Battery health state detection method and system in all-vanadium redox flow battery energy storage system

Abstract

The invention relates to the field of redox flow batteries, in particular to a battery health state detection method and system in an all-vanadium redox flow battery energy storage system. The method comprises the following steps: firstly, connecting an SOH reference battery into an all-vanadium redox flow battery energy storage system, connecting electrolyte for operation, then collecting the cathode voltage of the SOH reference battery, and calculating a reaction quotient corresponding to the collected cathode voltage through a Nernst equation, and finally, calculating the concentration of vanadium ions generated by the oxidation-reduction reaction in the SOH reference battery cathode electrolyte according to the reaction quotient, and calculating the health state of the battery. The system comprises an SOH reference battery, a data acquisition unit and a calculation unit. The method can effectively solve the problems of complex calculation and low accuracy of the battery health state in the all-vanadium redox flow battery energy storage system, and realizes accurate calculation of the battery health state in the all-vanadium redox flow battery energy storage system.

Description

Technical Field

[0001] The present invention relates to the technical field of flow batteries, and particularly to a method and system for detecting the state of health of a battery in a vanadium redox flow battery energy storage system. Background Art

[0002] At present, clean energy mainly based on solar and wind energy is in a stage of rapid development. However, its instability has been restricting the further development of new energy. The emergence of large-scale energy storage systems has effectively improved the energy utilization rate. Energy storage devices connect large-scale solar energy, wind energy, ocean energy, hydrogen energy, etc. to the power grid, and at the same time have functions such as peak shaving and frequency modulation, and load shifting. At present, traditional energy storage technologies widely used, such as pumped storage, have disadvantages such as harsh physical site selection and long construction periods, which can no longer meet the requirements of the increasingly developing new energy industry. In this context, electrochemical energy storage makes up for these disadvantages. It not only has flexible site selection, but also the containerized energy storage device greatly shortens the construction period. Among many electrochemical energy storage batteries, flow batteries rely on chemical elements as energy storage media, with very flexible designs, excellent performance, recyclable electrolyte solutions, long service life, green and clean, and high energy efficiency. They are very ideal power storage devices and are generally used in scenarios such as load shifting, and wind and solar power generation. The vanadium redox flow battery (VRFB), as an efficient and reliable energy storage technology, has many remarkable technical advantages. First of all, its safety is extremely high. The electrolyte is a non-flammable aqueous solution, fundamentally avoiding the risk of combustion or explosion, and is particularly suitable for large-scale energy storage applications. Secondly, the vanadium redox flow battery has an extremely long life. During the charge and discharge process, only the vanadium ions in the electrolyte change their valence states, and the electrode materials do not participate in the reaction. Therefore, the cycle life of the battery can reach more than 20 years, significantly reducing the maintenance and replacement costs for long-term use. In addition, the power and capacity of the vanadium redox flow battery can be designed independently. The power is determined by the size of the stack, while the capacity is determined by the volume and concentration of the electrolyte. This flexibility enables it to be customized according to actual needs and adapt to different application scenarios. At the same time, the vanadium redox flow battery has excellent environmental friendliness. The electrolyte can be recycled and does not produce harmful substances, meeting the requirements of green and sustainable development. Finally, its response speed is fast, and it can quickly switch between charge and discharge states, making it suitable for fields that require rapid response such as power grid frequency modulation and standby power supplies. These technical advantages make the vanadium redox flow battery have broad application prospects in large-scale energy storage, renewable energy grid connection, and improvement of power grid stability.

[0003] During the use of a vanadium redox flow battery, it is affected by both external and internal factors. It is necessary to accurately understand the health state of the battery for its use. Accurately estimating the health state of the battery can prevent overcharging and over-discharging of the battery, and set a cut-off voltage to limit overcharging and over-discharging. During charging and discharging of the vanadium redox flow battery, the capacity loss gradually increases due to the self-discharge reaction of vanadium ions in the positive and negative electrolytes mixing and crossing through the ion exchange membrane, resulting in a decrease in the health state value. Therefore, it is necessary to accurately estimate the health state to achieve the health management of the vanadium redox flow battery system.

