Balancing and measuring device for redox flow battery

Abstract

The invention relates to a device for electrochemically balancing an electrolyte of a redox flow battery, a redox flow battery system device, a method of use and use thereof.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an electrolyte for an electrochemically balanced redox flow battery, a device for measuring state of charge, measuring copper content in electrolyte and capable of correcting for electrolyte volume discrepancies, which is particularly suitable for use in copper-based redox flow batteries. BACKGROUND

[0002] The energy production market has undergone a significant shift from fossil fuel generation to renewable energy generation such as photovoltaics and wind power for environmental and geopolitical reasons. However, to incorporate intermittent renewable energy into existing power grids, sufficient energy storage is required to stabilize the power generation of renewable energy and to ensure the stability of the power grid. Energy storage can perform system peak shaving, frequency regulation, price arbitrage, and renewable energy stabilization, and meet other needs such as backup power systems. Frequency regulation and price arbitrage are two major application scenarios for utility-scale energy storage, but more and more energy storage systems are performing one or more applications.

[0003] Compared with competitive energy storage technologies, redox flow batteries have high rated power, large capacity, fast response time, and long-term operability, which are very suitable for providing the capacity required for further integration of renewable energy storage. The working principle of redox flow batteries is to circulate two different electrolytes through a battery separated by a separator and / or ion exchange membrane. During charging, one active species in the negative electrolyte is reduced, thereby reducing the oxidation state of the active species, while the active species in the positive electrolyte is oxidized during this process. Charging is usually achieved by applying external power from the grid or directly from the energy generation source. During discharging, the oxidation state of the active species in the negative electrolyte is again oxidized, while the active species in the positive electrolyte is reduced, thereby allowing energy to be extracted from the system during discharging.

[0004] Aqueous all-copper redox flow batteries are one of the chemicals used in redox flow batteries. In copper redox flow batteries, Cu(I) is used as an active species at 0% state of charge in both the negative electrolyte and the positive electrolyte. During charging, Cu(I) in the negative electrolyte is reduced to metallic copper and deposited on the conductive substrate and / or electrode, while Cu(I) present in the positive electrolyte is oxidized to Cu(II) on the conductive substrate and / or electrode. Like most flow batteries, copper flow batteries suffer from gradual loss of capacity over time. For copper redox flow batteries, this capacity loss comes from the separator and / or ion exchange membrane, which allows the Cu(I) / Cu(II) species to be transferred from the electrolyte with the highest concentration of species to the electrolyte with the lower concentration of species by permeation transfer.

[0005] For copper batteries, this situation is further exacerbated by a compensatory reaction, where 2Cu(I) ions are formed when Cu(II) comes into contact with copper deposited in the negative electrode electrolyte during the charging phase. This effectively reduces discharge capacity and leads to semi-permanent capacity loss (unless addressed). This imbalance results in a lack of available copper ions during charging, leading to reduced charge capacity in each subsequent cycle. Tracking the amount of copper ions present in the electrolyte is difficult and typically requires expensive equipment (such as ultraviolet measuring devices) to determine the copper content in both the positive and negative electrode electrolytes. System operation is further complicated because real-time state of charge (SOC) values ​​cannot be obtained from the system during operation, as open-circuit voltage is usually required to determine SOC, which effectively pauses system operation to measure both open-circuit voltage and SOC.

[0006] Therefore, a device is needed to continuously measure the system's state of charge from an external source. Furthermore, a device is needed to determine the copper concentration in both the positive and negative electrode electrolytes to a certain extent and to perform the necessary operations to rebalance the copper content in both electrolytes to the desired level. By correcting the copper content in the two electrolytes, the system's capacity can be restored, and a method is needed to perform this operation continuously without interrupting the main system. Finally, a device is needed to correct for changes in electrolyte volume over time due to osmosis effects without causing a shutdown of the main redox flow battery system. Summary of the Invention

[0007] Rebalancing

[0008] The purpose of this disclosure is to provide a simple and continuous method for electrochemically rebalancing the electrolyte used in redox flow batteries that use copper as the main active material.

[0009] Another object of this disclosure is to provide a method for continuously electrochemically rebalancing the electrolyte used in a redox flow battery that uses copper as the main active material without affecting the main function of the redox flow battery.

[0010] Another object of this disclosure is to provide a method for continuous electrochemical rebalancing of the electrolyte used in a redox flow battery that uses copper as the main active material with minimal energy input.

[0011] Another object of this disclosure is to provide a method for continuously electrochemically rebalancing the electrolyte used in a redox flow battery that uses copper as the main active material without generating hydrogen, oxygen or other harmful gases.

[0012] It is yet another object of the present disclosure to provide a method for continuous electrochemical rebalancing of electrolytes used in redox flow batteries using copper as the primary active species, by which the capacity of the battery can be continuously maintained at its highest operational level.

[0013] It is yet another object of the present disclosure to provide a method for continuous electrochemical rebalancing of electrolytes used in redox flow batteries using copper as the primary active species, which can be implemented for large scale rebalancing by repeating multiple half-cells.

[0014] In one preferred embodiment, the device circulates the negative electrolyte containing a mixture of Cu(I) and Cu(II) into the device, and by applying an external voltage, copper undergoes an electrochemical reaction to form metallic copper and deposits on the electrode substrate. For the reverse reaction, the positive electrolyte containing a mixture of Cu(I) and Cu(II) is applied a positive potential, which changes the oxidation state of the majority species to Cu(II). The valves are then arranged in such a way that the positive electrolyte is circulated through the chamber where copper has been deposited on the electrode substrate. When Cu(II) comes in contact with the copper deposited on the electrode substrate through a well-known reaction known as the homing reaction (also known as copper leaching process), metallic copper dissolution occurs, and Cu(II) is reduced to Cu(I) state, resulting in 2Cu(I). This results in the transfer of dissolved copper species from the negative electrolyte to the positive electrolyte. As a result, copper can be transferred from the negative electrolyte to the positive electrolyte, thereby recovering the capacity lost through the maturation capacity loss mechanism. After performing the above process, the system capacity can be restored to its initial state or adjusted to the desired state.

[0015] In another embodiment, the device has Figure 1 A shown configuration, where the positive electrolyte containing a mixture of Cu(I) and Cu(II) is circulated into the device, and by applying an external voltage, copper undergoes an electrochemical reaction to form metallic copper and deposits on the electrode substrate. For the reverse reaction, the negative electrolyte containing a mixture of Cu(I) and Cu(II) is applied a positive potential, which changes the oxidation state of the majority species to Cu(II). The valves are then arranged in such a way that the negative electrolyte is circulated through the chamber where copper has been deposited on the electrode substrate. When Cu(II) comes in contact with the copper deposited on the electrode substrate through a well-known reaction known as the homing reaction (also known as copper leaching process), metallic copper dissolution occurs, and Cu(II) is reduced to Cu(I) state, resulting in 2Cu(I). This results in the transfer of dissolved copper species from the positive electrolyte to the negative electrolyte. As a result, copper can be transferred from the positive electrolyte to the negative electrolyte, thereby recovering the capacity lost through the maturation capacity loss mechanism. After performing the above process, the system capacity can be restored to its initial state or adjusted to the desired state.

[0016] Charge state determination

[0017] It is another object of the present disclosure to provide a simple method for determining the relative state of charge of a copper-based redox flow battery by using an external battery.

[0018] It is yet another object of the present disclosure to provide a simple method for determining the relative amount of copper species present in the positive and negative electrolytes.

[0019] In another embodiment, a negative electrolyte containing a mixture of Cu(I) and Cu(II) is supplied to one half-cell of a device as set forth in the present disclosure, and a negative potential is applied to cause the copper species to be electrodeposited on the electrode substrate. A positive electrolyte containing a mixture of Cu(I) and Cu(II) is supplied to a second half-cell of a device as set forth in the present disclosure, and a positive potential is applied to cause some or all of the species to be converted to Cu(II). After an initial thin layer is deposited on the electrode substrate, no voltage is applied to either of the two half-cells, and the open circuit voltage of the device as set forth in the present disclosure is measured, i.e., no current is observed. This open circuit voltage can then be used to determine the amount of Cu(II) species in the negative electrolyte.

