CN114551911A - Preparation and application of a negative electrode structure for zinc-based flow batteries - Google Patents

Abstract

A carbon felt electrode structure design capable of remarkably improving the capacity of a zinc negative electrode surface of a zinc-based flow battery. And cutting the surface of the carbon felt electrode to obtain a plurality of cuboid grooves, and embedding a three-dimensional porous insulating material with certain mechanical strength in the grooves to obtain the carbon felt electrode. Simple operation, stable process and low cost. The electrode designed by the invention greatly slows down the deposition pressure of zinc between the carbon felt and the membrane, provides a large amount of zinc deposition space, effectively improves the cycling stability of the zinc-based flow battery under the condition of high deposition surface capacity, and greatly prolongs the service life of the battery.

Description

Preparation and application of a negative electrode structure for zinc-based flow batteries

technical field

The present invention relates to the field of liquid flow batteries, in particular to the field of zinc-based liquid flow batteries.

Background technique

With the depletion of fossil energy and the intensification of the global greenhouse effect, renewable energy plays an increasingly important role in the energy structure. However, renewable energy sources such as wind energy and solar energy are discontinuous and unstable, making their direct utilization difficult. Therefore, the use of energy storage technology to achieve continuous supply of renewable energy has become the key to solving the above problems. Zinc-based flow batteries have the advantages of low cost, high theoretical energy density and strong safety, and have become one of the most promising technologies in the large-scale energy storage market.

Unlike liquid-liquid flow batteries (e.g. vanadium flow batteries, all-iron flow batteries) in which the redox couple exists as a liquid phase in the anolyte and catholyte, the zinc anode of zinc-based flow batteries has The liquid-solid phase transition process, that is, the deposition/dissolution process of metallic zinc in the negative electrode. When there is insufficient space for anode deposition at high areal capacities, a series of consequences, such as increased deposition overpotential, irreversible hydrogen evolution side reactions, and short circuits caused by dendrites piercing the separator, can result. All of these issues will be reflected in battery performance, i.e. low battery capacity, low voltage efficiency, low coulombic efficiency, and short cycle life. At the same time, the high deposition surface capacity of the battery will inevitably bring about the problem of aggravated zinc dendrite growth. However, for zinc-based flow batteries, the stored energy is directly related to the amount of metal zinc plated on the negative electrode. It is necessary but challenging to increase the zinc deposition area capacity and solve the zinc deposition problem under high areal capacity conditions. .

SUMMARY OF THE INVENTION

A high areal capacity negative electrode structure design for zinc-based flow batteries. The production process of the electrode is simple and easy. Several cuboids are cut on the surface of the carbon felt, and the cutting depth is 10-90% of the thickness of the carbon felt, preferably 50-80%, and a three-dimensional porous insulating material with a certain mechanical strength is embedded in the cutting part. (eg, high-density sponge, etc.), the upper surface of the embedded material is 0.5-3mm (preferably 1-1.5mm) higher than the upper surface of the carbon felt, and an electrode with staggered distribution can be obtained. When assembling the zinc-based flow battery, the negative electrode uses a high-low distributed electrode structure, the positive electrode uses the original carbon felt structure, the separator uses a porous membrane, and the electrolyte on the negative electrode side of the positive electrode circulates.

A negative electrode structure for a zinc-based liquid flow battery, comprising a carbon felt electrode body, and two or more strip-shaped protrusions of mutually spaced and parallel porous insulating materials are sequentially arranged on one side surface of the carbon felt electrode body from left to right .

The height of the protrusions of the porous insulating material on the surface of the carbon felt (the distance from the plane of the protrusions away from the surface of the carbon felt to the surface of the carbon felt) is 0.5-2mm, preferably 1-1.2mm; the spacing between adjacent strip-like protrusions is 0.5-1.5 cm, preferably 0.8-1 cm.

The distance between the two ends of the strip (the upper and lower ends in FIG. 1 ) and the upper and lower edges of the adjacent carbon felt is 0.3-1 cm, preferably 0.5-0.8 cm; the leftmost strip and the carbon felt The distance between the side edges is 0.3-1 cm, preferably 0.5-0.8 cm; the distance between the rightmost strip protrusion and the right edge of the carbon felt is 0.3-1 cm, preferably 0.5-0.8 cm.

