NO344360B1

NO344360B1 - Rechargeable iron-ion battery

Info

Publication number: NO344360B1
Application number: NO20180939A
Authority: NO
Inventors: Yansong Zhao; Yingpeng Zhen; Tobias Boström; Stefano Passerini; Dominic Bresser; Arianna Moretti
Original assignee: Univ I Tromsoe Norges Arktiske Univ
Priority date: 2018-07-03
Filing date: 2018-07-03
Publication date: 2019-11-18
Also published as: WO2020007911A1

Description

Technical Field

The present invention relates to a rechargeable iron-ion battery cell.

Background

Lithium (Li) based batteries are important as energy storage devices nowadays. However, Li based batteries have many disadvantages such as high cost, low safety, low Li abundance in the earth, etc. According to the literatures, a shortage of Li is possible in the near future, possibly within 65 years. Therefore, many researchers try to develop new types of batteries to replace Li based batteries, including sodium (Na) battery, and magnesium (Mg) battery. However, the cost of the Na battery and Mg battery is still high. Actually, iron (Fe) is the cheapest metal among all the metallic materials. In addition, there are plenty of mineable Fe in the earth, ca. 230 billion tons, which is about 15 000 times as high as the amount of mineable Li in the earth. If the consumption of the amount of Fe is the same as the amount of Li, the nowadays mineable Fe can be utilized for as long as ca. 1 million years for ironion (Fe-ion) battery fabrication is it replaces all the Li-ion batteries. The element abundance of Fe ranks number 1 in the universe and number 2 in the earth among the metallic elements. It means that there are plenty of Fe in the nature for Fe-ion battery fabrication.

Ionic liquids are types of salts. Many of ionic liquids are liquid at room temperature. Furthermore, many ionic liquids are liquid at temperatures as low as -60 °C and can be utilized in cold climate areas. The phase behavior of ionic liquids can be controlled by polarity modulation and they have a favorable solubility in inorganic and organic chemicals. Their chemical and functional groups can be designed to form task-specific ionic liquids.

Ionic liquids are regarded as green solvents, and are widely utilized in CO2capture and storage, extraction and separation processes, catalysis, nanoscience, petroleum science, cellulose science and biotechnology.

Ionic liquids have a number of favorable characteristics, including: (1) a vapor pressure that is either nonexistent or very low, (2) non-flammability or fireretarding properties, (3) ionic conductivity, (4) a higher decomposition voltage than water, (5) a broader liquid temperature range than water, and (6) handleability in air.

Such characteristics are put to good use by employing these ionic liquids as electrolytes capable of being utilized at room temperature or lower in a variety of applications, including the electrodeposition of metals or alloys, electrolytic plating baths and as solvents for organic synthesis electrolytes for energy storing electrochemical devices including solar cells, batteries and supercapacitors.

WO 2017/106337 A1 discloses a s-ion battery that includes: 1) an anode including a metal; 2) a cathode; and 3) an ionic liquid electrolyte disposed between the anode and the cathode, wherein the ionic liquid electrolyte corresponds to a mixture of a metal halide and an organic compound, wherein the metal is aluminum.

US 20140342249 A1 discloses a rechargeable Li-ion cell comprising a cathode having a cathode active material and/or a conductive supporting structure, an anode having an anode active material and/or a conductive supporting nano-structure, a porous separator electronically separating the anode and the cathode, a highly concentrated electrolyte in contact with the cathode active material and the anode active material, wherein the electrolyte contains a lithium salt dissolved in an ionic liquid solvent.

The main object of the present invention is to provide a battery that can replace the existing Li-based batteries, and improve the performance of battery, supercapacitor and concentration cell.

Another object of the present invention is to provide a magnetic battery, and a magnetic supercapacitor.

Another object of the present invention is to provide ionic liquids based magnetic electrolytes.

Another object of the present invention is to increase the utilization degree of intermitted renewable energy sources.

Another object of the present invention is to provide a low-cost and high safety battery.

Another object of the present invention is to provide an energy storage battery for wireless charging smart road.

Summary of the invention

The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention.

The present invention provides an iron-ion (Fe-ion) battery, a magnetic battery, and a magnetic supercapacitor. The Fe-ion battery can be utilized in stationary energy storage device in buildings, railways, road, and large scale renewable energy storage systems. Fe-ion batteries with high capacity, such as a specific charge/discharge capacity being higher than 200 mAh/g, can be utilized in inter alia wireless charging smart road, electrical cars, electric ships, mobile devices, and space technology.

In addition, Fe-ion battery is a highly safe battery, which is much safer than Li-ion battery.

The present invention concerns a rechargeable or secondary Fe-ion battery comprising an iron-containing electrolyte. The iron-ion can be obtained from the electrolyte itself and/or from the anode or the cathode.

The Fe-ion battery cell according to the present invention comprises:

- an anode,

- a cathode, and

- an electrolyte interposed between the anode and the cathode, wherein the electrolyte transports Fe-ions between said anode and cathode.

The term “Fe-ion” should be interpreted as an ion containing Fe element, such as Fe<2+>, Fe<3+>, FeCl4-, FeCl2<+>, FeO4<2->, FeO4<3->, FeO2-, etc.

Due to plenty of Fe-element in the earth and the universe, the Fe-ion battery is a low-cost battery. In addition, the Fe-ion batteries of the present invention are safe batteries compared to for example existing Li-ion batteries. The anode and cathode are selected from materials that are not oxygen or water sensitive.

The electrolyte separates the anode and the cathode preventing short-circuit of the battery cell. Further, the electrolyte contains Fe-ions itself or comprises Fe-ions dissolved in the electrolyte during use. The electrolyte does not allow a significant flow of electrons which causes the electrons to flow in an external circuit with electrons following the same direction as the positive Fe-ions to maintain charge neutrality.

During discharging, the positive Fe-ions move from the negative electrode, anode, and enters the positive electrode, cathode, through the electrolyte. During charging, potential energy builds up by applying a voltage to the cell, and the complete opposite process occurs being that the positive Fe-ions move from the cathode to the anode.

In an embodiment of the invention the anode comprises carbon which may by in the form of graphite, graphene or nanotube carbon, such as multi-walled carbon nanotube. During charging of the battery Fe-ions undergo chemical intercalation within the anode creating iron intercalated graphite, graphene or nanotube carbon depending on the selected material of the anode. When the battery is in a discharged state, the anode has no or very little iron in it.

In order to have an acceptable capacity for the battery, it may be necessary to have a current collector, which is usually a metal grid or sheet, to provide a conducting path to minimize the resistance of the battery. The current collector also acts as a substrate being a physical support for the anode material which often is a brittle structure.

