A flow battery test platform

Abstract

The application discloses a kind of liquid flow battery test platform, including liquid flow battery system, multi-physical field parameter coupling detection system and data acquisition system, liquid flow battery system includes: liquid flow battery and visual fixture, liquid flow battery includes electrode and liquid storage tank;Visual fixture includes diaphragm, two graphite plates and two end plates, at least one of two end plates is transparent end plate;Multi-physical field parameter coupling detection system includes: optical detection unit, electrolyte detection unit, gas detection unit and battery tester, optical detection unit is used to obtain the internal image data of liquid flow battery;Electrolyte detection unit is used to obtain the concentration data of electrolyte;Gas detection unit is used to obtain the concentration data of gas;Battery tester is used to charge and discharge to liquid flow battery;Data acquisition system is used to obtain key feature data according to image data, the concentration data of electrolyte and the concentration data of gas, to adjust the operating state of battery.

Description

[0001] This application is a divisional application of the invention patent application with the application date of October 22, 2024, the Chinese application number of 202411477732.X, and the invention name of "Liquid flow battery test platform". TECHNICAL FIELD

[0002] The present application relates to the technical field of batteries, in particular to a liquid flow battery test platform. BACKGROUND

[0003] The liquid flow battery generally uses electrochemical redox reaction to realize charging and discharging, so it is a new type of large electrochemical energy storage battery. It is different from the battery using solid material electrode or gas electrode, and its active material is a flowing electrolyte solution. The positive and negative electrolytes are separated and circulated respectively. Its most prominent feature is that the scale of power storage can be designed independently, and it has the characteristics of high capacity, wide application field, long cycle life, etc.

[0004] In order to reveal the complex reaction mechanism of the liquid flow battery, the PNNL laboratory in the United States developed a liquid flow battery X-ray tomography imaging system, which realized the nondestructive reconstruction of the three-dimensional microstructure inside the electrode, and quantitatively analyzed the influence of porosity, specific surface area and other geometric parameters on mass transfer behavior. The Fraunhofer Institute in Germany uses neutron scattering technology to reveal the distribution of electrolyte inside the carbon felt electrode and its correlation with current density. The Hydrogenics company in Canada developed an online infrared thermal imaging system, which realized real-time monitoring and hotspot diagnosis of the temperature distribution inside the VRFB stack. However, the above test platforms are mainly for offline multi-physical field detection or online single-physical field detection, and cannot realize real-time acquisition of the coupling effect and dynamic law between different physical fields in the charging and discharging process of the liquid flow battery, so as to realize integrated in-situ characterization and real-time monitoring of the multi-physical field characteristics of the liquid flow battery.

[0005] Therefore, how to provide a test platform capable of realizing integrated in-situ characterization and real-time monitoring of the multi-physical field characteristics of the liquid flow battery is a problem to be solved. SUMMARY

[0006] The present application provides a liquid flow battery test platform, which aims to provide a test platform capable of realizing integrated in-situ characterization and real-time monitoring of the multi-physical field characteristics of the liquid flow battery.

[0007] In one aspect, the embodiments of the present application provide a flow battery test platform, comprising a flow battery system, a multi-physical field parameter coupling detection system and a data acquisition system; the flow battery system comprises a flow battery and a visual fixture, the flow battery comprises an electrode and a liquid storage tank, the electrode comprises a positive electrode and a negative electrode arranged in a stack, the liquid storage tank comprises a positive electrode liquid storage tank and a negative electrode liquid storage tank arranged on both sides of the electrode; the visual fixture comprises a separator, two graphite plates and two end plates, the separator is arranged between the positive electrode and the negative electrode, the two graphite plates are arranged on the opposite sides of the electrode away from the separator, and the two end plates are arranged on the opposite sides of the graphite plates away from the electrode, wherein at least one of the two end plates is a transparent end plate; the multi-physical field parameter coupling detection system comprises an optical detection unit, an electrolyte detection unit, a gas detection unit and a battery tester, the optical detection unit is used to acquire internal images of the flow battery in real time to obtain internal image data of the flow battery; the electrolyte detection unit is used to acquire electrolyte in the liquid storage tank in real time through a micro-sampling loop to obtain concentration data of the electrolyte; the gas detection unit is used to acquire gas in the liquid storage tank in real time to obtain concentration data of the gas; the battery tester is used to charge and discharge the flow battery and acquire electrochemical data; and the data acquisition system is used to acquire key feature data according to the image data, the concentration data of the electrolyte and the concentration data of the gas, and calculate corresponding deviation values according to a mapping relationship between the key feature data and preset performance indicators of the flow battery, so as to adjust the running state of the flow battery according to the deviation values.

[0008] Optionally, in some embodiments of the present application, the end plate close to the side of the optical detection unit is a transparent end plate, and the material of the transparent end plate comprises polymethyl methacrylate.

[0009] Optionally, in some embodiments of the present application, the side of the graphite plate close to the electrode is provided with a plurality of flow channels arranged at intervals, and the flow channels are used to guide the electrolyte in the liquid storage tank to flow on the surface of the electrode.

[0010] Optionally, in some embodiments of the present application, the optical detection unit comprises an optical microscope or a high-speed camera, and the image data comprises at least one of flow parameters of the electrolyte in the flow channels, characteristic parameters of side reaction bubbles and characteristic parameters of the surface of the electrode.

[0011] Optionally, in some embodiments of the present application, the electrolyte detection unit comprises an in-situ ultraviolet spectrometer, and the concentration data of the electrolyte comprises curve data of the concentration of cations and anions in the electrolyte changing with time.

[0012] Optionally, in some embodiments of the present application, the electrolyte composition comprises tracer particles or fluorescein.

[0013] Optionally, in some embodiments of the present application, the gas detection unit comprises an in-situ gas chromatograph, and the gas concentration data comprises type data of the gases evolved during the operation of the flow battery and curve data of the concentration of each of the gases over time.

