WO2018103517A1

WO2018103517A1 - Alkaline zinc-iron flow battery

Info

Publication number: WO2018103517A1
Application number: PCT/CN2017/111224
Authority: WO
Inventors: 李先锋; 张华民; 袁治章; 段寅琦; 谢聪鑫
Original assignee: 中国科学院大连化学物理研究所
Priority date: 2016-12-10
Filing date: 2017-11-16
Publication date: 2018-06-14
Also published as: CN108461784A

Abstract

Provided is an alkaline zinc-iron flow battery; the ion-conducting membrane thereof is made from aromatic polymers containing nitrogen heterocyclic rings, and the electrodes are carbon felt or carbon paper; the positive-electrode electrolyte solution is a mixed aqueous solution of ferrocyanide and a strong alkali; the negative-electrode electrolyte is a mixed aqueous solution of zinc salts and/or zinc oxides with a strong alkali; the concentration of strong alkali in the aqueous solutions of the positive and negative electrolyte solutions is 0.001-10 mol/L, and the concentration of active substance in the electrolyte solutions of the positive and negative electrodes is 0.001-3 mol/L. The alkaline zinc-iron flow battery has the features of high energy density, high power density, and long service life; it exhibits battery performance that is equivalent or superior to the battery performance of vanadium flow batteries currently available, and has very good prospects for application.

Description

Alkaline zinc iron flow battery

Technical field

The invention relates to the field of flow batteries, and in particular to the technical field of zinc iron flow batteries.

Background technique

The flow battery is a new electrochemical energy storage technology. Compared with other energy storage technologies, it has flexible system design, large storage capacity, free site selection, high energy conversion efficiency, deep discharge, safety and environmental protection, and low maintenance cost. Other advantages, can be widely used in wind energy, solar energy and other renewable energy power generation, emergency power systems, backup power stations and power system peaking and valley filling. Vanadium flow battery (VFB) is considered to have good application prospects due to its high safety, good stability, high efficiency, long life (lifetime >15 years), and low cost. The solution is more expensive, which limits its large-scale application to a certain extent. Therefore, the development of electrochemical storage cells with excellent performance and low cost is very important for the popularization of renewable energy.

In addition to all-vanadium flow batteries, the more mature flow batteries are mainly zinc-bromine flow batteries, sodium polysulfide bromine and zinc-nickel battery systems. Among them, the zinc bromine flow battery and the sodium sulfide bromine battery cause environmental pollution due to the formation of bromine element during charging of the positive electrode side electrolyte, which restricts its large-scale application; and the electrolyte of the zinc-nickel battery system needs 10 to 14 mol/ The strong base of L acts as a supporting electrolyte, and this high concentration of alkali solution is severely corroded to the equipment.

Zinc-iron liquid flow battery has a good application prospect in large-scale liquid flow batteries because of its low electrolyte cost. Patent 201180016873.6 discloses a class of alkaline zinc-iron liquid flow batteries comprising conductive mesh and non-conductive mesh; screen; belt; foam structure; array of cones, cylinders or pyramids; and wires or tubes Other arrangements are made, the electrode is a porous mesh metal electrode, although it shows better performance, its structure is more complicated, the electrochemical performance is lower, and the membrane material is selected from a perfluorosulfonic acid membrane (Nafion), and the cost is high. Poor stability.

Summary of the invention

In order to solve the above technical problems, it is particularly important to develop a zinc-iron liquid flow battery which is low in cost, simple in structure, and excellent in electrochemical performance, in order to achieve the above object,

The invention develops an alkaline zinc-iron liquid flow battery, and the specific technical solutions are as follows:

The battery includes a single battery or a battery module in which two or more single cells are connected in series/parallel, a liquid storage tank equipped with positive and negative electrolytes, a circulation pump and a circulation line, and the single battery includes a positive current collecting plate, The negative current collecting plate, the electrode, the ion conductive membrane, and the ion conductive membrane are prepared from an aromatic polymer containing a nitrogen heterocycle, preferably a dense membrane, the electrode is carbon felt or carbon paper; the positive electrolyte is ferrocyanide and strong a mixed aqueous solution of a base, the negative electrode electrolyte is a mixed aqueous solution of a zinc salt or/and a zinc oxide and a strong alkali, and the concentration of the strong base in the positive and negative electrolytes in the aqueous solution is 0.001 to 10 mol/L, in the positive electrode electrolyte The active material is one or two of ferricyanide (Fe(CN) ₆ ^3- ) or ferrocyanide (Fe(CN) ₆ ^4- ), and the active material in the negative electrolyte is Zn(OH) ₄ ^{2 -} The concentration of the active material in the positive and negative electrolytes is 0.001 to 3 mol/L; and the aromatic polymer containing the nitrogen heterocycle is polybenzimidazole, polyvinylimidazole, polypyridine, polyvinylpyridine, polypyrazole, Polypyrimidine, polythiazole, polybenzothiazole, polyoxazole, polybenzoxazole, polyoxadiazole Polyquinoline, polyquinoxaline, poly-thiadiazole, purine polytetramethylene of one or more polymers. The polybenzimidazole dense film is preferred, and its ultra-high mechanical strength (elastic modulus > 2.9 GPa) and extremely low swelling effect (swelling rate: 4.348%) can effectively solve the zinc deposition caused by uneven deposition of zinc during battery charging. The dendrite pierces the diaphragm causing a problem with the battery being shorted.

