WO2024123067A1 - Polybenzimidazole-based separator for secondary battery and method for manufacturing same - Google Patents

Abstract

A method for manufacturing a polybenzimidazole-based film according to the present invention comprises the steps of: dissolving polybenzimidazole in an amide-based organic solvent to form a polybenzimidazole solution; impregnating a porous membrane with the polybenzimidazole solution; and drying the porous membrane impregnated with the polybenzimidazole solution at a temperature of 80℃ or lower.

Description

Polybenzimidazole-based separator for secondary batteries and method for manufacturing the same

The present invention relates to a polybenzimidazole-based separator, a method of manufacturing the same, and a secondary battery including the separator.

As global economic growth continues along with global warming, the need for renewable and sustainable energy systems based on renewable energy, such as solar and wind energy, is becoming more urgent. To improve the stability of the grid network against fluctuations due to the intermittent availability of this form of energy, advanced energy storage systems (ESS) can be used to store surplus power and deliver it to end customers or the grid when needed. Among them, ESS based on electrochemical energy, such as rechargeable or secondary batteries, can provide a cost-effective and clean energy storage solution. Electrochemical energy storage systems are secondary batteries in a broad sense, and examples include lithium ion batteries, fuel cells, and redox flow batteries. Various types of electrochemical energy storage systems have different physical and/or chemical properties. Generally, a secondary battery includes the following elements: two electrodes, an electrolyte, and a separator (or ion exchange membrane). Each of the above factors may affect the performance of the secondary battery.

Meanwhile, polybenzimidazole (PBI), a polymer material for producing a separator, is a glassy thermoplastic resin with high thermal stability and chemical resistance, and is known to have properties suitable for moving cations, hydrogen, and water, so it is used in secondary batteries. There have been attempts to use a polybenzimidazole-based separator as a separator material.

As the conditions under which secondary batteries are used become increasingly harsh and they are required to exhibit excellent durability while operating for long periods of time, research is continuing to improve the mechanical strength of separators. Accordingly, there is a need to further improve the mechanical strength of the polybenzimidazole-based separator while maintaining the charge/discharge efficiency of the secondary battery and improving its lifespan. At the same time, it is necessary to develop a method that can improve process efficiency in manufacturing polybenzimidazole-based separation membranes.

The present invention provides a method for producing a polybenzimidazole-based separator that can improve the mechanical strength of the polybenzimidazole-based separator without using a backup film (or base film). The purpose is to provide

In addition, the polybenzimidazole-based separator prepared according to the present invention not only has excellent ion exchange characteristics, but can also improve the performance (charge/discharge efficiency and lifespan) of secondary batteries containing the separator, even under harsh conditions. The purpose is to contribute to stably driving secondary batteries.

In the present invention, a redox flow battery or a sealed redox battery using a redox couple has been described as an example of a secondary battery, but the subject to which the separator of the present invention is applied is not limited thereto.

According to the first aspect of the present invention, dissolving a polybenzimidazole-based compound in an amide-based organic solvent to form a polybenzimidazole solution; Impregnating a porous membrane with the polybenzimidazole solution; and drying the porous membrane impregnated with the polybenzimidazole solution at a temperature of 80° C. or lower to obtain a polybenzimidazole-based separator.

It is characterized in that no backing film is used to form the polybenzimidazole-based separator.

The step of impregnating the porous membrane includes impregnating one or both sides of the porous membrane.

The porous membrane may be made of a material containing polypropylene, polyethylene, or a combination thereof.

The thickness of the porous membrane may be in the range of 1 to 30 μm, and the thickness of the polybenzimidazole-based separator may be in the range of 2 to 40 μm.

In the step of forming the polybenzimidazole solution, surfactants may be mixed together. Based on 100% by weight of the polybenzimidazole solution, the surfactant may be included in an amount of more than 0.1% by weight and less than 5.0% by weight.

The surfactant may include one or more of an ionic surfactant, a nonionic surfactant, and an organic surfactant.

In the step of forming the polybenzimidazole solution, the polybenzimidazole solution may be dissolved in an amide-based organic solvent under temperature conditions of 130°C or higher and/or pressure conditions of 0.1 MPa or higher.

When the amide-based organic solvent is 100% by weight, the maximum dissolution rate of the polybenzimidazole-based compound may be 8 to 20% by weight.

Based on 100% by weight of the polybenzimidazole solution, a viscosity adjusting solvent may be included in an amount of 10% by weight to 25% by weight.

The viscosity adjusting solvent may include one or more of acetone, methyl ethyl ketone, methyl isobutyl ketone, methanol, ethanol, isopropanol, butanol, and isobutanol.

According to the second aspect of the present invention, a ribenzimidazole-based separation membrane manufactured according to the first aspect of the present invention can be provided.

According to a third aspect of the present invention, a secondary battery including a ribenzimidazole-based separator manufactured according to the first aspect of the present invention can be provided.

The secondary battery includes a redox battery including oxidation and reduction reactions of a vanadium redox couple.

According to the method for manufacturing a polybenzimidazole-based separator according to the present invention, process efficiency can be significantly improved because a backing film that must be removed after forming the separator is not used.

In addition, the polybenzimidazole-based separator manufactured according to the present invention has high mechanical strength and can contribute to improving the performance of secondary batteries.

1 is a schematic diagram of an exemplary redox flow battery.

Figure 2A is a schematic diagram of a sealed redox battery according to an embodiment.

FIG. 2B is a schematic diagram of a sealed redox battery including a plurality of sealed redox battery cells in a stacked configuration according to some embodiments.

Figure 2C is a schematic diagram of a sealed redox battery including a plurality of sealed redox battery cells in a stacked configuration according to some other embodiments.

Figure 2D is a schematic diagram of a sealed redox battery including a plurality of sealed redox battery cells in a cylindrical stacked configuration according to an embodiment.

The above-described objects, features, and advantages will be described in detail later with reference to the attached drawings, so that those skilled in the art will be able to easily implement the technical idea of the present invention. In describing the present invention, if it is determined that a detailed description of known technologies related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description will be omitted. Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the attached drawings. In the drawings, identical reference numerals are used to indicate identical or similar components.

In this specification, when “includes,” “has,” “consists of,” “arranges,” “provides,” etc. are used as constituent elements, other parts may be added unless “only” is used. When a component is expressed in the singular, the plural is included unless specifically stated otherwise.

In interpreting the components in this specification, they are interpreted to include the margin of error even if there is no separate explicit description.

In this specification, the “top (or bottom)” of a component or the arrangement of any component on the “top (or bottom)” of a component means that any component is disposed in contact with the top (or bottom) of the component. In addition, it may mean that other components may be interposed between the component and any component disposed on (or under) the component.

As discussed above, competing factors considered in the selection and design of an electrochemical energy storage system suitable for a particular application include, among other things, investment cost, power, energy, lifetime, recyclability, efficiency, scalability and maintenance costs. . Among various electrochemical energy storage systems, redox flow batteries (RFBs) are considered promising for stationary energy storage. RFB is an electrochemical energy conversion device that utilizes the redox process of redox species dissolved in solution. The solution is stored in an external tank and introduced into the RFB cell when required. Some of the advantageous features of RFB technology are independent scalability of power and energy, high depth of discharge (DOD) and reduced environmental impact. These features allow for a wide range of operating powers and discharge times, making RFBs desirable for storing electricity generated from renewable sources.

Certain disadvantages of some secondary batteries known in the art, such as lithium ion batteries, include the generation of excessive heat and internal pressure during operation. To mitigate this effect, some secondary batteries use gaps between battery cells and/or separate cooling devices. Advantageously, in batteries according to embodiments disclosed herein, the generation of heat and pressure is significantly lower, which in turn lowers the risk of explosion, and no spacing or cooling device is required between battery cells, resulting in compactness of the battery cells and the battery itself. Enables integration.