[0014] Optionally, in some embodiments of the present application, the electrode material comprises carbon felt or carbon cloth.

[0015] Optionally, in some embodiments of the present application, the key characteristic data at least comprises active material concentration, ion crossover degree, hydrogen evolution rate, coulombic efficiency, energy efficiency and capacity decay rate.

[0016] Optionally, in some embodiments of the present application, the flow battery system further comprises a flow control unit for controlling the electrolyte flow of the flow battery, an electric control unit for controlling the charge-discharge current density of the flow battery, and a temperature control unit for controlling the temperature of the flow battery; the battery tester is connected with the flow control unit, the electric control unit and the temperature control unit, and the battery tester is further used for collecting the deviation value corresponding to the parameter characteristic data output by the data acquisition system in real time and outputting to the flow battery system, so as to adjust at least one of the electrolyte flow, the charge-discharge current density and the temperature of the flow battery.

[0017] The liquid flow battery test platform provided by the application integrates a liquid flow battery system, a multi-physical field parameter coupling detection system and a data acquisition system, wherein the liquid flow battery system comprises a liquid flow battery and a visual fixture, the liquid flow battery comprises electrodes and liquid storage tanks, the electrodes comprise positive electrodes and negative electrodes arranged in layers, and the liquid storage tanks comprise positive electrode liquid storage tanks and negative electrode liquid storage tanks arranged on the two sides of the electrodes; the visual fixture comprises a diaphragm, two graphite plates and two end plates, the diaphragm is arranged between the positive electrodes and the negative electrodes, the two graphite plates are arranged on the opposite sides of the electrodes away from the diaphragm, and the two end plates are arranged on the opposite sides of the graphite plates away from the electrodes, wherein at least one of the two end plates is a transparent end plate; the multi-physical field parameter coupling detection system comprises an optical detection unit, an electrolyte detection unit, a gas detection unit and a battery tester, the optical detection unit is used for acquiring internal image data of the liquid flow battery by acquiring internal images of the liquid flow battery in real time; the electrolyte detection unit is used for acquiring concentration data of electrolyte in the liquid storage tank by acquiring the electrolyte in the liquid storage tank through a micro sampling loop in real time; the gas detection unit is used for acquiring concentration data of gas in the liquid storage tank by acquiring the gas in the liquid storage tank in real time; and the battery tester is used for charging and discharging the liquid flow battery and acquiring electrochemical data; the data acquisition system is used for acquiring key feature data according to the image data, the concentration data of the electrolyte and the concentration data of the gas, and calculating corresponding deviation values according to a mapping relationship between the key feature data and preset performance indicators of the liquid flow battery, so as to adjust the running state of the liquid flow battery according to the deviation values. That is, the liquid flow battery test platform integrates multiple test methods such as optics, electrochemistry, spectroscopy and chromatography, can synchronously acquire multiple physical field information such as light field, electric field, flow field and concentration field in the charging and discharging process of the liquid flow battery, acquires the coupling effect and dynamic law between different physical fields through comprehensive analysis of multi-source characterization data, avoids the limitation caused by single characterization, and realizes integrated in-situ characterization and real-time monitoring of the multi-physical field characteristics of the liquid flow battery. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 FIG. 1 is a first schematic diagram of the liquid flow battery test platform provided by the application;

[0019] Figure 2 FIG. 2 is a schematic diagram of the visual fixture and the liquid flow battery provided by the application;

[0020] Figure 3 FIG. 3 is a second schematic diagram of the liquid flow battery test platform provided by the application;

[0021] Figure 4 FIG. 4 is a schematic diagram of the flow field under different battery voltages provided by the application;

[0022] Figure 5 is a schematic diagram of absorbance of the mixed electrolyte under light of different wavelengths provided by the present application;

[0023] Figure 6 is a schematic diagram of the relationship between cycle number, hydrogen evolution concentration and time of a liquid flow battery in the prior art;

[0024] Figure 7 is a schematic diagram of the relationship between cycle number and hydrogen volume of a liquid flow battery in the prior art;

[0025] Figure 8 is a schematic diagram of the relationship between the capacity and volume of hydrogen and the size of voltage provided by the present application;

[0026] Figure 9 is a schematic diagram of the relationship between the capacity, cycle number and energy efficiency of a battery provided by the present application;

[0027] Figure 10 is a schematic diagram of the SOC-voltage curve of a charging model of a hydrogen evolution reaction model and a coupled hydrogen evolution reaction model provided by the present application;

[0028] Figure 11 is a schematic diagram of a concentration distribution cloud map of hydrogen;

[0029] Figure 12 is a schematic diagram of an overpotential distribution cloud map. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be described below with reference to the accompanying drawings in the embodiments of the present application. The described technical solutions are only used to explain and illustrate the idea of the present application, and should not be regarded as limiting the protection scope of the present application.

[0031] The various embodiments provided by the present application are similar, and the features in different embodiments can be combined with each other.

[0032] As shown in the accompanying drawings, Figure 1 Embodiments of the present application provide a liquid flow battery test platform 100, which comprises a liquid flow battery system 10, a multi-physical field parameter coupling detection system 20 and a data acquisition system 30.

[0033] In the embodiments of the present application, the liquid flow battery system 10 comprises a liquid flow battery 11 and a visualization clamp 12. The liquid flow battery 11 comprises an electrode 111 and a liquid storage tank 112, the electrode 111 comprises a positive electrode 111 and a negative electrode 111 arranged in layers, and the liquid storage tank 112 comprises a positive electrode liquid storage tank 112 and a negative electrode liquid storage tank 112 arranged on both sides of the electrode 111.

[0034] As shown in the accompanying drawings, Figure 2As shown, the visualization clamp 12 includes a diaphragm 121, two graphite plates 122, and two end plates 123, the diaphragm 121 is arranged between the positive electrode 111 and the negative electrode 111, the two graphite plates 122 are arranged on the opposite sides of the electrode 111 away from the diaphragm 121, and the two end plates 123 are arranged on the opposite sides of the graphite plate 122 away from the electrode 111, wherein at least one of the two end plates 123 is a transparent end plate 123.

