specialized temperature sensing is urgently needed to address signal crosstalk.

[0004] Ratio-modulated fluorescence thermometry has attracted considerable attention due to its rapid response, high resolution, and high accuracy. It is performed by deciphering the relationship between the fluorescence intensity ratio (FIR) of the emission spectrum in a luminescent material and temperature. Typically, ratio-modulated fluorescence thermometry can be performed in rare-earth ion-doped upconversion luminescent materials due to the nonlinear luminescence behavior excited by low-energy light (near-infrared light). Rare-earth ions possess abundant stepped energy levels, where energy levels with appropriate gaps thermally couple during temperature changes. Furthermore, the particle population in thermally coupled energy levels (TCELs) typically exhibits a Boltzmann distribution. Therefore, the FIR of TCEs is monotonically dependent on temperature, indicating its potential for optical thermometry applications. Moreover, after subsequent processing, the initially synthesized luminescent material can be implemented as an optical film or fiber in practical applications. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide an upconversion flexible fluorescent optical fiber and a real-time temperature monitoring device for pouch cells. The preparation method is simple, easy to operate, has low equipment cost, and is pollution-free. The temperature measuring device can monitor temperature changes during the operation of the pouch cell in real time and in situ. The upconversion luminescent material of this invention has multiple emission peaks with wavelengths of approximately 530, 550, and 660 nm, can be excited by low-energy near-infrared light, and exhibits good chemical and thermal stability. The intensity ratio of the emission peaks at 530 nm and 550 nm shows a specific response to temperature changes during temperature variations, possessing potential for use in fluorescence thermometry.

[0006] The objective of this invention is achieved through at least one of the following technical solutions.

[0007] An upconversion luminescent material comprising an inorganic compound having the chemical formula NaLa 1-x- y Ti2O6:x%Yb 3+ / y%Er 3+ Where 0≤x≤10, 0≤y≤2.

[0008] Preferably, x is 5.

[0009] Preferably, y is 1.

[0010] Preferably, the luminescent material produces bright green upconversion emission under 980nm excitation, and the adjacent energy levels corresponding to the emission wavelengths of 530nm and 550nm undergo thermal coupling upon heating, with its fluorescence intensity showing a specific response to temperature changes. The excitation source emitted by the luminescent material is a 980nm laser, and the emission wavelengths corresponding to the thermally coupled energy levels are 530nm and 550nm.

[0011] Preferably, the chemical formula of the luminescent material is NaLa. 0.94 Ti2O6:5% Yb 3+ / 1%Er 3+ Its emission wavelength range under 980nm near-infrared light excitation is 500-800nm, of which the wavelengths corresponding to thermally coupled energy level emission are 530nm and 550nm.

[0012] Preferably, the absolute sensitivity of the luminescent material based on fluorescence intensity ratio thermometry at 343 K is 2.87 × 10⁻⁶. - 3 K -1 The maximum relative sensitivity was achieved at 253 K, which is 1.05% K. -1 .

[0013] The above-mentioned method for preparing upconversion luminescent materials includes the following steps:

[0014] 1) According to the general chemical formula NaLa 1-x-y Ti2O6:x%Yb 3+ / y%Er 3+ Weigh the raw materials according to the stoichiometric ratio and grind them in an agate mortar for 30 minutes.

[0015] 2) Place the mixture obtained in step 1) into an alumina crucible and sinter it in a muffle furnace;

[0016] 3) Grind the solid obtained in step 2) into powder in an agate mortar.

[0017] Preferably, in step 1), the x value is 5 and the y value is 1.

[0018] Preferably, in step 2), the high-temperature sintering temperature is 1300℃ and the heating time is 0.5-8h.

[0019] A flexible fluorescent optical fiber material includes a single-mode silica optical fiber, polydimethylsiloxane, silicone rubber, and the aforementioned upconversion luminescent material. The luminescent material is uniformly dispersed in the silicone rubber. The material is injected into a plastic template, and the end is inserted into the single-mode silica optical fiber. After heating and curing, the core of the flexible optical fiber material is removed. The core is then immersed in polydimethylsiloxane, centrifuged at high speed, and cured to obtain the flexible optical fiber.