[0004] In the prior art, it is inclined to calculate the offset value between the reference voltage RCV and the open circuit voltage OCV, and calculate the SOH of the battery system through this offset value combined with the fitting coefficient. However, for data with complex non-linear relationships, especially in the case of local extreme points, it may be difficult to accurately capture local details by this method, and it is easy to cause large calculation errors. The existing methods for testing the health state of batteries in vanadium redox flow battery energy storage systems can be mainly divided into two categories, namely the characteristic method and the model method. Among them, the characteristic method mainly includes the internal resistance analysis method, the electrochemical impedance spectroscopy analysis method and the differential analysis method, and the model method mainly includes the aging mechanism model method and the probability model method. However, the above methods all have obvious defects. The difficulty of the internal resistance analysis method lies in the establishment and extraction of the mapping relationship between SOH and the battery internal resistance, and the extracted characteristic relationship is usually only applicable to a certain specification of the battery, and the generality between different specifications of batteries is poor. The electrochemical impedance spectroscopy analysis method involves very complex measurement of electrochemical impedance spectroscopy and requires special instruments, and it can generally only be applied offline, and also has the problem of poor generality. It is difficult to establish the mapping relationship between the voltage at the peak point of the curve and the battery SOH in the differential analysis method. The aging mechanism model method has problems such as large workload, long time consumption and complex model, and it is difficult to be applied in engineering practice. The extraction of the characteristic mapping relationship of the probability model method needs to consider multiple factors and has a large workload.

[0005] Since the vanadium redox flow battery energy storage system generally does not perform full charge and discharge during operation, it is difficult to calculate the SOH based on the actual electrical energy capacity during partial charge and discharge. To sum up, the essence of battery aging and capacity attenuation is a complex, multi-factor electrochemical and physical process, and most of the real-time electrochemical parameters inside the battery are difficult to accurately measure, and it is difficult to accurately describe this process mathematically. The calculation of the SOH of the vanadium redox flow battery is affected by the actual working conditions, with a huge workload and strong randomness, which increases the calculation difficulty and it is difficult to ensure accuracy. At the same time, the generality of the SOH estimation technology is also poor, and relatively few achievements have been obtained so far. Summary of the Invention

[0006] In view of the deficiencies of the prior art, the present invention provides a method and system for detecting the state of health of a battery in a vanadium redox flow battery energy storage system. By setting an improved reference battery in the vanadium redox flow battery energy storage system and measuring the open-circuit voltage between different units of the reference battery, the corresponding vanadium ion concentration in the vanadium electrolyte is obtained, and then the state of health of the battery is determined. It can effectively solve the problems of complex calculation and low accuracy of the state of health calculation of the battery in the vanadium redox flow battery energy storage system, and realize the accurate calculation of the state of health of the battery in the vanadium redox flow battery energy storage system.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is: a method for detecting the state of health of a battery in a vanadium redox flow battery energy storage system, comprising the following steps: S01. Connect an SOH reference battery to the vanadium redox flow battery energy storage system and operate it with the electrolyte; the SOH reference battery includes a positive electrode unit, a negative electrode unit, and an intermediate unit. The positive electrode unit is connected to the positive half-cell of the vanadium redox flow battery, the negative electrode unit is connected to the negative half-cell of the vanadium redox flow battery, and the intermediate unit is independent of the vanadium redox flow battery system. A pump independent of the vanadium redox flow battery system provides electrolyte circulation power for the intermediate unit; S02. Collect the negative electrode voltage of the SOH reference battery and calculate the reaction quotient corresponding to the collected negative electrode voltage through the Nernst equation; S03. Calculate the vanadium ion concentration generated by the redox reaction in the negative electrode electrolyte of the SOH reference battery according to the reaction quotient P, and then calculate the state of health of the battery; Reaction quotient , where represents the concentration of trivalent vanadium ions generated by the redox reaction, represents the concentration of divalent vanadium ions participating in the redox reaction, A represents the ratio of ion changes in the electrolyte of the intermediate unit, and A is obtained by combining the sensor measurement value and the total ion concentration in the electrolyte of the intermediate unit. Substitute A into the reaction quotient calculation formula to obtain , and combine the total vanadium ion concentration under the negative electrode voltage of the SOH reference battery to obtain ; The formula for calculating the actual electric energy capacity of the negative electrode is: , where C represents the vanadium ion concentration generated by the redox reaction in the negative electrode electrolyte of the SOH reference battery, that is, the above , V represents the volume of the negative electrode electrolyte of the vanadium redox flow battery energy storage system, z represents the number of electrons gained or lost during the reaction process, and F is the Faraday constant; State of health of the battery , is the actual electric energy capacity of the negative electrode of the vanadium redox flow battery energy storage system, is the maximum electric energy capacity of the vanadium redox flow battery energy storage system.