[0035] In the embodiment of the present application, the multi-physical field parameter coupling detection system 20 includes an optical detection unit 21, an electrolyte detection unit 22, a gas detection unit 23, and a battery tester 24. The optical detection unit 21 is used to collect the internal image of the flow battery 11 in real time to obtain internal image data of the flow battery 11. The electrolyte detection unit 22 is used to collect the electrolyte in the liquid storage tank 112 in real time through a micro-sampling loop to obtain concentration data of the electrolyte. The gas detection unit 23 is used to collect the gas in the liquid storage tank 112 in real time to obtain concentration data of the gas. The battery tester 24 is used to charge and discharge the flow battery 11 and collect electrochemical data.

[0036] In the embodiment of the present application, the data acquisition system is used to obtain key feature data according to the image data, the concentration data of the electrolyte, and the concentration data of the gas, and calculate a corresponding deviation value according to a mapping relationship between the key feature data and a preset performance index of the flow battery 11, so as to adjust the running state of the battery according to the deviation value.

[0037] In the flow battery test platform 100 provided by the present application, the flow battery system 10, the multi-physical field parameter coupling detection system 20, and the data acquisition system 30 are integrated, that is, the flow battery test platform 100 integrates multiple testing means such as optics, electrochemistry, spectroscopy, and chromatography, can synchronously obtain multiple physical field information such as light field, electric field, flow field, and concentration field in the charging and discharging process of the flow battery 11, and obtains the coupling effect and dynamic law between different physical fields through comprehensive analysis of multi-source characterization data, thereby avoiding the limitation caused by single characterization, and realizing a test platform for integrated in-situ characterization and real-time monitoring of the multi-physical field characteristics of the flow battery 11.

[0038] In the embodiment of the present application, the visualization clamp 12 is locked by bolts and nuts. The visualization clamp 12 is arranged to solve the problem that the internal state of the flow battery 11 cannot be directly observed.

[0039] In the embodiment of the present application, the transparent end plate 123 is provided with a sealing groove to prevent the electrolyte from leaking.

[0040] In the embodiments of the present application, the material of the transparent end plate 123 includes Polymethyl Methacrylate (PMMA). PMMA is a kind of high-molecular organic glass, which has excellent optical performance and mechanical strength. In the visible light band, the light transmittance of PMMA can be as high as 92% or more, which can ensure the clear visibility of the internal state of the battery. At the same time, PMMA material has good impact resistance and chemical corrosion resistance, which can meet the requirements of the battery operating environment.

[0041] In the embodiments of the present application, the graphite plate 122 is a composite bipolar plate, which has the dual functions of electric conduction and fluid conduction. Graphite material has excellent electrical conductivity, which can effectively collect the electrons generated on the surface of the electrode 111 and conduct to the external circuit.

[0042] In the embodiments of the present application, the side of the graphite plate 122 close to the electrode 111 is provided with a plurality of spaced flow channels, which are used to guide the electrolyte in the liquid storage tank 112 to flow on the surface of the electrode 111. Specifically, the flow channels serve as channels for distributing and circulating the electrolyte, guiding the electrolyte to flow uniformly on the surface of the electrode 111, and ensuring the effective mass transfer of the active material. The geometric parameters of the flow channels such as width, depth, shape, etc. can be optimized according to actual requirements to achieve the best mass transfer effect. One side of the graphite plate 122 is closely attached to the electrode 111, and the other side is in contact with the transparent end plate 123.

[0043] In the embodiments of the present application, the material of the electrode 111 includes carbon felt or carbon cloth. Specifically, the electrode 111 is made of porous carbon materials such as carbon felt and carbon cloth, which is responsible for providing the site for electrochemical reaction. The electrode 111 made of porous carbon materials has high specific surface area and excellent electrical conductivity, which can promote the contact between the electrolyte and the active material and the charge transfer. Among them, the thickness, porosity and other parameters of the electrode 111 can be optimized according to the requirements of specific capacity, rate performance, etc. During assembly, the electrode 111 is placed between the graphite plate 122 and the transparent end plate 123, and is closely attached to the flow channel side of the graphite plate 122.

[0044] In the embodiments of the present application, the flow control unit 13 is used to control the flow of the electrolyte of the flow battery 11, the electric control unit 14 is used to control the charge and discharge current density of the flow battery 11, and the temperature control unit 15 is used to control the temperature of the flow battery 11. The battery tester 24 is connected with the flow control unit 13, the electric control unit 14 and the temperature control unit 15, and the battery tester 24 is also used to output the deviation value corresponding to the parameter characteristic data output by the data acquisition system to the flow battery system 10, so as to adjust at least one of the electrolyte flow, the charge and discharge current density and the temperature of the flow battery 11.

[0045] In the embodiments of the present application, the optical detection unit 21 includes an optical microscope or a high-speed camera, and the image data includes at least one of the flow parameters of the electrolyte in the flow channel, the characteristic parameters of the side reaction bubbles, and the characteristic parameters of the surface of the electrode 111. Specifically, by using the optical microscope and / or the high-speed camera, a series of key information such as the flow state of the electrolyte in the flow channel, the nucleation and growth process of the side reaction bubbles, and the microscopic changes of the surface morphology of the electrode 111 are dynamically tracked and recorded, which provides valuable experimental data support for in-depth understanding of the reaction mechanism of the liquid flow battery 11.

[0046] In the embodiments of the present application, the visualization observation is realized by the optical detection unit 21 and the visualization clamp 12, so that the size distribution, number density, and generation frequency of the side reaction bubbles can be quantitatively analyzed, and the influence of the side reaction bubbles on the battery performance can be more comprehensively and systematically evaluated, which provides an important basis for optimizing the structure of the electrode 111 and inhibiting the side effects of the bubbles, reveals the evolution law of the bubbles in the long-term charge and discharge cycle, and clarifies the intrinsic mechanism of the attenuation of the electrode 111.