[0020] Preferably, the upconversion luminescent material is 0.2g and the silicone rubber is 1g; the heating curing temperature is 100℃ and the curing time is 0.5-2h.

[0021] A flexible fluorescent fiber optic temperature sensing device includes an excitation light source connected to a fiber optic spectrometer via the flexible fluorescent fiber optic cable. The flexible fluorescent fiber optic cable is inserted into a pouch cell, and the pouch cell is connected to an electrochemical workstation via electrode plates. Under 980nm near-infrared light excitation, the flexible fluorescent fiber optic cable emits upconversion green light. The fluorescence intensity ratio changes specifically with temperature variations, which can be deciphered as a temperature signal through a reference curve. This allows for real-time, in-situ temperature monitoring during the battery's charge-discharge cycle.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1) The upconversion luminescent material of this invention exhibits good thermal stability and causes no environmental pollution. The emission peak intensity under low-energy near-infrared light excitation shows a specific temperature response, which can be fitted using a function.

[0024] 2) The upconversion luminescent material of this invention can be thermometric by fluorescence intensity ratio when the temperature changes, with a relative sensitivity of up to 1.05% K. -1 .

[0025] 3) The preparation method of the present invention is simple, easy to operate, low in equipment cost and pollution-free, and is suitable for widespread use; it is expected to be widely used in the field of flexible fluorescent fiber optic temperature measurement.

[0026] 4) The flexible fluorescent temperature sensing device of the present invention can monitor the temperature of an object in real time by changing the fluorescence intensity ratio of a flexible optical fiber that emits upconverted green light, and has been successfully applied to the temperature measurement of pouch batteries.

[0027] 5) The flexible fluorescent temperature sensing device of the present invention can monitor the temperature change inside the pouch battery in real time, which helps to assist in the thermal management of the pouch battery and avoid damage caused by battery thermal runaway. Attached Figure Description

[0028] Figure 1 This is the X-ray diffraction pattern of the upconversion luminescent material prepared in Example 1 of this application;

[0029] Figure 2 These are scanning electron microscope images of the upconversion luminescent material prepared in Example 1 of this application;

[0030] Figure 3 This is the fluorescence spectrum of the upconversion luminescent material prepared in Example 1 of this application;

[0031] Figure 4 These are emission spectra of the upconversion luminescent material prepared in Example 1 of this application at different temperatures;

[0032] Figure 5 This is a schematic diagram showing the relationship between the fluorescence intensity ratio of the thermally coupled energy level emission peak of the upconversion luminescent material prepared in Example 1 of this application and temperature.

[0033] Figure 6 This refers to the temperature-sensing properties of the upconversion luminescent material prepared in Example 1 of this application;

[0034] Figure 7 This is the X-ray diffraction pattern of the upconversion luminescent material prepared in Example 2 of this application;

[0035] Figure 8 This is the fluorescence spectrum of the upconversion luminescent material prepared in Example 2 of this application;

[0036] Figure 9 This is the X-ray diffraction pattern of the upconversion luminescent material prepared in Example 3 of this application;

[0037] Figure 10 This is a cross-sectional photograph of the flexible fluorescent optical fiber material prepared in Example 4 of this application;

[0038] Figure 11 These are distribution photographs of the upconversion phosphor prepared in Example 1 of this application in Example 4;

[0039] Figure 12 This is the flexible fluorescent temperature sensing and measuring device prepared in Example 5 of this application;

[0040] Figure 13 This is a graph showing the temperature change of a pouch cell during a charge-discharge cycle measured by the flexible fluorescent temperature sensing device prepared in Example 5 of this application. Detailed Implementation

[0041] The present invention will be specifically described below with reference to the embodiments, but the implementation and protection scope of the present invention are not limited to the following embodiments.

