WO2018004466A1

WO2018004466A1 - Bipolar plate module for redox flow batteryand redox flow battery stack employing same

Info

Publication number: WO2018004466A1
Application number: PCT/SG2017/050335
Authority: WO
Inventors: Ming Han; Chun Yu LING; Yunzhong Chen; Lijun Liu; Mei Lin Chng
Original assignee: Temasek Polytechnic
Priority date: 2016-07-01
Filing date: 2017-07-03
Publication date: 2018-01-04

Abstract

A plate module for a redox battery comprising a frame having an internal side and an opposing, peripheral external side; a separator, the frame and separator defining a first reaction space; a first porous and conductive member positioned within the first reaction space; a first flow inlet channel extending from the first reaction space to a first inlet on the external side of the frame; and a first flow outlet channel, fluidly connected with the first flow inlet channel by the first reaction space, the first flow outlet channel extending from the first reaction space to a first outlet on the external side of the frame; wherein the first inlet is configured to be fluidly connected with a first detachable inlet manifold; and the first outlet is configured to be fluidly connected with a first detachable outlet manifold.

Description

BIPOLAR PLATE MODULE FOR REDOX FLOW BATTERY AND REDOX FLOW BATTERY STACK

EMPLOYING SAME

Technical Field

The present disclosure relates to a plate module for a redox flow battery and a redox flow battery stack. The present invention generally relates to redox flow battery technology, more particularly to a new design for a bipolar plate module which can simplify the structure of a redox flow battery stack, reduce undesirable shunt current and improve the stack performance in an economical way.

Background of the Invention

In recent years, renewable energy sources such as solar and wind have been deployed in larger numbers than ever before. This has created a demand for energy storage systems to stabilize the intermittent and often unpredictable primary power sources before the power can be jointed to grid safely or utilized in on- site loads. Redox flow batteries (RFBs) are regarded as promising electrochemical energy storage devices due to their special features. In contrast with packed, integrated cells, such as lead-acid, NaS, Li Ion, etc., where the energy and power are rated during manufacture, the energy and power assigned to redox flow batteries are separable. The energy of the system is stored in the volume of electrolytes and thus depends on the size of the electrolyte storage tanks. The power capability of the system is determined by the size of the stack of electrochemical cells in the redox battery.

The separation of power and energy provides design flexibility in the application of RFBs. The power capability (stack size) can be directly tailored to the associated load or generating asset. The storage capability (size of storage tanks) can be independently tailored to the energy storage needs of the specific application. Therefore, RFBs can economically provide optimized energy storage for many applications, such as peak shaving, backup power, and primary power stabilizing. RFBs can be used in a wide array of energy storage systems due to their storage tanks and flow controls being easily scalable and affordable. In addition, electrochemical stacks can have repeat units with standard power ratings.

However, RFBs have one main architectural disadvantage when compared with electrochemical storage devices employing integrated cell architectures. RFBs tend to have lower energy densities than integrated cell architectures. Many approaches have been studied to improve the energy density of RFBs. Among them, reducing shunt current loss and other parasitic loss is of particular interest.

Depending on the instantaneous power demands, a redox flow battery system can include any number and configuration of single cells, which are usually integrated into stacks. In a stack, the single cells are arranged in series electrically with parallel electrolyte solution flow paths. However, since the reactant electrolyte solutions are conductive, an electric current can be induced. The electrical losses associated with these "shunt currents" are commonly known as "shunt losses". Those losses occur because a conductive path exists between adjacent cells that are at a different electrical potentials. This difference of potential is small between immediately adjacent cells. However, when many cells are combined into a stack, as is typical practice, the electrical potential is increased. Thus, the electrical current through the fluid connections increases, resulting in increased shunt losses. In a medium-scale system the shunt current loss can account for up to 1 1 % of the power generation capacity. In addition, the parasitic current consumed by the supplementary devices such as pumps and valves are also considerable when complex balance of plant (BOP) is used to supply electrolyte solutions to individual stacks.

A common strategy for reducing shunt current is to limit the number of cells that are directly combined into a single stack. However, this limits the number of cells that can share common electrical and electrolyte solution connection hardware and thus increases system cost.

Another strategy uses air bubbles to reduce the effective conductivity of the process connections. This process is impractical due to high cost. GB-2085475 discloses an electrochemical battery in which shunt currents are minimized by forcing the conductive fluid to fall from the top of the manifold vertically into a pool.

CN 101 562253A discloses electrochemical cells using artificially long channels or shunts between cells. These increase the length of the fluid path and, thus, the electrical resistance between adjacent cells, thereby reducing the shunt losses. US 7682728 B2 discloses an electrochemical cell containing manifold plates and serpentine paths inside the stacks as shunt passages for electrolyte solution. The main problems with this configuration is that the long channels or serpentine electrolyte paths inside the stacks enhance the flow resistance, resulting in high pressure loss and parasitic current consumption by the pumps. In addition, the convoluted electrolyte paths result in a higher frequency of debris blockage and thus increase maintenance cost.

In addition, in conventional stack assemblies, highly accurate cell alignment is needed to ensure all the vertical holes on the compartment plates of adjacent cells are well aligned. There is a very low alignment tolerance since misalignment causes leakage in the manifold and flow channels formed by misaligned vertical through holes for conducting electrolyte between adjacent cells.

Therefore, it is desirable to develop an alternative technology which can minimize shunt current loss without increasing maintenance cost or assembly complexibility, or at least provide a useful alternative.

Summary of the Invention

In accordance with the present invention, there is provided a plate module for a redox battery, comprising:

(a) a frame having an internal side and an opposing, peripheral external side;

(b) a separator, the frame and separator defining a first reaction space;

(c) a first porous and conductive member positioned within the first reaction space;

(d) a first flow inlet channel extending from the first reaction space to a first inlet on the external side of the frame; and

(e) a first flow outlet channel, fluidly connected with the first flow inlet channel by the first reaction space, the first flow outlet channel extending from the first reaction space to a first outlet on the external side of the frame;

wherein the first inlet is configured to be fluidly connected with a first detachable inlet manifold; and

the first outlet is configured to be fluidly connected with a first detachable outlet manifold.

