CN118336041A

CN118336041A - Zinc-based flow battery test device, control method and zinc-based flow battery

Info

Publication number: CN118336041A
Application number: CN202410472447.2A
Authority: CN
Inventors: 杜念慈
Original assignee: Weijing Energy Storage Technology Co ltd
Current assignee: Weijing Energy Storage Technology Co ltd
Priority date: 2024-04-18
Filing date: 2024-04-18
Publication date: 2024-07-12

Abstract

The invention discloses a zinc-based flow battery test device, a control method and a zinc-based flow battery, wherein the test device is used for testing the metal deposition effect of the cathode side of a target cell stack comprising one flow battery cell; wherein, a plurality of negative side liquid storage tanks in the flow battery circulation system are used for storing the mixed liquid of the negative electrolyte and the electrolyte additive, the electrolyte additives in the negative electrode side liquid storage tanks have respective preset types, preset volumes and preset concentrations; when the flow battery management system controls the mixed liquid in one target liquid storage tank to continuously circulate through the negative electrode side cavity of the target electric pile each time, the power supply system performs a preset number of charge and discharge tests on the target electric pile; the electrochemical workstation acquires electrochemical impedance spectrums of the cathode side of the target pile in each charge-discharge test process; the flow battery management system compares the metal deposition effect of the cathode side of the target pile based on electrochemical impedance spectroscopy analysis, and finally determines the optimal additive formula of the electrolyte of the cathode side of the target pile. The invention realizes the technical effects of parallel analysis and rapid screening aiming at the additive formula at the negative electrode side of the flow battery.

Description

Zinc-based flow battery test device, control method and zinc-based flow battery

Technical Field

The embodiment of the invention relates to the technical field of flow batteries, in particular to a zinc-based flow battery test device, a control method and a zinc-based flow battery.

Background

In metallurgical electrolytic production, in order to obtain a cathode product with fine and dense crystals, the appropriate current density and additives must be chosen to ensure that the electrode process is in the electrochemical polarization range, that is to say that the electrolytic system is in the tafel region. The tafel region refers to a range of current densities where overpotential is linear with the logarithm of current density. Meanwhile, in electrolytic production, by adding a certain amount of additive, the range of electrochemical polarization can be increased, i.e. the tafel region is enlarged. It is pointed out that the use of the additive has the problem that there is an optimum amount of the additive, i.e. there is an optimum concentration of the additive, and the electrochemical polarization is gradually increased in the course of reaching this optimum concentration, and when this optimum concentration is reached, almost all of the electrode surface is covered with the additive, the electrochemical resistance reaches a maximum, and thus the electrochemical polarization also reaches a maximum, after which the increase in the amount of the additive has no effect.

Similar concepts and technical means exist for improving the density of a metal deposit coating by using additives in the Tafil zone, the method for increasing electrochemical polarization and the use of additives in metallurgical electrolysis production. For the flow battery, metallic zinc in the flow battery is deposited on the negative electrode, and along with the continuous extension of charging time, zinc generates a black spongy loose zinc layer and dendritic zinc dendrites on the negative electrode, and the black spongy loose zinc layer and dendritic zinc dendrites further grow, and possibly puncture a diaphragm to mix positive and negative electrolyte, so that the short circuit of the battery is caused, the battery is disabled, and the cycle life of the battery is shortened.

Therefore, for zinc-based flow batteries, referring to the method of obtaining a fine-crystalline, dense cathode product in metallurgical electrolytic production, in order to effectively obtain a fine-crystalline, dense anode metal deposit, it is necessary to find a test apparatus capable of parallel analysis and rapid screening for additive formulations.

Disclosure of Invention

The embodiment of the invention provides a zinc-based flow battery test device, a control method and a zinc-based flow battery, so that parallel analysis and rapid screening can be performed on an additive formula at the negative electrode side of the flow battery.

In a first aspect, an embodiment of the present invention provides a zinc-based flow battery test apparatus, where the test apparatus is configured to test a negative electrode side metal deposition effect of a target stack, where the target stack includes a flow battery cell, and the test apparatus includes a flow battery management system, an electrochemical workstation, a power supply system, and a flow battery circulation system;

The flow battery management system is connected with the electrochemical workstation and the power supply system; the power supply system is respectively and electrically connected with the electrochemical workstation, the positive electrode of the target pile and the negative electrode of the target pile;

The electrochemical workstation comprises a working electrode, an auxiliary electrode and a reference electrode; the working electrode is electrically connected with the negative electrode of the target electric pile; the reference electrode is electrically connected with the positive electrode of the target pile; the auxiliary electrode of the electrochemical workstation is electrically connected with the counter electrode in the negative electrode side cavity of the target pile, or the auxiliary electrode of the electrochemical workstation is electrically connected with the positive electrode of the target pile;

The flow battery circulating system comprises a plurality of negative electrode side liquid storage tanks, a positive electrode side liquid storage tank and corresponding circulating pipelines;

The negative electrode side liquid storage tanks are respectively connected with the negative electrode side cavity of the target electric pile; the positive electrode side liquid storage tank is connected with a positive electrode side cavity of the target electric pile;

The plurality of negative electrode side liquid storage tanks are used for storing mixed liquid of negative electrode electrolyte and electrolyte additives; wherein the electrolyte additives in each of the negative-side liquid tanks have respective preset types, preset volumes, and preset concentrations, and the negative electrolytes in each of the negative-side liquid tanks have respective preset concentrations; the preset concentration of the negative electrode electrolyte in any two of the negative electrode side liquid storage tanks is one of the following: the preset concentrations are the same and different; any two of the electrolyte additives in the negative-side liquid tanks are present in one of the following cases: the preset types are the same but different in preset concentration, the preset types are different but the preset concentration is the same, the preset types and the preset concentration are different, and the preset types and the preset concentration are the same; the preset categories include at least one of: complexing agents, inhibitors, conductive salts;

The flow battery management system is used for controlling a target liquid storage tank to be communicated with a negative electrode side cavity of the target electric pile and controlling mixed liquid in the target liquid storage tank to flow through the negative electrode side cavity of the target electric pile at a preset flow rate and then return to the target liquid storage tank, wherein the target liquid storage tank is one of a plurality of negative electrode side liquid storage tanks;

The power supply system is used for carrying out a preset number of charge and discharge tests on the target cell stack under the control of the flow battery management system when the flow battery management system controls the mixed liquid in one target liquid storage tank to continuously circulate through the negative electrode side cavity of the target cell stack each time;

The electrochemical workstation is used for acquiring electrochemical impedance spectrums of the cathode side of the target pile in each charge and discharge test process under the control of the flow battery management system, and transmitting the electrochemical impedance spectrums to the flow battery management system;

The flow battery management system is also used for comparing the metal deposition effect of the cathode side of the target galvanic pile based on the received electrochemical impedance spectrum analysis and finally determining the optimal additive formula of the electrolyte of the cathode side of the target galvanic pile.

In a second aspect, an embodiment of the present invention further provides a control method of a zinc-based flow battery test apparatus, where the control method includes:

The flow battery management system controls a target liquid storage tank to be communicated with a negative electrode side cavity of a target electric pile, and controls mixed liquid in the target liquid storage tank to flow through the negative electrode side cavity of the target electric pile at a preset flow rate and then return to the target liquid storage tank, wherein the target liquid storage tank is one of a plurality of negative electrode side liquid storage tanks; the plurality of negative electrode side liquid storage tanks are used for storing mixed liquid of negative electrode electrolyte and electrolyte additives; the electrolyte additives in each negative electrode side liquid storage tank have respective preset types, preset volumes and preset concentrations, and the negative electrode electrolyte in each negative electrode side liquid storage tank has respective preset concentrations; the preset concentration of the negative electrode electrolyte in any two of the negative electrode side liquid storage tanks is one of the following: the preset concentrations are the same and different; any two of the electrolyte additives in the negative-side liquid tanks are present in one of the following cases: the preset types are the same but different in preset concentration, the preset types are different but the preset concentration is the same, the preset types and the preset concentration are different, and the preset types and the preset concentration are the same; the preset categories include at least one of: complexing agents, inhibitors, conductive salts;

Under the control of the flow battery management system, the power supply system performs a preset number of charge and discharge tests on the target electric pile when the flow battery management system controls the mixed liquid in one target liquid storage tank to continuously circulate through the negative electrode side cavity of the target electric pile each time;

Under the control of the flow battery management system, the electrochemical workstation acquires electrochemical impedance spectrums of the cathode side of the target pile in each charge and discharge test process and transmits the electrochemical impedance spectrums to the flow battery management system;

The flow battery management system compares the metal deposition effect of the cathode side of the target cell stack based on the received electrochemical impedance spectroscopy analysis, and finally determines an optimal additive formulation of the cathode side electrolyte of the target cell stack.