[0042] Example 1

[0043] The chemical formula of the upconversion phosphor in this embodiment is NaLa. 1-x-y Ti2O6:x%Yb 3+ / y%Er 3+ Where x = 5 and y = 1. Accurately weigh 0.1059g Na₂CO₃, 0.3062g La₂O₃, 0.1597g TiO₂, 0.0098g Yb₂O₃, and 0.0019g Er₂O₃ according to the stoichiometric ratios of the elements in the chemical formula. Then, grind the raw material powder in an agate mortar for 30 minutes, transfer it to an alumina crucible, cover it, and sinter it in an air-atmosphere high-temperature reactor at 1300℃ for 6 hours. After natural cooling, remove it and grind it again for about 10 minutes to obtain NaLa. 0.94 Ti2O6:5% Yb 3+ / 1%Er 3+ The phosphor's XRD, SEM, and fluorescence spectra are as follows: Figure 1 , Figure 2 and Figure 3 As shown, from Figure 1 It can be seen from this that the phosphor is a single phase. Figure 2 It can be seen that the average particle size of the prepared upconversion luminescent material is about a few micrometers. Figure 3 It is known that this phosphor can emit visible light of 500-750nm under 980nm near-infrared light excitation, with the main emission peaks located around 530, 550, and 660nm. Figure 4 It can be seen that the emission peak position of the prepared upconversion luminescent material remains unchanged at different temperatures, but the emission peak intensity changes with temperature.

[0044] Figure 5 This is a schematic diagram showing the relationship between the intensity ratio of the thermally coupled energy level emission peak of the prepared upconversion luminescent material and temperature, where FIR is fitted by an exponential function.

[0045] Figure 6 This is a schematic diagram illustrating the temperature sensitivity of the luminescence of the prepared upconversion luminescent material, SA For absolute sensitivity, S R This is relative sensitivity. According to... Figure 6 It can be seen that at 443K, the highest absolute sensitivity reaches 7.51cm. -1 K -1 The highest relative sensitivity reaches 0.64% K at 303 K. -1 .

[0046] Example 2

[0047] The chemical formula of the upconversion phosphor in this embodiment is NaLa. 1-x-y Ti2O6:x%Yb 3+ / y%Er 3+ Where x = 0, y = 1. Accurately weigh 0.1059g Na₂CO₃, 0.3793g La₂O₃, 0.1597g TiO₂, and 0.0019g Er₂O₃ according to the stoichiometric ratio of each element in the chemical formula. Then grind the raw material powder in an agate mortar for 30 minutes, transfer it to an alumina crucible, cover it, and sinter it in an air-atmosphere high-temperature reactor at 1300℃ for 6 hours. After natural cooling, remove it and grind it again for about 10 minutes to obtain NaLa. 0.94 Ti2O6:1%Er 3+ The XRD diffraction pattern of the phosphor is as follows: Figure 7 This indicates that the synthesized upconversion phosphor is a single pure phase, and its upconversion emission spectrum is as follows: Figure 8 As shown, it exhibits green upconversion luminescence, but due to the lack of Yb ion sensitization, Er ions have a very low absorption cross-section for 980nm near-infrared light, which led to the use of a relatively high-power laser pump (1.5W) during the test. The laser thermal effect caused by the high power cannot be avoided, affecting the temperature measurement performance.

[0048] Example 3

[0049] The chemical formula of the upconversion phosphor in this embodiment is NaLa. 1-x-y Ti2O6:x%Yb 3+ / y%Er 3+ Where x = 5 and y = 0. Accurately weigh 0.1059g Na₂CO₃, 0.3640g La₂O₃, 0.1597g TiO₂, 0.0098g Yb₂O₃, and 0g Er₂O₃ according to the stoichiometric ratios of the elements in the chemical formula. Then grind the raw material powder in an agate mortar for 30 minutes, transfer it to an alumina crucible, cover it, and sinter it in an air-atmosphere high-temperature reactor at 1300℃ for 6 hours. After natural cooling, remove it and grind it again for about 10 minutes to obtain NaLa. 0.94 Ti2O6:5% Yb 3+ The XRD diffraction pattern of the phosphor is as follows: Figure 9 This indicates that the synthesized upconversion phosphor is a single pure phase, but due to the lack of luminescent centers, the synthesized phosphor does not exhibit upconversion luminescence.

[0050] Example 4

[0051] A flexible fluorescent optical fiber capable of temperature sensing. The flexible fluorescent optical fiber of the present invention was prepared according to the following method: 0.2 g of upconversion phosphor was uniformly dispersed in 1 g of silicone, injected into a plastic template, and the end was inserted into a single-mode silica optical fiber. After curing at 80°C for 2 hours, the fiber core was obtained. The prepared core was immersed in polydimethylsiloxane, centrifuged at high speed, and then cured to obtain the flexible optical fiber. The near-infrared phosphor is the upconversion phosphor of Example 1 above, with the chemical formula NaLa. 0.94 Ti2O6:5% Yb 3+ / 1%Er 3+ .

