Distributed energy storage system

An energy storage system reaction cell configured for distribution throughout a transport system. The length of the reaction cell is substantially greater than its width and is looped throughout the transport system in a serpentine configuration. A membrane within the reaction cell has a length substantially equal to the length of the reaction cell such that surface area of the membrane is maximized relative to volume of the reaction cell to increase electrical power provided to an electrical load of the transport system.

BACKGROUND

Aspects of the present invention generally relate to energy storage systems for transport systems, such as electric vehicles, robots, and the like. More particularly, aspects of the present invention relate to energy storage systems configured for distribution throughout a system.

Conventional transport systems utilize lithium-ion batteries for energy storage. Disadvantages of lithium-ion batteries include lengthy recharge times, bulkiness, and relatively short life due to mechanical and/or chemical degradation. Moreover, lithium-ion batteries require increasingly large physical sizes (e.g., volume) for adequate power generation for vehicles or the like because energy and power are dependent on each other.

Although conventional flow batteries provide advantages compared to lithium-ion batteries, including long cycle life, separation of energy and power ratings, and availability of deep discharge, they are too bulky and provide insufficient power for use in transport systems. Flow batteries include reaction cells within a confined volume, such as channels within a metallic, graphite, or composite plate. Increasing membrane surface area in the plate to increase power results in added weight from the additional material in the plate and increases the volume of the reaction cell. Utilizing these bulky reaction cells in a transport system would result inefficient space utilization, as well as unequal weight distribution. In other words, conventional flow batteries may be well-suited for stationary applications but are too heavy and bulky for utilization in transitory environments, such as electric vehicles and the like.

SUMMARY

Aspects of the invention utilize flow battery reaction cells configured for distribution throughout a transport system to increase electrical power by maximizing membrane surface area relative to reaction cell volume. Further aspects of the invention utilize a small space in a transport system relative to lithium-ion batteries and conventional flow batteries.

In an aspect, an energy storage system includes two tanks, an elongate reaction cell, and two pumps. One of the tanks is configured for storing an anolyte while the other tank is configured for storing a catholyte. The elongate reaction cell can be distributed throughout a transport system. The reaction cell includes an anode electrode in fluid communication with the first tank and a cathode electrode in fluid communication with the second tank. The reaction cell further includes a membrane configured to form an interface between the anode electrode and cathode electrode. One of the pumps is configured for pumping the anolyte from the first tank through the anode electrode of the reaction cell via a first input supply tube. The other pump is configured for pumping the catholyte from the second tank through the cathode electrode of the reaction cell via a second input supply tube. A length of the reaction cell is substantially greater than a width of the reaction cell. Moreover, the membrane has a length substantially equal to the length of the reaction cell such that surface area of the membrane is maximized relative to volume of the reaction cell.

In another aspect, an electrochemical reaction cell includes an anode electrode, a cathode electrode, a membrane, and an exterior flexible polymer sheath enveloping the anode electrode, the cathode electrode, and the membrane. The anode electrode is configured to receive and fluidly communicate an anolyte, and the cathode electrode is configured to receive and fluidly communicate a catholyte. The membrane is configured to form an interface between the anode electrode and the cathode electrode. A length of the electrochemical reaction cell is substantially greater than its width. The electrochemical reaction cell is moreover configured for winding throughout a transport system to provide greater surface area of the membrane relative to the volume of the electrochemical reaction cell.

In yet another aspect, a transport system includes two tanks, an elongate reaction cell that is substantially longer than it is wide, and two pumps. One of the tanks is configured for storing an anolyte and the other tank is configured for storing a catholyte. The elongate reaction cell includes an anode electrode in fluid communication with the first tank and a cathode electrode in fluid communication with the second tank. Furthermore, the reaction cell includes a membrane configured to form an interface between the anode electrode and the cathode electrode such that surface area of the membrane is maximized relative to volume of the reaction cell. A first pump of the two pumps is configured for pumping the anolyte from the first tank through the anode electrode of the reaction cell via a first supply tube that couples the first tank and the reaction cell. A second pump of the two pumps is configured for pumping the catholyte from the second tank through the cathode electrode of the reaction cell via a second supply tube that couples the second tank and the reaction cell. The reaction cell is distributed throughout the transport system in a serpentine configuration within an area defined by the width and length of the transport system.

