A Cr-based electrolyte for iron-chromium flow batteries 2+ In-situ online detection system, method and application of concentration

Abstract

This invention belongs to the field of energy storage and flow battery technology, and relates to an iron-chromium flow battery electrolyte Cr 2+ An in-situ online detection system, method, and application for Cr concentration. The system includes a detection battery module, an online spectral detection module, and a data processing and control unit. A characteristic wavelength of 800 nm was selected, and the relationship between absorbance and Cr was established. 2+ Concentration mapping model to eliminate Cr 3+ Interfering with and reducing Fe 2+ Impact on measurement; based on the linear relationship between the rate of change of state of charge and the rate of change of absorbance at 800 nm, online measurement of Cr 2+ The system enables real-time and accurate detection of molar absorbance at different concentrations and temperatures. Measurements are taken online via a series Venturi tube or in situ via a liquid sampling and return pipe connected to the side wall of the electrolyte storage tank or pipeline. The liquid sampling and return pipe allows for quick and fully sealed connection to the pipeline or storage tank, minimizing interference and preventing Cr contamination. 2+ Oxidation-induced measurement distortion provides high-precision real-time data support for monitoring electrolyte charge, health status, and stack performance.

Description

Technical Field

[0001] This invention belongs to the field of energy storage and flow battery technology, and relates to an iron-chromium flow battery electrolyte Cr 2+ In-situ online detection system, method and application of concentration. Background Technology

[0002] Iron-chromium redox flow batteries, with their advantages of long cycle life, high safety, and abundant electrolyte raw materials, are considered one of the most promising technologies for large-scale energy storage. Their energy storage mechanism relies on the Fe content in the cathode electrolyte. 2+ / Fe 3+ With Cr in the negative electrode electrolyte 2+ / Cr 3+ The reaction of redox couples. Therefore, the state of charge (SOC) of the electrolyte is closely related to the concentration of each active ion, among which the Cr at the negative electrode... 2+ The concentration of [something] often directly determines the actual energy storage state of the system.

[0003] However, iron-chromium flow batteries face the following key challenges in actual operation: 1. Interference from hydrogen evolution side reaction: During ideal charging, the Cr in the negative electrode solution... 3+ It should be reduced to Cr 2+ Meanwhile, Fe in the positive electrode liquid 2+ Oxidized to Fe 3+ However, Cr 2+ / Cr 3+ The standard reduction potential of the redox couple (E° = -0.41 V vs. SHE) is significantly lower than the standard potential of the hydrogen evolution side reaction (HER) (E° = 0 V vs. SHE). This results in some of the reduction current being consumed by the HER, hindering the Cr... 3+ Fully reduced to Cr 2+ This leads to the actual Cr generated during the charging process 2+ The amount is lower than the theoretical value, which in turn causes Cr to be lower during discharge. 2+ Insufficient discharge capacity leads to a decrease in the actual discharge capacity of the battery.

[0004] 2. Transmembrane migration of active ions: Limited by the ion-selective permeability of the battery separator, chromium and iron ions (Fe...) 2+ Fe 3+ Cr 2+ Cr 3+ During charging and discharging, transmembrane migration occurs, causing continuous changes in the concentration of metal ions in the positive and negative electrode electrolytes. These changes not only directly affect battery efficiency and capacity but also pose higher requirements and challenges for accurate online detection of ion concentration.

[0005] Existing technologies for detecting the State of Charge (SOC) and State of Health (SOH) of iron-chromium redox flow battery electrolytes are primarily designed for electrolytes without significant imbalances, which is insufficient for practical applications. Detection of electrolyte ion concentrations mainly relies on offline sampling combined with titration or offline spectrophotometry. Among these, titration requires the determination of Fe... 2+ / Fe 3+ and Cr 3+ Different titrants were used, and Cr could not be distinguished. 2+ and Cr 3+ Offline spectrophotometry faces challenges related to Fe. 2+ / Fe 3+ and Cr 3+ Interference from overlapping absorption peaks in the UV-Vis spectral region, and the lack of effective Cr 2+ In-situ detection methods. These offline methods all suffer from significant drawbacks such as cumbersome operation and disruption of sampling continuity, making real-time detection impossible. Furthermore, due to Cr... 2+ It has extremely strong reducing properties and is easily oxidized when exposed to air or residual oxygen in the container during sampling, leading to severe distortion of concentration measurements. Furthermore, simultaneous multi-ion detection requires multiple steps, is costly, and lacks timeliness, failing to meet the needs of dynamic detection.