The width of the strip-like protrusions is 1-8 mm, preferably 2-5 mm.

The carbon felt is in the shape of a rectangular flat plate, and the side of the strip protrusions close to the surface of the carbon felt is embedded into the carbon felt, and the embedded depth is 10-90% of the thickness of the carbon felt, preferably 50-80%.

The porous insulating material is one or more of high-density sponges, the density of which is greater than or equal to 45 g/cm ³ and the porosity is greater than or equal to 90%.

The preparation method of the negative electrode structure,

The strip-shaped porous insulating material is bonded to the surface of one side of the carbon felt to obtain an electrode with a staggered distribution of heights; It is 10-90% of the thickness of the carbon felt, preferably 50-80%; put it into the groove with its corresponding length (length from top to bottom in Figure 1) and width (width from left to right in Figure 1) The strip-shaped porous insulating material is embedded, and the upper surface of the strip-shaped porous insulating material is 0.5-3mm (preferably 1-1.5mm) higher than the upper surface of the carbon felt after embedding, so as to obtain an electrode with staggered distribution.

Application of the negative electrode structure in a zinc-based liquid flow battery.

The negative electrode structure is used as the negative electrode of the zinc-based liquid flow battery. When the zinc-based liquid flow battery is assembled, the strip-shaped protrusions are placed on the side facing the separator.

The electrolyte flows into the negative electrode side at one end of the negative electrode of the zinc-based flow battery, the area between the strip protrusions and the edge of the carbon felt, and flows into the negative electrode side of the zinc-based flow battery. The length to the downward direction) is the same and straight.

A carbon felt electrode structure design that can significantly improve the surface capacity of the zinc negative electrode of a zinc-based liquid flow battery; several cuboid grooves are cut on the surface of the carbon felt electrode, and a three-dimensional porous insulating material with a certain mechanical strength is embedded in the grooves to obtain . The electrode designed by the invention greatly slows down the deposition pressure of zinc between the carbon felt and the membrane, provides a large amount of zinc deposition space, effectively improves the cycle stability of the zinc-based liquid flow battery under the high deposition surface capacity, and makes the battery The lifespan is greatly improved.

The operation is simple, the process is stable and the cost is low. The electrode designed by the invention greatly slows down the deposition pressure of zinc between the carbon felt and the diaphragm, provides a large amount of zinc deposition space, effectively improves the cycle stability of the zinc-based liquid flow battery under the high deposition surface capacity, and makes the battery The lifespan is greatly improved.

Compared with the pristine structure, the electrodes fabricated using this method not only provided more space to accommodate the electrochemically reduced zinc, but also created a spatial barrier for dendrite growth. In addition, the macroscopic three-dimensional structure of the electrode optimizes the flow field distribution, making it easier for the electrolyte to reach the reaction site and alleviating the concentration polarization.

Electrodes fabricated using this method exhibit high coulombic efficiency and long cycle life at high areal capacities. Operating the zinc-iodine flow battery at 40 mAcm- ² , the deposited surface capacity can be as high as 160mAh cm ^-2 , and the Coulombic efficiency is maintained at 88%, while the coulombic efficiency of the battery with the original structure drops sharply after 40 cycles.

Description of drawings

1 is a schematic cross-sectional view of the electrode structure of the present invention;

FIG. 2 is a schematic diagram of the surface of the electrode structure of the present invention;

Fig. 3 is the battery performance data chart of Example 1;

Fig. 4 is the battery performance data chart of embodiment 2;

Fig. 5 is a battery performance data graph of Comparative Example 1;

Fig. 6 is the battery performance data chart of Comparative Example 2;

Figure 7 is a graph of the battery performance data of Comparative Example 3.