DETAILED DESCRIPTION

FIG. 1illustrates an exemplary energy storage system100and an exemplary transport system10within which an embodiment of the energy storage system100may be incorporated. The energy storage system100includes tanks102-A and102-B, pumps104-A and104-B, input supply tubes106-A and106-B, a reaction flow cell108, and output supply tubes110-A and110-B. The exemplary reaction flow cell108illustrated inFIG. 1includes a sheath112, a cathode current collector114, a cathode electrode116, optional cathode flow channels118, a membrane120, optional anode flow channels122, an anode electrode124, and an anode current collector126. In an embodiment, energy storage system100comprises a vanadium redox battery (i.e., vanadium flow battery).

The input supply tube106-A couples the tank102-A to the pump104-A and pump104-A to reaction flow cell108. The input supply tube106-B couples the tank102-B to the pump104-B and pump104-B to reaction flow cell108. The output supply tubes110-A,110-B couple reaction flow cell108to tanks104-A and104-B, respectively. In an embodiment, tanks102-A,102-B, pumps104-A,104-B, input supply tubes106-A,106-B, reaction flow cell108, and/or output supply tubes110-A,110-B are mechanically coupled to portions of transport system10. For example, mechanical fasteners (e.g., brackets, braces, etc.) may couple the components of energy storage system100to structural elements (e.g., undercarriage, frame, etc.) of transport system10.

Although the transport system10illustrated inFIG. 1is an automobile, one having ordinary skill in the art will understand that aspects of energy storage system100may be incorporated within other types of transport systems. Additional transport systems within which energy storage system100may be incorporated include, but are not limited to, motor vehicles (e.g., automobiles, motorcycles, scooters, trucks, buses, etc.), railed vehicles (e.g., trains, trams, etc.), watercraft (e.g., ships, boats, etc.), aircraft (e.g., airplanes, unmanned aerial vehicles, etc.), spacecraft, self-propelled robots, and the like. The energy storage system100may be particularly useful in electric vehicles and other types of transport systems that require a clean power source.

The tanks102-A,102-B are each configured for storing electrolytes. In an embodiment, tank102-A is configured for storing an anolyte and tank102-B is configured for storing a catholyte. The tanks102-A,102-B may be comprised of a metal and/or polymer compatible with the stored electrolytes. An exemplary material from which tanks102-A,102-B may be manufactured includes polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), high-density polyethylene (HDPE), low-density polyethylene (LDPE), and the like. The size (e.g., volume capacity) and shape of tanks102-A,102-B may be altered depending upon the environment in transport system10in which they will be installed. The size of tanks102-A,102-B can also be modified to satisfy energy storage requirements of the specific application. In other words, the energy capacity and power capacity of energy storage system100are independent of each other. In an embodiment, tanks102-A,102-B each include an opening configured to allow emptying and re-filling of the tanks with electrolytes. For instance, the openings may allow the tanks102-A,102-B to undergo a refueling operation similar to adding gasoline to a conventional internal combustion vehicle. An exemplary anolyte for use with energy storage system100includes vanadium electrolyte solution (V+2, V+3) and an exemplary catholyte includes vanadium electrolyte solution (V+5, V+4).

The pumps104-A,104-B are each configured for pumping electrolytes (e.g., anolyte, catholyte, etc.) from tanks102-A,102-B through input supply tubes106-A,106-B, respectively, to reaction flow cell108. Exemplary pumps include SMART Digital DDA 7.5-16AR-PVC/V/C model pumps manufactured by Grundfos, Bjerringbro, Germany.

The input supply tubes106-A,106-B are each configured for fluidly communicating electrolytes from tanks102-A,102-B, respectively, to reaction flow cell108. The output supply tubes110-A,110-B are each configured for fluidly communicating electrolytes from reaction flow cell108to tanks102-A,102-B, respectively. The input supply tubes106-A,106-B and output supply tubes110-A,110-B may be comprised of any polymer compatible with the electrolytes, such as PVC, PTFE, HDPE, LDPE, and the like.

