Method for verifying distribution uniformity of electrolyte in flow cell stack flow channel structure

Abstract

The invention relates to the technical field of flow batteries, in particular to a method for verifying the distribution uniformity of an electrolyte in a flow battery stack flow channel structure, which comprises the following steps: S1, adjusting the flow of the electrolyte according to a set electrolyte chemical stoichiometric ratio; s2, acquiring the charge state of the electrolyte flowing through the galvanic pile in real time; s3, carrying out a charge and discharge test under a constant current, and recording coulombic efficiency, voltage efficiency, energy efficiency and electrolyte utilization rate under different stoichiometric ratios; and S4, evaluating the electrolyte distribution uniformity of the flow channel structure based on the change trend of the indexes. According to the present invention, by introducing the electrolyte chemical stoichiometric ratio and constructing the closed-loop electrochemical test platform, the quantitative evaluation of the electrolyte distribution uniformity in the flow cell stack flow channel structure is achieved, and the test accuracy and the structure optimization efficiency are effectively improved.

Description

Technical Field

[0001] This invention relates to the field of flow battery technology, and in particular to a method for verifying the uniformity of electrolyte distribution in the flow channel structure of a flow battery stack. Background Technology

[0002] With the advancement of the dual-carbon strategy, energy storage technology is playing an increasingly prominent role in building new power systems. Flow batteries, with their core advantages such as long cycle life, high safety, and suitability for long-term energy storage, have performed exceptionally well among many energy storage technologies. Their unique power and capacity decoupling characteristics, low self-discharge rate, abundant raw material resources, and simple manufacturing process make them an important solution to address the intermittency of renewable energy, and they are particularly suitable for large-capacity, long-term energy storage scenarios.

[0003] As the core device for energy conversion, the flow battery stack directly determines the system's output power and operating efficiency. In the process of improving stack performance, the stack flow channel structure plays a key role, affecting the uniformity of electrolyte distribution in the electrode reaction area, which in turn affects the effective utilization of electrolyte, stack voltage efficiency, energy efficiency, and energy consumption during system operation. Therefore, how to evaluate and optimize the impact of flow channel structure on electrolyte distribution has become an important aspect of improving the overall performance of flow batteries.

[0004] However, existing methods for verifying the distribution performance of flow channel structures mainly include pressure drop testing, transparent battery observation, and CFD simulation, which have problems such as high experimental costs, long cycles, and feedback lag, making it difficult to support the rapid optimization of flow channel structures. At the same time, simulation methods are limited by the accuracy of coupled modeling and boundary simplification, making it difficult to truly reflect complex actual operating conditions. Summary of the Invention

[0005] This invention provides a method for verifying the uniformity of electrolyte distribution in the flow channel structure of a flow battery stack.

[0006] A method for verifying the uniformity of electrolyte distribution in the flow channel structure of a flow battery stack includes the following steps: S1, adjust and control the flow rate of electrolyte into the stack according to the set electrolyte stoichiometry; S2, real-time acquisition of the state of charge (SOC) of the electrolyte flowing through the flow battery stack. S3, under constant current conditions, charge and discharge tests were performed on the flow battery stack, and the coulombic efficiency, voltage efficiency, energy efficiency and electrolyte utilization were recorded under different stoichiometric ratios. S4. Based on the changing trends of the obtained coulombic efficiency, voltage efficiency, energy efficiency and electrolyte utilization, evaluate the uniformity of electrolyte distribution by the flow channel structure.

[0007] Optionally, the method for verifying the uniformity of electrolyte distribution in the flow channel structure of the flow battery stack adopts an electrochemical testing method. The electrochemical testing method is implemented on a flow battery stack testing platform, which includes a circulation pump, a flow sensor, a flow control unit, a temperature sensor, a temperature control unit, a pressure sensor, and an electrolyte SOC monitoring unit.

[0008] Optionally, the stoichiometric ratio is the ratio of the mass of active material contained in the electrolyte actually supplied to the fuel cell stack to the mass of active material consumed in the electrochemical reaction, expressed as: ; ; in, This refers to the actual flow rate of electrolyte supplied to the fuel cell stack. The electrolyte flow rate is the number of active ions consumed in the electrochemical reaction, I(t) is the actual reaction current of the flow battery stack, n is the number of electrons exchanged during the reaction, F is the Faraday constant, and C is the electrolyte flow rate. V δ(SOC) represents the total concentration of vanadium ions, and is a factor related to the state of charge (SOC) of the electrolyte.

