CN118336040A

CN118336040A - Zinc-based flow battery test device, control method and zinc-based flow battery

Info

Publication number: CN118336040A
Application number: CN202410471609.0A
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 each flow battery monomer in a target pile, and a power supply system performs charge and discharge tests for the target pile for preset times under the control of a flow battery management system; the flow battery management system controls the on-off and switching of each switch unit in the switch module in each charge and discharge test process so as to replace and connect different flow battery monomers; in the process of each charge and discharge test, when the connected flow battery cells are replaced, the electrochemical workstation acquires the electrochemical impedance spectrum of the negative side of each flow battery cell in the target pile; and the flow battery management system compares the metal deposition effect of the cathode side of each flow battery cell in the target electric pile based on the received electrochemical impedance spectrum analysis, and finally determines the optimal cathode side functional device selection scheme of the target electric pile. The invention realizes the technical effects of parallel analysis and rapid screening aiming at the functional device scheme which needs to be added on the negative 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. 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.

The maximum current density of the current mainstream vanadium redox flow battery reaches 120mA/cm ² (i.e. 1200A/m ²), and is generally in the range of 15-80 mA/cm ² (i.e. 150-800A/m ²). If the zinc-iron flow battery is based on the current density and the current density in the charging process is considered to be further improved, the negative electrode side (zinc side) of the flow battery of the system cannot work in the Tafil region even if an additive is used, and the high current density in the charging process is necessarily in the mixed control region of the Tafil curve. Thus, in addition to the improvement of the electrochemical polarization level of the electrode, the improvement of the diffusion level of the electrolyte (i.e., the improvement of the mass transfer level of the electrolyte in the stack) is considered for the zinc-based flow battery, so that it is possible to obtain a cathode metal deposit with fine and compact crystals.

Therefore, in order to effectively obtain the cathode metal deposit with fine and compact crystals, a functional device capable of improving the diffusion level (mass transfer level) of the electrolyte at the cathode electrode side needs to be found, and a test device for parallel analysis and rapid screening of relevant characteristic parameters is needed.

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 aiming at a functional device scheme to be added on the negative 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 tests a metal deposition effect on a negative side of each flow battery cell in a target stack, where the target stack is composed of a first number of flow battery cells, a functional device is disposed at a negative plate of each flow battery cell, and the functional device of each flow battery cell has a respective structural form, a functional parameter, a kind, and a material, and the kind of the functional device includes at least one of: a negative electrode multi-level hole electrode and a multi-level space structure;

The test device comprises a flow battery management system, an electrochemical workstation, a power supply system, a switch module and a flow battery circulation system; the flow battery circulating system comprises a negative electrode side liquid storage tank, a positive electrode side liquid storage tank and corresponding circulating pipelines;

The flow battery management system is respectively connected with the electrochemical workstation, the switch module and the power supply system; the positive electrode and the negative electrode of the power supply system are respectively and electrically connected with a positive electrode current collecting plate and a negative electrode current collecting plate of the target electric pile through wires;

The switch module comprises two groups of switch units, each group of switch units are connected in parallel, one group of switch units are respectively used for realizing the connection between the electrochemical workstation and one side of a bipolar plate and a negative electrode of each flow battery cell, the other group of switch units are respectively used for realizing the connection between the electrochemical workstation and a counter electrode of each flow battery cell, the counter electrode of each flow battery cell is arranged in a cavity on the negative electrode side of each flow battery cell, the bipolar plate of each flow battery cell is electrically connected with an anode electrode and a cathode electrode, and a pair of switch units correspondingly connected with one flow battery cell are simultaneously connected and disconnected;

The negative electrode side liquid storage tank is communicated with a negative electrode side cavity of each flow battery cell in the target electric pile, and negative electrode electrolyte in the negative electrode side liquid storage tank uniformly flows through the negative electrode side cavity of each flow battery cell through the circulating pipeline and returns to the negative electrode side liquid storage tank under the control of the flow battery management system; the positive electrode side liquid storage tank is communicated with a positive electrode side cavity of each flow battery cell in the target electric pile, and positive electrode electrolyte in the positive electrode side liquid storage tank uniformly flows through the positive electrode side cavity of each flow battery cell through the circulating pipeline and returns to the positive electrode side liquid storage tank under the control of the flow battery management system;

The power supply system is used for carrying out charge and discharge tests on the target pile for preset times under the control of the flow battery management system;

In the process of each charge and discharge test, the electrochemical workstation controls the on-off and the switching of each switch unit in the switch module through the flow battery management system under the control of the flow battery management system, the connected flow battery monomers are replaced, and the electrochemical workstation acquires the electrochemical impedance spectrum of the negative side of each flow battery monomer in the target electric pile and transmits the electrochemical impedance spectrum to the flow battery management system;

The flow battery management system is further used for comparing the metal deposition effect of the cathode side of each flow battery cell in the target electric pile based on the received electrochemical impedance spectrum analysis, and finally determining the optimal cathode side functional device selection scheme of the target electric 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 power supply system performs a preset number of charge and discharge tests on a target electric pile under the control of the flow battery management system, wherein the target electric pile is composed of a first number of flow battery monomers, functional devices are arranged at negative plates of each flow battery monomer, each functional device of each flow battery monomer has a respective structural form, functional parameters, types and materials, and the types of the functional devices comprise at least one of the following: a negative electrode multi-level hole electrode and a multi-level space structure;

In the process of each charge and discharge test, an electrochemical workstation controls the on-off and the switching of each switch unit in the switch module through the flow battery management system under the control of each flow battery management system, the connected flow battery monomers are replaced, and the electrochemical workstation acquires the electrochemical impedance spectrum of the negative side of each flow battery monomer in the target electric pile and transmits the electrochemical impedance spectrum to the flow battery management system;

The flow battery management system compares the metal deposition effect of the cathode side of each flow battery cell in the target electric pile based on the received electrochemical impedance spectrum analysis, and finally determines the optimal cathode side functional device selection scheme of the target electric pile.

In a third aspect, an embodiment of the present invention further provides a zinc-based flow battery, where the zinc-based flow battery includes a plurality of flow battery monomers, and a functional device is disposed at a negative plate of each flow battery monomer, and the types of the functional devices include at least one of the following: a negative electrode multi-level hole electrode and a multi-level space structure;

The functional device is determined by an optimal negative side functional device selection scheme, wherein the optimal negative side functional device selection scheme is a corresponding optimal negative side functional device selection scheme determined by using the zinc-based flow battery test device in any embodiment.