In accordance with the present invention, there is also provided a bipolar plate which comprises the above-mentioned plate module and further comprises:

(a) an inset frame, the inset frame coupling the separator to the frame, the separator and inset frame defining a second reaction space;

(b) a second porous and conductive member positioned within the second reaction space;

(c) a second flow inlet channel extending from the second reaction space to a second inlet on the external side of the frame;

(d) a second flow outlet channel, fluidly connected with the second flow inlet channel by the second reaction space, the second flow outlet channel extending from the second reaction space to a second outlet on the external side of the frame,

wherein the second inlet is configured to be fluidly connected with a second detachable inlet manifold, and the second outlet is configured to be fluidly connected with a second detachable outlet manifold. In accordance with the present invention, there is also provided a redox flow battery stack formed by:

(a) a plurality of plate modules as described above as having a first reaction space and a second reaction space (the "first" plates);

(b) a plurality of ion conducting membranes,

the plate modules alternating with the ion conducting membranes, the stack further comprising: (c) a pair of plate modules as described above as having only the first reaction space, one located at each opposite end of, and separated by an ion conducting membrane from, the first plates;

(d) a pair of current collectors;

(e) a pair of end plates;

(f) a first and second external inlet manifold; and

(g) a first and second external outlet manifold,

wherein the pair of plate modules is located between the pair of current collectors; and the pair of current collectors is located between the pair of end plates.

In accordance with the present disclosure, there is also provided a bipolar plate modular, comprising: a first and a second carbon felts;

a flow frame;

a inset frame; and

a separator;

wherein the first carbon felts is located in the first active reaction space formed by the frame body of the said flow frame and the first side of the separator that attached on the said frame body; the second carbon felt is located in the second active reaction space formed by the second side of the separator and the inset frame that attached to on the said separator and flow frame;

both of the first and second active spaces are fluidly connected to outside due a pair of through holes located in across corners of the spaces; the said through holes are formed and/or installed laterally on the said flow frame.

In accordance with the present disclosure, there is also provided a monopolar plate modular comprising : a carbon felt;

a flow frame;

a separator;

wherein the carbon felt is located in the active reaction space formed by the frame body of the said flow frame and the first side of the separator that attached on the said frame body; through holes are formed and/or installed laterally on the said flow frame.

In accordance with the present disclosure, there is also provided a redox flow battery stack comprising: a stacking of single cells that formed by a plurality of the said bipolar plate modulars and a pairs of monopolar plate modular at both terminal, as well as ion conductive membranes inserted in each of the interface between adjacent pair of bipolar plate modulars and interface between adjacent bipolar plate modular and monopolar plate modular;

a pair of current collectors;

a pair of endplates;

two pairs manifold sets; and

bolt & nuts;

wherein the said current collectors are attached in both side of the said stacking of single cells, and the endplate pairs, as well as the bolts & nuts are used to hold the stack together; and wherein the said two pairs manifold sets with a plurality of channels are connected to each of the across corners of the said first active reactive space and the second reactive space of the bipolar plate modulars, as well as the active reaction space of the monopolar palate modulars, to conduct electrolytes

The present disclosure also provides a new design for a bipolar plate module, which can include first and second felts (e.g. "porous and conductive layers"), such as carbon felts; a frame or "flow frame", an inset frame and a separator; wherein the first felt is located in a first active reaction compartment (e.g. a "reaction space") formed by the frame body of the flow frame and a first side of the separator when attached to the frame; the second felt is located in a second active reaction compartment formed by a second side of the separator and the inset frame when attached to the separator and flow frame; both the first and second active reaction compartments are fluidly connected to outside of the frame via a pair of through holes located in diagonally opposite corners of the active reaction compartments; the through holes being formed and/or installed laterally on the flow frame. A design of monopolar plate module is also provided. The monopolar plate module is a modification of the bipolar plate module, and uses a thick separator plate to replace the space occupied by the common separator, inset frame and second felt of the bipolar plate module.

The present disclosure further provides a redox flow battery stack containing a stacking of single cells formed by a plurality of the bipolar plate modules described above, and a pair of monopolar plate modules, one monopolar plate module being located at each terminal of the stack. The stack further includes: ion conductive membranes, a membrane inserted at each interface between an adjacent pair of bipolar plate modules and between a bipolar plate module and the adjacent monopolar plate module; a pair of current collectors, a pair of endplates, two paired manifold sets, bolts and nuts, wherein the current collectors are attached to opposite sides of the stack, and the endplates, as well as the bolts and nuts are used to hold the stack together. Moreover, the two paired manifold sets provide a plurality of flow channels connected to each of the diagonally opposite corners of the first active reaction compartment and the second reaction compartment of the bipolar plate module, as well as the active reaction space of the monopolar plate module, to conduct electrolytes.

This presently described plate modules and battery stack may reduce the problem relating shunt current losses. The length of conductive path between adjacent single cells can be increased by increasing the length of the channels, without using complex internal serpentine structure. Extra flexibility to optimize the system performance and minimize shunt current is thus possible since it is convenient to adjust the length of the flow channels on the manifold sets according to specific operation conditions. Should further adjustments need to be made after installation, the lengths of the flow channels are easily adjustable on site. Additionally, the external manifolds provide users with an easy way of diagnosing issues associated with clogging of the flow channels, for example sediments of the carbon felt.

It may be possible to operate the redox flow battery stack disclosed herein in a variety of electrochemical cell systems, such as an all vanadium, vanadium/bromine, iron/chromium, bromine/polysulfide, lithium battery and other electrochemical cell systems, by appropriate section of the electrolytes supplied to the first and second active reaction compartments.

For example, in an all vanadium system, the electrolytes and reactions occurring at negative electrodes and positive electrodes may be represented as:

V²⁺ <-> V³⁺ + e^" , and

V⁵⁺ , V⁴⁺ - e^" , respectively.

