CN112968190B

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

Info

Publication number: CN112968190B
Application number: CN201911276551.XA
Authority: CN
Inventors: 李先锋; 宋杨; 张华民
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2019-12-12
Filing date: 2019-12-12
Publication date: 2022-06-07
Anticipated expiration: 2039-12-12
Also published as: CN112968190A

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

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

Technical Field

The invention belongs to the field of flow batteries, and particularly relates to a processing method and application of a zinc-bromine flow battery diaphragm.

Background

With the increasing exhaustion of fossil energy, the development and utilization of renewable energy sources such as wind energy and solar energy become the focus of attention of various countries. Because wind energy and solar energy are affected by factors such as weather and the like, the wind energy and the solar energy are discontinuous and unstable, and impact can be caused to a power grid in the renewable energy power generation grid connection process, so that the power supply quality and the stability of the power grid are affected. The energy storage technology can solve the problem and ensure the efficient and stable operation of the renewable energy power generation grid connection. Energy storage technologies are mainly classified into two categories, physical energy storage and chemical energy storage. The chemical energy storage represented by the all-vanadium redox flow battery and the zinc-bromine redox flow battery has the most advantages in large-scale energy storage due to the advantages of mutual independence of power and capacity, quick response, simple structure, easiness in design, long cycle life, environmental friendliness and the like. Compared with the electrolyte of the all-vanadium redox flow battery, the electrolyte of the zinc-bromine redox flow battery has the advantages of low price, abundant resources and wide sources.

For zinc-bromine system flow batteries, the self-discharge of the batteries always restricts important factors for the development of the batteries. In the charging process of the battery and the laying process after charging, bromine molecules generated in the positive electrode can diffuse to the negative electrode through the diaphragm micropores, and further undergo redox reaction with a zinc simple substance generated by the negative electrode, so that the capacity of the battery is reduced, and the coulombic efficiency is reduced.

The inner micropores of the existing commercial PE porous membrane are too large, and even the PE porous membrane manufactured by the most mature manufacturing process has the diameter of more than 0.1um, so that the membrane aperture is still large for the zinc-bromine flow battery.

Disclosure of Invention

Based on the background technology, the invention provides a processing method of a zinc-bromine flow battery diaphragm, which is characterized in that a hot pressing method is utilized, a PE porous membrane is heated to a certain temperature, and then the inner micropores of the PE porous membrane are reduced by a recompression method. The diaphragm with the reduced diaphragm hole has higher capacity of blocking bromine molecules, inhibits the diffusion of the bromine molecules, improves the battery capacity, improves the coulombic efficiency of the battery, and accordingly relieves the self-discharge of the battery.

The invention combines the structural characteristics of the diaphragm of the zinc-bromine flow battery, adopts a high-temperature hot-pressing method, reduces the internal micropores of the diaphragm to prevent the diffusion of bromine molecules of the positive electrode to the negative electrode, reduces the self-discharge of the battery and improves the capacity of the battery.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a processing method of a zinc-bromine flow battery diaphragm cuts a commercial PE porous membrane on the market into a proper area (the area is 36 cm) by using a hot pressing method²～1000cm²After the thickness of the film is 200-900um, hot pressing is carried out; the temperature range during hot pressing treatment is 160-190 ℃, the pressure intensity during hot pressing is 2-10 MPa, and the hot pressing time range is 5-20 mins. And after the hot pressing is finished, naturally cooling the diaphragm to room temperature.

The hot pressing device is a 100T flat plate machine, and the PE porous membrane is placed on a pure flat metal hot pressing die which is heated to the hot pressing temperature in advance for hot pressing treatment.

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

Based on the technical scheme, the preferable pore diameter of the PE porous membrane is 0.1-0.15um of average pore diameter, and the porosity is 58-65%.

The invention also provides the diaphragm obtained by the treatment method, wherein the pore diameter of the diaphragm (of the PE porous membrane) after hot pressing is 0.05-0.07 um, and the porosity is 65-75%.

The invention also provides an application of the diaphragm in a zinc-bromine flow battery.

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

Based on the technical scheme, the preferable use temperature of the zinc-bromine flow battery is-30 ℃ to 60 ℃.