Detailed ways

A zinc-iodine flow battery was used to test the performance of electrodes with a high and low distribution structure, but this structure is not limited to zinc-iodine flow batteries, and can be used in all zinc-based flow batteries. During the test, the negative electrode (Example 1 and Example 2) used a carbon felt with a length × width × height dimension of 6cm × 6cm × 5mm, and cut 5 parallel cuboid grooves on the upper surface, and the cutting depth was 80% of the thickness of the carbon felt, The dimensions of the grooves are length × width × height 5cm × 0.4cm × 4mm, the distance between the grooves is 0.8cm, and the leftmost and rightmost grooves are respectively 0.4cm away from the left and right edges of the adjacent carbon felt. The upper and lower ends of the groove (as shown in Figure ¹ ) are 0.5cm away from the upper and lower edges of the carbon felt. After the high-density sponge, the upper surface of the sponge is 1mm higher than the surface of the carbon felt. Embed the high-density sponge into the above-mentioned rectangular grooves to obtain strip-shaped protrusions with a size of length × width × height 5 cm × 0.4 cm × 4 mm, the distance between the strip-shaped protrusions is 0.8 cm, and the leftmost and rightmost strip-shaped protrusions are The distances are respectively 0.4 cm from the left and right edges of the adjacent carbon felt, and the upper and lower ends of the strip protrusions (as shown in Figure 1) are 0.5 cm from the upper and lower edges of the carbon felt. The positive electrode is made of carbon felt, and the dimensions are 6cm×6cm×6mm in length×width×height. The zinc-iodine flow battery was assembled in a conventional way. The high and low electrodes were used for the negative electrode, the positive electrode used untreated carbon felt electrodes, and the separator was a commercial daramic porous membrane. The electrolyte is a conventional electrolyte corresponding to zinc and iodine (the concentration of potassium iodide is 4 mol/L, the concentration of zinc bromide is 2 mol/L, and the concentration of potassium chloride is 2 mol/L).

Example 1

Figure 3 shows the assembly of a zinc-iodine flow battery using high-low staggered electrodes (the above-mentioned high-low staggered electrodes are used in the negative electrode, and the positive electrode uses a 6cm×6cm×6mm carbon felt), and the separator uses a commercial daramic porous membrane. Coulombic efficiency data at 240mAh/ ^cm2 . The results show that the battery can not only reach the given value of the areal capacity but also have a high Coulomb efficiency under the condition of increasing areal capacity. Zinc ions will preferentially deposit on the surface of the carbon felt near the diaphragm. The structure of the high and low electrodes greatly increases the deposition area and deposition space of zinc near the diaphragm, and reduces the deposition pressure of zinc between the diaphragm and the carbon felt. The possibility of dendrite formation is reduced, which greatly expands the supportable surface capacity of Zn anodes.

Example 2

Figure 4 shows the assembly of a zinc-iodine flow battery using high-low staggered electrodes (the above-mentioned high-low staggered electrodes are used in the negative electrode, and the positive electrode uses a carbon felt with a size of 6cm×6cm×6mm), and a commercial daramic porous membrane is used for the separator. Battery performance data under ^cm conditions. The battery can be cycled stably for 300 times at a Coulombic efficiency of around 88%, proving that the electrode design of the high-low staggered structure greatly improves the cycling stability of the zinc-based flow battery at high areal capacity.

Comparative Example 1

Figure 5 shows the assembly of a zinc-iodine flow battery using uncut original carbon felt electrodes (both positive and negative electrode sizes are 6cm×6cm×6mm). The separator uses a commercial porous membrane with a capacity of 80-240mAh/cm on the zinc deposition surface Coulombic efficiency data under ² conditions. In the process of increasing the area capacity, the area capacity of the zinc that can be deposited by the original electrode structure is less than 80mAh/cm ² . When the deposition amount increases, the coulombic efficiency of the battery drops sharply, indicating that the zinc dendrites are squeezed to grow thorns. Through the separator, it caused a micro short circuit inside the battery.

Comparative Example 2

Figure 6 shows the assembly of a zinc-iodine flow battery using uncut original carbon felt electrodes ( ^both positive and negative electrode sizes are 6cm × 6cm × 6mm). battery performance data below. The coulombic efficiency dropped sharply after the battery was cycled less than 40 times, indicating that the excessively deposited zinc continued to accumulate and pierce the separator near the side of the separator, resulting in a micro-short circuit of the battery and shortening the battery life.