[0047] As shown in Figure 3 The electrolyte detection unit 22 includes an in-situ ultraviolet spectrometer, and the concentration data of the electrolyte includes curve data of the concentration of the anions and cations in the electrolyte changing with time.

[0048] In the embodiments of the present application, the composition of the electrolyte includes tracer particles or fluorescein. By adding tracer particles or fluorescein in the electrolyte and combining with the image velocimetry technology, the velocity field distribution in the flow channel can be accurately measured, and the dead zones, bypasses and other areas that are not conducive to mass transfer can be identified, thereby providing quantitative guidance for optimizing the flow field design.

[0049] Specifically, there is a mutual consumption phenomenon between the ions in the battery, which affects the capacity retention rate of the battery. In the past, the problems of ion cross and capacity attenuation of the electrolyte were evaluated by observing the volume change in the liquid storage tank 112, offline sampling and the like, but there are problems such as oxidation of the electrolyte when sampling, difficulty in dynamically reflecting the real situation inside the battery, and the like, which limit the in-depth understanding of the ion cross and performance capacity attenuation mechanism.

[0050] In the embodiments of the present application, the in-situ ultraviolet spectrometer is combined with the optical visualization technology. Specifically, a micro-sampling circuit is introduced into the liquid storage tank 112 of the liquid flow battery system 10, and the electrolyte sample is introduced into the in-situ ultraviolet spectrometer in real time. The online acquisition platform is as shown in Figure 3As shown. Because of its analysis method based on electronic transition, using the selective absorption of ultraviolet-visible light when the electrons in the molecule jump between different energy levels, the spectrum of absorbance change with wavelength is obtained, and then the qualitative and quantitative analysis of the composition and content of the substance is realized, that is, the curve of the concentration of anion and cation changes with time, the correlation between ion cross rate and battery capacity attenuation is quantitatively evaluated. At the same time, the introduction of visual clamp 12 can directly observe the penetration of electrolyte on the membrane side, and combined with fluorescein or tracer substances can more intuitively reflect the cross-penetration phenomenon of ions. From the perspective of fluid field and electrochemical field combination, the dynamic process of ion cross can be more accurately evaluated, and the internal relationship between ion cross and battery capacity attenuation is revealed.

[0051] Because gas will be precipitated during the operation of the flow battery 11, the bubbles formed due to the escape of the gas will affect the volume of the electrolyte and reduce the active surface area available for electrochemical reactions. This situation hinders the effective use of the electrode 111, resulting in a decrease in mass and charge transfer rate. Therefore, concentration polarization and ohmic polarization problems occur. Secondly, the gas escape side reaction competes with the normal chemical reaction in the flow battery 11, resulting in a decrease in battery charging current. Therefore, after multiple cycles, the coulombic efficiency, energy efficiency, capacity retention rate and other performance indicators all decrease. In addition, due to the significant potential difference between the positive and negative half-cells during operation, the influence of hydrogen and oxygen precipitation side reactions becomes more pronounced at the end of the charging process, and therefore, real-time detection of the state of gas precipitation is particularly important.

[0052] In the embodiment of the present application, the gas detection unit 23 includes an in-situ gas chromatograph, and the concentration data of the gas includes type data of the gas precipitated during the operation of the battery and curve data of the concentration of each gas changing with time.

[0053] In the embodiment of the present application, the in-situ gas chromatograph and optical visualization technology are combined. Specifically, by introducing the gas in the liquid storage tank 112 into the gas chromatograph in real time, the qualitative and quantitative analysis of the gas components is realized by using the different adsorption of different gases in the gas chromatograph, the concentration-time curve of by-products such as hydrogen and oxygen is obtained, and the real-time occurrence rate of the side reaction is calculated accordingly. At the same time, by using the visual clamp 12, the difference in bubble behavior under different electrode 111 materials, surface structures and flow field designs can be compared by quantitative analysis of the morphological parameters (such as diameter, contact angle, coverage rate, etc.) of the bubbles, and the correlation between the bubbles and the side reaction is revealed, providing design ideas for inhibiting bubbles and strengthening mass transfer. Further, the quantitative relationship between bubble behavior and side reaction kinetics is established by corresponding the bubble signal observed by visualization with the by-product concentration detected by chromatography, and the spatiotemporal law of bubble evolution is formed.

[0054] In the embodiments of the present application, the data acquisition system 30 is used to enhance, segment, and extract features of the obtained images after the battery tester 24 charges and discharges the visualization fixture 12 and obtains image data of the porous electrode 111, electrolyte flow, and bubble behavior inside the battery through the microscope, so as to obtain the porosity, specific surface area, and liquid saturation of the porous electrode 111, and obtain the variation rules of the porosity, specific surface area, and liquid saturation with time and current density.

[0055] In the embodiments of the present application, the data acquisition system 30 is also used to calculate the coulombic efficiency, energy efficiency, and self-discharge index of the battery after in-situ ultraviolet spectrometry is performed on the inside of the battery to measure the concentration variation of the electrolyte in real time, and continuously monitor the variation of the active ion concentration and valence state, and obtain the spatial distribution of the ion concentration by scanning and imaging different positions of the electrolyte, so as to obtain the charge transport and cross-contamination degree data.

[0056] In the embodiments of the present application, the data acquisition system 30 is also used to obtain bubble feature data by calculating and processing the obtained porosity, specific surface area, and liquid saturation data, and obtain electrolyte ion cross signal by calculating and processing the obtained electrolyte ion concentration, charge transport, and ion cross-contamination degree data. When the data acquisition system 30 detects the corresponding bubble feature or receives the electrolyte ion cross signal, the in-situ gas chromatograph is started to monitor the gas components precipitated during the operation of the battery, so as to obtain the concentration data of hydrogen or oxygen gas in the liquid storage tank 112 of the flow battery 11.