Thus, in an embodiment of the present invention, the anode material may be a coating material arranged on the surface of a substrate material. The substrate material is preferably a current collector. In a preferred embodiment the substrate material is not in contact with the electrolyte.

The current collector material is selected according to its electrical stability window, and chemical and electrochemical stability.

However, there is always a risk that the current collector will come into contact with the electrolyte, thus the current collector should be chosen from materials that will not react significantly with the electrolyte, thereby avoiding destruction of the battery cell if they come into contact. In an embodiment of the invention the current collector is chosen from one of Ni-foil, Fe-foil and Co-foil. In a preferred embodiment the current collector is Ni-foil, which does not undergo any significant chemical reaction with an electrolyte comprising Fe-ions.

The cathode of the battery cell comprises a Fe-containing material which may be selected from at least one of Fe-foil, Fe powder, FeO, Fe2O3-powder, Fe3O4-powder, carbon coated with Fe nanoparticles (C-Fe), Fe3C, FeSO4, Fe(ClO4)2, Fe(C5H5)2, Fe(IO3)3,Ferrate, Ferrite, Fe (-II) compound, Fe (-I), Fe (0) compound, Fe (I) compound, Fe (II) compound, Fe (III) compound, Fe (IV) compound, Fe (V) compound, Fe (VI) compound, or other Fe element-containing materials.

In an embodiment the Fe-containing material is selected from Fe-foil, Fe2O3-powder or carbon coated with Fe nanoparticles (C-Fe),

During discharging of the battery Fe-ions undergo chemical intercalation within the cathode. When the battery is in a charged state, the cathode has no or very little iron in it.

Also, the cathode may be a coating material arranged on the surface of a substrate material preferably being a current collector. Further, the substrate should preferably not come into contact with the electrolyte. The current collector may be the same as described for the substrate/current collector of the anode comprising nickel, such as Ni-foil.

In an embodiment of the invention, the current collector substrate of the anode and cathode comprises a Ni-foil of pure nickel having a thickness in the range from 0.05 to 1.5 mm, preferably from 0.07 to 1.0 mm, more preferably from 0.09 to 0.5 mm, for example 0.1 mm thickness.

Pure nickel or Ni-foil should be understood as a composition having from 50 to 100 wt% Ni.

Fe-foil comprises from 50 to 100 wt% Fe.

Co-foil comprises from 50 to 100 wt% Co.

In an embodiment of the present invention the electrolyte is a so-called conventional electrolyte such as an aqueous solution electrolyte or organic electrolyte. However, the conventional electrolyte must be able to transfer Fe-ions between the cathode and anode. The electrolyte solution may comprise the Fe-ions itself, or the Fe-ions may arrive from the cathode or anode being subjected to a redox reaction.

The electrolyte should be operable over the entire range of temperatures the battery is exposed to. Thus, the electrolyte should be selected from electrolytes being liquid in the temperature range from 5 °C to 25 °C, preferably in the range from -20 °C to 30 °C, more preferably in the range from -40°C to 50 °C, even more preferably in the range from -60 °C to 100 °C. If the electrolyte is not in a liquid state during the operation of the battery, the battery will not work, as the electrolyte will not be able to transfer the Fe-ions between the anode to the cathode.

In an embodiment of the invention the electrolyte comprises an ionic liquid. An ionic liquid electrolyte is not flammable, and not oxygen or water sensitive. Therefore, there is almost no risk of explosion for the Fe-ion battery using ionic liquid based electrolyte. Thus, ionic liquids can be utilized for electrolyte preparation to further improve the safety of Fe-ion battery.

In an embodiment of the invention the electrolyte is selected from ionic liquids having a high thermal stability/decomposition temperature. Preferably the decomposition temperature is higher than 250 °C, more preferably higher than 300 °C, even more preferably higher than 400 °C, for example 459 °C.

In an embodiment of the invention the ionic liquid electrolyte is selected from ionic liquids having a low viscosity in the range from 0.01 to 100 mPa·s at 20 °C, preferably from 5 to 60 mPa·s at 20 °C, more preferably from 10 to 50 mPa·s at 20 °C, even more preferably from 20 to 40 mPa·s at 20°C, for example about 35 mPa·s at 20 °C. Further, the ionic liquid electrolyte should have a viscosity from 0.01 to 90 mPa·s within the operable temperature range of the battery. A low viscosity allows for faster transportation of ions in the liquid.

In an embodiment of the invention the ionic liquid electrolyte is selected from ionic liquids having a high density thereby providing an electrolyte that will take smaller space with the same mass. The density should be in the range from 1.0 to 1.5 g/cm<3>at 20 °C, preferably from 1.1 to 1.4 g/cm<3>at 20 °C, more preferably from 1.2 to 1.4 g/cm<3>at 20 °C, for example about 1.37 g/cm<3>at 20 °C.

In an embodiment of the invention the ionic liquid electrolyte is selected from ionic liquids having a high ionic conductivity, which is above 0.01 mS/cm at 20 °C, preferably above 0.1 mS/cm at 20 °C, more preferably above 0.5 mS/cm at 20 °C, even more preferably above 1.0 mS/cm at 20 °C, for example 8 mS/cm at 20 °C.

In an embodiment of the invention the ionic liquid electrolyte is selected from ionic liquids having an electric window of at least 2 V, preferably of at least 3 V, more preferably of at least 3.5 V, for example 4V.

In an embodiment the electrolyte comprises a pure ionic liquid containing one ionic liquid.

In another embodiment the electrolyte comprises a mixture of different pure ionic liquids.

In another embodiment the electrolyte comprises one or more pure ionic liquid(s) mixed with other solvent(s). The solvent can be selected from at least one of vinyl carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate and methyl ethyl carbonate.

In an embodiment the ionic liquid is selected from an ionic liquid having at least one of the following anions: Cl-, Br-, NO3-, SO4<2->, COO-, ClO4-, BF4-, PF6-, CF3COO-, CF3SO3-, Tf2N<->and MeSO4-;

and at least one of the following cations:

a) imidazolium b) ammonium c) phosphonium

d) pyridinium e) pyrrolidinium f) triazolium

wherein R1, R2, R3, R4, R5and R6are carbon chains having from 0 to 25 carbon atoms.

An ionic liquid according to the present invention may have only one kind of anion and cation, or several kinds of anions or cations.

The ionic liquid may comprise ions that are ferromagnetic, giving the ionic liquid magnetic properties. An ionic liquid electrolyte with magnetic properties is hereinafter referred to as a magnetic ionic liquid electrolyte. Magnetic electrolytes change properties and behavior when exposed to an external magnetic field.