In iron/chromium system, the electrolytes and reactions occurring at negative electrodes and positive electrodes may be represented as:

Cr²⁺ -> Cr³⁺ + e and

Fe²⁺ < > Fe³⁺ + e^" , respectively. In lithium battery system, the electrolytes and reactions occurring at negative electrodes and positive electrodes may be represented as:

LiFeP0₄ <→ Li⁺ + FeP0₄ + e^", and

Ti0₂ + Li⁺ <→ LiTi0₂ - e^", respectively.

The benefits include better stack performance, low shunt current / parasitic current loss, low maintenance cost, robust sealing, and simplifying the assembly process. Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. Brief Description of the Drawings

Some embodiments of the invention are hereafter described, by way of non-limiting example only, with reference to the accompanying drawings, in which: FIG. 1 A is a schematic side view of a redox flow battery stack in accordance with some embodiments;

FIG. 1 B is partial enlargement of the side view of a redox flow battery stack in accordance with some embodiments;

FIG. 2 is an exploded view of a redox flow battery stack in accordance with some embodiments;

FIG. 3 is an exploded view of a bipolar plate module in accordance with some embodiments;

FIG. 4A is a partial enlargement view of the flow frame from the first side;

FIG. 4B is a partial enlargement view of the flow frame from the second side;

FIG. 5 is a partial enlargement view of the inset frame;

FIG. 6A is a schematic side view of a bipolar plate module of the first side;

FIG. 6B is a schematic side view of a bipolar plate module of the second side;

FIG. 7 is an exploded view of a mono plate module in accordance with some embodiments;

FIG. 8 is a partial enlargement view of the mono polar module flow frame from the second side;

FIG. 9 is a schematic side view of a manifold set;

FIG. 10 is a schematic side view of a bipolar plate module in other embodiments;

FIG. 1 1 is a schematic side view of a redox flow battery stack in accordance with other embodiments; FIG. 12 is a partial enlargement view of an inset frame in accordance with some embodiments.

FIG. 13 is an exploded view of a plate module in accordance with some embodiments; and

FIG. 14 is an exploded view of a bipolar plate module in accordance with some embodiments.

Detailed Description of Embodiments of the Invention

The detailed description below describes some embodiments of the invention but does not represent the only forms in which the invention may be practised or performed.

The embodiments described herein may be combined, and individual features from one embodiment may be introduced into, or substituted for a similar feature in, a similar embodiment. For example, much of the description applicable to FIG. 7 may similarly be applied to FIG. 13, much of the description applicable to FIG. 3 may similarly be applied to FIG. 14, and much of the description relating to FIG. 4B may similarly be applied to FIG. 12. FIG.1 A illustrates a schematic side-view of a redox flow battery stack. The battery stack has an essentially symmetrical structure, with an end plate at either end and located adjacent a respective monopolar plate module and with one or more bipolar plate modules between the monopolar plate modules. Fig. 1 B is a partial enlargement of the side-view of FIG. 1 A. As mentioned above, the redox flow battery stack 1 comprises: one or more, presently a plurality of, bipolar plate modules 2, the bipolar plate modules presently being stacked together; a pair of mono-polar plate modules 3 (a, b) located on either side of the stack of the bipolar plate modules 2; a pair of current collectors 4(a, b); a pair of end plates 5 (a, b); an ion conductive membrane (see reference 1 12 in FIG. 13 and 13) sandwiched between each pair of adjacent bipolar plate modules and each adjacent bipolar plate module and mono-polar module; two pairs of manifold sets 7 (a and b, c and d) for conducting active electrolytes in and out from the stack respectively; and bolts 6 for tightening the stack.

FIG. 2 is an exploded view of a redox flow battery stack in accordance with some embodiments. The central parts are the bipolar plate modules 2 (a, b, c and d) and the pairs of mono-polar plate modules 3a and 3b, together forming the active region for electrochemical reactions. In the stack, one layer of ion conductive membrane (1 12 In FIG. 13 and 14) is inserted into each interface between adjacent bipolar module pairs (e.g. between 2a and 2b; 2b and 2c; 2c and 2d) as well as between each of the interfaces between a bipolar module and an adjacent mono-polar plate module (e.g. between 3a and 2a; 2d and 3b). Electrochemical reactions take place on both sides of the ion conductive membrane. The functions of the bipolar plate modules 2 (a to d) and mono-polar plate modules 3 (a, b) include reactant distribution, catalysis and electron conduction.

In the embodiment shown, five single cells (2a to 2d, 3a and 3b) are formed in total. Although FIG. 2 shows an example in which four bipolar plate modules 2 are used, it would be clear to a person skilled in the art that the stack may contain any number of bipolar plate modules 2 as required by the system. Preferably, a pair of current collectors 4 (a, b) is located on both sides or ends of the active region (the region formed by the stack of bipolar and monopolar plate modules) on the outside of which is a pair of end plates 5a and 5b. The current collectors 4 (a, b) are preferably made from a good electrically conductive material such as copper or an alloy. The end plates 5 can be made from metal, plastic or composite, the material preferably chosen to provide structural strength to the stack and to hold the stack together. Resistance coating or other measures can be used to ensure good electrical insulation between the current collectors 4(a, b) and end plates 5 (a, b). The embodiments described above are a contrast to conventional redox flow battery stacks. There are no flow channels of the present embodiments that are formed vertically to the above-mentioned component layers as evidence by the absence of inlet/outlet holes on the end plates 5 (a, b) and vertical holes on the rims of the bipolar plate modules 2 (a to d) and mono-polar plate modules 3 (a, b). This is due to a special design of the bipolar plate modules 2 (a to d) and mono-polar plate modules 3 (a, b) whereby electrolytes are conducted in and out the active reaction region in a lateral direction.

Referring now to FIG. 3, which illustrates an exploded view of a bipolar plate module 2 in accordance with some embodiments. The bipolar plate module 2 is consists of a first porous and conductive layer, presently a carbon felt 25, a flow frame 21 , a separator 22, an inset frame 23, and a second porous and conductive layer, presently also a carbon felt 24.