[0057] In the embodiments of the present application, the key feature data at least includes active material concentration, ion cross degree, hydrogen evolution rate, coulombic efficiency, energy efficiency, and capacity attenuation rate. Specifically, the data acquisition system 30 is also used to perform cleaning, filtering, and normalization preprocessing operations on the obtained concentration data of the electrolyte, concentration data of the gas, energy efficiency, coulombic efficiency, and self-discharge rate, and extract key feature parameters that can reflect the performance of the battery, such as active material concentration, ion cross degree, hydrogen evolution rate, coulombic efficiency, energy efficiency, and capacity attenuation rate.

[0058] Further, the data acquisition system 30 compares the real-time data obtained by preprocessing with the initial value (for example, energy efficiency deviation = (real-time energy efficiency - initial energy efficiency) / initial energy efficiency x 100%), calculates the deviation value, and then performs weighted average on the ion crossover degree, hydrogen evolution side reaction degree, energy efficiency deviation, coulomb efficiency deviation, self-discharge rate and other indicators (comprehensive score = ∑ (indicator weight x indicator score) / ∑ indicator weight), compares the comprehensive score with the set threshold value, and gives the comprehensive score of the battery health status. When the evaluation result is lower than the preset threshold value, a warning or alarm signal is sent in time. The diagnosis of the electrolyte ion concentration and the electrode 111 surface state is realized, and the health status of the flow battery system 10 is obtained.

[0059] In the embodiments of the present application, the data acquisition system 30 is also used to establish the mapping relationship between the performance indicators and the key parameters, and to construct the evaluation system and prediction model of the performance of the flow battery 11. The concentration data and ion crossover degree data of the electrolyte monitored by the ultraviolet spectrometer are combined with the hydrogen concentration data monitored by the gas chromatograph, and the health status of the battery is comprehensively evaluated. The test analysis results are combined with the battery management system to realize online monitoring, fault diagnosis, life prediction and other functions of the battery operating state, and to dynamically adjust the pump speed, voltage window, current and other information of the battery in real time, forming a regulation closed loop of data monitoring-data feedback-data mapping-data feedback-data monitoring, and ensuring the safe and efficient operation of the battery.

[0060] In the embodiments of the present application, as shown in Figure 1 The multi-physical field coupling effect jointly acts on the electrochemical field of the flow battery 11 (for example, the all-vanadium flow battery 11), and affects the performance parameters such as current, voltage, capacity, energy efficiency and coulomb efficiency of the battery. These data are collected in the battery tester 24 and the electrochemical workstation by the data acquisition system 30. With the real-time feedback data, the flow control system, the electric control system and the temperature control system of the flow battery 11 can make corresponding adjustments in time to optimize the operating state of the battery. In this way, real-time online measurement of the multi-physical field coupling parameters of the flow battery 11 is realized.

[0061] As a specific embodiment of the present application, taking observation of the hydrogen evolution side reaction of the all-vanadium flow battery as an example, the flow field area of the flow battery visual clamp is 4 cm x 4 cm, the flow channel width is 2 mm, the depth is 2 mm, the serpentine flow field is adopted, and the membrane is a cation exchange membrane 211 of DuPont Company. At room temperature, 0.5 mol / L VO 2+ solution (5 mL / min) is supplied to the negative electrode, and 0.5 mol / L V 3+The battery electrochemical data were measured using an Arbin BT‑2000 (Arbin Instruments) battery tester, and optical data were obtained using a GP-680V electron microscope. The charging current was 200 mA·cm -2 ,like Figure 4 As shown in the figure, from left to right, are microscopic images of the flow field at battery voltages of 1.5, 1.6, and 1.7 V. When a side reaction occurs inside the battery and bubbles are generated, it can be clearly observed that the bubbles escape into the flow channel. Based on the situation in the flow channel, it can be observed that the battery's hydrogen evolution voltage is 1.6 V. Therefore, setting the battery's charge cutoff voltage to 1.6 V will help avoid the occurrence of the battery's hydrogen evolution side reaction. This test can accurately quantify the battery's hydrogen evolution voltage and provide the battery's recommended operating cutoff voltage.

[0062] In addition, when the charging current is 100 mA·cm -2 Through further visualization experiments, it was found that hydrogen bubbles were generated only when the battery voltage was about 1.67 V. Therefore, at this current density, it is more appropriate to set the battery charging cut-off voltage to 1.67 V. When the charging current is 300 mA·cm -2 Through the visualization observation experiment, it was found that the hydrogen evolution reaction was observed when the battery voltage was about 1.56 V. Therefore, at this current density, setting the battery charge cut-off voltage to 1.56 V is beneficial to avoid the occurrence of long-cycle hydrogen evolution reaction. It should be pointed out that the voltage of hydrogen evolution is affected by many factors such as electrolyte state, temperature and charging current. In traditional charging and discharging devices, due to the lack of effective observation means, the battery charge cut-off voltage is uniformly set to 1.6 V or 1.65 V for charging and discharging. The root cause of this unscientific one-size-fits-all approach is that it is difficult to observe the battery state online, and the result will lead to too low capacity utilization of the electrolyte, increasing the electrolyte cost of the system. Or the depth of charging is too large, resulting in serious side reactions, thereby affecting the efficiency and life of the battery. It should be noted that the quantified parameters in this embodiment will provide quantified parameters for the establishment of relevant models, and the numerical membrane model containing hydrogen evolution is verified by experimental results.

[0063] As a specific embodiment of the present application, taking the all-vanadium redox flow battery as an example, the Shimadzu UV2600 ultraviolet spectrophotometer is used to detect the ion crossover degree of the all-vanadium redox flow battery. Before the battery test, a series of V 3+ Concentrations from 0 to 50% of 0.1 MV 3+ / VO 2+The mixed solution was measured by UV spectrophotometer in the wavelength range of 300 nm to 1100 nm. Then, the full vanadium flow battery was charged and discharged, and 1 mL of electrolyte was taken from each side of the tank every interval for 1 cycle and sent to the UV spectrophotometer for testing.