[0009] Optionally, the electrolyte SOC monitoring unit includes a small flow battery connected in parallel with the flow battery stack. The open-circuit voltage of the small flow battery and the state of charge (SOC) of the electrolyte have a functional relationship determined by the Nernst equation. The state of charge (SOC) of the electrolyte is obtained by detecting the open-circuit voltage of the small flow battery.

[0010] Optionally, the electrolyte SOC monitoring unit further includes a concentration detection unit for periodically detecting the concentration of active ions in the positive and negative electrode electrolytes and calibrating the SOC detection results.

[0011] Optionally, the flow control unit calculates the target electrolyte flow rate in real time using a PID control algorithm based on a preset electrolyte stoichiometry and adjusts the rotation speed of the circulating pump to ensure that the flow rate value detected by the flow sensor is consistent with the target value.

[0012] Optionally, the constant current charge-discharge test adopts a fixed current density mode.

[0013] Optionally, the charge-discharge test is performed by recording the charging capacity C during each charge-discharge cycle. chg Discharge capacity C dischg Charging energy E chg Discharge energy E dischgThe state of charge of the electrolyte at the end of charging is denoted as SOC´, and the state of charge of the electrolyte at the end of discharging is denoted as SOC´´. The coulombic efficiency CE, voltage efficiency VE, energy efficiency EE, and electrolyte utilization rate are calculated respectively, and expressed as: CE=C chg / C dischg ×100%; VE = EE / CE × 100%; EE=E chg / E dischg ×100%; Electrolyte utilization rate = SOC´ - SOC´´.

[0014] Optionally, the uniformity of electrolyte distribution is determined by the minimum stoichiometric ratio of coulombic efficiency (CE), voltage efficiency (VE), energy efficiency (EE), and electrolyte utilization rate.

[0015] The beneficial effects of this invention are: This invention, by introducing a control mechanism for the stoichiometry of the electrolyte, can maintain a constant supply-demand ratio of active ions inside the stack under different operating conditions, thereby quantifying the relationship between electrolyte supply and electrochemical reaction consumption. This effectively eliminates the interference of changes in the state of charge (SOC) of the electrolyte on the evaluation of the flow channel structure, improves the stability and reliability of the test, and, combined with charge-discharge testing in constant current mode, can accurately reflect the influence of the flow channel structure on the uniformity of electrolyte distribution. This helps to scientifically define structural performance differences and supports the optimization and iteration of the stack structure.

[0016] This invention constructs an electrochemical testing platform comprising a flow sensor, a temperature control system, a SOC monitoring unit, and a PID control module. This platform enables closed-loop control of the entire process, including stoichiometry, electrolyte state, and test parameters. It can collect performance indicators such as coulombic efficiency, voltage efficiency, energy efficiency, and electrolyte utilization rate under multiple stoichiometric conditions, and determine the minimum stoichiometric ratio accordingly. This allows for the evaluation of the electrolyte distribution uniformity of the flow channel structure. The method is simple to implement, highly applicable, and has significant value for engineering promotion and R&D guidance. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic flowchart of a method for achieving electrolyte distribution uniformity according to an embodiment of the present invention; Figure 2 This is a schematic diagram illustrating the performance of a flow battery stack structure (Version V1) under different electrolyte stoichiometric ratios according to an embodiment of the present invention. Figure 3 This is a schematic diagram showing the number of active ions in the reactive region of the flow battery stack and the number of ions consumed by the electrochemical reaction in an embodiment of the present invention. Figure 4 This is a schematic diagram showing the performance comparison of two flow battery stack structures (Version V1 and Version V2) under different electrolyte stoichiometric ratios according to embodiments of the present invention. Detailed Implementation

[0019] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Those skilled in the art may employ other alternative methods to implement some well-known technologies; moreover, the accompanying drawings are only for more specific description of the embodiments and are not intended to specifically limit the present invention.

