Thermoplastic flow battery bipolar plate assembly

Abstract

An electrochemical flow battery bipolar plate assembly (BPPA) comprising a conductive center plate comprising a thermoplastic polymer material and a conductive filler dispersed throughout the thermoplastic polymer material. The thermoplastic polymer material has a coefficient of thermal expansion of about 60 ppm / °C to about 110 ppm / °C. The BPPA has a first frame element and a second frame element. Both the first frame element and the second frame element are made of a thermoplastic material without a conductive filler. The thermoplastic material has a coefficient of thermal expansion within ± 20 ppm / °C of the thermoplastic polymer material.

Description

ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page l of 27THERMOPLASTIC FLOW BATTERY BIPOLAR PLATE ASSEMBLYTECHNICAL FIELD

[0001] The present invention relates to conductive center plates for bipolar plates for electrochemical applications and their methods for making and materials and methods for fabricating bipolar plate assemblies incorporating the conductive center plates.BACKGROUND

[0002] Electrochemical cells, including flow battery cells, using separator membranes, can be configured in cell stacks having bipolar separator plates between adjacent cells. These bipolar separator plates are typically made from either a variety of metals, such as titanium and stainless steel, or non-metallic conductors, such as graphitic carbon / polymer composites. Bipolar separator plates have been made by molding or machining fluid flow fields into a solid sheet of the material.

[0003] In contrast with sealed batteries, such as lead acid and lithium ion, flow batteries hold charge in liquid electrolytes which are stored in external tanks. This feature allows power and energy to be sized independently - power scaling with the number of cells, and energy scaling with the volume of electrolyte. The decoupling of energy and power provides durability (capacity retention) and affordability advantages, making flow batteries attractive for long duration, stationary energy storage.

[0004] During operation, the positive and negative electrolytes - posolyte and negolyte, respectively - are circulated through stacks of electrochemical cells. While charging, power is converted from its source to direct current (DC) which flows into the stacks, simultaneously oxidizing the posolyte and reducing the negolyte, to increase the battery state-of-charge. Ions cross the membrane which separates the electrolytes to maintain the overall charge balance. While discharging, the electrolytes flow in the same direction, but the electrical and ionic currents are reversed, and power is converted from DC to match the source. Since the electrolytes flow in only one direction, flow batteries can rapidly switch from charging to discharging.

[0005] Coordination chemistry flow battery (CCFB) unit cells are comprised of two half-cells, one configured for posolyte and one configured for negolyte. At the center of each cell is a polymer membrane which conducts ions but not electrons, and separates the posolyte and negolyte fluids in the half-cells. On either side of this membrane is a carbon electrode which facilitates the redoxACTIVE 509969662.6 1ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page 2 of 27 reactions. The membrane and its associated pair of electrodes is sandwiched between bipolar plate assemblies (BPPA) which distribute the electrolytes and provide an electrical connection between the positive and negative electrodes of adjacent cells.SUMMARY

[0006] The need for providing improved method of forming a bipolar plate conductive center plate and associated materials will be apparent from the remainder of this disclosure. The method comprises providing a conductive thermoplastic polymer comprising a plastic and a conductive filler dispersed throughout the plastic matrix. The conductive thermoplastic polymer may have a melt flow index of 1.1 g / 10 min to 24.8 g / 10 min at 230 °C and 15 kg pressure, and may have a coefficient of thermal expansion of about 60 to about 110 ppm / °C. The thermoplastic polymer is melted and injection molded to form a CCFB bipolar plate conductive center (inner) plate.

[0007] In an aspect, a bipolar plate conductive inner plate comprises either a binary thermoplastic material or a thermoplastic polymer blend, which is a combination of two or more binary conductive thermoplastic materials.

[0008] A component of a bipolar plate may comprise a polymer blend, at least one polypropylene material, and a conductive filler dispersed throughout the polymer blend. The polymer blend may have a melt flow index of 1.1 g / 10 min to 24.8 g / 10 min or more specifically, 4.5 g / 10 min to 17.8 g / 10 min at 230 °C and 15 kg pressure, and a coefficient of thermal expansion of about 60 to about 110, more specifically, about 72 to about 90, ppm / °C.

[0009] Conductive thermoplastic materials are provided which are injection moldable and provide a conductive center panel having designed flow channel architectures for a bipolar plate having superior properties and durability. In still other aspects, material compatibility with flow battery posolyte and negolyte electrolyte solutions is provided.

[0010] In other aspects, a non-conductive thermoplastic material compatible with a conductive thermoplastic polymer material in terms of close CTE matching is provided for fabricating bipolar plate frame elements that in some aspects may be welded to the conductive center plate to form a unitary bipolar plate assembly whose parts (two frames and a conductive inner plate) can be fabricated separately by injection molding.

[0011] It is desirable to make bipolar plates by injection molding, which will require new materials and methods of making. There is a long felt and continuing need for improved methodsACTIVE 509969662.6 2ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page 3 of 27 for fabricating bipolar plates, especially in the field of coordination chemistry flow batteries (CCFB), flow batteries, and bi-polar plates. This is described in detail below.

[0012] In other aspects, a bi-polar plate or flow battery may be created with materials that are both conductive, yet capable of being injection molded or extruded while also maintaining compatibility with flow battery electrolytes.

[0013] These and other objects and advantages shall be made apparent from the accompanying drawings and the description thereof.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments, and together with the general description given above, and the detailed description of the embodiments given below, serve to explain the principles of the present disclosure.

[0015] FIG. 1 depicts an exploded view of bipolar plate components which can be joined together to provide a unitary bipolar plate assembly.

[0016] FIG. 2A depicts a surface of an 8” x 11” x 2.54 mm test plaque made during injection mold test with PP Blend A in accordance with the methods of this disclosure.