[0020] In another embodiment, a negative electrolyte containing a mixture of Cu(I) and Cu(II) is supplied to one half-cell of a device as set forth in the present disclosure, and a negative potential is applied to cause the copper species to be electrodeposited on the electrode substrate. A positive electrolyte containing a mixture of Cu(I) and Cu(II) is supplied to a second half-cell of a device as set forth in the present disclosure, and a positive potential is applied to cause some or all of the species to be converted to Cu(II). After an initial thin layer is deposited on the electrode substrate, no voltage is applied to either of the two half-cells, and the open circuit voltage of the device as set forth in the present disclosure is measured, i.e., no current is observed. This open circuit voltage can then be used to determine the amount of Cu(II) species in the negative electrolyte.

[0021] In another embodiment, a negative electrolyte containing a mixture of Cu(I) and Cu(II) is supplied to one half-cell of a device as set forth in the present disclosure, and a negative potential is applied to cause the copper species to be electrodeposited on the electrode substrate. A positive electrolyte containing a mixture of Cu(I) and Cu(II) is supplied to a second half-cell of a device as set forth in the present disclosure, and a positive potential is applied to cause some or all of the species to be converted to Cu(II). After an initial thin layer is deposited on the electrode substrate, no voltage is applied to either of the two half-cells, and the open circuit voltage of the device as set forth in the present disclosure is measured, i.e., no current is observed. This open circuit voltage can then be used to determine the amount of Cu(II) species in the negative electrolyte.

[0022] Electrolyte volume correction

[0023] It is a further object of the present disclosure to provide a simple method for maintaining the electrolyte volume of an electrolyte used by a redox flow battery using copper as the primary active species.

[0024] In another embodiment of the device presented in the present disclosure, the weight of the positive electrolyte and negative electrolyte reservoirs can be determined by a suitable device, or their volume can be determined by a suitable device. This information can then be used to transfer measured amounts of positive electrolyte to negative electrolyte, or vice versa, by using the device presented in the present disclosure and its associated valves, depending on the preferred negative electrolyte to positive electrolyte ratio for the operation of a redox flow battery using copper as the primary active species. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a schematic representation of a device that can rebalance the electrolyte of a redox flow battery using copper as the primary active species.

[0026] Figure 2 Electrochemical energy storage using copper as active species

[0027] Figure 3 Advantages of copper electrochemical energy storage

[0028] Figure 4 Competing solutions and performance comparison of various battery systems

[0029] Figure 5 Prototype according to the present invention DETAILED DESCRIPTION

[0030] In one aspect, there is provided a device for electrochemically balancing the electrolyte of a redox flow battery, wherein the battery comprises a first half-cell and a second half-cell separated by a separator (12), wherein the device comprises:

[0031] a first tank (1) for receiving electrolyte;

[0032] a second tank (6) for receiving electrolyte;

[0033] a plurality of connecting conduits (16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27) for passing electrolyte therethrough;

[0034] a first pump (2) and a second pump (5) for pumping electrolyte, wherein the first pump (2) is configured to pump electrolyte between the first tank (1), the first half-cell, the second half-cell and / or the second tank (6), and wherein the second pump (5) is configured to pump electrolyte between the second tank (6), the second half-cell, the first half-cell and / or the first tank (1); and

[0035] four three-way valves (3, 4, 7, 8) configured to provide fluidic connections between the first tank (1), the second tank (6) and / or the redox flow battery together with the plurality of connection pipes and the first pump and / or the second pump.

[0036] Additionally or alternatively, the four three-way valves comprise a first three-way valve (3), a second three-way valve (4), a third three-way valve (8) and a fourth three-way valve (7), wherein

[0037] the first three-way valve (3) is configured to transfer electrolyte between the first tank (1) and / or the first half-cell and / or the second tank (6),

[0038] the second three-way valve (4) is configured to transfer electrolyte between the first tank (1) and / or the second half-cell and / or the second tank (6),

[0039] the third three-way valve (8) is configured to transfer electrolyte between the first tank (1) and / or the first half-cell and / or the second tank (6), and

[0040] the fourth three-way valve (7) is configured to transfer electrolyte between the first tank (1) and / or the second half-cell and / or the second tank (6).

[0041] Additionally or alternatively, the first pump (2) is configured to pump electrolyte from the first tank (1) through the first three-way valve (3), at least two connection pipes (17, 18) of the plurality of connection pipes and the first half-cell, and to pump electrolyte from the first tank (1) through the second three-way valve (4), at least two connection pipes (16, 21) of the plurality of connection pipes and the second half-cell; and

[0042] the second pump (5) is configured to pump electrolyte from the second tank (6) through the second three-way valve (4), at least two connection pipes (19, 21) of the plurality of connection pipes and the second half-cell, and to pump electrolyte from the second tank (6) through the first three-way valve (3), at least two connection pipes (18, 20) of the plurality of connection pipes and the first half-cell; wherein

[0043] The first half-cell is configured to be fluidly connected to the first tank (1) via a connection pipe (27, 22) of the plurality of connection pipes by a third three-way valve (8) and to the second tank (6) via a connection pipe (27, 25) of the plurality of connection pipes by the third three-way valve (8), and wherein the second half-cell is configured to be fluidly connected to the second tank (6) via a connection pipe (26, 24) of the plurality of connection pipes by a fourth three-way valve (7) and to the first tank (1) via a connection pipe (26, 23) of the plurality of connection pipes by the fourth three-way valve (7).

[0044] Additionally or alternatively, the first flow battery comprises a first electrode (10), an electrically conductive material (11) and a non-conductive separator (9); and the second flow battery comprises a second electrode (13), an electrically conductive material (15) and a non-conductive separator (14).

[0045] Additionally or alternatively, the apparatus further comprises means for applying a voltage to the redox flow battery.

[0046] Additionally or alternatively, the apparatus further comprises means for applying a voltage to the first electrode (10) and the second electrode (13).

[0047] Additionally or alternatively, the apparatus further comprises means for measuring the content of a relative conductive species (e.g. a copper species) in the electrolyte.

[0048] Additionally or alternatively, the means for measuring the relative conductive species is means for determining the weight of the first tank and / or the second tank.

[0049] Additionally or alternatively, the means for measuring the relative conductive species is means for determining the volume of the electrolyte in the first tank and / or the electrolyte in the second tank.

[0050] Additionally or alternatively, the electrolyte comprises or consists of a copper species, a zinc species, a bromine species and / or an iron species, preferably the electrolyte comprises or consists of a copper species.

[0051] Additionally or alternatively, the redox flow battery is a copper-based redox flow battery.

[0052] In one aspect, there is provided a redox flow battery system, comprising:

[0053] A redox flow battery comprising: a first half-cell for receiving an electrolyte and comprising a first electrode (10), an electrically conductive material (11) and an electrically non-conductive separator (9); and a second half-cell for receiving an electrolyte and comprising a second electrode (13), an electrically conductive material (15) and an electrically non-conductive separator (14), wherein the first half-cell and the second half-cell are separated by a separator (12); and

[0054] A device as defined in the present disclosure.

[0055] Additionally or alternatively, the device and / or the redox flow battery further comprises an electrolyte, for example in the first and second half-cells and / or in the first and second tanks.

[0056] Additionally or alternatively, the system further comprises a power source removably attached to the system for applying a voltage to the redox flow battery, preferably to the first and second electrodes.