In an embodiment of the invention the ionic liquid electrolyte is a magnetic ionic liquid electrolyte which comprises a cation selected from the group consisting of imidazolium, ammonium, pyridinium, phosphonium, pyrrolidinium, and triazolium, and an anion selected from [MCl4]<->and/or [MBr4]-, wherein M is selected from at least one of Fe, Co, Ni, Mn and Gd.

According to an embodiment of the invention, the magnetic ionic liquid electrolyte can be selected from 1-butyl-3-methylimidazolium tetrachloroferrate (BmimFeCl4) or 1-methyl-3-octylimidazolium tetrachloroferrate (OmimFeCl4).

BmimFeCl4and OmimFeCl4both have magnetic properties due to the presence of Fe-ions.

In an embodiment of the invention BmimFeCl4is chosen as the preferred magnetic ionic electrolyte having a low cost, easy to obtain in a single step synthesis method, is not flammable, not oxygen or water sensitive as most ionic liquid electrolytes. Experiments have shown that BmimFeCl4has the most suitable electrical window, when compared to other ionic liquid electrolytes as well as having a high thermal stability, high ionic conductivity and low viscosity.

To increase the ionic conductivity of the magnetic ionic liquid electrolytes, Fe containing material such as FeCl2or other kinds of low viscosity electrolytes, including low viscosity ionic liquid electrolytes, low viscosity aqueous electrolyte, or low viscosity organic electrolyte, can be added to the magnetic ionic electrolyte to increase the number of ions able to migrate to the electrodes. Low viscosity electrolytes will decrease the concentration of for example BmimFeCl4or OmimFeCl4, in order to increase the ionic conductivity of electrolyte. Adding Fe element containing ion (for example, forming a Fe<3+>/Fe<2+>redox) will increase the number of Fe-ions able to migrate to the anode or the cathode during charge or discharge respectively.

Due to the Fe-ions in the electrolyte the Fe-ion battery according to the present invention is a magnetic battery. This may have the potential to change the current battery market due to the low cost. In addition, the concept of Fe-ion magnetic battery can reduce the battery charge time when using a magnetic ionic liquid because the magnetic ionic liquid electrolyte can serve as “ion transport vehicle” (ITV) carrying Fe-ions fast and effectively to or from the cathode to anode under an external magnetic field during the charge and/or discharge process.

Thus, in an embodiment of the invention, the battery cell is exposed to an external magnetic field during charge of the battery cell. The external magnetic field may in an embodiment of the invention alternate the direction of the filed enabling faster charging of the battery.

The charge-discharge speed, the specific capacity, ion transport behaviour, electrolyte properties and behaviour, anode properties and behaviour, cathode properties and behaviour, and/or structure of magnetic battery/supercapacitor can change with an external magnetic field.

In an embodiment of the invention the battery cell further comprises a separator arranged between the anode and the cathode. The separator must be chemically stable to the electrolyte and to the active materials at the temperatures of operation. It is also necessary for the separator to have the correct qualities of wettability, selectivity, resistivity and flexibility for the particular battery system. The separator must however be permeable allowing the Fe-ions to pass through, but must not allow a significant amount of electrons to pass therethrough, thereby avoiding that the battery cell short-circuits or self-discharges.

The separator may comprise polyolefin, filtering paper, nylon, cellophane or glass fibre.

Fe-ion batteries with high specific capacity can be utilized in electric cars, electric ships, mobile devices (such as cell phones and laptops), and space technology due to the excellent performance and properties of this kind of battery. Further, Fe-ion batteries can be utilized in stationary energy storage device in buildings, railways, and large scale renewable energy storage systems.

Fe-ion batteries can also be utilized for new supercapacitor development. Supercapacitor is a safe and durable electrical energy storage device with fast charge-discharge capability. Supercapacitors store energy by accumulating charges to form electrical double layers at the interface between the electrode surface and the electrolyte. Aqueous electrolyte or organic electrolyte can be utilized for supercapacitor fabrication. Ionic liquid electrolytes can also be utilized to improve the double layer capacitance of the carbon electrode and increase the operational voltage range. In addition, ionic liquid electrolyte based supercapacitors have the potential to be utilized in cold climate, such as climates below -30 °C. Due to the “smart” magnetic property of magnetic ionic liquid electrolytes, they are utilized for magnetic supercapacitor fabrication. Magnetic supercapacitors have the magnetic property compared with the conventional supercapacitors since magnetic supercapacitors can be produced using magnetic ionic liquids in order to improve the energy storage capacity.

Fe-ion batteries can be utilized as energy storage devices to wireless charge electric cars on “smart roads”. Wireless charging smart roads can for example be built by solar panel, wind turbine, Fe-ion batteries, and a wireless charging system. The wind turbines and solar panels can be installed on both sides of the road. Road surface can also be built by solar panel. Electric power from the solar panel and wind turbine can be transferred to the batteries along the smart road. Then, the electric car driving on a smart road can be charged by the wireless charging system under the smart road using the electric power from the batteries, solar panels, and wind turbines. There are four primary benefits of this smart road technology: 1) electric power is from solar and wind energy, 2) vehicles running on smart roads can be charged by the wireless charging system and Fe-iron batteries, 3) electric power from solar and wind energy can melt snow and ice on the road which can be very important to roads in the cold areas, 4) the electric power in the batteries on the road can also benefit driverless car technology development and other future smart technology developments on this smart road. Fe-ion batteries are much better than Li-ion battery to build the smart way of the future inter alia because Fe-ion batteries are much cheaper than a Li-ion battery, and there is enough iron raw material in the earth and universe to make Fe-ion batteries for the smart road in the future which is not the case for lithium.

The rechargeable supercapacitor has the same structure as the Fe-ion battery:

- an anode,

- a cathode, and

Brief description of the drawings

Fig. 1 illustrates the structure of a Fe-ion battery cell according to the invention.

Fig. 2 illustrates the structure of a Fe-ion battery cell according to the invention exposed to an external magnetic field.

Fig. 3 is showing the density of a selection of ionic liquids as a function of temperature.

Fig. 4(a) is showing the viscosity of a selection of ionic liquids, and fig. 4(b) shows the viscosity of BmimFeCl4at various temperatures.

Fig. 5(a) to (i) show DSC curves of a selection of ionic liquids.

Fig. 6 shows TGA curves of a selection of ionic liquids

Fig. 7(a) and (b) show Rahman analysis of BmimFeCl4and OmimFeCl4respectively.

Fig. 8 shows ionic conductivity measurements of a selection of ionic liquids.

Fig. 9(a) to (f) show the electrochemical windows measurement of a selection of ionic liquids.

Fig. 10(a) to (c) show the CV tests of a Cu - Cu symmetric cell.

Fig. 11(a) to (d) show the CV tests of an Al - Al symmetric cell.

