CN112968190B - Processing method of zinc-bromine flow battery diaphragm, diaphragm and application - Google Patents

Abstract

The invention relates to a processing method and application of a diaphragm in a zinc bromine flow battery. The method has the advantages of simple operation, stable process, obvious application effect and the like. The diaphragm operating zinc-bromine flow battery manufactured by the method can effectively improve the coulomb efficiency of the battery and prolong the service life of the battery.

Description

A kind of treatment method and membrane of zinc-bromine flow battery diaphragm and application

technical field

The invention belongs to the field of liquid flow batteries, and in particular relates to a treatment method and application of a zinc-bromine liquid flow battery diaphragm.

Background technique

With the increasing depletion of fossil energy, the development and utilization of renewable energy such as wind energy and solar energy have become the focus of attention of all countries. Due to the discontinuity and instability of wind energy and solar energy due to the influence of weather and other factors, this will cause an impact on the grid during the integration of renewable energy power generation into the grid, affecting the quality of power supply and the stability of the grid. Energy storage technology can solve this problem and ensure the efficient and stable operation of renewable energy generation and grid connection. Energy storage technology is mainly divided into two categories: physical energy storage and chemical energy storage. Among them, chemical energy storage represented by all-vanadium flow battery and zinc-bromine flow battery has many advantages such as independence of power and capacity, rapid response, simple structure, easy design, long cycle life, and environmental friendliness. the most advantageous. Zinc-bromine flow battery electrolyte has advantages over all-vanadium redox flow battery electrolyte due to its cheap price, abundant resources and wide range of sources.

For zinc-bromine system flow batteries, battery self-discharge has always been an important factor restricting the development of such batteries. During the charging process of the battery and the shelving process after charging, the bromine molecules generated in the positive electrode will diffuse to the negative electrode through the micropores of the separator, and then undergo a redox reaction with the zinc element generated by the negative electrode, resulting in a decrease in battery capacity and a decrease in Coulombic efficiency.

Existing commercial PE porous membranes have too large internal micropores. Even the PE porous membrane produced by the most mature production process has a micropore diameter of more than 0.1um. The aperture is still too large.

SUMMARY OF THE INVENTION

Based on the above background technology, the present invention provides a method for treating the separator of a zinc-bromine flow battery, which uses a hot pressing method to heat the PE porous membrane to a certain temperature, and then reduces its internal micropores by recompressing. The separator with the narrowed membrane pores has a higher ability to block bromine molecules, inhibits the diffusion of bromine molecules, improves battery capacity, improves battery coulombic efficiency, and relieves battery self-discharge.

Combining the structural characteristics of the zinc-bromine flow battery separator, the invention adopts the method of high temperature hot pressing to reduce the micropores in the separator to block the diffusion of positive bromine molecules to the negative electrode, reduce the self-discharge of the battery, and improve the battery capacity.

For achieving the above object, the technical scheme adopted in the present invention is as follows:

A method for treating a separator of a zinc-bromine flow battery, using a hot-pressing method to cut an existing commercial PE porous membrane into an appropriate area (the area is 36cm ² to 1000cm ² , and the film thickness is (200um to 900um). The temperature range during hot pressing is 160℃～190℃, the pressure during hot pressing is 2MPa～10MPa, and the time range of hot pressing is 5mins～20mins. After the hot pressing, let the diaphragm naturally cool to room temperature.

The hot-pressing device is a 100T flatbed machine, and the PE porous film is placed on a flat metal hot-pressing mold that has been preheated to the hot-pressing temperature for hot-pressing treatment.

Based on the above technical solutions, preferably, the separator used is a commercial PE porous membrane; the thickness of the PE porous membrane is 200um-900um. The thickness of the separator after hot pressing accounts for 50-65% of the thickness of the PE porous membrane.

Based on the above technical solutions, preferably, the pore size of the PE porous membrane is an average pore size of 0.1-0.15um, and a porosity of 58%-65%.

The present invention also provides a diaphragm obtained by the above-mentioned treatment method. The diaphragm (of the PE porous membrane) after hot pressing has a pore diameter of 0.05-0.07um and a porosity of 65%-75%.

The present invention also provides an application of the above-mentioned separator in a zinc-bromine liquid flow battery.

Based on the above technical solutions, preferably, the energy density of the zinc-bromine flow battery is 110Wh/L-200Wh/L.

