Separator for secondary battery and method for manufacturing same

Abstract

The method for manufacturing a separator for a secondary battery according to the present invention includes the steps of dissolving an ion conductive resin and a surfactant in an organic solvent to form a mixture solution, and impregnating at least one surface of a porous membrane with the mixture solution.

Description

[Technical Field]

[0001] The present invention relates to a separator for a secondary battery, a method for manufacturing the same, and a secondary battery including the separator. [Background technology]

[0002] As the global economy grows alongside global warming, the need for renewable and sustainable energy systems based on renewable energy, such as solar and wind energy, is increasing. To improve grid network stability in the face of fluctuations due to the intermittent availability of these forms of energy, advanced energy storage systems (ESS) can be used to store excess power and transmit it to end users or the power grid when needed. Among these, electrochemical energy-based ESSs, such as rechargeable secondary batteries, can provide a cost-effective and clean form of energy storage solution. Electrochemical energy storage systems are broadly classified as secondary batteries, 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. Typically, secondary batteries comprise two electrodes, an electrolyte, and a separator (or ion-exchange membrane). Each of these components can affect the performance of the secondary battery. Summary of the Invention [Problem to be solved by the invention]

[0003] An object of the present invention is to provide a method for manufacturing a separator for a secondary battery, which can improve the mechanical strength of the separator and increase process efficiency without using a substrate film.

[0004] Furthermore, in a process of forming a membrane by immersing a porous membrane in a solution containing an ion conductive resin and then drying the membrane, if the porous membrane is hydrophobic and the electrolyte solution used in the electrode assembly is hydrophilic, there may be portions of the hydrophobic separator membrane where the hydrophilic electrolyte solution does not come into contact, resulting in charge / discharge defects in the secondary battery. An object of the present invention is to provide a method for manufacturing a separator that solves this problem.

[0005] In the present invention, a redox flow battery or a sealed redox battery using a redox couple is described as an example of a secondary battery, but the application of the separator of the present invention is not limited thereto. [Means for solving the problem]

[0006] According to a first aspect of the present invention, there is provided a method for manufacturing a separator for a secondary battery, the method including: dissolving an ion conductive resin and a surfactant in an organic solvent to form a mixed solution; and impregnating at least one surface of a porous membrane with the mixed solution.

[0007] The porous membrane that is not impregnated with the mixed solution may be hydrophobic, and the impregnation step may make the porous membrane hydrophilic.

[0008] The surfactant may be contained in an amount of more than 0.1% by weight and less than 5.0% by weight relative to 100% by weight of the mixed solution.

[0009] The surfactant may include one or more of an ionic surfactant, a non-ionic surfactant, and an organic surfactant.

[0010] The organic surfactant may include a silicon-based organic surfactant.

[0011] The ion-conductive resin may include a polybenzimidazole-based polymer.

[0012] The porous membrane may be made of materials including polypropylene, polyethylene, or a combination thereof.

[0013] The mixed solution may contain a viscosity adjusting solvent in an amount of 10% by weight to 25% by weight relative to 100% by weight of the mixed solution.

[0014] The viscosity adjusting solvent may include one or more of acetone, methyl ethyl ketone, methyl isobutyl ketone, methanol, ethanol, isopropanol, butanol, and isobutanol.

[0015] After the step of impregnating at least one surface of the porous membrane with the mixed solution, a step of drying may be further included.

[0016] The secondary battery may use an aqueous electrolyte as a liquid electrode.

[0017] The aqueous electrolyte may contain vanadium ions and an acidic aqueous solution.

[0018] According to a second aspect of the present invention, there is provided a separator for a secondary battery manufactured by the method for manufacturing a separator for a secondary battery according to the first aspect of the present invention.

[0019] According to a third aspect of the present invention, there is provided a secondary battery including a separator for a secondary battery manufactured by the method for manufacturing a separator for a secondary battery according to the first aspect of the present invention. [Effects of the Invention]

[0020] According to the method for manufacturing a separator for a secondary battery according to the present invention, the effect of efficiently and uniformly hydrophilizing a porous membrane can be maximized, and the separator manufactured thereby can eliminate the problem of poor contact with an electrolyte, thereby contributing to improving the performance of a secondary battery.

[0021] Furthermore, according to the method for manufacturing a separator for a secondary battery according to the present invention, the drying speed can be increased in the subsequent drying step, thereby improving the process efficiency of the separator manufacturing process. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic diagram of an exemplary redox flow battery. [Figure 2a] 1 is a schematic diagram of a sealed redox battery according to an embodiment. [Figure 2b] 1 is a schematic diagram of a sealed redox battery including multiple sealed redox battery cells in a stacked configuration, according to some embodiments. [Figure 2c] 1 is a schematic diagram of a sealed redox battery including multiple sealed redox battery cells in a stacked configuration according to some other embodiments. [Figure 2d] 1 is a schematic diagram of a sealed redox battery including a plurality of sealed redox battery cells in a cylindrically stacked configuration according to an embodiment; DETAILED DESCRIPTION OF THE INVENTION

[0023] The above-mentioned objects, features, and advantages will be described in detail below with reference to the accompanying drawings, so that those skilled in the art can easily implement the technical concept of the present invention. In describing the present invention, if a detailed description of known technologies relating to the present invention is deemed to obscure the gist of the present invention, the detailed description will be omitted. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings are used to indicate the same or similar components.

[0024] When the elements in this specification are described as "comprising," "having," "consisting of," "arranged," "comprising," etc., other parts may be added unless "only" is used. When an element is expressed in the singular, it also includes the plural unless otherwise expressly stated.

[0025] When interpreting the elements in this specification, they are interpreted as including a margin of error unless otherwise explicitly stated.

[0026] In this specification, when an arbitrary structure is arranged "on (or under)" a component or "above (or below)" a component, it means that the arbitrary structure is not only arranged in contact with the upper surface (or lower surface) of the component, but also that other structures may be interposed between the component and the arbitrary structure arranged above (or below) the component.

[0027] As previously mentioned, competitive factors considered in selecting and designing an electrochemical energy storage system suitable for a particular application include, among others, investment cost, power, energy, lifespan, recyclability, efficiency, scalability, and maintenance costs. Among the various electrochemical energy storage systems, redox flow batteries (RFBs) are considered preferable for stationary energy storage. RFBs are electrochemical energy conversion devices that utilize the redox process of redox species dissolved in a solution. The solution is stored in an external tank and introduced into the RFB cell when needed. Some of the advantageous features of RFB technology are the independent scalability of power and energy, high depth of discharge (DOD), and reduced environmental impact. These features allow for a wide range of operating power and discharge times, making RFBs preferable for storing electricity generated from renewable sources.

[0028] Specific 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 these effects, some secondary batteries use spacing between battery cells and / or a separate cooling device. Preferably, batteries according to embodiments disclosed herein generate significantly less heat and pressure, which ultimately reduces the risk of explosion and eliminates the need for spacing between battery cells or a cooling device, allowing for compact integration of the battery cells and the battery itself.