In a third aspect, an embodiment of the present invention further provides a zinc-based flow battery, where a negative electrode side electrolyte of the zinc-based flow battery is added with a target additive, and a component of the target additive is determined by an optimal additive formula, where the optimal additive formula is an optimal additive formula of a corresponding negative electrode side electrolyte determined by using the zinc-based flow battery test device according to any embodiment of the present invention.

The embodiment of the invention discloses a zinc-based flow battery test device, a control method and a zinc-based flow battery, wherein the test device is used for testing the metal deposition effect of the cathode side of a target cell stack comprising one flow battery cell; wherein, a plurality of negative side liquid storage tanks in the flow battery circulation system are used for storing the mixed liquid of the negative electrolyte and the electrolyte additive, the electrolyte additives in the negative electrode side liquid storage tanks have respective preset types, preset volumes and preset concentrations; when the flow battery management system controls the mixed liquid in one target liquid storage tank to continuously circulate through the negative electrode side cavity of the target electric pile each time, the power supply system performs a preset number of charge and discharge tests on the target electric pile; the electrochemical workstation acquires electrochemical impedance spectrums of the cathode side of the target pile in each charge-discharge test process; the flow battery management system compares the metal deposition effect of the cathode side of the target pile based on electrochemical impedance spectroscopy analysis, and finally determines the optimal additive formula of the electrolyte of the cathode side of the target pile. The invention realizes the technical effects of parallel analysis and rapid screening aiming at the additive formula at the negative electrode side of the flow battery.

Drawings

FIG. 1 is a block diagram of a zinc-based flow battery test apparatus provided by an embodiment of the present invention;

FIG. 2 is an equivalent circuit diagram of an electrode provided by an embodiment of the present invention;

FIG. 3 is a schematic diagram of a charging process (electrolytic cell) provided by an embodiment of the present invention;

Fig. 4 is a schematic diagram of a discharging process (primary battery) provided by an embodiment of the present invention;

fig. 5 is a complex plan view of electrochemical impedance over a full frequency range provided by an embodiment of the present invention.

A 10-flow battery management system, a 20-electrochemical workstation, a 30-power system, a 40-flow battery circulation system; 41-a negative electrode side liquid storage tank; 42-positive side liquid storage tank; 43-a deionized water liquid storage tank; 44-an electric control liquid inlet valve; 45-an electric control liquid outlet valve; 46-a first circulation pump; a 47-negative side filter; 48-a second circulation pump; 49-positive electrode side filter; 50-target galvanic pile; 60-externally connecting a liquid supplementing-changing system; PS 1-a first pressure transmitter; PS 2-second pressure transmitter; FM 1-a first flow sensor; PS 3-third pressure transmitter; PS 4-fourth pressure transmitter; FM 2-a second flow sensor; 70-stacking a tray; 80-a water bath tray; 90-liquid leakage sensor; 100-a third circulation pump; 101-thermocouple thermometer; 102-level sensor.

Detailed Description

The invention is described in further detail below with reference to the drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting thereof. It should be further noted that, for convenience of description, only some, but not all of the structures related to the present invention are shown in the drawings.

It should be noted that the terms "first," "second," and the like in the description and the claims of the present invention and in the drawings are used for distinguishing between different objects and not for limiting a particular order. The following embodiments of the present invention may be implemented individually or in combination with each other, and the embodiments of the present invention are not limited thereto.

In the flow battery field, the main flow point of view for zinc deposition electrodes is: when electrodepositing metallic zinc from zinc ions, the crystalline form of zinc is greatly affected by the overpotential. When the concentration of zinc ions is high, the deposition current is small (the overpotential is low at this time), and mossy or pebble zinc crystals are easy to form; when the current density is high and the concentration of zinc ions on the electrode surface is low (the overpotential is high), dendrites are easily formed. Factors affecting dendrite growth are mainly three: electrochemical polarization of the electrode process; mass transfer conditions of the reactants; the kind and content of the surface active substances in the solution. From the perspective of improving the quality of a zinc deposition layer of a negative electrode plate of a zinc-based flow battery and avoiding dendritic crystals of zinc during electrodeposition, referring to the mainstream viewpoints and experience of a zinc deposition process in the field of flow batteries, the possible situations of zinc during electrodeposition are summarized as follows:

(1) When zinc is electrodeposited, if the electrochemical polarization is quite high, zinc can not only electrodeposit on some active sites on the electrode surface, but also generate nuclei on the relatively intact crystal surface. When the electrochemical overpotential is high, the growth of crystals is uniform, and dendrites are not easy to form.

(2) In the later stage of charging, the overpotential of the flow battery is higher, the concentration of zinc ions is lower, the concentration polarization is larger, and therefore dendrite growth is more serious.

(3) In the flow battery, the concentration of the electrolyte near the liquid inlet is highest, and as the electrolyte flows through the electrode reaction zone from bottom to top and electrochemically reacts with the electrode plate, the concentration of the reaction ions in the electrolyte gradually decreases, so that a concentration gradient is formed in the electrolyte at one side of the electrode reaction zone. Therefore, the concentration polarization phenomenon is more easily generated in the upper half area of the electrode plate, and zinc dendrite is more easily generated.

(4) The thin liquid layer near the electrode surface is relatively lean in reactive ions during charging, concentration polarization is large, and the reactive ions diffuse more easily to the electrode surface protrusions than to other positions, so that the zinc deposition rate tends to be accelerated at the electrode surface protrusions, and zinc dendrites (zinc dendrites) are formed.

(5) When zinc electrodeposition is carried out at high current density, reactant ions in the solution near the electrode surface are very deficient because the transfer rate of the ions in the solution is smaller than the reaction rate of the electrode surface, and great concentration polarization is caused at the moment, and the reactant ions in the solution are easier to diffuse to the protrusions on the electrode surface than to other parts on the electrode surface, so zinc dendrites are easy to form.

(6) The raised portions of the electrodes tend to accumulate more charge, forming a point discharge, accelerating zinc deposition near the locations.

(7) Any one of the crystal growth processes involves both nucleation and crystal growth. When the (zinc) metal ions are reduced on the electrode surface, the (zinc) metal ions may not only continue to grow on the existing crystal face, but also generate new crystal nuclei (grains). Generally, deposited particles formed on an existing crystal plane consist of coarse particles; new nuclei (grains) are generated, and a fine, dense deposit layer is formed. Increasing the overpotential, such as by increasing the current density, helps to obtain a dense deposit with fine grains.

Thus, reference may be made to the experience of the electroplating industry to increase electrode polarization to improve the quality of the metal coating, by electrochemical polarization, generally by the following measures:

(a) Adding complexing agent. Because complex ions are more difficult to reduce on the negative electrode plate than simple ions, more electrons can be accumulated on the negative electrode, so that the polarization degree of the negative electrode is improved; for example, ammonia (water) is added to the negative electrode side of the current zinc-iron flow battery system (alkaline water electrolyte), tetrammine zinc ion-zinc ammonification complex (Zn [ (NH ₃)₄]²⁺) is generated near the negative electrode plate, for example, a certain organic compound is added to the negative electrode side of the future zinc-iron flow battery system (organic electrolyte), and an organic zinc-based complex, such as an amino acid zinc complex, is generated near the negative electrode plate.

(B) Adding additives and inhibitors. The additive is adsorbed on the surface of the electrode plate on the negative side, so that the speed of metal ions reaching the surface of the electrode plate on the negative side and the reaction speed of the metal ions and electrons can be reduced, and the metal ions are prevented from discharging, thereby improving the polarization effect of the negative electrode, refining grains, improving brightness and the like. In industrial practice, it is common to add polyethylene glycol and thiourea to ammonium salt galvanization solutions, citrate galvanization solutions.

(C) The current density through the negative electrode is increased. In the case where the anode polarization increases with an increase in the anode current density, the anode polarization can be increased by increasing the anode current density.

(D) The electrolyte temperature is suitably reduced. The temperature is reduced, the complexing capacity of the complexing agent can be improved, the diffusion speed of metal ions to the surface of the electrode plate on the negative side is slowed down, and the polarization effect of the negative electrode is improved.

(E) Conductive salt is added. In the case where the degree of polarization of the negative electrode is not zero, the improvement in the conductivity of the solution can promote more uniform distribution of the current on the surface of the negative electrode plate. For example, it is conceivable to add a conductive salt containing lead, tin (in addition to bismuth, titanium and palladium) to the electrolyte. The lead ions are added into the electrolyte to obtain smooth zinc deposition, which is favorable for inhibiting dendrite formation, and the tin ions have the same effect and better effect. The effect of the addition of lead and tin is due to their co-deposition with zinc, slowing the zinc deposition rate and providing additional nuclei. In industrial practice, zinc sulfate is the main salt in zinc sulfate plating solutions, and too high a content may roughen the plating crystallization. Aluminum sulfate, sodium sulfate, ammonium chloride, and potassium chloride are all conductive salts.