Fig. 12(a) to (d) show the CV tests of a Ni - Ni symmetric cell.

Fig. 13(a) to (c) show the CV tests of a graphite-graphite symmetric cell.

Fig. 14(a) and (b) show a corrosion test of BmimFeCl4on Cu, Al, and Ni.

Fig. 15(a) and (b) show the stripping and plating results of a Fe-foil – Fe-foil symmetric cell.

Fig. 16(a) to (c) show the stripping and plating results of a C-Fe - C-Fe symmetric cell.

Fig. 17 shows the CV test of a Fe-foil - graphite full cell.

Fig. 18(a) and (b) shows the CV test of a C-Fe - graphite full cell.

Fig. 19 shows the capacity of a Fe-foil - graphite battery using BmimFeCl4as electrolyte and Cu as current collector.

Fig. 20 shows the capacity of a Fe-foil - graphite battery using OmimFeCl4as electrolyte and Cu as current collector.

Fig. 21 shows the capacity of a Fe-foil - graphite battery using BmimFeCl4as electrolyte and Ni as current collector.

Fig. 22(a) to (c) shows the charge-discharge test of C-Fe - graphite battery in a Swage-type cell.

Fig. 23(a) to (c) shows the charge-discharge test of C-Fe - graphite battery in coin cell.

Fig. 24(a) to (d) show SEM images of an unused C-Fe cathode.

Fig 25(a) to (c) show SEM images of a used C-Fe electrode from a Fe-ion Swagetype cell (with C-Fe electrode as working electrode and graphite as counter electrode) after charge and discharge cycles.

Fig. 26(a) to (d) show SEM images of a used C-Fe electrode from a Fe-ion Swagetype cell (with C-Fe electrode as counter electrode and graphite as working electrode) after charge and discharge cycles.

Fig. 27(a) shows XRD characterization result of an unused graphite anode, Fig. 27(b) a shows XRD characterization result of used a graphite anode and fig. 27(c) shows XRD characterization results of both a new and used C-Fe cathode.

Fig 28(a) and (b) shows charge-discharge test of a Fe-ion battery (with C-Fe electrode as working electrode and graphite as counter electrode) using electrochemical instrument VMP. (a) start with discharge; (b) start with charge.

Fig. 29(a) and (b) shows charge-discharge test of a Fe-ion battery (with C-Fe electrode as counter electrode and graphite as working electrode) using electrochemical instruments VMP and Maccor, respectively.

Fig. 30 illustrates a structure of a wireless charging smart road built of Fe-ion batteries, solar panels, wind turbines, and a wireless charging system.

Detailed description of the invention

Embodiments of the invention will now be described with reference to the enclosed drawings.

Fig. 1 illustrates the Fe-ion battery cell 1 having an anode 2, a cathode 3 and an electrolyte 4 interposed between the anode and the cathode. The electrolyte separates the anode and the cathode preventing short-circuit of the battery cell. However, a separator 5 is also inserted into the electrolyte 4 to prevent electrons from being transported therethrough further protecting the battery cell 1 from shortcircuit.

The electrolyte 4 may contain the Fe-ions itself, and/or it may obtain Fe-ions from anode or cathode during the redox reaction. Since neither the electrolyte 4 nor the separator 5 allow a significant flow of electrons, the electrons are forced to flow in an external circuit 8. The electrons are following the same direction as the positive Fe-ions to maintain charge neutrality within the battery cell 1.

During discharging of the battery cell 1, the positive Fe-ions are moved within the electrolyte from the negative electrode, anode 2, to the the positive electrode, cathode 3, and the electrons flow in the same directions in the external circuit 8. The built up potential energy produced is spent powering a device such as a cell phone, laptop or electric car.

During charging, potential energy builds up by applying a voltage to the battery cell 1, and the complete opposite process occurs being that the positive Fe-ions move from the cathode 3 to the anode 2 within the ionic liquid electrolyte 4, and the electrons flow in the same directions in the external circuit 8.

Fig. 2 illustrates the same battery cell 1 as shown in Fig. 1, where the battery cell 1 is exposed to an external magnetic field by the magnet 9. The magnetic field forces the magnetic ionic liquid comprising Fe-ions to be transported from the anode 2 to the cathode 3. The external magnetic field is particularly useful during charge of the battery. During the charge process, Fe-ions will move from cathode to anode due to the applied electric field, which forces Fe-ion transport in the Fe-ion battery cell. Besides, in Fe-ion battery cells, magnetic ionic liquids can be utilized as “ion transport vehicle” (ITV) to transport Fe-ions from the cathode to anode in the presence of the external magnetic field during the charge process.

The working mechanism of magnetic ionic liquids in Fe-ion batteries is shown in Fig. 2. In the absence of an external magnetic field (as shown in Fig. 1), Fe-ions will move due to the electric field between anode and cathode, which is the method for Fe-ion transport in Fe-ion batteries not being exposed to an external magnetic field.

However, in the presence of external magnetic field (as shown in Fig. 2), the Feions will move not only by the normal ion transport method but also move together with the magnetic ionic liquid from the cathode to the anode during the charge process when magnetic ionic liquid moves under magnetic field force. The magnetic ionic liquid electrolyte in the Fe-ion battery cells can thus also work as ITV to carry Fe ions fast and effectively from the cathode to the anode under an external magnetic field.

After the Fe-ions are transported to the anode by ITV, the Fe-ions will be unloaded from ITV by the strong electrostatic attraction of the anode surface. Subsequently, the magnetic field direction is reversed in order to move the Fe unloaded ITV from anode to cathode side. After arriving the cathode side, the ITV can load Fe-ions again. And then, by reversing the magnetic field direction the ITV loaded with Feions will move to the anode side. Thus, this Fe-ion transport process can alternate from the cathode to the anode by reversing the magnetic field direction and loading/unloading Fe-ions using ITV. In addition, the magnetic field direction can be increased by alternating the frequency, thus the Fe-ion loading/unloading rate can be increased significantly.

Fig. 30 illustrate a structure of a wireless charging of a car using smart road built of Fe-ion batteries, solar panels, wind turbines, and a wireless charging system.

Wireless charging smart roads can for example be built by solar panel, wind turbine, Fe-ion batteries, and a wireless charging system. The wind turbines and solar panels can be installed on both sides of the road. Road surface can also or alternatively be built by solar panel. Electric power from the solar panel and wind turbine can be transferred to the batteries along the smart road. Then, the electric car driving on the smart road can be charged by the wireless charging system under the smart road using the electric power from the batteries, solar panels, and wind turbines.