[0017] FIG. 2B depicts a surface of an 8” x 11” x 2.54 mm test plaque made during injection mold test with PP Blend B in accordance with the methods of this disclosure.

[0018] FIG. 2C depicts a surface of an 8” x 11” x 2.54 mm test plaque made during injection mold test with a comparative blend (PVE1, polyvinyl ester 1) in accordance with the methods of this disclosure, the comparative blend having a higher flow rate during injection molding than PP Blend B, and shows plate defects on the top edge of the test plaque.DETAILED DESCRIPTION

[0019] FIG. 1 provides an exploded view of the main components of a representative bipolar plate assembly 100. As shown, the flow plate assembly will typically include a center (inner flow) plate 108, which will generally include designed flow channels on either or both of the positive electrolyte and negative electrolyte faces of the center plate. First frame element 104 and second frame element 106 are assembled on either side of the inner plate, overlapping respective edges thereof, as shown, overlapping the entire perimeter of the center panel. Gaskets (not shown) mayACTIVE 509969662.6 3ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page 4 of 27 be used to seal the junctions of the frame elements and the inner plate. First and second electrodes 110, 112 abut opposite sides of the bipolar plate assembly. Openings such as 114 and 116 are provided to accommodate conduits that provide liquid positive and negative electrolytes to unit cells within a cell stack. Conduits 114a, 114b, 116a, and 116b comprise inlet (source) and outlet (drain) conduits for first and second electrolytes. First frame element 104 and second frame element 106 may have substantially similar (e.g., less than 1% difference) coefficients of thermal expansion to center plate 108. In some embodiments, first frame element 104 and second frame element 106 may have coefficients of thermal expansion that are compatible with center plate 108 by being in a range of ± 20 ppm / °C, ± 15 ppm / °C, ± 10 ppm / °C, or ± 5 ppm / °C of center plate 108. In some embodiments first frame element 104 may have a different or similar coefficient of thermal expansion as second frame element 108.

[0020] Overall, Figs. 2A, 2B, and 2C show that the PP blends show superior performance to PVE1 in terms of avoiding edge (flange) area degradation at the top edge of the test plaques. Otherwise, PVE1 (a thermoset material) shows good characteristics for a conductive polymer material. See additional comparative data relevant to these examples on Tables 1 and 2, below. Fig. 2A depicts an example embodiment of a PP Blend A test plaque 205. PP Blend A test plaque 205 may exhibit properties similar to that of PP Blend A as referenced and discussed blow. Fig. 2B depicts an example embodiment of a PP Blend A test plaque 210. PP Blend B test plaque 210 may exhibit properties similar to that of PP Blend B as referenced and discussed blow. Fig. 2C depicts an example embodiment of a PVE1 test plaque 215. PVE1 test plaque 215 may exhibit properties similar to that of PVE1 as referenced and discussed blow. PVE1 test plaque 215 may comprise a degraded edge 220.

[0021] The primary objective of this disclosure is to provide an injection moldable material and methods of fabrication of bipolar plates for CCFBs which exhibit a lack of porosity during fabrication and properties that will provide plates of long service life that withstand degraded conditions in which leakage or crossflow of electrolyte through the bipolar plate may occur. The fabricated bipolar plate will also have a fluid flow region with designed channel architectures which result from the mold tooling of the injection flow process.

[0022] Conventionally, the bipolar plate assembly (BPPA) is a unitary assembly of non- conductive frames having four holes which support the electrolyte distribution conduits in theACTIVE 509969662.6 4ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page 5 of 27 assembled stack. The frames have electrolyte distribution ports which present posolyte and negolyte to opposite sides of the bipolar plate (BPP), an electrically conductive composite center panel with flow features which spread electrolyte uniformly across the active area of the cell.

[0023] Various techniques for fabricating BPPA components are known. These include compression molding, milling, and deposition of materials having varied porosity or permeability to liquid in designed patterns. The BPP is typically fabricated by compression molding a composite material, generally a thermoset polymer filled with one or more morphologies of carbon to provide electrical conductivity on the order of 30-40 S / m. Such a structure can be produced with good dimensional stability, but is subject to the following drawbacks which are addressed by the present disclosure:(i) Compression molding of high-carbon fill composites requires high applied pressure. This limits the size of a BPP (BPP refers to bipolar plate, and BPPA refers to bipolar plate assembly) which can be produced by conventional equipment, and thereby limits the effective cell active (electrically conductive) area. Larger cell active areas are desirable, because they allow for higher power stacks at a given cell voltage and current density.(ii) The thermoset / carbon bulk molding compound exhibits poor flowability, making large parts difficult to mold with a consistent, uniform surface and volume, and without defects such as porosity and knit lines.(iii) High carbon fill thermoset materials are brittle, making the BPP susceptible to damage from handling.(iv) Thermoset polymers are not thermally weldable, so joining the BPP to the frames - which must be mechanically robust and liquid tight - is accomplished with adhesives or elastomer seals.(v) Since the frames are typically manufactured from non-conductive thermoplastic materials, there is a mismatch in coefficient of thermal expansion (CTE) between the BPP conductive center plate and the frames. This CTE difference causes internal mechanical stress when the assembly is thermally cycled during transportation, storage, and operation. This can lead to BPP failure (particularly inACTIVE 509969662.6 5ATTORNEY DOCKET PATENT APPLICATION019843.0736 (MC-04344)Page 6 of 27 the presence of latent defects from the molding process), or failure of the BPP / frame joint.

[0024] The present disclosure overcomes the technical challenges enumerated above in that it replaces the thermoset polymer in the BPP composite with a thermoplastic material such as polyethylene, polypropylene, polyvinyl chloride (PVC), or acrylonitrile butadiene styrene (ABS).