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 each flow battery monomer in a target pile, and a power supply system performs charge and discharge tests for the target pile for preset times under the control of a flow battery management system; the flow battery management system controls the on-off and switching of each switch unit in the switch module in each charge and discharge test process so as to replace and connect different flow battery monomers; in each charge and discharge test process, the electrochemical workstation acquires the electrochemical impedance spectrum of the negative side of each flow battery cell in the target pile when the connected flow battery cell is replaced; and the flow battery management system compares the metal deposition effect of the cathode side of each flow battery cell in the target electric pile based on the received electrochemical impedance spectrum analysis, and finally determines the optimal cathode side functional device selection scheme of the target electric pile. The invention realizes the technical effects of parallel analysis and rapid screening aiming at the functional device scheme which needs to be added on the negative 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 enlarged view of a portion of a zinc-based flow battery test apparatus according to an embodiment of the present invention;

FIG. 3 is a partial enlarged view of a target stack tested by a zinc-based flow battery test device according to an embodiment of the present invention;

fig. 4 (a) is a schematic diagram illustrating the structure of integrating a bipolar plate and an electrode plate of a first flow battery according to an embodiment of the present invention;

fig. 4 (b) is a schematic diagram illustrating the structure of the bipolar plate and electrode plate integrated structure of the second flow battery according to the embodiment of the present invention;

Fig. 4 (c) is a schematic diagram illustrating the structure of integrating a bipolar plate and an electrode plate of a third flow battery according to an embodiment of the present invention;

Fig. 4 (d) is a schematic diagram illustrating the structure of integrating a bipolar plate and an electrode plate of a fourth flow battery according to an embodiment of the present invention;

fig. 4 (e) is a schematic diagram illustrating the structure of integrating a bipolar plate and an electrode plate of a fifth flow battery according to an embodiment of the present invention;

FIG. 5 is an equivalent circuit diagram of an electrode provided by an embodiment of the present invention;

FIG. 6 is a schematic view of an electrolytic cell provided by an embodiment of the invention;

FIG. 7 is a schematic illustration of a galvanic cell according to an embodiment of the invention;

fig. 8 is a complex plan view of electrochemical impedance over a full frequency range provided by an embodiment of the present invention.

1-A bipolar plate; 2-a negative electrode plate; 3-a positive electrode plate; 4-a first electrolyte solution; 5-a second electrolyte solution; 6-conducting blocks for fixedly connecting the electrode plates and the bipolar plates; 7-a negative electrode hierarchical pore electrode; 8-an anode multi-level hole electrode; 9-a negative electrode side multilayer spatial structure; 10-positive electrode side multilayer space structure; s1-surface area of the electrode side of the electrochemical reaction between the negative electrode plate and the first electrolyte solution; the surface area of the electrode side of the electrochemical reaction between the S1' -positive electrode plate and the second electrolyte solution; s2-adding a conductive block, and then adding the surface area of the other side of the electrode of the electrochemical reaction between the negative electrode plate and the first electrolyte solution; s2' -the surface area of the other side of the electrode of the electrochemical reaction between the positive electrode plate and the second electrolyte solution after the conductive block is added; s3, adding a conductive body, and then adding the surface area of one side of the bipolar plate close to the negative electrode plate; s3' -adding the surface area of one side of the bipolar plate close to the positive electrode plate after the electric conductor; s4-specific surface area of the hierarchical pore electrode at one side of the negative electrode plate; specific surface area of the multistage pore electrode on one side of the S4' -positive electrode plate; 21-flow battery management system, 22-electrochemical workstation, 23-power system, 24-switch module, 25-flow battery circulation system; 251-negative side reservoir; 252-positive side reservoir; 253-a first electrically controlled valve; 254-a second electrically controlled valve; 26-target galvanic pile; 26-1-pile front end plate; 26-2-pile rear end plate; 26-3-negative side current collector plate; 26-4-positive electrode side current collector plate; 26-5-flow battery cell; 26-6-ion exchange membrane; 26-7-function devices; 27-1-a first circulation pump; 28-1-negative side filter; 27-2-a second circulation pump; 28-2-positive side filter; 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; 29-1-stacking trays; 29-2-liquid storage tank tray; 31-1-a first thermocouple thermometer; 32-1-a first level sensor; 33-1-a first electric heater; 34-1-a first pressure relief valve; 31-2-a second thermocouple thermometer; 32-2-a second level sensor; 33-2-a second electric heater; 34-2-a second pressure relief valve; 35-a liquid leakage sensor; 36-a heat preservation layer at the periphery of the liquid storage tank.

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.

According to the above description, the mass transfer efficiency of the contact interface between the electrode and the electrolyte is improved, so that the reactive ions in the electrolyte can more easily reach the surface of the electrode, and the concentration of the reactive ions in the electrolyte (particularly in the later stage of charging, particularly in the upper half area of the electrode plate) is improved, so as to reduce the concentration polarization phenomenon near the electrode (in the direction parallel to the electrode plate and in the direction perpendicular to the electrode plate); the current density passing through the negative electrode during charging is improved and is matched with the concentration of electrolyte active substance ions required by each stage in the process, so that the phenomenon that the concentration polarization phenomenon on the surface of the electrode is caused because the number (concentration) of the active substance ions in the electrolyte cannot be matched in time under the condition of high current density charging at the moment is avoided, and zinc dendrite is generated in the electrodeposition process.

In practice, it is understood that the concentration of each active material in the negative electrode side electrolyte is increased, particularly at the end of charging. Namely, under the condition that a saturated electrolyte solution is obtained on the negative electrode side, the storage capacity of the electrolyte on the negative electrode side is improved (so that the storage capacity is larger than the total capacity of the electrolyte on the negative electrode side required by the rated full charge process), the concentration of zinc ions (Zn ²⁺) in the electrolyte at the end of charging is improved, and the contact frequency and the contact effect of the zinc ions and a negative electrode plate are improved; the multi-layer space structure body with the function of a static mixer is arranged near the negative electrode plate to change the mixing and mass transfer state of the negative electrode electrolyte in the space of the galvanic pile, so that the contact frequency and the contact effect of zinc ions and the negative electrode plate are improved; the flow rate of the liquid flow circulation of the negative electrode side in the later stage of charging is improved, so that the quantity of zinc ions entering the inner cavity of the pile along with electrolyte in unit time is improved, and the contact frequency of the zinc ions and the electrode plate of the negative electrode side is improved; in the electrode plate manufacturing process, the flatness and roughness of the electrode plate (the substrate and the coating thereof) are strictly controlled, so that machining defects such as sharp angles, burrs, scratches and the like are avoided, artificial protrusions, sharp positions or areas are avoided, and the boundary (edge) of the electrode plate is subjected to insulation protection treatment, so that zinc deposition is avoided from excessively accumulating or irregularly growing in the areas.