Wherein the ion-conducting membrane is used for blocking the positive and negative electrolytes, preventing the positive and negative electrodes from short-circuiting and transmitting ions to form an internal circuit; and the circulating pump is for circulating the electrolyte through the electrochemical of the positive and negative half-cells. Reaction zone.

The electrochemical reaction of deposition and dissolution occurs on the electrode after the zinc salt of the negative electrode side or/and the oxide of zinc is dissolved in a strong alkali to form Zn(OH) ₄ ^2- , and the reaction equation is as follows:

The ferrocyanide or/and ferricyanide on the positive electrode side undergoes a valence reaction of iron on the electrode, and the reaction equation is as follows:

During charging, the negative electrode side, zinc oxide or zinc oxide is dissolved in a strong alkali to form Zn(OH) ₄ ^{2- and} then two electrons are obtained on the carbon felt or carbon paper electrode to be reduced to zinc elemental substance; On the positive electrode side, Fe(CN) ₆ ^4- loses electrons on the carbon felt or carbon paper electrode and is oxidized to Fe(CN) ₆ ^3- .

The active material in the positive electrode electrolyte is one or two of ferricyanide (Fe(CN) ₆ ^3- ) or ferrocyanide (Fe(CN) ₆ ^4- );

The oxide of zinc in the negative electrode electrolyte is zinc oxide (ZnO), and the zinc salt is one of zinc chloride (ZnCl ₂ ) and zinc sulfate (ZnSO ₄ ).

The strong base is one or more of sodium hydroxide (NaOH), potassium hydroxide (KOH) or lithium hydroxide (LiOH) as a supporting electrolyte.

The concentration of the strong base is from 0.001 mol/L to 10 mol/L, preferably from 2 to 5 mol/L; a certain amount of auxiliary electrolyte may also be added to the above electrolyte solution (the concentration of the auxiliary electrolyte is 0.1 to 6 mol/L, preferably 2 to 4 mol). /L) Soluble salts such as potassium chloride (KCl), sodium sulfate (Na ₂ SO ₄ ), sodium chloride (NaCl), potassium sulfate (K ₂ SO ₄ ) to increase the conductivity of the supporting electrolyte.

The positive and negative electrolyte storage tanks are connected to the positive and negative inlets and outlets of the pipeline unit or the stack via the liquid transfer pump.

It is preferable that the concentration of the active material in the negative electrode electrolyte is 1/2 of the concentration of the active material in the positive electrode electrolyte to a saturated concentration in the corresponding strong alkali solution.

The electrolyte solution must be disposed at different temperatures depending on the concentration, and the temperature range is between 5 and 90 °C.

When charging a single cell or a stack, the electrolyte is transported from the positive and negative liquid storage tanks to the positive and negative electrodes via a pump, and the active material Fe(CN) ₆ ^4- in the positive electrode storage tank undergoes electrochemical oxidation to form Fe (CN). ₆ ^3- , Zn(OH) ₄ ^2- ion is deposited directly on the carbon felt or carbon paper anode as a simple substance of zinc; when discharged, the anode zinc element is oxidized to Zn(OH) ₄ ^2- ion in an alkaline solution environment. The pump returns to the negative liquid storage tank, and the active material Fe(CN) ₆ ^3- in the positive electrode electrolyte reacts electrochemically to form Fe(CN) ₆ ^{4 -} and returns to the positive liquid storage tank via the pump.

The ion-conducting membrane may or may not be activated in a concentration of 0 mol/L < alkali aqueous solution < 10 mol/L.

An appropriate amount of quaternary ammonium salt, thiourea, polyvinyl alcohol, Bi ³⁺ , Ti ⁺ , Pd ²⁺ , Pb ²⁺ dendrite formation inhibitor may be added to the negative electrode electrolyte to control the deposition morphology of zinc. The dendrite formation inhibitor concentration ranges from 0 to 0.02 mol/L.