[0006] Patent CN120652334A discloses an online monitoring method for the aging of the negative electrode in an iron-chromium redox flow battery. This method involves designing a dedicated negative electrode storage tank system to periodically collect trace amounts of electrolyte and using ultraviolet spectroscopy to detect chromium complex ions (Cr(H2O)). 6-n Cl n (3-n)+ The content of chromium complex ions (n ​​= 0-3) is correlated with the number of cycles to construct an aging mathematical model and form an offline monitoring database. A specially designed online spectroscopic detection experimental platform is built to collect chromium complex ion spectral data in real time, analyze the evolution law of chromium complex ions during the charge-discharge stage and cycling process, and establish an online monitoring mechanism. Based on the analysis of the dynamic behavior and reaction mechanism of chromium complex ions in the negative electrode, an online monitoring mechanism for battery aging is established. Based on offline results and experimental platform data, the concentration distribution / attenuation trend and formation mechanism of chromium complex ions are correlated and analyzed to quantitatively predict the battery aging time point. However, the core of this patent lies in establishing a correlation model between spectroscopic detection data and the number of cycles to monitor chromium complex ions in different hydration states (such as Cr(H2O)4Cl2) online. + Cr(H2O)5Cl 2+ Cr(H2O)6 3+ The evolution of the proportion of chromium complex ions is used to predict the aging state. Since its monitoring target is the proportion of chromium complex ions characterizing the "healthy state," rather than chromium ions directly involved in the core redox reaction, this method focuses on the evolution of the proportion of chromium complex ions, rather than chromium ions directly involved in the core redox reaction. 3+ With Cr 2+The concentration of ions is a limiting factor, therefore this technical solution lacks the ability to assess battery SOC in real time. This is precisely the core technical problem that this application aims to solve.

[0007] The above problems severely restrict the detection of SOH, optimization of electrolyte rebalancing strategies, and improvement of overall system operating efficiency in iron-chromium redox flow batteries. Therefore, it is urgent to develop an in-situ, online ion concentration detection method to meet the following core requirements: (1) Real-time online detection to avoid sampling oxidation errors and directly obtain Cr 2+ (2) Supporting long-term stable online detection of electrolyte SOC / SOH. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide a Cr-based electrolyte for iron-chromium flow batteries. 2+ In-situ online detection system, method and application of concentration.

[0009] The objective of this invention can be achieved through the following technical solutions: A Cr-based electrolyte for iron-chromium flow batteries 2+ The in-situ online concentration detection system includes a detection battery module, an online spectral detection module, and a data processing and control unit; The battery detection module includes a detection battery and a charge / discharge detector; the charge / discharge detector is electrically connected to the electrode group of the detection battery and is used to regulate the charge / discharge state of the detection battery. The online spectral detection module includes a light source, a flow-through detection cell, and a spectral detection unit; the light incident end of the flow-through detection cell is connected to the light source through an incident optical fiber, and its light emitting end is connected to the spectral detection unit through an emitting optical fiber. The flow-through detection cell is connected in series to the electrolyte circulation path of the detection battery, forming a closed-loop electrolyte flow path. The data processing and control unit is electrically connected to the detection battery module and the online spectral detection module, respectively, and is used to synchronously acquire the charging and discharging parameters of the detection battery and collect and process spectral data.

[0010] Specifically, the data processing and control unit is electrically connected to the charge and discharge detector to synchronously acquire the charge and discharge parameters of the test battery; the data processing and control unit is electrically connected to the spectral detection unit to synchronously acquire and process spectral data; the data processing and control unit is electrically connected to the electrically controlled on / off valve on the liquid inlet line of the test battery to control the start and stop of the test battery, the switching of working modes, and the monitoring of the operating status by controlling the opening and closing state of the electrically controlled on / off valve.

[0011] Furthermore, the electrode assembly of the detection battery includes an upstream porous electrode and a downstream porous electrode.

[0012] Furthermore, the thickness of the upstream porous electrode The porosity is 1.0~3.5 mm. >0.6; downstream porous electrode thickness (i.e., not less than twice the thickness of the upstream porous electrode), with a porosity of >0.6.

[0013] Furthermore, the light source is a tungsten lamp or an LED light source; The optical path length b of the flow-through detection cell is 0.05~0.2 cm; The spectral detection unit is a fiber optic spectrometer with a wavelength range of 300~1000 nm. Based on the principle of ultraviolet-visible absorption spectroscopy (UV-Vis), the spectral detection unit is used to receive and process spectral signals from the flow-through detection cell to perform in-situ, non-contact dynamic analysis of the electrolyte components.

[0014] The present invention also provides an iron-chromium redox flow battery electrolyte Cr based on the system described in any of the preceding claims. 2+ In-situ online detection methods for concentration, including Cr 2+ Calibration of molar absorbance and Cr 2+ Concentration detection.

[0015] For initial testing, or when the electrolyte state (such as electrolyte temperature and chloride ion concentration) may change significantly, Cr should be tested first. 2+ Calibration of molar absorbance.