[0008] Further, in step S02, the negative electrode voltage of the SOH reference battery is the potential difference between the negative electrode unit and the intermediate unit. Setting the potential of the intermediate unit to 0, the Nernst equation is expressed as: , where U is the negative electrode voltage of the SOH reference battery collected, U0 is the initial value of the negative electrode voltage of the SOH reference battery, R is the universal gas constant, T is the Kelvin temperature, F is the Faraday constant, z is the number of electrons gained or lost during the reaction process, and P is the reaction quotient, that is, the ratio of the real-time concentration of the product to the real-time concentration of the reactant when the redox reaction between the negative electrode and the intermediate unit has not reached equilibrium; the reaction quotient P corresponding to the collected negative electrode voltage is calculated through the Nernst equation.

[0009] Further, in step S03, the total concentration of vanadium ions at the negative electrode voltage of the SOH reference battery is measured through experiments.

[0010] Further, steps S02 and S03 are carried out in real time to achieve real-time monitoring of the battery health state.

[0011] Further, z = 1.

[0012] Further, the electrolyte of the intermediate unit of the SOH reference battery is an electrolyte containing divalent and trivalent iron ions. Then, in step S03, the reaction quotient , where represents the concentration of divalent iron ions generated by the redox reaction, represents the concentration of trivalent iron ions participating in the redox reaction. The concentration of iron ions in a certain valence state in the electrolyte of the intermediate unit is detected through a selective electrochemical sensor. The total concentration of iron ions in the electrolyte minus the concentration detected by the selective electrochemical sensor gives the concentration of iron ions in the other valence state. Substituting , into the reaction quotient calculation formula, is obtained. Combining with the total concentration of vanadium ions at the negative electrode voltage of the SOH reference battery, is obtained.

[0013] Further, the SOH reference battery includes two groups of battery units. Each group of battery units includes a bipolar plate (1), a cell frame (2), an electrode (3), an ion exchange membrane (4), and an end plate (5). The electrode and the ion exchange membrane are arranged on the cell frame. The electrode is located on both sides of the ion exchange membrane. The bipolar plate is located at both ends of the cell frame. The end plate is located outside the bipolar plate. The two groups of battery units share one end plate and are connected together through the shared end plate.

[0014] Further, the ion exchange membrane of the negative electrode unit is a polymer membrane based on porphyrin or calixarene.

[0015] The present invention also discloses a battery health state detection system in a vanadium redox flow battery energy storage system, which includes an SOH reference battery. The SOH reference battery includes a positive electrode unit, a negative electrode unit, and an intermediate unit. The positive electrode unit is connected to the positive half-cell in the vanadium redox flow battery, the negative electrode unit is connected to the negative half-cell in the vanadium redox flow battery, and the intermediate unit is independent of the vanadium redox flow battery system. A pump independent of the vanadium redox flow battery system provides electrolyte circulation power for the intermediate unit; A data acquisition unit is used to acquire the negative electrode voltage of the SOH reference battery, the total vanadium ion concentration corresponding to the negative electrode voltage of the SOH reference battery, and the electrolyte ion concentration of the intermediate unit; A calculation unit is used to calculate the reaction quotient corresponding to the acquired negative electrode voltage through the Nernst equation, calculate the vanadium ion concentration generated by the redox reaction in the negative electrode electrolyte of the SOH reference battery according to the reaction quotient, and then calculate the battery health state.