[0057] In one aspect, there is provided a method of determining the relative state of charge of a redox flow battery, wherein the method comprises:

[0058] i) providing a redox flow battery system as defined in the present disclosure, wherein the device is configured to be in fluid connection with the redox flow battery;

[0059] ii) providing an electrolyte to the redox flow battery system, preferably to the first and second tanks of the device;

[0060] iii) providing electrolyte from the first tank to or through the first half-cell and electrolyte from the second tank to or through the second half-cell, or electrolyte from the second tank to or through the first half-cell and electrolyte from the first tank to or through the second half-cell, preferably by pumping with the first and second pumps;

[0061] iv) applying a negative potential to the first electrode and a positive potential to the second electrode, or applying a positive potential to the first electrode and a negative potential to the second electrode, thereby causing reduction of the electrically conductive species of the electrolyte in the half-cell comprising the electrode to which the negative potential is applied, and thereby causing electro-deposition of the electrically conductive species, preferably a metallic copper species, on the electrically conductive material comprised in the half-cell comprising the electrode to which the negative potential is applied, and oxidation of at least a portion of the electrically conductive species of the electrolyte in the half-cell comprising the electrode to which the negative potential is applied on the electrically conductive material comprised in the half-cell comprising the electrode to which the negative potential is applied, preferably oxidation of the electrically conductive species of the electrolyte in the half-cell comprising the electrode to which the negative potential is applied to Cu(II);

[0062] v) stopping the application of voltage to the first and second electrodes; and

[0063] vi) measuring the open circuit voltage of the device, thereby determining the state of charge of the electrolyte.

[0064] Additionally or alternatively, in iii) the three-way valve is arranged such that only the second tank is in fluid connection with the first half-cell and electrolyte is provided from the second tank through the first half-cell, preferably pumped by the second pump, and the three-way valve is arranged such that only the first tank is in fluid connection with the second half-cell and electrolyte is provided from the first tank through the second half-cell, preferably pumped by the first pump; and

[0065] In iv) a negative potential is applied to the first electrode, thereby causing reduction of the electrically conductive species of the electrolyte in the first half-cell and thereby causing electro-deposition of the electrically conductive species, preferably a metallic copper species, on the electrically conductive material (1 1 ); and a positive potential is applied to the second electrode, thereby causing oxidation of at least a portion of the electrically conductive species of the electrolyte in the second half-cell on the electrically conductive material (15), preferably oxidation of the electrically conductive species of the electrolyte in the second half-cell to Cu(II), or

[0066] a negative potential is applied to the second electrode, thereby causing reduction of the electrically conductive species of the electrolyte in the second half-cell and thereby causing electro-deposition of the electrically conductive species, preferably a metallic copper species, on the electrically conductive material (15); and a positive potential is applied to the first electrode, thereby causing oxidation of at least a portion of the electrically conductive species of the electrolyte in the first half-cell on the electrically conductive material (1 1 ), preferably oxidation of the electrically conductive species of the electrolyte in the first half-cell to Cu(II).

[0067] Additionally or alternatively, in iii) the three-way valve is arranged such that only the first tank is in fluid connection with the first half-cell and electrolyte is provided from the first tank through the first half-cell, preferably pumped by the first pump; and the three-way valve is arranged such that only the second tank is in fluid connection with the second half-cell and electrolyte is provided from the first tank through the second half-cell, preferably pumped by the second pump; and

[0068] In iv) a negative potential is applied to the first electrode, thereby causing reduction of the electrically conductive species of the electrolyte in the first half-cell and thereby causing electro-deposition of the electrically conductive species, preferably a metallic copper species, on the electrically conductive material (1 1 ); and a positive potential is applied to the second electrode, thereby causing oxidation of at least a portion of the electrically conductive species of the electrolyte in the second half-cell on the electrically conductive material (15), preferably oxidation of the electrically conductive species of the electrolyte in the second half-cell to Cu(II), or

[0069] applying a negative potential to the second electrode, thereby causing reduction of the electrically conductive species of the electrolyte in the second half-cell and thereby causing electro-deposition of the electrically conductive species, preferably a metallic copper species, on the electrically conductive material (15); and applying a positive potential to the first electrode, thereby oxidizing at least a portion of the electrically conductive species of the electrolyte in the first half-cell, preferably oxidizing the electrically conductive species of the electrolyte in the first half-cell to Cu(II), on the electrically conductive material (11).

[0070] Additionally or as an alternative, in iii) the three-way valve is arranged such that electrolyte is provided from the first tank through the first half-cell and back to the first tank, and electrolyte is provided from the second tank through the second half-cell and back to the second tank, or electrolyte is provided from the second tank through the first half-cell and back to the second tank, and electrolyte is provided from the first tank through the second half-cell and back to the first tank.

[0071] Additionally or as an alternative, iv) further comprises ending the provision of electrolyte from the first tank through the first half-cell, preferably by ending the pumping of the first pump and / or arranging the three-way valve such that only the second tank is fluidly connected with the second half-cell, while the first tank is not fluidly connected with the first half-cell; and providing electrolyte from the second tank through the second half-cell; and

[0072] v) stopping the application of the voltage to the first and second electrodes when substantially all of the electrolyte captured within the first half-cell is fully oxidized, preferably when the electrolyte comprising Cu(I) and Cu(II) captured within the first half-cell is fully oxidized to Cu(II).

[0073] Additionally or as an alternative, iv) further comprises ending the provision of electrolyte from the second tank through the second half-cell, preferably by ending the pumping of the second pump and / or arranging the three-way valve such that only the first tank is fluidly connected with the first half-cell, while the second tank is not fluidly connected with the second half-cell; and providing electrolyte from the first tank through the first half-cell; and

[0074] v) stopping the application of the voltage to the first and second electrodes when substantially all of the electrolyte captured within the second half-cell is fully oxidized, preferably when the electrolyte comprising Cu(I) and Cu(II) captured within the second half-cell is fully oxidized to Cu(II).

[0075] In one aspect, there is provided a method for electrochemically rebalancing electrolyte of a redox flow battery, wherein the method comprises:

[0076] i) providing a redox flow battery system as defined in the present disclosure, wherein the device is configured to be fluidly connected with the redox flow battery;

[0077] ii) providing an electrolyte to the redox flow battery system, preferably to the first tank and the second tank of the device;

[0078] iii) providing electrolyte from the first tank to the first half-cell and from the second tank to the second half-cell, or from the second tank to the first half-cell and from the first tank to the second half-cell, preferably by pumping with the first pump and the second pump;

[0079] iv) applying a negative potential to the first electrode and a positive potential to the second electrode, or applying a positive potential to the first electrode and a negative potential to the second electrode, thereby causing reduction of the electrically conductive species of the electrolyte in the half-cell comprising the electrode to which the negative potential is applied, thereby causing electro-deposition of the electrically conductive species, preferably a metallic copper species, on the electrically conductive material comprised in the half-cell comprising the electrode to which the negative potential is applied, and oxidation of at least a part of the electrically conductive species of the electrolyte in the half-cell comprising the electrode to which the negative potential is applied on the electrically conductive material comprised in the half-cell comprising the electrode to which the negative potential is applied, preferably oxidation of the electrically conductive species of the electrolyte in the half-cell comprising the electrode to which the negative potential is applied to Cu(II);

[0080] v) stopping the application of the voltage to the first electrode and the second electrode; and

[0081] viii) arranging the three-way valve such that only the first tank is in fluid connection with the first half-cell, and providing electrolyte from the first tank through the first half-cell, preferably by pumping with the first pump, thereby dissolving the electro-deposited electrically conductive species, preferably metallic copper, and reducing Cu(II) to Cu(I), or

[0082] arranging the three-way valve such that only the second tank is in fluid connection with the first half-cell, and providing electrolyte from the second tank through the first half-cell, preferably by pumping with the second pump, thereby dissolving the electro-deposited electrically conductive species, preferably metallic copper, and reducing Cu(II) to Cu(I).

[0083] Additionally or as an alternative, the electrolyte comprises one or more electrically conductive species, such as a copper species. Examples of copper species include, but are not limited to, Cu(I), Cu(II) and metallic copper.

[0084] Additionally or as an alternative, the method further comprises:

[0085] ix) measuring the content of the relative electrically conductive species, such as a copper species, in the electrolyte, thereby obtaining a result value.

[0086] Additionally or as an alternative, in ix), measuring the relative electrically conductive species is determining the weight of the first tank and / or the second tank, thereby obtaining one or more result values.

[0087] Additionally or alternatively, in ix), the measuring of the relative conductive substance is determining the volume of electrolyte in the first tank and / or the volume of electrolyte in the second tank, thereby obtaining one or more result values.