Comparative Example 3

Figure 7 shows that the negative electrode uses a carbon felt with a length x width x height of 6cm x 6cm x 5mm, with 5 parallel cuboid grooves cut on the upper surface, the cutting depth is 80% of the thickness of the carbon felt, and the groove size is length x width x height 5cm ×0.4cm×4mm, the distance between the grooves is 0.8cm, the leftmost and rightmost grooves are respectively 0.4cm away from the left and right edges of the adjacent carbon felt, and the upper and lower ends of the grooves (as shown in Figure 1) (shown) 0.5cm from the upper and lower edges of the carbon felt, without adding a high-density sponge support layer; the positive electrode uses a 6cm×6cm×6mm original carbon felt to assemble a zinc-iodine flow battery, and the separator uses a commercial porous membrane, with a capacity of 160mAh on the zinc deposition surface Battery performance data under the condition of / ^cm2 . Without the high-density sponge support layer, the carbon felt is not in close contact with the current collector after cutting under the scouring of the liquid flow, resulting in a decrease in battery performance and large fluctuations.

Claims (10)

1. The negative electrode structure for the zinc-based flow battery comprises a carbon felt electrode body, wherein more than 2 strip-shaped bulges made of parallel porous insulating materials and spaced from left to right are sequentially arranged on the surface of one side of the carbon felt electrode body.

2. The negative electrode structure of claim 1, wherein: the height of the porous insulating material protrusions on the surface of the carbon felt (the distance from the plane of the protrusions away from the surface of the carbon felt to the surface of the carbon felt) is 0.5-2mm, preferably 1-1.2 mm; the distance between adjacent strip-shaped protrusions is 0.5-1.5cm, preferably 0.8-1 cm.

3. The negative electrode structure of claim 1 or 2, wherein: the distance between the two ends (the upper end and the lower end in the figure 1) of the strip-shaped protruding strip and the upper edge and the lower edge of the adjacent carbon felt is 0.3-1cm, and preferably 0.5-0.8 cm; the distance between the strip-shaped protrusion at the leftmost side and the edge at the left side of the carbon felt is 0.3-1cm, preferably 0.5-0.8 cm; the distance between the rightmost strip-shaped protrusion and the right edge of the carbon felt is 0.3-1cm, and preferably 0.5-0.8 cm.

4. The negative electrode structure of claim 1 or 2, wherein: the width of the strip-shaped protrusion is 1-8mm, preferably 2-5 mm.

5. The negative electrode structure of claim 1 or 2, wherein: the carbon felt is in a rectangular flat plate shape, one side of the strip-shaped protrusion, which is close to the surface of the carbon felt, is embedded into the carbon felt, and the embedding depth is 10-90% of the thickness of the carbon felt, and is preferably 50-80%.

6. The negative electrode structure of claim 1 or 2, wherein: the porous insulating material is one or more than two of high-density sponges, and the density of the porous insulating material is more than or equal to 45g/cm³The porosity is 90% or more.

7. A method of making the negative electrode structure of any of claims 1-6, characterized by:

bonding the strip-shaped porous insulating material on the surface of one side of the carbon felt to obtain an electrode with high-low staggered distribution; or more than 2 mutually spaced and parallel strip-shaped grooves are cut on the surface of one side of the carbon felt, and the cutting depth is 10-90% of the thickness of the carbon felt, preferably 50-80%; and (3) putting strip-shaped porous insulating materials with corresponding length (the length in the direction from top to bottom in the figure 1) and width (the width in the direction from left to right in the figure 1) in the groove, wherein the upper surface of the embedded strip-shaped porous insulating materials is 0.5-3mm (preferably 1-1.5mm) higher than the upper surface of the carbon felt, so as to obtain the electrode with staggered distribution.

8. Use of a negative electrode structure according to any of claims 1 to 6 in a zinc-based flow battery.

9. Use according to claim 8, characterized in that:

the negative electrode structure of any of claims 1-6 as a negative electrode of a zinc-based flow battery, wherein the protrusions are disposed facing a side of the separator when the zinc-based flow battery is assembled.

10. Use according to claim 8 or 9, characterized in that: the electrolyte flows into the negative side in the area among one end of the negative electrode of the zinc-based flow battery, the strip-shaped protrusions and the edge of the carbon felt, and the flowing direction of the electrolyte flowing into the negative side of the zinc-based flow battery is consistent with the length of the strip-shaped protrusions (the length of the direction from top to bottom in the figure 1).

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