[0029] Various batteries use bus bars to electrically connect battery cells and / or the batteries themselves. For compact integration, the bus bars must be efficiently arranged to reduce the amount of space they occupy. In addition to electrically connecting battery cells and batteries, it is also necessary to physically and mechanically secure 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. Furthermore, embodiments disclosed herein provide batteries and energy storage devices including the same that are easy to maintain after installation.

[0030] FIG. 1 is a schematic diagram of an exemplary redox flow battery (RFB). The RFB 100 includes a battery cell 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 positive electrode electrolyte reservoir 106A containing a first positive electrode electrolyte and a positive electrode electrolyte, and the second half-cell 104B includes a negative electrode electrolyte reservoir 106B containing a second negative electrode electrolyte and a negative electrode electrolyte. The positive electrode is electrically connected to a positive electrode current collector 108A, and the negative electrode is electrically connected to a negative electrode current collector 108B. Positive electrode electrolyte reservoir 106A is physically connected in fluid communication with positive electrode electrolyte tank 116A, and negative electrode electrolyte reservoir 106B is physically connected in fluid communication with negative electrode electrolyte tank 116B. In operation, positive electrode electrolyte is circulated between positive electrode electrolyte tank 116A and positive electrode electrolyte reservoir 106A via outlet and inlet conduits 120A and 124A, as represented by arrows, using positive electrode electrolyte pump 128A. Similarly, negative electrode electrolyte is circulated between negative electrode electrolyte tank 116B and negative electrode electrolyte reservoir 106B via outlet and inlet conduits 120B and 124B.

[0031] In some configurations, multiple battery cells 104-1, 104-2, ..., 104-n are stacked to form an RFB cell 150, where each cell is configured in a manner similar to battery cell 104. The multiple battery cells 104-1, 104-2, ..., 104-n include respective positive electrode electrolyte reservoirs 106A in fluid communication with one another and respective negative electrode electrolyte reservoirs 106B in fluid communication with one another. The multiple positive electrode electrolyte reservoirs 106A are coupled to one another and in fluid communication with a positive electrode electrolyte tank 116A, and the multiple negative electrode electrolyte reservoirs 106B are coupled to one another and in fluid communication with a negative electrode electrolyte tank 116B.

[0032] Compared to other electrochemical storage technologies, such as lithium-ion, lead-acid, and sodium-sulfur batteries, RFBs offer several advantages, enabling independent power and energy scalability by separating power conversion from energy storage. For example, RFBs are flexible and can be scaled in a distributed manner depending on the application, providing power and energy ranging from a few kW / kWh for home storage to systems up to tens of MW / MWh for grid storage. Also, unlike fuel cells, reactions in RFBs are reversible, allowing the same cell to serve as a converter of electricity to chemical energy and vice versa. RFBs operate by changing the valence of metal ions without consuming ionic metals, allowing for long life cycles. Cell temperature can be relatively easily controlled by adjusting electrolyte flow, due in part to the electrolyte's relatively high thermal mass. State of charge (SOC) can be easily monitored via cell voltage, and very deep depths of discharge (DOD) can be achieved.

[0033] Despite the many advantages of RFBs, and despite decades of relatively large capital, research, and development investments in this technology, RFBs have not been widely commercialized compared to other electrochemical storage technologies. In particular, the recent surge in battery demand for ESS applications and the increasing need for safety due to frequent fires and explosions indicate the suitability of RFBs, but widespread commercialization has yet to be achieved. This suggests that while there has long been a need for RFB commercialization, there are significant obstacles. The inventors have identified several of these obstacles, including relatively low reliability, low efficiency, large system footprint, and high system complexity.

[0034] A primary obstacle to widespread commercialization of RFBs relates to the relatively high complexity and associated reliability issues of RFBs, such as the RFB 100 described above with reference to FIG. 1. As previously described, an RFB includes multiple conduits 120A, 120B, 124A, and 124B for transporting electrolyte to and from the battery cells 104, pumps 128A and 128B for circulating the electrolyte, and tanks 116A and 116B for storing the electrolyte. Due to the relatively high complexity, the various connection points associated with the conduits 120A, 120B, 124A, and 124B between the battery cells 104 and the tanks 116A and 116B can create problems, such as leaks. The likelihood and frequency of failures increases proportionally with the number of these conduits, which scales with the size of the ESS. Failures pose stability risks as well as unscheduled repairs. Furthermore, reducing the likelihood of these failures through preventative maintenance to ensure uninterrupted operation adds to operating costs.

[0035] A second obstacle to the widespread commercialization of RFBs relates to their relatively low efficiency. One factor behind this relatively low efficiency is the energy consumed in circulating the electrolyte. For example, the electrolyte for vanadium-based RFBs may contain sulfuric acid and have a relatively high viscosity. Circulating an electrolyte, especially an electrolyte with a relatively high viscosity, through the microporous structure of electrodes based on randomly oriented carbon fiber felt can reduce the external efficiency of RFBs by consuming a relatively large amount of external energy. The low external efficiency of RFB systems is one of the main reasons why they are less commercially competitive than competing secondary battery technologies, such as lithium-ion batteries (LIBs).

[0036] A third obstacle to the widespread commercialization of RFBs relates to their relatively low power and energy densities compared to other electrochemical storage technologies, hindering their application in mobile applications. As explained herein, power and energy density refer to the power output and energy storage, respectively, of a storage device relative to the total volume of the energy storage device. Therefore, the power and energy densities of an RFB refer to the ratio of power output and energy storage to the total volume, including the cell volume, tank volume, and conduit volume for electrolyte transport. To partially compensate for the low power and energy densities, RFBs often have relatively large cell active areas and membranes, increasing cell size and potentially causing high cross-electrolyte gradients within the electrolyte reservoirs 116A, 116B. As a result, the average current density and nominal current of an RFB may be significantly lower than the theoretical maximum based on a uniform maximum current density. Furthermore, the need for a circulation system, including a separate tank and conduits, further reduces overall system-level space efficiency.

[0037] A fourth obstacle to widespread commercialization of RFBs relates to system complexity, which is comparable to that of a chemical plant. The high complexity of RFB system design results in long development cycles, which significantly slows technology development. System complexity also makes the system labor- and capital-intensive, requiring a high level of expertise for on-site installation, maintenance, and removal. System complexity is a deterrent to consumers due to the potential increase in manpower and training required to deploy and maintain the system, as well as the associated increase in overall costs.

[0038] To address these and other limitations while maintaining most of the advantages offered by RFBs, the present disclosure relates to a sealed redox battery that is not separately connected to an electrolyte tank. The present disclosure also relates to a secondary battery that includes bus bars that allow for efficient integration of multiple redox battery cells that can be further sealed. However, the present disclosure is not limited to only the battery configurations described above.