In the following preparations and comparisons are shown for the two different magnetic ionic liquids, BmimFeCl4and OmimFeCl4. Thereafter, experiments are shown using these BmimFeCl4or OmimFeCl4as electrolyte in Fe-ion battery cells.

Preparations and comparisons of ionic liquids

The synthesis of 1-butyl-3-methylimidazolium tetrachloroferrate (BmimFeCl4)and 1-methyl-3-octylimidazolium tetrachloroferrate (OmimFeCl4) is known from the publication with the title “Extraction of magnetic nanoparticles using magnetic ionic liquids” by Z. Zhao, J.H. Hansen and T. Boström, published in IET Micro & Nano Letters, Vol. 11 (2016), Issue 5.

In order to obtain BmimFeCl4, 1-butyl-3-methylimidazolium chloride (BmimCl, CAS registry number 79917-90-1 having a mass fraction purity of ≥ 98 %) was reacted with FeCl3·6H2O.

The reaction for BmimFeCl4is:

In order to obtain OmimFeCl4, 1-methyl-3-octylimidazolium chloride (OmimCl, CAS registry number 64697-40-1 having a mass fraction purity of ≥ 97.0%) was reacted with FeCl3·6H2O.

Other known conventional ionic liquids studied were 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF6,CAS registry number 174501-64-5 having a mass fraction purity of ≥ 97.0%), 1-Methyl-3-octylimidazolium tetrafluoroborate (OmimBF4, CAS registry number 244193-52-0 having a mass fraction purity of ≥ 97.0%), 1-Methyl-3-octylimidazolium hexafluorophosphate (OmimPF6, CAS registry number 304680-36-2 having a mass fraction purity of ≥ 95.0%), 1-Butyl-3-methylimidazolium iodide (BmimI, CAS registry number 65039-05-6 having a mass fraction purity of ≥ 98.0%), 1-methyl-3-octylimidazolium chloride (OmimCl, CAS registry number 64697-40-1 having a mass fraction purity of ≥ 97.0%) and 1-Butyl-3-methylimidazolium chloride (BmimCl, CAS registry number 79917-90-1 having a mass fraction purity of ≥ 98.0%).

All the ionic liquids, BmimFeCl4, OmimFeCl4, BmimPF6, OmimBF4, OmimPF6, BmimI, OmimCl, and BmimCl, were dried using a vacuum pump in a dry room having a water content of < 25 ppm before they were studied. The drying process was as follows: The ionic liquids were dried in the dry room using the membrane pump for at least 2 days. The vacuum pressure of the final dried ionic liquids was ca. 10<-3>mbar. Subsequently, the pre-dried ionic liquid were dried further using a high vacuum pressure pump for at least 3 days until the final vacuum pressure of the dried ionic liquids were ca. 10<-7>-10<-8>mbar.

Density measurements:

The densities of the ionic liquids BmimFeCl4, OmimFeCl4, BmimPF6, OmimPF6and OmimBF4were measured using a density meter (Anton Paar DMA 4100, Anton Paar Co., Austria). The temperature was between 20 °C and 80 °C, at 5 °C intervals. The temperature error was ± 0.01<o>C. The measurement was performed in the dry room (water content of the dry room was < 25 ppm). The absolute room pressure was approximately 101 kPa during the measurement.

The results are shown in table 1 and fig. 3.

Fig. 3 illustrates that the density of the ionic liquids decreases with the increasing temperature ranging from 20 °C to 80 °C. It also shows that BmimFeCl4has a higher density than the other ionic liquids.

Table 1. Density of ILs at temperatures from 20 °C to 80 °C.

Viscosity and rheological property measurements

Viscosity and rheological property of the ionic liquids BmimFeCl4, OmimFeCl4, OmimBF4, OmimPF6, and OmimCl, were measured using a rheometer (MCR 102, Anton Paar Modular Compact Rheometer) at temperature of 20 °C. The viscosity of the ionic liquids was measured at shear rates ranging from 1 s<-1>to 100 s<-1>.

In addition, the viscosity of BmimFeCl4is measured at various temperatures ranging from 10 °C to 50 °C.

The results are shown in Figs. 4a and 4b.

In Fig. 4a it is shown that BmimFeCl4has lower viscosity than other ionic liquids. It illustrates that BmimFeCl4has excellent viscosity to utilize as electrolyte, being as low as about 38 mPa·s at 20 °C. In addition, as shown in Fig. 4b, the viscosity of BmimFeCl4decreases with the increasing of temperatures ranging from 10 °C to 50 °C, which is in agreement with the viscosity versus temperature trend of conventional ionic liquids.

DSC curve measurements

The melting point of the ionic liquids were measured using DSC (TA instruments, USA) and DSC (Netzsch, Germany). The measurement procedure was carried out by loading a sample in a pan, and cooling the sample to -150 °C followed by keeping the sample at -150 °C for 5 minutes. Afterwards, the sample was heated to -120 °C at a cooling rate of 5 °C/min and maintained at -120 °C for 5 min. Subsequently, the sample was heated to 20 °C at a heating rate of 1 °C/min and heat flow was measured during the process.

The DSC curve of BmimFeCl4is shown in Fig. 5(a). It illustrates that BmimFeCl4has a very low melting point, namely ca. -85 °C. That means that this ionic liquid electrolyte can be utilized in very low temperature areas, such as the arctic area. Fig. 5(b) to 5(i) show the DSC curves of OmimBF4, OmimPF6, BmimI, BmimBF4, BmimPF6, BmimCl, OmimCl, and OmimFeCl4respectively. When comparing all the Figs. 5(a) to 5(i), it can be seen that many ionic liquids have very low melting point. However, the melting point of BmimCl is very high, being around about 70 °C.

TGA curve measurements

Thermal stability of ionic liquid electrolytes was measured using TGA (TA instruments, USA). A sample was loaded in a pan. Subsequently, the sample was maintained at 35 °C for 10 min. The sample was heated to 600 °C at a heating rate of 5 °C/min from 35 °C. Heat flow was measured during the heating process. The weight of pan and sample were needed for the experiments.

The TGA curves are shown in Fig. 6. It is shown that BmimFeCl4has high thermal stability compared to the other ionic liquids, having a decomposition temperature of ca. 459 °C.

Raman analysis

The chemical structure of magnetic BmimFeCl4and OmimFeCl4was characterized using Raman spectroscopy (Bruker, Vertex 70V).

The results are shown in Fig. 7 (a) and (b) illustrates that there is an FeCl4-function group in the two ionic liquids BmimFeCl4and OmimFeCl4respectively being the reason for their magnetic properties.