Various batteries use bus bars to electrically connect the battery cells and/or the battery itself. For compact integration, bus bars must be placed efficiently to reduce the amount of space they occupy. In addition to electrically connecting the battery cells and batteries, it is separately necessary to physically and mechanically fasten the battery cells or batteries together in an efficient manner. To address these and other needs, various embodiments disclosed herein provide bus bars that enable high-density integration of battery cells and/or batteries and energy storage devices including the same. Additionally, embodiments disclosed herein provide a battery that is easy to maintain after installation and an energy storage device including the same.

1 is a schematic diagram of an exemplary redox flow battery (RFB). RFB 100 includes battery cells 104 . The battery cell 104 has a first half cell 104A and a second half cell 104B separated by a separator or ion exchange membrane 112. The first half cell 104A includes a first or positive electrolyte disposed therein and a positive electrolyte reservoir 106A containing the positive electrolyte, and the second half cell 104B includes a second or negative electrolyte disposed therein. and a cathode electrolyte reservoir 106B containing the cathode electrolyte. The positive electrode is electrically connected to the positive electrode current collector 108A, and the negative electrode is electrically connected to the negative electrode current collector 108B. Anode electrolyte reservoir 106A is in fluid communication and physically connected to anode electrolyte tank 116A, and cathode electrolyte reservoir 106B is in fluid communication and physically connected to cathode electrolyte tank 116B. In operation, the anode electrolyte is circulated between the anode electrolyte tank 116A and the anode electrolyte reservoir 106A through outlet and inlet conduits 120A, 124B as indicated by arrows using an anode electrolyte pump 128A. Similarly, cathode electrolyte is circulated between cathode electrolyte tank 116B and cathode electrolyte reservoir 106B through outlet and inlet conduits 120B, 124B.

In some configurations, a plurality of battery cells 104-1, 104-2, ..., 104-n are stacked to form an RFB cell 150, where each cell is configured in a similar manner to battery cell 104. . A plurality of battery cells (104-1, 104-2, ..., 104-n) have respective anode electrolyte reservoirs (106A) in fluid communication with each other and respective cathode electrolyte reservoirs (106B) in fluid communication with each other. Includes. The plurality of anode electrolyte reservoirs 106A are connected to each other and in fluid communication with the anode electrolyte tank 116A, and the plurality of cathode electrolyte reservoirs 106B are connected to each other and in fluid communication with the cathode electrolyte tank 116B.

Compared to other electrochemical storage technologies such as lithium-ion, lead acid and sodium-sulfur batteries, RFB offers several advantages, enabling independent power and energy scalability by decoupling power conversion from energy storage. For example, RFBs can be adjusted in a flexible and decentralized way depending on the application, e.g. for power and power ranging from a few kW/kWh for household storage up to a few to tens of MW/MWh for grid storage. It can be scaled up to provide energy. Additionally, unlike fuel cells, the reactions in RFBs are reversible, allowing the same cell to function as a converter of electricity into chemical energy and vice versa. RFBs operate by changing metal ion valence without consuming ionic metal, allowing for a long life cycle. Cell temperature can be controlled relatively easily by regulating electrolyte flow, in part due to the relatively high thermal mass of the electrolyte. State of charge (SOC) can be easily monitored through cell voltage and very deep depth of discharge (DOD) can be achieved.

Despite the numerous advantages of RFB, its commercialization has not been as widespread as other electrochemical storage technologies, despite relatively large capital, research and development investments made in this technology over several decades. In particular, the current situation in which the demand for batteries for ESS applications is rapidly increasing and the demand for safety due to frequent fires and explosions is increasing, shows that RFB is suitable, but widespread commercialization has not yet been realized. This suggests that, although the need for RFB commercialization has been felt for a long time, there are significant obstacles. The inventors have recognized several of these obstacles, including relatively low reliability, low efficiency, large system footprint, and high system complexity.

The first obstacle to widespread commercialization of RFBs concerns the relatively high complexity and associated reliability issues of RFBs, such as RFB 100 described above with respect to FIG. 1 . As described above, the RFB has a plurality of conduits 120A, 120B, 124A, 124B for delivering electrolyte to and from the battery cell 104, pumps 128A, 128B for circulating the electrolyte, and a storage device for storing the electrolyte. It includes tanks 116A and 116B. Due to the relatively high complexity, the various connection points associated with the conduits 120A, 120B, 124A, 124B between the battery cells 104 and the tanks 116A, 116B may cause problems, such as resulting in leaks. The probability and frequency of failure increases proportionally with the number of these conduits, which scales with the size of the ESS. If a breakdown occurs, it not only causes unscheduled repairs but also poses a safety risk. Additionally, reducing the likelihood of these failures through preventive maintenance and ensuring uninterrupted operation adds to operating costs.

A second obstacle to widespread commercialization of RFBs concerns their relatively low efficiency. One factor in the relatively low efficiency is related to the energy consumed in the circulation of the electrolyte. For example, the electrolyte for vanadium-based RFB may contain sulfuric acid and have a relatively high viscosity. Circulating electrolytes, especially electrolytes with relatively high viscosity, through the microporous structure of randomly oriented carbon fiber felt-based electrodes consumes a relatively large amount of external energy, which can reduce the external efficiency of the RFB. The low external efficiency of RFB systems is one of the main reasons for their lower commercial competitiveness compared to competitive secondary battery technologies such as lithium-ion battery (LIB) technology.

A third obstacle to widespread commercialization of RFBs concerns their relatively low power and energy densities compared to other electrochemical storage technologies, impeding mobile applications. As described herein, power and energy density refer to the power output and energy storage of a storage device relative to the total volume of the energy storage device, respectively. Therefore, power and energy density in RFB refers to the ratio of power output and energy storage to the total volume, including cell volume, tank volume, and conduit volume for electrolyte delivery. To partially compensate for the low power and energy density, RFBs often have relatively large cell active areas and membranes, which can lead to increased cell size and consequently high transverse gradients of electrolyte within electrolyte reservoirs 116A, 116B. As a result, the average current density and nominal current of the RFB can be significantly lower compared to the maximum theoretical value based on uniform maximum current density. Additionally, the need for a circulation system involving separate tanks and conduits further reduces space efficiency at the overall system level.

A fourth obstacle to widespread commercialization of RFBs concerns system complexity compared to chemical plants. The high complexity of RFB system design leads to long development cycles and consequently significantly slows technology development. Additionally, the system complexity is labor and capital intensive and requires a high level of expertise for installation, maintenance and demolition at the ESS site. As systems become more complex, consumers are deterred by the potential need for increased staffing and training to build and maintain the systems, as well as the overall cost increases that come with it.

To address these and other limitations while retaining most of the advantages conferred by RFB, the present disclosure is directed to a sealed redox cell that is not connected to a separate electrolyte tank. Additionally, the present disclosure relates to a secondary battery including a bus bar that enables efficient integration of a plurality of redox battery cells that can be additionally sealed. However, the content of the present invention is not limited to the above-described battery form.

Sealed redox battery

In one aspect, various embodiments of the redox battery disclosed herein relate to redox batteries. Redox cells according to embodiments maintain the advantages of RFBs while at least partially overcoming or mitigating some of the commercialization obstacles of RFBs discussed above. In particular, while using a redox couple that participates in the redox reaction, unlike some RFBs, embodiments of the redox battery disclosed herein include a sealed redox battery cell and a separate battery cell connected to the redox battery cell. It does not have an electrolyte tank and does not have an electrolyte circulation device such as a pump to supply electrolyte from outside the redox battery cell.