[0020] like Figures 1-4 The method shown illustrates the verification of electrolyte distribution uniformity in the flow channel structure of a flow battery stack. The flow channel structure refers to the guide plates, carbon paper flow channels, and other structural components in the flow battery stack that affect electrolyte distribution. Specifically, it includes the following steps: Electrolyte flow control steps: Adjust and control the flow rate of electrolyte flowing into the stack according to the set electrolyte stoichiometry. Electrolyte state of charge monitoring steps: Real-time acquisition of the state of charge (SOC) of the electrolyte flowing through the flow battery stack. Battery stack performance testing steps: Charge and discharge tests are performed on the flow battery stack under constant current conditions, and the coulombic efficiency, voltage efficiency, energy efficiency and electrolyte utilization rate are recorded under different stoichiometric ratios; Electrolyte uniformity assessment steps: Based on the changing trends of efficiency and capacity parameters obtained in the previous step, assess the uniformity of electrolyte distribution due to the flow channel structure.

[0021] The verification method employs an electrochemical testing approach. Its testing platform requires the following components: a circulating pump for adjusting the electrolyte flow rate, controlling the flow by changing its rotation speed; a flow sensor for monitoring the real-time flow rates of the positive and negative electrolytes; a flow control unit for dynamically adjusting the circulating pump's rotation speed based on real-time data from the flow sensor to ensure the actual flow rate matches the preset flow rate; a temperature sensor for detecting the temperatures of the positive and negative electrolytes; a temperature control unit for adjusting the power of the heating or cooling devices based on the temperature sensor's signal to maintain the electrolyte temperature at the set temperature; pressure sensors for detecting the pressure of the positive and negative electrolytes before and after reactor loading; and an electrolyte SOC monitoring unit for real-time monitoring of the electrolyte's state of charge (SOC). The verification method specifically includes the following steps: The electrolyte flow rate is adjusted based on the stoichiometric ratio of the electrolyte. The stoichiometric ratio of the electrolyte refers to the ratio of the amount of active material contained in the electrolyte to the amount of active material consumed in the electrochemical reaction. The amount of material consumed in the electrochemical reaction is related to the charging and discharging current and the number of electrons exchanged during the reaction. In practical control, the stoichiometric ratio of the positive and negative electrode electrolytes is controlled by adjusting the flow rate of the electrolyte supplied to the fuel cell stack. The specific relationship is as follows: ; Where λ is the stoichiometric ratio of the electrolyte; F real F0 is the actual electrolyte flow rate supplied to the fuel cell stack, measured in L / min; F0 is the electrolyte flow rate corresponding to the amount of active ions consumed by the electrochemical reaction, measured in L / min.

[0022] The state of charge of the electrolyte changes in real time during the charging and discharging process of the flow battery stack. Therefore, the actual electrolyte flow rate required for the electrochemical reaction of the flow battery stack also changes in real time. The specific relationship is as follows: ; Where I(t) is the actual reaction current of the flow battery stack, in amperes (A); n is the number of electrons exchanged during the reaction; F is the Faraday constant (96485.3321 C / mol); C V The total concentration of vanadium ions is expressed in mol / L; δ(SOC) is a factor related to the state of charge (SOC) of the electrolyte. During charging, δ(SOC) = 1 - SOC, and during discharging, δ(SOC) = SOC.

[0023] The electrolyte's state of charge (SOC) is acquired in real time using an electrolyte SOC detection unit. This unit is a small flow battery connected in parallel with the flow battery stack in the electrolyte circulation loop, ensuring that the electrolyte flowing into both batteries has the same SOC. According to the Nernst equation, the SOC of the electrolyte has a definite functional relationship with the open-circuit voltage (OCV) between the positive and negative electrode electrolytes. By acquiring the open-circuit voltage value of the small SOC battery in real time, the electrolyte's SOC can be obtained. Furthermore, the concentrations of the positive and negative electrode electrolytes need to be periodically monitored and compared with the results from the electrolyte SOC detection unit.

[0024] Based on the set stoichiometric ratio of the positive and negative electrolytes, the flow control unit calculates the electrolyte flow rate required for the operation of the fuel cell stack in real time using a PID algorithm, and dynamically adjusts the flow rates of the positive and negative electrolytes in real time by controlling the speed of the circulating pump.