[0016] Cr 2+ The specific steps for calibrating molar absorbance are as follows: S1. The electrolyte to be tested is introduced into the detection system, so that it flows through the closed-loop flow path of the electrolyte, which is connected in series with the detection battery and the flow-through detection cell. S2. The absorption spectrum of the electrolyte flowing through the flow-through detection cell at time t0 is collected using the spectral detection unit in the 300~1000 nm wavelength range, and the absorbance at 800 nm is recorded. Then, calculate Cr at time t0 according to Equation 2. 2+ initial concentration : (Equation 2) In the formula, Fe, the negative electrode liquid 2+ Actual concentration or initial nominal concentration (If the actual concentration is known or measurable, it should be used preferentially to improve detection accuracy.) The unit is mol·L. -1 ; For Fe 2+Actual or nominal molar absorbance at 800 nm wavelength The unit is L·mol -1 ·cm -1 ; For Cr 2+ The previous calibrated or nominal value of the molar absorbance at a wavelength of 800 nm, in L·mol⁻¹. -1 ·cm -1 b represents the optical path length of the flow-through detector cell, in cm. S3, when ≤0.35 mol·L -1 At this time, the upstream porous electrode acts as the negative electrode, and the downstream porous electrode acts as the positive electrode (ensuring the electrolyte in the upstream porous electrode remains intact after charging). ≤0.65 mol·L -1 (to reduce the impact of hydrogen evolution reaction on measurement accuracy); when >0.35 mol·L -1 At this time, the upstream porous electrode acts as the positive electrode, and the downstream porous electrode acts as the negative electrode (ensuring the electrolyte in the upstream porous electrode remains intact after charging). >0.05 mol·L -1 Ensure that all the charging power is used to convert Cr 2+ Oxidized to Cr 3 + Then, at a lower current density i = 5~50 mA·cm -2 Charge the test battery; The charging time Δt is calculated according to Equation 3: (Equation 3) In the formula, F is the Faraday constant (F = 96485 C·mol⁻¹). -1 ); For Cr 2+ The absolute value of the concentration change ranges from 0.1 to 0.3 mol·L⁻¹. -1 ; The thickness of the upstream porous electrode is in cm. Porosity of the upstream porous electrode; S4. After charging is complete, introduce fresh electrolyte into the detection system, collect the absorption spectrum of the electrolyte as it flows through the flow-through detection cell, and record the absorbance at 800 nm. Calculate the change in absorbance Let the maximum value of its absolute value be denoted as And Cr was calculated according to Equation 4. 2+ molar absorbance calibration value : (Equation 4) In the formula, F is the Faraday constant (F = 96485 C·mol⁻¹). -1 ); The thickness of the upstream porous electrode is in cm. The porosity of the upstream porous electrode is denoted by ; i is the current density, in mA·cm⁻¹. -2 b represents the optical path length of the flow-through detector cell, in cm.

[0017] After the electrolyte in the battery to be tested is updated, based on the calibration results and measurement requirements, steps S1 to S4 above can be repeated to complete the Cr test. 2+ Secondary calibration of molar absorbance, or if applicable Cr is available. 2+ The molar absorbance calibration value can then be monitored online in real time or detected by in-situ sampling. 2+ concentration.

[0018] Cr 2+ The specific steps for concentration detection are as follows: S1. The electrolyte to be tested is introduced into the detection system, so that it flows through the closed-loop flow path of the electrolyte, which is connected in series with the detection battery and the flow-through detection cell. S2. The absorption spectrum of the electrolyte in the 300~1000 nm wavelength range at time t is collected by the spectral detection unit as the electrolyte flows through the flow-through detection cell, and the absorbance of the electrolyte at 800 nm is recorded. Then, Cr at time t is calculated according to Equation 1. 2+ concentration : (Equation 1) In the formula, b is the optical path length of the flow-through detection cell, in cm; For Fe 2+ The molar absorbance at a wavelength of 800 nm, expressed in L·mol⁻¹. -1 ·cm -1 ; Fe, the negative electrode liquid 2+ The actual concentration or initial nominal concentration (if the actual concentration is known or measurable, it should be used preferentially to improve detection accuracy), in mol·L⁻¹. -1 ; For Cr 2+ The latest calibrated value of molar absorbance at 800 nm wavelength, in L·mol⁻¹. -1 ·cm -1 .

[0019] The 800 nm wavelength mentioned above is used for detecting Cr. 2+ The characteristic wavelength of Cr; the characteristic wavelength used for detecting Cr 2+The characteristic wavelength range can be extended to 780 nm to 830 nm, and measurements at this wavelength can effectively suppress Cr. 3+ Spectral interference and correction of Fe 2+ The impact on measurement accuracy is as follows: In the wavelength range of 780~830 nm, Cr 3+ The molar absorptivity of Fe is extremely low, and its absorption signal is negligible; meanwhile, Fe... 2+ The molar absorbance in this wavelength range is significantly lower than that of Cr. 2+ The molar absorbance, therefore, can be subtracted from Fe. 2+ The absorbance contribution within this wavelength range, thereby achieving the effect of Cr 2+ Concentration detection.

[0020] The present invention also provides a system as described in any of the preceding claims for use in iron-chromium redox flow battery electrolytes with Cr... 2+ Application in concentration detection: The system is used to detect the Cr content in the electrolyte during the operation of an iron-chromium redox flow battery. 2+ Concentration is detected in situ online in real time.

[0021] Specifically, it includes any of the following detection modes: (1) Online real-time monitoring: The system is connected to the pipeline of the flow battery system, and the electrolyte is extracted using the Venturi effect for online real-time monitoring; or (2) In-situ sampling and detection: The system is connected to the side wall of the electrolyte storage tank or pipeline, and the electrolyte is driven by a pump to form a closed loop for sampling and detection.

[0022] Compared with the prior art, the present invention has the following beneficial effects: (1) Fully enclosed testing to completely avoid sampling leakage, contamination and oxidation errors. The flow-through detection cell in the system's spectral detection module is directly connected in series with the electrolyte circulation pipeline embedded in the battery, forming a fully enclosed flow path. During detection, the light source and spectrometer are fixed outside the optical windows on both sides of the flow-through detection cell, achieving non-contact measurement. This method fundamentally eliminates electrolyte leakage and contamination caused by opening the battery cap for sampling, and in particular avoids Cr... 2+ The oxidation problem caused by contact with air significantly improves the authenticity and reliability of the measurement results.