Based on the above technical solutions, preferably, the operating temperature of the zinc-bromine flow battery is -30°C to 60°C.

beneficial effect

(1) The present invention utilizes the method of hot pressing, placing the diaphragm on the hot pressing tool of the flat metal mold that has been heated in advance, and reducing the overall micropores by the method of hot pressing. The separator with the narrowed membrane pores has a higher ability to block bromine molecules, inhibits the diffusion of bromine molecules to the negative electrode, improves the battery capacity, improves the battery coulombic efficiency, and relieves the battery self-discharge. Through the hot-pressing experiment, the pore size after hot-pressing is negatively correlated with the hot-pressing pressure or hot-pressing time.

(2) Using the separator made by the method of the present invention to operate the zinc-bromine flow battery, the battery coulombic efficiency is 2% to 3% higher than that of using the untreated PE porous membrane, and compared with the use of the commercial membrane coated with Nafion resin The chemical PE porous membrane is 2% to 3% higher, which is 1% to 2% higher than the commercial PE porous membrane using chemical shrinkage. Using the hot-pressed battery separator, the pore size is reduced, and the application in the zinc-bromine flow battery obviously inhibits the diffusion of bromine molecules, inhibits the self-discharge of the battery, significantly improves the coulombic efficiency of the battery, and greatly improves the battery capacity.

(3) The method of the present invention has low cost, quick effect and simple operation. The self-discharge problem of zinc-bromine flow batteries is solved in a short time and high efficiency, which promotes the development of zinc-bromine system flow batteries.

(4) the diaphragm that the treatment method of the present invention obtains operates the zinc-bromine liquid flow battery, and the battery also shows better bromine resistance performance in the shelving process after charging, and the battery capacity retention rate is higher.

Description of drawings

FIG. 1 is a charge-discharge cycle stability diagram of the battery of Example 1. FIG.

Detailed ways

In the following specific embodiments, commercial PE porous membranes are used with a pore size of 0.1-0.15um, a porosity of 50-65%, and a thickness of 200-900um.

Example 1

The separator after hot pressing was tested using a single cell, and the embodiment is as follows.

Single cell structure: The single cell includes the positive electrode plate, the positive electrode current collector, the positive electrode placed in the positive electrode frame, the battery separator, the negative electrode placed in the negative electrode frame, the negative electrode current collector, and the negative electrode. Plate, the negative electrolyte in the negative electrolyte storage tank flows through the negative electrode through the pump, and the positive electrolyte does not flow and is sealed in a closed chamber surrounded by the positive current collector, the positive electrode frame, the positive electrode, and the battery diaphragm; Extremely carbon felt; the negative electrode is also a deposited carbon felt electrode, and the positive and negative electrolytes are conventional zinc-bromine electrolytes. The negative electrode is enclosed in an electrode frame made of PVC material, and the thickness of the electrode frame is 3 mm. The positive electrode is enclosed in an electrode frame made of PVC material, and the thickness of the electrode frame is 4 mm. The effective area of the positive and negative electrodes is 6*6cm; the material of the positive and negative current collectors is graphite. The separator used in this example is the separator after hot pressing, and the hot pressing conditions are: 170°C, 2MPa, 10mins. The obtained diaphragm parameters are shown in Table 1.

Comparative Example 1

Single cells were run using a commercial PE porous membrane coated with Nafion resin.

The method of making the separator: use the Nafion solution with a mass concentration of 5% to coat the surface of the commercial PE porous membrane with a coating thickness of 30um to 50um, dry the solution, and leave the pure Nafion resin on the side of the membrane near the positive electrode s surface.

A single cell was run using the separator fabricated as described above.

Single cell structure: The single cell includes the positive electrode plate, the positive electrode current collector, the positive electrode placed in the positive electrode frame, the battery separator, the negative electrode placed in the negative electrode frame, the negative electrode current collector, and the negative electrode. Plate, the negative electrolyte in the negative electrolyte storage tank flows through the negative electrode through the pump, and the positive electrolyte does not flow and is sealed in a closed chamber surrounded by the positive current collector, the positive electrode frame, the positive electrode, and the battery diaphragm; Extremely carbon felt; the negative electrode is also a deposited carbon felt electrode, and the positive and negative electrolytes are conventional zinc-bromine electrolytes. The negative electrode is enclosed in an electrode frame made of PVC material, and the thickness of the electrode frame is 3 mm. The positive electrode is enclosed in an electrode frame made of PVC material, and the thickness of the electrode frame is 4 mm. The effective area of the positive and negative electrodes is 6*6cm; the material of the positive and negative current collectors is graphite.

Comparative Example 2

Single cells were run using a chemically pored commercial PE porous membrane.

The method of making the diaphragm: using chemical methods, the silicon dioxide component inside the commercial PE porous membrane is converted into nickel silicate. Because the molecular size of nickel silicate is larger than that of silicon dioxide, it occupies the micropores of the PE diaphragm. A larger volume, thereby reducing the micropore diameter of the PE separator, with an average diameter of 0.09-0.094um.