[0039] Sealed Redox Battery In one aspect, various embodiments of the redox battery disclosed herein relate to a redox battery. The redox battery according to the embodiments overcomes or alleviates at least some of the above-mentioned obstacles to commercialization of RFBs while maintaining the advantages of RFBs. In particular, while using a redox couple that participates in a redox reaction, unlike some RFBs, the embodiments of the redox battery disclosed herein include a sealed redox battery cell and do not have a separate electrolyte tank connected to the redox battery cell or an electrolyte circulation device such as a pump for supplying electrolyte from outside the redox battery cell.

[0040] FIG. 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. The first half-cell 204A includes a positive electrode electrolyte reservoir 106A having a first positive electrode electrolyte in contact with a positive electrode disposed therein. The first electrolyte contains a first redox couple dissolved therein, configured for a first redox half reaction to occur. The second half-cell 204B includes a negative electrode electrolyte reservoir 106B having a second negative electrode electrolyte in contact with a negative electrode disposed therein. The second electrolyte contains a second redox couple dissolved therein, configured for a second redox half reaction to occur. The positive and negative electrode electrolyte reservoirs 106A and 106B define reaction spaces for their respective half reactions. The sealed redox battery 200A further includes an ion exchange membrane or separator 112 separating the positive electrode electrolyte reservoir 106A and the negative electrode 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, a first bipolar plate 208A is interposed between the positive electrode current collector 108A and the positive electrode electrolyte reservoir 106A, and a second bipolar plate 208B is interposed between the negative electrode current collector 108B and the negative electrode electrolyte reservoir 106B.

[0041] Unlike conventional RFBs, 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 define a redox battery cell that is partially enclosed or sealed by a frame 212 or casing that surrounds at least four sides of the battery cell. The illustrated sealed redox battery 200A is shown in cross section, so only the top and bottom sides of the casing 212 are shown. However, it should be understood that the casing 212 continuously surrounds the top, bottom, front, and rear of the illustrated battery cell. Additionally, first and second separator plates 208A and 208B contact the left and right edges or lips of the casing 212, respectively, to surround / enclose or seal the battery cell within a sealed space defined by the casing 212 and the first and second separator plates 208A and 208B. Thus, the enclosed / sealed or sealed frame or casing 212, first separator 208A, and second separator 208B define an enclosed or sealed volume divided by separator 112 into two spaces: a negative electrode electrolyte reservoir 106B containing the positive electrode and a positive electrode electrolyte reservoir 106A containing the negative electrode. The volume sealed by casing 212 and first and second separators 208A, 208B is physically inaccessible to its internal contents from the outside during normal operation. That is, the positive and negative electrode electrolytes are not in fluid communication with an external container, such as an electrolyte tank. The casing 212 and first and second separators 208A, 208B can hermetically and / or permanently seal redox battery 200A. These configurations are in contrast to conventional redox flow batteries, in which redox battery cells are in fluid communication with an external tank. That is, in sealed redox battery 200A, unlike RFB 100 described above with reference to Figure 1, neither positive electrode electrolyte reservoir 106A nor negative electrode electrolyte reservoir 106B within the sealed cell is in fluid communication with or physically connected to a separate electrolyte tank storing the first or second electrolyte, respectively. Thus, substantially the entire volume of positive and negative electrode electrolytes is stored within the redox battery cell and is sealed and enclosed by casing 212 and first and second separator plates 208A, 208B.That is, first electrolyte reservoir 106A stores substantially the entire volume of the first electrolyte for first half-cell 204A, and second electrolyte reservoir 106B stores substantially the entire volume of the second electrolyte for second half-cell 204B. In part, because sealed redox battery 200A is not separately connected to a storage tank, unlike RFB 100 shown in FIG. 1, sealed redox battery 200A does not include conduits 120A, 120B, 124A, 124B (FIG. 1) for conveying electrolyte to and from the redox battery cells, or pumps 128A, 128B (FIG. 1) for circulating the electrolyte.

[0042] As previously mentioned, a notable structural difference in sealed redox battery 200A is the omission of pumps 128A and 128B (FIG. 1). Instead, sealed redox battery 200A according to an embodiment is configured so that first and second electrolytes circulate spontaneously within positive electrode electrolyte reservoir 106A of first half-cell 204A and negative electrode electrolyte reservoir 106B of second half-cell 204B, respectively. In various configurations, the spontaneous circulation of the first and second electrolytes is caused by one or more of the following: an osmotic pressure difference between the first and second electrolyte reservoirs; density changes of one or both of the first and second electrolytes; diffusion or migration of one or both of the first and second electrolytes; affinity of one or both of the first and second electrolytes for the first and second electrodes, respectively; the first and second redox half reactions; and thermal expansion or contraction of one or both of the first and second electrolytes.

[0043] The inventors have found that self-circulation is effective in providing stability in power and energy output when the thickness of the positive and negative electrolyte reservoirs 106A, 106B in the cross-sectional view of FIG. 2a does not exceed a range defined as 20 cm, 15 cm, 10 cm, 5 cm, 2 cm, 1 cm, or any value therein.

[0044] Referring now to FIG. 2a, the casing 212 is formed of a corrosion-resistant material suitable for containing the positive and negative electrolytes, which may be highly acidic. In addition to providing corrosion resistance, the casing 212 may be rigid to provide mechanical support to the sealed redox battery 200A. In some embodiments, at least a portion of the casing 212 may be formed of a flexible material configured to deform to accommodate changes in internal pressure within the positive and negative electrolyte reservoirs 106A, 106B. Increases in internal pressure may be caused by various effects, for example, as described below for pressure-controlled sealed redox batteries. In configurations in which only a portion of the casing is formed of a flexible material, other portions may be formed of a rigid material. The flexible portion can be configured to expand in response to an increase in pressure, for example, to accommodate a respective volume increase of greater than 0.1%, 0.2%, 0.5%, 1%, 2%, 5%, 10%, 20%, 50% or more for one or both of the positive and negative electrolyte reservoirs 106A, 106B. Suitable materials for the casing 212 may include polyvinyl chloride (PVC), polyethylene (PE), polystyrene (PS), polypropylene (PP), polycarbonate (PC), ABS, reinforced plastics, and the like.