Fig. 1 is a structural diagram of a zinc-based flow battery test device provided by an embodiment of the invention.

The zinc-based flow battery test device is used for testing the metal deposition effect of the cathode side of a target electric pile, wherein the target electric pile comprises a flow battery monomer, and as shown in fig. 1, the zinc-based flow battery test device comprises a flow battery management system 10, an electrochemical workstation 20, a power supply system 30 and a flow battery circulation system 40; flow battery management system 10 is connected with electrochemical workstation 20 and power supply system 30; the power supply system 30 is electrically connected to the electrochemical workstation 20, the positive electrode of the target stack 50, and the negative electrode of the target stack 50, respectively. It should be noted that, the flow battery management system 10 is further configured to control opening and closing of each valve in the flow battery circulation system 40, and obtain measurement values of each pressure transmitter, flow sensor, liquid leakage sensor, etc., and a connection between the flow battery management system 10 and the flow battery circulation system 40 is roughly indicated by a dashed line in fig. 1, which is not described herein.

The electrochemical workstation 20 includes a working electrode, an auxiliary electrode, and a reference electrode, the working electrode being electrically connected to the negative electrode of the target stack 50; the reference electrode is electrically connected with the positive electrode of the target stack 50; the auxiliary electrode of the electrochemical workstation 20 is electrically connected to a counter electrode (exemplarily, a schematic diagram provided with a counter electrode (Counter Electrode, CE) is given in fig. 1) in the negative side chamber of the target stack 50, or the auxiliary electrode of the electrochemical workstation 20 is electrically connected to the positive electrode of the target stack 50.

The flow battery circulation system 40 includes a plurality of negative-side liquid tanks 41, a positive-side liquid tank 42, and corresponding circulation pipes;

The plurality of negative electrode side liquid tanks 41 are connected to the negative electrode side chambers of the target cell stack 50, respectively; the positive electrode side reservoir 42 is connected to the positive electrode side chamber of the target cell stack 50; a plurality of negative electrode side liquid tanks 41 for storing a mixed liquid of a negative electrode electrolyte and an electrolyte additive; wherein the electrolyte additives in each negative electrode side liquid storage tank 41 have respective preset types, preset volumes and preset concentrations, and the negative electrode electrolyte in each negative electrode side liquid storage tank 41 has respective preset concentrations; the preset concentration of the negative electrode electrolyte in any two negative electrode side tanks 41 is one of the following: the preset concentrations are the same and different; the electrolyte additive in any two negative-side tanks 41 is present in one of the following cases: the preset types are the same but different in preset concentration, the preset types are different but the preset concentration is the same, the preset types and the preset concentration are different, and the preset types and the preset concentration are the same; the predetermined category includes at least one of: complexing agent, inhibitor and conductive salt.

The flow battery management system 10 is configured to control the target liquid tank to be in communication with the negative side chamber of the target stack 50, and control the mixed liquid in the target liquid tank to flow through the negative side chamber of the target stack 50 at a preset flow rate and return to the target liquid tank, where the target liquid tank is one of the plurality of negative side liquid tanks 41.

The power supply system 30 is configured to perform a charge-discharge test on the target cell stack 50 for a preset number of times under the control of the flow battery management system 10, when the flow battery management system 10 controls the mixed liquid in one target liquid storage tank to continuously circulate through the negative electrode side chamber of the target cell stack 50 each time; the electrochemical workstation 20 is used for acquiring an electrochemical impedance spectrum of the cathode side of the target pile 50 in each charge-discharge test process under the control of the flow battery management system 10, and transmitting the electrochemical impedance spectrum to the flow battery management system 10; the flow battery management system 10 is also configured to compare the metal deposition effects on the negative side of the target stack 50 based on the received electrochemical impedance spectroscopy analysis and ultimately determine the optimal additive formulation for the negative side electrolyte of the target stack 50.

The electrochemical workstation is provided with a reference electrode besides a working electrode and an auxiliary electrode, the reference electrode is connected with or not connected with the positive electrode of the target pile, and when the reference electrode is connected with the positive electrode, the accuracy of parameter measurement can be improved, so that the connection relation between the reference electrode and the positive electrode can be set according to the requirement of measurement accuracy.

In the embodiment of the present invention, the amounts of the negative electrode electrolyte and the additive in each liquid storage tank are sufficient to complete the charge-discharge experiment for the preset times, and will not be described herein.

In particular, the use of additives based on various mechanisms, in combination with experience from the production practice of the metallurgical electrolysis and electroplating industries, helps to inhibit zinc deposition, resulting in a finely crystalline, dense deposit of negative metal. According to different additive reaction mechanisms, comparison, analysis and screening are required for different additive formulas, so that a test device shown in fig. 1 is established to perform parallel test and analysis of the additive formulas.

As shown in fig. 1, the zinc-based flow battery test device adopts a single-chip flow battery (namely, the target pile comprising one flow battery cell) as a test and analysis object. The positive and negative electrolyte solutions are respectively stored in a positive-electrode-side liquid storage tank 42 and a negative-electrode-side liquid storage tank 41, additives of different preset types, preset volumes and preset concentrations are further added to the negative-electrode-side liquid storage tanks 41 according to different negative-electrode-electrolyte additive formulations, the additives and the negative-electrode electrolyte solutions in the negative-electrode-side liquid storage tanks 41 form mixed liquids, and the flow battery circulation system 40 is further provided with a plurality of pipeline configurations capable of circulating the mixed liquids in parallel on the negative electrode side of the target cell stack 50 so that the target liquid storage tank can be communicated with a negative-electrode-side cavity of the target cell stack 50.

The flow battery management system 10 is used as an upper control system, and can control mixed liquid in different target liquid storage tanks to flow through a negative electrode side cavity of the target electric pile 50 at a preset flow rate and then return to the target liquid storage tanks, when each time the mixed liquid in one target liquid storage tank is controlled to continuously circulate and flow through the negative electrode side cavity of the target electric pile 50, the flow battery management system 10 also controls the power supply system 30 to perform a preset number of charge and discharge tests on the target electric pile 50, and through the test function provided by the electrochemical workstation 20, electrochemical impedance spectrum data of a negative electrode side electrode (and a metal deposition layer), a counter electrode and an electrolyte system of the target electric pile 50 are measured, so that corresponding electrochemical impedance spectrums are obtained; flow battery management system 10 discriminates the functional level of different additives to suppress dendrites of the negative side metal deposit layer of target stack 50 by comparing and analyzing the electrochemical impedance spectra.

The mixed liquid of different additives and the negative electrode side electrolyte is added into the negative electrode side liquid flow circulation of the target galvanic pile by using the test device shown in fig. 1 for test, the additive proportion influencing the density of the negative electrode side metal deposition layer is analyzed and compared by electrochemical impedance spectroscopy, and finally, the granularity of metal deposition is reduced, the density of the negative electrode side metal deposition is improved by comparing the optimal additive formula, and the phenomenon that the zinc deposition layer accumulates and pierces an ion exchange membrane caused by the long-term charge-discharge process of the zinc-based flow battery is effectively inhibited.

In the test process, except that the types, the volumes and the concentrations of the additives can be used as single variables for comparison test, the concentration of the negative electrode electrolyte and the charge and discharge parameters of the power supply system in the charge and discharge process can be used as single variables for comparison test so as to determine the optimal additive formula of the negative electrode side electrolyte under certain conditions.

The electrochemical workstation 20 is selected to obtain the electrochemical impedance spectrum of the cathode side of the target stack 50 for analysis of the metal deposition effect because for the electrode process, a number of methods may be used to test the parameters of the relevant process, such as cyclic voltammetry, linear scanning, transient step-method, etc. Both of these methods require a relatively long time. The problem is whether the electrode interface state can be maintained unchanged during this time frame, at least, it is difficult to ensure that the surface state of the metal electrode interface remains unchanged throughout the test. The core idea of ac impedance method, also called electrochemical impedance spectroscopy, is to apply a micro disturbance to the electrode process and to deviate the electrode (and electrolyte) system from the equilibrium state, but to ensure linearization. And testing the relevant parameters of the electrode process through the response characteristics of the test system to the micro-disturbance.

Important information such as double electric layer differential capacitance, charge transfer resistance, solution resistance, polarization resistance, quasi-capacitance and quasi-inductance caused by electrochemical adsorption can be measured according to electrochemical impedance spectroscopy. In the electrochemical impedance experiment, the direct current component can be overlapped with the perturbation (small-amplitude sine wave alternating current component), so that all physical quantities in an electrochemical system, such as electrode potential, polarization current, electrolyte concentration and surface adsorption concentration, comprise the direct current component and the alternating current component. When the DC component is in a stable state, the DC component of all physical quantities has zero angular frequency omega derivatives, which indicates that the electrochemical impedance spectroscopy technology can separate AC components from the physical quantities containing DC and AC components for the electrode (and electrolyte) system with the DC component, so that the phase and amplitude of the AC components are kept unchanged, and the intrinsic impedance value of the electrode can be accurately measured.