The electrochemical oxidation-reduction potential of the negative electrode varies with the alkali concentration in the electrolyte solution, and its electrochemical redox potential ranges from -0.74 V vs. Hg/HgO to -1.44 V vs. Hg/HgO.

The alkaline zinc-iron flow battery has an operating current density of between 1 mA cm ^-2 and 200 mA cm ^-2 .

In the alkaline zinc-iron flow battery, the charge and discharge time can be controlled according to the concentration of the electrolyte and the volume of the electrolyte.

The transport mechanism of the ion-conducting membrane containing a nitrogen-containing heterocycle in an alkaline zinc-iron battery is as shown in FIG. 10: conduction through a free aqueous solution adsorbed in the region or alternately dissociative adsorption between the ion exchange group and the aqueous solution. Conduction.

By screening the electrode and the ion-conducting membrane to optimize the electrolyte composition, the assembled alkaline zinc-iron flow battery can be continuously and stably operated between the working current densities of 1 mA cm ^-2 to 200 mA cm ^-2 , showing the total vanadium solution The flow battery is quite or even better battery performance.

The beneficial results of the invention:

1. For the first time, this patent uses a nitrogen-containing heterocyclic ion exchange membrane, a carbon felt electrode and a high concentration and high stability electrolyte in an alkaline zinc-iron battery to invent a class of high energy density, high power density and long life. Alkaline zinc iron flow battery. The proposed alkaline zinc-iron flow battery uses a conductive carbon felt or carbon paper as an electrode, an ion exchange membrane such as a nitrogen-containing heterocycle, and an ion-conducting membrane such as a nitrogen-containing heterocycle as a battery separator, and the battery is represented. The performance is comparable to or better than that of the currently mature all-vanadium redox flow battery, and the positive and negative redox couples of alkaline zinc-iron flow battery are Fe(CN) ₆ ^3- /Fe(CN) ₆ ^4- And Zn(OH) ₄ ^2- /Zn, zinc iron is rich in reserves, and the cost is much lower than that of the whole vanadium redox flow battery, which meets the demand of large-scale applications and shows a good application prospect.

2. An ion-conducting membrane such as a nitrogen-containing heterocycle exhibits excellent chemical stability and mechanical stability as a battery separator in an alkaline electrolyte system, and particularly a preferred polybenzimidazole-based ion-conducting membrane, which is extremely high The mechanical stability (elastic modulus > 2.9GPa), combined with the porous carbon felt with 3D network structure, effectively alleviates the short circuit problem caused by zinc dendrite piercing the diaphragm during zinc deposition. Due to the ultra-high mechanical strength of the polybenzimidazole-based ion-conducting membrane, the deposition process of zinc along the film direction is resisted, and is deposited along the interior of the porous carbon felt to form a metal zinc/3D porous carbon felt composite electrode. Inside the composite electrode, the metal zinc and the 3D porous carbon felt have excellent bonding ability. During the discharge process, the zinc gradually dissolves from the outside to the inside, and the internal metal zinc maintains good contact with the 3D porous carbon felt, effectively alleviating the battery. Accumulation of metallic zinc during discharge.

3. The carbon felt electrode can be activated in situ in the alkaline electrolyte to effectively improve its electrochemical performance. In addition, the carbon felt electrode can effectively alleviate the damage caused by zinc dendrite and zinc accumulation, resulting in short battery life. The problem. These batteries exhibit battery performance comparable to or higher than that of all vanadium redox flow batteries, but at a much lower cost than all vanadium redox flow batteries, which are excellent in large-scale energy storage. Application prospects.

4. The potential of the negative electrode to Zn(OH) ₄ ^2- /Zn can be adjusted according to the alkali concentration in the electrolyte. At high pH, the potential of the negative electrode is more negative for Zn(OH) ₄ ^2- /Zn. The unit cells assembled after pairing with the positive Fe(CN) ₆ ^3- /Fe(CN) ₆ ^4- have a higher open circuit voltage and thus have higher power density.

5. This alkaline zinc-iron liquid flow battery has the characteristics of high safety, good stability, low cost, simple structure and manufacturing process.

6. The concentration of the positive and negative active materials can be increased by adjusting the concentration of the supporting strong alkali, thereby increasing the energy density of the battery.