The first carbon felt 25 and second carbon felt 24 are preferably made of porous fibers that are chemically treated to provide the requisite electrochemical functions e.g. redox (oxidation-reduction) reaction. The felts 24 and 25 are constrained within the inset frame 23 and flow frame 21 respectively. A separator 22 is inserted to separate the felts 24 and 25. The separator 22 can be made of graphite sheet, carbon plate, metal sheet or other electrically conductive material - a separator or separator layer are both terms presently used to describe any material the purpose of which is to prevent cross-mixing of positive and negative electrolytes, while still permitting the transport of ions to complete a circuit during passage of current. The carbon felts 24, 25 and the related frames 23, 21 form two separated reaction spaces whereby different electrolytes are supplied into the spaces through specially designed through holes. The felts 24 and 25 function as electrodes to promote electrochemical reactions. Ions generated pass though the adjacent ion conductive membrane, while electrons pass through out the circuit to form a complete electrical circuit.

FIG. 4A, 4B illustrate a partial enlarged view of the flow frame 21 from the first side and from the second side respectively. The flow frame 21 is a symmetrical structure, comprising a rectangular frame body 21 1 , a pair of mountings 214 (a, b) in each end and bolts 215 to fix the mountings 214 (a, b) on to the frame body 21 1 . In each end of the frame body 21 1 there are a pair of assembly members 213 (a, b), which contain related mounting holes 21 5. Bolts 215 can pass through relative mounting holes to fasten the mountings 214 (a, b) on to the assembly members 213 (a, b). Through holes 216a pass through mountings 214a and assembly members 213a and couple to form a flow passage for a first electrolyte - the term "electrolyte" shall be understood to include, but not be limited to, an electrolyte and an electrolyte solution. Similarly, through holes 216b pass through mountings 214b and assembly members 213b and couple to form a flow passage for a second electrolyte of opposite polarity to the first electrolyte. The manifold 7a and 7b (shown in Fig 1 A & 1 B) can be connected to the through holes 216 (a, b) respectively to deliver the electrolytes. O-rings may be used in the contact region for proper sealing. The detail of the manifold 7a and 7b will be described in further detail below.

In some embodiments, the other end of the frame body 21 1 has a similar structure for electrolytes passing through.

In the first side of the frame body 21 1 , there is a groove 212 along the inner edge of the frame body 21 1 for the purpose of housing the first carbon felt 25. In the second side of the frame body, as shown in Fig 4B, there is a flange 21 7 at the end and terrace 218. The flange 217 can be considered as the back face of the assembly members 213 (a, b). There are through holes 216b' that are fluidly connected to the through holes 216b. Similarly, there are through holes 216a' formed on the frame body 21 1 that are fluidly connected to the through holes 216a. The terrace 21 8 is a flat surface on the second side of the frame body 21 1 .

Separator 22 is located on terrace 218. The separator 22 may be sealed against the terrace 218, or adhered to the terrace 218, by a sealant. The inset frame 23 has the shape and size as the separator 22. The insert frame 23 is glued on a surface of the separator 22. That surface, together with the inset frame 23, define a reaction space. Second carbon felt 24 is constrained within the inset frame 23, in the reaction space.

Fig 5 is a partial enlarged side view of the inset frame from a second side to that shown in FIG. 3. It is a symmetrical, rectangular frame 231 made of plastic, metal, polymer or composite. Preferably, there are through holes 216b" located at the end of the frame 231 , coupling with the through holes 216b' and 216b to establish a flow passage for the electrolyte. A similar structure is formed at the cross end of the frame 231 . The space 120 within the inset frame 23 forms an active reaction compartment. The compartment is fluidly connected with the through holes 216b' and 216b. Electrolyte can be conducted in and out the active reaction compartment laterally - in other words, in the plane of the frame or inset frame as the case may be, as opposed to normal to that plane.

As shown in Fig. 14, two reaction compartments 120 and 304 are formed, one on either side of the separator 303. One compartment 304 is in the space outlined by the inset frame 302 and the porous carbon felt 306, or by the inset frame 302 and separator 303. The other compartment 120, is in the space outlined by the frame body 102 of flow frame 308 and the porous carbon felt 106, or by the frame body 102 and separator 303. Electrolytes can flow in and out of the reaction compartments 120 and 302 through the through holes, such as 216 (a, b), and flow freely inside the reaction compartments. The through holes are located at or towards diagonally opposite corners of the flow frame 308.

A complete bipolar module can be made by assembling all the components shown in Fig. 3, including carbon felt 25, flow frame 21 , separator 22, inset frame 23, ion membranes 1 12 and carbon felt 24.

FIG. 6A & 6B are schematic side views of the bipolar plate module 2 of the first side and second side, respectively. In the first and second side, the first carbon felt 25 and second carbon felt 24 are constrained within the frame body 21 1 of the flow frame 21 and the inset frame 23 respectively. The first carbon felt 25 and second carbon felt 24 thus form the first and second active reaction compartments 120b and 120a that are separated by the separator 22.

The first active reaction compartment is fluidly connected with the through holes 216a and 216c which can laterally conduct the first electrolyte liquid in and out of the first active reaction compartment. Similarly, the second active reaction compartment is fluidly connected with the through holes 21 6b and 216c which can laterally conduct the second electrolyte liquid in and out the second active reaction compartment. Advantageously, the bipolar plate module can be used to form a single electrochemical cell. In a typical structure, a layer of ion conductive membrane with the same dimension as the felts is sandwiched between two adjacent bipolar plate layers. The first active reaction compartment contains the first electrolytes and is coupled with the first side of the ion conductive membrane, while the second active reaction compartment contains the second electrolytes and is coupled to the second side of the ion conductive membrane. Consequently, a single electrochemical cell is formed. Electrochemical reactions are conducted on both sides of the membrane, accompanied by ion exchange through the membrane. Continuous reactions can be sustained by continuously flowing electrolytes in and out the related active reaction compartments.