A single cell was run using the separator fabricated as described above.

Single cell structure: The single cell includes the positive electrode plate, the positive electrode current collector, the positive electrode placed in the positive electrode frame, the battery separator, the negative electrode placed in the negative electrode frame, the negative electrode current collector, and the negative electrode. Plate, the negative electrolyte in the negative electrolyte storage tank flows through the negative electrode through the pump, and the positive electrolyte does not flow and is sealed in a closed chamber surrounded by the positive current collector, the positive electrode frame, the positive electrode, and the battery diaphragm; Extremely carbon felt; the negative electrode is also a deposited carbon felt electrode, and the positive and negative electrolytes are conventional zinc-bromine electrolytes. The negative electrode is enclosed in an electrode frame made of PVC material, and the thickness of the electrode frame is 3 mm. The positive electrode is enclosed in an electrode frame made of PVC material, and the thickness of the electrode frame is 4 mm. The effective area of the positive and negative electrodes is 6*6cm; the material of the positive and negative current collectors is graphite.

Comparative Example 3

The pristine commercial PE porous membrane was hot-pressed using a continuous temperature rise.

Single cell structure: The single cell includes the positive electrode plate, the positive electrode current collector, the positive electrode placed in the positive electrode frame, the battery separator, the negative electrode placed in the negative electrode frame, the negative electrode current collector, and the negative electrode. Plate, the negative electrolyte in the negative electrolyte storage tank flows through the negative electrode through the pump, and the positive electrolyte does not flow and is sealed in a closed chamber surrounded by the positive current collector, the positive electrode frame, the positive electrode, and the battery diaphragm; Extremely carbon felt; the negative electrode is also a deposited carbon felt electrode, and the positive and negative electrolytes are conventional zinc-bromine electrolytes. The negative electrode is enclosed in an electrode frame made of PVC material, and the thickness of the electrode frame is 3 mm. The positive electrode is enclosed in an electrode frame made of PVC material, and the thickness of the electrode frame is 4 mm. The effective area of the positive and negative electrodes is 6*6cm; the material of the positive and negative current collectors is graphite. The diaphragm used in this embodiment is the diaphragm after hot pressing. The hot pressing method is as follows: first place the diaphragm in a flat hot pressing metal mold, and the pressing pressure of the upper and lower metal plates is 4MPa. Under this condition, the upper and lower metal molds are continuously To heat up, the initial temperature of the upper and lower metal molds is 25°C, and the upper and lower metal molds are heated at a heating rate of 5°C/min, and the temperature rises to 160°C to stop. The septum was then removed and allowed to cool naturally to room temperature.

Table 1 shows the technical parameters of the hot-pressed films made with different hot-pressing conditions and different hot-pressing conditions. (Example 2-5 in Table 1 changes the temperature of hot pressing, hot pressing pressure and hot pressing time, other conditions are the same as Example 1, and Comparative Example 4-7 changes hot pressing temperature, hot pressing pressure and hot pressing time, other The conditions are the same as the comparative example 1)

Table 1

The commercialized PE porous membranes of the examples in Table 1 before hot pressing have a membrane thickness of 900um, a pore size range of 0.1-0.12, and a porosity of 58%.

Table 2 compares the performance of single cells operating with different separators. The operating conditions of the single cell are: charging 60mins, current density 40mA/cm ² , discharge current density 40mA/cm ² As can be seen from the table, the zinc-bromine single-flow battery operated by the hot-pressed PE porous membrane of the present invention, the battery The Coulombic efficiency is significantly improved (compared to using other methods to make batteries), and the battery also shows better bromine resistance during the shelving process after charging, and the battery capacity retention rate is high.

Table 2

Comparative Example 4 When the hot pressing temperature is lower than 160°C, the PE porous membrane cannot reach the molten state required by the present invention because the temperature is too low. The pore size of the diaphragm is too large, and the average pore size is only 0.095um, which cannot meet the requirements of bromine blocking.

Comparative Example 5 When the hot pressing pressure exceeds 10MPa, due to the excessive pressure, the average pore size of the diaphragm after hot pressing is only 0.021um, the membrane pores are compacted, and the pore size is too small to ensure the normal ion selectivity of the diaphragm, resulting in the battery not operating normally. .

Comparative Example 6 Because the hot pressing temperature is too high, the inner membrane pores of the PE film have basically collapsed under the high temperature melting state. At this time, the hot pressing will reduce the membrane pores to a nearly closed state. At this time, the pore size of the membrane pores is only 0.012 um, the same as the experimental results of Comparative Example 5, resulting in the battery not operating normally.