[0025] Carbon-filled thermoplastic BPP materials offer the following improvements over the state of the art:(i) Due to higher flowability than thermoset bulk molding compound, they can be fabricated by injection molding or extrusion at large size and with high yield.(ii) Higher toughness and resistance to cracking, improving robustness to rough handling.(iii) Closer CTE match to frame materials, reducing thermally-induced internal stresses.(iv) The frames (non-conductive) and central panel (center section) (conductive) should be the same thermoplastic material (the frames without conductive filler, the central panel with conductive filler) to allow for the frames and central panel to be welded together into a unitary structure rather than relying on adhesives or some other form of bonding. The frame elements will overlap the edges of the central panel to protect the flanges (edges) from direct contact or direct exposure to environmental conditions within an electrochemical half-cell to protect the flange areas from degradation. The overlap can occur over the entire perimeter of the center panel. Fabricating the three main components separately and welding them to form a unitary structure also avoids the need to fabricate the entire structure from one molded entity.

[0026] In an embodiment, the BPP and at least a portion of the frame are co-molded with a carbon-filled (conductive) polymer forming the BPP center section and a non-filled (non- conductive) polymer forming the perimeter frame. The process of co-molding the BPP with the frame may greatly increase manufacturing efficiency by reducing manufacturing steps. A comolded BPP and frame may also provide superior mechanical and sealing properties as compared to a traditional BPP and frame assembly comprising the BPP and separate frame unit(s). A comolded BPP and frame may have a higher conductivity for the BPP than the frame itself due toACTIVE 509969662.6 6ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page 7 of 27 the presence of carbon-filler in the BPP. For example, a co-molded BPP may have a bulk conductivity greater than 10 S / m while the co-molded frame has a conductivity less than 10 S / m.

[0027] The thermoplastic polymer materials of the disclosure are known at least as much by their properties as by their composition. Essential properties of materials are described in detail in the disclosure and some of the main essential properties may be summarized as: flowability, surface conductivity, melt flow index after addition of conductive additive, and CTE, LCTE (linear coefficient of thermal expansion) range.

[0028] Thermoplastic materials may also comprise a blend of the similar materials. For example, a binary blend may comprise two thermoplastic materials such as polypropylene with graphitic carbon additive; the first material will have a composition by weight of polypropylene : carbon of X:Y and the second material will have a composition by weight of polypropylene : carbon of Y:X. If for a particular material X:Y have values of 4: 1 (so that the binary blend of A : B is 4: 1 and 1 :4, proportional range), the upper and lower limits may vary ± 20% such that a range is 4.8 : 1.2; 3.2 : 0.8; 4.8 : 0.8; or 3.2 : 1.2, 0.8 : 3.2, 1.2 : 4.8, and so on, and each range includes every integer or fractional value within the entire range including the ± variation included. These characteristics of proportions and ranges are to be applied throughout this disclosure and the claims. Other types of blends may be used as well.

[0029] Some compositions may be simple binary compositions of X (polymer) and Y (conductive filler) and not blended with a second binary composition. In either case, the composition of the material is typically expressed in terms of the percentage of X : the percentage of Y, which may typically be expressed as weight percentages of each. Proportions of X and Y are expressed in this disclosure as weight percentage of the entire weight of the material unless otherwise noted.

[0030] In addition to the desired properties of the material as part of a fabricated bipolar plate as enumerated herein, the material must also be capable of manufacture resulting in a product that has essential mechanical properties. Too low carbon concentration will result in a material that is too highly resistive, while too high carbon concentration will result in a highly conductive material but one which is not processable because the melt temperature is either too high, or the thermoplastic binding material is too scarce to hold the conductive matrix together under any applied stress. Ranges of polymer : carbon that are suitable for bipolar plate materials while alsoACTIVE 509969662.6 7ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page 8 of 27 providing manufacturable material are given elsewhere in this disclosure, and may vary depending on the thermoplastic material, the conductive material, and mixtures of conductive materials with ratios of high aspect ratio materials to low aspect ratio materials.

[0031] It is also essential that the materials be compatible with the electrolytes (posolyte, negolyte) to which they are exposed within electrochemical cells, as well as overall environmental conditions: heat, fluid pressure, chemical reactions on the surface areas of the central panel, mechanical stresses, and so on. An example of a posolyte as used herein may include that as disclosed in U.S. Pat. No. 11,249,141, which is incorporated by reference herein. An example of a negolyte as used herein may include that as disclosed in U.S. Pat. No. 9,382,274, which is incorporated by reference.

[0032] A materials compatibility test procedure exposes a variety of candidate materials to both posolyte and negolyte in conditions that simulate actual chemical and environmental conditions in a working electrochemical cell. Test specimens are immersed in two electrolyte solutions:(i) Negolyte at 35-65% state of charge (SOC), and(ii) Posolyte at -95% SOC.

[0033] The specimens were kept at an elevated temperature of 50° C under a blanket of inert gas in a sealed vessel. In this test, the materials are immersed unstressed and therefore do not undergo any flexural strain. The posolyte and negolyte are maintained at elevated SOC.

[0034] Samples are soaked for at least sixty days, and some for up to eighteen months. Sixty days of soaking is based on the minimum testing period by UL standard. Longer soaking, up to eighteen months, was done for some sample specimens to ascertain lifetime compatibility.