Ionic conductivity measurements

Ionic conductivity of the ionic liquids OmimFeCl4, BmimPF6and OmimBF4was measured using conductivity meter at temperatures ranging from -30 °C to 80 °C. The ionic conductivity of BmimFeCl4was measured at temperatures ranging from -30 °C to 100 °C. The results are shown in Fig. 8, which shows that the BmimFeCl4has a higher ionic conductivity than the other ionic liquids.

Electrochemical windows measurements

The electrochemical windows of the ionic liquids BmimFeCl4, OmimFeCl4,OmimBF4, OmimPF6, BmimI, and BmimPF6were measured using VMP (Bio-Logic, France). The experiments were performed at potential versus Ag/Ag<+>(using Ag/AgCl as standard electrode) ranging from -5.0 V to 5.0 V with scanning rate of 0.5 mV/s. The working electrode was Pt wire with cross sectional area of 0.0078 cm<2>. Counter electrode was Ni (cross sectional area: 1.13 cm<2>). The reference electrode was silver wire. The electrochemical windows of the ionic liquids were measured using VMP. The results are shown in Fig. 9(a) to (f) for BmimFeCl4, OmimFeCl4,OmimBF4, OmimPF6, BmimI, and BmimPF6respectively. Fig. 9(a) shows that the electrochemical window of BmimFeCl4is ca. 4 V, from -2.1 V to 1.9 V versus Ag/Ag<+>(using Ag/AgCl as standard electrode). BmimFeCl4has wide electrochemical windows. Therefore, BmimFeCl4was the preferred electrolytes in the examples of Fe-ion battery cells below.

In the following examples various Fe-ion battery cells are shown. In all the examples glass fiber is used as separator within the battery cells.

Examples of Fe-ion battery cells

Electrolyte

In the following experiments magnetic ionic liquids of BmimFeCl4and OmimFeCl4were used as electrolytes in the Fe-ion battery cells. Their preparation is described above. The mass fractions purities of BmimFeCl4and OmimFeCl4are ≥ 99.0 %, 97 %, respectively.

Cathode materials

Three various cathodes were tested in the Fe-ion battery cells; a) Fe-foil being a pure iron cathode, b) carbon coated with Fe nanoparticles (C-Fe NPs cathode) and c) Fe2O3-powder which is carbon reduced Fe2O3(Fe2 cathode). The three cathode preparation methods were as follows:

(a) Fe-foil (Pure Fe cathode): Fe-foil having a thickness of 0.25 mm and a purity of ≥99.99% trace metals basis was utilized as cathode for Fe-ion battery directly.

(b) C-Fe cathode: The C-Fe cathode was prepared by the following steps: 1) dissolving carboxymethyl cellulose (CMC) in H2O forming a gel-like sample by stirring for at least 2 hours; 2) adding carbon coated with Fe nanoparticles (CAS number 7439-89-6, nanopowder, 25 nm average particle size, 99.5% trace metals basis) and carbon 45 (C45 conductive carbon black) was added into the gel-like sample. Afterwards, the sample was stirred for at least 12 hours to obtain a slurry; 3) coating the slurry on a surface of a Ni foil (having a thickness of 0.1 mm and a purity of ≥99.99% trace metals basis) using doctor blade to form a 200 μm thin film; 4) heating the Ni foil comprising the thin film 80<°>C for at least 12 hours to remove the water; and 5) Cutting the Ni foil comprising the thin film to obtain the C-Fe electrodes. Afterwards, the C-Fe electrodes were further dried using high vacuum pump. Finally, the C-Fe electrodes were utilized in the Fe-ion battery cell.

(c) Fe2 cathode. The Fe2 cathode was prepared by a method similar to the method for C-Fe NPs cathode preparation. However, in step 2), the Fe powder reduced from Fe2O3by carbon 45 was added into the gel-like sample where the reduced Fe powder was prepared by burning a mixture of Fe2O3nanoparticles (CAS number 1309-37-1, having an average size < 50 nm), sucrose (CAS number 57-50-1), and super C65 carbon black at 1000<°>C for 1 hour providing a powder. The other remaining steps of the Fe2 cathode preparation was similar to that of C-Fe cathode preparation.

A Fe-foil symmetric cell and C-Fe symmetric cell were studied in a stripping and plating test. The electrolyte in the symmetric cells is BmimFeCl4. The stripping and plating test of the two symmetric cells was performed using VMP. The reference electrode was Ag. The test results of Fe-foil symmetric cell are shown in fig. 15(a) showing voltage vs. time and fig. 15(b) showing current change vs. time. The test results of the C-Fe symmetric cell are shown in fig. 16(a) showing voltage vs. time, fig. 16(b) showing current change vs. time and fig. 16(c) showing efficiency vs. cycle number. It can be seen that C-Fe symmetric cell has good stripping and plating results, and that C-Fe has a better performance than Fe-foil as electrode in the Fe-ion battery.

Anode materials

Graphite was used as anode in Fe-ion battery experiments. The graphite electrode was prepared by the following steps: 1) CMC was dissolved in H2O forming a gellike sample by stirring for at least 2 hours; 2) adding graphite and carbon 45 into the gel-like sample. Afterwards, the sample was stirred for at least 12 hours to obtain a slurry; 3) coating the slurry as a 150μm thin film on the surface of a Ni foil using doctor blade; 4) heating the Ni foil comprising the thin graphite film at 80<°>C for at least 12 hours to remove the water; and 5) cutting the Ni foil comprising the thin graphite film into the graphite electrodes. Afterwards, the graphite electrode was further dried using high vacuum pump. Finally, the graphite electrodes were obtained for battery preparation.

Current collector

The current collector for electrodes preparation were investigated among Cu foil, Ni foil, and Al foil. A Ni-Ni symmetric cell, Cu-Cu symmetric cell, and Al-Al symmetric cell were prepared. The electrolyte utilized in the cells was BmimFeCl4. All the symmetric cells were fabricated in a glovebox (MBraun UNIlab; H2O content < 0.1 ppm, O2content < 0.1 ppm) filled with ultrapure Argon. The cyclic voltammetry (CV) test of the three symmetric cells was performed using galvanostat/potentiostat VMP (Bio-Logic, France). In addition, a graphite-graphite symmetric cell was prepared. Also here, the electrolyte in the cell was BmimFeCl4. Subsequently, the CV test of the graphite-graphite cell was performed.

The test results of the three symmetric cells were:

(a) Cu test: CV test of the Cu symmetric cell is performed. The CV curves are shown in Fig. 10 (a) to (c). It is shown that Cu symmetric cell is irreversible at the scanning voltage ranging from -1.0 V to 1 V, -1.5 V to 1.5 V, and -2.0 V to 2.0 V. That means Cu foil cannot be utilized as current collector for the cell using BmimFeCl4as electrolyte.