In Comparative Example 7, the hot pressing time is too long, more than 20mins. The longer heating time will make the diaphragm completely melt from the outside to the inside, and the internal membrane pores have basically collapsed. The aperture is only 0.010um, which causes the battery to not operate normally.

It can be seen from the hot-pressing conditions and the treated diaphragm parameters in Table 1 and the battery performance data in Table 2 that different hot-pressing temperatures and pressures and hot-pressing time have a greater impact on the performance of the diaphragm. Under the hot-pressing conditions protected by the present invention (Examples 1-5), when the hot-pressing temperature and hot-pressing time are constant, the size of the membrane pores is inversely proportional to the hot-pressing pressure, and the thickness of the diaphragm is inversely proportional to the hot-pressing pressure. When the hot-pressing pressure is constant, the higher the hot-pressing temperature, the smaller the micropores and the thinner the thickness of the prepared diaphragm; the longer the hot-pressing time, the smaller the micropores and the thinner the thickness of the prepared diaphragm. As can be seen from Table 2, the zinc-bromine flow battery operated by the diaphragm made by the above conditions, the coulombic efficiency of the battery and the capacity retention rate when the battery is put on hold for 24 hours are relatively high, which can effectively alleviate the self-discharge problem of the zinc-bromine flow battery.

The separators made under the hot-pressing conditions not protected by the present invention (Comparative Examples 4-7) have relatively poor battery performance and cannot achieve the purpose of alleviating the self-discharge of the zinc-bromine flow battery. When the hot-pressing temperature is lower than the hot-pressing temperature range protected by the present invention, because the diaphragm cannot be heated to a molten state, the PE material around the diaphragm film hole cannot be compressed and expanded, and the purpose of shrinkage cannot be achieved. When the hot-pressing pressure is higher than the range of hot-pressing pressure protected by the present invention, the diaphragm membrane loses its original ion-selective function due to the compaction of the membrane pores, so that the battery cannot operate normally. Similarly, if the hot-pressing temperature is increased Or if the hot-pressing time is beyond the protection range of the present invention, the hot-pressed separator cannot have the normal ion selection function, so that the battery cannot operate normally.

In addition, if the temperature program is used (experimental conditions described in Comparative Example 3), this method is equivalent to increasing the hot pressing time, which will eventually lead to the compaction of the membrane pores, making the battery unable to operate normally.

Table 3 Diaphragm properties of PE porous membranes with different thicknesses after different hot pressing conditions (both hot pressing temperature is 160℃)

From Table 3, it can be concluded that the preferred hot-pressing conditions are that the hot-pressing pressure is >4-6Mpa, and the hot-pressing time is >10-15min. The hot-pressing diaphragm prepared under these conditions has a membrane pore size distribution range of: 0.064-0.075um , under the condition that the assembled battery has the least impact on its energy efficiency, the separator has the strongest bromine blocking ability. The most preferred hot-pressing conditions are: before hot-pressing: diaphragm thickness range >600-900um, hot-pressing temperature: 160°C, hot-pressing pressure range >4-6Mpa, hot-pressing time >10-15min, after hot-pressing The thickness of the diaphragm is in the range of 440-580um, the pore size of the membrane is in the range of 0.064-0.068um, and the membrane porosity is 66%.

Claims (4)

1. the application of a separator in a zinc-bromine flow battery, it is characterized in that: using the method of hot pressing, polyethylene porous membrane is carried out hot pressing to obtain described separator; The average pore size of polyethylene porous membrane is 0.1～0.15 μm , the porosity is 58%~65%; The temperature range during hot pressing is 160°C~190°C, the pressure during hot pressing is 2MPa~10MPa, and the hot pressing time range is 5mins~20mins; during the hot pressing process, the polyethylene porous membrane is placed in a place that has been preheated to hot pressing. Hot-pressing treatment is performed on a flat metal hot-pressing die at a high temperature; the diameter of the diaphragm is 0.01-0.07 μm, and the energy density of the zinc-bromine flow battery is 110Wh/L-200 Wh/L; the thickness of the polyethylene porous membrane is 200μm ~900μm. 2. application according to claim 1, is characterized in that: The thickness of the separator obtained after hot pressing is 50-65% of the thickness of the polyethylene porous membrane. 3. The application according to claim 1, wherein the diaphragm has a pore diameter of 0.05-0.07 μm and a porosity of 65% to 75%. 4. The application according to claim 1, wherein the operating temperature of the zinc-bromine flow battery is -30°C-60°C.

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