[0088] Additionally or alternatively, the method further comprises:

[0089] x) comparing the one or more result values obtained from the measuring with one or more predetermined values;

[0090] xi) providing electrolyte from the first tank to the second tank if the result value obtained from the measuring is equal to or lower than the predetermined value, or providing electrolyte from the second tank to the first tank if the result value obtained from the measuring is higher than the predetermined value.

[0091] Additionally or alternatively, a method for continuously electrochemically rebalancing electrolytes of a redox flow battery as defined in the present disclosure, wherein the method comprises two or more times the procedures of iii) to xi).

[0092] In one aspect, a method for rebalancing electrolytes of a redox flow battery system is provided, wherein the method comprises:

[0093] i) providing a redox flow battery system as defined in the present disclosure, wherein the device is configured to be in fluid connection with the redox flow battery;

[0094] ii) providing electrolytes to the redox flow battery system, preferably to the first tank and the second tank of the device;

[0095] iii) providing electrolyte from the first tank to the second tank through the first half-cell or the second half-cell, preferably by pumping with the first pump, or providing electrolyte from the second tank to the first tank through the second half-cell or the first half-cell, preferably by pumping with the second pump.

[0096] Additionally or alternatively, in iii), the three-way valve is arranged such that the first tank is in fluid connection with the second tank only via the first three-way valve (3), the first half-cell, the third three-way valve (8) and the connecting conduits (17, 20, 27, 25), or such that the first tank is in fluid connection with the second tank only via the second three-way valve (4), the second half-cell, the fourth three-way valve (7) and the connecting conduits (16, 21, 26, 24).

[0097] In one aspect, there is provided use of a device as defined in the disclosure or a redox flow battery system as defined in the disclosure for determining the relative state of charge of a redox flow battery, preferably a copper-based redox flow battery, for determining the relative amount of a conducting species, for example a copper species, in an electrolyte, for maintaining the electrolyte volume of an electrolyte used in a redox flow battery, preferably using copper as the primary active species, and for electrochemical balancing, preferably continuous electrochemical balancing, of an electrolyte.

[0098] In one aspect, there is provided use of a redox flow battery system device as defined in the disclosure for storing energy for time shifting, load balancing, and backup power systems.

[0099] Rebalancing

[0100] Figure 1 A schematic of a preferred embodiment of the present invention for electrolyte rebalancing of an electrolyte used in a redox flow battery using copper as the primary active species, but the present invention is not limited to this description. It consists of one electrode 10 that can apply a positive or negative potential and another electrode 13 that can apply a positive or negative potential, electrode 10 and electrode 13 are separated by a membrane 12, which can be a porous membrane or a non-porous membrane, but is not limited to these two. A positive electrolyte tank 1 and a negative electrolyte tank 6 are connected to pumps 2 and 5, respectively. The outlet of pump 2 can be configured by a three-way valve 3 or a three-way valve 4 to pump to a chamber containing electrode 10 or electrode 13. The output of pump 2 can be sent back to the positive electrolyte tank 1 or to the negative electrolyte tank 6 by using a three-way valve 8 or a three-way valve 7. Likewise, the electrolyte of the negative electrolyte tank 6 can be pumped by pump 5 through a chamber containing electrode 10 or electrode 13 via switching of the three-way valve 3 or the three-way valve 4, respectively. The output can then be sent back to the negative electrolyte tank 6 via switching of the three-way valve 7 or via switching of the three-way valve 8. Within each half-cell there is a conducting material 11 and 15, which can consist of a metal foam or a carbon-based foam to form a reaction surface where electrochemical reactions take place. Membrane 12 is separated from conducting material 11 by a non-conducting separator 9, which can be made of a material such as a reverse osmosis separator, but is not limited to this. Membrane 12 is also separated from conducting material 15 by a non-conducting separator 14, which can be made of a material such as a reverse osmosis separator, but is not limited to this.

[0101] In another embodiment, the positive electrolyte from the positive electrolyte tank 1 is pumped through the pipe 17 into the half-cell containing the conductive material 11 by using the three-way valve 3 to connect the pipe 17 to the pipe 20. By applying a negative voltage to the electrode 10, thereby having a negative voltage on the conductive material 11, any Cu(I) or Cu(II) in contact with the conductive material 11 will be reduced and deposited on the conductive material 11 in the form of metallic copper. The positive electrolyte then leaves the half-cell through the pipe 27 and is recirculated to the positive electrolyte tank 1 by using the three-way valve 8 to connect the pipe 27 to the pipe 22. At the same time this process is taking place, the negative electrolyte from the tank 6 is circulated into the half-cell containing the conductive material 15 by using the pump 5 to circulate into the pipe 19, which is connected to the pipe 21 by using the three-way valve 4. A positive voltage is subsequently applied to the electrode 13, thereby causing a positive voltage to be applied to the conductive material 15. The negative electrolyte is pumped into a system containing a mixture of Cu(I) and Cu(II), and by the positive voltage applied to the conductive material 15, the Cu(I) species is oxidised to Cu(II). The negative electrolyte now containing Cu(II) species is returned to the negative electrolyte tank 6 by using the three-way valve 7 to connect the pipe 26 and the pipe 24. At this point the negative electrolyte in the negative electrolyte tank 6 contains an excess of Cu(II) ions, while part of the copper in the positive electrolyte is deposited on the conductive material 11. To proceed to the subsequent step, the pump 2 and the pump 5 are turned off, the three-way valve 4 is closed, and the three-way valve 7 is closed. The negative electrolyte containing the excess Cu(II) ions is then circulated through the pipe 18 to the pipe 20 by reactivating the pump 5 and using the three-way valve 3. This causes the excess Cu(II) ions to come into contact with the copper deposited on the conductive material 11 and then to react using the disproportionation reaction of mature copper, where Cu(II) reacts with metallic Cu to produce 2Cu(I). The negative electrolyte is then recirculated to the negative electrolyte tank 6 through the pipe 27 and the pipe 25 by using the three-way valve 8. Thereby achieving an efficient and low energy consumption transfer of copper ions from the positive electrolyte tank 1 to the positive electrolyte tank 6 by electrochemical means.

[0102] In another embodiment, the positive electrolyte from the positive electrolyte tank 1 is pumped through the pipe 17 into the half-cell containing the conductive material 11 by using the three-way valve 3 to connect the pipe 17 to the pipe 20. By applying a positive voltage to the electrode 10, thereby causing a positive voltage on the conductive material 11, any Cu(I) in the positive electrolyte will come into contact with the conductive material 11 and be oxidized to Cu(II) by the conductive material 11. The positive electrolyte then exits the half-cell through the pipe 27 and is recirculated to the positive electrolyte tank 1 by using the three-way valve 8 to connect the pipe 27 to the pipe 22. At the same time this process is occurring, the negative electrolyte from the tank 6 is circulated through the pump 5 to the pipe 19 (which is connected to the pipe 21 by using the three-way valve 21) into the half-cell containing the conductive material 15. A negative voltage is subsequently applied to the electrode 13, thereby causing a negative voltage to be applied to the conductive material 15. The negative electrolyte is pumped into the system containing a mixture of Cu(I) and Cu(II) species, and by the negative voltage applied to the conductive material 15, the Cu(I) and Cu(II) species are reduced to metallic copper and deposited on the conductive material 15. The negative electrolyte now containing a reduced amount of copper species is returned to the electrolyte tank 6 by using the three-way valve 7 to connect the pipe 26 and the pipe 24. At this point, the positive electrolyte in the positive electrolyte tank 1 contains an excess of Cu(II) ions, while some copper from the negative electrolyte is deposited on the conductive material 11. To proceed to the next step, the pump 2 and the pump 5 are turned off, and the three-way valve 3 and the three-way valve 8 are closed. The electrolyte containing the excess Cu(II) is now circulated through the pipe 16 using the pump 2 to the pipe 21 by switching the three-way valve 4 above the conductive material 15. The excess Cu(II) species in the positive electrolyte then reacts with the copper from the negative electrolyte deposited on the conductive material 15 to form 2Cu(I) species by the well-known disproportionation reaction. At this point, the positive electrolyte containing an increased amount of copper is circulated back to the positive electrolyte tank by using the switching of the three-way valve 7 through the pipe 26 and the pipe 23. Thus, copper ions are efficiently and with low energy consumption transferred from the negative electrolyte in the tank 6 to the positive electrolyte in the tank 1.