[0016] The beneficial effects of the present invention: By connecting an external reference battery and using the method of measuring the substance concentration of vanadium ions to calculate the battery health state SOH, the detection process is simplified, and the accuracy of SOH calculation is increased through calculation, which can effectively solve the problems of complex calculation and low accuracy of the battery health state in the vanadium redox flow battery energy storage system, and achieve accurate calculation of the battery health state in the vanadium redox flow battery energy storage system. Description of the Drawings

[0017] Figure 1 is a flowchart of the method described in Embodiment 1; Figure 2 is a schematic diagram of a vanadium redox flow battery energy storage system with an SOH reference battery connected; Figure 3 is a schematic diagram of the overall structure of the SOH reference battery; In the figure: 1. Bipolar plate, 2. Cell frame, 3. Electrode, 4. Ion exchange membrane, 5. End plate. Detailed Embodiments

[0018] The present invention will be further described below in conjunction with the drawings and specific embodiments.

[0019] Embodiment 1 This embodiment discloses a method for detecting the battery health state in a vanadium redox flow battery energy storage system, as Figure 1 shown, including the following steps: S01. Connect an SOH reference battery to the vanadium redox flow battery energy storage system and connect the electrolyte to operate; as Figure 2As shown, the SOH reference cell includes a positive electrode unit, a negative electrode unit, and an intermediate unit. The positive electrode unit is connected to the positive half-cell in the all-vanadium redox flow battery, the negative electrode unit is connected to the negative half-cell in the all-vanadium redox flow battery, the electrolyte of the intermediate unit is an electrolyte containing divalent and trivalent iron ions, independent of the all-vanadium redox flow battery system, and there is a pump independent of the all-vanadium redox flow battery system to provide electrolyte circulation power for the intermediate unit.

[0020] S02. Collect the negative electrode voltage of the SOH reference cell, and calculate the reaction quotient corresponding to the collected negative electrode voltage through the Nernst equation.

[0021] In electrochemistry, the Nernst equation is used to calculate the equilibrium voltage of a specified redox pair on the electrode relative to the standard electrode potential. According to the Nernst equation, the voltage U1 in the SOH reference cell can be expressed as the concentration difference between the electrolyte VO 2+ (V 5+ ) in the positive reference unit and the electrolyte (Fe 2+ / Fe 3+ ) in the intermediate reference unit. The voltage U2 can be expressed as the concentration difference between the electrolyte VO 2+ (V 2+ ) in the negative reference unit and the electrolyte (Fe 2+ / Fe 3+ ) in the intermediate reference unit. Since there are different electric potentials between the positive electrode unit, negative electrode unit, and intermediate unit in the SOH reference cell, there will be a potential difference U1 between the positive electrode unit and the intermediate unit, and there will be a potential difference U2 between the intermediate unit and the negative electrode unit. According to the aforementioned Nernst equation, U1 and U2 are related to the ion concentration in the electrolyte. Setting the potential of the intermediate unit to 0, the total potential difference U in the SOH reference cell is U = U1 + U2. According to the above Nernst equation, the voltage U1 is related to the ion concentration of the electrolyte. Taking the positive reference unit as an example, at different ion concentrations (V 4+ / V 5+ ), there will be different voltages U1. When the concentration of VO2+(V 5+ ) increases, the voltage U1 will also increase; when the concentration of VO2+(V 5+ ) decreases, the voltage U1 will also decrease. The same is true for the voltage U2 in the negative reference unit.