DRAWINGS

Figure 1 is a schematic view showing the structure of an alkaline zinc-iron liquid flow battery;

Figure 2 shows the electrochemical performance test of the positive and negative active materials. (a) 0.1 mol/L Zn(OH) ₄ ^2- +3 mol/L NaOH solution and 0.2 mol/L Fe(CN) ₆ ^3- +0.2 mol/L Fe(CN) ₆ ^4- +3 mol/L NaOH solution Cyclic voltammetry; (b) Cyclic voltammogram of 0.1 mol/L Zn(OH) ₄ ^2- +3 mol/L NaOH solution at a sweep rate of 10 to 60 mV s ^-1 ; (c) 0.2 mol/L Fe (CN) ₆ ^3- +0.2 mol/L Fe(CN) ₆ ^4- +3 mol/L NaOH solution cyclic voltammogram at a sweep speed of 10 to 60 mV s ^-1 ; (d) Redox corresponding to Figure c A linear plot of peak current ip and one-half of the sweep speed (v ^1/2 ).

Figure 3 is a schematic view showing the structure of an ion-conducting membrane containing nitrogen-containing heterocyclic rings for an alkaline zinc-iron flow battery;

Figure 4 is a graph showing the battery performance of a basic zinc-iron flow battery assembled with a Nafion 115 ion exchange membrane at a current density of 80 mA cm ^-2 in Comparative Example 1. (a) Charge and discharge curves for the 5th cycle; (b) Cycle performance test. Positive electrolyte composition: 0.6mol/L Fe(CN) ₆ ^4- +5mol/L OH ^- solution; negative electrolyte composition: 0.3mol/L Zn(OH) ₄ ^2- +5mol/L OH ^- solution; positive and negative The volume of the electrolyte is 60 mL each; the battery is charged in a constant current charge and discharge mode, charged at a current density of 80 mA cm ^-2 for 10 min, then the voltage is cut off, and discharged to 0 V at a current density of 80 mA cm ^-2 .

Figure 5 is a graph showing the battery performance test of an alkaline zinc-iron flow battery assembled in a PBI ion exchange membrane of Example 4. (a) charge and discharge curve of the 5th cycle; (b) partial charge and discharge cycle curve (variation of voltage with time); (c) long cycle performance test; (d) discharge capacity and discharge energy during cycle test The curve of the number of cycles. Positive electrolyte composition: 0.6mol/L Fe(CN) ₆ ^4- +5mol/L OH ^- solution; negative electrolyte composition: 0.3mol/L Zn(OH) ₄ ^2- +5mol/L OH ^- solution; positive and negative The volume of the electrolyte is 60 mL each; the battery is charged in a constant current charge and discharge mode, charged at a current density of 60 mA cm ^-2 for 12 min, then the voltage is cut off, and discharged to 0 V at a current density of 60 mA cm ^-2 .

Figure 6 is a graph showing the battery performance test of an alkaline zinc-iron flow battery assembled in a PBI ion exchange membrane of Example 4. (a) Battery performance test at different current densities; (b) Charge and discharge curves for the 5th cycle; (c) Partial charge and discharge cycle curves (voltage vs. time); (d) Cycle performance test. Positive electrolyte composition: 0.6mol/L Fe(CN) ₆ ^4- +5mol/L OH ^- solution; negative electrolyte composition: 0.3mol/L Zn(OH) ₄ ^2- +5mol/L OH ^- solution; positive and negative The volume of the electrolyte is 60 mL each; the battery is charged in a constant current charge and discharge mode, charged at a current density of 60 mA cm ^-2 for 12 min, then the voltage is cut off, and discharged to 0 V at a current density of 60 mA cm ^-2 ; 80 mA cm ^- Charge at a current density of ² for 10 min, then the voltage is cut off, and discharge to 0 V at a current density of 80 mA cm ^-2 ; charge at a current density of 100 mA cm ^-2 for 8 min, then the voltage is cut off, 100 mA cm ^-2 The current density was discharged to 0 V; the current density of 120 mA cm ^-2 was charged for 8 min, and then the voltage was cut off, and the current was discharged to 0 V at a current density of 120 mA cm ^-2 .

Figure 7. Battery performance test of an alkaline zinc-iron flow battery assembled with a PBI ion exchange membrane. (a) charge and discharge curve of the 5th cycle; (b) partial charge and discharge cycle curve (variation of voltage with time); (c) cycle performance test; (d) discharge capacity and discharge energy with cycle during cycle test The change curve of the number. Positive electrolyte composition: 1mol / L Fe (CN) ₆ ^4- +3mol / L OH ^- solution; negative electrolyte composition: 0.5mol / L Zn (OH) ₄ ^2- +3mol / L OH ^- solution; positive and negative The volume of the electrolyte was 60 mL each; the battery was charged in a constant current charge and discharge mode, charged at a current density of 60 mA cm ^-2 for 30 min, then the voltage was cut off, and discharged to 0 V at a current density of 60 mA cm ^-2 .