When the current density of the negative electrode is increased, the contact area (contact interface) between the electrode and the electrolyte is limited, so that the number of active substances in the electrolyte actually contacted with the electrode plate cannot be matched with the high current density, and concentration polarization phenomenon is easily generated on the contact interface. According to the principle of a microporous vortex mixing reactor, a multipolar hole electrode is used for replacing a flat electrode, so that the reaction site of a negative electrode side electrode is improved, meanwhile, the flow state of electrolyte flowing through the electrode is changed by changing the shape of the multipolar hole electrode, the mass transfer efficiency of the electrolyte in the electrode is enhanced, and the problem of limited capacity of the negative electrode side surface is solved; the problem that the concentration of reactive ions of the electrolyte is matched under the high current density of the negative electrode is solved, so that the concentration polarization phenomenon of the surface of the electrode is relieved, and zinc dendrite is generated in the electrodeposition process; the hydrogen evolution potential can be simultaneously improved by changing the proportion, structural components or surface constitution and the like of the electrode materials, so that the effective working voltage of the flow battery is effectively improved (for example, the potential of hydrogen generated by electrochemical reaction of the anode can be reduced to about-1.0V by changing the inert electrode into porous active carbon with high specific surface area). The multipolar pore electrode can provide larger specific surface area and specific volume than the flat electrode, so that more active substances in the electrolyte can be contained into the multipolar pore electrode, and the internal space structure of the multipolar pore electrode is used as a reaction bed to perform electrochemical reaction with the multipolar pore electrode. The electrodeposition and electrolysis process of zinc will also be completed inside the multipolar pore electrode.

Fig. 1 is a structural diagram of a zinc-based flow battery test device provided by an embodiment of the invention. Fig. 2 is a partial enlarged view of a zinc-based flow battery test device according to an embodiment of the present invention. Fig. 3 is a partial enlarged view of a target stack tested by the zinc-based flow battery test device according to the embodiment of the invention. The zinc-based flow battery test device is used for testing the metal deposition effect of the cathode side of each flow battery cell 26-5 in the target electric pile 26, wherein the tested target electric pile 26 consists of a first number of flow battery cells, the negative plate of each flow battery cell 26-5 is provided with a functional device 26-7, the functional devices 26-7 of each flow battery cell 26-5 have respective structural forms, functional parameters, types and materials, and the types of the functional devices 26-7 comprise at least one of the following: a cathode multi-level hole electrode and a multi-level space structure.

As shown in fig. 1-3, the zinc-based flow battery test device comprises a flow battery management system 21, an electrochemical workstation 22, a power supply system 23, a switch module 24 and a flow battery circulation system 25; the flow battery circulation system 25 includes a negative electrode side liquid storage tank 251, a positive electrode side liquid storage tank 252, and corresponding circulation pipes; the flow battery management system 25 is respectively connected with the electrochemical workstation 22, the switch module 24 and the power supply system 23; the positive and negative poles of the power supply system 23 are electrically connected with the positive and negative pole current collecting plates 26-4 and 26-3 of the target stack 26, respectively, by wires.

The switch module 24 includes two groups of switch units, each group of switch units are connected in parallel, one group of switch units is respectively used for realizing connection between the electrochemical workstation 22 and one side of the bipolar plate 1 and the negative electrode 2 of each flow battery cell 26-5, the other group of switch units is respectively used for realizing connection between the electrochemical workstation 22 and the opposite electrode of each flow battery cell 26-5, the opposite electrode of the flow battery cell 26-5 is arranged in the cavity of the negative electrode side of the flow battery cell 26-5, the bipolar plate 1 of each flow battery cell 26-5 is electrically connected with the positive electrode plate 3 and the negative electrode plate 2, and a pair of switch units correspondingly connected with one flow battery cell 26-5 are simultaneously turned on and turned off.

The negative electrode side liquid storage tank 251 is communicated with the negative electrode side chamber of each flow battery cell in the target stack 26, and the negative electrode electrolyte in the negative electrode side liquid storage tank 251 uniformly flows through the negative electrode side chamber of each flow battery cell through a circulation pipeline and returns to the negative electrode side liquid storage tank 251 under the control of the flow battery management system 21; the positive electrode side liquid storage tank 252 is communicated with the positive electrode side chamber of each flow battery cell in the target stack 26, and the positive electrode electrolyte in the positive electrode side liquid storage tank 252 uniformly flows through the positive electrode side chamber of each flow battery cell through a circulation pipeline and returns to the positive electrode side liquid storage tank 252 under the control of the flow battery management system 21.

The power supply system 23 is used for carrying out a preset number of charge and discharge tests on the target pile 26 under the control of the flow battery management system 21; in each charge and discharge test process, the electrochemical workstation 22 controls on-off and switching of each switch unit in the switch module 24 through the flow battery management system 21 under the control of the flow battery management system 21, and replaces the connected flow battery cells, and the electrochemical workstation 22 acquires the electrochemical impedance spectrum of the cathode side of each flow battery cell in the target stack 26 and transmits the electrochemical impedance spectrum to the flow battery management system 21; the flow battery management system 21 is further configured to compare the metal deposition effect on the negative side of each flow battery cell in the target stack 26 based on the received electrochemical impedance spectroscopy analysis, and ultimately determine an optimal negative side functional device selection scheme for the target stack 26.

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

Specifically, according to the principle of a microporous vortex mixing reactor and the principle of a static mixing reactor, in order to improve the functional device and the functional characteristics of the diffusion level (mass transfer level) of the electrolyte at the negative electrode side of the zinc-based flow battery, the mass transfer efficiency of the electrolyte at the negative electrode side in the inner cavity of the flow battery is improved, the capacity of bearing larger current density of the zinc-based flow battery is improved, concentration polarization in the charging and discharging process is reduced, and the energy storage capacity and maintenance-free capacity of the flow battery are improved through preparation and combination of a negative electrode multi-stage hole electrode and a multi-stage space structure (multi-stage three-dimensional fiber composite structure).

Therefore, with respect to the negative electrode side of the zinc-based flow battery, different negative electrode multi-level porous electrodes or multi-level spatial structures are adopted, and a test device as shown in fig. 1 needs to be established to compare, analyze and screen physical and morphological parameters of related materials of the functional device and the effect of the related materials on improving the diffusion level (mass transfer level) of the electrolyte at the negative electrode side and inhibiting zinc deposition.