[0103] Charge state assessment

[0104] In another embodiment, the positive electrolyte from tank 1 is circulated through the use of pump 2 through the use of three-way valve 3 through conduit 17 into conduit 20 into the half-cell containing conductive material 11. A positive potential is applied to electrode 10 resulting in a positive voltage on conductive material 11 and the positive electrolyte containing a mixture of Cu(I) and Cu(II) is subsequently oxidized to Cu(II) and recirculated back to the positive electrolyte tank 1 through the use of three-way valve 8 through conduit 27 and conduit 22. Likewise, the negative electrolyte from tank 6 is circulated through the use of pump 5 through the use of three-way valve 4 through conduit 19 and conduit 21 into the half-cell containing conductive material 14. A negative potential is applied to electrode 13 resulting in a negative potential on conductive material 15 and the negative electrolyte containing a mixture of Cu(I) and Cu(II) is subsequently reduced to metallic copper and deposited on conductive material 15. At this point, the circulation pump 5 is stopped and three-way valves 3 and 8 are closed, essentially trapping a finite amount of positive electrolyte within the half-cell. The negative electrolyte continues to circulate and current is applied until all of the positive electrolyte trapped within the half-cell is fully oxidized to Cu(II), which is indicated by a sharp rise in the cell voltage. At this point, zero current is applied and the open circuit voltage is measured and then using the Nernst equation, an approximate concentration of Cu(II) in the positive electrolyte can be determined.

[0105] In another embodiment, the positive electrolyte from tank 1 is circulated through the use of pump 2 through the use of three-way valve 3 through conduit 17 into conduit 20 into the half-cell containing conductive material 11. A positive potential is applied to electrode 10 resulting in a positive voltage on conductive material 11 and the positive electrolyte containing a mixture of Cu(I) and Cu(II) is subsequently oxidized to Cu(II) and recirculated back to the positive electrolyte tank 1 through the use of three-way valve 8 through conduit 27 and conduit 22. Likewise, the negative electrolyte from tank 6 is circulated through the use of pump 5 through the use of three-way valve 4 through conduit 19 and conduit 21 into the half-cell containing conductive material 14. A negative potential is applied to electrode 13 resulting in a negative potential on conductive material 15 and the negative electrolyte containing a mixture of Cu(I) and Cu(II) is subsequently reduced to metallic copper and deposited on conductive material 15. At this point, the circulation pump 5 is stopped and three-way valves 3 and 8 are closed, essentially trapping a finite amount of positive electrolyte within the half-cell. The negative electrolyte continues to circulate and current is applied until all of the positive electrolyte trapped within the half-cell is fully oxidized to Cu(II), which is indicated by a sharp rise in the cell voltage. At this point, zero current is applied and the open circuit voltage is measured and then using the Nernst equation, an approximate concentration of Cu(II) in the positive electrolyte can be determined.

[0106] In another embodiment, the positive electrolyte from tank 1 is circulated through the use of pump 2 through the use of three-way valve 3 through pipe 17 to pipe 20 into the half-cell containing the conductive material 11. A negative potential is applied to the electrode 10 causing the conductive material 11 to take on a negative potential and subsequently the positive electrolyte containing a mixture of Cu(I) and Cu(II) is reduced to metallic copper and deposited on the conductive material 11 which is recirculated through the use of three-way valve 8 through pipe 27 and pipe 22 to the positive electrolyte tank 1. Likewise, the negative electrolyte from tank 6 is circulated through the use of pump 5 through the use of three-way valve 4 through pipe 19 and pipe 21 into the half-cell containing the conductive material 14. A positive potential is applied to the electrode 13 causing the conductive material 15 to take on a positive potential and subsequently the negative electrolyte containing a mixture of Cu(I) and Cu(II) is oxidized to Cu(II). At this point, the circulation pump 2 is stopped and the three-way valve 4 and three-way valve 7 are closed, effectively trapping a finite amount of negative electrolyte within the half-cell. The positive electrolyte is continued to be circulated and a current is applied until all of the negative electrolyte trapped within the half-cell is oxidized to Cu(II) as indicated by a sharp rise in the cell voltage. At this point the current is applied and the open circuit voltage is measured and then using the Nernst equation, the approximate concentration of Cu(II) in the positive electrolyte can be determined.

[0107] In another embodiment, the positive electrolyte from tank 1 is circulated through the use of three-way valve 4 through pipe 16 to pipe 21 into the half-cell containing the electrode 13. The positive electrolyte is then further circulated through the use of three-way valve 7 through pipe 26 and pipe 24 to the negative electrolyte tank 6. The amount of positive electrolyte moved from tank 1 to tank 6 is measured to achieve the desired volume ratio of positive electrolyte to negative electrolyte. Thereby any volume ratio of positive electrolyte to negative electrolyte can be achieved which would normally change over time due to the osmotic effect.

[0108] In another embodiment, the negative electrolyte from tank 6 is circulated through the use of three-way valve 3 through pipe 18 and pipe 20 to the half-cell containing the electrode 10. The negative electrolyte is then recirculated through the use of three-way valve 8 through pipe 27 and pipe 22 to the positive electrolyte tank 1. The amount of negative electrolyte moved from tank 6 to tank 1 is measured to achieve the desired volume ratio of negative electrolyte to positive electrolyte. Thereby any volume ratio of positive electrolyte to negative electrolyte can be achieved which would normally change over time due to the osmotic effect.

[0109] It is to be understood that the term “positive electrolyte tank” can refer to a first tank for receiving an electrolyte, the term “electrolyte” can refer to a positive electrolyte or a negative electrolyte, generally referring to the combination of a positive electrolyte with a positive electrolyte tank. Likewise, the term “negative electrolyte tank” can refer to a second tank for receiving an electrolyte, the term “electrolyte” can refer to a positive electrolyte or a negative electrolyte, generally referring to the combination of a negative electrolyte with a negative electrolyte tank.

[0110] It is to be understood that the terms “first half-cell” and “second half-cell” can refer to a chamber.

[0111] The terms “only negative electrolyte tank is in fluid connection with the second half-cell” and “only the second tank is in fluid connection with the second half-cell” used herein and hereafter can refer to the case where only the negative electrolyte tank (of the negative electrolyte tank and the positive electrolyte tank) is in fluid connection with the second half-cell, i.e. the positive electrolyte tank is not in fluid connection with the second half-cell, while only the negative electrolyte tank is in fluid connection with the second half-cell. Similarly, the terms “only positive electrolyte tank is in fluid connection with the first half-cell” and “only the first tank is in fluid connection with the first half-cell” used herein and hereafter can refer to the case where only the positive electrolyte tank (of the negative electrolyte tank and the positive electrolyte tank) is in fluid connection with the first half-cell, i.e. the negative electrolyte tank is not in fluid connection with the first half-cell, while only the positive electrolyte tank is in fluid connection with the first half-cell. Thus, the use of “only” with “negative electrolyte tank” (second tank) or “positive electrolyte tank” (first tank) can refer to the specified tank of the available tanks being in fluid connection with the specified half-cell of the available half-cells only.

[0112] What customer problem does your invention / idea plan to solve?

[0113] Due to the unstable supply of fossil fuel energy in Europe, energy insecurity is increasing, and there is a need to increase energy storage capacity to promote the transformation of the energy industry to renewable energy. Although aqueous all-copper redox flow batteries can store electrical energy during periods of low energy consumption, such technologies often suffer from capacity loss over time, and the present disclosure seeks to address this issue through a continuous electrochemical rebalancing system. The present disclosure aims to develop an electrical power storage technology stack that can store large amounts of electrical energy for time-shifting, load balancing, and backup power systems at remote locations or facilities, and maintain a high level of energy storage for a longer period of time.

[0114] How does your invention / idea solve this problem?