The equivalent circuit of the electrode is obtained through the following steps:

the following charge transfer reactions occur at the electrodes: O+ne→R; wherein: o represents an oxidation state, R represents a reduction state; n is the electron transfer number of the electrode reaction. In the case of the above-described reactions occurring on the electrodes, the electrode process undergoes four basic steps: (1) an electric double layer charging step. When a current is passed through the electrode, the electric double layer of the electrode is charged first. Since the impedance generated during the charging process is caused by an electric double layer, the equivalent capacitance element in the electrode equivalent circuit is represented by an electric double layer capacitor C _d. (2) ion migration process. When current passes through the electrodes, the ions in the electrolyte undergo electromigration. The resistance to electromigration is represented by resistance R _L, which is referred to as the solution resistance, and its value is the resistance of the electrolyte solution in which the electrodes are located. (3) diffusion process of reactant O and product R. The current passes through the electrodes, forming a diffusion layer at the electrode interface. The diffusion layer is composed of numerous dx thin layers, each of which can be represented by a capacitance Cdx and a resistance Rdx. Cdx corresponds to the mass capacity in each dx lamina solution and is therefore proportional to the concentration of the mass O; Rdx corresponds to the diffusion resistance of the dx thin layer solution and is inversely proportional to the diffusion coefficient and the solution concentration C. Therefore, the equivalent circuit of concentration polarization consists of concentration capacitance and concentration polarization resistance. They are denoted by C _w and R _w, respectively. It has been shown in theory that they are connected in series to form an equivalent circuit for concentration polarization. (4) a charge transfer process. An electrochemical reaction occurs when an electrical potential is applied across the electrodes. the resistance generated by the charge transfer across the electrode and solution two-phase interface is equivalent to a resistance, denoted by R _t. It represents a measure of the ease of charge transfer. R _t is large, which means that the charge transfer process is difficult to carry out; r _t is small, indicating that the charge transfer process is easy to perform. the magnitude of R _t is related to the nature of the electrode reaction and the degree of polarization of the electrode process, and different electrode reactions and different degrees of polarization will have different values of R _t. In the electrochemical literature, R _t is referred to as a charge transfer resistor.

The electrode process is mainly composed of the four basic steps, and each step can be equivalently represented by an electrotechnical element. These electrotechnical elements are sequentially connected in the direction of charge transfer to form a circuit called an electrode equivalent circuit. Ions that react with the electrode are discharged at the electrode interface by diffusing through the diffusion layer and then into the electric double layer, and the concentration difference polarization equivalent circuit is seen in series with the charge transfer resistor R _t. Experiments have shown that the electric double layer charging first occurs and then the electrochemical reaction occurs when the current passes through the electrodes, and therefore, the charge transfer resistor R _t and the concentration polarization equivalent circuit form a serial equivalent circuit in parallel with the electric double layer capacitor C _d. The solution resistance R _L refers to the resistance of the electrolyte solution in which the electrode is located (also referred to as the electrolyte resistance or ohmic resistance), so that R _L is connected in series with the parallel circuit formed by other electrotechnical equivalent elements to finally form an equivalent circuit (Warburg circuit model) of the electrode, as shown in fig. 2, and fig. 2 is a diagram of the equivalent circuit of the electrode provided by the embodiment of the invention.

The impedance characteristic analysis method of the flow battery will be described below.

The flow battery monomer consists of an ion conducting membrane, electrodes, an electrode frame, a sealing gasket, a bipolar plate (a central polar plate), a current collecting plate, an insulating plate, an end plate, a fastener combination and the like which are symmetrically arranged on two sides of the ion conducting membrane; the flow battery pile is formed by superposing and fastening a plurality of flow battery monomers in a filter press mode. In the charging process of the flow battery, the flow battery stack functions as an electrolytic cell, and when the flow battery discharges a load, the flow battery stack functions as a primary battery, as shown in fig. 3 and fig. 4, fig. 3 is a schematic diagram of the charging process (electrolytic cell) provided by the embodiment of the present invention, and fig. 4 is a schematic diagram of the discharging process (primary battery) provided by the embodiment of the present invention.

As shown in fig. 3 and fig. 4, in the charge and discharge process of the flow battery monomer, there are redox reactions respectively participated in by electrolyte active materials on the cathode side and the anode side of the ion exchange membrane and the positive electrode and the negative electrode, and the specific reaction process is as follows: Therefore, in the charging and discharging process of the flow battery cell, an equivalent circuit of a positive electrode and a negative electrode exists at the same time. When charging, the phenomenon that electrons are obtained by the negative electrode and electrons are lost by the positive electrode exists; the phenomenon that electrons are lost from a negative electrode and obtained from a positive electrode during discharging exists; and the number of the obtained and lost electrons is the same, and the corresponding exchange current density is the same.

The exchange current density can describe the degree of reversibility of the electrode reaction, the greater the exchange current density, the greater the net current through the electrode, indicating that the electrode reaction is readily carried out, referred to as the greater the reversibility of the electrode reaction; conversely, the smaller the exchange current density, the smaller the net current through the electrode, and the more difficult it is to perform the electrode reaction, referred to as the less reversible the electrode reaction. Taking the charging process of the negative electrode as an example, the potential of the negative electrode has the following relationship with the electrode surface concentrations of the reactant O and the product R participating in the reduction reaction:

Wherein E _An is the potential at which current passes through the negative electrode; is the standard electromotive force of the negative electrode; r is the gas constant, r= 8.3144J/(mol·k); t is the temperature of the solution, and the unit is K; n is the electron transfer number; f is faraday constant, f= 96485C/mol; c _o (0, t) and C _R (0, t) are electrode surface concentrations (activities) of reactant O and product R, respectively, when current is passed through the electrodes, which values change as the state of charge of the battery changes during charge and discharge on the negative side of the flow battery. The above equation shows that the exchange current density has a very large electrochemical system, typically greater than 10A/cm ²(10000mA/cm²), and that the electrode obeys the Nernst equation when current is passed through the electrode, which can be considered as a reversible electrode reaction. On both sides of the ion exchange membrane of the flow battery cell, there are (two) relatively independent half electrochemical systems consisting of electrodes and electrolyte. At this time, the total potential of the flow battery will be different according to the positive and negative electrode potentials, and the following relationship is satisfied:

E_emf＝E_Cat-E_An；

In combination with the current density range (15-120 mA/cm ²) used by the current flow battery system, the flow battery system can be considered to generate incomplete reversible reaction on the positive electrode and the negative electrode in the charge and discharge process, namely electrochemical polarization and concentration polarization exist simultaneously. Taking the negative electrode charging process as an example, when current passes through the electrode, the current is split into two parts. The first partial current is used for electrode double layer charging, and this partial current does not follow the faraday law, called the non-faraday current, and the impedance generated by the non-faraday current is called the non-faraday impedance. The second part of the current is used for the electrode reaction o+ne→r, which follows the faraday law, the impedance called faraday impedance, which is generated by the faraday current, is denoted by Z _F. The diffusion of the reactant O to the electrode surface and the charge transfer of the reactant O at the electrode interface obey faraday's law, and the faraday impedance Z _F should be composed of two parts, namely electrochemical polarization impedance and concentration polarization impedance when electrochemical polarization and concentration polarization exist at the same time. As can be seen from the electrode equivalent circuit in fig. 2, the equivalent circuit of concentration polarization and the charge transfer resistor Rt form a series circuit, so the total faraday impedance is the complex sum of the impedance parts in the series circuit, namely:

When electrochemical polarization and concentration polarization exist simultaneously, and the existence of solution resistance R _L is considered, the total electrochemical impedance of the electrode is:

FIG. 5 is a complex plan view of electrochemical impedance in the full frequency range provided by the embodiment of the invention, as shown in FIG. 5, the complex plan view of electrochemical impedance can show different electrode process rules in different frequencies, and the high frequency region is represented by electrochemical polarization and mainly represented by charge transfer; the low frequency region exhibits concentration polarization, primarily as mass transfer; the medium frequency region is characterized by processes associated with adsorption and intermediate product formation. In fig. 5, R _ct＝R_t,R_Ω =r, Wherein α is the negative electrode reaction transfer coefficient; c _o (0, t) is the electrode surface concentration (activity) of reactant O, and D ₀ is the diffusion coefficient of reactant. The electrochemical impedance complex plane diagram in the full frequency range can be obtained, and four basic steps correspond to the electrotechnical element parameters (R _L,R_t,C_d,R_w,C_w) of the electrode equivalent circuit in the incomplete reversible reaction process of the electrode. There is also a similar process of incomplete reversible reaction of the electrode on the positive side of the flow battery, basic steps and electroengineering element parameters (R _L′,R_t′,C_d′,R_w′,C_w') of the electrode equivalent circuit. Of the three parameters, R _L is related to the comprehensive concentration of the electrolyte, and the state of charge (SOC) of the flow battery during charging and discharging; r _t is related to the charge transfer resistance on the electrode, and is related to the thickness and the densification degree of the metal deposition layer of the electrode on the negative side, the larger the thickness of the deposition layer is, the larger the charge transfer resistance is, and the denser the deposition layer is for the same thickness of the deposition layer, the smaller the charge transfer resistance is; c _d is used to represent an electric double layer capacitor formed at the interface between the electrode and the electrolyte, and if the metal deposition layer of the negative electrode has a loose and porous structure (similar to the case of using a porous electrode on the basis of a negative plate electrode, the electric double layer effect becomes more remarkable, and the electric double layer capacitance value becomes larger). R _w、C_w is related to the concentration change of the reactant O on the surface of the electrode, and increasing the frequency can eliminate concentration polarization.