The reaction flow cell108is configured to provide an environment through which the electrolytes flow, resulting in ion exchange that provides a flow of electric current. The reaction flow cell108may be comprised of various cross-sectional configurations, as further described herein. Although the cross-sections of reaction flow cell108described herein are substantially circular, one having ordinary skill in the art will understand that reaction flow cell108may have different cross-sectional shapes, such as rectangular, square, elliptical, triangular, hexagonal, octagonal, U-shaped, and the like. The reaction flow cell108is distributed throughout transport system10. For example, reaction flow cell108may be distributed in a serpentine configuration in an area defined by the length and width of transport system10, as shown inFIG. 1. In an embodiment, the serpentine configuration may also be referred to as looped and/or wound. Although the serpentine configuration illustrated inFIG. 1includes loops in a direction transverse to transport system10, one having ordinary skill in the art will understand that the loops may be in other directions, such as longitudinally relative to transport system10and the like. The reaction flow cell108may also be wound like a coil and/or distributed throughout transport system10in three dimensions. In an embodiment, distribution of reaction flow cell108throughout transport system10is configured to efficiently utilize available space in transport system10, distribute the weight of reaction flow cell108, and/or increase (e.g., maximize) the length of the membrane120relative to the volume of reaction flow cell108(e.g., to increase electrical power capacity). In another embodiment, reaction flow cell108is configured to permit charging of energy storage system100. One having ordinary skill in the art will understand that the various configurations of reaction flow cell108described herein may be interchanged without departing from the scope of the present invention.

The sheath112is configured to contain and protect the cathode current collector114, the cathode electrode116, the optional cathode flow channels118, the membrane120, the optional anode flow channels122, the anode electrode124, and the anode current collector126. The sheath112may be manufactured from any polymer compatible with the electrolytes, such as PVC, PTFE, HDPE, and LDPE. In the embodiment illustrated inFIG. 1, sheath112is a tubular structure that has a substantially circular cross-section and is hollow. As described above, sheath112may have a cross-section of various other shapes. The sheath112is flexible, which at least in part allows reaction flow cell108to be distributed throughout transport system10in various configurations (e.g., serpentine, etc.).

The cathode current collector114and anode current collector126are configured to carry electrical current from the cathode electrode116and the anode electrode124, respectively, to electrical contacts connected to an electrical load of transport system10. In an embodiment, cathode current collector114and anode current collector126are comprised of graphite. The cathode current collector114may comprise one or more wires extending throughout the length of reaction flow cell108or may be a layer of graphite between sheath112and cathode electrode116. The anode current collector126may also comprise one or more wires extending throughout the length of reaction flow cell108, may be a layer of graphite between sheath112and anode electrode124, or may be a layer of graphite inside anode electrode124.FIGS. 2A-D,4A-E,6A-E, and8A-E illustrate exemplary configurations of reaction flow cell108having wire cathode current collectors114and anode current collectors126. For purposes of better illustrating the wire cathode current collectors114and anode current collectors126, the exemplary configurations of reaction flow cell108inFIGS. 2C-D,4C-E,6C-E, and8C-E omit the cathode electrode116and the anode electrode124.FIGS. 3A-D,5A-E,7A-E, and9A-E illustrate exemplary configurations of reaction flow cell108having cathode current collectors114and anode current collectors126in a layer configuration. For purposes of better illustrating the layer cathode current collectors114and anode current collectors126, the exemplary configurations of reaction flow cell108inFIGS. 3C-D,5C-E,7C-E, and9C-E omit the cathode electrode116and the anode electrode124.

Referring again toFIG. 1, the cathode electrode116is configured to fluidly communicate catholyte through reaction flow cell108. In an embodiment, cathode electrode116is a porous carbon set. The cathode electrode116may have a substantially half-circular cross-section (e.g., half-cell) or a substantially circular cross-section that is coaxial with sheath112and anode electrode124, as further described herein. The anode electrode124is configured to fluidly communicate anolyte through reaction flow cell108. In an embodiment, anode electrode124is a porous carbon set. The anode electrode124may have a substantially half-circular cross-section or a substantially circular cross-section that is coaxial with sheath112and cathode electrode116, as further described herein.FIGS. 2A-D,3A-D,4A-E, and5A-E illustrate exemplary configurations of reaction flow cell108having a substantially circular cross-section in which cathode electrode116and anode electrode124are each substantially half-circular.FIGS. 6A-E,7A-E,8A-E, and9A-E illustrate exemplary configurations of reaction flow cell108having a substantially circular cross-section in which cathode electrode116and anode electrode124each have substantially circular cross-sections and are coaxial.