[0064] As shown in Figure 5 , the absorbance peak of V 2+ ion corresponds to a wavelength of about 550 nm, the absorbance peak of V 3+ ion corresponds to a wavelength of about 400 nm, and the absorbance peak of VO 2+ corresponds to a wavelength of about 760 nm. As the charging and discharging proceed, the absorbance peak of the mixed electrolyte at 760 nm gradually rises, while the absorbance peaks at 400 and 550 nm gradually decrease, indicating that the ion valence is gradually shifting from 3.5 to 4. In addition, the higher the absorbance peak at 760 nm, the more serious the ion crossover.

[0065] The volume of the positive and negative electrodes before the battery operation was 80 mL respectively, and the volume of the electrolyte was 80 mL respectively. -2 After running for 200 cycles, the discharge capacity decreased from 1896 mAh to 1086 mAh, and we found that the volume of the electrolyte on the negative side decreased, and the volume of the electrolyte on the positive side increased. Through volume detection, we found that the volume of the negative electrode of the battery was 72 mL, and the volume of the positive electrode was 88 mL. Through the quantitative conversion of UV spectroscopy, we can get the concentration of V 3+ on the negative side is 0.68 mol / L, the concentration of V 2+ on the negative side is 0.61 mol / L, and the concentration of VO 2+ on the negative side is 1.85 mol / L. According to the law of conservation of mass of vanadium ions:

[0066] ,

[0067] In the formula, represents the volume of the solution on the negative side in the initial state, represents the concentration of vanadium ions on the negative side in the initial state, represents the volume of the solution on the positive side in the initial state, represents the concentration of vanadium ions on the positive side in the initial state, represents the volume of the solution on the negative side at time t, represents the concentration of vanadium ions on the negative side at time t, represents the volume of the solution on the positive side at time t, represents the concentration of vanadium ions on the positive side at time t.

[0068] VO 2+The concentration is 0.1439 mol / L. It was found that the concentration and volume of the active material on the positive electrode side are higher than those on the negative electrode side, and at this time the capacity limit of the battery is determined by the negative electrode. Therefore, reducing the diffusion of active materials and volume at the negative electrode has become the main reason for the reduction in capacity. During the entire battery operation process, the volume, concentration, valence state and other information can be calculated through the data collected by the online testing platform established, and coupled with the online real-time change of capacity. The theoretical capacity of the positive and negative electrodes calculated from multiple aspects such as volume, concentration and valence state are analyzed and compared with the actual capacity of the battery to obtain the polarization information of the battery, and the capacity attenuation is diagnosed to accurately find the most critical parameters causing polarization and capacity attenuation, so as to make targeted improvements.

[0069] As a specific embodiment of the present application, taking the negative electrode side of the all-vanadium liquid flow battery as an example, an ultraviolet spectrophotometer is used to in-situ detect the change in the ion concentration of the battery. The sampling device is placed in the negative electrode liquid storage tank of the battery, and the all-vanadium liquid flow battery is subjected to charge and discharge tests. It is set to sample 1 mL of electrolyte from the liquid storage tank every 1 minute and send it to the ultraviolet spectrophotometer for testing. After the test is completed, the electrolyte is pumped back into the liquid storage tank. During the charging process, the absorbance peak of the electrolyte at a wavelength of 400 nm gradually decreases, while the absorbance peak at a wavelength of 340 nm gradually increases, which indicates that the ion valence is gradually shifting from 3 valence to 2 valence. On the contrary, during the discharge process, the absorbance peak of the electrolyte at a wavelength of 400 nm gradually increases, while the absorbance peak at a wavelength of 340 nm gradually decreases, which indicates that the ion valence is gradually shifting from 2 valence to 3 valence. In addition, the absorbance peak at a wavelength of 400 nm during discharge is lower than the peak at the beginning of charging, reflecting the utilization rate of the electrolyte.

[0070] As a specific embodiment of this application, using the hydrogen evolution side reaction on the negative electrode side of an all-vanadium redox flow battery as an example, when bubbles were detected in the flow battery visualization fixture using an optical microscope, 1 mL of gas was extracted from the liquid reservoir at the battery's negative electrode using a Fuli GC9720Plus gas chromatograph. The gas chromatograph then analyzed the differences in the order of adsorption of different gases, performing qualitative and quantitative analysis of the gas components, focusing on the hydrogen concentration at 0.2-0.25 min.

[0071] like Figure 6 As shown, at 200 mA·cm -2The battery was run for 10 charge and discharge cycles under the following conditions, with the charge cutoff voltage set to 1.65 V and the discharge cutoff voltage set to 0.9 V. As the number of charge and discharge cycles of the battery increases, the peak value of hydrogen gradually increases, from the initial 0 ppm to 253 ppm, which indicates that the concentration of hydrogen is gradually increasing. The occurrence of side reactions leads to the accumulation of hydrogen. In addition, by calculating the difference in hydrogen concentration between the two cycles and dividing it by the charge and discharge time of the battery, the average hydrogen production rate is calculated to be 25.3 ppm, and this rate is used to evaluate the degree of occurrence of battery side reactions. Based on the measured hydrogen concentration of the liquid storage tank and the gas phase volume on the negative electrode side of the liquid storage tank, the hydrogen evolution current was tested online, and the amount of hydrogen in the system can be calculated. According to Faraday's law:

[0072] ,

[0073] In the formula is the amount of hydrogen evolved; is the Faraday constant, and the amount of electricity corresponding to hydrogen evolution can be obtained , and thus calculated that the proportion of hydrogen evolution current to charging current under 200 mA·cm-2 conditions is about 0.1%.