Optionally, as shown in fig. 1, the flow battery circulation system 40 further includes a deionized water reservoir 43; the deionized water reservoir 43 is connected to the negative side chamber of the target cell stack 50 through a corresponding circulation line for cleaning the negative side chamber of the target cell stack 50 and the corresponding circulation line before each replacement of the target reservoir in communication with the negative side chamber of the target cell stack 50 under the control of the flow battery management system 10.

Specifically, after testing of a set of mixed liquids of negative electrolyte and additives is completed, the negative electrolyte circulation pipe and the negative side chamber of the target stack 50 may be cleaned and residual ions diluted by deionized water in the deionized water tank 43 in the flow battery circulation system 40, and discharged to the outside of the system by a proper manner, and then testing of another set of mixed liquids of negative electrolyte and additives is performed, and so on.

Optionally, as shown in fig. 1, the flow battery circulation system 40 further includes a plurality of pairs of electrically controlled liquid inlet valves 44 and electrically controlled liquid outlet valves 45;

A pair of electric control liquid inlet valves 44 and electric control liquid outlet valves 45 are correspondingly arranged on the negative electrode side liquid storage tank 41; a pair of electronically controlled inlet valves 44 and electronically controlled outlet valves 45 are used to open under control of the flow battery management system 10 to place the negative side reservoir 41 in communication with the negative side chamber of the target stack 50, and the mixed liquid in the negative side reservoir 41 flows through the negative side chamber of the target stack 50 and back to the negative side reservoir 41.

The deionized water liquid storage tank 43 is correspondingly provided with two pairs of electric control liquid inlet valves 44 and electric control liquid outlet valves 45; one pair of the electric control liquid inlet valve 44 and the electric control liquid outlet valve 45 is used for being opened under the control of the flow battery management system 10 so that the deionized water liquid storage tank 41 is communicated with the negative electrode side cavity of the target electric pile 50, deionized water in the deionized water liquid storage tank 43 flows through the negative electrode side cavity of the target electric pile 50 and then returns to the deionized water liquid storage tank 43, and the other pair of the electric control liquid inlet valve 44 and the electric control liquid outlet valve 45 is used for realizing the communication between the deionized water liquid storage tank 43 and the external liquid supplementing-changing system 60.

Optionally, as shown in fig. 1, the positive electrode side liquid storage tank 42 is correspondingly provided with an electric control liquid outlet valve 45, which is used for being opened under the control of the flow battery management system 10, so that the positive electrode electrolyte in the positive electrode side liquid storage tank 42 flows into the positive electrode side chamber of the target stack 50 and then flows back to the positive electrode side liquid storage tank 42.

Optionally, as shown in fig. 1, the flow battery circulation system 40 further includes a first circulation pump 46, a negative side filter 47, a first pressure transmitter PS1, a second pressure transmitter PS2, and a first flow sensor FM1; one end of the first circulating pump 46 is respectively connected with each negative electrode side liquid storage tank 41 and the deionized water liquid storage tank 43 through each electric control liquid outlet valve 45; the other end of the first circulation pump 46 is connected to the negative side of the target stack 50 through a negative side filter 47.

The first pressure transmitter PS1 is disposed between the anode side filter 47 and the anode side chamber inlet of the target stack 50; the second pressure transmitter PS2 is arranged between each electric control liquid inlet valve 44 and the outlet of the negative electrode side cavity of the target electric 50 stack; the difference between the measurements of the first pressure transmitter PS1 and the second pressure transmitter PS2 is used to characterize the pressure loss of the negative side chamber of the target stack 50; the first flow sensor FM1 is provided between the anode side filter 47 and the anode side chamber inlet of the target cell stack 50 for measuring the flow rate of the mixed liquid passing through the anode side chamber of the target cell stack 50.

Optionally, as shown in fig. 1, the flow battery circulation system 10 further includes a second circulation pump 48, a positive electrode side filter 49, a third pressure transmitter PS3, a fourth pressure transmitter PS4, and a second flow sensor FM2; one end of the second circulating pump 48 is connected with the positive electrode side liquid storage tank 42 through an electric control liquid outlet valve 45; the other end of the second circulation pump 48 is connected to the positive electrode side of the target stack 50 through a positive electrode side filter 49.

The third pressure transmitter PS3 is provided between the positive electrode side filter 49 and the positive electrode side chamber inlet of the target stack 50; the fourth pressure transmitter PS4 is disposed between the inlet of the positive-side liquid storage tank 42 and the positive-side chamber outlet of the target stack 50; the difference between the measurements of the third pressure transmitter PS3 and the fourth pressure transmitter PS4 is used to characterize the pressure loss of the positive side chamber of the target stack 50; the second flow sensor FM2 is provided between the positive electrode side filter 49 and the positive electrode side chamber inlet of the target cell stack 50, for measuring the flow rate of the positive electrode electrolyte passing through the positive electrode side chamber of the target cell stack 50.

Optionally, as shown in fig. 1, the test apparatus further includes a stack placement tray 70 and a plurality of water bath trays 80; the target stack 50 is placed on the stack placement tray 70; the plurality of negative electrode side liquid tanks 41, deionized water liquid tank 43 and positive electrode side liquid tank 42 are each provided on one water bath tray 80.

As shown in fig. 1, the test device further includes a plurality of liquid leakage sensors 90; the plurality of liquid leakage sensors 90 are provided on the stack placement tray 70 and outside the plurality of water bath trays 80 in one-to-one correspondence; the water bath tray 80 is used for controlling the temperature of the liquid in the negative electrode side liquid storage tank 41, the deionized water liquid storage tank 43 and the positive electrode side liquid storage tank 42.

By way of example, fig. 1 only shows a schematic view of the liquid leakage sensor 90 provided on the stack placement tray 70.

Optionally, as shown in fig. 1, the test device further includes an external fluid replacement system 60; the external fluid supplementing-changing system 60 is connected with the deionized water storage tank 43; the electric control liquid inlet valve 44 is arranged between the inlet of the deionized water liquid storage tank 43 and the external liquid supplementing-changing system 60, and the electric control liquid outlet valve 45 is arranged between the outlet of the deionized water liquid storage tank 43 and the external liquid supplementing-changing system 60; a third circulating pump 100 is also arranged between the electric control liquid outlet valve 45 and the external liquid supplementing-changing system 60; the external fluid replacement system 60 is used for supplementing the deionized water reservoir 43 and periodically replacing deionized water in the deionized water reservoir 43.

Alternatively, as shown in fig. 1, each of the negative electrode side liquid tanks 41 is provided therein with a thermocouple thermometer 101 and a liquid level sensor 102, the thermocouple thermometer 101 in the negative electrode side liquid tank 41 being used for detecting the temperature of the mixed liquid therein during each of the charge-discharge tests; the thermocouple thermometer 101 and the liquid level sensor 102 are arranged in the positive electrode side liquid storage tank 42, and the thermocouple thermometer 101 in the positive electrode side liquid storage tank 42 is used for detecting the temperature of positive electrode electrolyte in the thermocouple thermometer during each charge and discharge test; the deionized water reservoir 43 is provided with a thermocouple thermometer 101 and a liquid level sensor 102, and the thermocouple thermometer 101 in the deionized water reservoir 43 is used for detecting the temperature of the deionized water therein. The liquid level sensors 102 are used for assisting in measuring water migration levels in positive and negative electrode cavities on two sides of the ion exchange membrane, side reaction gassing levels in the charge-discharge process and the like, are suitable for the liquid capacity of each liquid storage tank, and are matched with information provided by the flow sensors.

The information detected by each flow sensor and each pressure transmitter in the cathode side circulating pipeline can provide auxiliary information for researching the surface deposition condition of the electrode plate in the cathode side chamber of the target pile and the blocking condition in the cathode side chamber of the target pile.