With renewed reference toFIG. 1, the membrane120is configured to provide an interface between cathode electrode116and anode electrode124(e.g., between catholyte and anolyte). In an embodiment, membrane120is configured to prevent electron transfer and allow ion transfer between cathode electrode116and anode electrode124to maintain charge equilibrium. For example, membrane120may be comprised of a polymer, such as Nafion 117, Nafion 115, Nafion 211, and the like. As further described herein, membrane120may bisect a substantially circular cross section of reaction flow cell108. The membrane120may also have a substantially circular cross-section that is coaxial with sheath112, cathode electrode116, and anode electrode124.

In an embodiment, reaction flow cell108may include one or more cathode flow channels118and/or one or more anode flow channels122. The optional cathode flow channels118are configured to improve the flow of catholyte through cathode electrode116and the optional anode flow channels122are configured to improve the flow of anolyte through anode electrode124. As illustrated inFIG. 1, cathode flow channels118may have a substantially rectangular cross-section and anode flow channels122may have a substantially circular cross-section. But one having ordinary skill in the art will understand that cathode flow channels118and anode flow channels122may each have cross-sections of various shapes including, but not limited to, substantially triangular, substantially hexagonal, substantially octagonal, and the like.FIGS. 2A-D,3A-D,6A-E, and7A-E illustrate exemplary configurations of reaction flow cell108without cathode flow channels118or anode flow channels122.FIGS. 4A-E,5A-E,8A-E, and9A-E illustrate exemplary configurations of reaction flow cell108with cathode flow channels118and at least one anode flow channel122.

In an exemplary operation of energy storage system100, pump104-A pumps anolyte from tank102-A through anode electrode124and pump104-B pumps catholyte from tank104-B through cathode electrode116. Optionally, pump104-A also pumps anolyte through anode flow channels122and/or pump104-B also pumps catholyte through cathode channels118. During discharge of energy storage system100, electrons are released from anode electrode124(e.g., negative) and ions pass through membrane120. For example, the electrons may be released via an oxidation reaction. The released electrons pass through anode current collector126and through an electrical load of transport system10such that the movement of electrons creates an electrical current. The cathode electrode116(e.g., positive) accepts electrons, such as via a reduction reaction for example. As understood by one having ordinary skill in the art, the potential difference between anode electrode124and cathode electrode116determines the voltage (e.g., electromotive force) generated by energy storage system100. And because the product of voltage and current is electric power (e.g., P=V*I), energy storage system100delivers electrical energy to the electrical load of transport system10.

EXAMPLE

An experimental energy storage system included tanks, pumps, input supply tubes, a reaction cell, and output supply tubes, as described herein. The pumps were model number SMART Digital DDA 7.5-16AR-PVC/V/C manufactured by Grundfos, Bjerringbro, Germany. The supply tubes were comprised of PVC, PTFE, HDPE, and LDPE. The reaction cell was 10 centimeters in length and comprised of a PVC, PTFE, HDPE, and LDPE sheath, a graphite cathode current collector, a graphite felt cathode electrode, a Nafion 117 membrane, a graphite felt anode electrode, and a graphite rod or platinum wire anode current collector. The reaction cell in this experiment did not include flow channels.

FIG. 10Aillustrates a voltage waveform representing a direct current voltage produced by the experimental energy storage system over a time of about 19 seconds. The voltage peaks of the illustrated waveform represent the end of charging cycles and the voltage troughs represent the end of discharging cycles. As shown, each charge-discharge cycle completes over a time period of about four seconds and the maximum voltage potential is about 1.7 volts.

FIG. 10Billustrates a profile indicating a calculated voltage from a conventional energy storage system relative to a charge state of the conventional system. As illustrated, increasing chemical height by 25% results in the same maximum voltage of about 1.7 volts with a slightly less state of charge as compared to the original height (e.g., 0.65 vs. 0.7). Also shown, decreasing height by 25% requires a state of charge of about 0.8 in order to prove the maximum voltage of about 1.7 volts. The results from the conventional cell indicate that adding channels into the distributed reaction cell may improve performance.

FIG. 10Cis another voltage waveform produced by an exemplary energy storage system according to an embodiment of the invention.