[0115] The capacity loss in the system occurs due to the imbalance in the distribution of active copper species between electrolytes. Using the unique properties of copper, we can continuously remove excess copper in one electrolyte as metallic copper while oxidizing copper in a second electrolyte to a copper species that can dissolve metallic copper. Then, by contacting the metallic copper with the copper species in the second electrolyte, the copper will redissolve, and thus we can effectively transfer copper from one electrolyte to another, effectively rebalancing the system and restoring the capacity lost due to the imbalance. This allows us to continuously correct and mitigate capacity loss, ensuring that the system is always able to achieve optimal capacity, avoiding downtime due to the non-continuous rebalancing techniques presented in this document.

[0116] What are the benefits to the customer?

[0117] The benefits gained by the customer depend on their individual needs and use cases. In the case of energy time shifting, customers will store excess energy during high production periods and resell it during high demand periods. The technology described in this document will allow customers to ensure that the system is always running at peak or near-peak storage capacity, ensuring that the equipment is getting the maximum return.

[0118] For users who may use this technology as a backup power source for critical infrastructure, such as cellular networks, they can also ensure that the redox flow battery is running at optimal energy capacity and can easily rebalance to the optimal capacity level continuously. That is, without the need for downtime maintenance, as it can pose a risk if done while the equipment is needed to provide backup power. Additionally, the technology also allows end users to replace older systems that have a greater environmental impact, such as backup diesel generators.

[0119] In all these cases, the aqueous full copper redox flow battery equipped with the additional electrochemical rebalancing technology allows users to invest in a long-term and long-service-life energy storage system. Compared to lithium-ion backup power devices, the redox flow battery has a significantly longer service life, as lithium-ion backup power devices cannot regenerate capacity once the capacity falls below the minimum viable capacity.

[0120] How big is the whole market? What is the growth rate per year in the future? Please describe the first customer you assume?

[0121] Depending on the source from which you get your information, Allied Market Research estimates the redox flow battery market size to be $1.3 billion in 2018 and projects it to grow at a CAGR of 15.2% to reach $4.03 billion by 2026. Market and Markets estimates the redox flow battery market slightly higher, projecting it to grow at a CAGR of 18% to reach $2.14 billion by 2021 and $4.89 billion by 2026. According to MarketWatch, redox flow batteries can replace a portion of the uninterruptible power supply market, which is projected to reach $140.3 billion by 2023.

[0122] The first assumed customer would be end users controlling critical infrastructures such as telecommunications and power generation, and possible specific end users are Telia Oy, Fortum Oy, and Caruna Oy. For Fortum Oy and Caruna Oy, the technology could act as a backup power source for telecommunications and load balancing.

[0123] How is this problem currently solved? What are the alternative competitors (companies, products, technologies)? How are you different from your competitors?

[0124] There are few viable options for large-scale energy storage, mainly including hydroelectric storage, lithium-ion battery storage, and redox flow battery storage. As for hydroelectric storage, the technology is limited by geographical conditions, usually has a large environmental impact, and requires a large initial investment. Lithium-ion batteries can also be used as backup power systems, but they are usually not suitable for time-shifting or load balancing operations because they have a limited number of cycles and their capacity decreases significantly.

[0125] More direct competitors are vanadium redox flow batteries and iron-chromium redox flow batteries. The former has a higher cost associated with vanadium, equipment, and materials, is difficult to rebalance the vanadium system to maintain high energy storage capacity, and is sensitive to temperature during operation, complicating its application in high-temperature areas. As for iron-chromium redox flow batteries, due to their operating potential, they have a lower efficiency, waste energy to produce hydrogen and oxygen during charging, and more importantly, the oxidation state of the chromium element has a serious harmful effect on health. In addition, for both vanadium and iron-chromium systems, there is a significant amount of work to dispose of the electrolyte after the plant is decommissioned, and the electrolyte poses a high environmental and health risk.

[0126] All copper redox flow battery systems are different in that copper is significantly less expensive than vanadium (3 to 6 times less) and because of the existing copper recycling infrastructure, all the copper can be recycled at minimal cost and resold or used for other applications if the system reaches its useful life. Additionally, copper systems operate at lower voltages, so there is less efficiency loss because the system does not typically produce hydrogen or oxygen gas as a byproduct during charging. More importantly, for the purposes of this disclosure, the unique chemistry of copper allows us to easily rebalance the system to continuously proactively restore lost capacity without the need for complex rebalancing procedures or system downtime.

[0127] 7.1. What customer problems do you plan to solve with your invention / idea?

[0128] Due to the instability of fossil fuel energy supply in Europe, energy insecurity is increasing, and there is a need to increase energy storage capacity to drive the energy industry to renewable energy transformation. Although aqueous all-copper redox flow batteries can store electrical energy during periods of low energy consumption, such technologies often suffer from capacity loss over time, and the present disclosure seeks to address this issue through a continuous electrochemical rebalancing system. The present disclosure aims to develop an electrical power storage technology stack that can store large amounts of electrical energy for time-shifting, load balancing, and backup power systems in remote locations or facilities, and maintain high energy storage levels over a long period of time.

[0129] 7.2. How does your invention / idea solve the problem?

[0130] Capacity loss in the system occurs due to the imbalance in the distribution of active copper species between the electrolytes. Taking advantage of the unique properties of copper, we can continuously remove excess copper in one electrolyte in the form of metallic copper, while oxidizing copper in the second electrolyte to a copper species that can dissolve metallic copper. Then, by contacting the metallic copper with the copper species in the second electrolyte, the copper will redissolve, so we can effectively transfer copper from one electrolyte to another, effectively rebalancing the system and restoring the capacity lost due to imbalance. This allows us to continuously correct and mitigate capacity loss to ensure that the system always reaches optimal capacity, avoiding downtime due to the non-continuous rebalancing techniques presented herein.

[0131] 7.3. What benefits are there for customers?

[0132] The benefits customers gain depend on their individual needs and use cases. In the case of energy time-shifting, customers will store excess energy during periods of high production and resell it during periods of high demand, and the technology described herein will allow customers to ensure that the system is always operating at peak or near-peak storage capacity, ensuring maximum returns for the equipment.

[0133] For users who can use this technology as a backup power source for critical infrastructure (e.g. cellular networks), they can also ensure that the redox flow battery is operated at the optimal energy capacity and can easily rebalance to the optimal capacity level continuously. That is, there is no need for downtime for maintenance, as it can be risky if maintenance is performed when the device is needed to provide backup power. In addition, this technology also allows end users to replace old systems that have a greater impact on the environment, such as backup diesel generators.

[0134] In all these cases, the aqueous all-copper redox flow battery equipped with additional electrochemical rebalancing technology enables users to invest in long-term and long-service-life energy storage systems. Compared with lithium-ion backup power devices, the service life of redox flow batteries is greatly extended, and lithium-ion backup power devices cannot regenerate capacity when the capacity is below the minimum feasible capacity.

[0135] 7.4. How do you make money? What do you sell? Who are your customers?

[0136] There are many different ways to make money using this technology, the simplest being to license the technology to existing redox flow battery manufacturers, of which there are many.

[0137] The second way is to manufacture redox flow batteries and sell them to end users, who are often renewable energy companies that want to store excess energy during low-price periods rather than sell it during high-price periods. Other end users include those who must safeguard critical infrastructure during possible power outages, such as telecommunications, defense contractors, and healthcare providers.

[0138] The third way is to manufacture self-use redox flow batteries to store energy during periods of energy overproduction, and then sell the energy back to the grid at a higher price during periods of high demand.

[0139] 7.6. How is this problem currently solved? What are the alternative competitors (companies, products, technologies)? How are you different from the competitors?

[0140] There are few viable options for large-scale energy storage, including hydroelectric storage, lithium-ion battery storage, and redox flow battery storage. As for hydroelectric storage, this technology is limited by geographical conditions, often has a greater impact on the environment, and requires a large initial investment. Lithium-ion batteries can also be used as backup power systems, but are generally not suitable for time-shifting or load balancing operations, as they have a limited number of cycles and a significant drop in capacity.