[0025] The flow battery stack uses a constant current mode for charging and discharging to maintain a constant operating current density. This is to facilitate comparison and verification between flow battery stacks with different active areas and to ensure that the degree of electrochemical reaction within a unit active area is consistent.

[0026] For any charge-discharge cycle, record the charging capacity C. chg Discharge capacity C dischg Charging energy E chg Discharge energy E dischg The state of charge of the electrolyte at the end of charging is denoted as SOC', and the state of charge of the electrolyte at the end of discharging is denoted as SOC''. Calculate the coulombic efficiency CE=C chg / C dischg ×100%, calculate energy efficiency EE=E chg / E dischg ×100%, voltage efficiency VE=EE / CE×100%, calculate the difference between SOC´-SOC´´ and record it as the current cycle electrolyte utilization rate.

[0027] Figure 2 This data represents the coulombic efficiency, voltage efficiency, energy efficiency, and electrolyte utilization rate obtained under constant current charge-discharge conditions for the flow battery stack channel structure (Version V1) under different electrolyte stoichiometric ratios. When the electrolyte stoichiometric ratio increases from 12 to 8, the corresponding coulombic efficiency, voltage efficiency, energy efficiency, and electrolyte utilization rate remain relatively consistent. However, when the electrolyte stoichiometric ratio decreases from 8 to 6, the corresponding voltage efficiency, energy efficiency, and electrolyte utilization rate decrease significantly. This indicates that the minimum electrolyte stoichiometric ratio required for the flow battery stack channel structure (Version V1) to maintain optimal operating conditions is 8.

[0028] The relationship between the flow channel structure of a flow battery stack and the uniformity of electrolyte distribution is illustrated by the minimum stoichiometry of the electrolyte. The function of the flow channel structure in a flow battery stack is to uniformly distribute active ions in the electrolyte to the electrochemical reaction sites. The more uniform the distribution of active ions, the higher the electrolyte utilization rate, the lower the polarization overpotential required for the electrochemical reaction, and the higher the voltage efficiency and energy efficiency of the flow battery stack. The minimum electrolyte stoichiometry required for the above-mentioned stack flow channel structure (Version V1) to maintain optimal operating conditions is 8. Figure 3This diagram illustrates the number of active ions in the reaction region of a flow battery stack and the number of ions consumed by the electrochemical reaction. When the electrolyte stoichiometry is 8, the stack's coulombic efficiency, voltage efficiency, energy efficiency, and electrolyte utilization are at optimal values, indicating a relatively uniform distribution of active ions in the electrolyte. When the electrolyte stoichiometry is reduced to 7 or 6, the voltage efficiency and electrolyte utilization decrease significantly, indicating that there are localized areas with low active ion concentrations, failing to meet the demands of the electrochemical reaction. This manifests as an increase in the electrochemical reaction overpotential. This is due to the uneven distribution of electrolyte in the stack's flow channel structure, leading to a decrease in voltage efficiency and electrolyte utilization. Therefore, the minimum electrolyte stoichiometry required to maintain peak voltage efficiency, energy efficiency, and electrolyte utilization while meeting design requirements is a key indicator of the uniformity of electrolyte distribution in the stack's flow channel structure: the smaller the value, the better the distribution uniformity.

[0029] Figure 4 The results show the coulombic efficiency, voltage efficiency, energy efficiency, and electrolyte utilization rate of different flow channel structures (Version V1 and Version V2) of flow battery stacks under constant current charge-discharge conditions with different electrolyte stoichiometric ratios. The results indicate that, under the same electrolyte stoichiometric ratio, the improved flow channel structure V2 version shows a slight improvement in voltage efficiency, energy efficiency, and electrolyte utilization rate compared to Version V1, suggesting that the V2 version has better electrolyte distribution uniformity.

[0030] This invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of this invention. To provide the public with a thorough understanding of this invention, specific details are described in detail in the following preferred embodiments; however, those skilled in the art will fully understand the invention even without these details. Furthermore, to avoid unnecessary misunderstanding of the essence of this invention, well-known methods, processes, procedures, components, and circuits are not described in detail.