Advantageous effects

(1) The invention uses the hot pressing method to place the diaphragm on the pure flat metal mold hot pressing tool which is heated in advance, and the whole micropore is reduced by the hot pressing method. The diaphragm with the reduced diaphragm hole has higher capacity of blocking bromine molecules, inhibits the diffusion of the bromine molecules to a negative electrode, improves the battery capacity, improves the coulombic efficiency of the battery, and accordingly relieves the self-discharge of the battery. The pore size after hot pressing is inversely related to the hot pressing pressure or the hot pressing time obtained in the hot pressing experiment.

(2) The coulombic efficiency of the diaphragm running zinc-bromine flow battery manufactured by the method is 2-3% higher than that of a PE porous membrane without treatment, 2-3% higher than that of a commercial PE porous membrane coated with Nafion resin, and 1-2% higher than that of a commercial PE porous membrane shrunk by a chemical method. The battery diaphragm after hot pressing is used, the aperture is reduced, the diffusion of bromine molecules is obviously inhibited when the diaphragm is applied to a zinc-bromine flow battery, the self-discharge of the battery is inhibited, the coulomb efficiency of the battery is obviously improved, and the battery capacity is greatly improved.

(3) The method has the advantages of low cost, quick response and simple operation. The self-discharge problem of the zinc-bromine flow battery is solved efficiently in a short time, and the development of the zinc-bromine system flow battery is promoted.

(4) The diaphragm obtained by the processing method provided by the invention runs the zinc-bromine flow battery, and the battery also shows good bromine resistance performance in the process of placing after charging, and the capacity retention rate of the battery is high.

Drawings

Fig. 1 is a graph of charge-discharge cycle stability of the battery of example 1.

Detailed Description

In the following embodiments, the pore diameter of the commercial PE porous membrane is 0.1-0.15um, the porosity is 50-65%, and the thickness is 200-900 um.

Example 1

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

Single cell structure: the monocell comprises a positive electrode end plate, a positive electrode current collector, a positive electrode arranged in a positive electrode frame, a cell diaphragm, a negative electrode arranged in a negative electrode frame, a negative electrode current collector and a negative electrode end plate which are sequentially overlapped from bottom to top, wherein negative electrolyte in a negative electrolyte storage tank flows through the negative electrode by a pump, the positive electrolyte does not flow and is sealed in a closed cavity surrounded by the positive electrode current collector, the positive electrode frame, the positive electrode and the cell diaphragm; wherein the positive electrode is a carbon felt; the negative electrode is also a deposition type carbon felt electrode, and the positive electrolyte and the negative electrolyte are zinc-bromine conventional 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 areas of the positive electrode and the negative electrode are 6 cm; the positive and negative current collectors are made of graphite. The diaphragm used in this example is a diaphragm after hot pressing treatment, and the hot pressing conditions are as follows: 170 ℃, 2MPa and 10 mins. The resulting membrane parameters are shown in table 1.

Comparative example 1

A single cell was run using a commercial PE porous membrane with a Nafion resin coating.

The method for manufacturing the diaphragm comprises the following steps: a commercial PE porous membrane is coated with Nafion solution with the mass concentration of 5%, the coating thickness is 30-50 um, and the solution is dried to leave pure Nafion resin on the surface of the membrane close to the anode.

The separator fabricated using the above method operates a single cell.

Single cell structure: the monocell comprises a positive electrode end plate, a positive electrode current collector, a positive electrode arranged in a positive electrode frame, a cell diaphragm, a negative electrode arranged in a negative electrode frame, a negative electrode current collector and a negative electrode end plate which are sequentially overlapped from bottom to top, wherein negative electrolyte in a negative electrolyte storage tank flows through the negative electrode by a pump, the positive electrolyte does not flow and is sealed in a closed cavity surrounded by the positive electrode current collector, the positive electrode frame, the positive electrode and the cell diaphragm; wherein the positive electrode is a carbon felt; the negative electrode is also a deposition type carbon felt electrode, and the positive electrolyte and the negative electrolyte are zinc-bromine conventional 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 areas of the positive electrode and the negative electrode are 6 cm; the positive and negative current collectors are made of graphite.

Comparative example 2

The cells were run using a commercial PE porous membrane that was chemically necked.