[0035] Physical integrity tests performed after immersion include weight / dimension changes, appearance changes (photograph, microscopy at lOOx and up to lOOOx magnification), and tensile testing according to related ASTM standards. Sets of at least four specimens per material were used. Additionally, a set of four control specimens are kept in controlled humidity chamber (23° C, 50% RH (relative humidity)), and subjected to identical test protocol. The specimens were collected, cleaned using water, patted dry and placed in the humidity chamber under conditions given for a couple of days to dry prior to any measurements.ACTIVE 509969662.6 8ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page 9 of 27

[0036] Materials were identified for possible CCFB system uses, such as: seal, bipolar / monopolar plate frame, bipolar / monopolar plate conductive center plate, electrolyte storage tank liner, bipolar plate-frame bonding, tank, tubing, negolyzer, membrane, soft goods assembly (SGA) frame, electrode, centrifugal pump, SGA adhesive, heat exchanger, tank sealant, positive BPP frame, negative BPP frame, membrane. Results indicated that for unitary monopolar plate assemblies (MPPA) and BPP As, new materials with a multiplicity of desired properties are needed.

[0037] Thermoplastics are good bipolar plate materials and can be used for the frame element of a plate assembly. ABS shows very good properties for frame elements.

[0038] A bipolar plate is formed of components (frame elements, conductive center panel) by providing a thermoplastic polymer, with conductive filler for the center panel, melting the polymer, and injection molding the polymer. In some embodiments, the polymer comprises at least one polypropylene material and a conductive filler dispersed throughout the polymer, which may be a binary material or a polymer blend. In some embodiments, the polypropylene material may have a melt flow index of 4.5 g / 10 min to 17.8 g / 10 min at 230 °C and 15 kg pressure, and may have a coefficient of thermal expansion of about 72 to about 90 ppm / °C. The melt flow index is measured after the conductive filler is added to the polymer blend. The polymer blend is melted, and injection molded to form a coordination chemistry flow battery bipolar plate.

[0039] A variety of materials may be useful in the fabrication of bipolar plates. In some embodiments, the polymer blend comprises at least one polypropylene (“PP”) material and a conductive filler dispersed throughout the polymer blend. Examples of the polypropylene material include PP Blend A, PP Blend B, and PP Blend C, respectively. Other particular examples are presented elsewhere in this disclosure. In some embodiments, the polymer blend may have a melt flow index of 4.5 g / 10 min to 17.8 g / 10 min at 230 °C and 15 kg pressure, and may have a coefficient of thermal expansion of about 72 to about 90 ppm / °C. The melt flow index is measured after the conductive filler is added to the polymer blend. In some embodiments, the polymer blend may have an area specific resistance (ASR) of less than about 1 Q / cm2at 35 psi, such as about 1 Q / cm2to about 0.01 Q / cm2, about 0.5 Q / cm2to about 0.01 Q / cm2, about 0.15 to about 0.01 Q / cm2, about 0.11 to about 0.01 Q / cm2, and about 0.11 to about 0.02 Q / cm2at 35 psi. In fabricating a CCFB bipolar plate, material composition choice is important, while properties such as theACTIVE 509969662.6 9ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page 10 of 27 rheology of the material in the melt phase during fabrication is of very high importance. As shown in more detail below, a blend with melt flow index of 4.5 g / 10 min generally has superior physical and mechanical properties to one having a melt flow index at the top end of the range (17.8 g / 10 min), although properties such as the coefficient of thermal expansion and electrical conduction are the same (Table 1). Rheology of the materials is vital because if the process of filling a mold for a plate is too slow or too fast, necessary physical and mechanical properties of the plate may be compromised. These properties include: tensile strength, uniformity of material composition, and uniformity of thickness across the entire plate element. Lack of uniformity in any of these properties can result in hindered performance or failure altogether, requiring shutdowns for unscheduled maintenance and costly replacement of parts. As shown in Example 1 an experimental blend designated as PVE1 in the disclosure, which was a blend of two graphite / vinyl ester materials provided the right conductivity, formed flow channel architectures, and provided flow properties that were adequate but not deemed sufficient for large scale commercial operations. The PVE1 test plaque also showed degradation at the top edge (top flange area) of the test plaque (FIG. 2C). Further, CCFBs use two different electrolyte compositions, typically metal-ligand coordination compounds, which have different chemistries. The material used in the bipolar plate must be chemically inert with respect to both the negative electrolyte and the positive electrolyte.

[0040] Materials are chosen on the basis of mechanical properties and flow characteristics as well as resistance to fatigue, temperature, chemical exposure and other environmental factors that can lead to degradation in an environment such as the interior of CCFB unit cells and exposure to the two different liquid electrolytes present in CCFBs. Acetonitrile butadiene styrene (ABS) terpolymer is a widely used material having very favorable thermal expansion properties (72-108 ppm / °C) but can degrade into harmful materials at elevated temperatures. Polypropylene has similar thermal expansion properties as well as mechanical strength, resistance to fatigue, resistance to chemical exposure, and in particular formulations has very favorable flow properties for injection molding that can produce a material having highly uniform composition and thickness. The thermal expansion properties of polypropylene provides materials that are sufficiently resistant to thermal stress to be useful in CCFB applications. Polypropylene is also more stable under reducing conditions and has superior thermal expansion properties in comparison with vinyl ester graphite copolymer blends that we have tested.ACTIVE 509969662.6 10ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page 11 of 27

[0041] Examples of conductive filler include carbon or stainless steel, such as carbon black, carbon powder, graphite, carbon fibers, carbon nanotubes, or nickel-plated graphite. The conductive filler and the concentration of the filler will be based on the desired conductivity and the effect of the filler on CTE of the plate material, including mechanical and flexural strength provided by high aspect ratio materials such as carbon fibers and carbon nanotubes that can form networks or lattices within the supporting polymer matrix.