[0074] In order to further explore the effect of cut-off voltage on the proportion of hydrogen evolution current, at 200 mA·cm -2 The battery was run for 10 charge and discharge cycles under the following conditions. The battery charge cut-off voltage was set to 1.6 V and the discharge cut-off voltage was set to 0.9 V. The experimental results were analyzed and calculated to show that the proportion of the charging current occupied by the hydrogen evolution current was about 0.08%. Through online analysis, it can be seen that the cut-off voltage significantly affects the current of hydrogen evolution and its proportion. At the same time, in order to explore the effect of current density on the proportion of hydrogen evolution current, the battery was tested at 300 mA·cm -2 Ten charge-discharge cycles were run under these conditions, with the battery charge cutoff voltage set at 1.65 V and the discharge cutoff voltage set at 0.9 V. Analysis of the experimental results revealed that the hydrogen evolution current accounted for approximately 0.14% of the charge current. Online analysis shows that increasing current density significantly affects the hydrogen evolution current and its proportion.

[0075] In addition, in order to explore the effect of the electrode on the hydrogen evolution current ratio, the -2 Under these conditions, a carbon felt electrode loaded with bismuth particles was used for 10 charge-discharge cycles, with the battery charge cutoff voltage set at 1.65 V and the discharge cutoff voltage set at 0.9 V. Analysis of the experimental results revealed that the hydrogen evolution current accounted for approximately 0.02% of the charge current. Online analysis shows that the bismuth-modified electrode significantly reduces the hydrogen evolution current and its proportion.

[0076] Through our online platform, we can accurately analyze the hydrogen evolution current and some of its key influencing factors. From Figure 6 and 7 It can be seen that the past analysis of the effect of hydrogen evolution on the battery is some qualitative analysis, and the real-time online hydrogen evolution quantitative reaction current can be obtained through the system. The relationship between hydrogen evolution current and temperature, charge and discharge cutoff voltage, and flow rate can be analyzed through the online measurement platform.

[0077] As a specific embodiment of the present application, taking the hydrogen evolution side reaction of the negative side of the all-vanadium redox flow battery as an example, the degree of hydrogen evolution side reaction is detected in situ by coupling multiple physical field parameters of electrochemical workstation-optical microscope-gas chromatograph-ultraviolet spectrophotometer. On the electrochemical workstation, set a gradient charge interval of 0.1 V, when charged to a specified voltage, the gas chromatograph extracts 1 mL of gas from the negative electrode of the battery, and quantitatively analyzes the hydrogen. At the same time, the optical microscope detects the generation of bubbles in the flow battery visual clamp, and calculates the number and volume of bubbles in parallel, as Figure 8 shown.

[0078] In a single cycle, when the battery voltage is less than 1.8 V, the concentration of hydrogen gas increases linearly and slowly; when the battery voltage is greater than 1.8 V, the volume of hydrogen gas increases exponentially and rapidly, from 0.2 mL to 24.8 mL, and the number and volume of bubbles also increase rapidly with the concentration. At the same time, the ultraviolet spectrophotometer detects the change of ion concentration in the negative electrode tank in situ, and it can be found that the valence state deviates. This shows that when the battery cutoff voltage is greater than 1.8 V, the side reaction of the battery is very serious, which will seriously affect the performance of the battery and have a significant impact on the cycle stability of the battery.

[0079] As a specific embodiment of the present application, taking the all-vanadium redox flow battery as the research object, the degree of internal capacity attenuation and side reaction during long-term operation of the battery under different flow rates is measured by combining electrochemical workstation, optical microscope and gas chromatograph. The flow field area is 4 cm × 4 cm, the flow channel width is 2 mm, the depth is 2 mm, the serpentine flow field is used, and the membrane is DuPont cation exchange membrane 211. The experiment is carried out at room temperature, and 1 M VO 2+ solution is supplied to the negative electrode, and 1 M V 3+ solution is used for the positive electrode. The Arbin BT 2000 (Arbin Instruments) battery tester is used to measure and collect the electrochemical data of the battery, and the GP-680V electron microscope is used to collect optical data, and the charge and discharge cycle number is set to 350 times.

[0080] To study the effect of different flow rates on the performance of the battery, the flow rate gradient was set to 3, 5, 9 mL·min -1 ·cm -2 , and the capacity of the battery and the change in gas concentration were detected, as shown in Figure 9 From the results, it can be seen that as the flow rate gradually increases from 3 mL·min -1 ·cm -2 to 5 mL·min -1 ·cm -2 , the capacity decay rate of the battery gradually decreases and reaches a minimum decay rate of 0.285 mAh / cycle. However, when the flow rate continues to increase from 5 mL·min -1 ·cm -2 to 9 mL·min -1 ·cm -2 , the capacity decay of the battery gradually increases, up to 1.143 mAh / cycle. At the same time, the gas generation rate shows that as the flow rate of the battery increases, the gas generation rate gradually slows down.

[0081] As a specific embodiment of the present application, the present embodiment collects online information such as hydrogen evolution overpotential, hydrogen evolution rate, and electrolyte change state obtained by online measurement, performs multi-physical simulation on the charge and discharge state of the battery, and couples the hydrogen generation in the model with multiphase flow. By adding the influence of side reactions and the multiphase flow model, the fitting degree of the model is higher and closer to the actual running state, as shown in Figure 10 Under the battery operating conditions of a charging current of 300 mA·cm -2 and a flow rate of 5 mL·min -1 ·cm -2 , by comparing the SOC-voltage curves of the actual battery test, the model without hydrogen evolution reaction, and the charging model coupled with the hydrogen evolution reaction, it can be seen that the model coupled with the hydrogen evolution reaction has a higher fitting degree with the actual battery test and is closer to the actual running state.