Fig. 4 (a) - (e) are schematic diagrams illustrating the structure of bipolar plates and electrode plates of various flow batteries according to embodiments of the present invention. As shown in fig. 4 (a) - (e), the first electrolyte solution 4 and the second electrolyte solution 5 respectively flow through the two chambers of the respective battery cells on both sides of the ion exchange membrane 26-6, and undergo electrochemical oxidation-reduction reaction with the interfaces of the positive and negative electrodes. By using the preparation and recombination of the functional devices (i.e., the anode multi-level porous electrode and the multi-level spatial structure), the specific surface areas of the positive and negative electrodes themselves, the contact area (contact site) with the electrolyte solution, and the mass transfer efficiency (level) of the electrolyte solution flowing through the positive and negative electrode reaction regions can be improved. Therefore, the functional device arranged on the negative electrode side of the flow battery can effectively improve the electrolyte diffusion level of the negative electrode side of the flow battery and inhibit zinc deposition on the negative electrode side.

Specifically, as shown in fig. 1 and 2, the target stack 26 is composed of a plurality of flow battery cells 26-5, which include an ion exchange membrane 26-5, a bipolar plate 1, a positive electrode plate 3, a negative electrode plate 2, and functional devices 26-7. The functional device 26-7 is used to increase the active site of the negative electrode plate, to increase the level of mass transfer of the active material in the negative side electrolyte, and to increase the frequency of contact of the active material in the negative side electrolyte with the negative electrode. Thereby, a finer and denser metal deposition layer can be obtained in cooperation with the polarization level of the negative electrode 2.

The cathode electrode 2 of each flow cell 26-5 in the target stack 26 includes functional devices 26-7 with different structural forms and different functional parameter characteristics for parallel testing and analysis. The method comprises the steps of arranging counter electrodes (Counter Electrode, CE) in each flow battery cell 26-5, arranging an integrated structure of a bipolar plate 1 and a negative electrode 2 as a working electrode (Working electrode, WE), taking the negative electrode 2, electrolyte and a functional device 26-7 of each flow battery cell 26-5 as research objects, connecting the research objects with a power supply system 23 and an electrochemical workstation 22 (potentiometer/ammeter), obtaining the characteristics of a metal deposition layer on the negative electrode side of each flow battery cell 26-5 in the charging and discharging process of a target galvanic pile 26 through an electrochemical impedance spectroscopy method, wherein the characteristics comprise characteristic parameters such as a charge transfer resistor R _t, an electric double layer capacitor C _d, a solution resistor R _L, a concentration polarization resistor R _w, a concentration capacitor C _w and the like, and carrying out parallel test, comparison and analysis on each flow battery cell 26-5 to obtain an optimal negative electrode side functional device selection scheme.

Specifically, the flow battery management system 21 serves as a higher-level control system; the power supply system 23 also controls the flow battery management system 21 for the charge/discharge test of the target cell stack 26. The flow battery management system 21 can control on-off and switching of each switch unit in the switch module 24, and in each charge-discharge test process, when the connected flow battery cells 26-5 are replaced, the flow battery management system 21 also controls the electrochemical workstation 22 to obtain electrochemical impedance spectrums of the cathode side of each flow battery cell 26-5 in the target pile 26, namely, through the test function provided by the electrochemical workstation 22, electrochemical impedance spectrum data of the cathode side electrode (and the metal deposition layer) of the target pile 26, the counter electrode and the electrolyte system are measured, and corresponding electrochemical impedance spectrums are obtained; the final flow battery management system 21 determines the functional level of the different functional device schemes to suppress dendrites of the negative side metal deposition layer of the target stack 26 by comparing and analyzing the electrochemical impedance spectra.

Specifically, referring to fig. 2, the electrochemical workstation 22 includes a potentiometer/amperometer, a microcontroller unit, an arithmetic controller, a flow battery management unit, a current/potential feedback signal AD conversion unit, a potential/current scan signal DA conversion unit, and a display; the micro control unit, the flow battery management unit, the current/potential feedback signal AD conversion unit and the potential/current scanning signal DA conversion unit are electrically connected with the operation controller; the display is electrically connected with the flow battery management unit; the external input/output is electrically connected with the flow battery management unit; the potentiometer/current meter is respectively and electrically connected with the operation controller, the current/potential feedback signal AD conversion unit and the potential/current scanning signal DA conversion unit; the current/potential feedback signal AD conversion unit and the potential/current scanning signal DA conversion unit are electrically connected with the micro-control unit.

Due to the structural reasons of the target galvanic pile 26, the electrolyte flow rate flowing into each flow battery cell 26-5 has a certain range of difference, and according to the difference, position replacement tests are required to be carried out on different anode side functional device schemes, and the average number of anode side impedance spectrum characteristic values of the functional devices 26-7 is found to carry out comprehensive comparison and analysis. Meanwhile, the number of flow battery cells 26-5 included in the target stack 26 for parallel testing is not likely to be excessive, and the number of flow battery cells 26-5 is exemplarily set to 10 in fig. 1 and 2.

During an electrochemical impedance experiment, the power supply system 23 provides a direct current component (direct current or direct voltage) of the target pile 26 in a charging process and a resistance load in a discharging process, the electrochemical workstation 22 provides a small-amplitude sine wave alternating current component (micro disturbance) in an electrochemical impedance spectrum experiment, and through the combination of test equipment and a charging and discharging device, the electrochemical impedance spectrum of each flow battery cell 26-5 in the target pile 26 in any charge state can be tested in parallel, so that the real-time performance and the comparison authenticity are high.

In the test process, considering the referenceability of parallel test, comparison and analysis, the anode multi-level hole electrode with different structural forms, different functional parameters, different types or different materials is generally taken as one group, the multi-level space structure with different structural forms, different functional parameters, different types or different materials is taken as another group, and the parallel test is carried out as the functional device 26-7 used by the anode electrode 2 of each flow battery cell 26-5 in each target stack 26 respectively, and the local optimal solution in the group is found.

The functional device 26-7 is added into the inner cavity of the cathode side of the target galvanic pile 26 to improve the electrolyte mass transfer level of the cathode side, so that the metal deposition effect of the cathode side is improved, the effects of reducing the granularity of metal deposition and improving the density of metal deposition of the cathode side are realized, and the phenomena of accumulating zinc deposition layers and penetrating through ion exchange membranes caused by long-term charging and discharging processes of the zinc-based flow battery are effectively inhibited.

Optionally, the materials of functional device 26-7 include: when the type of the functional device is a negative electrode multi-level hole electrode, the material of the functional device includes one of the following: metal-based materials, carbon-based materials, metal-based and carbon-based composite materials; when the kind of the functional device is a multi-layered spatial structure, the material of the functional device includes one of the following: insulating polymer, conductive polymer, wherein, conductive polymer includes the conductive polymer doped with transition metal compound.

