Separator for zinc secondary battery

Abstract

The present invention relates to a method for producing a separator for a zinc secondary battery, and a separator for a zinc secondary battery produced thereby, the method comprising the steps of: producing a polyacrylonitrile (PAN) nanofiber mat by means of electrospinning; and producing a PAN nanofiber mat containing gelatin by impregnating the PAN nanofiber mat with a gelatin solution and drying same.

Description

Separator for zinc secondary batteries

[0001] The present invention relates to a separator for a zinc secondary battery.

[0002] Aqueous zinc-ion secondary batteries are actively being researched and developed for use as energy storage secondary batteries because they fundamentally address fire and explosion risks, are low-cost, and have low toxicity. Zinc-ion secondary batteries utilize zinc metal as the anode active material and manganese dioxide as the cathode active material. At the cathode, zinc metal / zinc ions undergo oxidation / reduction reactions, while at the anode, manganese undergoes oxidation / reduction reactions through insertion / deintercalation reactions between zinc ions and hydrogen ions.

[0003] The problem with zinc-ion batteries (ZIBs) is that their lifespan, energy density, and practical universality are limited by the narrow electrochemical stable potential window of the aqueous electrolyte, water, which has a theoretical voltage of only 1.23 V.

[0004] In theory, if the anode reaction potential energy level is higher than the lowest unoccupied molecular orbital of the aqueous solvent, water molecules are easily reduced to produce hydrogen molecules through the hydrogen evolution reaction (HER), and if the cathode reaction potential energy level is lower than the highest unoccupied molecular orbital of the aqueous solvent, oxygen molecules are produced through the oxygen evolution reaction (OER). These two reactions consume water in the electrolyte, which increases the electrolyte concentration, reduces the ionic conductivity of the electrolyte, and there is also a risk of explosion if hydrogen and oxygen in the ZIB are released simultaneously during charging.

[0005] Meanwhile, when the pH value is lowered locally, corrosion occurs on the zinc surface, which is highly reactive with water, and when the electrolyte is dissolved on the irregular zinc surface, Zn dendrites are also created.

[0006] Therefore, the host design, coating modification, uniform Zn electrodeposition, and structural composition of the anode must be reviewed. The essential components of the aqueous electrolyte are six water molecules and Zn, which have strong interactions. 2+ A coordination structure exists between ions, and numerous hydrogen bonds form between water molecules. Thus, zinc coordination structure and hydrogen bonds, two important indicators affecting battery performance, can be reconfigured by modifying the electrolyte, such as by changing the anion, using a high-concentration electrolyte, or using an organic solvent.

[0007] Therefore, the present invention aims to provide a zinc secondary battery (ZIB) with good performance by developing an electrolyte membrane that serves as a basis for such electrolyte change.

[0008] In the present invention, an electrolytic membrane having excellent porosity and breathability and excellent mechanical strength is manufactured using an electrospinning machine.

[0009] The present invention provides a method for manufacturing a separator for a zinc secondary battery, comprising the steps of: manufacturing a polyacrylonitrile (PAN) nanofiber mat by electrospinning; and impregnating the polyacrylonitrile (PAN) nanofiber mat with a gelatin solution and drying it to manufacture a polyacrylonitrile (PAN) nanofiber mat containing gelatin.

[0010] In addition, the present invention provides a separator for a zinc secondary battery manufactured by the above manufacturing method.

[0011] In addition, the present invention provides a zinc secondary battery including the separator.

[0012] According to the present invention, a separator for a zinc secondary battery can be provided that has excellent porosity and air permeability, high mechanical strength, and thus excellent life characteristics and discharge capacity retention characteristics.

[0013] In addition, the present invention can provide a zinc secondary battery having excellent life characteristics and discharge capacity retention characteristics including the separator.

[0014] Figure 1 is a photograph of an early electrospinning machine.

[0015] Figure 2 is a photograph of the shape of the radiated material.

[0016] Figure 3 is a photograph of the radial shape according to the radial speed (left: radial speed 1.5 ml / hr, right: radial speed 1.2 ml / hr).

[0017] Figure 4 is a photograph of the electrospinning condition experiment process (1: appearance of fibers spun from a syringe coming out stably, 2: appearance of fibers when electrospinning does not go well)

[0018] Figure 5 is a photograph of a drum-type collector.

[0019] Figure 6 is a photograph of a syringe holder and a controller.

[0020] Figure 7 is a photograph of the drum collector and regulator.