[0082] As shown in Figure 11 and Figure 12 , according to the hydrogen concentration distribution cloud map and the overpotential distribution cloud map, it can be seen that the overpotential is low in the under-rib part, which is prone to hydrogen evolution reaction, and is closer to the actual situation. The platform provides online monitoring for the real running of the battery, which is beneficial to the health state detection of the battery and improves the performance of the battery.

[0083] As a specific embodiment of the present application, the embodiment is based on the state of health observation to inhibit the occurrence of battery side reactions from multiple aspects of electrodes, separators and operating parameters. For the electrode, 0.005 mol of bismuth nanoparticle catalyst is introduced and loaded on the carbon felt electrode; for the separator, 0.003 mol of SiO2 nanoparticles is added to the negative side surface to block the diffusion of the solution and active material on the negative side; in terms of flow rate, the flow rate is kept at 6 mL·min -1 ·cm -2 at the end of the charging period, the flow rate is increased to 9 mL·min -1 ·cm -2 . After testing, the capacity retention rate of the improved battery is increased from 36% to 86%, and the energy efficiency is increased from 76% to 88%. It is shown that after the relationship between the online parameters and the performance is mastered, targeted improvement can greatly improve the performance of the battery, which further illustrates the importance of the online parameter acquisition platform and the health state detection for the flow battery.

[0084] The above describes a flow battery test platform input by the embodiment of the present application in detail, and the above embodiment description is only used to help understand the core idea of the present application, and the above description should not be understood as limiting the protection scope of the present application.

Claims

1. A flow battery testing platform, characterized in that: Including liquid flow battery system, multi-physics field parameter coupling detection system and data acquisition system; The flow battery system comprises: A flow battery comprises electrodes and liquid storage tanks, wherein the electrodes comprise a positive electrode and a negative electrode arranged in a stacked manner, and the liquid storage tanks comprise a positive electrode liquid storage tank and a negative electrode liquid storage tank arranged on both sides of the electrodes; Visualization fixture for directly observing the internal state of the flow battery; The multi-physics field parameter coupling detection system includes: an optical detection unit, configured to capture an internal image of the flow battery in real time to obtain internal image data of the flow battery; the image data comprising at least one of flow parameters of the electrolyte in the flow channel, characteristic parameters of side reaction bubbles, and characteristic parameters of the electrode surface; an electrolyte detection unit, configured to collect electrolyte in the liquid storage tank in real time through a micro-sampling circuit to obtain concentration data of the electrolyte; A gas detection unit, used to collect gas in the liquid storage tank in real time to obtain concentration data of the gas; a battery tester for charging and discharging the flow battery and collecting electrochemical data; The data acquisition system is used to obtain key feature data based on the image data, the concentration data of the electrolyte, and the concentration data of the gas, and calculate corresponding deviation values ​​based on a mapping relationship between the key feature data and preset performance indicators of the liquid flow battery, so as to adjust the operating state of the liquid flow battery according to the deviation value; the key feature data includes at least active material concentration, ion crossover degree, hydrogen evolution rate, coulombic efficiency, energy efficiency, and capacity decay rate; The battery tester is also used to collect the deviation value corresponding to the parameter characteristic data output by the data acquisition system in real time and output it to the liquid flow battery system to adjust at least one of the electrolyte flow, charge and discharge current density and temperature of the liquid flow battery.

2. The flow battery testing platform according to claim 1, characterized in that: The visualization fixture includes a diaphragm, two graphite plates and two end plates, wherein the diaphragm is arranged between the positive electrode and the negative electrode, the two graphite plates are arranged on opposite sides of the electrode away from the diaphragm, and the two end plates are arranged on opposite sides of the graphite plates away from the electrode, wherein at least one of the two end plates is a transparent end plate.

3. The flow battery testing platform according to claim 2, characterized in that: The end plate close to the optical detection unit is a transparent end plate, and the material used for the transparent end plate includes polymethyl methacrylate.

4. The flow battery testing platform according to claim 2 or 3, characterized in that: A plurality of flow channels arranged at intervals are provided on one side of the graphite plate close to the electrode, and the flow channels are used to guide the electrolyte in the liquid storage tank to flow on the surface of the electrode.

5. The flow battery testing platform according to claim 4, characterized in that: One side of the graphite plate is in close contact with the electrode, and the other side is in contact with the transparent end plate.

6. The flow battery testing platform according to claim 4, characterized in that: The optical detection unit includes an optical microscope or a high-speed camera.

7. The flow battery testing platform according to claim 6, characterized in that: The optical detection unit includes an optical microscope; the data acquisition system is also used to, after the battery tester charges and discharges the visualization fixture and obtains image data of the porous electrodes, electrolyte flow, and bubble behavior inside the battery through the microscope, use a digital image processing algorithm to enhance, segment, and extract features from the obtained images to obtain the porosity, specific surface area, and liquid saturation of the porous electrode, and obtain the change pattern of the porosity, specific surface area, and liquid saturation with time and current density.

8. The flow battery testing platform according to claim 7, characterized in that: The data acquisition system is also used to obtain bubble characteristic data by calculating and processing the obtained porosity, specific surface area, and liquid saturation data, and to obtain electrolyte ion crossover signals by calculating and processing the obtained electrolyte ion concentration, charge transfer, and ion crossover contamination degree data.

9. The flow battery testing platform according to claim 8, characterized in that: When the data acquisition system detects the corresponding bubble characteristics or receives the electrolyte ion cross signal, it starts the in-situ gas chromatograph to monitor the gas components released during the battery operation, thereby obtaining the concentration data of hydrogen or oxygen gas in the liquid flow battery storage tank.

10. The flow battery testing platform according to claim 1, characterized in that: The liquid flow battery system further includes a flow control unit, an electronic control unit, and a temperature control unit. The flow control unit is used to control the electrolyte flow of the liquid flow battery. The electronic control unit is used to control the charge and discharge current density of the liquid flow battery. The temperature control unit is used to control the temperature of the liquid flow battery. The battery tester is connected to the flow control unit, the electronic control unit, and the temperature control unit.

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