Figure 8 is a graph showing the battery performance test of an alkaline zinc-iron flow battery assembled in a PBI ion exchange membrane of Example 4. (a) charge and discharge curve of the 5th cycle; (b) partial charge and discharge cycle curve (variation of voltage with time); (c) cycle performance test; (d) discharge capacity and discharge energy with cycle during cycle test The change curve of the number. Positive electrolyte composition: 1mol / L Fe (CN) ₆ ^4- +3mol / L OH ^- solution; negative electrolyte composition: 0.5mol / L Zn (OH) ₄ ^2- +3mol / L OH ^- solution; positive and negative The volume of the electrolyte was 60 mL each; the battery was charged in a constant current charge and discharge mode, charged at a current density of 80 mA cm ^-2 for 20 min, then the voltage was cut off, and discharged to 0 V at a current density of 80 mA cm ^-2 .

Figure 9(a) Battery performance of a vanadium redox flow cell assembled with a Nafion 115 membrane at a current density of 80 mA cm ^-2 and an alkaline zinc-iron flow battery assembled with a PBI ion exchange membrane at 80 mA cm ^-2 Comparison of battery performance under current density conditions; (b) discharge capacity of a vanadium redox flow battery assembled with Nafion 115 membrane at a current density of 80 mA cm ^-2 , discharge energy and basicity assembled with PBI ion exchange membrane The discharge capacity and discharge energy of a zinc-iron flow battery at a current density of 80 mA cm ^-2 . All vanadium redox flow battery: positive and negative electrolyte concentration 1.5mol / L, H ₂ SO ₄ concentration 3mol / L, positive and negative electrolyte volume 60mL each; battery using constant current charge and discharge mode, charge and discharge cutoff voltage are 1.55V, 1V; alkaline zinc-iron flow battery: positive electrolyte composition: 1mol / L Fe (CN) ₆ ^4- +3mol / L OH ^- solution; negative electrolyte composition: 0.5mol / L Zn (OH) ₄ ^2- +4mol/L OH ^- solution; positive and negative electrolyte volume 60mL each; battery used in constant current charge and discharge mode, charged at 80mA cm ^-2 current density for 20min, then voltage cutoff condition, 80mA cm ^-2 Discharge to 0V under current density conditions.

Figure 10 is a diagram showing the transport mechanism of an ion-conducting membrane containing a nitrogen-containing heterocycle in an alkaline zinc-iron battery.

detailed description

Cyclic voltammetry (CV) test of positive active material: 0.2 mol/L Fe(CN) ₆ ^4- +0.2 mol/L Fe(CN) ₆ ^3- dissolved in 3 mol/L NaOH, working with graphite plate The electrode (working electrode area: 1 cm ² ) and the counter electrode, the Hg/HgO electrode is the reference electrode, and the current and potential curves are measured at a sweep speed of 10 to 60 mV s ^-1 (Fig. 2c). Fe(CN) ₆ ^3- /Fe(CN) ₆ ^4- exhibits excellent electrochemical activity and electrochemical reversibility. Electrochemical oxidation of Fe(CN) ₆ ^3- /Fe(CN) ₆ ^4- electrode was found by plotting the peak current ip and the sweep rate (v ^1/2 ) (Fig. 2d). The reduction reaction is diffusion control.

Cyclic voltammetry (CV) test of negative active material: 0.1 mol/L ZnO was dissolved in 3.2 mol/L NaOH, with graphite plate as working electrode (working electrode area: 1 cm ² ) and counter electrode, Hg/HgO electrode For the reference electrode, the current and potential curves were measured at a sweep speed of 10 to 60 mV s ^-1 (Fig. 2b). It can be seen that the negative electrode has little effect on the sweep rate of Zn(OH) ₄ ^2- /Zn.

It can be seen from the half-wave potential analysis of Zn(OH) ₄ ^2- /Zn pair and Fe(CN) ₆ ^3- /Fe(CN) ₆ ^4- electrode at 40mV s ^-1 sweep speed. The potential difference is 1.74V (Fig. 2a), which is much higher than the open circuit voltage (1.2V) of all vanadium.

Single cell assembly: Single cells are assembled in the following order: positive end plate, graphite current collector, positive 6x8 cm ² carbon felt, ion conductive membrane (ion exchange membrane containing nitrogen heterocycle and porous ion conduction such as nitrogen heterocycle) The film is partially structured as shown in Fig. 3), the negative electrode is 6x8 cm ² carbon felt, the graphite current collector, and the negative electrode end plate. The structure of the single cell is shown in Figure 1.