[0023] (2) Achieve low-interference, in-situ, online, and real-time detection The inlet and outlet of the detection system are fully sealed and fixedly connected to the pipeline or storage tank of the system under test through a sealed interface, without requiring changes to the main system circulation or interruption of operation. This enables low-interference, in-situ, online, and continuous detection of flow battery systems, ensuring the real-time nature and representativeness of the data.

[0024] (3) Low-cost in-situ calibration of key parameters A characteristic wavelength of 800 nm was selected to establish the relationship between absorbance and Cr. 2+ Concentration mapping model for Cr at this wavelength 3+ No obvious absorption peak, Cr can be directly eliminated 3+ Spectral interference of detection, while Fe 2+ The absorbance signal at this wavelength is weak and stable, which can effectively reduce its influence on Cr. 2+ The impact of measurement accuracy; By utilizing the built-in detection battery unit of the detection system and relying on the linear correlation between the rate of change of state of charge (SOC) and the rate of change of absorbance at 800 nm, Cr can be measured online in real time without the need for additional calibration devices. 2+ molar absorbance; Based on the above linear relationship and in-situ detection data, the molar absorbance of divalent chromium ions and the background absorbance of divalent iron ions (i.e., Fe) were simultaneously measured. 2+ In-situ real-time calibration of characteristic absorbance at 800 nm is performed without removing the electrolyte from the system or adding any additional standard reagents. This in-situ calibration method can dynamically adapt to complex operating conditions such as changes in electrolyte composition (e.g., fluctuations in chloride ion concentration) and environmental changes (e.g., temperature changes). It effectively solves the parameter inaccuracy problem caused by differences in operating conditions in traditional offline calibration, significantly improving the accuracy and stability of long-term continuous monitoring. Simultaneously, it simplifies the calibration process, reduces calibration costs, and enhances the system's adaptability to the complex operating environment of iron-chromium redox flow batteries. Ultimately, it enables the determination of Cr in the electrolyte under different concentrations and temperatures. 2+ Real-time, accurate measurement of concentration.

[0025] (4) Reduce operation and maintenance costs and empower intelligent battery management The system automates the entire process from spectral acquisition and data analysis to result storage, significantly reducing manual intervention, human error, and labor costs. It provides ion concentration data with second-level response, laying a data foundation for battery management (such as SOC / SOH) and fault diagnosis. Real-time, accurate ion concentration data directly guides the initiation and optimization of electrolyte rebalancing strategies, mitigating capacity decay. Simultaneously, it supports predictive maintenance, reducing unplanned downtime, extending lifespan, and improving the economy and reliability of energy storage systems. It is suitable for intelligent operation and maintenance of megawatt-level iron-chromium redox flow batteries. Attached Figure Description

[0026] Figure 1 The Cr content in the iron-chromium redox flow battery electrolyte of this invention is shown in the embodiment. 2+ A schematic diagram illustrating the basic components and principles of an in-situ online concentration detection system; Figure 2 In order to be in Figure 1A schematic diagram of the structure of the detection system of this invention after adding a Venturi tube suction and supply device; Figure 3 In order to be in Figure 1 A schematic diagram of the structure of the detection system of this invention after adding a sampling return system and connecting it to the sampling port of the iron-chromium flow battery electrolyte storage tank; The attached figures are labeled as follows: 1-1 Battery for testing, 1-2 Charge / discharge detector, 1-3 Battery inlet for testing, 1-4 Electrically controlled on / off valve, 1-5 Upstream porous electrode, 1-6 Flow-through detection cell inlet, 1-7 Flow-through detection cell outlet, 1-8 Downstream porous electrode, 1-9 Battery outlet for testing, 2-1 Light source, 2-2 Incident optical fiber, 2-3 Flow-through detection cell, 2-4 Outgoing optical fiber, 2-5 Spectroscopic detection unit, 3-1 Data processing and control unit, 4-1 Venturi tube, 4-2 Venturi tube inlet flange, 4-3 Venturi tube outlet flange, 4-4 Inlet sampling tube, 4-5 Return pipe port, 5-1 Electrolyte storage tank, 5-2 Sampling return pipe, 5-3 Sampling return pipe flange, 5-4 Sampling return pipe inlet, 5-5 Sampling return pipe return port, 5-6 Sampling return pump. Detailed Implementation

[0027] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0028] Unless otherwise specified, all raw materials and equipment used in this invention are commercially available products.

[0029] A Cr-based electrolyte for iron-chromium flow batteries 2+ In-situ online detection system for concentration, such as Figure 1 As shown, it includes a battery detection module, an online spectral detection module, and a data processing and control unit 3-1; The battery testing module includes a testing battery 1-1 and a charge / discharge testing instrument 1-2. The testing battery 1-1, along the electrolyte flow direction, is sequentially equipped with a testing battery inlet 1-3, an electronically controlled on / off valve 1-4, an upstream porous electrode 1-5, a flow-through testing cell inlet 1-6, a flow-through testing cell outlet 1-7, a downstream porous electrode 1-8, and a testing battery outlet 1-9. The upstream porous electrode 1-5 has a thickness of 1.0~3.5 mm and a porosity >0.6, while the downstream porous electrode 1-8 has a thickness not less than twice the thickness of the upstream porous electrode 1-5 and a porosity >0.6. The charge / discharge testing instrument 1-2 is electrically connected to the two porous electrodes and is used to regulate the charge / discharge state of the testing battery.