(b) Al test: CV test of Al symmetric cell is performed. CV curves are shown in Fig. 11(a) to (d). It is shown that Cu symmetric cell is irreversible at the scanning voltage ranging from -0.5 V to 0.5 V, -0.75 V to 0.75 V, -1.0 V to 1.0 V, and -1.25 V to 1.25 V. Similar to Cu foil, Al foil cannot be utilized as current collector for the cell using BmimFeCl4as electrolyte.

(c) Ni test: CV test of Ni symmetric cell is performed. The CV curves are shown in Fig. 12(a) to (d). It is shown that the BmimFeCl4is reversible in the Ni symmetric cell. Therefore, Ni foil may be utilized as current collector in Feion battery cells.

(d) Graphite test: Graphite symmetric cell is prepared. The electrolyte in the cell is BmimFeCl4. Subsequently, CV test of graphite symmetric cell is performed. CV curves of the symmetric cell are shown in Fig. 13(a) to (c). It is shown that graphite symmetric cell is reversible at the voltage ranging from -1 V to 1 V, and -1.5 V to 1.5 V, which means graphite can be utilized as anode in the Fe-ion battery.

The corrosion effect of BmimFeCl4on Cu, Al, and Ni foils was also studied. The corrosion experiment was performed in a period of 40 days. The test results are shown in Fig. 14. Fig. 14(a) shows the Ni, Cu and Al foils before testing, and fig.

14(b) shows the Ni, Cu and Al foil after the 4 months period of corrosion testing. It is shown that the BmimFeCl4has a chemical reaction with Cu or Al. However, for Ni foil, there is no significant chemical reaction than can be seen.

Based on the results above, Ni-foil was preferred as current collector in the following Fe-ion battery experiments.

Separator

Glass fiber is utilized as separator in the following Fe-ion battery experiments.

Experiment 1

Two Fe-ion battery cells were prepared. The first battery cell was using Fe-foil as cathode and graphite as anode while the other cell used C-Fe cathode and graphite anode. Reference electrode was Ag. The electrolyte in both cells was BmimFeCl4. The CV test results Fe-foil - graphite cell is shown in Fig. 17 illustrating that Fe-foil as cathode will not be as good as C-Fe as cathode. Fig 18(a) shows the results of the C-Fe graphite cell at a voltage ranging from -1 V to 1 V, and fig. 18(b) shows the same cell at the voltage ranging from -1.5 V to 1.5 V. It is shown that C-Fe graphite full cell is completely reversible at -1.5 V to 1.5 V.

Experiment 2

Fe-ion battery cells having different compositions were prepared, and charge and discharge tests were performed.

Battery cell composition 1:

Battery cell: Swagelok type cell

Cathode: Fe-foil

Anode: graphite

Current collector: Cu-foil

Electrolyte: BmimFeCl4

The charge and discharge test results are shown in Fig. 19. It is found the cell was dead after 10 cycles. The reason is that the Cu current collect has had a chemical reaction with the BmimFeCl4electrolyte, which leads to the cell destruction not allowing the cell to continue to be charged or discharged.

Battery cell composition 2:

Battery cell: Swagelok type cell

Cathode: Fe-foil

Anode: graphite

Current collector: Cu-foil

Electrolyte: OmimFeCl4

The second composition is very similar to the first composition, except for the electrolyte being a OmimFeCl4electrolyte. The charge discharge test results of this cell are shown in Fig. 20. Similarly, the second cell is also dead after 10 charge discharge cycles. This means that Cu current collector cannot utilized for neither BmimFeCl4nor OmimFeCl4.

Battery cell composition 3:

Battery cell: Swagelok type cell

Cathode: Fe-foil

Anode: graphite

Current collector: Ni-foil

Electrolyte: BmimFeCl4

Ni-foil was utilized as current collector for the third cell, and BmimFeCl4as electrolyte. The charge and discharge test results of the cell is shown in Fig 21. It was found that the cell still works after 40 cycles. That means Ni can be utilized as current collector for the Fe graphite full cells using IL BmimFeCl4as electrolyte.

Battery cell composition 4:

Battery cell: Swagelok type cell

Cathode: C-Fe

Anode: graphite

Current collector: Ni-foil

Electrolyte: BmimFeCl4

The charge and discharge test of battery cell (Swaglok-type, T-cell) was performed. The results are shown in Fig. 22(a) showing capacity vs. cycle number, fig. 22(b) showing voltage vs. capacity in the first 5 cycles, and fig. 22(c) showing voltage vs. capacity in the 10<th>, 15<th>and 20<th>cycle. As shown in fig. 22(a), the discharge and charge capacity of the Swaglok-type cell is very high, around 262 mAh/g charge capacity 262 mAh/g and 245 mAh/g discharge specific capacity at the potential range from -0.4 V to 0.8 V vs. Ag/Ag<+>after 15 cycles.

Figs 22(b) and 22(c) show the specific capacity versus potential profiles. It is found the cell is not stable at the first 5 cycles. However, after the 5<th>cycle, the cell become more and more stable. As shown in Fig 22(c), the stable specific capacity versus potential profiles are obtained.

Battery cell composition 5:

Battery cell: coin cell

Cathode: C-Fe

Anode: graphite

Current collector: Ni-foil

Electrolyte: BmimFeCl4

The charge and discharge test of C-Fe graphite cell (Coin-type) was performed. The results are shown in Figs. 23(a), 23(b), and 23(c). As shown in Fig. 23(a) showing capacity vs. cycle number and 23(b) showing voltage vs. capacity, the specific capacity of the Fe-ion battery C-Fe graphite cell (Coin-type) can still as high as 40 mAh/g.

Characterization of the cathode using SEM:

The morphology of the cathode was investigated using scanning electrochemical microscopy (SEM, ZEISS 1550VP Field Emission Scanning Electron Microscope operated at 5 kV).

SEM images of the cathode are shown in Figs. 24-26. Fig. 24(a) to (d) show SEM images of an unused C-Fe cathode magnified 10 000 times, 30 000 times, 50 000 times and 100 000 times respectively. As shown the C-Fe nanoparticles is found on the surface of the cathode.

Figs. 25(a) to (c) shows the C-Fe cathode from the Swagelok type battery cell (with C-Fe electrode as working electrode and graphite as counter electrode) composition after 5 charge-discharge cycles. The SEM image in in figs. 25(a) to (c) are magnified 1000 times, 5000 times and 10 000 times respectively. The images show that the C-Fe nanoparticles of the cathode are broken and forming a large size structure. That means the Fe in the C-Fe cathode take actively function in the charge and discharge process.