Comparative example 1

Nafion 115 is used as ion exchange membrane, both positive and negative electrodes are carbon felt, positive electrode electrolyte is 0.6mol/L Fe(CN) ₆ ^4- +5mol/L OH ^- solution; negative electrolyte is 0.3mol/L Zn(OH ₄ ^2- +5mol/L OH ^- solution; the volume of the positive and negative electrolytes is 60mL each; the battery is charged in a constant current charge and discharge mode, charged at a current density of 80mA cm ^-2 for 10min, then the voltage is cut off, 80mA cm Discharge to 0V at a current density of ^-2 . It can be seen from the charge-discharge curve of the battery (Fig. 4a) that the discharge voltage of the battery is close to 1.8V, the initial coulombic efficiency (CE) of the battery is close to 100%, and the energy efficiency (EE) and voltage efficiency (VE) are close to 80%. After 100 cycles, the coulombic efficiency of the battery remained essentially unchanged, while the voltage efficiency and energy efficiency dropped to around 70% (Fig. 4b).

Example 1

A polyoxadiazole (POD) dense membrane containing a nitrogen heterocyclic ring, a positive electrode electrolyte of 0.6 mol/L Fe(CN) ₆ ^4- +3 mol/L OH ^- solution; a negative electrode electrolyte of 0.3 mol/L Zn (OH) ₄ ^2- +3mol/L OH ^- solution; the volume of the positive and negative electrolytes is 60mL each; the battery is charged in a constant current charge and discharge mode, charged at a current density of 80mA cm ^-2 for 10min, then the voltage is cut off, 80mA cm Discharge to 0V at a current density of ^-2 . According to the charge and discharge curve of the battery, the discharge voltage of the battery is about 1.76V, and the CE, EE and VE of the battery are 99%, 81% and 82%, respectively. Within 70 cycles, the charge and discharge capacity and charge and discharge energy of the battery were kept stable, and the battery performance was not significantly attenuated.

Example 2

A branched nitrogen-containing heterocyclic imidazole cross-linked chloromethylated polysulfone porous ion-conducting membrane (CMPSF-Im), and battery test conditions are consistent with battery test conditions assembled with a POD film. According to the charge and discharge curve of the battery, the battery polarization is lower than that of the single cell assembled with the POD film, so that in addition to having high ion selectivity (CE to 99%), the ionic conductivity is also high, and the VE is about 82%. . This may be because the pore structure in the porous membrane contributes to the liquid retention rate in the membrane and thus facilitates the conduction of ions. Within 100 cycles, the charge and discharge capacity and charge and discharge energy of the battery are stable, showing good stability and battery performance.

Example 3

A 4,4'-bipyridine crosslinked chloromethylated polysulfone ion exchange membrane (CMPSF-Biy) having a branched nitrogen-containing heterocyclic ring was used, and the battery test conditions were the same as those of the battery assembled with the POD film. According to the charge and discharge curve of the battery, the battery polarization is higher than that of the single cell assembled with the POD film, and the VE assembled by the single cell has a VE of about 78% and a CE of about 99%. Although such membranes have lower VE in alkaline zinc-iron batteries, the assembled batteries have better cycle stability. After more than 100 cycles, the charge and discharge capacity and charge and discharge energy of the batteries remain stable.

Example 4

The ion conductive membrane is a polybenzimidazole ion exchange membrane (PBI) containing a nitrogen heterocyclic ring, the positive electrolyte is 0.6 mol/L Fe(CN) ₆ ^4- +5 mol/L OH ^- solution; the negative electrolyte is 0.3 mol /L Zn(OH) ₄ ^2- +5mol/L OH ^- solution; the volume of the positive and negative electrolytes is 60mL each; the battery is charged in a constant current charge and discharge mode, charged at a current density of 60mA cm ^-2 for 12min, then the voltage is cut off. Under the condition, the current density of 60 mA cm ^-2 was discharged to 0 V. Since the current density is 60 mA cm ^-2 , the charging time is extended from the initial 10 min to 12 min. It can be seen from Fig. 5a that the ohmic polarization inside the battery is low, and the voltage efficiency and energy efficiency of the battery are both close to 90%, showing excellent performance. Battery performance. A random selection of the partial voltage versus time curve (Fig. 5b) shows that during the long-cycle operation (the battery is running for about 90 hours), the voltage curve during the cycle does not change significantly, showing excellent stability. After more than 500 cycles, the battery's CE, VE, EE (Fig. 5c), discharge capacity and discharge energy (Fig. 5d) showed no significant attenuation, showing excellent stability.