[0030] The online spectral detection module is built based on the UV-Vis absorption spectroscopy principle and includes a light source 2-1, an incident fiber optic cable 2-2, an exiting fiber optic cable 2-4, a flow-through detection cell 2-3, and a spectral detection unit 2-5. The optical path length of the flow-through detection cell 2-3 is 0.05~0.2 cm. The spectral detection unit 2-5 is a fiber optic spectrometer with a wavelength range of 300~1000 nm. The light source 2-1 is either a tungsten lamp or an LED light source. The two ends of the flow-through detection cell 2-3 are sealed to the inlet 1-6 and outlet 1-7 of the detection cell 1-1, respectively, to achieve a closed-loop flow path for the electrolyte. Simultaneously, the light incident end of the flow-through detection cell 2-3 is connected to the light source 2-1 via the incident fiber optic cable 2-2, and its light exit end is connected to the spectral detection unit 2-5 via the exiting fiber optic cable 2-4.

[0031] The data processing and control unit 3-1 is electrically connected to the charge and discharge detector 1-2, the spectral detection unit 2-5, and the electronically controlled on / off valve 1-4, respectively. It synchronously acquires the charge and discharge parameters of the test battery, collects and processes spectral data, and controls the start and stop, working mode switching and operation status monitoring of the test battery 1-1 by controlling the opening and closing state of the electronically controlled on / off valve 1-4, thereby realizing the overall control of the entire test system operation process.

[0032] Example 1 Online monitoring of divalent chromium ion concentration in the electrolyte of the negative electrode pipeline of iron-chromium flow battery This embodiment addresses the need for online real-time monitoring of the concentration of divalent chromium ions in the electrolyte of the negative electrode pipeline during the operation of an iron-chromium redox flow battery energy storage system. Based on the Venturi tube suction supply principle, it realizes the pumpless layout and installation of the detection system.

[0033] Figure 2 This is a schematic diagram showing the detection system of the present invention equipped with a Venturi tube suction and liquid supply device. The components and markings of the detection system are shown below. Figure 1 Same. In this embodiment, the effective reaction area of ​​the detection battery is 10 cm². 2 The upstream porous electrode 1-5 has a thickness of 2 mm (porosity of 0.9), and the downstream porous electrode 1-8 has a thickness of 5 mm (porosity of 0.9); the optical path of the flow-through detection cell 2-3 is 0.1 cm; the spectral detection unit 2-5 uses a fiber optic spectrometer (model: SPEC-CMS 960, manufacturer: Linax (Shenzhen) Technology Co., Ltd.); the data processing and control unit 3-1 uses a SmartSoft 2.5.8 processing unit (manufacturer: Linax (Shenzhen) Technology Co., Ltd.), which is responsible for spectral data acquisition and processing.

[0034] Figure 2The newly added components are described as follows: 4-1 is a Venturi tube (throat inner diameter D1 = 4.9 cm), connected in series to the test pipeline with inner diameter D0 = 9 cm via Venturi tube inlet flange 4-2 and Venturi tube outlet flange 4-3; 4-4 is the liquid inlet sampling tube, used to lead out the electrolyte to be tested; 4-5 is the liquid return port, used to return the tested electrolyte to the test pipeline. When the flow rate of the electrolyte in the test pipeline is 10 L·s... -1 At this time, the pressure difference between the inlet sampling tube 4-4 and the return tube 4-5 is approximately 16 kPa; under this pressure difference, when the electrically controlled on / off valve 1-4 is opened, the electrolyte flow rate through the detection system is approximately 0.75 mL·s. -1 .

[0035] Taking an iron-chromium redox flow battery system with an initial electrolyte formulation of 1 M FeCl2·4H2O + 1 M CrCl3·6H2O + 3 M HCl as an example, the specific steps for real-time monitoring of divalent chromium ion concentration and calibration of molar absorbance are as follows: 1. Cr 2+ Online real-time monitoring of ion concentration: S1. Maintain a stable electrolyte flow rate of 10 L·s in the pipeline under test. -1 This creates a pressure difference of approximately 16 kPa between the inlet sampling tube 4-4 and the return port 4-5. The electrically controlled on / off valve 1-4 is then opened, using this pressure difference to guide the electrolyte to be tested from the inlet sampling tube 4-4 of the Venturi tube 4-1 at a rate of approximately 0.75 mL / s. -1 The flow rate sequentially passes through the detection battery 1-1 and the flow-through detection pool 2-3, constructing a stable online detection flow path.

[0036] S2. Continuously detect the absorption spectrum of the electrolyte in the 300~1000nm wavelength range as it flows through the flow-through detection cell 2-3 using the spectral detection unit 2-5, and record the absorbance at 800 nm at time t. Then, Cr at time t is calculated according to Equation 1. 2+ concentration : (Equation 1) In the formula, b is 0.1 cm; 0.3 L·mol -1 ·cm -1 ; 1.0 mol·L -1 ; Take the nominal value of 7.7 L·mol -1 ·cm -1 However, during the initial test or when electrolyte conditions (such as electrolyte temperature and chloride ion concentration) change, Use the latest calibration value.