More single electrochemical cells can be fabricated by stacking a plurality of bipolar plate modules and ion exchange membranes in the same way. Each bipolar plate module has two sides and, thus, dual functions. One side is the anode of one single cell while the opposite side is the cathode side of an adjacent single cell, thereby deriving its name, bipolar plate module. At the end of the stacks, no electrode is required on the outer side. While bipolar plate modules may still be used, the outer active reaction compartment would be redundant. Therefore, monopolar plate modules are used at opposite ends of the stack. Monopolar plate modules 3 (a, b) are similar to that of the bipolar plate module 2 (as shown in Fig. 3) except that in a monopolar plate module, one side of the active reaction compartment is omitted as shown in Fig. 7 showing an exploded view of a monopolar plate module.

Fig. 7 shows the monopolar plate module 3, which contains a thick separator 32, a flow frame 31 and a porous and conductive layer, presently carbon felt 35. The partial enlargement of the flow frame 31 is shown in Fig. 8. Again, the flow frame 31 is similar to the flow frame 21 shown in Fig 4A & 4B except through hole structure is omitted in one side. The through holes 316a are formed in the related assembly member 313a and mounting 314a. The through holes 316a' formed in the edge of the frame body 31 1 are fluidly connected with the through holes 316a for electrolyte to pass though. There is no through hole formed on the flange 317. The thick separator 32 is attached on the terrace 31 8 with sealing materials. Its thickness is equal to the combination of the common separator 22, inset frame 23 and carbon felt 24. In other words, the thick separator 32 is used to replace the combination because no active reaction compartment is needed on side yet it is useful to fill the space so as to avoid contaminant ingress or retention. One active reaction compartment is formed in the other side when the carbon felt 35 is located in the space formed by the frame body 31 1 and the thick separator 32. Through holes formed on both ends of the frame body 31 1 enable the active reaction compartment to be fluidly connected with outside. Notably, both monopolar plate modules 3a & 3b can be modified to the structure of described monopolar plate module 3. Alternatively, it is possible to modify the monopolar plate module 3 as long as only one active reaction compartment is retained. For example, the second active reaction compartments shown in Fig. 6 (A, B) are retained while the first reaction compartments are omitted by inserting a layer of carbon plate or other conductive solid plate. Preferably, the monopolar plate modules 3a & 3b are preferably the same structure as it is likely to be more cost effective. However, they can adopt a different structure as long as only one active reaction compartment is formed.

A single electrochemical cell can be formed when an ion conductive membrane is inserted in the interface between a monopolar plate module 3 and the adjacent bipolar plate module 2. During assembly, the active reactive compartment of the monopolar plate 3 should face the ion conductive membrane. The other side of the monopolar plate 3 is coupled with current collector 4.

An electrochemical cell stack can be assembled with the above described components, including, a plurality of bipolar plate modules 2 stacked together; a pair of mono-polar plate modules 3 (a, b) located on both ends of the stack of bipolar plate modules 2; a pair of current collectors 4(a, b); a pair of end plates 5 (a , b); one layer of ion conductive membrane sandwiched between each pair of adjacent bipolar plate module and each adjacent bipolar plate module and mono-polar plate module pair.

Notably, there are no vertical holes on the different layers of the components. This is distinct to conventional redox flow battery stacks in which the flow channels are formed vertical to the above mentioned component layers. In embodiments of this invention, electrolytes flow in and out the active reaction compartments in a lateral way. Advantageously, a manifold set is used to conduct electrolytes in and out the stacks. This manifold set comprises one or more manifolds that can be detachably attached to the frame 21 . Thus individual manifolds can be replaced if they become clogged, or if longer paths between adjacent cells are required in order to mitigate shunt current losses (i.e. lengthen the manifold branches or flow channels 72 of FIG. 9, that convey fluid between the frame 21 at the inlets of adjacent cells).

Fig. 9 is a schematic side view of a manifold set. The manifold set 7 includes a manifold 71 and a plurality of flow channels 72. The flow channels 72 are manifold branches that are fluidly connected to the manifold 71 . The flow channels 72 are couplable to the through holes (e.g. inlet 1 08 or outlet 124 on FIG. 13 and 14) located at the ends of the bipolar plate modules and the monopolar plate modules to conduct electrolytes in and out the active reaction compartments of the cells. The flow channels 72 are coupled with the single cells within the stack. O-rings may be used in the contact region when inserting the flow channels for proper sealing.

Referring now to Fig 1 A, a pair of manifold sets 7a and 7c are diagonally opposite each other with respect to the redox flow battery stack. The manifold sets 7a and 7c conduct the first electrolytes into and out of the first active reaction compartments respectively. Similarly, a pair of manifold sets 7d and 7b are diagonally opposite each other and conduct the second electrolytes in to and out of the second active reaction compartments respectively. Therefore, the electrolytes are supplied into the single cells in parallel. The length of the conductive path between adjacent single cells can be adjusted by changing the length of the flow channels 72. This embodiment of the invention is distinct to the conventional design where fixed length serpentine flow channels are formed inside the stacks, either located in the ends of the active reaction area or the whole region of the active area, in order to reduce the shunt current creating a long conductive path between the adjacent single cells. In conventional design, this conductive path is of fixed length so that in the event it does not need to be so long in order to adequately mitigate shunt current, it cannot be changed and, conversely, where the conductive path is too short, shunt current can dramatically reduce battery efficiency.

In embodiments of this invention, an alternative way is provided to solve the shunt current problem. The length of conductive path between adjacent single cells is easily modified and can be increased by increasing the length of the flow channels 72, without using a complex internal serpentine structure. This is achieved by making the conductive path length adjustable by providing an adjustable portion of the conductive (namely the portion passing through the manifold) on an external side of the frame 21 of individual cells. An advantage of embodiments of this invention is in providing extra flexibility to optimize the system performance. The length of the flow channels can be easily modified on the manifold sets according to specific operating conditions. This is in contrast to conventional designs whereby it is not easy to amend the length of the internal shunt channels or serpentine paths once the stack is assembled. Further, embodiments of the invention provide a simplified single cell structure by eliminating the internal manifold and serpentine structure. The flow resistance of the electrolytes passing through the porous and conductive layer or carbon felt is considerably lower than flowing through the complex serpentine structure. Therefore, fluid pressure losses can be reduced and thus the parasitic current consumed by supplementary devices such as pumps can be reduced.