Figure 2A is a schematic diagram of a sealed redox battery according to an embodiment. The illustrated sealed redox battery 200A includes a first half cell 204A and a second half cell 204B. First half cell 204A includes an anode electrolyte reservoir 106A having a first or anode electrolyte in contact with an anode disposed therein. The first redox couple configured to cause the first redox half reaction is dissolved in the first electrolyte. The second half cell 204B includes a cathode electrolyte reservoir 106B having a second or cathode electrolyte in contact with a cathode disposed therein. A second redox couple configured to cause a second redox half reaction is dissolved in the second electrolyte. Anode and cathode electrolyte reservoirs 106A, 106B define the reaction space for each half reaction. The sealed redox battery 200A additionally includes an ion exchange membrane or separator 112 that separates the anode electrolyte reservoir 106A and the cathode electrolyte reservoir 106B. The positive electrode is electrically connected to the positive electrode current collector 108A and the negative electrode is electrically connected to the negative electrode current collector 108B. In some embodiments, the first bipolar plate 208A is interposed between the positive electrode current collector 108A and the positive electrolyte reservoir 106A, and the second bipolar plate 208B is interposed between the negative electrode current collector 108B and the positive electrode current collector 108B. It is sandwiched between the cathode electrolyte reservoirs 106B.

Unlike the conventional RFB, in the sealed redox battery (200A) according to the embodiment, the first half cell (204A), the second half cell (204B), and the ion exchange membrane or separator 112 are at least four of the battery cells. It defines a redox battery cell that is partially sealed or sealed by a frame 212 or casing surrounding the side. The illustrated sealed redox battery 200A is a cross-sectional view, so only the top and bottom sides of the casing 212 are shown. However, the casing 212 will be understood as continuously surrounding the top, bottom, front, and back of the illustrated battery cell. In addition, the first and second separator plates 208A and 208B are in contact with the left and right edges or ribs of the casing 212, respectively, to form a space defined by the casing 212 and the first and second separator plates 208A and 208B. The battery cells are surrounded and/or sealed in a sealed space. Accordingly, the sealed and/or sealed frame or casing 212, the first separator plate 208A and the second separator plate 208B are separated by the separator 112 into two spaces, namely the cathode electrolyte reservoir 106B, which accommodates the anode. ) and an anode electrolyte reservoir 106A containing the cathode. The volume sealed by the casing 212 and the first and second separator plates 208A and 208B is such that its internal contents are physically inaccessible from the outside during normal operation. That is, the anode and cathode electrolytes are not in fluid communication with an external vessel, such as an electrolyte tank. The casing 212 and the first and second separator plates 208A and 208B may hermetically and/or permanently seal the redox battery 200A. This configuration contrasts with conventional redox flow batteries where the redox battery cells are in fluid communication with an external tank. That is, in the sealed redox cell 200A, unlike the RFB 100 described above with reference to FIG. 1, neither the anode electrolyte reservoir 106A nor the cathode electrolyte reservoir 106B in the sealed cell is the first or second It is not in fluid communication or physically connected to the separate electrolyte tanks that store each electrolyte. In this way, substantially the entire volume of the anode and cathode electrolytes are stored in the redox battery cell, and are sealed and sealed by the casing 212 and the first and second separator plates 208A and 208B. That is, the first electrolyte reservoir 106A stores substantially the entire volume of the first electrolyte for the first half cell 204A, and the second electrolyte reservoir 106B stores substantially the entire volume of the first electrolyte for the second half cell 204B. Store the entire volume of the second electrolyte. In part, because the sealed redox battery 200A is not connected to a separate storage tank, unlike the RFB 100 shown in FIG. 1, the sealed redox battery 200A transfers the electrolyte to the redox battery cell and It does not include conduits 120A, 120B, 124A, 124B (FIG. 1) for delivery therefrom, or pumps 128A, 128B (FIG. 1) for circulating the electrolyte.

As described above, a notable structural difference of the sealed redox cell 200A is that the pumps 128A and 128B (FIG. 1) are omitted. Instead, the sealed redox cell 200A according to the embodiment has the first and second electrolytes in the positive electrolyte reservoir 106A of the first half cell 204A and the negative electrolyte reservoir 106A of the second half cell 204B ( 106B), each is configured to circulate on its own. In various configurations, self-circulation of the first and second electrolytes is triggered by one or more of the following: an osmotic pressure difference between the first and second electrolyte reservoirs; a change in density of one or both of the first and second electrolytes; diffusion or migration of one or both of the first and second electrolytes; the affinity of one or both of the first and second electrolytes for each of the first and second electrodes; first and second redox half reactions; and thermal expansion or contraction of one or both of the first and second electrolytes.

The inventors found that in the cross-sectional view of Figure 2a, when the thickness of the anode and cathode electrolyte reservoirs 106A, 106B does not exceed a range defined by 20 cm, 15 cm, 10 cm, 5 cm, 2 cm, 1 cm, or any of these values, Cycling was found to be effective in providing stability of power and energy output.

With continued reference to Figure 2A, casing 212 is formed of a corrosion resistant material suitable for housing anode and cathode electrolytes, which may be strongly acidic. In addition to providing corrosion resistance, casing 212 may be a rigid casing to provide mechanical support to sealed redox cell 200A. In some embodiments, at least a portion of casing 212 according to embodiments may be formed from a flexible material configured to deform to accommodate changes in internal pressure within the anode and cathode electrolyte reservoirs 106A, 106B. An increase in internal pressure may be caused, for example, by various effects described below in relation to pressure-controlled sealed redox cells. In configurations where only a portion of the casing is formed of a flexible material, the remaining portion may be formed of a rigid material. The flexible portion may be, for example, one or both of the anode and cathode electrolyte reservoirs 106A, 106B at 0.1%, 0.2%, 0.5%, 1%, 2%, 5%, 10%, 20%, 50%. It may be configured to expand in response to increased pressure to accommodate each additional increase in volume. Suitable materials for casing 212 may include polyvinyl chloride (PVC), polyethylene (PE), polystyrene (PS), polypropylene (PP), polycarbonate (PC), ABS, reinforced plastic, etc.

The sealed redox battery (200A) configured in this way provides various technical and commercial advantages. For example, a variety of reliability failures associated with conduits between redox battery cells and tanks, such as pipe joints and pumps for electrolyte circulation, are substantially reduced or eliminated, preventing unscheduled repairs as well as sealed redox cells ( Reduces the safety risks and operating costs associated with the operation of 200A). Additionally, as described above with respect to the RFB 100 (FIG. 1), there is no need to use a pump to circulate the electrolyte between the redox battery cell and the tank, thereby substantially improving external efficiency. The inventors found that, depending on the size of the system, the sealed redox battery (200A) can improve power or energy density by up to 2 to 50 times compared to a conventional RFB because it does not require circulating electrolyte between the cell and the electrolyte tank. I realized that there was. As previously discussed, power or energy density refers to the power or energy output of a storage device relative to the total volume of the energy storage device, respectively. Accordingly, power or energy density in a sealed redox cell refers to the ratio of power or energy output to the total volume of the sealed redox cell, respectively. Additionally, space efficiency is greatly improved by omitting a circulation system including separate tanks, pumps, and conduits. Additionally, system complexity is greatly reduced, significantly lowering the barrier to commercial implementation of sealed redox cells (200A). For example, unlike conventional RFBs, sealed redox cells (200A) can be manufactured in packs similar to lithium-ion cells for modular implementation and thus automation without the need for intrusive configuration that may be required for conventional RFB installations. and becomes more suitable for mass production.

Below, the operating principle and aspects of the sealed redox battery 200A are explained using the example of a sealed vanadium (V) redox battery based on a vanadium-based redox pair. However, it will be understood that the embodiments are not so limited and that the principles described herein can be applied to redox cells according to various other redox pairs.