It can be seen from the experiment of variable current density (60-120 mA cm ^-2 ) that the alkaline zinc-iron flow battery assembled with PBI ion exchange membrane has a current density of 120 mA cm ^-2 (Fig. 6a), and the CE retention of the battery At 99% or more, EE is maintained at 82% or more, and VE is maintained at 83% or more, exhibiting excellent rate performance. At the charge and discharge current density of 80 mA cm ^-2 , the initial discharge voltage of the battery assembled with PBI can reach 1.8 V or more (Fig. 6b), and the change trend of charge and discharge voltage is consistent with time (Fig. 6c). It indicates that the internal polarization of the battery remains basically unchanged during the operation of the battery, which is beneficial to obtain stable and excellent battery performance. The alkaline zinc-iron flow battery assembled with PBI has no significant attenuation of battery performance and battery capacity after continuous operation for more than 100 cycles under the current density of 80 mA cm ^-2 (Fig. 6d), further showing excellent circulation. stability.

In order to further confirm the practicability of the alkaline zinc-iron flow battery, the battery performance (capacity and power density) comparable to that of the all-vanadium flow battery currently in the demonstration stage is increased, and the concentration of the positive active material is increased to 1 mol/L Fe. (CN) ₆ ^4- , the concentration of the base is reduced to 3 mol/L OH ^- , and the corresponding negative electrode electrolyte is 0.5 mol/L Zn(OH) ₄ ^2- +3 mol/L OH ^- solution. The positive and negative electrolyte volumes are each 60 mL; PBI is used as an ion exchange membrane to assemble a single cell, which is charged in a constant current charge and discharge mode, charged at a current density of 60 mA cm ^-2 for 30 min, and then the voltage is cut off, 60 mA cm ^-2 Discharge to 0V under current density conditions. It can be seen from Fig. 7a that the ohmic polarization of the battery is further reduced, and the initial discharge voltage of the battery is close to 1.9V. After more than 135 hours of charge and discharge cycles, the initial discharge voltage of the battery is always maintained at about 1.9V (Fig. 7b). ), indicating that the ohmic polarization inside the battery does not change significantly under the condition of high concentration of active material. After more than 150 cycles, the CE of the battery is always above 99%, and VE and EE are always above 91% (Fig. 7c), showing excellent battery performance and cycle stability. Due to the increase of active substances in the electrolyte, the discharge specific capacity of the battery is close to 25Ah/L, and the discharge specific energy is close to 40Wh/L (Fig. 7d), and it remains basically unchanged within 150 cycles, showing a good application prospect. .

Further increasing the operating current density from 60 mA cm ^-2 to 80 mA cm ^-2 , the ohmic polarization inside the battery increases due to the increase in current density, and the initial discharge voltage of the battery is reduced from 1.9 V to about 1.8 V (Fig. 8a). After more than 90 hours of charge and discharge cycle investigation, the initial discharge voltage of the battery is always maintained at about 1.8V (Fig. 8b), indicating that the ohmic polarization inside the battery will not be under the condition of high concentration of active material and high current density. Significant changes have occurred. After more than 200 cycles, the CE of the battery is always above 99%, and VE and EE are always above 88% (Fig. 8c), showing excellent battery performance and cycle stability. Due to the increase in the active material in the electrolyte, the discharge specific capacity of the battery was maintained above 21 Ah/L for more than 200 cycles, and the discharge specific energy was always maintained at 35 Wh/L (Fig. 8d).

All vanadium redox flow battery assembled with Nafion 115 membrane (positive and negative active material concentration 1.5mol/L, H ₂ SO ₄ concentration 3mol/L, positive and negative electrolyte volume 60mL each; battery adopts constant current charge and discharge mode The charge-discharge current density of the battery is 80 mA cm ^-2 , and the charge-discharge cut-off voltage is 1.55 V, 1 V). The alkaline zinc-iron flow battery assembled with PBI is at a current density of 80 mA cm ^-2 , and the battery is used. The CE is 99.61%, the EE is 89.90%, and the EE is 90.24% (Fig. 9a). The performance is much better than that of the all-vanadium flow battery assembled with Nafion 115 membrane (CE is 96.62%, EE is 83.55%, VE). It is 86.47%). After 200 cycles of the all-vanadium flow battery assembled with Nafion 115 membrane, the discharge specific capacity of the battery was 8.7 Ah/L from the initial 26.5 Ah/L (Fig. 9b), and the alkaline zinc iron assembled with PBI. The discharge specific capacity of the flow battery is always above 21 Ah/L (Fig. 9b); on the other hand, the discharge specific energy of the alkaline zinc-iron flow battery assembled with PBI is always maintained at about 35 Wh/L (Fig. 9b). After 200 cycles of the all-vanadium flow battery assembled with Nafion 115 membrane, the discharge specific energy of the battery was 10.8 Wh/L from the initial 33.4 Wh/L (Fig. 9b), and the performance was much better than that of the all-vanadium flow battery. Shows good application prospects.