Figs. 26(a) to (d) show images of the surface of a C-Fe anode used as in the Swagelok-type cell (with C-Fe electrode as counter electrode and graphite as working electrode). The SEM image in in figs. 26(a) to (d) are magnified 1000 times, 5000 times, 10 000 times and 20 000 times respectively. The images show that the C-Fe cathode hardly changes after the charge-discharge cycles.

It means that in the Fe-ion battery C-Fe electrode should be the working electrode and graphite should be the counter electrode.

Characterization of the cathode and anode using XRD:

X-ray diffraction analysis was conducted using a Bruker D8 Advance diffractometer (Bruker, Germany) with Cu−Kα. XRD is conducted ranging from 10° to 90° with a step size of 0.02°.

The XRD characterization results are shown in Fig. 27(a) showing a fresh graphite anode, Fig. 27(b) showing a used graphite anode and Fig. 27(c) showing both a new and used C-Fe cathode. As shown in Figs. 27(a) and 27(b), the chemical composition of the fresh graphite electrode and used graphite electrode changes significantly, showing that the Fe-ions undergo chemical intercalation with the graphite during the charge/discharge process. In Fig. 27(c) it is shown that the chemical composition of the fresh C-Fe electrode and used C-Fe electrode did not change significantly.

Experiment 3

A charge-discharge test was performed using electrochemical instrument VMP of an Fe-ion battery having a C-Fe cathode, graphite anode and BmimFeCL4electrolyte. It means that in the test C-Fe electrode is working electrode and graphite is counter electrode. Glass fiber was used as separator. Characterization results are shown in Fig. 28 (a) showing discharge first and then charge. Fig. 28 (b) shows charge first and then discharge. As shown in Fig. 28 (a) and (b) the charge and discharge performance of the battery is similar.

Experiment 4

A charge discharge test was performed using electrochemical instruments Maccor and VMP (an electrochemical instrument for battery test) in a Swagelok-type cell with graphite as working electrode and C-Fe as counter electrode. BmimFeCl4was used as electrolyte. The results are shown in Fig. 29(a) showing data from VMP and Fig. 29(b) showing data from Maccor. The results show that C-Fe cannot be utilized as counter electrode in the cell, but should be utilized as working electrode. The graphite should be utilized as counter electrode.

List of reference numerals / letters

1 Battery cell

2 Anode

3 Cathode

4 Electrolyte

5 Separator

6 Substrate of anode

7 Substrate of cathode

8 External circuit

9 Magnet

Claims

1. A rechargeable Fe-ion battery cell (1) comprising

- an anode (2),

- a cathode (3), and

- an electrolyte (4) interposed between the anode and the cathode, characterized in that the electrolyte (4) transports Fe-ions between said anode (2) and cathode (3).

2. The battery cell (1) according to claim 1, wherein the anode (2) comprises carbon.

3. The battery cell (1) according to claim 1 or 2 wherein the anode (2) comprises carbon in the form of graphite, graphene and/or nanotube carbon.

4. The battery cell (1) according to any one of the preceding claims, wherein anode (2) is a coating material arranged on the surface of a substrate material (6) such that the substrate material (6) is not in contact with the electrolyte.

5. The battery cell (1) according to claim any one of the preceding claims, wherein the cathode (3) comprises a Fe-containing material.

6. The battery cell (1) according to claim 5, wherein the Fe-containing material is selected from at least one of Fe-foil, Fe2O3-powder or carbon coated with Fe nanoparticles (C-Fe), Fe powder, FeO, Fe2O3-powder, Fe3O4-powder, Fe3C, FeSO4, Fe(ClO4)2, Fe(C5H5)2, Fe(IO3)3,Ferrate, Ferrite, Fe (-II) compound, Fe (-I), Fe (0) compound, Fe (I) compound, Fe (II) compound, Fe (III) compound, Fe (IV) compound, Fe (V) compound, or Fe (VI) compound.

7. The battery cell (1) according to any one of the preceding claims, wherein cathode (3) is a coating material arranged on the surface of a substrate material (7) such that the substrate material (7) is not in contact with the electrolyte.

8. The battery cell (1) according to claim 4 or 7, wherein the substrate material (6,7) is a current collector.

9. The battery cell (1) according to claim 8, wherein the substrate material (6,7) is chosen from one of Ni-foil, Fe-foil, and Co-foil.

10. The battery cell (1) according to any one of the preceding claims, wherein the electrolyte material (4) comprises Fe-ions.

11. The battery cell (1) according to any one of the preceding claims, wherein the electrolyte (4) comprises at least one Fe-ion selected from the group consisting of Fe<2+>, Fe<3+>, FeCl4-, FeCl2<+>, FeO4<2->, FeO4<3->, and FeO2.

12. The battery cell (1) according to any one of the preceding claims wherein the electrolyte (4) is an aqueous solution electrolyte or organic electrolyte.

13. The battery cell (1) according to any one of the preceding claims, wherein the electrolyte (4) comprises Fe-ions arrived from anode or cathode.

14. The battery cell (1) according to any one of the preceding claims, wherein the electrolyte (4) comprises at least one ionic liquid.

15. The battery cell (1) according to claim 14, wherein the ionic liquid comprises at least one cation selected from the group consisting of imidazolium, ammonium, pyridinium, phosphonium, pyrrolidinium, and triazolium, and at least one anion selected from [MCl4]-and/or [MBr4]-wherein M is selected from at least one of Fe, Co, Ni, Mn and Gd.

16. The battery cell (1) according to claim 14 or 15, wherein the ionic liquid electrolyte (4) comprises 1-butyl-3-methylimidazolium tetrachloroferrate (BmimFeCl4) or 1-methyl-3-octylimidazolium tetrachloroferrate (OmimFeCl4).

17. The battery cell (1) according to any one of the preceding claims, wherein the electrolyte (4) is magnetic.

18. The battery cell (1) according to any one of the preceding claims, wherein battery cell (1) further comprises a separator (5) arranged between the anode (2) and the cathode (3).

19. The battery cell (1) according to claim 18, wherein the separator (5) comprises glass fibre.

20. The battery cell (1) according to any one of the preceding claims, wherein the battery cell (1) is exposed to an external magnetic field during charge and discharge of the battery cell (1), said external magnetic field alternates when the battery cell (1) alternates from charging to discharging and vice versa.

21. Use of the battery cell (1) according to any one of claims 1-20 in a rechargeable device such as electric cars, cell phones, laptops and the like.

22. Use of the battery cell (1) according to any one of claims 1-20 in a rechargeable device such as buildings, railways, road, large scale renewable energy storage systems, and space technology.

23. Use of the battery cell (1) according to any one of claims 1-20 in a rechargeable device such as wireless charging smart road and driverless technology.

24. Use of the battery cell (1) according to any one of claims 1-20 as a

supercapacitor.