Advantageously, the maintenance cost of systems can be reduced using embodiments of the invention. In conventional designs the debris of carbon felt or other materials may accumulate and obstruct the internal shunt channels and/or serpentine paths, which may in turn incur a high maintenance load. In embodiments of the invention, the manifold is installed external to the stack (i.e. to an external, peripheral edge of the frame), and can be readily dismantled or replaced if there are obstructions.

Additionally, the assembly and installation of embodiments of the invention is simplified compared to systems with a closed manifold or internal flow channels. This is because aligning cells should be easier since there are no vertical holes on the plates, which require precise alignment. Further, the risk of electrolytes leakage may also be minimized. The advantages of the embodiments of the invention may provide better energy efficiency and cost savings compared to conventional designs. In other embodiments, the through holes formed in the lateral direction of the bipolar plate module and/or monopolar plate module can be replaced with other structures as long as the structure can be connected with the flow channel 72 of the manifold 71 for electrolyte delivery. One embodiment with such structure is illustrated in Fig. 10 and Fig. 1 1 . Referring now to Fig. 10, a partial enlargement of a bipolar plate module in another preferred embodiment is illustrated. In this embodiment, the bipolar plate module 2S is similar to the one shown in Fig. 6A, except the through holes formed by assembly members 213(a, b) and mountings 214(a, b), are replaced by a plurality of barbed connectors 216S. The barbed connectors 216 can be directly formed on the edge of the flow frame. The flow channels 72 can be conveniently coupled with the barbed connectors and conduct electrolytes in and out the first and second active reaction compartments. The barbed connectors can be used in a similar manner in the monopolar plate module.

Fig.1 1 shows the assembled redox flow battery stack with the barbed connectors. A manifold set can be connected to the stack by simply inserting the barbed connectors into a related flow channel.

With reference to FIG. 13, a plate module 1 00 for a redox battery (such as redox battery 1 of FIG. 1 A) is shown. The plate module 100 comprises a frame 102 (being the same as flow frame 31 of FIG. 7), a separator 104, a first porous and conductive member 106, a first flow inlet channel 108, and a first flow outlet channel 1 10.

The frame 102 has an internal side and an opposing, peripheral external side 122. The external side 1 14 forms an edge around the frame 102. The external side 1 14 defines the periphery of the surfaces 1 1 6, 1 18 of the frame 102 that face other plate modules or an end plate (such as plate 5a of FIG. 2) in a battery stack.

The separator 104 and the frame 102 define a reaction space 120 (indicated by cross-hatching in frame 102, and having a thickness X, between rib 200 and surface 202 of FIG. 13). The separator 104 may be planar. The separator 104 may alternatively not be a planar member. In either case, the separator 104 is any body the purpose of which is to isolate an electrolyte within the flow path comprising the reaction space 120, while permitting electron exchange as described above.

The first porous and conductive member 106 is positioned within the reaction space 120. The first porous member 106 permits the through flow of electrolyte between the separator and ion membrane 1 12 (indicated by broken lines since it does not form part of the plate module per se but will, in practice, be present in a battery stack). The first porous and conductive member 106 may be formed from carbon, such as a carbon felt, or may be any other member capable of performing the abovementioned function.

The first flow inlet channel 108 extends from the reaction space 120 to a first inlet 124 on the external side 1 14 of the frame 102. The first inlet channel 124 conveys fluid from the external side 1 14 to the internal side - in other words, from the external side 1 14 into the reaction space 120.

The first flow channel 1 08 may form a straight channel. The frame 102 may be substantially planar (e.g. may have a flat rectangular shape). The frame 102 thus comprises a plane (e.g. plane 126), and the first flow inlet channel 108 is presently parallel to, or coplanar with, that plane 126. The first flow inlet channel 108 is thus similarly parallel to, or coplanar with, the frame 102.

In some embodiments, the first flow inlet channel 1 08, the first outlet channel 1 10 each form a line that is substantially parallel to the plane, and the first reaction space 120 forms a second plane that is parallel to the plane of the frame.

The first flow channel 108 may comprise one or more conduits. Presently the first flow channel 108 comprises three conduits 128. However, greater or fewer conduits may be used as needed to facilitate electrolyte flow and distribution across the reaction space 120.

The first inlet 124 is configured to be fluidly connected with a first detachable inlet manifold such as manifold 7 of FIG. 9. It is configured to be fluidly connected with that manifold via a suitable connection, such as luer connection 216S of FIG. 2S. Another appropriate fitting, such as a standard tap adaptor or an interference fit connector (of which the luer fitting is one), may be used as appropriate for the particular pressure rating and application. Similar comments apply to the other inlets and outlets discussed below.

The first flow outlet channel 1 10 is fluidly connected with the first flow inlet channel 1 08 by the reaction space 120. Thus electrolyte can flow from the inlet channel 108, through the reaction space 120 to the outlet channel 1 1 0. The first flow outlet channel 1 10 extends from the reaction space 120 to a first outlet 130 on the external side 1 14 of the frame 102.

The first flow outlet channel 1 10 may similarly form a straight channel. The first flow outlet channel 1 10 is presently parallel to, or coplanar with, plane 126. The first flow outlet channel 1 10 is thus similarly parallel to, or coplanar with, the frame 102.

The first outlet 130 is configured to be fluidly connected with a first detachable outlet manifold such as manifold 7 of FIG. 9. Fluid connection may be achieved as described above for the first flow inlet channel 108.

The first flow outlet channel 1 10 may comprise one or more conduits. Presently the first flow outlet channel 1 10 comprises a three conduits 1 50. However, greater or fewer conduits may be used as needed to facilitate electrolyte flow and distribution across the reaction space 120. The reaction space 120 of the plate module 100 is substantially rectangular. It is aligned with the frame 102 which, in the present embodiments, is similarly substantially rectangular. In other words, the long sides 132, 134 of the reaction space 120 are parallel to the long sides 136, 138 of the frame 102.