[0141] More direct competitors are vanadium redox flow batteries and iron-chromium redox flow batteries. The former has higher costs related to vanadium, equipment, and materials, making it difficult to rebalance the vanadium system to maintain high energy storage capacity. Furthermore, it is temperature-sensitive during operation, complicating its application in high-temperature regions. As for iron-chromium redox flow batteries, their efficiency is lower due to their limited operational potential. They waste energy and produce hydrogen and oxygen during charging, and more importantly, the oxidized state of chromium can have serious harmful health effects. In addition, both vanadium and iron-chromium systems require significant electrolyte disposal after plant decommissioning, and the electrolytes pose high environmental and health risks.

[0142] All-copper redox flow battery systems differ because copper is significantly cheaper than vanadium (3 to 6 times cheaper), and due to existing copper recycling infrastructure, all copper can be recovered at minimal cost and resold or used for other applications once the system reaches the end of its lifespan. Furthermore, copper systems operate at lower voltages, resulting in less efficiency loss, as the system typically does not produce hydrogen or oxygen as byproducts during charging. More importantly, for the purposes of this disclosure, the unique chemistry of copper allows for easy rebalancing of the system to continuously and actively recover lost capacity without complex rebalancing procedures or system downtime.

Claims

1. An apparatus for electrochemically balancing electrolytes of a redox flow battery, wherein the battery comprises a first half-cell and a second half-cell separated by a separator (12), wherein the apparatus comprises: a first tank (1) for receiving an electrolyte; a second tank (6) for receiving an electrolyte; a plurality of connection conduits (16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27) for passing electrolytes therethrough; a first pump (2) and a second pump (5) for pumping electrolytes, wherein the first pump (2) is configured to pump electrolytes between the first tank (1), the first half-cell, the second half-cell and / or the second tank (6), and wherein the second pump (5) is configured to pump electrolytes between the second tank (6), the second half-cell, the first half-cell and / or the first tank (1); and four three-way valves (3, 4, 7, 8) configured to provide fluid connections between the first tank (1), the second tank (6) and / or the redox flow battery together with the plurality of connection conduits and the first pump and / or the second pump.

2. The apparatus according to claim 1, wherein the four three-way valves comprise a first three-way valve (3), a second three-way valve (4), a third three-way valve (8) and a fourth three-way valve (7), wherein the first three-way valve (3) is configured to pass electrolytes between the first tank (1) and / or the first half-cell and / or the second tank (6), the second three-way valve (4) is configured to pass electrolytes between the first tank (1) and / or the second half-cell and / or the second tank (6), the third three-way valve (8) is configured to pass electrolytes between the first tank (1) and / or the first half-cell and / or the second tank (6), and the fourth three-way valve (7) is configured to pass electrolytes between the first tank (1) and / or the second half-cell and / or the second tank (6).

3. The apparatus according to any of the preceding claims, wherein the first pump (2) is configured to pump electrolytes from the first tank (1) through the first three-way valve (3), at least two connection conduits (17, 18) of the plurality of connection conduits and the first half-cell, and to pump electrolytes from the first tank (1) through the second three-way valve (4), at least two connection conduits (16, 21) of the plurality of connection conduits and the second half-cell; and the second pump (5) is configured to pump electrolytes from the second tank (6) through the second three-way valve (4), at least two connection conduits (19, 21) of the plurality of connection conduits and the second half-cell, and to pump electrolytes from the second tank (6) through the first three-way valve (3), at least two connection conduits (18, 20) of the plurality of connection conduits and the first half-cell; wherein The first half-cell is configured to be fluidly connected to the first tank (1) via a connection pipe (27, 22) of the plurality of connection pipes by a third three-way valve (8) and to the second tank (6) via a connection pipe (27, 25) of the plurality of connection pipes by the third three-way valve (8), and wherein the second half-cell is configured to be fluidly connected to the second tank (6) via a connection pipe (26, 24) of the plurality of connection pipes by a fourth three-way valve (7) and to the first tank (1) via a connection pipe (26, 23) of the plurality of connection pipes by the fourth three-way valve (7).

4. The device according to any of the preceding claims, wherein the first redox flow cell comprises a first electrode (10), an electrically conductive material (11) and a non- conductive separator (9); and the second redox flow cell comprises a second electrode (13), an electrically conductive material (15) and a non-conductive separator (14).

5. The device according to any of the preceding claims, wherein the device further comprises means for applying a voltage to the redox flow battery.

6. The device according to any of the preceding claims, wherein the device further comprises means for measuring the content of a relative conductive species, such as a copper species, in the electrolyte.

7. The device according to claim 6, wherein the means for measuring the relative conductive species is means for determining the weight of the first tank and / or the second tank.

8. The device according to claim 6, wherein the means for measuring the relative conductive species is means for determining the volume of the electrolyte in the first tank and / or the electrolyte in the second tank.

9. The device according to any of the preceding claims, wherein the electrolyte comprises or consists of a copper species, a zinc species, a bromine species and / or an iron species, preferably the electrolyte comprises or consists of a copper species.

10. The device according to any of the preceding claims, wherein the redox flow battery is a copper-based redox flow battery.

11. A redox flow battery system, comprising: a redox flow battery comprising: a first half-cell for receiving an electrolyte and comprising a first electrode (10), an electrically conductive material (11) and a non-conductive separator (9); and a second half-cell for receiving an electrolyte and comprising a second electrode (13), an electrically conductive material (15) and a non-conductive separator (14), wherein the first half-cell and the second half-cell are separated by a separator (12); and a device according to any of claims 1 to 10.

12. The redox flow battery system according to claim 11, wherein the device and / or the redox flow battery, for example in the first half-cell and the second half-cell and / or in the first tank and the second tank, further comprises an electrolyte.

13. The redox flow battery system according to claim 11 or 12, wherein the system further comprises a power source removably attached to the system for applying a voltage to the redox flow battery, preferably to the first electrode and the second electrode.

14. A method of determining the relative state of charge of a redox flow battery, wherein the method comprises: i) providing a redox flow battery system according to any one of claims 11 to 13, wherein the device is configured to be fluidly connected to the redox flow battery; ii) providing the redox flow battery system with electrolyte, preferably with electrolyte to the first tank and the second tank of the device; iii) providing electrolyte from the first tank through the first half-cell and electrolyte from the second tank through the second half-cell, or electrolyte from the second tank through the first half-cell and electrolyte from the first tank through the second half-cell, preferably by pumping with the first pump and the second pump; iv) applying a negative potential to the first electrode and a positive potential to the second electrode, or applying a positive potential to the first electrode and a negative potential to the second electrode, thereby causing reduction of the electrically conductive species of the electrolyte in the half-cell comprising the electrode to which the negative potential is applied, and thereby causing deposition of electrically conductive species, preferably metallic copper species, on the electrically conductive material comprised in the half-cell comprising the electrode to which the negative potential is applied, and oxidation of at least a portion of the electrically conductive species of the electrolyte in the half-cell comprising the electrode to which the negative potential is applied on the electrically conductive material comprised in the half-cell comprising the electrode to which the negative potential is applied, preferably oxidation of the electrically conductive species of the electrolyte in the half-cell comprising the electrode to which the negative potential is applied to Cu(II); v) stopping the application of voltage to the first electrode and the second electrode; and vi) measuring the open circuit voltage of the device, thereby determining the state of charge of the electrolyte.

15. The method according to claim 14, wherein, in iii) the three-way valve is arranged such that only the second tank is fluidly connected to the first half-cell, and electrolyte is provided from the second tank through the first half-cell, preferably by pumping with the second pump, and the three-way valve is arranged such that only the first tank is fluidly connected to the second half-cell, and electrolyte is provided from the first tank through the second half-cell, preferably by pumping with the first pump; and in iv) a negative potential is applied to the first electrode, thereby causing reduction of the electrically conductive species of the electrolyte in the first half-cell, and thereby causing deposition of electrically conductive species, preferably metallic copper species, on the electrically conductive material (1 1 ); and a positive potential is applied to the second electrode, thereby oxidizing at least a portion of the electrically conductive species of the electrolyte in the second half-cell on the electrically conductive material (15), preferably oxidizing the electrically conductive species of the electrolyte in the second half-cell to Cu(II), or a negative potential is applied to the second electrode, thereby causing reduction of the electrically conductive species of the electrolyte in the second half-cell, and thereby causing deposition of electrically conductive species, preferably metallic copper species, on the electrically conductive material (15); and a positive potential is applied to the first electrode, thereby oxidizing at least a portion of the electrically conductive species of the electrolyte in the first half-cell on the electrically conductive material (1 1 ), preferably oxidizing the electrically conductive species of the electrolyte in the first half-cell to Cu(II).