[0022] Under the initial operating conditions, the molar concentration C1 of vanadium ions in the positive electrode is equal to the vanadium ion concentration C2 in the negative electrode, i.e., C1 = C2. However, as the reaction proceeds, the vanadium ion concentration in the positive electrode will increase to C1', and the vanadium ion concentration in the negative electrode will decrease to C2'. At this time, the vanadium ion concentration in the positive and negative electrodes is C1' > C2'. Then, the voltage U1 of the positive electrode will rise, and the voltage U2 of the negative electrode will drop. At the same time, the sum of U1 and U2, that is, the total voltage U in the SOH reference battery, remains unchanged. Due to the overflow structure set between the positive and negative storage tanks in the all-vanadium redox flow battery energy storage system, when the volume of the positive electrolyte increases, it can overflow into the negative storage tank, and the electrolyte volume V1 in the positive storage tank and the electrolyte volume V2 in the negative storage tank do not change. As the reaction proceeds, the vanadium ion concentration in the positive electrolyte increases, so the amount of substance n 正 of vanadium ions in the positive electrolyte will increase (n 正’ = C1'×V1). Similarly, the amount of substance of vanadium ions in the negative electrolyte will decrease accordingly. Due to the existence of the cask effect, the actual capacity of the redox flow battery energy storage system depends on the side with less reactive substances in the positive and negative electrolytes. Therefore, the actual capacity depends on the electrical energy capacity of the negative electrode. The state of health SOH of the redox flow battery = Q / Q max , where Q is the actual electrical energy capacity and Q max is the maximum electrical energy capacity of the system. The vanadium ion concentration C2' in the negative electrode can be determined by the open-circuit voltage of the negative electrode unit. The vanadium ion concentration C2' in the negative electrode is correlated with the electrical energy capacity Q of the negative electrode. At this time, the state of health of the all-vanadium redox flow battery energy storage system can be calculated.

[0023] Specifically, in step S02, the negative electrode voltage of the SOH reference battery is the potential difference between the negative electrode unit and the intermediate unit. By setting the potential of the intermediate unit to 0, the Nernst equation is expressed as: , where U is the negative electrode voltage of the SOH reference battery collected, U0 is the initial value of the negative electrode voltage of the SOH reference battery, R is the universal gas constant, T is the Kelvin temperature, F is the Faraday constant, z is the number of electrons gained and lost during the reaction. In this embodiment, z = 1; P is the reaction quotient, that is, the ratio of the real-time concentration of the product to the real-time concentration of the reactant when the redox reaction between the negative electrode and the intermediate unit has not reached equilibrium; the reaction quotient P corresponding to the collected negative electrode voltage is calculated through the Nernst equation.

[0024] S03. Calculate the vanadium ion concentration generated by the redox reaction in the negative electrode electrolyte of the SOH reference battery according to the reaction quotient P, and then calculate the state of health of the battery.

[0025] The reaction quotient , where represents the concentration of trivalent vanadium ions generated by the redox reaction, It represents the concentration of divalent vanadium ions participating in the redox reaction. A represents the ratio of ion change in the electrolyte of the intermediate unit. A is obtained by combining the sensor measurement value and the total ion concentration in the electrolyte of the intermediate unit. Substitute A into the reaction quotient calculation formula to obtain , and it is obtained by combining the total vanadium ion concentration at the negative electrode voltage of the SOH reference battery ; The calculation formula for the actual electrical energy capacity of the negative electrode is: , where C represents the concentration of vanadium ions generated by the redox reaction in the negative electrode electrolyte of the SOH reference battery, that is, the above , V represents the volume of the negative electrode electrolyte of the all-vanadium redox flow battery energy storage system, z represents the number of electrons gained or lost during the reaction, and z = 1 in this embodiment; F is the Faraday constant; the state of health of the battery , is the actual electrical energy capacity of the negative electrode of the all-vanadium redox flow battery energy storage system, is the maximum electrical energy capacity of the all-vanadium redox flow battery energy storage system.

[0026] In step S03, the total vanadium ion concentration at the negative electrode voltage of the SOH reference battery is measured experimentally.

[0027] In this embodiment, steps S02 and S03 are carried out in real time to realize real-time monitoring of the state of health of the battery.

[0028] In this embodiment, the electrolyte of the intermediate unit of the SOH reference battery is an electrolyte containing divalent and trivalent iron ions. Then, in step S03, the reaction quotient , where represents the concentration of divalent iron ions generated by the redox reaction, represents the concentration of trivalent iron ions participating in the redox reaction. The concentration of a certain valence state of iron ions in the electrolyte of the intermediate unit is detected by a selective electrochemical sensor. The total concentration of iron ions in the electrolyte minus the concentration detected by the selective electrochemical sensor to obtain the concentration of the other valence state of iron ions. Substitute , into the reaction quotient calculation formula to obtain , and it is obtained by combining the total vanadium ion concentration at the negative electrode voltage of the SOH reference battery .