[0045] The sealed redox battery 200A configured in this manner offers various technical and commercial advantages. For example, various reliability failures associated with conduits between the redox battery cells and the tank, e.g., pipe joints and electrolyte circulation pumps, are substantially reduced or eliminated, reducing unscheduled repairs as well as safety risks and operational costs associated with the operation of the sealed redox battery 200A. Furthermore, as previously described for the RFB 100 (FIG. 1), the need to circulate electrolyte between the redox battery cells and the tank using a pump is eliminated, substantially improving external efficiency. The inventors have found that, depending on the system size, the sealed redox battery 200A can achieve up to 2-50 times the power or energy density compared to conventional RFBs because it does not require electrolyte circulation between the cells and the electrolyte tank. As previously described, power or energy density refers to the power or energy output, respectively, of a storage device relative to the total volume of the energy storage device. Therefore, the power or energy density of a sealed redox battery refers to the ratio of power or energy output, respectively, to the total volume of the sealed redox battery. In addition, space efficiency is greatly improved by omitting a separate circulation system including a tank, pump, and conduits. Furthermore, system complexity is greatly reduced, significantly lowering the barrier to commercial implementation of the sealed redox battery 200A. For example, unlike conventional RFBs, the sealed redox battery 200A can be manufactured into a pack similar to a lithium-ion battery for modular implementation, eliminating the need for the intrusive structure required for the installation of conventional RFBs and making it more suitable for automation and mass production.

[0046] Hereinafter, the operating principles and aspects of the sealed redox battery 200A will be described using an example of a sealed vanadium (V) redox battery based on a vanadium-based redox pair, but the embodiments are not limited thereto, and it will be understood that the principles described herein can be applied to redox batteries based on various other redox pairs.

[0047] In the sealed V redox battery according to the embodiment, the first redox couple dissolved in the first positive electrode electrolyte of the first half-cell 204A is V 4+ / V 5+ The second redox couple dissolved in the second negative electrode electrolyte of the second half-cell 204B may be V 2+ / V 3+ The redox reactions during charging and discharging can be described using the following equations, where → indicates the direction of the discharge reaction and ← indicates the direction of the charge reaction:

[0048] Second half cell / negative electrode: V 2+ ←→V 3+ +e - First half cell / positive electrode: V 5+ +e - ←→V 4+ Overall response: V 2+ +V 5+ ←→V 3+ +V 4+

[0049] During charging, the first half-cell 204A converts tetravalent vanadium ions, V 4+ is the pentavalent vanadium ion V 5+ In the second half-cell 204B, the trivalent ions V 3+ is a divalent ion V 2+ During discharge, in the first half-cell 204A, pentavalent vanadium ions, V 5+ is tetravalent vanadium ion V 4+ In the second half-cell 204B, the divalent ions V 2+ is a trivalent ion V 3+ During these redox reactions, electrons are transferred through an external circuit and specific ions diffuse across the ion exchange or separation membrane 112, balancing the electroneutrality of the positive and negative half-cells, respectively.

[0050] Other redox reactions can be implemented in the sealed redox battery 200A according to various embodiments. In various embodiments, the first or second redox couple includes one or more ions of vanadium (V), zinc (Zn), bromine (Br), chromium (Cr), manganese (Mn), titanium (Ti), iron (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 battery described above. In these embodiments, mixing of the positive and negative electrode electrolytes preferably does not result in cross-contamination of the electrolytes.

[0051] As described herein, the electrolyte of a redox battery is a solution that conducts electric current through ionization. The electrolyte supports the reduced and oxidized forms of the redox couple and the corresponding cations and anions to balance the ionic charge in the solution during the oxidation and reduction of the redox couple. According to an embodiment, the positive and negative electrode electrolytes 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. A higher energy density can be advantageous in reducing the volume of the positive and negative electrode electrolyte reservoirs 106A, 106B required for a given positive energy and power output. However, if the V ion concentration is too high, the stability of the V ions may be reduced. 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 1.0 M, 1.5 M, 2.0 M, 2.5 M, or any value within the range defined above. On the one hand, V ion concentrations below 1.0 M may result in energy levels that are not suitable for some applications. On the other hand, V ion concentrations above 2.5 M may result in V ion levels above 50° C., for example. 5+ This can reduce the stability of ions, e.g., V in the electrolyte at operating temperatures below -20°C. 2+ and V 3+ The solubility limit of the ion can be reached.

[0052] Preferably, depending on the embodiment, the positive and negative electrode electrolytes may contain the same solvent and / or the same metal ions. In these embodiments, mixing of the positive and negative electrode electrolytes through an ion exchange membrane or separator 112 does not cause contamination of the respective half-cells. The positive and negative electrode electrolytes may also be prepared from the same starting solvent and solute. For example, in the case of a sealed V redox battery according to some embodiments, both the positive and negative electrode electrolytes contain sulfuric acid. The electrolyte is prepared, for example, by dissolving 0.1M to 2.5M VOSO4 (vanadyl sulfate) in a 0.1M to 6M aqueous solution of MH2SO4, and the tetravalent vanadium ions (V 4+ ) and / or trivalent vanadium ions (V 3+ ) can be formed. The tetravalent and trivalent vanadium ions can be electrochemically oxidized to form pentavalent vanadium ions (V 5+ Conversely, the tetravalent / trivalent vanadium ions can be electrochemically reduced to divalent vanadium ions (V 2+ A negative electrode electrolyte (cathode solution) can be formed containing a solution of

[0053] Referring now to FIG. 2a, in various embodiments, the positive and negative electrodes disposed in the positive and negative electrolyte reservoirs 106A and 106B, respectively, comprise carbon-based materials such as carbon or graphite felt, carbon cloth, carbon black, graphite powder, and graphene. Carbon-based materials preferably provide a relatively high operating range, excellent stability, and high reversibility. The electrodes are optimized for relatively high electrochemical activity, low bulk resistance, and large specific area. Improving the electrochemical activity of the electrodes increases the energy efficiency of the sealed redox battery 200A. To improve the performance of the sealed redox battery 200A, the electrode surfaces can be modified, for example, by metal coating, increasing surface roughness, or doping with additives.

[0054] The positive and negative electrode electrolyte reservoirs 106A, 106B, which define the reaction spaces, are filled partially or completely with the respective electrodes between the first and second separator plates 208A, 208B, respectively, or between the ion exchange membrane or separator 112 and the positive and negative electrode current collectors 108A, 108B, respectively, if an ion exchange membrane or separator 112 is present. After filling the respective electrodes, the remaining space in the positive and negative electrode electrolyte reservoirs 106A, 106B is filled partially or completely with the respective electrolyte between the first and second separator plates 208A, 208B, respectively, if an ion exchange membrane or separator 112 is present, or between the ion exchange membrane or separator 112 and the positive and negative electrode current collectors 108A, 108B. In various embodiments, unless intentionally perforated or made porous, the ion exchange or separation membrane 112 substantially separates the two half-cells, substantially preventing mixing of the two electrolytes and redox couples and allowing H + ion exchange membrane 112. The ion exchange membrane or separation membrane 112 may be an anion exchange membrane or a cation exchange membrane.

[0055] Although various embodiments shown include an ion exchange or separation membrane 112 that may be selective for a particular type of ion, e.g., cations or anions, embodiments are not limited thereto. For example, in various embodiments, the ion exchange or separation membrane 112 may be a non-selective membrane, e.g., a porous membrane.