Optionally, the structural form and the functional parameters of the functional device include: when the types of the functional devices are anode multi-level hole electrodes, the structural forms and the functional parameters of the functional devices comprise: the synthesis mode, porosity, aperture, surface roughness, wettability to liquid, flow resistance, specific surface area and pore volume of the multistage pore material; when the kinds of the functional devices are multi-level space structures, the structural forms and the functional parameters of the functional devices comprise: the weaving section patterns of each interval fabric layer, the tightness change rule among each interval fabric layer, the weaving mode and the connecting mode of each interval fabric layer, the wettability to liquid and the flow resistance.

In the test process, except that the structural form, the functional parameters, the types and the materials of the functional devices 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 negative electrode side functional device selection scheme under certain conditions.

The electrochemical workstation 22 is selected to obtain the electrochemical impedance spectra of the cathode side of the target stack 26 for analysis of the metal deposition effect because for electrode processes, 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. 5, and fig. 5 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 plays a role of an electrolytic cell, and when the flow battery discharges a load, the flow battery stack plays a role of a primary battery, as shown in fig. 6 and fig. 7, fig. 6 is a schematic diagram of the electrolytic cell provided by the embodiment of the invention, and fig. 7 is a schematic diagram of the primary battery provided by the embodiment of the invention.

As shown in fig. 6 and fig. 7, 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. 8 is a complex plan view of electrochemical impedance in the full frequency range provided by the embodiment of the invention, as shown in FIG. 8, wherein the complex plan view of electrochemical impedance can display 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 the view of figure 8 of the drawings, Z _Im＝-Z″,Z_Re = Z', where α is the negative electrode reaction transmission 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 multi-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 25 further includes a first electrically controlled valve 253 and a second electrically controlled valve 254.

A first electronically controlled valve 253 is disposed between the electrolyte outlet of the negative side reservoir 251 and the negative side chamber inlet of the target stack 26 for opening under control of the flow battery management system 21 to place the negative side reservoir 251 in communication with the negative side chamber of each flow battery cell 26-5 of the target stack 26, and the negative electrolyte in the negative side reservoir 251 flows back to the negative side reservoir 251 after passing through the negative side chambers of the flow battery cells 26-5.

The second electrically controlled valve 254 is disposed between the electrolyte outlet of the positive electrode side reservoir 252 and the positive electrode side chamber inlet of the target stack 26, and is used for being opened under the control of the flow battery management system 21, so that the positive electrode side reservoir 252 is communicated with the positive electrode side chamber of each flow battery cell 26-5 of the target stack 26, and the positive electrode electrolyte in the positive electrode side reservoir 252 flows back to the positive electrode side reservoir 252 after passing through the positive electrode side chamber of the flow battery cell 26-5.

Optionally, as shown in FIG. 1, the test apparatus further includes a first circulation pump 27-1, a negative side filter 28-1, a first pressure transmitter PS1, a second pressure transmitter PS2, and a first flow sensor FM1.

The first circulating pump 27-1 and the negative electrode side filter 2-18 are sequentially arranged on a circulating pipeline between the electrolyte outlet of the negative electrode side liquid storage tank 251 and the first electric control valve 253; the first circulation pump 27-1 is used to pump the anode-side electrolyte in the anode-side reservoir 251 into the target stack 26 at a preset flow rate.

The first pressure transmitter PS1 is disposed on the circulation pipe between the first electric control valve 253 and the anode side chamber inlet of the target stack 26; the second pressure transmitter PS2 is disposed on the circulation pipe between the anode side chamber outlet of the target stack 26 and the electrolyte inlet of the anode side reservoir 251; the difference between the measurements of the first pressure transmitter PS1 and the second pressure transmitter PS2 is used to characterize the sum of the pressure losses of the negative side chambers of each flow cell 26-5; a first flow sensor FM1 is provided on the circulation line between the first electronically controlled valve 253 and the anode side chamber inlet of the target stack 26 for measuring the sum of the flows of the anode electrolyte through the anode side chambers of the respective flow cell 26-5.

Specifically, since there is some metal deposition on the anode side of the target stack 26 over time, which may cause some blockage to the anode side chamber, thereby affecting the fluid pressure and flow in the anode side chamber, the cumulative effect of the anode side metal deposition layer of the target stack 26 may be systematically collected and analyzed using various pressure transmitters and flow sensors on the anode side electrolyte circulation line. Specifically, the information detected by each flow sensor and each pressure transmitter in the cathode side circulation 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 blockage condition in the cathode side chamber of the target pile.

Optionally, as shown in FIG. 1, the test apparatus further includes a second circulation pump 27-2, a positive side filter 28-2, a third pressure transmitter PS3, a fourth pressure transmitter PS4, and a second flow sensor FM2.

The second circulation pump 27-2 and the positive electrode side filter 28-2 are sequentially arranged on a circulation pipeline between the electrolyte outlet of the positive electrode side liquid storage tank 252 and the second electric control valve 254; the second circulation pump 27-2 is used to pump the positive electrode side electrolyte in the positive electrode side reservoir tank 252 into the target cell stack 26 at a preset flow rate.

The third pressure transmitter PS3 is disposed on the circulation pipe between the second electric control valve 254 and the positive electrode side chamber inlet of the target stack 26; the fourth pressure transmitter PS4 is disposed on the circulation pipe between the anode side chamber outlet of the target stack 26 and the electrolyte inlet of the anode side reservoir 252; the difference between the measurements of the third pressure transmitter PS3 and the fourth pressure transmitter PS4 is used to characterize the sum of the pressure losses of the positive side chambers of each flow cell 26-5; a second flow sensor FM2 is provided on the circulation line between the second electronically controlled valve 254 and the positive side chamber inlet 6 of the target stack 2 for measuring the sum of the flow rates of the positive electrolyte through the positive side chambers of the flow battery cells 26-5.

Specifically, since foreign matters, reactants, etc. may enter the positive electrode side of the target stack 26 as time passes, a certain blockage may also exist in the positive electrode side chamber of the target stack 26, so that the liquid pressure and flow rate in the positive electrode side chamber are affected, and thus each pressure transmitter and flow sensor on the positive electrode side electrolyte circulation pipeline can be used for monitoring the same in real time.

Optionally, as shown in FIG. 1, the test apparatus further includes a stack placement tray 29-1 and a plurality of liquid storage tank trays 29-2; the target stack 26 is placed on the stack placement tray 29-1; the negative electrode side reservoir 251 and the positive electrode side reservoir 252 are each provided on one reservoir tray 29-2.