[0021] Figure 8 is a photograph of the electrospinning device of the present invention.

[0022] Figure 9 is a photograph of an electrospinning machine capable of constantly adjusting the width of the present invention.

[0023] Figure 10 is a photograph of the PAN manufacturing process.

[0024] Figure 11 is a photograph showing the shape of electrospinning according to changes in radiation speed (1: radiation speed 2.1 ml / hr, 2: radiation speed 1.4 ml / hr).

[0025] Figure 12 is a photograph taken when the radiation speed is 1.45 ml / hr.

[0026] Figure 13 is a photograph of the shape when the radiation interval is changed.

[0027] Figure 14 is a photograph showing the experimental process of electrospinning conditions according to the increase in atmospheric temperature.

[0028] Figure 15 is a photograph of an electrolyte membrane made of PAN.

[0029] Figure 16 is a photograph showing the PAN electrospinning process in the electrospinning machine of the present invention.

[0030] Figure 17 is a photograph of PAN attached to aluminum foil.

[0031] Figure 18 is a photograph showing the process of peeling a PAN electrolyte membrane using a fiber foil.

[0032] Figure 19 is a photograph showing the shape of PAN fibers according to changes in collector drum speed.

[0033] Figure 20 is a photograph of the gelatin manufacturing process.

[0034] Figure 21 is a photograph of gelatin-impregnated PAN.

[0035] Figure 22 is a photograph of PAN containing gelatin.

[0036] Figure 23 is an SEM structure of PAN when impregnated with gelatin (1: PAN before gelatin inclusion, 2: PAN with a large amount of gelatin, 3: PAN with an appropriate amount of gelatin inclusion).

[0037] Figure 24 shows the appearance of gelatin-containing PAN when the PAN thickness is different (left: when the PAN thickness is thick, middle: when the PAN thickness is appropriate, right: when the PAN thickness is too thin)

[0038] Figure 25 shows the cycle life of a cell using a water-soluble electrolyte and a polymer manufactured in the present invention.

[0039] Hereinafter, the present invention will be described in detail.

[0040]

[0041] The present invention provides a method for manufacturing a separator for a zinc secondary battery, comprising the steps of: manufacturing a polyacrylonitrile (PAN) nanofiber mat by electrospinning; and impregnating the polyacrylonitrile (PAN) nanofiber mat with a gelatin solution and drying it to manufacture a polyacrylonitrile (PAN) nanofiber mat containing gelatin.

[0042] In one embodiment of the present invention, the gelatin solution can be prepared by mixing gelatin, potassium persulfate, zinc sulfate, manganese sulfate, and distilled water, stirring, and then adding acrylamide and N,N' methylenebisacrylamine in portions.

[0043] In one embodiment of the present invention, the electrospinning can be performed by an electrospinning machine including a syringe part; a syringe holder that supports the syringe part and allows free movement left and right and forward and backward; a controller that is connected to the syringe part and controls the amount of solution to be spun; and a drum collector that controls the rotation speed.

[0044] The amount of gelatin contained in the above PAN may be 50% to 120% of the weight of the PAN. When gelatin is contained in the PAN within the above range, as illustrated in Fig. 23, an appropriate amount of gelatin exists between the PAN fibers, allowing sufficient pores to be formed.

[0045] The thickness of the PAN may be 50 μm to 500 μm. As illustrated in Fig. 24, if the thickness of the PAN exceeds the above range, swelling may occur after drying, and if it is less than the above range, the amount of gelatin may be relatively excessive, forming a gelatin film that completely blocks the pores of the PAN fiber.

[0046] In addition, the present invention provides a separator for a zinc secondary battery manufactured by the above manufacturing method.

[0047] In addition, the present invention provides a zinc secondary battery including the separator.

[0048] Hereinafter, the composition and resulting effects of the present invention will be described in more detail through specific examples and comparative examples. However, these examples are intended to more specifically illustrate the present invention, and the scope of the present invention is not limited to these examples.

[0049]

[0050] <Example>

[0051] Example 1. Manufacturing of an electrospinning machine

[0052] Early electrospinning machines were operated in the form of electrospinning onto a plate-shaped collector, and the spun sample was produced in the shape of a cotton ball as shown in Fig. 1, making it difficult to use.

[0053] Accordingly, a drum-shaped collector as in Fig. 5 was manufactured to produce a plate-shaped sample having a shape as in Fig. 3, but the width could not be controlled as in Fig. 5, and therefore, it was a one-time production without any aspect.