In the sealed V redox battery according to the embodiment, the first redox couple dissolved in the first or anode electrolyte of the first half cell 204A may be a V ⁴⁺ /V ⁵⁺ redox couple, and the second The second redox couple dissolved in the second or cathode electrolyte of the half cell 204B may be a V ²⁺ /V ³⁺ redox couple. The redox reaction during charging and discharging can be described using the following equation, where → represents the direction of the discharge reaction and ← represents the direction of the charge reaction:

Second half cell/cathode: V ²⁺ ←→ V ³⁺ + e ^-

First half cell/anode: V ⁵⁺ + e ^- ←→ V ⁴⁺

Total reaction: V ²⁺ + V ⁵⁺ ←→ V ³⁺ + V ⁴⁺

During charging, in the first half cell 204A, the tetravalent vanadium ions V ⁴⁺ are oxidized to pentavalent vanadium ions V ⁵⁺ , while in the second half cell 204B the trivalent ions V ³⁺ are oxidized to divalent ions V It is reduced to ²⁺ . During discharge, pentavalent vanadium ions V ⁵⁺ are reduced to tetravalent vanadium ions V ⁴⁺ in the first half cell 204A, while divalent ions V ²⁺ are reduced to trivalent ions V in the second half cell 204B. It is oxidized to ³⁺ . While this redox reaction occurs, electrons are transferred through the external circuit and specific ions diffuse across the ion exchange membrane or separator 112 to balance the electrical neutrality of the anode and cathode half cells, respectively.

Other redox reactions may be implemented in the sealed redox battery (200A) according to the embodiment. According to various embodiments, the first redox couple or the second redox couple is vanadium (V), zinc (Zn), bromine (Br), chromium (Cr), manganese (Mn), titanium (Ti), iron ( It contains one or more ions of Fe), cerium (Ce), and cobalt (Co). In some embodiments, the first and second redox couples include ions of the same metal as in the sealed V redox cell described above. In this embodiment, advantageously mixing the anode and cathode electrolytes does not result in cross-contamination of the electrolytes.

As described herein, the electrolyte in a redox cell is a solution that conducts electric current through ionization. The electrolyte serves to support the reduced and oxidized forms of the redox couple and also supports the corresponding cations and anions to balance the ionic charges in solution during the oxidation and reduction of the redox couple. The anode and cathode electrolytes according to embodiments include an acidic aqueous solution. In the case of a sealed V redox battery, the concentration of V ions is related to the energy density of the electrolyte. Higher energy densities can advantageously reduce the volume of the anode and cathode electrolyte reservoirs 106A, 106B required for a given amount of energy and power output. However, if the concentration of V ions is too high, the stability of V ions may decrease. Therefore, there is an optimal V ion range for a given application. For example, the vanadium ions dissolved in one or both of the first and second electrolytes may exceed a value in a range defined as 1.0 M, 1.5 M, 2.0 M, 2.5 M, or any of these values. . On the one hand, V ion concentrations below 1.0 M may result in unsuitable energy levels for some applications. On the other hand, V ion concentrations above 2.5 M may lower the stability of V ⁵⁺ ions, for example at operating temperatures above 50°C, and may reduce the stability of V ions in the electrolyte, for example at operating temperatures below -20°C. The solubility limit of ²⁺ and V ³⁺ ions may be reached.

Advantageously, depending on the embodiment, the positive and negative electrolytes may comprise the same solvent(s) and/or the same metal ions. In these embodiments, mixing of the anode and cathode electrolytes through the ion exchange membrane or separator 112 does not cause contamination of the respective half cells. Additionally, the anode and cathode electrolytes can be prepared from the same starting solvent(s) and solute(s). For example, in the case of sealed V redox cells according to some embodiments, both the anode and cathode electrolytes include sulfuric acid. The electrolyte is prepared, for example, by dissolving 0.1 M to 2.5 M VOSO ₄ (vanadyl sulfate) in 0.1 M to 6 M MH ₂ SO ₄ in an aqueous solution to form tetravalent vanadium ions (V ⁴⁺ ) and/or trivalent vanadium ions. Vanadium ions (V ³⁺ ) can be formed. Tetravalent/trivalent vanadium ions can be electrochemically oxidized to form an anode electrolyte (catholyte) containing a solution of pentavalent vanadium ions (V ⁵ + ). Conversely, tetravalent/trivalent vanadium ions can be electrochemically reduced to form a cathode electrolyte (anolyte) containing a solution of divalent vanadium ions (V ²⁺ ).

Still referring to Figure 2A, in various embodiments, the anode and cathode disposed in the anode and cathode electrolyte reservoirs 106A and 106B, respectively, are made of carbon or carbon, such as graphite felt, carbon cloth, carbon black, graphite powder, and graphene. Contains substances. Carbon-based materials advantageously provide a relatively high operating range, good stability and high reversibility. The electrode is optimized for relatively high electrochemical activity, low bulk resistivity and large specific area. Improvement of the electrochemical activity of the electrode increases the energy efficiency of the sealed redox battery (200A). To improve the performance of the sealed redox battery 200A, the electrode surface can be modified through, for example, metal coating, increasing surface roughness, or additive doping.

The anode and cathode electrolyte reservoirs 106A, 106B defining the reaction space are between the ion exchange membrane or separator 112 and, if present, each of the first and second separators 208A, 208B, or between the ion exchange membrane or separator 112. ) and each of the positive and negative electrode current collectors 108A and 108B is partially or completely filled with each electrode. After filling each electrode, the remaining space of the anode and cathode electrolyte reservoirs 106A, 106B is between the ion exchange membrane or separator 112 and the first and second separators 208A, 208B, if present, or the ion exchange membrane or separator. Between (112) and the positive and negative electrode current collectors (108A, 108B) is partially or completely filled with the respective electrolyte. In various embodiments, except when intentionally perforated or made porous, the ion exchange membrane or separator 112 substantially separates the two half-cells and substantially prevents mixing of the two electrolytes and the redox couple while H It allows the transfer of ions such as ⁺ to balance the charge between the two half cells, completing the circuit while the current flows. The ion exchange membrane or separation membrane 112 may be an anion exchange membrane or a cation exchange membrane.

Various depicted embodiments include, but are not limited to, an ion exchange membrane or separator 112 that may be selective for certain types of ions, for example cations or anions. For example, in various embodiments, the ion exchange membrane or separator 112 may be a non-selective membrane, for example, a porous membrane.

Still referring to Figure 2A, in some implementations, the output power can be scaled by connecting multiple single redox battery cells in series, for example, to form a cell stack. In this configuration, the first and second separator plates 208A and 208B can facilitate serial connection of single cells and the current collectors 108A and 108B between adjacent separator plates can be eliminated. The first and second separator plates 208A, 208B may be formed of a suitable material such as graphite, carbon, carbon plastic, etc. to provide high electrical conductivity and low internal resistance of the cell stack. Additionally, the first and second separator plates 208A, 208B support the contact pressure applied when pressed against the electrodes, thereby increasing electrical conductivity. Additionally, the first and second separator plates 208A and 208B are provided with high acid resistance to prevent corrosion or oxidation of the current collectors 108A and 108B.

The anode and cathode current collectors 108A and 108B contain a highly electrically conductive metal such as copper or aluminum, and serve to flow current during charging and discharging processes.

The single sealed redox cell 200A described above has an output voltage characteristic of the electrochemical reaction, e.g., about 1.65 V or less, by connecting additional cells in electrical series or electrical parallel as described herein. Higher voltage and current can be achieved, respectively.

FIG. 2B is a schematic diagram of a sealed redox battery including a plurality of sealed redox battery cells in a stacked configuration according to some embodiments. The illustrated sealed redox battery (200B) includes a plurality of stackable redox battery cells (200B-1, 200B-2, ..., 200B-n), where each cell is a sealed redox battery (200A) It is configured in a similar way (Figure 2a). Each of the plurality of redox battery cells (200B-1, 200B-2, ..., 200B-n) includes an anode electrolyte reservoir (106A), a cathode electrolyte reservoir (106B), and an ion exchange membrane or separation membrane (112). In the illustrated embodiment, each of the plurality of redox battery cells 200B-1, 200B-2, ..., 200B-n is sealed with a separate casing 212. The output voltage can be increased by connecting a plurality of redox battery cells (200B-1, 200B-2, ..., 200B-n) in electrical series.