As shown in FIG. 1, the test device further comprises a first thermocouple thermometer 31-1, a first liquid level sensor 32-1, a first electric heater 33-1 and a first pressure relief valve 34-1; the first thermocouple thermometer 31-1, the first liquid level sensor 32-1, the first electric heater 33-1 and the first pressure relief valve 34-1 are all arranged on the negative side liquid storage tank 251; the first electric heater 33-1 is used to control the experimental temperature of the negative electrode electrolyte in the negative electrode side reservoir 251 during each charge-discharge test.

As shown in FIG. 1, the test device further comprises a second thermocouple thermometer 31-2, a second liquid level sensor 32-2, a second electric heater 33-2 and a second pressure relief valve 34-2; the second thermocouple thermometer 31-2, the second liquid level sensor 32-2, the second electric heater 33-2 and the second pressure relief valve 34-2 are all arranged on the positive electrode side liquid storage tank 252; the second electric heater 33-2 is used to control the experimental temperature of the positive electrode electrolyte in the positive electrode side reservoir 252 during each charge-discharge experiment.

As shown in fig. 1, the test device further includes a plurality of liquid leakage sensors 35; the plurality of liquid leakage sensors 35 are provided on the stack placement tray 29-1 and the plurality of liquid storage tank trays 29-2 in one-to-one correspondence.

In the embodiment of the invention, although the additive and the functional device can reduce the granularity of metal sediment at the negative electrode side of the zinc-based flow battery, improve the density of metal sediment at the negative electrode side and effectively inhibit the phenomenon that a zinc sediment layer accumulates and pierces an ion exchange membrane caused by long-term charge and discharge processes of the zinc-based flow battery, the action mechanisms of the two main schemes are different, and the following comparison is carried out between the two schemes:

(1) Influence on the original zinc-based flow battery system. The use of additives changes the basic composition and formulation of the electrolyte on the negative side of the flow battery, whereby the possible side effects during charge and discharge depend on the choice of additives and their interaction with the original electrolyte system during charge and discharge, and careful and comprehensive consideration is required. But the use of the functional device does not affect the original electrolyte system.

(2) As the component of the electrode impedance spectrum of the flow battery, concentration polarization resistance and concentration capacitance are not negligible, they act on the interface between the electrode and the electrolyte, and the electrochemical impedance only appears in the low frequency area and is directly coupled with the direct current component in the charge and discharge process, thus generating unnecessary current loss. According to the analysis, the solution using the additive cannot improve the mass transfer level of the negative electrode side electrolyte on the electrode surface, namely, the contact frequency of the active substance in the negative electrode side electrolyte and the electrode is improved, so that concentration polarization impedance (concentration polarization resistance and concentration capacitance) cannot be fundamentally eliminated; however, the scheme of using the functional device is based on the principle of a microporous vortex mixing reactor and the principle of a static mixing reactor, and can improve the mass transfer level and the mass transfer efficiency of electrolyte in the inner cavity of the flow battery, thereby greatly reducing the concentration polarization impedance.

(3) 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. In the process, the discharge behavior of active substance ions is inhibited, the negative electrode may in turn tend to generate hydrogen evolution reaction, which puts higher requirements on the safety of the zinc-based flow battery system, and the flow battery is reduced in current efficiency due to the hydrogen evolution phenomenon, so that the efficiency of the flow battery system is reduced, the compactness of the metal deposition layer at the negative electrode side is influenced in the hydrogen evolution process, and the structure of the metal deposition layer is loose.

(4) Whether an additive or a functional device is used, the function of the additive is to obtain a more compact metal deposition layer on the negative electrode plate of the flow battery. The appearance of a loose metal deposit on the negative electrode plate is similar to electrically connecting a multi-level porous electrode on the negative electrode plate, resulting in an increase in the electric double layer capacitance C _d of the negative electrode. When current is passed through this electrode, a portion of the current is used for electrode double layer charging, and although this portion of the current does not follow the faraday law, this portion of the electrical energy is rapidly stored and released to the load upon discharge, similar to the case when an electric double layer capacitor is charged. The sparse metal deposition layer may cause the charge transfer resistor R _t to become larger, further affecting the current efficiency during metal deposition, resulting in a reduction in the efficiency of the flow battery system. In addition, the compact metal deposition layer can effectively inhibit the phenomenon that the zinc deposition layer accumulates and pierces the ion exchange membrane caused by the long-term charge and discharge process of the zinc-based flow battery.

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, a power supply system performs a preset number of charge and discharge tests on a target electric pile under the control of a flow battery management system, wherein the target electric pile is composed of a first number of flow battery monomers, functional devices are arranged at negative plates of all the flow battery monomers, the functional devices of all the flow battery monomers have respective structural forms, functional parameters, types and materials, and the types of the functional devices comprise at least one of the following: a cathode multi-level hole electrode and a multi-level space structure.

In the embodiment of the present invention, a functional device may be not provided in one of the flow battery cells as required, and a single control group may be used to control the flow battery cells with the experimental group provided with the functional device.

S2, in the process of each charge and discharge test, the electrochemical workstation controls the on-off and the switching of each switch unit in the switch module through the flow battery management system under the control of the flow battery management system, the connected flow battery units are replaced, the electrochemical workstation obtains the electrochemical impedance spectrum of the cathode side of each flow battery unit in the target pile, and the electrochemical impedance spectrum is transmitted to the flow battery management system.

And S3, the flow battery management system compares the metal deposition effect of the negative side of each flow battery cell in the target electric pile based on the received electrochemical impedance spectrum analysis, and finally determines the optimal negative side functional device selection scheme of the target electric pile.

Based on the above technical solutions, the electrochemical workstation obtaining the electrochemical impedance spectrum of the cathode side of each flow battery cell in the target stack in each charge-discharge test process includes:

The electrochemical workstation obtains the electrochemical impedance spectrum of the cathode side of each flow battery cell in the target pile at the following moments in the process of each charge and discharge test: when a first preset charging time period passes in each charging and discharging test process; 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.

Specifically, in the process of adding the functional device, the system of the zinc-based flow battery is not changed, and as the functional device for improving the electrolyte mass transfer level is added in the inner cavity of the negative electrode side, the electrolyte enters a steady-state mass transfer process in the inner cavity of the negative electrode side after a period of 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 incomplete reversible electrode reactions, there is: R _w＝σ′w^-1/2,The mass transfer level of the interface between the electrode and the electrolyte is improved, the contact frequency of the active substances in the electrolyte and the interface between the electrode is improved, and the concentration polarization can be eliminated by increasing the frequency, namely R _w→0,C_w -0 when w-infinity is achieved. ) While the electrolyte resistance R _L in the system is unchanged. Reflecting that as the electrolyte mass transfer level at the electrode surface increases, the concentration polarization level of the electrolyte at the electrode surface decreases, and R _w reflects the functional feature level of the device to some extent, and comparing this value helps to understand the ability of a functional device with different functional feature parameters to influence the electrolyte mass transfer level near the electrode.