The first flow inlet channel 108 and the first flow outlet channel 1 10 are adjacent to diagonally opposed corners 137, 140 of the rectangular reaction space 120. The corners are diagonally opposed insofar as one corner is the furthest distance across the reaction space 120 from the other corner. Notably, the term "adjacent to" is intended to include within its scope channels 1 08, 1 10 located at the corners, as well as channels located nearby the corners. In either case, the location of the channels 108, 1 10 is intended to provide a long average fluid path through the reaction space 120 to ensure the electrolyte spreads across the porous and conductive member 106.

The above-described plate module 100 is form a monopolar plate module. Another embodiment of the invention consists of modifying the above-described monopolar plate module to be a bipolar plate module, such as module 300 of FIG. 14. In addition to the features described above with reference to plate module 100, plate module 300 further comprises an inset frame 302. The inset frame 302 couples separator 303 to the frame 102. The separator 303 and inset frame 302 thus define a second reaction space 304. Since the present embodiment is a bipolar plate module, the separator 303 may be thinner than separator 104, since there must be room for the second reaction space 304.

A second porous and conductive member 306 positioned within the second reaction space 304. The purpose of the second porous and conductive member 306 is the same as that of the first porous and conductive member 106, except that that second porous and conductive member 306 sits within a reaction space of opposite polarity to that associated with the first porous and conductive member 106.

A second flow inlet channel 308 extends from the second reaction space 304 to a second inlet 310 on the external side 1 14 of the frame 102. It may have the same properties as the first flow inlet channel 108 described above, which thus need not be reiterated.

A second flow outlet channel 310 is fluidly connected with the second flow inlet channel 308 by the second reaction space 304. The second flow outlet channel 310 extends from the second reaction space 304 to a second outlet 314 on the external side 1 14 of the frame 102.

As with the first inlet 124, the second inlet 312 is configured to be fluidly connected (e.g. through an interference fit or other fitting as described above) with a second detachable inlet manifold such as manifold 7 of FIG. 9. Similarly, as with the first outlet 126, the second outlet 314 is configured to be fluidly connected (e.g. through an interference fit or other fitting as described above) with a second detachable inlet manifold such as manifold 7 of FIG. 9.

The second flow inlet channel 308 and second flow outlet channel 310 may, similar to the first flow inlet channel 1 08 and first flow outlet channel 1 10, comprise one or more conduits. It is thus clear that any variations envisaged or described herein as variations of the first inlet flow channel 108 and first outlet flow channel 1 10, shall be similarly possible in the second flow inlet channel 308 and second flow outlet channel 310.

In contrast to the first flow inlet channel 1 08 and first flow outlet channel 1 1 0, however, the second flow inlet channel 308 and the second flow outlet channel 310 extend not just through the frame 102, but through the inset frame 302 and the frame 102. The portion of each channel extending through the inset frame 302 may have a larger aperture on the end at the interface between inset frame 302 and frame 102, than the portion of the respective channel extending from the inset frame 302 through the frame 102. This will increase the tolerance in the alignment of the inset frame 302 and frame 102. The alternative is similarly possible, where the portion of each channel extending through the inset frame 302 has a smaller aperture on the end at the interface between inset frame 302 and frame 102, than the portion of the respective channel extending from the inset frame 302 through the frame 102.

To enable the same frame 102 to be used for both monopolar plate modules and bipolar plate modules, the separator may have a thickness of at least a thickness of the inset frame as shown in FIG. 14.

As set out above, the first reaction space 120 may be substantially rectangular. The same may also apply to the second reaction space 304. Thus each space 120, 304 has two long edges and two short edges, the respective inlet channel 108, 308 and respective flow outlet channel 1 10, 310 in each case forming a line that is substantially parallel to the long edges of the corresponding reaction space 120, 304.

While the first flow inlet channel 108 and first flow outlet channel 1 10 may be configured to directly connect to respective ones of the first detachable inlet manifold and first detachable outlet manifold such as flow channels 72 of manifold 7 of FIG. 9. As shown in FIG. 12, the present embodiment provides a respective mounting member 152, 154 through which the first flow inlet channel 108 and second flow inlet channel 108 are connected to the respective detachable manifolds. These mounting members 152, 154 are shown as being detachable from the frame 102 in FIG. 12, and may similarly be detachable in the present embodiment, or may alternatively form an integral part with the frame 102. The mounting members 152, 154 provide a fluid path for conveying fluid between the frame and the respective detachable inlet manifolds of manifold 7 of FIG. 9. Particularly where the mounting members 152, 154 are formed separately from the frame 102, the fluid path may have an opening abutting the frame 102 (i.e. at the interface between the respective mounting block 152, 154 and the frame 102) that is larger than the respective first inlet or first outlet. Similar to the second flow inlet channel 308 and second flow outlet channel 310, this affords some tolerance in the alignment between the mounting blocks 152, 154 and the frame 102. It also permits the same mounting block design to be used regardless of whether the module is a mono-polar plate module or a bipolar plate module, since the inlet or outlet conduits will simply open into a slightly different position in the opening of the fluid path through the mounting block 152, 154.

Similar mounting blocks may be provided for the second flow inlet channel 308 and second flow outlet channel 310, for similar purposes. The separator 104, 303 may be made from conductive material. Similarly, the frame 102 and inset frame 302 may be made from non-conductive material. Moreover, the first and second porous and conductive members made from carbon felt.

Another embodiment provides a redox flow battery stack 1 formed as shown in FIG. 1 A. The battery stack comprises:

(a) a plurality of plate modules 300, being bipolar plates;

(b) a plurality of ion conducting membranes 1 12,

the plate modules 300 alternating with the ion conducting membranes 1 12, the stack 1 further comprising:

(c) a pair of plate modules 100, one located at each opposite end of, and separated by an ion conducting membrane 1 12 from, the plurality of plate modules 300;

(d) a pair of current collectors 4a, 4b;

(e) a pair of end plates 5a, 5b;

(f) a first and second external inlet manifold 7; and

(g) a first and second external outlet manifold 7,

wherein the pair of plate modules 100 is located between the pair of current collectors 4a, 4b; and the pair of current collectors 4a, 4b is located between the pair of end plates 5a, 5b.