The embodiment of the invention also provides a control method of the zinc-based flow battery test device, which specifically comprises the following steps:

S1, controlling a target liquid storage tank to be communicated with a negative electrode side cavity of a target electric pile by a flow battery management system, and controlling mixed liquid in the target liquid storage tank to flow through the negative electrode side cavity of the target electric pile at a preset flow rate and then return to the target liquid storage tank, wherein the target liquid storage tank is one of a plurality of negative electrode side liquid storage tanks; the plurality of negative electrode side liquid storage tanks are used for storing mixed liquid of negative electrode electrolyte and electrolyte additives; the electrolyte additives in each negative electrode side liquid storage tank have respective preset types, preset volumes and preset concentrations, and the negative electrode electrolyte in each negative electrode side liquid storage tank has respective preset concentrations; the preset concentration of the negative electrode electrolyte in any two negative electrode side liquid storage tanks is one of the following conditions: the preset concentrations are the same and different; the electrolyte additives in any two negative side reservoirs are one of the following: the preset types are the same but different in preset concentration, the preset types are different but the preset concentration is the same, the preset types and the preset concentration are different, and the preset types and the preset concentration are the same; the predetermined category includes at least one of: complexing agent, inhibitor and conductive salt.

In the embodiment of the present invention, only the negative electrode electrolyte may be stored in one of the negative electrode side liquid tanks without adding the additive as required, and the negative electrode electrolyte may be used as a separate control group for comparison with the experimental group to which the additive is added.

And S2, under the control of the flow battery management system, the power supply system performs a preset number of charge and discharge tests on the target cell stack when the flow battery management system controls the mixed liquid in one target liquid storage tank to continuously circulate through the negative electrode side cavity of the target cell stack each time.

And S3, under the control of the flow battery management system, the electrochemical workstation acquires electrochemical impedance spectrums of the cathode side of the target pile in each charge and discharge test process and transmits the electrochemical impedance spectrums to the flow battery management system.

And S4, the flow battery management system compares the metal deposition effect of the cathode side of the target galvanic pile based on the received electrochemical impedance spectrum analysis, and finally determines the optimal additive formula of the electrolyte of the cathode side of the target galvanic pile.

On the basis of the above technical solutions, each charge-discharge test includes a preset number of charge-discharge cycles, and obtaining the electrochemical impedance spectrum of the cathode side of the target stack during each charge-discharge test includes:

The electrochemical workstation obtains electrochemical impedance spectrums of the cathode side of the target pile respectively at the following moments in the process of each charge and discharge test: when a first preset charging time length passes through each charging and discharging cycle in each charging and discharging test process; a preset time within the final stage of the first charge; when the first charge-discharge cycle is finished; and (3) when the preset times of charge and discharge cycles are finished.

One set of tests performed using a combination of certain additives and negative electrolyte is called a charge-discharge test, and one charge-discharge test includes a predetermined number of charge-discharge cycles.

Specifically, in the process of adding an additive (complexing agent, inhibitor or conductive salt), the system of the zinc-based flow battery is changed, and in order to make the additive fully play a role in the charging and discharging process of the flow battery, the additive needs to be uniformly mixed with the original electrolyte system at the negative electrode side of the flow battery to form a stable solution. For the scheme of adding the complexing agent or the inhibitor, the action mechanism is to inhibit the charge and discharge behavior of active material ions in the original system on the negative electrode side of the flow battery on the surface of the negative electrode, so that the negative electrode is fully polarized. It follows that the additives (complexing agents, inhibitors) are thoroughly mixed with the negative side electrolyte and circulated with the liquid flow into the negative side cavity of the stack, after a period of time, the mixed solution enters the steady-state mass transfer process in the negative side cavity (the concentration of the electrode surface reactant and the diffusion coefficient of the reactant are decreasing, i.e. C _O (0, t) and D ₀ are decreasing). The size of the electrolyte resistance in the negative side lumen, as compared to the electrolyte without the additive, will change from R _L to R _L',R_L and R _L' depending on the ease of charge transfer (which can be quantified experimentally) of the flow battery negative side electrolyte system before and after the addition of the additive. As the additive (and product) is effectively adsorbed near the negative electrode, the concentration polarization level near the electrode is increasing, i.e., at this time the negative side electrode surface reactant concentration polarization resistance R _w becomes R _w ', the concentration capacitance C _w becomes C _w', and R _w'>R_w,C_w'<C_w (for an incomplete reversible electrode reaction, there is: The mass transfer level of the negative electrode side electrolyte and the mass transfer level of the electrode surface reactant are unchanged. In the case where w is unchanged, R _w is increasing and C _w is decreasing since C _O (0, t) and D ₀ are decreasing.

Δr _L reflects the effect of the additive on the flow battery negative side electrolyte system and Δr _w reflects the functional level of the additive. Namely, comparing the difference values is helpful for understanding the influence of different additives on the electrolyte system of the negative electrode side of the flow battery, and the effect and the capability of the different additives on inhibiting the discharge behavior of active material ions in the original system of the negative electrode side of the flow battery on the surface charge of the negative electrode; the additive (conductive salt) is thoroughly mixed with the negative side electrolyte and circulated with the liquid flow into the negative side cavity of the stack, after a period of time, the mixed solution enters the steady-state mass transfer process in the negative side cavity (the concentration of the whole negative side electrolyte system and the diffusion coefficient of the active substance are increased, thereby leading to an increase in the concentration of the reactant at the electrode surface and the diffusion coefficient of the reactant, i.e., C _O (0, t) and D ₀ are increased).

The size of the electrolyte resistance in the negative side lumen will change from R _L to R _L',R_L and R _L' compared to the electrolyte without the additive, depending on the effect of the flow battery negative side electrolyte system on the ease of charge transfer before and after the addition of the additive, where it is apparent that the additive (conductive salt) can increase the ability of the electrolyte system to transfer charge, resulting in a smaller electrolyte resistance, i.e., R _L'<R_L. As the resistance of the electrolyte on the negative side of the flow battery decreases, the concentration polarization level near the electrode also decreases, i.e., at this time the reactant concentration polarization resistance R _w on the surface of the negative side electrode becomes R _w ', the concentration capacitance C _w becomes C _w', and R _w'<R_w,C_w'>C_w (for the incomplete reversible electrode reaction, there is: The mass transfer level of the negative electrode side electrolyte and the mass transfer level of the electrode surface reactant are unchanged. In the case where w is unchanged, R _w is decreasing and C _w is increasing, since C _O (0, t) and D ₀ are increasing.

Δr _L reflects the effect of the additive on the flow battery negative side electrolyte system and Δr _w reflects the functional level of the additive. That is, comparing the above differences helps to understand the effect of different additives on the electrolyte system of the negative electrode side of the flow battery, and understand the effect and capability of different additives in promoting the charge discharging behavior of active material ions on the surface of the negative electrode in the original system of the negative electrode side of the flow battery, and understand the effect and capability of different additives in promoting the uniform distribution of current on the surface of the electrode plate of the negative electrode.

Specifically, additives (complexing agents, inhibitors) are used to influence the effect of the negative side metal deposition during charging and compare the electrodeposition accumulation of the negative side electrode plate (with the same current density) over multiple charging events:

(1) And (3) carrying out electrochemical impedance spectrum analysis on the negative electrode when the same charging time (t, t+delta t) passes (namely, the preset charging time length of each charging and discharging cycle in the charging and discharging test process).

In this process, by fully mixing the additive (complexing agent/inhibitor) with the negative electrode side electrolyte, the complexing agent/inhibitor is used for inhibiting the charge discharge behavior of active material ions in the original system on the negative electrode side of the flow battery on the surface of the negative electrode, so that the concentration of the reactant on the surface of the electrode and the diffusion coefficient of the reactant are reduced, namely, the concentration of C _O (0, t) and the diffusion coefficient of D ₀ are reduced. I.e. before and after the addition of complexing agent/inhibitor, the discharge behavior of the active substance at the electrode surface has a maximum.

As the metal deposition layer builds up on the electrode surface, the charge transfer resistance R _t during the electrode gradually increases to R _t', i.e., Δr _t(R_t'-R_t) becomes larger. In this process, the cumulative thickness of the metal deposition layer per unit time is not uniform. In the early stages of the process, the efficiency of charge transfer is high and the thickness of metal deposited per unit time is high. However, as the metal deposition layer is accumulated, the charge transfer resistance R _t in the electrode process gradually increases, the charge transfer efficiency gradually decreases, and the thickness of the metal deposition per unit time gradually decreases. The difference between the different additives (complexing agent/inhibitor) and the difference between the change value DeltaR _t of the charge transfer resistance in the unit time t and the t+Deltat reflects the difference of the capability of the additives (complexing agent/inhibitor) exists in the capability of reducing the concentration of the reactant and the diffusion coefficient of the reactant on the surface of the electrode.