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

(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 (mass transfer efficiency of the active material in the anode-side electrolyte increases to another level, contact frequency of the active material in the anode-side electrolyte with the anode electrode increases to another level, there is an optimum match of electrolyte concentration and electrode current density near one electrode for discharge behavior of the active material at the electrode surface), and 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 of the change value delta R _t of the charge transfer resistance in the unit time t and t+delta t reflects the capability difference of the functional devices. 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 functional device has poor capability of improving the mass transfer level of the interface of the electrode and the electrolyte.

(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). In particular, in the final stage of the first charge, when the electrochemical impedance spectrum analysis is performed on the negative electrode at a certain same charge state, the total concentration of the negative electrode electrolyte is equivalent (unchanged), that is, the electrolyte resistance R _L is equivalent (unchanged), and the ion quantity participating in the metal deposition of the negative electrode increases as the concentration polarization level of the electrolyte on the electrode surface decreases (mass transfer level increases). 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 functional device has poor capability of improving the mass transfer level of the interface between the electrode and the electrolyte.

Further, since the total concentration of the negative electrode side electrolyte at the end of the first charge-discharge cycle is considered to be substantially unchanged, that is, the total concentration of the negative electrode side electrolyte is equivalent (unchanged), but after a plurality of charge-discharge cycles, there is a certain precipitation of a substance on the negative electrode side, and there is a certain concentration change in the total concentration of the negative electrode side electrolyte as compared with the concentration at the end of the first charge-discharge cycle, it is necessary to detect the concentration of the negative electrode side electrolyte at the end of the charge-discharge cycle at the end of each subsequent charge-discharge cycle, compare the concentrations with the total concentration of the negative electrode side electrolyte at the end of the first charge-discharge cycle as a reference, and then consider the difference obtained by the comparison to the test conditions of the control test, so that the test results are more accurate.

(3) At the end of the first charge-discharge cycle (i.e., at the end of the first charge-discharge cycle). Electrochemical impedance spectroscopy analysis was performed on the negative electrode side at the beginning and end of the first charge-discharge cycle (SOC: 0%), and electrochemical impedances R _L0、R_t0 and C _d0 corresponding to the beginning and electrochemical impedances R _L'、R_t 'and C _d' corresponding to the end and differences Δr _L、ΔR_t and Δc _d of the two were measured. It is understood that Δr _t and Δc _d reflect the metal deposit remaining on the negative electrode plate after one charge-discharge cycle and its thickness and porosity. DeltaR _L relates to the release of metal deposit material from the electrolyte system in a cycle, which metal deposit material is difficult to reuse once it enters the flow cycle, and is one of the causes of energy decay of the flow battery. Loose metal deposits are more prone to metal deposit detachment into the flow cycle, reflecting the capabilities and roles of the functional device.

(4) At the end of the multiple charge-discharge cycles (i.e., at the end of the preset number of charge-discharge cycles). Electrochemical impedance spectroscopy analysis was performed on the negative electrode at the beginning of the first charge-discharge cycle and at the end of the multiple charge-discharge cycles (SOC: 0%), and electrochemical impedances R _L0、R_t0 and C _d0 corresponding to the beginning and electrochemical impedances R _L"、R_t "and C _d" corresponding to the end and differences Δr _L'、ΔR_t 'and Δc _d' between the two were measured. It is understood that Δr _t 'and Δc _d' reflect the accumulation of the metal deposition layer remaining on the negative electrode plate and the thickness and porosity thereof after a plurality of charge and discharge cycles. ΔR _L' is related to the cumulative release of metal deposit material from the electrolyte system over multiple cycles, which metal deposit material once in the flow cycle is difficult to reuse and can be one of the causes of energy decay in flow batteries. Loose metal deposits are more prone to metal deposit detachment into the flow cycle, reflecting the capabilities and roles of the functional device.

In addition, more test variables can be added in combination with the test procedures in the processes (1) - (4), for example, a charging and discharging mode can be changed, and the concentration polarization phenomenon in the flow battery in the charging process can be slowed down by adopting pulse current (intermittent charging mode) or adopting alternating current superposition current (mode of superposing reverse discharging current), so that the growth of zinc dendrite is inhibited (obviously, the current/voltage input in the charging and discharging process and the tiny disturbance input in the test process can be mutually unaffected). And the charge and discharge technological parameters of the zinc-based flow battery are optimized through the cooperation and cooperative test of different charge and discharge modes and the processes (1) - (4).

In addition, the functional device with conductivity is used and is effectively and electrically connected with the electrode, so that the internal resistance of a negative electrode side system of the flow battery is reduced, and the charging and discharging efficiency of the flow battery is further improved.

In addition, the concentration of each active material in the negative electrode side electrolyte is reasonably increased, particularly in the end stage of charging, the contact frequency and the contact effect of active material ions and a negative electrode plate in the stage are facilitated, and the compactness of a metal deposition layer is facilitated to be improved.

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, which comprises a plurality of flow battery monomers, wherein a negative plate of each flow battery monomer is provided with a functional device, and the types of the functional devices comprise at least one of the following: a cathode multi-level hole electrode and a multi-level space structure.

The functional device is determined by an optimal negative side functional device selection scheme, wherein the optimal negative side functional device selection scheme is the corresponding optimal negative side functional device selection scheme determined by the zinc-based flow battery test device in any embodiment.

The negative plate of each flow battery cell of the zinc-based flow battery provided by the embodiment of the invention is provided with the functional device, and the functional device is determined by using the corresponding optimal negative side functional device selection scheme 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 in that the test device tests the metal deposition effect on the negative side of each flow battery cell in a target electric pile, the target electric pile consists of a first number of flow battery cells, a functional device is arranged at the negative plate of each flow battery cell, the functional device of each flow battery cell has a respective structural form, functional parameters, types and materials, and the types of the functional devices comprise at least one of the following: a negative electrode multi-level hole electrode and a multi-level space structure;

2. The zinc-based flow battery test device of claim 1, wherein the flow battery circulation system further comprises a first electrically controlled valve and a second electrically controlled valve;

The first electric control valve is arranged between an electrolyte outlet of the negative electrode side liquid storage tank and a negative electrode side chamber inlet of the target electric pile and used for being opened under the control of the flow battery management system so as to enable the negative electrode side liquid storage tank to be communicated with the negative electrode side chamber of each flow battery cell of the target electric pile, and negative electrolyte in the negative electrode side liquid storage tank flows through the negative electrode side chamber of the flow battery cell and then flows back to the negative electrode side liquid storage tank;

the second electric control valve is arranged between an electrolyte outlet of the positive electrode side liquid storage tank and an inlet of a positive electrode side chamber of the target electric pile and used for being opened under the control of the flow battery management system so that the positive electrode side liquid storage tank is communicated with each positive electrode side chamber of the flow battery monomer of the target electric pile, and positive electrode electrolyte in the positive electrode side liquid storage tank flows through the positive electrode side chamber of the flow battery monomer and then flows back to the positive electrode side liquid storage tank.