The method for manufacturing the diaphragm comprises the following steps: the silica component inside the commercial PE porous membrane is converted into nickel silicate using a chemical method, and the nickel silicate occupies a larger volume in the micropores of the PE membrane due to its larger molecular size than silica, thereby reducing the pore size of the micropores of the PE membrane, with an average pore size of 0.09-0.094 um.

The separator fabricated using the above method operates a single cell.

Comparative example 3

The original commercial PE porous separator was hot pressed using a continuous temperature increase.

Single cell structure: the monocell comprises a positive electrode end plate, a positive electrode current collector, a positive electrode arranged in a positive electrode frame, a battery diaphragm, a negative electrode arranged in a negative electrode frame, a negative electrode current collector and a negative electrode end plate which are sequentially overlapped from bottom to top, wherein negative electrolyte in a negative electrolyte storage tank flows through the negative electrode through a pump, the positive electrolyte does not flow and is sealed in a closed cavity surrounded by the positive electrode current collector, the positive electrode frame, the positive electrode and the battery diaphragm; wherein the positive electrode is a carbon felt; the negative electrode is also a deposition type carbon felt electrode, and the positive electrolyte and the negative electrolyte are zinc-bromine conventional 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 areas of the positive and negative electrodes are 6 cm; the positive and negative current collectors are made of graphite. The diaphragm used in the embodiment is a diaphragm subjected to hot pressing treatment, and the hot pressing method comprises the following steps: the diaphragm is placed in a flat hot-pressing metal mould, the pressing pressure of an upper metal plate and a lower metal plate is 4MPa, the upper metal mould and the lower metal mould are continuously heated under the condition, the initial temperature of the upper metal mould and the lower metal mould is 25 ℃, the upper metal mould and the lower metal mould are heated at a heating rate of 5 ℃/min, and the temperature is stopped when the temperature is increased to 160 ℃. The diaphragm was then removed and allowed to cool naturally to room temperature.

Table 1 shows the hot-pressing film parameters for different hot-pressing conditions and different hot-pressing conditions. (examples 2 to 5 in Table 1 changed the autoclave temperature, autoclave pressure and autoclave time, the other conditions were the same as in example 1, comparative examples 4 to 7 changed the autoclave temperature, autoclave pressure and autoclave time, the other conditions were the same as in comparative example 1)

TABLE 1

The commercial PE porous membranes before hot pressing in the examples in Table 1 all had a membrane thickness of 900 μm and a pore size in the range of 0.1-0.12 with a porosity of 58%.

Table 2 shows a comparison of the performance of the cells operated with different membranes. The operating conditions of the cells are: charging for 60mins, and current density of 40mA/cm²Discharge Current Density 40mA/cm²As can be seen from the table, the coulomb efficiency of the zinc-bromine single flow battery operated by the PE porous membrane after the hot pressing treatment of the invention is obviously improved (compared with the battery manufactured by other methods), and the battery also shows better bromine resistance performance in the laying process after the charging is finished, and the capacity retention rate of the battery is higher.

TABLE 2

Comparative example 4 when the hot pressing temperature is lower than 160 ℃, the PE porous membrane cannot reach the molten state required by the present invention due to too low temperature, and at this time, the separator is hot pressed, and the purpose of shrinkage cannot be achieved, resulting in too large pore diameter of the separator after hot pressing, with an average pore diameter of only 0.095um, which cannot meet the requirement of bromine inhibition.

Comparative example 5 when the hot-pressing pressure exceeds 10MPa, the average pore diameter of the diaphragm after hot-pressing is only 0.021um due to too large pressure, the pores of the diaphragm are compacted, and the pore diameter is too small to ensure the normal ion selectivity of the diaphragm, so that the battery cannot normally operate.

Comparative example 6 because the hot pressing temperature is too high, the PE membrane is under the high temperature molten state, and inside membrane hole has basically collapsed, and hot pressing again can shrink the membrane hole to be close to the dead-shut state this moment, and the aperture of membrane hole is only 0.012um this moment, and with the experimental result of comparative example 5, leads to the battery can not normally operate.