[0056] Referring now to FIG. 2A, in some embodiments, output power can be scaled by connecting multiple single redox battery cells, for example, in series, to form a cell stack. In these configurations, first and second separators 208A, 208B can facilitate the series connection of the single cells, and the current collectors 108A, 108B between adjacent separators can be eliminated. The first and second separators 208A, 208B can be formed of a suitable material, such as graphite, carbon, carbon plastic, etc., to provide high electrical conductivity and low internal resistance to the cell stack. The first and second separators 208A, 208B also support contact pressure when pressed against the electrodes, increasing electrical conductivity. The first and second separators 208A, 208B are also designed to have high acid resistance to prevent corrosion or oxidation of the current collectors 108A, 108B.

[0057] The positive and negative electrode current collectors 108A and 108B contain a metal with high electrical conductivity, such as copper or aluminum, and serve to pass current during charge and discharge processes.

[0058] The single sealed redox battery 200A described above has an output voltage characteristic of the electrochemical reaction, and additional cells, for example, up to about 1.65 V, can be connected electrically in series or electrically in parallel as described herein to obtain higher voltages and currents, respectively.

[0059] 2b is a schematic diagram of a sealed redox battery including multiple sealed redox battery cells in a stacked configuration, according to some embodiments. The illustrated sealed redox battery 200B includes multiple stackable redox battery cells 200B-1, 200B-2,..., 200B-n, where each cell is configured in a manner similar to sealed redox battery 200A (FIG. 2a). Each of the multiple redox battery cells 200B-1, 200B-2,..., 200B-n includes a positive electrode electrolyte reservoir 106A, a negative electrode electrolyte reservoir 106B, and an ion exchange or separation membrane 112. In the illustrated embodiment, each of the multiple redox battery cells 200B-1, 200B-2,..., 200B-n is separately sealed in a casing 212. A plurality of redox battery cells 200B-1, 200B-2, . . . , 200B-n can be electrically connected in series to increase the output voltage.

[0060] 2c is a schematic diagram of a sealed redox battery including multiple stacked sealed redox battery cells according to some other embodiments. The illustrated sealed redox battery 200C includes multiple stackable redox battery cells 200C-1, 200C-2,..., 200C-n, where each of the multiple redox battery cells 200C-1, 200C-2,..., 200C-n is configured in a manner similar to sealed redox battery 200A (FIG. 2a), including a positive electrode electrolyte reservoir 106A, a negative electrode electrolyte reservoir 106B, and an ion exchange or separation membrane 112. However, unlike sealed redox battery 200B (FIG. 2b), in the illustrated embodiment, the multiple redox battery cells 200C-1, 200C-2,..., 200C-n are sealed within a common casing 222. In a manner similar to the sealed redox battery 200B (FIG. 2b), multiple redox battery cells 200C-1, 200C-2, ..., 200C-n can be electrically connected in series to increase the output voltage. In some embodiments, the positive electrode electrolyte reservoirs 106A of the multiple redox battery cells 200C-1, 200C-2, ..., 200C-n can be fluidly connected to each other, and the negative electrode electrolyte reservoirs 106B of the multiple redox battery cells 200C-1, 200C-2, ..., 200C-n can be fluidly connected to each other. The sealed redox battery 200C can be configured as a pouch-type redox battery or a rigid case-type redox battery.

[0061] 2d is a schematic diagram of a sealed redox battery including multiple sealed redox battery cells in a cylindrically stacked configuration according to an embodiment. The illustrated sealed redox battery 200D includes multiple cylindrically stackable redox battery cells 200D-1, 200D-2,..., 200D-n, where each of the multiple redox battery cells 200D-1, 200D-2,..., 200D-n is configured in a manner similar to sealed redox battery 200A (FIG. 2A), including a positive electrode electrolyte reservoir 106A, a negative electrode electrolyte reservoir 106B, and an ion exchange or separation membrane 112. The multiple redox battery cells 200D-1, 200D-2,..., 200D-n may be individually sealed within a casing in a manner similar to that described above for sealed redox battery 200B (FIG. 2b). Alternatively, the multiple redox battery cells 200D-1, 200D-2, ..., 200D-n may be enclosed by a common casing 222 in a manner similar to that described above for the sealed redox battery 200C (FIG. 2c). The multiple redox battery cells 200D-1, 200D-2, ..., 200D-n may be electrically connected in series to increase the output voltage in a manner similar to that for the sealed redox battery 200B (FIG. 2b). Additionally, in some embodiments, the positive electrode electrolyte reservoirs 106A of the multiple redox battery cells 200D-1, 200D-2, ..., 200D-n may be fluidly connected to one another, and the negative electrode electrolyte reservoirs 106B of the multiple redox battery cells 200D-1, 200D-2, ..., 200D-n may be fluidly connected to one another.

[0062] It will be appreciated that some or all of the multiple redox battery cells in each of the stack configurations described above with respect to Figures 2b-2c can be electrically connected in series by appropriately electrically connecting the opposite polarity current collectors of some or all of the cells, or can be electrically connected in parallel by appropriately electrically connecting the same polarity current collectors of some or all of the cells.

[0063] Differences between sealed redox batteries and conventional secondary batteries The differences and advantages of the sealed redox batteries according to the embodiments over conventional RFBs include the elimination of the electrolyte tank, pumping system, and conduit network that contributed to the slow commercialization of conventional RFBs, as previously described. While the separate electrolyte tank is not required, the sealed redox batteries 200A-200D (FIGS. 2a-2d) maintain some of the inherent design flexibility found in conventional RFBs. For example, due to the inherent flexibility of liquids, cell geometry design is substantially more flexible than conventional secondary batteries. Furthermore, power and energy storage capacity can be independently decoupled and scaled within a limited range, for example, by adjusting the ratio of electrolyte volume to electrode surface area. This ratio can be adjusted, for example, by adjusting the thickness of the positive and negative electrode electrolyte reservoirs 106A, 106B, as previously described. On the other hand, the sealed redox batteries according to the embodiments also share the key advantages of conventional batteries, such as being fully sealed and modularized. It will be understood that although the sealed redox battery according to the embodiment and a conventional secondary battery, e.g., a LIB, may have components designated using similar terms, the components and operating principles of the sealed redox battery according to the embodiment can be distinguished from the conventional secondary battery described herein.

[0064] Although the following comparison is made between a sealed redox battery according to an embodiment and a LIB, it will be understood that the comparison can also be applied to other conventional secondary batteries.