3. The zinc-based flow battery test device of claim 2, further comprising a first circulation pump, a negative side filter, a first pressure transmitter, a second pressure transmitter, and a first flow sensor;

The first circulating pump and the negative electrode side filter are sequentially arranged on a circulating pipeline between an electrolyte outlet of the negative electrode side liquid storage tank and the first electric control valve; the first circulating pump is used for pumping the negative electrode side electrolyte in the negative electrode side liquid storage tank into the target pile at a preset flow;

the first pressure transmitter is arranged on a circulating pipeline between the first electric control valve and the negative electrode side cavity inlet of the target electric pile; the second pressure transmitter is arranged on a circulating pipeline between a negative electrode side cavity outlet of the target electric pile and an electrolyte inlet of the negative electrode side liquid storage tank; the difference between the measurements of the first pressure transmitter and the second pressure transmitter is used to characterize the sum of the pressure losses of the negative side chambers of each of the flow battery cells;

The first flow sensor is arranged on a circulating pipeline between the first electric control valve and the inlet of the negative electrode side chamber of the target electric pile and is used for measuring the sum of the flows of the negative electrolyte passing through the negative electrode side chambers of the flow battery monomers.

4. The zinc-based flow battery test device of claim 2, further comprising a second circulation pump, a positive side filter, a third pressure transmitter, a fourth pressure transmitter, and a second flow sensor;

the second circulating pump and the positive electrode side filter are sequentially arranged on a circulating pipeline between an electrolyte outlet of the positive electrode side liquid storage tank and the second electric control valve; the second circulating pump is used for pumping the positive electrode side electrolyte in the positive electrode side liquid storage tank into the target pile at a preset flow;

The third pressure transmitter is arranged on a circulating pipeline between the second electric control valve and the positive electrode side cavity inlet of the target electric pile; the fourth pressure transmitter is arranged on a circulating pipeline between the positive electrode side cavity outlet of the target electric pile and the electrolyte inlet of the positive electrode side liquid storage tank; the difference between the measurements of the third pressure transmitter and the fourth pressure transmitter is used to characterize the sum of the pressure losses of the positive side chambers of each of the flow battery cells;

The second flow sensor is arranged on a circulating pipeline between the second electric control valve and the inlet of the positive electrode side chamber of the target electric pile and is used for measuring the sum of the flow of positive electrode electrolyte passing through the positive electrode side chamber of each flow battery cell.

5. The zinc-based flow battery test device of claim 1, further comprising a stack placement tray and a plurality of reservoir trays;

the target electric stack is arranged on the electric stack placing tray; the negative electrode side liquid storage tank and the positive electrode side liquid storage tank are respectively arranged on one liquid storage tank tray;

The test device further comprises a first thermocouple thermometer, a first liquid level sensor, a first electric heater and a first pressure relief valve;

The first thermocouple thermometer, the first liquid level sensor, the first electric heater and the first pressure relief valve are all arranged on the negative side liquid storage tank; the first electric heater is used for controlling the experimental temperature of the negative electrode electrolyte in the negative electrode side liquid storage tank in each charge and discharge test process;

the test device further comprises a second thermocouple thermometer, a second liquid level sensor, a second electric heater and a second pressure relief valve;

The second thermocouple thermometer, the second liquid level sensor, the second electric heater and the second pressure relief valve are all arranged on the positive electrode side liquid storage tank; the second electric heater is used for controlling the experimental temperature of the positive electrolyte in the positive-side liquid storage tank in each charge-discharge experimental process;

the test device further comprises a plurality of liquid leakage sensors; the liquid leakage sensors are arranged on the pile placing tray and the liquid storage tank tray in a one-to-one correspondence mode.

6. The zinc-based flow battery test apparatus of claim 1, wherein the material of the functional device comprises:

when the type of the functional device is a negative electrode hierarchical pore electrode, the material of the functional device includes one of the following: metal-based materials, carbon-based materials, metal-based and carbon-based composite materials;

when the kind of the functional device is a multi-layer space structure, the material of the functional device includes one of the following: insulating polymer, conductive polymer, wherein, conductive polymer includes the conductive polymer doped with transition metal compound.

7. The zinc-based flow battery test device according to claim 1, wherein the structural form and the functional parameters of the functional device include:

when the types of the functional devices are anode multi-level hole electrodes, the structural form and the functional parameters of the functional devices comprise: the synthesis mode, porosity, aperture, surface roughness, wettability to liquid, flow resistance, specific surface area and pore volume of the multistage pore material;

when the types of the functional devices are multi-level space structures, the structural forms and the functional parameters of the functional devices comprise: the weaving section patterns of each interval fabric layer, the tightness change rule among each interval fabric layer, the weaving mode and the connecting mode of each interval fabric layer, the wettability to liquid and the flow resistance.

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

In the process of each charge and discharge test, under the control of the flow battery management system, an electrochemical workstation controls the on-off and the switching of each switch unit in a switch module through the flow battery management system, the connected flow battery monomers are replaced, and the electrochemical workstation acquires the electrochemical impedance spectrum of the negative electrode side of each flow battery monomer in the target electric pile and transmits the electrochemical impedance spectrum to the flow battery management system;

9. The method of claim 8, wherein each of the charge and discharge tests comprises a predetermined number of charge and discharge cycles, and wherein the electrochemical workstation obtaining an electrochemical impedance spectrum of a negative side of each of the flow battery cells in the target stack during each of the charge and discharge tests comprises:

the electrochemical workstation obtains the electrochemical impedance spectrum of the cathode side of each flow battery cell in 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.

10. A zinc-based flow battery, characterized in that, the zinc-based flow battery includes a plurality of flow battery single, every flow battery single's negative plate department all is provided with functional device, the kind of functional device includes at least one of following: a negative electrode multi-level hole electrode and a multi-level space structure;

the functional device is determined by an optimal negative side functional device selection scheme, wherein the optimal negative side functional device selection scheme is a corresponding optimal negative side functional device selection scheme determined by the zinc-based flow battery test device according to any one of claims 1 to 7.