Figure 2c is a schematic diagram of a sealed redox battery including a plurality of sealed redox battery cells stacked according to some other embodiments. The illustrated sealed redox battery (200C) includes a plurality of stackable redox battery cells (200C-1, 200C-2, ..., 200C-n), where a plurality of redox battery cells (200C-1, 200C-2,..., 200C-n) a sealed redox cell 200A (FIG. 2A), each comprising an anode electrolyte reservoir 106A, a cathode electrolyte reservoir 106B, and an ion exchange membrane or separator 112. It is structured in a similar way. However, unlike the sealed redox battery 200B (FIG. 2b), in the illustrated embodiment, a plurality of redox battery cells 200C-1, 200C-2, ..., 200C-n are stored in a common casing 222. It is sealed. In a manner similar to the sealed redox battery (200B) (FIG. 2b), the output voltage can be increased by connecting a plurality of redox battery cells (200C-1, 200C-2, ..., 200C-n) in electrical series. there is. Additionally, in some embodiments, the anode electrolyte reservoirs 106A of the plurality of redox battery cells 200C-1, 200C-2, ... 200C-n can be in fluid communication with each other, and the plurality of redox battery cells 200C The cathode electrolyte reservoirs 106B (-1, 200C-2,..., 200C-n) may be in fluid communication with each other. The sealed redox battery (200C) may be configured as a pouch-type redox battery or a hard case-type redox battery.

Figure 2D is a schematic diagram of a sealed redox battery including a plurality of sealed redox battery cells in a cylindrical stacked configuration according to an embodiment. The illustrated sealed redox battery (200D) includes a plurality of redox battery cells (200D-1, 200D-2, ..., 200D-n) that can be stacked in a cylindrical shape, where a plurality of redox battery cells (200D- 1, 200D-2,..., 200D-n) sealed redox cells 200A, each comprising an anode electrolyte reservoir 106A, a cathode electrolyte reservoir 106B and an ion exchange membrane or separator 112 (FIG. 2A) ) is structured in a similar way. A plurality of redox battery cells (200D-1, 200D-2, ..., 200D-n) can be individually sealed within a casing in a manner similar to that described above for the sealed redox battery (200B) (FIG. 2B). . Alternatively, a plurality of redox battery cells 200D-1, 200D-2, ..., 200D-n are stored in a common casing 222 in a manner similar to that described above for the sealed redox battery 200C (FIG. 2C). ) can be sealed. In a manner similar to the sealed redox battery (200B) (FIG. 2b), the output voltage can be increased by connecting a plurality of redox battery cells (200D-1, 200D-2, ..., 200D-n) in electrical series. there is. Additionally, in some embodiments, the anode electrolyte reservoir 106A of the plurality of redox battery cells 200D-1, 200D-2, ..., 200D-n can be in fluid communication with each other, and the plurality of redox battery cells ( The cathode electrolyte reservoirs 106B (200D-1, 200D-2,..., 200D-n) may be in fluid communication with each other.

Some or all of the plurality of redox battery cells in each of the stacked configurations described above with respect to FIGS. 2B-2C are electrically connected in series by appropriately electrically connecting current collectors of opposite polarity to some or all of the cells, or It will be understood that some or all of the current collectors of the same polarity can be connected in electrical parallel by appropriately electrically connecting them.

Differences between sealed redox batteries and conventional secondary batteries

The differences and advantages of sealed redox cells according to embodiments over conventional RFBs have been described above, including the omission of electrolyte tanks, pumping systems, and conduit networks that have contributed to the slow commercial implementation of conventional RFBs. While there cannot be a separate electrolyte tank, sealed redox cells 200A-200D (FIGS. 2A-2D) retain some of the inherent design flexibility available in conventional RFBs. For example, the design of cell geometry is substantially more flexible compared to conventional secondary batteries due to the inherent compliance of liquids. Additionally, the power and energy storage capacities can be independently decoupled and scaled to a limited extent, for example, by adjusting the ratio of electrolyte volume to electrode surface area. The ratio can be adjusted using, for example, the thickness of the anode and cathode electrolyte reservoirs 106A, 106B, as described above. On the other hand, the sealed redox battery according to the embodiment also shares the main advantage of the conventional battery in that it is completely sealed and modularization is possible. The sealed redox battery according to the embodiment and the conventional secondary battery, for example, LIB, may have components referred to using similar terms, but the components of the sealed redox battery according to the embodiment and their operation It will be understood that the principles can be distinguished from the conventional secondary batteries described herein.

Below, a comparison will be made between the sealed redox battery and LIB according to the embodiment, but it will be understood that the comparison can also be applied to other conventional secondary batteries.

First, the structure, functional role, and operating principle of the electrolyte in the sealed redox battery according to the embodiment can be distinguished from that of a conventional secondary battery, for example, LIB. In operation, the electrolyte in LIB does not store energy itself and does not participate in electrochemical reactions during the charge/discharge process. Instead, in LIB, the electrolyte primarily serves to provide a path for lithium ions to pass between the anode and cathode during the charge/discharge process. Accordingly, the movement of the electrolyte is not substantially restricted by the separator. In contrast, in the sealed redox cell (200A) according to the embodiment, the electrochemical energy is in the form of dissolved active materials, for example, each dissolved in the anode and cathode electrolytes that cause electrochemical reactions during the charge/discharge process. Stored in electrolyte as redox pairs. Therefore, the electrolyte can be said to be a medium that stores energy in the sealed redox battery according to the embodiment. As described above, in the example of a V redox cell, the oxidation state of the V ion species dissolved in the anode and cathode electrolytes is changed by each Haff reaction. Therefore, the chemical composition of the anode and cathode electrolytes in a sealed redox battery are different from the electrolytes of LIB. Also, unlike LIB, in the sealed redox battery according to the embodiment, electromotive force due to the difference in chemical composition of the anode electrolyte and the cathode electrolyte leads to energy storage, so when the anode and cathode electrolytes are mixed, the stored energy is stored. A loss occurs.

Second, the structure, functional role, and operating principle of the electrode in the sealed redox battery according to the embodiment can be distinguished from that of a conventional secondary battery, for example, LIB. In LIB, the active material contained in the electrode directly participates in the electrochemical reaction. During operation, in LIB, lithium ions move between the active material of the anode and the active material of the cathode, achieving electrochemical equilibrium, and the electrode itself serves as the main medium for energy storage. In contrast, the electrodes of sealed redox cells according to embodiments play a very different role. The anode of the sealed redox battery does not participate in the first redox half reaction, and the cathode of the sealed redox battery does not participate in the second redox half reaction. As described herein, an electrode that does not participate in a redox half reaction does not preclude the electrode's ability to provide a physical site for an electrochemical reaction in a manner similar to a catalyst. However, the electrode itself is not involved in the electrochemical reaction, and redox ions do not move between the anode and cathode during charging and discharging of the redox cell. Depending on the composition, functional groups that act as catalysts may be present on the surface. However, this can be distinguished from electrodes that actively participate in electrochemical reactions, such as in the case of LIB. Rather, the electrode substantially passively transfers electrons generated by electrochemical reactions.