[0054] Therefore, the syringe and collector sections were newly manufactured and their mass production potential was examined.

[0055] First, in order to consider the stability and accurate width of the syringe part, a syringe holder device as shown in Fig. 6 was installed in the syringe part to enable free movement left and right and front and back, and a new controller was also attached to control the amount of solution emitted from the syringe.

[0056] In addition, as shown in Fig. 7, a device capable of controlling the rotation speed by attaching a regulator to the drum collector was also developed and attached.

[0057] An electrospinning machine manufactured by combining these newly configured devices is as shown in Fig. 8.

[0058] The above-mentioned electrospinning machine can independently control the syringe section and the drum collector section, and can move the syringe back and forth, thereby allowing the width of electrospinning to be controlled. In addition, the rotation and reciprocating movement of the drum collector can be smoothly controlled, and thus the shape of the spun material can be controlled in width as shown in Fig. 9.

[0059] That is, the electrospinning device of the present invention can control the width at a constant level.

[0060]

[0061] Example 2. Fabrication of PAN nanofiber mat by electrospinning

[0062] Conventional electrolyte membranes are made of glass wool, but polymer-based electrolyte membranes offer high mechanical strength, ease of thin-film production, and superior contact with electrodes / electrolytes. However, because typical polymers have low ionic conductivity, the present invention creates an electrolyte membrane capable of ionic conductivity.

[0063] Looking at the characteristics of some polymers, we can see that they have high ionic conductivity, as shown in Table 1 below.

[0064]

[0065]

[0066] Fabrication of PAN for electrospinning

[0067] 200 ml of DMF was added to 20 g of PAN, heated to 70°C in a double-jacketed stirrer, stirred at 200 rpm until no bubbles were present, and stored in the refrigerator.

[0068] Experimental conditions for electrospinning of PAN

[0069] Electrospinning was performed under the following conditions: syringe capacity 10 ml, voltage 12 to 15 kV, distance between collector and syringe 10 to 20 cm, and spinning speed 0.5 to 2.0 ml / hr or more.

[0070] The distance between the collector and the syringe was fixed at 15 cm, the voltage was fixed at 1.49 kV, and the experiment was conducted by changing the radiation speed to 2.1 and 1.4 ml / hr. As a result, different appearances were observed, as shown in Fig. 11. As shown in Fig. 11, when the radiation speed was 2.1 ml / hr, the radiation shape appeared constant and the radiation width also maintained a narrow shape. However, when the radiation speed was lowered to 1.4 ml / hr, the radiation shape became unstable, and as shown in Fig. 11 2-1 and 2-2, the shape of the Taylor cone, which is the shape of the solution in front of the syringe, gradually became longer, and as shown in Fig. 11 2-2, there were cases where it became long and attached to the collector in the shape of a bead.

[0071] PAN is manufactured to be used as an electrolyte membrane, and it is desirable to have a wide width and a constant thickness. However, in the case of 1-1 and 1-2 in Fig. 11, the radiation shape is constant but the width is narrow. In the case of 2-1, 2-2 and 2-3 in Fig. 11, the radiation width is wide and good, but since beads with a certain width are attached, it was difficult to manufacture the electrolyte membrane with a constant thickness and constant fiber.

[0072] When the radiation distance was fixed to 15 cm and the radiation voltage was changed to 14.0 kV and the radiation speed was changed to 1.45 ml / hr, the electrospinning showed a shape of the radiated solution as shown in Fig. 12 that was larger than that of 1-1 in Fig. 11, but smaller than that of 2-1 and 2-2 in Fig. 11. The radiation width was also slightly wider than that of 1-2 in Fig. 11, but much smaller than that of 2-3.

[0073] The shape of the Taylor cone in Fig. 12 is a drawing of the initial radiation of the radiation solution (Fig. 12, 1) and the final radiation (Fig. 12, 3).

[0074] Figure 13 shows the shape when the electrospinning conditions were changed to voltage 15.5 kV, spinning speed 1.0 ml / hr, and spacing 10 cm (1 in Figure 13) and 15 cm (2 in Figure 13).

[0075] As shown in Figure 13, when the voltage was increased to 15.5 kV, it was better to lower the radial velocity than in the previous example and set the distance to 15 cm.

[0076] As shown in Fig. 14, an electrospinning condition experiment was conducted according to the increase in atmospheric temperature. In order to investigate the effect of temperature when the atmospheric temperature increased to 27℃, the effect of temperature was observed when the radiation shape and constant radiation occurred at a radiation distance of 15 cm, a radiation voltage of 14.0 kV, and a radiation speed of 1.45 ml / hr among the above conditions.