[0037] 2. Cr 2+ In-situ calibration of molar absorbance: S1. At time t0, close the electrically controlled on / off valve 1-4, and record the absorbance at 800 nm at time t0 using the spectral detection unit 2-5. ; S2, Calculate Cr at time t0 according to Equation 2 2+ initial concentration : (Equation 2) In the formula, b is 0.1 cm; 1.0 mol·L -1 ; For Fe 2+ Actual or nominal molar absorbance at 800 nm (0.3 L·mol) -1 ·cm -1 (Unit: L·mol) -1 ·cm -1 ; For Cr 2+ The previous calibrated or nominal value of molar absorbance (7.7 L·mol⁻¹) -1 ·cm -1 (Unit: L·mol) -1 ·cm -1 ; S3, if ≤0.35 mol·L -1 Then, the upstream porous electrodes 1-5 act as the negative electrode, and the downstream porous electrodes 1-8 act as the positive electrode; if >0.35 mol·L -1 When the current density is i = 30 mA·cm, the upstream porous electrodes 1-5 are used as the positive electrode and the downstream porous electrodes 1-8 are used as the negative electrode; then the current density is i = 30 mA·cm. -2 Charge test battery 1-1; The charging time Δt is calculated according to Equation 3: (Equation 3) In the formula, F is the Faraday constant (F = 96485 C·mol⁻¹). -1 ); For Cr 2+ The absolute value of the concentration change is taken as 0.2 mol·L⁻¹. -1 ; The thickness of the upstream porous electrodes 1-5 is in cm; Porosity of upstream porous electrodes 1-5; The calculated charging time is Δt = 120 s; S4. After charging is complete, open the electronically controlled on / off valve 1-4 and continuously collect the absorption spectrum of the electrolyte in the upstream porous electrode 1-5 as it flows through the flow-through detection cell 2-3; record the absorbance at 800 nm. Calculate the change in absorbance Let its absolute value be denoted as And Cr was calculated according to Equation 4. 2+ molar absorbance calibration value : (Equation 4) In the formula, F is the Faraday constant (F = 96485 C·mol⁻¹). -1 ); The thickness of the upstream porous electrodes 1-5 is in cm; The porosity of the upstream porous electrodes 1-5 is given by i, where i is 30 mA·cm. -2 b represents the optical path length of flow-through detection cell 2-3, in cm.

[0038] S5. After the electrolyte in the battery to be tested 1-1 is updated, a second calibration is performed based on the calibration results and measurement requirements (repeating steps S1 to S4 above) or the Cr is restored. 2+ Ion concentration is monitored online in real time.

[0039] Example 2 In-situ monitoring of divalent chromium ion concentration in the electrolyte of the negative electrode storage tank of an iron-chromium flow battery This embodiment addresses the need for in-situ monitoring of the concentration of divalent chromium ions in the electrolyte of the negative electrode tank during the operation of an iron-chromium redox flow battery energy storage system. The detection system is equipped with a sampling return pump to achieve a closed-loop circulation of electrolyte extraction, internal circulation of the detection system, and return.

[0040] Figure 3 This is a schematic diagram of the in-situ monitoring of the detection system of the present invention, which is connected to the electrolyte storage tank 5-1 via the sampling return pipe 5-2. The components and markings of the detection system are shown below. Figure 1 Same. In this embodiment, the effective reaction area of ​​the detection battery is 10 cm². 2The upstream porous electrode 1-5 has a thickness of 2 mm (porosity of 0.9), and the downstream porous electrode 1-8 has a thickness of 5 mm (porosity of 0.9). The optical path of the flow-through detection cell 2-3 is 0.1 cm. The spectral detection unit 2-5 uses a fiber optic spectrometer (model: SPEC-CMS 960, manufacturer: Linax (Shenzhen) Technology Co., Ltd.). The data processing and control unit 3-1 uses a SmartSoft 2.5.8 processing unit (manufacturer: Linax (Shenzhen) Technology Co., Ltd.), which is responsible for spectral data acquisition, processing, and system operation control.

[0041] Figure 3 The newly added components are described as follows: 5-1 is the electrolyte storage tank, which stores the negative electrode liquid; 5-2 is the sampling return pipe, used for sampling and reflux of the electrolyte; 5-3 is the sampling return pipe flange, which achieves a sealed connection between the sampling return pipe 5-2 and the electrolyte storage tank 5-1; 5-4 is the sampling return pipe inlet, which is located far from the tank wall and can be flexibly adjusted to ensure that the electrolyte in the storage tank is collected in a uniformly mixed manner; 5-5 is the sampling return pipe return port, which is arranged close to the tank wall to reduce the interference of the refluxed electrolyte on the concentration distribution of the electrolyte in the tank; 5-6 is the sampling return pump (in this embodiment, a magnetically coupled centrifugal pump is used, with a flow rate adjustable range of 0.25~2.5 mL·s). -1 (with a pumping pressure differential of not less than 50 kPa), providing stable power for the flow of electrolyte in a closed-loop circulation.