[0029] Such as Figure 3As shown in the figure, the SOH reference battery includes two groups of battery units. Each group of battery units includes a bipolar plate 1, a pole frame 2, an electrode 3, an ion exchange membrane 4, and an end plate 5. The electrode 3 and the ion exchange membrane 4 are arranged on the pole frame 2. The electrode 3 is located on both sides of the ion exchange membrane 4. The bipolar plate 1 is located at both ends of the pole frame 2. The end plate 5 is located outside the bipolar plate 1. The two groups of battery units share one end plate and are connected together through the shared end plate. The middle end plate, that is, the shared end plate, and the electrodes 3 on both sides of it form the middle unit. The part on the left side of the left ion exchange membrane 4 is the positive electrode unit, and the part on the right side of the right ion exchange membrane 4 is the negative electrode unit. In order to enable the selective electrochemical sensor to exclude the interference of vanadium ions and specifically detect iron ions, the ion exchange membrane of the negative electrode unit is a polymer membrane based on porphyrin or calixarene, which has a selective response to Fe 3+ with selective response.

[0030] Example 2 This embodiment discloses a battery health state detection system in a vanadium redox flow battery energy storage system, including an SOH reference battery. The SOH reference battery includes a positive electrode unit, a negative electrode unit, and a middle unit. The positive electrode unit is connected to the positive half-cell in the vanadium redox flow battery, and the negative electrode unit is connected to the negative half-cell in the vanadium redox flow battery. The middle unit is independent of the vanadium redox flow battery system, and there is a pump independent of the vanadium redox flow battery system to provide electrolyte circulation power for the middle unit; A data acquisition unit for collecting the negative electrode voltage of the SOH reference battery, the total concentration of vanadium ions corresponding to the negative electrode voltage of the SOH reference battery, and the ion concentration of the electrolyte in the middle unit; A calculation unit for calculating the reaction quotient corresponding to the collected negative electrode voltage through the Nernst equation, calculating the concentration of vanadium ions generated by the redox reaction in the negative electrode electrolyte of the SOH reference battery according to the reaction quotient, and then calculating the battery health state.

[0031] The above description only presents the basic principles and preferred embodiments of the present invention. The improvements and substitutions made by those skilled in the art based on the present invention fall within the protection scope of the present invention.

Claims

1. A method for detecting the state of health of a battery in a vanadium redox flow battery energy storage system, characterized in that: The method includes the following steps: S01. Connect an SOH reference battery to the all-vanadium redox flow battery energy storage system and operate it with the electrolyte. The SOH reference battery includes a positive electrode unit, a negative electrode unit, and an intermediate unit. The positive electrode unit is connected to the positive half-cell in the all-vanadium redox flow battery, the negative electrode unit is connected to the negative half-cell in the all-vanadium redox flow battery, and the intermediate unit is independent of the all-vanadium redox flow battery system. A pump independent of the all-vanadium redox flow battery system provides the electrolyte circulation power for the intermediate unit. S02. Collect the negative electrode voltage of the SOH reference battery and calculate the reaction quotient corresponding to the collected negative electrode voltage through the Nernst equation. S03. Calculate the concentration of vanadium ions generated by the redox reaction in the negative electrode electrolyte of the SOH reference battery according to the reaction quotient P, and then calculate the state of health of the battery. Reaction quotient , where represents the concentration of trivalent vanadium ions generated by the redox reaction, represents the concentration of divalent vanadium ions participating in the redox reaction, A represents the ratio of ion change in the electrolyte of the intermediate unit, A is obtained by combining the sensor measurement value and the total ion concentration in the electrolyte of the intermediate unit, and A is substituted into the reaction quotient calculation formula to obtain , and is obtained by combining the total vanadium ion concentration at the negative electrode voltage of the SOH reference battery ; The calculation formula for the actual electrical energy capacity of the negative electrode is as follows: , where C represents the concentration of vanadium ions generated by the redox reaction in the negative electrode electrolyte of the SOH reference battery, that is, the above , V represents the volume of the negative electrode electrolyte of the all-vanadium redox flow battery energy storage system, z represents the number of electrons gained or lost during the reaction, and F is the Faraday constant; State of Health of the battery , is the actual electrical energy capacity of the negative electrode of the all-vanadium redox flow battery energy storage system, is the maximum electrical energy capacity of the all-vanadium redox flow battery energy storage system.