[0031] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method of verifying the uniformity of electrolyte distribution in a flow channel structure of a flow battery stack, characterized by, The method comprises the following steps: S1, adjusting and controlling the electrolyte flow into the stack according to a set stoichiometric ratio of electrolyte; S2, obtaining the state of charge of the electrolyte flowing through the flow battery stack in real time; S3, performing charge and discharge tests on the flow battery stack under constant current conditions, and recording the coulombic efficiency, voltage efficiency, energy efficiency and electrolyte utilization rate under different stoichiometric ratios; S4, evaluating the uniformity of electrolyte distribution in the flow channel structure based on the variation trend of the coulombic efficiency, voltage efficiency, energy efficiency and electrolyte utilization rate.

2. The method of claim 1, wherein the method is used to verify the uniformity of electrolyte distribution in a flow channel structure of a flow battery stack. The method for verifying the uniformity of electrolyte distribution in the flow channel structure of the flow battery stack adopts an electrochemical test method, which is implemented on a flow battery stack test platform. The test platform comprises a circulating pump, a flow sensor, a flow control unit, a temperature sensor, a temperature control unit, a pressure sensor and an electrolyte SOC monitoring unit.

3. The method of claim 2, wherein the method is used to verify the uniformity of electrolyte distribution in a flow channel structure of a flow battery stack. The stoichiometric ratio is the ratio of the amount of active substance contained in the electrolyte actually supplied to the stack to the amount of active substance consumed in the electrochemical reaction, which is expressed as: ； ； wherein, is the flow rate of electrolyte actually supplied to the stack, is the flow rate of electrolyte corresponding to the number of active ions consumed by the electrochemical reaction, I(t) is the actual reaction current of the flow battery stack, n is the number of exchanged electrons in the reaction process, F is the Faraday constant, C V is the total concentration of vanadium ions, and δ(SOC) is a factor related to the state of charge of the electrolyte.

4. The method of claim 3, wherein the method is used to verify the uniformity of electrolyte distribution in a flow channel structure of a flow battery stack. The electrolyte SOC monitoring unit comprises a small flow battery arranged in parallel with the flow battery stack. The open-circuit voltage of the small flow battery and the state of charge of the electrolyte have a functional relationship determined by the Nernst equation. The state of charge of the electrolyte is obtained by detecting the open-circuit voltage of the small flow battery.

5. The method for verifying the uniformity of electrolyte distribution in the flow channel structure of a flow battery stack according to claim 4, characterized in that, The electrolyte SOC monitoring unit further comprises a concentration detection unit for periodically detecting the concentration of active ions in the positive and negative electrolytes and calibrating the SOC detection results.

6. The method of claim 5, wherein the method is used to verify the uniformity of electrolyte distribution in a flow channel structure of a flow battery stack, and wherein the method comprises: The flow control unit calculates the target electrolyte flow in real time based on the preset stoichiometric ratio of electrolyte by a PID control algorithm, and adjusts the rotating speed of the circulating pump to keep the flow value detected by the flow sensor consistent with the target value.

7. The method for verifying the uniformity of electrolyte distribution in the flow channel structure of a flow battery stack according to claim 6, characterized in that, The constant current charge and discharge test adopts a fixed current density mode.

8. The method of claim 7, wherein the method is used to verify the uniformity of electrolyte distribution in a flow channel structure of a flow battery stack. The charge-discharge test calculates the coulombic efficiency CE, the voltage efficiency VE, the energy efficiency EE and the electrolyte utilization by recording the charge capacity C chg , the discharge capacity C dischg , the charge energy E chg , the discharge energy E dischg , the state of charge of the electrolyte at the end of charge noted SOC' and the state of charge of the electrolyte at the end of discharge noted SOC'', respectively, at each charge-discharge cycle, and expressing them as follows: CE = C chg / C dischg x 100%; VE=EE / CE×100%; EE = E chg / E dischg x 100%; Electrolyte utilization rate=SOC´-SOC´´.

9. The method for verifying the uniformity of electrolyte distribution in the flow channel structure of a flow battery stack according to claim 8, characterized in that, The uniformity of electrolyte distribution is determined by the minimum stoichiometric ratio of coulombic efficiency CE, voltage efficiency VE, energy efficiency EE and electrolyte utilization rate.

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