[0077] First, during the PAN solution manufacturing process, as the atmospheric temperature increased, a phenomenon occurred in which dissolution did not proceed well, as shown in Figure 14-1.

[0078] If the solution is not completely dissolved in DMF, the dissolved solution passes through the needle tip during the initial electrospinning, so that spinning is performed well as in 2-1 of Fig. 14. However, as time passes, as in 1-2 of Fig. 14, the Taylor cone gradually grows, and as time passes, as in 3-1 of Fig. 14, the solution solidifies at the needle tip, so that spinning is not performed as in 3-2 of Fig. 14. Therefore, when the weather is hot and the air temperature rises, it can be seen that in addition to the effect of the humidity mentioned above, the effect of the air temperature must also be considered.

[0079] A high-quality electrolyte film was produced by considering the conditions such as voltage, radiation speed, ambient temperature, and radiation distance.

[0080] Although it varies slightly depending on the atmospheric temperature, the voltage is 14.7 to 15 kV, the radiation speed is 1.69 to 1.96 ml / hr, the radiation distance is 15 cm, the atmospheric temperature is 26 to 27°C, and the humidity is 50 to 60%. 18 ml of PAN solution was produced twice in a size of 150 x 300 mm (Fig. 15).

[0081] Fabrication of PAN in a newly built electrospinning machine

[0082] Electrospinning of PAN solution was performed under spinning conditions: voltage 14.7 kV, spinning speed 1.8 ml / hr, spinning distance 15 cm, and spinning machine ambient temperature 26.7°C.

[0083] As shown in Fig. 16, it was found that electrospinning was performed well to a certain thickness, but the PAN electrolyte film collected using aluminum foil in the collector drum for PAN recovery was not well peeled off because the PAN was attached to the aluminum foil, as shown in Fig. 17.

[0084] Since it is difficult to peel off the PAN film that is manufactured uniformly and consistently from the attached foil, an experiment was conducted to purchase a new foil and make it easier to peel off.

[0085] This foil is made of fiber, and as a result of conducting an experiment using this fiber foil, it was easy to peel off, as shown in Fig. 18.

[0086] The left side of Fig. 18 shows covering a collector drum with fiber foil, the middle picture is electrospinning of PAN after attaching the fiber foil, the upper right side shows peeling of PAN from aluminum foil, and the lower right picture shows peeling from the fiber foil. As shown in the picture above, it was found that the peeling was complete when the fiber foil was used.

[0087] Another variable in the radiation conditions is the change in drum collector speed. In the present invention, PAN fiber formation was measured at two speeds: 180 rpm and 1050 rpm.

[0088] Figure 19 shows the shape when the speed of the collector drum was changed. It can be seen that when the speed was fast, the radiation was wider and smoother than when the speed was slow.

[0089] If it is too slow, the shape of the radiated surface will be relatively rough and the width will be small, and if it is too fast, it will be too dense and dense, which will cause problems in accommodating the electrolyte. Therefore, when producing PAN fibers with a new electrospinning machine, the speed was set to 500 rpm.

[0090] The electrolytic membrane fabricated above was prepared by dissolving PAN in DMF and using it as an electrospinning solution. Therefore, the added DMF was removed by drying it in a vacuum dryer at a vacuum of 0.1 MPa, 60°C, for 6 hours.

[0091] Example 3. Preparation of gelatin-containing PAN nanofiber mat

[0092] PAN electrolyte membrane treatment

[0093] In order to use PAN as an electrolyte membrane, it must be ionic conductive, so gelatin must be manufactured and infiltrated into the PAN membrane, and an electrolyte solution must be poured into it to facilitate the movement of electrons.

[0094] Gelatin manufacturing

[0095] In order to create ionic conductivity while dissolving gelatin, potassium persulfate, zinc sulfate, manganese sulfate, etc. must be added to the gelatin before it is prepared as a solution.

[0096] 10g of gelatin, 0.075g of potassium persulfate, 5ml / 100ml of 2M ZnSO4 (DI water), 1.51g of MnSO4, and 200ml of DI water were placed in a double jacket and stirred at 80℃ for 1 hour, then lowered to 40℃, and 15g of acrylamide and 15mg of N,N' methylenebisacrylamine were added in portions to produce a solution.