[0042] The development of superior materials for bipolar plates in the field of coordination chemistry flow batteries is challenging. The material is influenced not only by the starting material selected, such as polypropylene and any additional polymer added for a blend, but also by the addition of conductive filler. In some embodiments, the filler comprises most of the weight of the blend with the polymer (plastic) comprising a lower percentage of the weight of the final blend. The blend must have flow characteristics as a melt during the injection molding process, as described in more detail below, to produce a final product having uniformities of composition, thickness, and other desired properties, such as in-plane conductivity. Not all of the flow characteristics are reliably predictable, in any very precise sense, by theoretical properties of a blend - even those taken from empirical results observed from blends having similar weight ratios of polymer : conductive filler and the same or similar polymer blend compositions and conductive filler compositions. In addition to flow and fill characteristics of the melt during injection molding, the final product must have mechanical properties and performance characteristics making the final product suitable on a commercial scale, meeting or exceeding a variety of manufacturability, performance, and mechanical benchmarks. A non-exhaustive list of required mechanical properties and performance characteristics include: mechanical strength and durability, maintain flow structures (grooves, channels, ridges) over long term operation, prevent permeation and leakage, electrical conductivity, thermal conductivity, resistance to chemical corrosion and degradation from other operating environmental factors, resist expansion / contraction due to changes in temperature in operating environment. A Shore D hardness value greater than about 40 may promote maintenance of desired mechanical and some performance properties over long term operation. This disclosure focuses on injection molding processes as those are believed to promote the required superior uniformities as described elsewhere herein, although other methods of fabricating bipolar plates for CCFBs may also be suitable.ACTIVE 509969662.6 11ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page 12 of 27

[0043] The bipolar plate conductive center panel comprises a conductive thermoplastic polymer material. In some embodiments, the center plate may have an area specific resistance (ASR) of about 0.02 to about 0.11 Q / cm2at 35 psi. In some embodiments, the thermoplastic polymer material may have a standard reduction potential of less than -2 V. Examples of conductive filler include carbon or stainless steel, such as carbon black, carbon powder, graphite, carbon nanotubes, or nickel-plated graphite. In some embodiments, the bipolar plate assembly (two frame elements and a conductive center plate) is substantially planar. The bipolar plate center panel may comprise flow channels for electrolytes to flow through, and the frame elements may contain manifolds and plenum structures to deliver electrolyte from a conduit to the center panel and then out to a drain which returns the respective electrolyte to its own storage tank. The series of flow channels may be comprised of a single pattern of channels or more than one pattern of channels, and may be designed either to force electrolyte fluid above the horizontal plane, or to keep the fluid within the horizontal plane. Flow channel patterns may be different for the positive face of the center plate and the negative face of the center plate. In addition, a flow battery stack will also comprise a monopolar plate at each end the stack, one being a positive electrolyte monopolar plate, the other being a negative electrolyte monopolar plate. Everything in this disclosure relating to bipolar plates also applies to monopolar plates in a stack.

[0044] The bipolar plates can be evaluated for electrical conductivity, mechanical properties including tensile strength and rigidity, homogeneity of chemical composition, uniformity of thickness throughout the injection molded structure, compatibility with the liquid electrolytes to which the material will be exposed during CCFB operation, absence of defects such as gaps in the interior of the structure due to non-uniform injection flow of the melt, and other properties, such as whether there are impurities that may leach into electrolyte solutions. Mechanical properties are tested, for example, with a soak test followed by three-point bending. Electrolyte compatibility is tested, for example, with a soak test with leach testing and dimensional stability. The polymer materials may be evaluated with, for example, elemental testing by glow discharge mass spectrometry (GDMS) and inductively coupled plasma mass spectrometry (ICP-MS). Porosity is evaluated, for example, with pressure-driven (PD) infusion to measure pore size distribution and overall porosity based on the volume of material (such as mercury) intruded into the test material. The test plaques are also tested for durability and thermal resistance.ACTIVE 509969662.6 12ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page 13 of 27

[0045] In some embodiments, the bipolar plate has decreased porosity. In this context, porosity describes a mechanical failure of the plate material, in some instances due to nonuniformities in material composition and / or nonuniformities in thickness. As used in this disclosure, “porosity” and its variants are intended to mean the quality of a material having discontinuities of injection molding plate materials on the surface or in the bulk interior of the material, which can result in apertures through the entire thickness of the molded material allowing for leakage of liquid electrolyte or crossflow of liquid electrolyte from a half-cell to an adjacent half-cell of opposite polarity, or localized weaknesses of the material. Sufficient homogeneity and density of a material formed during injection molding can overcome porosity. In these applications, porosity can lead to permeability of the material to liquids. In some instances, it is especially challenging to eliminate porosity during the melt flow injection process at one or more edges of a bipolar plate.

[0046] Defects are primarily the result of non-uniformities in the plate, such as material composition and thickness, which can result from imperfections in the melt flow injection process or chemical degradation of material after periods of operation from such processes as oxidation or other forms of wear caused by fluid pressure and ionic and electronic interactions on or near the surface of the plate. Optimally uniform coverage of the plate material during the melt flow injection process will substantially reduce defects ab initio and result in extended service life of the plate. As noted above, in some instances otherwise uniform deposition by melt injection can result in nonuniformities such as porosity on one edge or more than one edge of a plate during fabrication. In some embodiments, a porosity pressure test using a 8” x 11” x 2.54 mm test plaque by P-D infusion with mercury, results in less than about 5 mL of permeation, such as less than about 4 mL, less than about 3 mL, less than about 2 mL, and less than about 1 mL. In addition, in the P-D infusion test, any penetration of the infusion test metal into the volume of the test plaque should be minimal, less than 15% of the thickness, or less than 10% of the thickness. Deeper penetration could be disqualifying.