In the stack 1 , the pair of current collectors 4a, 4b are made from conductive material. Also, the interface between the current collectors 4a, 4b and the end plates 5a, 5b are one or more of the following:

(i) a formed resistance coating; and

(ii) an insulating material.

When the stack 1 is in use a first reservoir is fluidly connected with the first external inlet manifold to convey a first electrolyte. Also, a second reservoir is fluidly connected with the second external inlet manifold to convey a second electrolyte. The second electrolyte and the first electrolyte have, in use, opposite polarities.

In certain embodiments, the stack comprises first and second external inlet and outlet manifolds such as manifold 7 of FIG. 9 which are positioned substantially normal to the frame's plane.

In certain embodiments, the electrolytes are at least one taken from a group comprising:

(a) a vanadium system ;

(b) a iron/chromium system ;

(c) a bromine/polysulfide system ;

(d) a vanadium/bromine system; and

(e) a lithium battery system. While preferred embodiments of the invention have been illustrated and described, it will be clear that the invention is not limited to the embodiments only. Numerous modifications, changes, variations, substitutions and equivalents will be apparent to those skilled in the art without departing from the scope of the invention as described in the claims.

Throughout this specification, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that the prior art forms part of the common general knowledge.

Claims

Claims Defining the Invention:

1 . A plate module for a redox battery, comprising:

(a) a frame having an internal side and an opposing, peripheral external side;

(b) a separator, the frame and separator defining a first reaction space;

2. The plate module claimed in claim 1 , wherein the frame defines a plane and:

(a) the first flow inlet channel forms a line that is substantially parallel to the plane;

(b) the first flow outlet channel forms a line that is substantially parallel to the plane; and

(c) the first reaction space forms a second plane that is parallel to the plane of the frame.

3. The plate module claimed in claim 1 or 2, wherein the first reaction space is substantially rectangular.

4. The plate module claimed in any preceding claim, wherein the first flow inlet channel and the first flow outlet channel are adjacent to diagonally opposed corners of the first reaction space.

5. The plate module claimed in any preceding claim, further comprising:

wherein the second inlet is configured to be fluidly connected with a second detachable inlet manifold, and the second outlet is configured to be fluidly connected with a second detachable outlet manifold.

6. The plate module claimed in claim 5, wherein the second flow inlet channel and the second flow outlet channel are adjacent to diagonally opposed corners of the second reaction space.

7. The plate module claimed in claim 5 or 6, wherein the second flow inlet channel and the second flow outlet channel extend through the inset frame and the frame.

8. The plate module claimed in any one of claims 1 to 4, further comprising an inset frame, the inset frame coupling the separator layer to the frame, the separator layer having a thickness of at least a thickness of the inset frame.

9. The plate module claimed in claim 3, wherein the substantially rectangular first reaction space has two long edges and two short edges, the first flow inlet channel and first flow outlet channel each forming a line that is substantially parallel to the long edges of the first reaction space.

10. The plate module claimed in claim 5, wherein the second reaction space is substantially rectangular, having two long edges and two short edges, wherein the second flow inlet channel and second flow outlet channel each form a line that is substantially parallel to the long edges of the second reaction space.

1 1 . The plate module claimed in any preceding claim, wherein:

(a) the separator is made from conductive material;

(b) the frame and inset frame are made from non-conductive material; and

(c) the first and second porous and conductive members are made from carbon felt.

12. The plate module claimed in any preceding claim, wherein the first inlet and first outlet are configured to connect to the respective first detachable inlet manifold and first detachable outlet manifold by interference fit.

13. The plate module claimed in any one of claims 5 to 7 and 1 0, wherein the second inlet and second outlet are configured to connect to the respective second detachable inlet manifold and second detachable outlet manifold by interference fit.

14. The plate module claimed in any preceding claim, wherein the first flow inlet channel and first flow outlet channel are configured to connect to respective ones of the first detachable inlet manifold and first detachable outlet manifold through a respective mounting member, the respective mounting member comprising a fluid path for conveying fluid between the frame and the respective first detachable inlet manifold or first detachable outlet manifold, the fluid path having an opening abutting the frame, the opening being larger than the respective first inlet or first outlet.

15. The plate module claimed in any one of claims 5 to 7, 10 and 13, wherein the second flow inlet channel and second flow outlet channel are configured to connect to respective ones of the second detachable inlet manifold and second detachable outlet manifold through a respective mounting member, the respective mounting member comprising a fluid path for conveying fluid between the frame and the respective second detachable inlet manifold or second detachable outlet manifold, the fluid path having an opening abutting the frame, the opening being larger than the respective second inlet or second outlet.

16. A redox flow battery stack formed by:

(a) a plurality of plate modules as claimed in claim 5;

(b) a plurality of ion conducting membranes,

the plate modules alternating with the ion conducting membranes, the stack further comprising: (c) a pair of plate modules claimed in claim 1 , one located at each opposite end of, and separated by an ion conducting membrane from, the plurality of plate modules as claimed in claim 5;

(d) a pair of current collectors;

(e) a pair of end plates;

(f) a first and second external inlet manifold; and

(g) a first and second external outlet manifold,

17. The stack claimed in any preceding claim, wherein:

(a) the pair of current collectors are made from conductive material; and

(b) the interface between the current collectors and the end plates are one or more of the following:

(i) a formed resistance coating; and

(ii) an insulating material.

18. The stack claimed in any preceding claim, wherein when the stack is in use:

(a) a first reservoir is fluidly connected with the first external inlet manifold to convey a first electrolyte; and

(b) a second reservoir is fluidly connected with the second external inlet manifold to convey a second electrolyte.

19. The stack claimed in any preceding claim, wherein the first and second external inlet and outlet manifolds are positioned substantially normal to the frame's plane.

20. The stack claimed in any preceding claim, wherein the electrolytes are at least one taken from a group comprising:

(a) a vanadium system ;

(b) a iron/chromium system ;

(c) a bromine/polysulfide system ;

(d) a vanadium/bromine system; and

(e) a lithium battery system.