A larger R _t' indicates a more relaxed accumulation of metal deposit during the (0, t) time period, and a larger ΔR _t indicates a higher level of charge transfer efficiency reduction during the Δt time period. C _d' is larger, which means that the metal deposition layer is loosely accumulated in the period of (0, t), the specific surface area is larger, and the corresponding electric double layer capacitance value is larger. The larger Δc _d indicates a more loose accumulation of the metal deposit during the Δt time period and a larger specific surface area. The corresponding additives (complexing agents/inhibitors) have a poor ability to reduce the concentration of the reactant and the diffusion coefficient of the reactant at the electrode surface.

(2) At the end of charge (i.e., at a preset time within the end-of-charge period of each charge-discharge cycle described above). When the electrochemical impedance spectrum analysis is performed on the cathode side electrode under a certain same charge state, the comprehensive concentration of the cathode side electrolyte at the moment changes due to the change of the additive (complexing agent/inhibitor), and the specific change of the concentration of the electrolyte system (R _L and R _L') depends on the difficulty of charge transfer of the cathode side electrolyte system of the flow battery before and after the addition of the additive (can be quantified through experiments).

The complexing agent/inhibitor is used for inhibiting charge and discharge behaviors of active material ions in an original system at the negative electrode surface of the flow battery, and the ion quantity participating in metal deposition at the negative electrode side is reduced along with the reduction of the electrolyte concentration at the electrode surface. The change in charge transfer resistance Δr _t reflects the degree of densification of the metal deposition layer on the electrode surface. When the metal deposition layer is not dense enough, the change value Δr _t of the charge transfer resistance corresponding to the layer is larger. When a porous structure-like loose layer appears on the metal deposition layer, the change value delta C _d of the electric double layer capacitor formed by the electrode and the metal deposition layer is larger, and the corresponding additive (complexing agent/inhibitor) has poor capability of reducing the concentration level of the interface solution of the electrode and the electrolyte.

(3) At the end of the first charge-discharge cycle (i.e., at the end of the first charge-discharge cycle). In the initial and final stages of the first charge-discharge cycle (SOC: 0%), electrochemical impedance spectroscopy analysis was performed on the negative electrode, and the initial corresponding electrochemical impedances (including the electrolyte resistance R _L0 of the negative original electrolyte system and the electrolyte resistances R _L0')R_L0、R_L0'、R_t0 and C _d0 after adding the complexing agent/inhibitor and mixing, and the final corresponding electrochemical impedances R _L'、R_t ' and C _d ' and the differences DeltaR _L、ΔR_L'、ΔR_t and DeltaC _d. It is understood that DeltaR _t and DeltaC _d reflect the metal deposit and the thickness and porosity thereof remaining on the negative electrode plate after one charge-discharge cycle. DeltaR _L reflects the influence of the complexing agent/inhibitor on the negative original electrochemical system. DeltaR _L ' is related to the detachment of the metal deposit material from the one cycle into the electrolyte system, and once the metal deposit is in the flow cycle, it is difficult to be reused, and thus the loose metal deposit is more likely to appear a phenomenon that the metal deposit is detached from the flow cycle, thus reflecting the ability and effect of the additive (complexing agent, inhibitor).

(4) At the end of the multiple charge-discharge cycles (i.e., at the end of the preset number of charge-discharge cycles). In the initial stage of the first charge-discharge cycle and the final stage of the multiple charge-discharge cycles (SOC: 0%), electrochemical impedance spectrum analysis is performed on the negative electrode, and electrochemical impedance corresponding to the initial stage (including electrolyte resistance R _L0 of the original electrolyte system on the negative electrode side and electrolyte resistances R _L0')R_L0、R_L0'、R_t0 and C _d0 after adding complexing agent/inhibitor and mixing, and electrochemical impedance corresponding to the final stage R _L"、R_t "and C _d" and differences Δr _L"、ΔR_t 'and Δc _d' between them are measured, it is understood that Δr _t 'and Δc _d' reflect the fact that the metal deposit layer accumulated on the negative electrode plate after the multiple charge-discharge cycles and its thickness and porosity are related to the accumulation of the metal deposit layer substance in the multiple cycles, and that the metal deposit is difficult to be reused once it becomes one of the causes of energy attenuation of the flow battery.

Specifically, the effect of the negative side metal deposition during charging was affected using an additive (conductive salt), and the electrodeposition accumulation condition of the negative side electrode plate during charging was compared (the same current density was adopted):

During this process (by thorough mixing of the additive (conductive salt) with the negative side electrolyte, the concentration of the whole negative side electrolyte system and the diffusion coefficient of the active substance increase to another level, resulting in an increase of the concentration of the electrode surface reactant and the diffusion coefficient of the reactant to another level, i.e. C _O (0, t) and D ₀ are increasing, the discharge behaviour of the active substance at the electrode surface presents a best match of the electrode nearby electrolyte concentration and electrode current density) as the metal deposit builds up on the electrode surface, the charge transfer resistance R _t during the electrode gradually increases to R _t', i.e. Δr _t(R_t'-R_t becomes larger. In this process, the cumulative thickness of the metal deposition layer per unit time is not uniform. In the early stages of the process, the efficiency of charge transfer is high and the thickness of metal deposited per unit time is high. However, as the metal deposition layer is accumulated, the charge transfer resistance R _t in the electrode process gradually increases, the charge transfer efficiency gradually decreases, and the thickness of the metal deposition per unit time gradually decreases.

The difference between the different additives (conductive salts) reflects the difference in the ability of the additives (conductive salts) to increase the concentration of the reactants at the electrode surface and the diffusion coefficient of the reactants, the difference in the change in charge transfer resistance ΔR _t per unit time t and t+Δt time. A larger R _t' indicates a more relaxed accumulation of metal deposit during the (0, t) time period, and a larger ΔR _t indicates a higher level of charge transfer efficiency reduction during the Δt time period. C _d' is larger, which means that the metal deposition layer is loosely accumulated in the period of (0, t), the specific surface area is larger, and the corresponding electric double layer capacitance value is larger. The larger Δc _d indicates a more loose accumulation of the metal deposit during the Δt time period and a larger specific surface area. The corresponding additive (conductive salt) has poor ability to increase the concentration of the reactant and the diffusion coefficient of the reactant at the electrode surface.

(2) At the end of charge (i.e., at a preset time within the end-of-charge period of each charge-discharge cycle described above). When the anode side electrode is in a certain same charge state, the electrochemical impedance spectrum analysis is carried out on the anode side electrode, and then the comprehensive concentration of the anode side electrolyte is increased due to the additive (conductive salt), namely the electrolyte resistance R _L' is reduced, and the ion quantity participating in metal deposition of the anode side electrode is increased along with the increase of the concentration of the electrolyte on the electrode surface. The change in charge transfer resistance Δr _t reflects the degree of densification of the metal deposition layer on the electrode surface. When the metal deposition layer is not dense enough, the change value Δr _t of the charge transfer resistance corresponding to the layer is larger. When a porous structure-like loose layer appears on the metal deposition layer, the change value delta C _d of the electric double layer capacitor formed by the electrode and the metal deposition layer is larger, and the corresponding additive (conductive salt) has poor capability of improving the concentration level of the interface solution of the electrode and the electrolyte.

(3) At the end of the first charge-discharge cycle (i.e., at the end of the first charge-discharge cycle). Electrochemical impedance spectrum analysis was performed on the negative electrode at the initial stage and the final stage (SOC: 0%) of the first charge-discharge cycle, and electrochemical impedances corresponding to the initial stage (including the electrolyte resistance R _L0 of the negative electrode-side original electrolyte system and the electrolyte resistances RL0 ') R _L0、R_L0'、R_t0 and C _d0 after addition of the conductive salt and mixing, and electrochemical impedances corresponding to the final stage R _L'、R_t ' and C _d ' and differences Δr _L、ΔR_L'、ΔR_t and Δc _d of both were measured. It is understood that Δr _t and Δc _d reflect the metal deposition layer remaining on the negative electrode plate after one charge-discharge cycle and the thickness and porosity thereof. DeltaR _L reflects the influence of the conductive salt on the original electrochemical system at the negative electrode side, deltaR _L' is related to the separation of the metal deposition layer substances from the electrolyte system in one cycle, and once the metal deposition substances enter the liquid flow cycle, the metal deposition substances are difficult to reuse, so that the metal deposition substances become one of the reasons of energy attenuation of the flow battery. Loose metal deposits are more prone to metal deposit detachment into the flow cycle, reflecting the additive (conductive salt) capability and effect.