[0047] In some embodiments, the bipolar plate center plate may have a tensile strength of about 20 MPa to about 57 MPa. The tensile strength must be sufficient to provide long-term structural integrity and long service life for the plate such that the plate and any associated mechanical support components such as a frame can maintain structural integrity against fluid pressure and environmental conditions during long periods of operation and provide a long serviceACTIVE 509969662.6 13ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page 14 of 27 life for the plate. In addition to tensile strength the plate surface must have sufficient rigidity to provide long term structural integrity. It is not necessary for a bipolar plate center plate to be flexible. The tensile strength may be at the upper range of 57 MPa or somewhat higher if needed to confer sufficient rigidity of the plate.

[0048] In a range of formulations good to excellent mechanical results were observed with materials, including PP thermoplastics, having MFI of between 3.5 and 12.0, and MFI between 4.0 and 10.0 and in addition, good to excellent electronic performance metrics were observed.

[0049] In the present disclosure the singular forms "a", "an" and "the" include the plural reference, and reference to a particular numerical value includes at least that particular value, unless the context clearly indicates otherwise. Thus, for example, a reference to "a material" is a reference to at least one of such materials and equivalents thereof known to those skilled in the art, and so forth.

[0050] The modifier "about" should be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the expression "from about 2 to about 4" also discloses the range "from 2 to 4." When used to modify a single number, the term "about" may refer to plus or minus 10% of the indicated number and includes the indicated number. For example, "about 10%" may indicate a range of 9% to 11%, and "about 1 " means from 0.9 to 1.1.

[0051] When a list is presented, unless stated otherwise, it is to be understood that each individual element of that list and every combination of that list is to be interpreted as a separate embodiment. For example, a list of embodiments presented as "A, B, or C" is to be interpreted as including the embodiments, "A," "B," "C," "A or B," "A or C," "B or C," or "A, B, or C."

[0052] Where present, all ranges are inclusive and combinable. That is, references to values stated in ranges include every value within that range. For example, a range defined as from 400 to 450 ppm includes 400 ppm and 450 ppm as independent embodiments. Ranges of 400 to 450 ppm and 450 to 500 ppm may be combined to be a range of 400 to 500 ppm. Percentage ranges include both low and high endpoints and any value between them, including whole integer values and all fractional values. Thus, a range of 1.00% to 3.00% includes 1.05% or 2.99%.

[0053] It is to be appreciated that certain features of the disclosure which are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. That is, unless obviously incompatible or excluded, each individualACTIVE 509969662.6 14ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page 15 of 27 embodiment is deemed to be combinable with any other embodiment s) and such a combination is considered to be another embodiment. Conversely, various features of the invention that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any sub-combination. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as "solely," "only" and the like in connection with the recitation of claim elements, or use of a "negative" limitation. Finally, while an embodiment may be described as part of a series of steps or part of a more general structure, each said step may also be considered an independent embodiment in itself.

[0054] While the present disclosure has illustrated by description several embodiments and while the illustrative embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications may readily appear to those skilled in the art. Furthermore, features from separate lists can be combined; and features from the examples can be generalized to the whole disclosure.EXAMPLE EMBODIMENTS

[0055] Table 1:

[0056] In Table 1, PVE1 is a blend of (i) a vinyl ester-graphite blend, and (ii) a graphite-vinyl ester blend in a 3: 1 ratio. Both PP Blend A, PP Blend B, and PP Blend C are polypropylene blendsACTIVE 509969662.6 15ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page 16 of 27 with more than 50% carbon fdler. The CTE of a composite will vary from the values in the table when a conductive filler is added. RHE stands for reversible hydrogen electrode.

[0057] Additional properties of these materials and also those of PP Blend C are give in Table 2, below.

[0058] Table 2:

[0059] Properties of additional selected materials are given in Table 3, below. Carbon black used below is CAS 1333-86-4, typically having low aspect ratio. Graphite is CAS 7782-42-5 which can be produced with high aspect ratio. In Table 3 below, HDPE stands for high density polyethylene and LCP stands for liquid-crystal polymer; CB stands for carbon black

[0060] Table 3:

[0061] Belt sanding test plaques at 400 grit surface treatment improved ASR of the polypropylene blends. The ABS test plaque did not show improvement with surface treatment, the average ASR for the samples tested was 0.928 Qcm2at 35 psi (the average for PP Blends E, G, H samples tested was 0.257 Qcm2at 35 psi.) Results of surface preparation vs no surface preparation of PP Blend A samples are shown below in Table 4.ACTIVE 509969662.6 16ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page 17 of 27

[0062] Table 4:

[0063] Table 5: General processing conditions for injection molding.

[0064] Table 6: Selected mold sampling, results.

[0065] Table 7: Comparative CTE properties.ACTIVE 509969662.6 17ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page 18 of 27

[0066] Table 8: CTE comparison, PVE1, PP Blend A.

[0067] Table 9: Mean CTE comparisons, ABS and filled PP.

[0068] The following features and aspects are provided in this disclosure:

[0069] A method of forming a bipolar plate conductive center plate comprising providing a material comprising a thermoplastic polymer and a conductive filler dispersed throughout the thermoplastic polymer blend wherein the material may have a melt flow index of 1.1 g / 10 min to24.8 g / 10 min at 230 °C and 15 kg pressure, and a coefficient of thermal expansion of about 60 to about 110 ppm / °C, melting the material, injection molding the material to form a coordination chemistry flow battery bipolar plate conductive inner plate.