Third, the structure, functional role, and operating principle of the ion exchange membrane in the sealed redox battery according to the embodiment can be distinguished from the separator in a conventional secondary battery, for example, LIB. In LIB, the active material of the electrode where the electrochemical reaction occurs is generally in a solid state, and the separator disposed between the anode and the cathode mainly serves to prevent electrical shorts between them. Therefore, although the separator serves to prevent electrical contact between the anode and cathode, in LIB the separator is not specifically designed to limit the transfer of lithium ions through it or limit the electrochemical reaction between them. In other words, in LIB, the separator mainly serves to electrically insulate the anode and cathode from each other without interfering with the movement of ions as part of the electrochemical reaction for charging and discharging. Therefore, the separator for LIB is designed to freely transfer lithium ions between electrodes. In contrast, in the sealed redox cell according to the embodiment, the redox active species are dissolved in the electrolyte, and the ion exchange membrane or separator 112 (FIG. 2A) electrically separates the anode and cathode electrolytes and prevents them from mixing with each other. It plays a role.

Typically, the ion exchange membrane or separator 112 includes a selectively permeable membrane through which cations or anions are transferred to balance the charge between two half cells. For example, an ion exchange membrane can be configured to selectively pass cations or anions through it. Therefore, since the electrolyte that stores energy in the sealed redox battery according to the embodiment is liquid, without the ion exchange membrane or separator 112, electrical energy is generated by mixing the anode and cathode electrolytes regardless of whether the anode and cathode are in contact with each other. A short circuit occurs.

Accordingly, in the sealed redox cell according to the embodiment, the first and second redox half reactions occur across the ion exchange membrane or separator 112 separating the anode electrolyte reservoir 106A and the cathode electrolyte reservoir 106B. This occurs without substantial ion transfer of the first redox couple or the second redox couple.

As described herein, the ion exchange membrane or separator 112, which does not substantially transfer ions of the redox couple, substantially prevents crossing of the electrolyte between the anode and cathode electrolyte reservoirs 106A, 106B (FIG. 2A). It refers to the ion exchange membrane or separation membrane 112 that plays the role. Accordingly, the base material of the ion exchange membrane or separator 112 preferably blocks the movement of redox species in the electrolyte, e.g., V ions in a V redox cell, while retaining other ions, e.g., charge between the half cells. It may be a membrane that selectively allows the movement of H ⁺ ions in a V redox cell for balance. However, an ion exchange membrane or separator 112 that does not substantially transfer ions of the redox couple may still allow unintended crossing or limited intended mixing to relieve internal pressure build-up.

Polybenzimidazole-based separator and method for manufacturing the same

As described above, the ion exchange membrane or separator performs, among other functions, the function of conducting ions of the supporting electrolyte between the anode and cathode electrolyte reservoirs while substantially inhibiting the passage of redox active ions, such as vanadium ions. To further improve the performance of redox battery cells, lowering ionic resistance to enable operation at higher current densities, improving barrier properties, and balancing net electrolyte transfer to minimize capacity imbalance, among other improvements. It is necessary to develop further improvements in membranes or separators and efficient manufacturing methods to achieve one or more of the following: and improving the chemical stability of the membrane or separator material.

In order to solve these and other needs, according to one embodiment of the present invention, a polybenzimidazole-based separator using polybenzimidazole (PBI) material is used as the separator. PBI has high chemical stability against acidic electrolytes used in redox battery cells, and when in contact with aqueous sulfuric acid used in the electrolyte, the imidazole group of PBI is protonated and PBI becomes positively charged, exhibiting ion exchange properties. .

Polybenzimidazole (PBI)-based separators can have excellent chemical resistance, heat resistance, and mechanical strength compared to other conventional separators, and can be applied to various secondary batteries.

In particular, it will be appreciated that the various embodiments of the ion exchange membrane or separator disclosed herein are particularly effective when integrated as part of a sealed redox cell (e.g., ion exchange membrane or separator 112 in FIG. 2A). This is primarily because sealed redox cells can be exposed to harsher conditions, including higher internal pressures, that conventional membranes may not be able to withstand effectively and reliably.

However, embodiments of the separator are not limited to use in sealed redox cells, and the ion exchange membranes or separators disclosed herein may advantageously be used in redox flow cells, e.g., in the redox flow cell described above with reference to Figure 1. It will be understood that the battery 100 may be integrated for use in any suitable secondary battery, including a lithium ion battery.

As a method for producing a polybenzimidazole-based separation membrane, a solution of polybenzimidazole in an organic solvent is coated on a hard backing film (or substrate film) to form a membrane ( After forming a film, a polybenzimidazole-based separator can be obtained by peeling, removing, and heat-treating the backing film.

However, conventionally produced polybenzimidazole-based films may not satisfy very high mechanical strength as a separator for secondary batteries.

On the other hand, backing films such as polyethylene terephthalate (PET)-based backing films used to improve mechanical strength when manufacturing separators can be a major factor in increasing process costs and reducing manufacturing efficiency. In addition, in the course of intensive research in the present invention, it was confirmed that a fine air layer is formed when a polybenzimidazole-based solution is coated on a backing film to form a film. In areas where such an air layer is formed, voltage efficiency is greatly reduced, and there is also a problem of reduced charge/discharge efficiency characteristics when driving the secondary battery. Therefore, there is a need to develop an efficient method for manufacturing a polybenzimidazole-based separator that can improve the mechanical strength of the film and improve the characteristics of secondary batteries without using a backing film.

Therefore, the method for producing a polybenzimidazole-based film according to an aspect of the present invention includes the steps of dissolving a polybenzimidazole-based compound in an amide-based organic solvent to form a polybenzimidazole solution; Impregnating a porous membrane with the polybenzimidazole solution; and drying the porous membrane impregnated with the polybenzimidazole solution under temperature conditions of 80° C. or lower. At this time, the porous membrane has the advantage of not having to be removed separately, unlike the backing film. For example, the amide-based organic solvent according to the present invention may be N,N-dimethylacetamide (DMAc), dimethylformamide (DMF), etc., and N,N-dimethylacetamide is preferably used.

The polybenzimidazole-based compound of the present invention is a polymer of polybenzimidazole, which is a mixture or co-polymer of polybenzimidazole precursors (repeating units or monomers to form polybenzimidazole polymer). it means. The precursor of polybenzimidazole is ab-PBI (Poly(2,5-benzimidazole)), oPBI (Poly[2,2'-(4,4'-oxybis(1,4-phenylene))-5,5 '-bibenzimidazole), m-PBI (meta-polybenzimidazole), pPBI (para-polybenzimidazole), s-PBI (sulfonated polybenzimidazole), f-PBI (fluorine-containing polybenzimidazole), 2OH-PBI (Dihydroxy polybenzimidazole), PIPBI (Phenylindane) -polybenzimidazole), PBI-OO (poly[(1-(4,4'-diphenylether)-5-oxybenzimidazole)-benzimidazole]), and combinations thereof, but are not necessarily limited thereto.

Meanwhile, it is known that the dissolution rate of PBI relative to 100% by weight of organic solvent is 2 to 6% by weight. Therefore, according to one embodiment of the present invention, in order to improve the solubility of the polybenzimidazole-based compound in the organic solvent, the step of dissolving the PBI precursor in the amide-based organic solvent is performed under a temperature condition of 130° C. or higher and/or 0.1 MPa. By performing the process at a pressure above, the dissolution rate of the polybenzimidazole-based compound with respect to 100 wt% of the organic solvent can be improved to 8 to 20 wt%.

According to one embodiment of the present invention, the porous membrane may be manufactured using one or more polyolefin-based materials. For example, the porous membrane of the present invention may be made of a material containing polypropylene (PP), polyethylene (PE), or a combination thereof, but is not necessarily limited thereto. For example, when using porous nylon film, Teflon film, cloth film, etc., rolling and wrinkling phenomena occur due to heat shrinkage during the process of forming and drying the separator. Since the problem of deterioration in the quality of the separator may occur, the present invention uses a porous membrane made of PP (polypropylene) or PE (polyethylene), which does not cause such a phenomenon.