[0042] Taking an iron-chromium redox flow battery system with an initial electrolyte formulation of 1 M FeCl2·4H2O + 1 M CrCl3·6H2O + 3 M HCl as an example, the steps and methods for in-situ monitoring of the concentration of divalent chromium ions in the negative electrode liquid and calibration of the molar absorbance are as follows: 1. Cr 2+ In-situ sampling and continuous monitoring of ion concentration: S1. Keep the electrically controlled on / off valve 1-4 in the open state, start the sampling return pump 5-6, and drive the electrolyte to be drawn in from the sampling return pipe inlet 5-4, flow sequentially through the detection battery 1-1 and the flow-through detection cell 2-3, and finally return to the electrolyte storage tank 5-1 through the sampling return pipe return port 5-5; set the circulation flow rate to 0.75 mL·s -1 .

[0043] S2. Continuously detect the absorption spectrum of the electrolyte in the 300~1000nm wavelength range as it flows through the flow-through detection cell 2-3 using the spectral detection unit 2-5, and record the absorbance at 800 nm at time t. Then, Cr at time t is calculated according to Equation 1. 2+ concentration : (Equation 1) In the formula, b is 0.1 cm; 0.3 L·mol -1 ·cm -1 ; 1.0 mol·L -1 ; Take the nominal value of 7.7 L·mol -1 ·cm -1 However, during the initial test or when electrolyte conditions (such as electrolyte temperature and chloride ion concentration) change, Use the latest calibration value.

[0044] 2. Cr 2+ In-situ calibration of molar absorbance: S1. At time t0, simultaneously close the sampling return pump 5-6 and the electrically controlled on / off valve 1-4, and record the absorbance at 800 nm at time t0 using the spectral detection unit 2-5. ; S2, Calculate Cr at time t0 according to Equation 2 2+ initial concentration : (Equation 2) In the formula, b is 0.1 cm; 1.0 mol·L -1 ; For Fe 2+ Actual or nominal molar absorbance at 800 nm (0.3 L·mol) -1 ·cm -1 (Unit: L·mol) -1 ·cm -1 ; For Cr 2+ The previous calibrated or nominal value of molar absorbance (7.7 L·mol⁻¹) -1 ·cm -1 (Unit: L·mol) -1 ·cm -1 ; S3, if ≤0.35 mol·L -1 Then, the upstream porous electrodes 1-5 act as the negative electrode, and the downstream porous electrodes 1-8 act as the positive electrode; if >0.35 mol·L -1 When the current density is i = 30 mA·cm, the upstream porous electrodes 1-5 are used as the positive electrode and the downstream porous electrodes 1-8 are used as the negative electrode; then the current density is i = 30 mA·cm. -2 Charge test battery 1-1; The charging time Δt is calculated according to Equation 3: (Equation 3) In the formula, F is the Faraday constant (F = 96485 C·mol⁻¹). -1 ), For Cr 2+ The absolute value of the concentration change is taken as 0.2 mol·L⁻¹. -1 ; The thickness of the upstream porous electrodes 1-5 Porosity of upstream porous electrodes 1-5; The calculated charging time is Δt = 120 s; S4. After charging is complete, open the electronically controlled on / off valve 1-4, resume the operation of the sampling return pump 5-6, and continuously collect the absorption spectrum of the electrolyte in the upstream porous electrode 1-5 during the flow-through detection cell 2-3; record the absorbance at 800 nm. Calculate the change in absorbance Let its absolute value be denoted as And Cr was calculated according to Equation 4. 2+ molar absorbance calibration value : (Equation 4) In the formula, F is the Faraday constant (F = 96485 C·mol⁻¹). -1 ), The thickness of the upstream porous electrodes 1-5 The porosity of the upstream porous electrodes 1-5 is given by i, where i is 30 mA·cm. -2 b is the optical path length (cm) of the flow-through detection cell 2-3.

[0045] S5. After the electrolyte in the battery to be tested 1-1 is updated, a second calibration is performed based on the calibration results and measurement requirements (repeating steps S1 to S4 above) or the Cr is restored. 2+ In-situ sampling and detection of ion concentration.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A Cr-based electrolyte for iron-chromium flow batteries 2+ The in-situ online concentration detection system is characterized by, It includes a battery detection module, an online spectral detection module, and a data processing and control unit (3-1). The detection battery module includes a detection battery (1-1) and a charge / discharge detector (1-2); the charge / discharge detector (1-2) is electrically connected to the electrode group of the detection battery (1-1) and is used to regulate the charge / discharge state of the detection battery (1-1); The online spectral detection module includes a light source (2-1), a flow-through detection cell (2-3), and a spectral detection unit (2-5); the light incident end of the flow-through detection cell (2-3) is connected to the light source (2-1) through an incident optical fiber (2-2), and its light emitting end is connected to the spectral detection unit (2-5) through an emitting optical fiber (2-4); The flow-through detection cell (2-3) is connected in series to the electrolyte circulation path of the detection battery (1-1) to form a closed-loop electrolyte flow path; The data processing and control unit (3-1) is electrically connected to the detection battery module and the online spectral detection module, respectively, and is used to synchronously acquire the charging and discharging parameters of the detection battery (1-1) and collect and process spectral data.

2. The iron-chromium redox flow battery electrolyte Cr as described in claim 1 2+ The in-situ online concentration detection system is characterized by, The electrode assembly of the detection battery (1-1) includes an upstream porous electrode (1-5) and a downstream porous electrode (1-8).