[0070] General conditions for injection molding are: injection pressure: 10000-15000 psi; melt temperature: 375-450° F; mold temperature: 50-175° F; followed by a suitable interval and temperature for drying.ACTIVE 509969662.6 18ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page 19 of 27

[0071] In aspects, the MFI under the conditions given may range from 3.7 g / 10 min to 11.50 g / 10 min, 12.0 g / 10 min to 22.0 g / 10 min. In other aspects, the MFI varies from 15.0 g / 10 min to 20 g / 10 min, and in aspects may range from 3.7 to 5.5 or 4.0 to 8.5.

[0072] The CTE in other aspects range from about 65 to about 100 or about 70 to about 95 or about 70 to about 90, ppm / °C.

[0073] The same thermoplastic polymer can be used without conductive filler for injection molding bipolar plate non-conductive frames. The non-conductive frames can then be thermal or laser welded to the conductive inner plate to form a unitary CCFB bipolar plate structure. Alternatively, a thermoplastic material different from that used in the inner plate may be used for the frame elements which may be weldable if their respectively CTE values are very close. Generally, the same thermoplastic is preferred for all three elements to be weldable and durable in unitary form.

[0074] The conductive center plate material may have an areas specific resistance (ASR, Q- cm2at 35 psi) of 0.01 to 0.200. The conductive filler comprises carbon or stainless steel. In aspects, the conductive filler comprises carbon black, carbon powder, graphite, carbon nanotubes, carbon fibers, or nickel-plated graphite. The conductive filler may contain particles of high aspect ratio, low aspect ratio, or combinations of the two.

[0075] For the method of molding the thermoplastic polymer material, the material is injected into a mold at a temperature from about 150 °C to about 270 °C. In aspects the injection melt temperature is in a range of from about 190° C to about 235° C.

[0076] The thermoplastic material has a standard reduction potential of less than -2 V.

[0077] A thermoplastic material comprising a plastic and conductive filler for fabricating central plate elements is used for methods, materials, and products of this disclosure. The conductive filler may be a single material or more than one material. The particles comprising conductive material may be of high aspect ratio, low aspect ratio, or combinations of these.

[0078] A thermoplastic material comprising a plastic comprising polypropylene (PP), HDCE, LCP, ABS. A conductive filler, materials enumerated above, is dispersed in the plastic component for conductive center plate thermoplastics. The material may be a binary material (a plastic component and conductive filler comprising at least one conductive material and may compriseACTIVE 509969662.6 19ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page 20 of 27 more than one different conductive material). The material may also be a blend of two or more binary materials.

[0079] The conductive filler will comprise 45% to 90% by weight of the binary thermoplastic or thermoplastic blend material. In aspects, the conductive filler concentration will range from 45% to 75%, 48% to 65%, from 50% to 60%, or from 50% to 55%. The ranges include all integer and fractional values within each range.

[0080] In other aspects, a binary conductive material or a blend conductive material will have 35% to 90% plastic and 10% to 65% conductive filler by weight of the material, in other aspects 20% to 55% plastic and 45% to 80% conductive filler. In aspects, a conductive material with a plastic and two conductive fillers will be a blended material, with each binary component of the blend providing one conductive filler.

[0081] Where there are at least two conductive fillers, there will be at least one filler with constituent molecular structures of high aspect ratio and at least one filler with constituent structures of low aspect ratios.

[0082] In aspects:(i) filler with high aspect ratio will be present in higher proportion than filler with low aspect ratio;(ii) filler with high aspect ratio and filler with low aspect ratio will be present in substantially equal proportion; or(iii) filler with high aspect ratio will be present in lower proportion than filler with low aspect ratio.

[0083] In aspects, high aspect ratio material may be present at 70% to 30% by weight of the total weight of the conductive filler while low aspect ratio material may be present at 30% to 70% by weight of the total weight of conductive filler.

[0084] Many useful materials for center plate fabrication will have a representative generic formula such as: a plastic : filler material that is up to 50% by weight plastic and 50% or more by weight filler where the filler may be a single material or more typically a combination of at least two conductive materials. This formula would include the following representative materials:(i) Polypropylene (thermoplastic) / 45% ± 2.5% graphite + carbon black filler(ii) Polypropylene (thermoplastic) / 50% ± 2.5% graphite + carbon black fillerACTIVE 509969662.6 20ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page 21 of 27(iii) Polypropylene (thermoplastic) / 55% ± 2.5% graphite + carbon black filler(iv) Polypropylene (thermoplastic) / 60% ± 2.5% graphite + carbon black filler

[0085] In the immediately foregoing list, 45% ± 2.5% is intended to mean 45% or an effective range of 42.5% to 47.5% with similar calculations for the other PP materials and respective percentages of fill material listed.

[0086] In the immediately foregoing examples of particular PP / conductive filler materials, the proportion of graphite (high aspect ratio) to carbon black (low aspect ratio) will be greater. It is generally, although not always, more favorable to have high aspect materials in larger proportion by weight than low aspect materials to provide for (a) sufficient mechanical support in the plastic matrix and (b) sufficiently high electrical conductivity.

[0087] Some particular thermoplastic materials include, by way of example:(i) Polypropylene (thermoplastic)Zcarbon black, graphite (50-55%);(ii) ABS (therm oplastic) / carbon fiber; Polypropylene (thermoplastic) / carbon black, graphite (> 70%), 9% to 29% plastic;(iii) ABS (thermoplastic) / carbon fiber (40%).

[0088] The thermoplastic material has properties and characteristics enumerated above.

[0089] A thermoplastic bipolar plate assembly for a coordination chemistry flow battery (CCFB) comprises two non-conductive framing elements and a conductive center plate element comprising a center plate comprising a thermoplastic material comprising a plastic / conductive filler composite. The plate is fabricated as a unitary structure. In aspects, the frame elements are welded to the center plate element such that the plate elements overlap and protect the flange (edge) elements of the enter plate. In aspects, the welding is accomplished through a thermal or laser welding process. The non-conductive frames may overlap the entire perimeter of the conductive inner plate, on both sides thereof.