Comparative example 2:

The ion conductive membrane is a polybenzimidazole ion exchange membrane (PBI) containing a nitrogen heterocyclic ring, the positive electrolyte is 0.6 mol/L Fe(CN) ₆ ^4- +5 mol/L OH ^- solution; the negative electrolyte is 0.3 mol /L Zn(OH) ₄ ^2- +5mol/L OH ^- solution; positive and negative electrolyte volume 60mL each; positive electrode using carbon felt electrode, negative electrode using zinc plate as electrode; battery using constant current charge and discharge mode, at 60mA cm The current density of ^-2 was charged for 12 min, then the voltage was cut off, and the current was discharged to 0 V at a current density of 60 mA cm ^-2 . The coulombic efficiency of the battery is maintained at about 99%, and the voltage efficiency is about 81%. After 70 cycles, the capacity of the battery gradually decreases, and the Coulomb efficiency drops from 99% to 92%. At the end of the battery charging, the battery was disassembled and found that the zinc uniformity deposited on the negative zinc sheet was very poor, and the surface of the PBI film had obvious metallic zinc, indicating that the metal electrode was used as the negative electrode of the alkaline zinc-iron battery, and the efficiency of the battery was The cycle performance and the deposition and dissolution of zinc have a negative impact.

Claims

An alkaline zinc-iron flow battery, the battery comprises a single battery, or a battery module with two or more cells and/or a parallel connection, a liquid storage tank with a positive and negative electrolyte, a circulation pump and a circulation The unit cell comprises a cathode current collecting plate, a negative electrode current collecting plate, a positive electrode, a negative electrode, and an ion conducting membrane, wherein the ion conducting membrane is prepared from an aromatic polymer containing a nitrogen heterocycle, and the positive electrode and the negative electrode are formed. They are carbon felt or carbon paper respectively; the positive electrode electrolyte is a mixed aqueous solution of ferrocyanide and strong alkali, and the negative electrode electrolyte is a mixed aqueous solution of zinc salt or/and zinc oxide and strong alkali, in positive and negative electrolytes. The concentration of the strong base in the aqueous solution is 0.001 to 10 mol/L, and the active material in the positive electrode electrolyte is one of ferricyanide (Fe(CN) 6 3- ) or ferrocyanide (Fe(CN) 6 4- ) Or two kinds, the active material in the negative electrode electrolyte is Zn(OH) 4 2- ; the concentration of the active material in the positive and negative electrolytes is 0.001-3 mol/L; the aromatic polymer containing the nitrogen heterocycle is the main chain One of an aromatic polymer containing a nitrogen heterocycle or an aromatic polymer containing a nitrogen heterocycle Or two or more.
The alkaline zinc-iron flow battery according to claim 1, wherein the aromatic polymer having a nitrogen heterocycle in the main chain is polybenzimidazole, polypyridine, polypyrazole, polypyrimidine, polythiazole, poly One or more polymers of benzothiazole, polyoxazole, polybenzoxazole, polyoxadiazole, polyquinoline, polyquinoxaline, polythiadiazole, polytetrazole; branched chain containing The nitrogen heterocyclic aromatic polymer is a 4,4'-linked group of polyvinylimidazole, polyvinylpyridine, a branched nitrogen-containing heterocyclic imidazole crosslinked chloromethylated polysulfone, and a branched nitrogen-containing heterocyclic ring. One or more of pyridine crosslinked chloromethylated polysulfones.
The alkaline zinc-iron flow battery according to claim 1, wherein the concentration of the active material in the negative electrode electrolyte is 1/2 of the concentration of the active material in the positive electrode electrolyte, which is in the corresponding strong alkali solution. Saturated concentration.
The negative half-cell according to claim 1, wherein the oxide of zinc is zinc oxide, the zinc salt is one or two of zinc chloride and zinc sulfate, and the strong base is sodium hydroxide or hydroxide. One or more of potassium or lithium hydroxide.
The alkaline zinc-iron flow battery according to claim 1 or 3, characterized in that one of the soluble salts of potassium chloride, sodium sulfate, sodium chloride and potassium sulfate may be added to the positive and/or negative electrolyte. One or two or more kinds are used as auxiliary electrolytes to increase the conductivity of the supporting electrolyte; the concentration of the auxiliary electrolyte is 0.1 to 6 mol/L, preferably 2 to 4 mol/L.
The alkaline zinc-iron flow battery according to claim 1, wherein the positive and negative current collecting plates are respectively graphite plates or copper plates.