[0065] First, the structure, functional role, and operating principle of the electrolyte in the sealed redox battery according to the embodiment may be distinguished from those of conventional secondary batteries, such as LIBs. During operation, the electrolyte in a LIB does not store energy itself and does not participate in electrochemical reactions during charge and discharge. Instead, the electrolyte in a LIB primarily serves to provide a path for lithium ions to be transferred between the positive and negative electrodes during charge and discharge. Thus, electrolyte movement is not substantially restricted by a separator. In contrast, electrochemical energy in the sealed redox battery 200A according to the embodiment is stored in the electrolyte in the form of dissolved active materials, e.g., redox couples dissolved in the positive and negative electrode electrolytes that undergo electrochemical reactions during charge and discharge. Thus, the electrolyte can be considered an energy storage medium in the sealed redox battery according to the embodiment. As described above, in the example of a V redox battery, the oxidation states of V ion species dissolved in the positive and negative electrode electrolytes change depending on their respective half-reactions. Therefore, the chemical compositions of the cathode and anode electrolytes in a sealed redox battery are different from those of a LIB. Also, unlike a LIB, in a sealed redox battery according to embodiments, the electromotive force resulting from the difference in the chemical compositions of the cathode and anode electrolytes leads to energy storage, and therefore, mixing of the cathode and anode electrolytes results in a loss of stored energy.

[0066] Second, the structure, functional role, and operating principle of the electrodes in a sealed redox battery according to embodiments may be distinguished from those of conventional secondary batteries, such as LIBs. In LIBs, the active materials contained in the electrodes directly participate in electrochemical reactions. During operation, lithium ions in a LIB transfer between the active materials of the positive electrode and the active materials of the negative electrode, achieving electrochemical equilibrium, with the electrodes themselves acting as the primary mediators for energy storage. In contrast, the electrodes in a sealed redox battery according to embodiments play very different roles. The positive electrode of a sealed redox battery does not participate in the first redox half reaction, and the negative electrode of a sealed redox battery does not participate in the second redox half reaction. As described herein, an electrode that does not participate in the redox half reaction does not eliminate the electrode's function of providing physical sites for the electrochemical reaction in a manner similar to a catalyst. However, the electrode itself does not participate in the electrochemical reaction, and redox ions do not transfer between the positive and negative electrodes during charging and discharging of the redox battery. Depending on the composition, functional groups may be present on the surface that act as catalysts, but this is distinct from electrodes that actively participate in electrochemical reactions, as in LIBs. Instead, electrodes essentially passively transfer electrons generated by the electrochemical reactions.

[0067] Third, the structure, functional role, and operating principle of the ion exchange membrane in a sealed redox battery according to an embodiment may be distinguished from the separator in a conventional secondary battery, such as a LIB. In a LIB, the active material of the electrode where the electrochemical reaction occurs is generally in a solid state, and the separator disposed between the positive and negative electrodes primarily serves to prevent an electrical short between them. Therefore, while the separator serves to prevent electrical contact between the positive and negative electrodes, the separator in a LIB is not specifically designed to restrict the transfer of lithium ions or the electrochemical reaction therebetween. That is, the separator in a LIB primarily serves to allow ion movement as part of the electrochemical reaction for charge and discharge, and to electrically insulate the positive and negative electrodes from each other. Therefore, the separator for a LIB is designed to allow the free transfer of lithium ions between the electrodes. In contrast, in a sealed redox battery according to an embodiment, the redox active species are dissolved in the electrolyte, and an ion exchange membrane or separator 112 (FIG. 2a) serves to electrically separate the positive and negative electrode electrolytes and prevent them from mixing with each other.

[0068] Typically, the ion exchange membrane or separator 112 includes a selectively permeable membrane through which cations or anions are transferred to maintain charge balance between the two half-cells. For example, the ion exchange membrane may be configured to selectively allow cations or anions to pass through. Therefore, since the electrolyte that stores energy in the sealed redox battery according to the embodiment is a liquid, without the ion exchange membrane or separator 112, an electrical short circuit would occur due to mixing of the positive and negative electrode electrolytes, regardless of whether the positive and negative electrodes are in contact with each other.

[0069] Thus, in the sealed redox battery according to the embodiment, the first and second redox half reactions occur without substantial ionic transport of the first or second redox couple across the ion exchange or separation membrane 112 separating the positive electrode electrolyte reservoir 106A and the negative electrode electrolyte reservoir 106B.

[0070] As explained herein, an ion exchange membrane or separator 112 that does not substantially transfer ions of a redox couple refers to an ion exchange membrane or separator 112 that substantially prevents electrolyte crossover between the positive and negative electrode electrolyte reservoirs 106A, 106B (FIG. 2a). Thus, the base material of the ion exchange membrane or separator 112 preferably blocks the migration of redox species in the electrolyte, e.g., V ions in a V redox battery, while allowing other ions, e.g., H ions in a V redox battery, to pass through for charge balance between half-cells. + It may be a membrane that selectively permits the movement of ions, but an ion exchange or separation membrane 112 that does not substantially transmit ions of the redox pair can still allow unintended crossover or limited intended mixing to alleviate internal pressure buildup.

[0071] Separator for secondary battery and method for manufacturing same As previously mentioned, ion exchange membranes or separators perform, among other functions, the function of conducting ions of a supporting electrolyte between the positive and negative electrode electrolyte reservoirs while substantially inhibiting the passage of redox-active ions, e.g., vanadium ions. To further improve the performance of redox battery cells, further improvements in membranes or separators and the development of efficient manufacturing methods are needed to achieve, among other improvements, one or more of: lowering ionic resistance to enable operation at higher current densities; improving barrier properties; balancing the transport of pure electrolyte to minimize capacity imbalance; and improving the chemical stability of the membrane or separator material.

[0072] The separator, one of the key materials in secondary batteries that use aqueous electrolytes, acts as an ion exchange membrane, mediating reactions to separate the anode and cathode and preventing shunting. Separator membranes must have high ion conductivity and ion selectivity. They also need to have excellent mechanical properties to withstand the pressure of circulating electrolytes, high chemical stability against strong acid environments, the oxidizing power of the electrolyte's redox couple, and radicals generated in aqueous electrolytes, as well as high efficiency in terms of process costs.

[0073] These separators are made of ion-conductive polymers or can be manufactured by coating a substrate with an ion-conductive polymer.

[0074] According to various embodiments of the present invention, an ion exchange membrane or separator (e.g., the ion exchange membrane or separator of FIG. 2a) 112 comprises an ion-conducting resin and has a structure and composition arranged to provide, among other advantages, superior chemical resistance, thermal resistance, and mechanical strength compared to various commercially available membranes. In particular, various embodiments of the ion exchange membrane or separator disclosed herein may prove particularly effective when integrated as part of a sealed redox battery (e.g., the ion exchange membrane or separator of FIG. 2a) 112. This is because, among other things, sealed redox batteries may be subjected to more severe conditions, including higher internal pressures, that existing membranes cannot effectively and stably withstand. However, embodiments of the separator are not limited to use in sealed redox batteries, and it will be understood that the ion exchange membrane or separator disclosed herein may be integrated for use in any suitable secondary battery, including, preferably, a redox flow battery, such as the redox flow battery 100 described above with reference to FIG. 1, as well as a lithium-ion battery.