2. The method for detecting the battery health state in the all-vanadium redox flow battery energy storage system according to claim 1, wherein: In step S02, the negative electrode voltage of the SOH reference battery is the potential difference between the negative electrode unit and the intermediate unit. When the potential of the intermediate unit is set to 0, the Nernst equation is expressed as: ， where U is the negative electrode voltage of the SOH reference battery collected, U0 is the initial value of the negative electrode voltage of the SOH reference battery, R is the universal gas constant, T is the Kelvin temperature, F is the Faraday constant, z is the number of electrons gained or lost during the reaction, and P is the reaction quotient, that is, the ratio of the real-time concentration of the product to the real-time concentration of the reactant when the redox reaction between the negative electrode and the intermediate unit has not reached equilibrium. The reaction quotient P corresponding to the collected negative electrode voltage is calculated through the Nernst equation.

3. The method for detecting the battery health state in the all-vanadium redox flow battery energy storage system according to claim 1, wherein: In step S03, the total concentration of vanadium ions at the negative electrode voltage of the SOH reference battery is measured through experiments.

4. The method for detecting the battery health state in the all-vanadium redox flow battery energy storage system according to claim 1, wherein: Steps S02 and S03 are carried out in real time to realize the real-time monitoring of the state of health of the battery.

5. The method for detecting the battery health state in the all-vanadium redox flow battery energy storage system according to claim 1 or 2, characterized in that: z=1。 6. The method for detecting the battery health state in the all-vanadium redox flow battery energy storage system according to claim 1, wherein: If the electrolyte of the intermediate unit of the SOH reference battery is an electrolyte containing divalent and trivalent iron ions, then in step S03, the reaction quotient , where represents the concentration of divalent iron ions generated by the redox reaction, represents the concentration of trivalent iron ions participating in the redox reaction. The concentration of iron ions in a certain valence state in the electrolyte of the intermediate unit is detected by a selective electrochemical sensor. The total concentration of iron ions in the electrolyte minus the concentration detected by the selective electrochemical sensor gives the concentration of iron ions in the other valence state. Substitute , into the reaction quotient calculation formula to obtain , and combine with the total concentration of vanadium ions under the negative electrode voltage of the SOH reference battery to obtain .

7. The method for detecting the battery health state in the all-vanadium redox flow battery energy storage system according to claim 1, wherein: The SOH reference battery includes two groups of battery units. Each group of battery units includes a bipolar plate (1), a cell frame (2), an electrode (3), an ion exchange membrane (4), and an end plate (5). The electrode and the ion exchange membrane are arranged on the cell frame. The electrodes are located on both sides of the ion exchange membrane. The bipolar plates are located at both ends of the cell frame. The end plates are located outside the bipolar plates. The two groups of battery units share one end plate and are connected together through the shared end plate.

8. The method for detecting the battery health state in the all-vanadium redox flow battery energy storage system according to claim 7, wherein: The ion exchange membrane of the negative electrode unit is a polymer membrane based on porphyrin or calixarene.

9. A battery state of health detection system in a vanadium redox flow battery energy storage system, characterized in that: An SOH reference battery is included. The SOH reference battery includes a positive electrode unit, a negative electrode unit, and an intermediate unit. The positive electrode unit is connected to the positive half-cell in the all-vanadium redox flow battery, the negative electrode unit is connected to the negative half-cell in the all-vanadium redox flow battery, and the intermediate unit is independent of the all-vanadium redox flow battery system. A pump independent of the all-vanadium redox flow battery system provides the electrolyte circulation power for the intermediate unit. A data acquisition unit is used to collect the negative electrode voltage of the SOH reference battery, the total concentration of vanadium ions corresponding to the negative electrode voltage of the SOH reference battery, and the ion concentration of the electrolyte in the intermediate unit. A calculation unit is used to calculate the reaction quotient corresponding to the collected negative electrode voltage through the Nernst equation, calculate the concentration of vanadium ions generated by the redox reaction in the negative electrode electrolyte of the SOH reference battery according to the reaction quotient, and then calculate the state of health of the battery.

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