[0090] Having now described some aspects of the disclosure, it should be apparent to those skilled in the art that the foregoing is merely illustrative and not limiting, having been presented by way of example only. Numerous modifications and other aspects are within the scope of one of ordinary skill in the art and are contemplated as falling within the scope of the present disclosure. In particular, although many of the examples presented herein involve specific combinations ofACTIVE 509969662.6 21ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page 22 of 27 method acts or system elements, it should be understood that those acts and those elements may be combined in other ways to accomplish the same or similar objectives.ACTIVE 509969662.6 22

Claims

ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page 23 of 27CLAIMSWhat is claimed is:

1. An electrochemical flow battery bipolar plate assembly (BPPA) comprising: a conductive center plate comprising a thermoplastic polymer material and a conductive filler dispersed throughout the thermoplastic polymer material, wherein the thermoplastic polymer material has: a coefficient of thermal expansion of about 60 ppm / °C to about 110 ppm / °C, a first frame element and a second frame element, both the first frame element and the second frame element made of a thermoplastic material without a conductive filler and the thermoplastic material has a coefficient of thermal expansion within ± 20 ppm / °C of the thermoplastic polymer material.

2. The BPPA of claim 1, wherein the conductive center plate has area specific resistance (ASR) of about 0.01 to 0.200 Q / cm2at 35 psi.

3. The BPPA of claim 1, wherein the conductive filler comprises carbon.

4. The BPPA of claim 3, wherein the conductive filler comprises carbon black, carbon powder, graphite, carbon nanotubes, carbon fiber, or combinations thereof.

5. The BPPA of claim 1, wherein the thermoplastic polymer material for the conductive center plate, first frame element, and second frame element, are injected into a mold at a temperature from about 150 °C to about 250 °C and under pressure of 69 MPa to 103 MPa.

6. The BPPA of claim 1, wherein the conductive center plate has a standard reduction potential of less than -2 V.

7. The BPPA of claim 1, wherein the conductive center plate:(i) comprises up to 45% plastic and 55% or more conductive filler, orACTIVE 509969662.6 23ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page 24 of 27(ii) comprises up to 50% plastic and 50% or more conductive filler, or(iii) provided that in both (i) and (ii) the conductive thermoplastic polymer material comprises at least 9% plastic.

8. The BPPA of claim 7, wherein the conductive filler:(i) is a single conductive material, or(ii) is a combination of two or more conductive materials.

9. The BPPA of claim 7, wherein the thermoplastic polymer material comprises: PP, polyethylene, HDPE, LCP, ABS.

10. The BPPA of claim 9, wherein the conductive filler comprises: carbon black, carbon powder, graphite, carbon nanotubes, carbon fibers, or combinations thereof.

11. The BPPA of claim 10, wherein conductive filler material has particles that may be of high aspect ratio, low aspect ratio, or combinations of these.

12. The BPPA of claim 11, wherein a relative proportion of high aspect ratio conductive material in the conductive filler is greater than a relative proportion of low aspect ratio conductive material.

13. The BPPA of claim 9, wherein the thermoplastic polymer material comprises:(i) Polypropylene (thermoplastic)Zcarbon black, graphite; or(ii) ABS (thermoplastic) / carbon fiber.

14. The BPPA of claim 1, wherein the conductive center plate has:ACTIVE 509969662.6 24ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page 25 of 27(a) ASR of 0.01 to 0.200; or(b) a standard reduction potential of less than -2V; or(c) a tensile strength of about 20 MPa to about 57 MPa; or(d) a melt flow index 1.1 g / 10 min to 24.8 g / 10 min at 230 °C and 15 kg pressure; or(e) a coefficient of thermal expansion of about 60 to about 110 ppm / °C; or(f) a melting point between 150° C and 270° C; or(g) any combination of (a) through (f).

15. The BPPA of claim 1, wherein the thermoplastic polymer material is formulated as a blend.

16. An electrochemical unit cell comprising a BPPA of claim 1.

17. The electrochemical unit cell of claim 16, comprising a first half-cell and a second half- cell, wherein the first half-cell is configured to receive a first electrolyte and the second half-cell is configured to receive a second electrolyte, wherein one of the first and second electrolytes is a positive electrolyte and the other of the first and second electrolytes is a negative electrolyte.

18. The electrochemical unit cell of claim 17, wherein:(i) The first electrolyte comprises an aqueous solution comprising a redox active material which comprises a metal-ligand coordination complex; or(ii) The second electrolyte comprises an aqueous solution comprising a redox active material which comprises a metal-ligand coordination complex; or(iii) Both (i) and (ii), wherein the redox active material of the first electrolyte and the redox active material of the second electrolyte are different.

19. An electrochemical flow battery comprising at least one unit cell of claim 16.ACTIVE 509969662.6 25ATTORNEY DOCKET PATENT APPLICATION 019843.0736 (MC-04344)Page 26 of 2720. An electrochemical cell stack comprising a multiplicity of flow batteries wherein at least one flow battery is an electrochemical flow battery of claim 19.

21. The BPPA of claim 1, wherein each of the conductive center plate, first frame element, and second frame element are fabricated separately by injection molding.

22. The BPPA of claim 1, wherein the conductive center plate and the first frame element are co-molded, and the second frame element is incorporated with a subsequent process to form the BPPA.

23. The BPPA of claim 1, wherein the conductive center plate, the first frame element, and the second frame element are co-molded to form the BPPA.

24. The BPPA of claim 1, wherein the conductive center plate has a bulk conductivity of at least 10 S / m.ACTIVE 509969662.6 26

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