[0075] The present invention employs a method in which a porous membrane is immersed in a solution containing an ion conductive resin and then dried to form a membrane. This method has the advantage of eliminating the substrate film removal step and shortening the drying process time compared to the method in which a substrate film is used. Furthermore, it has the advantage of being able to produce an excellent separation membrane by suppressing the formation of an air layer between the substrate film and the separation membrane.

[0076] Meanwhile, when a separator containing an ion conductive resin is applied to an aqueous secondary battery using a hydrophilic electrolyte, if the porous membrane is hydrophobic and the electrolyte used in the electrode assembly is hydrophilic, there may be portions where the hydrophilic electrolyte does not come into contact with the hydrophobic separator, which may result in defects in charging and discharging the electrodes of the secondary battery.

[0077] To solve the above problems, a method for manufacturing a separator for a secondary battery according to the present invention includes dissolving an ion conductive resin and a surfactant in an organic solvent to form a mixed solution, and impregnating at least one surface of a porous membrane with the mixed solution. This method can most efficiently and uniformly hydrophilize the porous membrane, compared to methods that do not use a surfactant, that apply a surfactant to the porous membrane in advance, or that treat the separator after manufacturing the separator, thereby solving problems related to electrode charge and discharge in secondary batteries and increasing the drying speed in a subsequent drying step, thereby improving process efficiency.

[0078] According to one embodiment of the present invention, the organic solvent may be at least one of N,N-dimethylacetamide (DMAc), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and N-methyl-2-pyrrolidone (NMP). Preferably, the organic solvent is an amide-based organic solvent. For example, the amide-based organic solvent may be at least one of N,N-dimethylacetamide (DMAc) and dimethylformamide (DMF), and preferably N,N-dimethylacetamide.

[0079] According to an embodiment of the present invention, the ion-conducting polymer may be a fluorine-based polymer or a hydrocarbon-based polymer.

[0080] For example, the ion-conductive polymer containing sulfonic acid groups as a fluorine-based polymer may include any one or more of perfluorosulfonic acid, poly(styrene sulfonic acid, PSSA), sulfonated poly(ether ether ketones, SPEEK), sulfonated polyether sulfone (SPES), sulfonated poly(aryl ether ketone, SPAEK), sulfonated polybenzimidazole (SPBI), sulfonated poly(phenylene oxide, SPPO), and sulfonated polyimide (SPI), but is not limited thereto.

[0081] For example, the hydrocarbon polymer may include a polyimide polymer, a polyetheretherketone polymer, a polyethersulfone polymer, a polybenzimidazole (PBI) polymer, or the like.

[0082] The polybenzimidazole polymer of the present invention is a polymer of polybenzimidazole, and refers to a mixture or copolymer of polybenzimidazole precursors (repeating units or monomers for forming polybenzimidazole polymers). The polybenzimidazole precursor may be, but is not necessarily limited to, 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]), etc.

[0083] In the present invention, a separator containing a polybenzimidazole-based polymer can be used because it exhibits excellent mechanical strength, heat resistance, chemical resistance, and durability even in the increasingly harsh operating environment of secondary batteries.

[0084] According to an embodiment of the present invention, the porous membrane may be made of one or more polyolefin-based materials, for example, polypropylene (PP), polyethylene (PE), or a combination thereof.

[0085] According to one embodiment of the present invention, the viscosity of the solution can be reduced by further adding a viscosity adjusting solvent to the mixed solution. In a membrane formation process using a solution, as in the present invention, if the viscosity of the solution is high, the fluidity during membrane formation becomes low, making it difficult to form a thin membrane and making it difficult to control the precision. Therefore, by further adding a viscosity adjusting solvent in addition to the oil solvent for dissolving the ion conductive resin, the performance and precision of the membrane formation can be improved.

[0086] Therefore, the viscosity adjusting solvent may be contained in an amount of, for example, 10% by weight to 25% by weight, for example, 12% by weight to 20% by weight, or for example, 15% by weight to 18% by weight relative to 100% by weight of the mixed solution, but is not necessarily limited to these.

[0087] According to an embodiment of the present invention, the viscosity adjusting solvent may be one or more of a ketone solvent or an alcohol solvent. More specifically, the ketone solvent may be acetone, methyl ethyl ketone, methyl isobutyl ketone, etc., and the alcohol solvent may be methanol, ethanol, isopropanol, butanol, isobutanol, etc.

[0088] According to an embodiment of the present invention, the surfactant can effectively hydrophilize the porous membrane, and therefore, depending on the type of ion-conductive resin, porous membrane, and electrolyte solution used, a silicone-based surfactant, an ionic surfactant, a nonionic surfactant, an organic surfactant, or a combination thereof can be used. Specific examples of the surfactant according to the present invention include, but are not limited to, nonionic surfactants such as Triton X-100 (registered trademark) and Tween (registered trademark), anionic surfactants such as SDS (sodium dodecyl sulfate) and SDBS (dodecylbenzenesulphonate), cationic surfactants such as DTAB (dodecyltrimethylammonium bromide), TTAB (tetradecyltrimethylammonium bromide), CTAB (cetyltrimethylammonium bromide), and DPC (dodecylpyridinium chloride), organic surfactants such as PVP (poly(vinylpolypyrrolidone)), and silicone-based organic surfactants such as Silwet (registered trademark).

[0089] The content of the surfactant may be, for example, more than 0.1 wt % and less than 5.0 wt %, for example, 0.2 wt % to 4.0 wt % or less, 0.5 wt % to 2.0 wt % or less, or 0.5 wt % to 1.0 wt % or less, based on 100 wt % of the solution containing the ion conductive resin, but is not necessarily limited thereto and may be appropriately adjusted depending on the types of ion conductive resin and surfactant used.

[0090] According to a specific embodiment of the present invention, when polybenzimidazole is used as the ion conductive resin and a polyethylene film is selected as the porous film, a silicon-based nonionic organic surfactant can be selected. The method for manufacturing a separator for a secondary battery according to an embodiment of the present invention can be performed without substantially increasing manufacturing costs, reducing efficiency, and / or reducing the performance of the resulting separator, which are known problems that occur when the surface of a porous membrane is hydrophilized using other processes.

[0091] In addition, the electrode assembly using the separator for a secondary battery of the present invention has improved contact with the electrolyte, resulting in improved charge / discharge performance of the electrode and improved performance of the secondary battery. [Example]

[0092] The following examples of the present invention will be described. However, the following examples are merely illustrative of the present invention and are not intended to limit the scope of the present invention.

[0093] <Production example> Example 1 Dimethylacetamide (DMAC) was mixed with m-PBI (poly[2,2-(m-phenylene)-5,5bibenzimidazole]) as an ion-conductive resin and [ TM Hydrostable 212 Silicone Surfactant (manufactured by Momentive) was added and dissolved at 160°C under normal pressure for 24 hours with stirring to prepare a PBI solution of Example 1 with a PBI concentration of 12 wt% and a surfactant concentration of 0.5 wt%. A polyethylene (PE) film (thickness: 20 μm) was then impregnated with the PBI solution of Example 1 and dried with hot air at 50°C for 2 minutes to obtain a 27 μm thick separator.