The thickness of the porous membrane according to the invention may be, for example, 1 to 30 μm, for example 3 to 20 μm, for example 5 to 15 μm, for example 8 to 10 μm. However, it is not necessarily limited to this and may be selected depending on the thickness of the final separator to be manufactured.

Furthermore, according to the present invention, the drying process after impregnating the porous membrane with the polybenzimidazole solution is performed at a temperature of 80°C or lower, which is lower than the conventional temperature of about 100°C, thereby preventing rolling due to heat shrinkage, It is possible to prevent degradation of the separator quality, such as wrinkling, and additionally, equipment such as a pinch roll can be used for the film forming and drying process. However, if the drying temperature is too low, the drying time may increase, resulting in process inefficiency. Therefore, it is advantageous for the drying process temperature to be 40°C or higher, so the drying process temperature may be, for example, 40 to 80°C. It may be 40 to 70°C, for example, 50 to 60°C.

On the other hand, when performing a drying process after forming a polybenzimidazole solution on a backing film as in the past, if the drying process is performed in a low drying temperature range as in the present invention, the drying time increases significantly, reducing process efficiency. This is presumed to be because hot air, IR, and UV energy for drying are difficult to transmit to one side of the separator due to the hard material.

When the porous membrane used in the polybenzimidazole-based separator according to the present invention is hydrophobic and the electrolyte solution used in the electrode assembly is hydrophilic, there is a portion where the hydrophilic electrolyte solution is not in contact with the hydrophobic separator, resulting in the secondary battery. Problems such as charging and discharging defects may occur.

Therefore, according to one embodiment of the present invention, in the step of preparing the polybenzimidazole solution, the surfactant may be mixed together. In this way, when the porous membrane is impregnated with a mixed solution of a polybenzimidazole-based compound, a solvent, and a surfactant, the porous membrane becomes hydrophilic due to the surfactant, thereby solving or reducing the problem of charging and discharging defects. At this time, based on 100% by weight of the total solution, the surfactant may be included, for example, in an amount greater than 0.1% by weight and less than 5.0% by weight, for example, it may be included in an amount of 2.0% by weight or more and 4.0% by weight or less, e.g. For example, it may be included in an amount of 0.5% by weight or more and 2.0% by weight or less, for example, it may be included in an amount of 0.5% by weight or more and 10.0% by weight or less, but is not necessarily limited thereto. The surfactant may include one or more of an ionic surfactant, a nonionic surfactant, and an organic surfactant, and may be, for example, a silicone-based organic surfactant.

According to one embodiment of the present invention, the viscosity of the solution can be lowered by further adding a viscosity adjusting solvent to the polybenzimidazole solution. In a film forming process using a solution as in the present invention, if the viscosity of the solution is high, fluidity during film forming becomes low and precision control becomes difficult, such as making it difficult to form a thin film. Therefore, film forming performance and precision can be improved by further adding a viscosity control solvent in addition to the organic solvent for dissolving the ion conductive resin.

Therefore, based on 100% by weight of the polybenzimidazole solution, the viscosity adjusting solvent may be included at, for example, 10% by weight to 25% by weight, for example, 12% by weight to 20% by weight, For example, it may be included at 15% by weight to 18% by weight, but is not necessarily limited thereto.

According to one embodiment of the present invention, the viscosity adjusting solvent may be one or more of a ketone solvent or an alcohol solvent. As a more specific example, the ketone solvent may be acetone, methyl ethyl ketone, methyl isobutyl ketone, etc., and an alcohol solvent. may be methanol, ethanol, isopropanol, butanol, isobutanol, etc.

According to the method for manufacturing a polybenzimidazole-based separator according to the present invention, it is possible to form a uniform separator and implement a low-cost and high-efficiency process without using a separate backing film. Additionally, if necessary, there is an advantage in that a single-sided film or a double-sided film can be produced by impregnating one or both sides of the porous membrane with a polybenzimidazole solution.

In particular, the polybenzimidazole-based separator manufactured according to the method for producing a polybenzimidazole-based separator according to the present invention has very excellent tensile strength, and its high tensile strength is maintained even when heat-treated or immersed in an acidic electrolyte solution. Conventional polybenzimidazole-based separators can be viewed as having very excellent quality compared to their tensile strength, which is very low after heat treatment or electrolyte immersion. The average tensile strength of the polybenzimidazole-based separator according to the present invention may be, for example, 100 MPa or more, for example, 120 MPa or more, and may be, for example, 150 MPa or more, resulting in excellent mechanical strength and uniform coating properties. has Depending on the embodiment, a secondary battery separator manufactured using a PBI film may contribute to improving the performance of the produced redox battery.

On the other hand, as the thickness of the polybenzimidazole-based separator increases, the resistance to hydrogen ion flow increases, which reduces the voltage efficiency of the secondary battery. As the thickness decreases, mechanical strength decreases, crossover phenomenon and osmosis occur. There may be a problem that coulombic efficiency decreases due to the increase in the phenomenon. From this point of view, the thickness of the polybenzimidazole-based separator according to the present invention may range from 2 to 40 μm, for example, from 5 to 30 μm, for example from 10 to 20 μm. It may be in the range of, but is not necessarily limited to, and the thickness may be changed as needed. Since the polybenzimidazole-based separator of the present invention is manufactured by drying the impregnated porous membrane and removing the solvent, the thickness of the polybenzimidazole-based separator can be adjusted by the content and amount of polybenzimidazole used, and the battery It can be selected taking into account the driving conditions, manufacturing condition, etc.

Hereinafter, embodiments of the present invention will be described. However, the following example is only an example of the present invention and is not limited thereto.

<Manufacture example>

Example 1

After adding m-PBI, a polybenzimidazole precursor, to dimethyl acetamide (DMAC), it was dissolved with stirring at a temperature of 160°C and normal pressure for 24 hours to prepare a PBI solution with a maximum dissolution rate of 12% by weight. did. Then, a PE film (thickness: 20㎛) was impregnated in the PBI solution and then dried with hot air at a temperature of 50°C for 2 minutes to obtain a separator with a thickness of 27㎛. The separator manufactured in this way exists as a PE film impregnated with PBI.

Comparative Example 1

m-PBI, a polybenzimidazole precursor, was added to DMAc and then dissolved with stirring at a temperature of 160°C and normal pressure for 24 hours to prepare a PBI solution with a maximum dissolution rate of 12% by weight. Then, using a slot die coater, a PBI solution was sprayed on one side of the PET film, which is a base film, to prepare a polybenzimidazole separator. After drying with hot air at a temperature of 80°C for 2 minutes, the PBI film was separated from the PET film. By peeling, a 22㎛ thick separator was obtained.

Assuming that the amount of PBI solution used to manufacture a 27㎛ thick separator in Example 1 was 10, the amount of PBI solution used to manufacture a 22㎛ separator in Comparative Example 1 was 22. Therefore, under the conditions of manufacturing a separator of the same thickness, the amount of PBI used is much reduced in the manufacturing method according to Example 1 of the present invention, so the efficiency in terms of cost and process is increased, and when the amount of PBI used is reduced, the drying temperature and Drying time could also be reduced, which had the advantage of lowering energy usage during manufacturing and reducing process time.

<Battery performance evaluation>

Two current collectors were manufactured by laminating a carbon current collector (graphite composite, thickness: 0.2 mm) and a metal current collector (aluminum foil, thickness: 0.2 mm), and were used as a positive electrode current collector and a negative electrode current collector, respectively, and carried out as described above. Unit cells including an anode electrolyte accommodating part and a cathode electrolyte accommodating part formed using the separator prepared in Example 1 or Comparative Example 1 were manufactured, respectively. V ^3.5+ electrolyte (manufactured by Standard Energy) with a concentration of 1.7M was supplied to each of the anode electrolyte accommodating part and the cathode electrolyte accommodating part. When charging, the electrolyte was charged with a constant current of 1 C until the voltage reached 1.55 V, and when discharging, it was charged at 1 C. While driving by discharging with a constant current until the voltage reached 1.10 V, the energy efficiency (VE, CE and EE) (%) was measured and shown in Table 1 below.