16. The method according to claim 14, wherein, ​ In iii) the three-way valve is arranged so that only the first tank is in fluid connection with the first half-cell and electrolyte is provided from the first tank through the first half-cell, preferably by pumping with the first pump; and the three-way valve is arranged so that only the second tank is in fluid connection with the second half-cell and electrolyte is provided from the second tank through the second half-cell, preferably by pumping with the second pump; and, In iv) a negative potential is applied to the first electrode, thereby causing reduction of the electrically conductive species of the electrolyte in the first half-cell and thereby causing electrically conductive species, preferably metallic copper species, to be electrodeposited on the electrically conductive material (11); and a positive potential is applied to the second electrode, thereby oxidizing at least a portion of the electrically conductive species of the electrolyte in the second half-cell on the electrically conductive material (15), preferably oxidizing the electrically conductive species of the electrolyte in the second half-cell to Cu(II), or a negative potential is applied to the second electrode, thereby causing reduction of the electrically conductive species of the electrolyte in the second half-cell and thereby causing electrically conductive species, preferably metallic copper species, to be electrodeposited on the electrically conductive material (15); and a positive potential is applied to the first electrode, thereby oxidizing at least a portion of the electrically conductive species of the electrolyte in the first half-cell on the electrically conductive material (11), preferably oxidizing the electrically conductive species of the electrolyte in the first half-cell to Cu(II).

17. The method according to any one of claims 14-16, wherein in iii) the three-way valve is arranged so that electrolyte is provided from the first tank through the first half-cell and back to the first tank, and electrolyte is provided from the second tank through the second half-cell and back to the second tank, or electrolyte is provided from the second tank through the first half-cell and back to the second tank, and electrolyte is provided from the first tank through the second half-cell and back to the first tank.

18. The method according to any one of claims 14-17, wherein iv) further comprises ending the provision of electrolyte from the first tank through the first half-cell, preferably by ending the pumping of the first pump and / or arranging the three-way valve so that only the second tank is in fluid connection with the second half-cell, while the first tank is not in fluid connection with the first half-cell; and providing electrolyte from the second tank through the second half-cell; and v) stopping the application of voltage to the first and second electrodes when substantially all of the electrolyte trapped in the first half-cell is oxidized, preferably when the electrolyte trapped in the first half-cell comprising Cu(I) and Cu(II) is fully oxidized to Cu(II).

19. The method according to any one of claims 14-18, wherein iv) further comprises ending the provision of electrolyte from the second tank through the second half-cell, preferably by ending the pumping of the second pump and / or arranging the three-way valve so that only the first tank is in fluid connection with the first half-cell, while the second tank is not in fluid connection with the second half-cell; and providing electrolyte from the first tank through the first half-cell; and v) stopping the application of voltage to the first and second electrodes when substantially all of the electrolyte trapped in the second half-cell is oxidized, preferably when the electrolyte trapped in the second half-cell comprising Cu(I) and Cu(II) is fully oxidized to Cu(II). ​ 20. A method of electrochemically rebalancing an electrolyte of a redox flow battery, wherein the method comprises: i) providing a redox flow battery system according to any one of claims 11 to 13, wherein the device is configured to be in fluid connection with the redox flow battery; ii) providing the electrolyte to the redox flow battery system, preferably to the first tank and the second tank of the device; iii) providing the electrolyte from the first tank to the first half-cell and from the second tank to the second half-cell, or from the second tank to the first half-cell and from the first tank to the second half-cell, preferably by pumping with the first pump and the second pump; iv) applying a negative potential to the first electrode and a positive potential to the second electrode, or applying a positive potential to the first electrode and a negative potential to the second electrode, thereby causing reduction of the electrically conductive species of the electrolyte in the half-cell comprising the electrode to which the negative potential is applied, and thereby causing electro-deposition of the electrically conductive species, preferably a metallic copper species, on the electrically conductive material comprised in the half-cell comprising the electrode to which the negative potential is applied, and oxidation of at least a part of the electrically conductive species of the electrolyte in the half-cell comprising the electrode to which the negative potential is applied on the electrically conductive material comprised in the half-cell comprising the electrode to which the negative potential is applied, preferably oxidation of the electrically conductive species of the electrolyte in the half-cell comprising the electrode to which the negative potential is applied to Cu(II); v) stopping the application of the voltage to the first electrode and the second electrode; and viii) arranging the three-way valve such that only the first tank is in fluid connection with the first half-cell, and providing the electrolyte from the first tank through the first half-cell, preferably by pumping with the first pump, thereby dissolving the electro-deposited electrically conductive species, preferably metallic copper, and reducing Cu(II) to Cu(I), or arranging the three-way valve such that only the second tank is in fluid connection with the first half-cell, and providing the electrolyte from the second tank to the first half-cell, preferably by pumping with the second pump, thereby dissolving the electro-deposited electrically conductive species, preferably metallic copper, and reducing Cu(II) to Cu(I).

21. The method according to any one of claims 14-20, wherein the method further comprises: ix) measuring the content of the relative electrically conductive species, such as copper species, in the electrolyte, thereby obtaining a result value.

22. The method according to claim 21, wherein in ix) the measuring of the relative electrically conductive species is determining the weight of the first tank and / or the second tank, thereby obtaining one or more result values.

23. The method according to claim 21, wherein in ix) the measuring of the relative electrically conductive species is determining the volume of the electrolyte in the first tank and / or the electrolyte in the second tank, thereby obtaining one or more result values.

24. The method according to any one of claims 21-23, wherein the method further comprises: x) comparing the measured result value(s) with a predetermined value; xi) if the measured result value(s) is / are equal to or lower than the predetermined value, providing the electrolyte from the first tank to the second tank, or if the measured result value(s) is / are higher than the predetermined value, providing the electrolyte from the second tank to the first tank.

25. The method according to any one of claims 21-24 for continuous electrochemical rebalancing of an electrolyte of a redox flow battery, wherein the method comprises two or more times the procedures of iii) to xi).

26. A method of rebalancing an electrolyte of a redox flow battery system, wherein the method comprises: i) providing a redox flow battery system according to any one of claims 11 to 13, wherein the device is configured to be in fluid connection with the redox flow battery; ii) providing an electrolyte to the redox flow battery system, preferably to the first tank and the second tank of the device; iii) providing the electrolyte from the first tank through the first half-cell or the second half-cell to the second tank, preferably by pumping through the first pump, or providing the electrolyte from the second tank through the second half-cell or the first half-cell to the first tank, preferably by pumping through the second pump.

27. The method according to claim 26, wherein in iii) the three-way valves are arranged such that the first tank is in fluid connection with the second tank only via the first three-way valve (3), the first half-cell, the third three-way valve (8) and the connecting conduits (17, 20, 27, 25), or such that the first tank is in fluid connection with the second tank only via the second three-way valve (4), the second half-cell, the fourth three-way valve (7) and the connecting conduits (16, 21, 26, 24).

28. Use of the device according to any one of claims 1-10 for determining the relative state of charge of a redox flow battery, preferably a copper-based redox flow battery, for determining the relative amount of a conducting species, such as a copper species, in an electrolyte, for maintaining the electrolyte volume of an electrolyte used in a redox flow battery, preferably using copper as the main active species, and for electrochemical rebalancing, preferably continuous electrochemical rebalancing, of an electrolyte.

29. Use of the redox flow battery system device according to any one of claims 11 to 13 for storing energy for time shifting, load balancing and backup power systems.

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