3. The iron-chromium redox flow battery electrolyte Cr as described in claim 2 2+ The in-situ online concentration detection system is characterized by, upstream porous electrode (1-5) thickness The porosity is 1.0~3.5 mm. >0.6; downstream porous electrode (1-8) thickness Porosity >0.

6.

4. The iron-chromium redox flow battery electrolyte Cr as described in claim 1 2+ The in-situ online concentration detection system is characterized by, The light source (2-1) is a tungsten lamp or an LED light source; The optical path length b of the flow-through detection cell (2-3) is 0.05~0.2 cm; The spectral detection unit (2-5) is a fiber optic spectrometer.

5. The iron-chromium redox flow battery electrolyte Cr as described in claim 4 2+ The in-situ online concentration detection system is characterized by, The wavelength range of the fiber optic spectrometer is 300~1000 nm.

6. A flow battery electrolyte using the iron-chromium redox electrolyte as described in any one of claims 1 to 5. 2+ A method for in-situ online detection of concentration, characterized in that, Including Cr 2+ The concentration was detected as follows: S1. The electrolyte to be tested is introduced into the detection system, so that it flows through the closed-loop flow path of the electrolyte, which is connected in series with the detection battery (1-1) and the flow-through detection cell (2-3); S2. The absorption spectrum of the electrolyte in the 300~1000nm band at time t is collected by the spectral detection unit (2-5) when the electrolyte flows through the flow-through detection cell (2-3), and the absorption spectrum of the electrolyte in the Cr band is recorded. 2+ absorbance at characteristic wavelength 800 nm Then, calculate Cr at time t according to Equation 1. 2+ concentration : (Equation 1) In the formula, For Cr 2+ The molar absorbance at 800 nm, expressed in L·mol⁻¹. -1 ·cm -1 b represents the optical path length of the flow-through detector cell, in cm. For Fe 2+ The molar absorbance at 800 nm, expressed in L·mol⁻¹. -1 ·cm -1 ; Fe, the negative electrode liquid 2+ The concentration, in mol·L -1 .

7. A Cr-based iron-chromium redox flow battery electrolyte based on the system described in claim 6. 2+ The in-situ online detection method for concentration is characterized by, In the initial testing or when electrolyte conditions change, Cr is also included. 2+ The calibration of molar absorbance is as follows: S1. The electrolyte to be tested is introduced into the detection system, so that it flows through the closed-loop flow path of the electrolyte, which is connected in series with the detection battery (1-1) and the flow-through detection cell (2-3); S2. The absorption spectrum of the electrolyte in the 300~1000nm band at time t0 when it flows through the flow-through detection cell (2-3) is collected by the spectral detection unit (2-5), and the absorbance at 800 nm is recorded. Then, calculate Cr at time t0 according to Equation 2. 2+ initial concentration : (Equation 2) In the formula, Fe, the negative electrode liquid 2+ The concentration, in mol·L -1 ; For Fe 2+ The molar absorbance at 800 nm, expressed in L·mol⁻¹. -1 ·cm -1 ; For Cr 2+ The previous calibrated or nominal value of molar absorbance, in L·mol⁻¹. -1 ·cm -1 b represents the optical path length of the flow-through detector cell, in cm. S3, with 5~50 mA·cm -2 The current density is used to charge the detection battery (1-1), and the charging time Δt is calculated according to Equation 3: (Equation 3) In the formula, F is the Faraday constant; For Cr 2+ The absolute value of the concentration change ranges from 0.1 to 0.3 mol·L⁻¹. -1 ; The thickness of the upstream porous electrode (1-5) is in cm; The porosity of the upstream porous electrode (1-5) is represented by ; i is the current density, in mA·cm⁻¹. -2 ; S4. After charging is complete, fresh electrolyte to be tested is reintroduced into the detection system. The absorption spectrum of the electrolyte as it flows through the flow-through detection cell (2-3) is collected, and the absorbance at 800 nm is recorded. Calculate the change in absorbance Let its absolute value be denoted as And Cr was calculated according to Equation 4. 2+ molar absorbance calibration value : (Equation 4) In the formula, F is the Faraday constant; The thickness of the upstream porous electrode (1-5) is in cm; The porosity of the upstream porous electrode (1-5) is represented by ; i is the charging current density, in mA·cm⁻¹. -2 b represents the optical path length of the flow-through detector cell, in cm.

8. The Cr-based iron-chromium redox flow battery electrolyte according to claim 7 2+ The detection method of the in-situ online concentration detection system is characterized by, when ≤0.35 mol·L -1 When the detection electrode (1-1) is charged, the upstream porous electrode (1-5) serves as the negative electrode and the downstream porous electrode (1-8) serves as the positive electrode.

9. The Cr-based iron-chromium redox flow battery electrolyte according to claim 7 2+ The detection method of the in-situ online concentration detection system is characterized by, when >0.35 mol·L -1 When the detection electrode (1-1) is charged, the upstream porous electrode (1-5) serves as the positive electrode and the downstream porous electrode (1-8) serves as the negative electrode.

10. A system according to any one of claims 1 to 5 in an iron-chromium flow battery electrolyte Cr 2+ Its application in concentration detection is characterized by, The system described above is used to control the Cr content of the electrolyte during the operation of the iron-chromium redox flow battery. 2+ Concentration is detected in situ online in real time.

Images