<Mechanical strength measurement>

For each of the separators prepared in Example 1 and Comparative Example 1, the average tensile strength (MPa) was measured according to ASTM D882. In addition, measurements were taken before and after heat treatment at 80°C and after immersion in 50ml of electrolyte for 1 hour and 24 hours, respectively, and are shown in Table 1 below. At this time, an electrolyte containing 1.7M concentration of V ^3.5+ vanadium ions and 1.7M concentration of sulfuric acid aqueous solution was used.

	Battery efficiency evaluation			Average tensile strength measurement (MPa)
	VE (%)	CE (%)	EE (%)	Before heat treatment	After heat treatment	electrolyte Support (1h)	electrolyte Support (24h)
Example 1	90.9	99.7	90.6	150.0	150.0	129.4	130.7
Comparative Example 1	90.3	99.6	90.0	78.2	107.9	45.1	47.9

As can be seen in Table 1, when the separator of Example 1 according to the present invention was used, the battery efficiency slightly increased compared to when the separator of Comparative Example 1 was used, and the average tensile strength was significantly improved. In particular, unlike Comparative Example 1, the separator of Example 1 showed little change in average tensile strength even after heat treatment. In addition, the decrease in tensile strength of the separator of Example 1 after being immersed in an electrolyte solution was very low compared to the decrease in tensile strength of the separator of Comparative Example 1, confirming that mechanical strength, durability, and acid resistance were all high.

< Experiment on drying process temperature conditions >

A PBI separator was manufactured in the same manner as Example 1 or Comparative Example 1, but the temperature of the drying process was changed as shown in Table 2 below.

A case in which a PBI separator was manufactured in the same manner as in Example 1, but only the drying temperature was different, was referred to as experimental group A, and a case in which a PBI membrane was manufactured in the same manner as in Comparative Example 1, but only the drying temperature was different, was referred to as experimental group B. For each separator, the drying temperature and drying time and whether shrinkage of the PE film occurred were confirmed and are shown in Table 2 below. Cases where contraction did not occur were indicated as “-“, and cases where contraction occurred were indicated.

	Drying temperature (℃)	drying time	Whether contraction occurs or not
Experimental group A	30	150 minutes or more	-
	35	50 minutes or more	-
	40	5 minutes	-
	50	2 minutes	-
	60	1 min	-
	70	42 seconds	-
	80	13 seconds	-
	90	10 seconds	contraction occurs
Experimental group B	40	150 minutes or more	-
	50	30 minutes	-
	60	14 minutes	-
	70	5 minutes	-
	80	2 minutes	-

As can be seen from Table 2, as the drying temperature increases, the drying time becomes shorter and the process efficiency increases. However, if the temperature becomes too high, there is a problem in that shrinkage of the PE film, which is a porous membrane, occurs. In addition, it can be seen that, unlike the present invention, experimental group B, which uses a conventional backing film, has a much longer drying time and lowers process efficiency even if it is dried at the same temperature as experimental group A.

< Experiment depending on the thickness of the PBI separator >

The PBI separator was manufactured in the same manner as in Example 1, but the thickness of the PBI separator was varied by controlling the amount of PBI solution used. The battery efficiencies were evaluated in the same manner as in the <Battery performance evaluation> above, and are shown in Table 3 below.

Thickness of separator (㎛)	VE (%)	CE (%)	EE (%)
2	92.5	98.2	90.8
4	92.1	98.9	91.1
8	90.7	99.4	90.2
10	90.9	99.2	90.2
15	90.1	99.6	89.7
18	88.3	99.5	87.9
20	88.0	99.6	87.6
25	86.8	99.4	86.3

As can be seen in Table 3 above, as the thickness of the separator increases by increasing the amount of PBI used, the resistance to hydrogen ion flow increases, thereby reducing the voltage efficiency (VE) of the battery. On the other hand, if the thickness of the separator is reduced by reducing the amount of PBI used, the probability of a crossover phenomenon in the vanadium electrolyte increases, thereby reducing the Coulombic efficiency (CE).

Since the PBI separator is affected by the thickness of the porous membrane (PE), in order to manufacture a thinner separator, the thickness of the separator can be manufactured thinner by selecting a thinner porous membrane and controlling the amount of PBI solution used.

Although specific embodiments have been described above, these embodiments are presented by way of example only and are not intended to limit the scope of the disclosure. Indeed, the novel devices, methods, and systems described herein may be implemented in a variety of different forms; Additionally, various omissions, substitutions, and changes may be made in the form of the methods and systems described herein without departing from the spirit of the disclosure. Any suitable combination of elements and acts of the above-described embodiments may be combined to result in further embodiments. The various features and processes described above may be implemented independently of each other or may be combined in various ways. All possible combinations and subcombinations of the features of the disclosure are intended to fall within the scope of the disclosure.

Claims (15)

1. Dissolving a polybenzimidazole-based compound in an amide-based organic solvent to form a polybenzimidazole solution;

   Impregnating a porous membrane with the polybenzimidazole solution; and

   Drying the porous membrane impregnated with the polybenzimidazole solution at a temperature of 80° C. or lower to obtain a polybenzimidazole-based separator;

   Method for producing a polybenzimidazole-based separation membrane comprising.
2. According to paragraph 1,

   A method of producing a polybenzimidazole-based separator without using a backing film to form the polybenzimidazole-based separator.
3. According to paragraph 1,

   The step of impregnating the porous membrane includes impregnating one or both sides of the porous membrane.
4. According to paragraph 1,

   A method of producing a polybenzimidazole-based separation membrane, wherein the porous membrane is made of a material containing polypropylene, polyethylene, or a combination thereof.
5. According to paragraph 1,

   The thickness of the porous membrane is 1 to 30 μm,

   A method of producing a polybenzimidazole-based separator, wherein the polybenzimidazole-based separator has a thickness of 2 to 40 μm.
6. According to paragraph 1,

   A method for producing a polybenzimidazole-based separator, wherein a surfactant is mixed together in the step of forming the polybenzimidazole solution.
7. According to clause 6,

   A method for producing a polybenzimidazole-based separator, wherein the surfactant is contained in an amount of more than 0.1% by weight and less than 5.0% by weight, based on 100% by weight of the polybenzimidazole solution.
8. According to clause 6,

   A method for producing a polybenzimidazole-based separation membrane, wherein the surfactant includes one or more of an ionic surfactant, a non-ionic surfactant, and an organic surfactant.
9. According to paragraph 1,

   The step of forming the polybenzimidazole solution is dissolving it in an amide-based organic solvent under temperature conditions of 130°C or higher and/or pressure conditions of 0.1 MPa or higher.
10. According to paragraph 1,

    When the amide-based organic solvent is 100% by weight, the maximum dissolution rate of the polybenzimidazole-based compound is 8 to 20% by weight.
11. According to paragraph 1,

    A method for producing a polybenzimidazole-based separator, comprising 10% by weight to 25% by weight of a viscosity adjusting solvent based on 100% by weight of the polybenzimidazole solution.
12. According to clause 11,

    The viscosity adjusting solvent includes one or more of acetone, methyl ethyl ketone, methyl isobutyl ketone, methanol, ethanol, isopropanol, butanol, and isobutanol.
13. A polybenzimidazole-based separator manufactured according to the method for producing a polybenzimidazole-based separator according to any one of claims 1 to 12.
14. A secondary battery comprising a polybenzimidazole-based separator manufactured according to the polybenzimidazole-based separator manufacturing method of any one of claims 1 to 12.
15. According to clause 14,

    A secondary battery comprising a redox battery comprising oxidation and reduction reactions of a vanadium redox couple.

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