(4) At the end of the multiple charge-discharge cycles (i.e., at the end of the preset number of charge-discharge cycles). In the initial stage of the first charge-discharge cycle and the final stage of the multiple charge-discharge cycles (SOC: 0%), electrochemical impedance spectrum analysis is performed on the negative electrode side electrode, and electrochemical impedance corresponding to the initial stage (including electrolyte resistance R _L0 of the original electrolyte system on the negative electrode side and electrolyte resistances R _L0')R_L0、R_L0'、R_t0 and C _d0 after adding conductive salt and mixing, and electrochemical impedance corresponding to the final stage R _L"、R_t "and C _d" and differences Δr _L"、ΔR_t 'and Δc _d' between them) is measured, where Δr _t 'and Δc _d' reflect the fact that the metal deposit layer accumulated on the negative electrode plate after the multiple charge-discharge cycles and its thickness and porosity are related to the accumulation and detachment of the metal deposit layer substance in the multiple cycles into the electrolyte system, and the metal deposit is difficult to be reused once it becomes one of the causes of energy attenuation of the flow battery.

The control method of the zinc-based flow battery test device provided by the embodiment of the invention has the same technical characteristics as the zinc-based flow battery test device provided by the embodiment, so that the same technical problems can be solved, and the same technical effects can be achieved.

The embodiment of the invention also provides a zinc-based flow battery, wherein a target additive is added into the negative electrode side electrolyte of the zinc-based flow battery, and the components of the target additive are determined by an optimal additive formula, wherein the optimal additive formula is the optimal additive formula of the corresponding negative electrode side electrolyte determined by the zinc-based flow battery test device in any embodiment.

The target additive in the negative electrode side electrolyte of the zinc-based flow battery provided by the embodiment of the invention is determined by using the optimal additive formula of the corresponding negative electrode side electrolyte determined by the zinc-based flow battery test device in the embodiment, so that the zinc-based flow battery provided by the embodiment of the invention also has the beneficial effects described in the embodiment, and the description is omitted here.

In the description of embodiments of the present invention, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.

Finally, it should be noted that the foregoing description is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, while the invention has been described in connection with the above embodiments, the invention is not limited to the embodiments, but may be embodied in many other equivalent forms without departing from the spirit or scope of the invention, which is set forth in the following claims.

Claims

1. The zinc-based flow battery test device is characterized by being used for testing the metal deposition effect of the cathode side of a target electric pile, wherein the target electric pile comprises a flow battery unit, and the test device comprises a flow battery management system, an electrochemical workstation, a power supply system and a flow battery circulating system;

2. The zinc-based flow battery test device of claim 1, wherein the flow battery circulation system further comprises a deionized water reservoir;

the deionized water liquid storage tank is connected with the negative electrode side cavity of the target electric pile through a corresponding circulating pipeline and is used for cleaning the negative electrode side cavity of the target electric pile and the corresponding circulating pipeline before the target liquid storage tank communicated with the negative electrode side cavity of the target electric pile is replaced each time under the control of the flow battery management system.

3. The zinc-based flow battery test device of claim 2, wherein the flow battery circulation system further comprises a plurality of pairs of electrically controlled inlet valves and electrically controlled outlet valves;

one of the negative side liquid storage tanks is correspondingly provided with a pair of electric control liquid inlet valves and an electric control liquid outlet valve; the pair of the electric control liquid inlet valves and the electric control liquid outlet valve are used for being opened under the control of the flow battery management system so that the negative electrode side liquid storage tank is communicated with the negative electrode side cavity of the target electric pile, and mixed liquid in the negative electrode side liquid storage tank flows through the negative electrode side cavity of the target electric pile and returns to the negative electrode side liquid storage tank;

The deionized water liquid storage tank is correspondingly provided with two pairs of the electric control liquid inlet valves and the electric control liquid outlet valves; the pair of electric control liquid inlet valves and the pair of electric control liquid outlet valves are used for being opened under the control of the flow battery management system so that the deionized water liquid storage tank is communicated with the negative electrode side cavity of the target electric pile, deionized water in the deionized water liquid storage tank flows through the negative electrode side cavity of the target electric pile and then returns to the deionized water liquid storage tank, and the other pair of electric control liquid inlet valves and the electric control liquid outlet valves are used for realizing the communication between the deionized water liquid storage tank and the external liquid supplementing-changing system.

4. The zinc-based flow battery test device according to claim 3, wherein the positive electrode side liquid storage tank is correspondingly provided with the electric control liquid outlet valve, and the electric control liquid outlet valve is used for being opened under the control of the flow battery management system, so that positive electrode electrolyte in the positive electrode side liquid storage tank flows into the positive electrode side chamber of the target electric pile and then flows back into the positive electrode side liquid storage tank.

5. The zinc-based flow battery test device of claim 3, wherein the flow battery circulation system further comprises a first circulation pump, a negative side filter, a first pressure transmitter, a second pressure transmitter, and a first flow sensor;

one end of the first circulating pump is respectively connected with the negative electrode side liquid storage tank and the deionized water liquid storage tank through the electric control liquid outlet valves; the other end of the first circulating pump is connected with the negative electrode side of the target electric pile through the negative electrode side filter;

The first pressure transmitter is arranged between the negative electrode side filter and a negative electrode side chamber inlet of the target electric pile; the second pressure transmitter is arranged between each electric control liquid inlet valve and the outlet of the negative side cavity of the target pile; the difference between the measurements of the first pressure transmitter and the second pressure transmitter is used to characterize the pressure loss of the negative side chamber of the target stack;

the first flow sensor is disposed between the negative side filter and a negative side chamber inlet of the target stack for measuring a mixed liquid flow through the negative side chamber of the target stack.

6. The zinc-based flow battery test device of claim 4, wherein the flow battery circulation system further comprises a second circulation pump, a positive side filter, a third pressure transmitter, a fourth pressure transmitter, and a second flow sensor;

one end of the second circulating pump is connected with the positive electrode side liquid storage tank through the electric control liquid outlet valve; the other end of the second circulating pump is connected with the positive electrode side of the target pile through the positive electrode side filter;

the third pressure transmitter is arranged between the positive electrode side filter and a positive electrode side cavity inlet of the target electric pile; the fourth pressure transmitter is arranged between the inlet of the positive electrode side liquid storage tank and the positive electrode side chamber outlet of the target electric pile; the difference between the measurements of the third pressure transmitter and the fourth pressure transmitter is used to characterize the pressure loss of the positive side chamber of the target stack;

The second flow sensor is arranged between the positive electrode side filter and the positive electrode side chamber inlet of the target electric pile and is used for measuring the flow of positive electrode electrolyte passing through the positive electrode side chamber of the target electric pile.

7. The zinc-based flow battery test apparatus of claim 4, further comprising a stack placement tray and a plurality of water bath trays;

The target electric stack is arranged on the electric stack placing tray; the negative electrode side liquid storage tanks, the deionized water liquid storage tanks and the positive electrode side liquid storage tanks are respectively arranged on one water bath tray;

the test device further comprises a plurality of liquid leakage sensors;

the liquid leakage sensors are arranged on the pile placing tray and the outer sides of the water bath trays in a one-to-one correspondence manner;

The water bath tray is used for controlling the temperature of the liquid in the negative electrode side liquid storage tank, the deionized water liquid storage tank and the positive electrode side liquid storage tank.

8. The zinc-based flow battery test device of claim 3, further comprising an external fluid replacement system;

the external liquid supplementing-changing system is connected with the deionized water liquid storage tank;

The electric control liquid inlet valve is arranged between the inlet of the deionized water liquid storage tank and the external liquid supplementing-changing system, and the electric control liquid outlet valve is arranged between the outlet of the deionized water liquid storage tank and the external liquid supplementing-changing system; a third circulating pump is arranged between the electric control liquid outlet valve and the external liquid supplementing-changing system;

The external liquid supplementing-changing system is used for supplementing liquid to the deionized water liquid storage tank and periodically changing deionized water in the deionized water liquid storage tank.

9. A control method of a zinc-based flow battery test device, the control method comprising:

10. The method of controlling a zinc-based flow battery test apparatus according to claim 9, wherein each of the charge and discharge tests includes a predetermined number of charge and discharge cycles, and wherein obtaining the electrochemical impedance spectrum of the negative side of the target stack during each of the charge and discharge tests includes:

the electrochemical workstation obtains electrochemical impedance spectrums of the cathode side of the target pile at the following moments in the process of each charge and discharge test:

When the preset charging time length of each charging and discharging cycle in each charging and discharging test process is longer than the preset charging time length; a preset time in a charge end period of each charge-discharge cycle; when the first charge-discharge cycle is finished; and when the charging and discharging cycles of the preset times are finished.

11. A zinc-based flow battery, characterized in that a target additive is added into a negative electrode side electrolyte of the zinc-based flow battery, and the composition of the target additive is determined by an optimal additive formula, wherein the optimal additive formula is determined by the zinc-based flow battery test device according to any one of claims 1 to 8.