[0094] Comparative Example 1 A separation membrane was produced in the same manner as in Example 1, except that a PBI solution was produced without adding a surfactant, and a separation membrane was obtained.

[0095] Comparative Example 2 DMAc solvent with surfactant " TM Hydrostable 212 Silicone Surfactant (manufactured by Momentive) was mixed to prepare a surfactant solution (silwet concentration: 5 wt%), which was then applied to the separation membrane prepared in Comparative Example 1 and dried at a temperature of 50°C to obtain a separation membrane with a thickness of 27 μm.

[0096] Comparative Example 3 A polyethylene (PE) film (thickness: 20 μm) was prepared and was not treated in any way. This was used as a separation membrane in Comparative Example 3.

[0097] Comparative Example 4 Polyethylene (PE) film (thickness: 20 μm) was coated with DMAc solvent and surfactant. TM A surfactant solution (silwet concentration: 5 wt%) prepared by mixing "Hydrostable 212 Silicone Surfactant (manufactured by Momentive)" was applied to the membrane, which was then dried with hot air at a temperature of 50°C for 2 minutes to obtain a separation membrane with a thickness of 20 μm.

[0098] <Battery performance evaluation> Two current collectors were fabricated by stacking a carbon current collector (graphite composite, thickness: 0.2 mm) and a metal current collector (aluminum foil, thickness: 0.2 mm). These current collectors were used as a positive electrode current collector and a negative electrode current collector, respectively. Unit cells including a positive electrode electrolyte reservoir and a negative electrode electrolyte reservoir formed using the separators fabricated in Example 1 and Comparative Examples 1 to 4 were fabricated.

[0099] The positive electrode electrolyte storage portion and the negative electrode electrolyte storage portion were each filled with 1.7M V 3.5+ An electrolyte (manufactured by Standard Energy) was supplied, and the battery was charged at a constant current of 1C until the voltage reached 1.55V, and discharged at a constant current of 1C until the voltage reached 1.10V. The energy efficiency (EE) (%) was measured according to Equation 1 below, and is shown in Table 1 below.

[0100] [Formula 1] Energy efficiency = (discharge energy (Wh) / charge energy (Wh)) x 100 (%)

[0101] [Table 1]

[0102] As can be seen from Table 1 above, Example 1 is characterized by mixing a surfactant into a PBI solution and then impregnating a PE film to produce a separation membrane, and it was confirmed that this resulted in significantly improved energy efficiency compared to Comparative Example 1, in which a surfactant was not mixed. Comparative Example 2 differs from Example 1 in that a separation membrane was produced in the same manner as Comparative Example 1, and then a surfactant solution was applied to the surfaces of the PBI and PE. However, it was confirmed that the number of membrane production processes had to be increased to two, which reduced process efficiency and also reduced energy efficiency (EE) compared to Example 1.

[0103] On the other hand, in Comparative Example 3, only a PE film was used as a separator, and therefore charging was not possible, making it impossible to evaluate the energy efficiency of the battery. In Comparative Example 4, treatment was performed using only a surfactant without PBI, but the energy efficiency was significantly reduced compared to Example 1.

[0104] <Experiment on surfactant content> Separation membranes were manufactured in the same manner as in Example 1 above, but with different surfactant contents (concentrations) as shown in Table 2 below. Energy efficiency (EE) (%) was measured as described above and is shown in Table 2 below.

[0105] [Table 2]

[0106] "No. 1" in Table 2 above is the same as Comparative Example 1, and "No. 4" is the same as Example 1, and it can be seen that both have the highest energy efficiency. The energy efficiency value changes as the surfactant concentration changes, and when the surfactant concentration is 0.1 wt% or less or 5.0 wt%, the energy efficiency decreases significantly. Furthermore, as can be seen from Table 2 above, the energy efficiency is well-represented at concentrations above 0.1 wt% and below 5.0 wt%, with the energy efficiency being even better at 0.2 wt% to 4.0 wt%, even better still at 0.5 wt% to 2.0 wt%, and the energy efficiency being the best at 0.5 wt% to 1.0 wt%.

[0107] Although specific embodiments have been described above, these embodiments are presented merely as examples and are not intended to limit the scope of the disclosure. Indeed, the novel devices, methods, and systems described herein may be embodied in a variety of different forms. Furthermore, various omissions, substitutions, and modifications may be made to 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 arrive at further embodiments. The various features and processes described above may be embodied independently of one another or combined in various ways. All possible combinations and subcombinations of features of the disclosure are intended to fall within the scope of the disclosure.

Claims

1. dissolving an ion conductive resin and a surfactant in an organic solvent to form a mixed solution; impregnating at least one surface of a porous membrane with the mixed solution; Including, A method for manufacturing a separator for a secondary battery.

2. The porous membrane not impregnated with the mixed solution exhibits hydrophobicity, The impregnation step hydrophilizes the porous membrane. The method for producing the separator for a secondary battery according to claim 1.

3. 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 mixed solution. The method for producing the separator for a secondary battery according to claim 1.

4. The surfactant includes one or more of an ionic surfactant, a nonionic surfactant, and an organic surfactant. The method for producing the separator for a secondary battery according to claim 1.

5. The organic surfactant includes a silicon-based organic surfactant. The method for producing the separator for a secondary battery according to claim 4.

6. The ion conductive resin includes a polybenzimidazole-based polymer. The method for producing the separator for a secondary battery according to claim 1.

7. The porous membrane is made of a material including polypropylene, polyethylene, or a combination thereof. The method for producing the separator for a secondary battery according to claim 1.

8. The viscosity adjusting solvent is contained in an amount of 10% by weight to 25% by weight based on 100% by weight of the mixed solution. The method for producing the separator for a secondary battery according to claim 1.

9. The viscosity adjusting solvent includes one or more of acetone, methyl ethyl ketone, methyl isobutyl ketone, methanol, ethanol, isopropanol, butanol, and isobutanol; The method for producing the separator for a secondary battery according to claim 8.

10. Further comprising a drying step after the impregnation step. The method for producing the separator for a secondary battery according to claim 1.

11. The secondary battery uses an aqueous electrolyte as a liquid electrode. The method for producing the separator for a secondary battery according to claim 1.

12. The aqueous electrolyte contains vanadium ions and an acidic aqueous solution. The method for producing the separator for a secondary battery according to claim 11.

13. Produced by the method for producing a separator for a secondary battery according to any one of claims 1 to 12, Separation membrane for secondary batteries.

14. Produced by the method for producing a separator for a secondary battery according to any one of claims 1 to 12, A secondary battery including a separator for a secondary battery.

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