[0052] Figure 10 This is a cross-sectional view of the prepared flexible optical fiber material. It can be seen that the optical fiber has a good core-cladding structure, with a core of about 600 micrometers and a cladding of about 50 micrometers. Figure 11 This shows the distribution of the upconversion phosphor from Example 1 in the flexible optical fiber material prepared in Example 2. The dotted circle indicates the upconversion phosphor particles, demonstrating the uniform dispersion of the phosphor in the flexible optical fiber.

[0053] Example 5

[0054] A flexible fluorescent fiber optic temperature sensing device includes an excitation source, a fiber optic spectrometer, a pouch battery, an electrochemical workstation, and the flexible fiber optic material described in Example 4. The excitation source is coupled to the flexible fiber optic material via a single-mode silica fiber. The excited upconversion emission is connected to the fiber optic spectrometer via another single-mode silica fiber, converting the optical signal into an electrical signal, which is then converted into temperature information according to a calibration curve. The flexible fiber optic material can absorb light emitted from the near-infrared excitation source and release upconverted green light. The intensity ratio of the green light peaks at two different wavelengths changes specifically with temperature variations. The flexible fiber optic material is inserted inside the pouch battery and sealed within a vacuum glove box. The device described in Example 5 is as follows... Figure 12 As shown in Example 5, real-time monitoring of the internal temperature rise of the pouch battery during one charge-discharge cycle is obtained. Figure 13 As can be seen from the figure, the device can perform fluorescence thermometry very well and accurately measure the internal temperature of the pouch battery, and it is expected to be applied to the thermal management of pouch batteries.

[0055] It should be understood that the above detailed description of the technical solutions of the present invention with reference to optimized embodiments is illustrative and not restrictive. It should not be considered that the specific implementation of the present invention is limited to this. For those skilled in the art, any modifications to the technical solutions described in the embodiments or equivalent substitutions of some technical features without departing from the concept of the present invention should be considered as falling within the scope of patent protection defined by the claims submitted by the present invention.

[0056] The above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. An upconversion luminescent material, characterized in that, The chemical formula is NaLa 1-x-y Ti2O6: x %Yb 3+ / y %Er 3+ Where, 0 < x ≤10, 0 < y ≤2.

2. The upconversion luminescent material according to claim 1, characterized in that, The x y is 5, and y is 1.

3. The upconversion luminescent material according to claim 1, characterized in that, The luminescent material produces bright green upconversion luminescence when excited at 980 nm, and the adjacent energy levels corresponding to the emission at wavelengths of 530 nm and 550 nm undergo thermal coupling when heated, and its fluorescence intensity shows a specific response to temperature changes.

4. A flexible fluorescent optical fiber material, characterized in that, The invention includes a single-mode silica optical fiber, polydimethylsiloxane, silicone, and the upconversion luminescent material as described in any one of claims 1 to 3. The luminescent material is uniformly dispersed in silicone, injected into a plastic template, inserted into a single-mode silica optical fiber at the tail end, heated and cured, and then removed to obtain a flexible optical fiber core. The obtained core is immersed in polydimethylsiloxane, centrifuged at high speed, and then cured to obtain a flexible optical fiber.

5. The flexible fluorescent optical fiber material according to claim 4, characterized in that, The upconversion luminescent material is 0.1~1.0 g, and the silicone rubber used is 1 g.

6. A real-time temperature monitoring device for a soft-pack battery, characterized in that, The device includes an excitation light source connected to a fiber optic spectrometer via the flexible fluorescent fiber material described in claim 4 or 5. The flexible fluorescent fiber material is inserted into the pouch cell, and the pouch cell is connected to an electrochemical workstation via electrode plates. Under 980 nm near-infrared light excitation, the flexible fluorescent fiber material releases upconversion green light. The fluorescence intensity ratio changes specifically with temperature variations, which can be deciphered as a temperature signal through a reference curve. This allows for real-time, in-situ temperature monitoring during the battery's charge-discharge cycle.

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