[0097] Figure 20 shows the process of manufacturing a gelatin solution. Figure 20-1 shows the appearance of undissolved gelatin particles at the beginning of manufacturing, and shows that the gelatin particles are completely dissolved and melted over time.

[0098] Figure 21 is a diagram illustrating a process for impregnating gelatin. PAN is placed in a mold, impregnated with gelatin, and then dried to produce gelatin-impregnated PAN as shown in the diagram. The gelatin-containing PAN was cut into a certain size as shown in Figure 22, and the degree of impregnation was measured.

[0099] Amount of gelatin in PAN [unit: g / cm²] Before injection After injection 0.0039 0.008 156 0.004 59 30.009 70 60.004 59 40.010 47 0.007 28 80.018 96 0.007 355 60.022 35 0.007 60.029 35 0.007 66 30.024 23 0.007 7 13 0.024 59

[0100]

[0101] Table 2 summarizes the results of an experiment to find out how the amount of gelatin injected changes depending on the shape or thickness of the gelatin through the weight ratio before and after gelatin injection into PAN. In the case of the same thickness, almost the same amount of gelatin was shown, so there was no quantitative change in the gelatin. The changes in the tissue before and after gelatin injection were observed and are shown in Fig. 23. Fig. 23 is an SEM photograph of PAN containing gelatin. Fig. 23-1 is a photograph when gelatin is not contained, showing that sufficient pores are formed between the PAN fibers because gelatin is not contained. Fig. 23-2 shows that the gelatin content is excessive, so that gelatin covers the PAN fibers, resulting in almost no pores. Fig. 23-3 shows that the PAN contains an appropriate amount of gelatin, forming sufficient pores.

[0102] Depending on the thickness of PAN, even when impregnated with gelatin, it is affected by gelatin, as shown in Figure 24. If the PAN thickness is too thick, swelling occurs after drying, and if it is too thin, the amount of gelatin may be relatively too large, forming a gelatin film that completely blocks the pores of the PAN fibers.

[0103] Example 4. Coin cell fabrication and measurement

[0104] - CR2032 Coin cell

[0105] - Electrolyte: 3 M Zn(CF3SO3)2

[0106] - Anode: NVO

[0107] - Cathode: 0.05 mm (t) Zn foil

[0108] - Electrolyte membrane: The gelatin-containing PAN nanofiber mat produced in Example 3 was used as an electrolyte membrane.

[0109] <Conditions>

[0110] - Battery cycler: WBCS 3000 L; WonATech

[0111] - Voltage range: 0.2 - 1.8 V

[0112] - Temperature: 30 ℃

[0113] <Result>

[0114] Figure 25 shows the cycle life of a cell using a water-soluble electrolyte and a polymer developed in this patent.

[0115] Cycle performance tests were conducted at a current density of 1 Ag-1.

[0116] Cells using aqueous electrolytes had a capacity retention rate of less than 50% at 1000th charge, and at 1400th charge, the cells no longer functioned normally.

[0117] On the other hand, the cell manufactured in the present invention showed a high capacity retention rate of 73.59% even at 2000th.

Claims

1. A step of manufacturing a polyacrylonitrile (PAN) nanofiber mat by electrospinning; and A step of impregnating the polyacrylonitrile (PAN) nanofiber mat with a gelatin solution and drying it to produce a polyacrylonitrile (PAN) nanofiber mat containing gelatin; A method for manufacturing a separator for a zinc secondary battery, comprising:

2. In paragraph 1, A method for manufacturing a separator for a zinc secondary battery, wherein the gelatin solution is manufactured by mixing and stirring gelatin, potassium persulfate, zinc sulfate, manganese sulfate, and distilled water, and then adding acrylamide and N,N' methylene bisacrylamine in portions.

3. In paragraph 1, A method for manufacturing a separator for a zinc secondary battery, wherein the amount of gelatin contained in the above PAN is 50% to 120% of the weight of the PAN.

4. In paragraph 1, A method for manufacturing a separator for a zinc secondary battery, wherein the thickness of the above PAN is 50 ㎛ to 500 ㎛.

5. In paragraph 1, A method for manufacturing a separator for a zinc secondary battery, wherein the electrospinning is performed by an electrospinning machine including a syringe part; a syringe holder that supports the syringe part and allows free movement left and right and forward and backward; a controller that is connected to the syringe part and controls the amount of solution spun; and a drum collector that controls the rotation speed.

6. A zinc secondary battery separator manufactured by the method of any one of claims 1 to 5.

7. A zinc secondary battery including the separator of clause 6.

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