Comparative example 7 hot pressing time overlength, exceed 20mins, longer heating time can let the diaphragm become the molten state from outside to inside whole, and inside membrane hole has basically collapsed, and with the experimental result of comparative example 6, the aperture of membrane hole is only 0.010um this moment, leads to the battery can not normally operate.

As can be seen from the hot pressing conditions and the processed separator parameters in table 1 and the battery performance data in table 2, different hot pressing temperatures, pressures and hot pressing times have a greater effect on the performance of the separator. Under the hot pressing condition protected by the invention (examples 1-5), when the hot pressing temperature and the hot pressing time are fixed, the size of the membrane hole is inversely proportional to the hot pressing pressure, and the thickness of the membrane is inversely proportional to the hot pressing pressure. When the hot-pressing pressure is fixed, the higher the hot-pressing temperature is, the smaller the micropores of the prepared diaphragm are, and the thinner the thickness is; the longer the hot pressing time, the smaller the micropores of the prepared diaphragm and the thinner the thickness. It can be seen from the table two that the zinc-bromine flow battery operated by the separator manufactured under the above conditions has relatively high coulombic efficiency and capacity retention rate after the battery is left for 24 hours, and can effectively alleviate the self-discharge problem of the zinc-bromine flow battery.

The diaphragm manufactured under the hot-pressing condition (comparative examples 4-7) which is not protected by the invention has relatively poor battery performance, and the purpose of relieving the self-discharge of the zinc-bromine flow battery cannot be achieved. When the hot-pressing temperature is lower than the hot-pressing temperature range protected by the invention, the PE material around the membrane pores of the membrane cannot be compressed and expanded because the membrane cannot be heated to a molten state, and the aim of shrinkage porosity cannot be achieved. When the hot-pressing pressure is higher than the hot-pressing pressure range protected by the invention, the diaphragm loses the original ion selection function due to the compaction of the diaphragm pores, so that the battery cannot normally operate.

In addition, if a temperature programming (experimental conditions described in comparative example 3) is used, this method corresponds to an increase in hot-pressing time, which eventually also results in the pores of the membrane being compacted, so that the battery cannot operate properly.

TABLE 3 diaphragm Properties of PE porous membranes of different thicknesses after different hot pressing conditions (both hot pressing temperatures are 160 deg.C.)

The preferable hot pressing conditions are that the hot pressing pressure is more than 4-6Mpa, the hot pressing time is more than 10-15min, and the pore size distribution range of the hot pressing diaphragm prepared under the conditions is as follows: 0.064-0.075um, the bromine-blocking ability of the separator is strongest with minimal impact on its energy efficiency when the cell is assembled for operation. The most preferred autoclave conditions are: before hot pressing: the thickness range of the diaphragm is more than 600-: 160 ℃, the hot-pressing pressure range is more than 4-6Mpa, the hot-pressing time is more than 10-15min, the hot-pressed diaphragm thickness range is 440-580um, the diaphragm aperture range is 0.064-0.068um, and the diaphragm porosity is 66%.

Claims

1. The application of the diaphragm in the zinc-bromine flow battery is characterized in that: carrying out hot pressing on the polyethylene porous membrane by using a hot pressing method to obtain the diaphragm; the average pore diameter of the polyethylene porous membrane is 0.1-0.15 mu m, and the porosity is 58% -65%;

the temperature range during hot pressing treatment is 160-190 ℃, the pressure intensity during hot pressing is 2-10 MPa, and the hot pressing time range is 5-20 mins; placing the polyethylene porous membrane on a pure flat metal hot-pressing mould which is preheated to the hot-pressing temperature in the hot-pressing process to carry out hot-pressing treatment; the aperture of the diaphragm is 0.01-0.07 mu m, and the energy density of the zinc-bromine flow battery is 110Wh/L-200 Wh/L; the thickness of the polyethylene porous membrane is 200-900 μm.

2. Use according to claim 1, characterized in that:

the thickness of the diaphragm obtained after hot pressing is 50-65% of that of the polyethylene porous film.

3. Use according to claim 1, characterized in that: the diaphragm has the aperture of 0.05-0.07 mu m and the porosity of 65-75%.

4. The use of claim 1, wherein the zinc-bromine flow battery is used at a temperature of-30 ℃ to 60 ℃.