Claims:1. A nickel-iron battery comprising:
a positive electrode comprising a nickel oxide (NiO) nano-particle layer located over a first current collector; and
a negative electrode comprising a hematite (a-Fe2O3) nano-particle layer located over a second current collector, wherein at least one of the positive electrode and the negative electrode is substantially free of carbon and binder material.

2. The nickel-iron battery of claim 1, wherein the first current collector and the second current collector are made of same material.

3. The nickel-iron battery of claim 1, wherein the first current collector and the second current collector are made of different materials.

4. The nickel-iron battery of claim 1, wherein the nickel-iron battery exhibits a specific capacity value of at least 40 mAh/g at a scan rate of 2 mV/s in a potential window between 0 V and 1.4 V.

5. The nickel-iron battery of claim 1, wherein the nickel oxide (NiO) nano-particle layer comprises a nickel oxide (NiO) nano-flake layer, and wherein the hematite (a-Fe2O3) nano-particle layer comprises a hematite (a-Fe2O3) nano-rod layer.

6. The nickel-iron battery of claim 1, wherein the nickel oxide (NiO) nano-particle layer is directly grown on the first current collector.

7. The nickel-iron battery of claim 1, wherein the hematite (a-Fe2O3) nano-particle layer is directly grown on the second current collector.

8. The nickel-iron battery of claim 1, wherein the nickel oxide (NiO) nanoparticle layer comprises arrays of interconnected NiO nano-particles, and wherein the hematite (a-Fe2O3) nano-particle layer comprises hematite nano-particles with oxygen vacancies within hematite lattice structure.

9. A battery comprising an electrode comprising:
a substrate; and
a hematite (a-Fe2O3) nano-particle layer located over the substrate;
wherein the electrode is substantially free of carbon and binder material; and
wherein the hematite (a-Fe2O3) nano-particle layer comprises hematite nano-particles with oxygen vacancies within hematite lattice structure.

10. A battery comprising an electrode comprising:
a substrate; and
a nickel oxide (NiO) nano-particle layer located over the substrate;
wherein the electrode is substantially free of carbon and binder material; and
wherein the nickel oxide (NiO) nano-particle layer comprises arrays of interconnected NiO nano-particles.
, Description:TECHNICAL FIELD
[0001] The disclosure generally relates to the field of electrochemical energy storage devices. In particular, the present disclosure relates to a substrate-integrated nano-structured nickel-iron ultra-battery.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Iron electrodes have been used in energy storage batteries and other devices for over one hundred years. Iron-based alkaline rechargeable batteries are particularly attractive for large-scale electrical energy storage as iron is inexpensive, globally-abundant and has large theoretical specific-capacity. Iron electrodes are often combined with a nickel cathode to form a nickel-iron battery. The nickel-iron battery (Ni—Fe battery) is a rechargeable battery having a nickel (III) oxide-hydroxide cathode and an iron anode, with an electrolyte such as potassium hydroxide.
[0004] Iron-based batteries are both mechanically and electrically rugged as these batteries are tolerant to variety of abuses (overcharge, over discharge, and short-circuiting) and can have a relatively long life (~20 years or longer). Besides, iron electrodes are environmentally benign unlike other battery electrode materials, such as cadmium and lead. These batteries are often used in backup situations where they can be continuously charged. The ability of these batteries to survive frequent cycling is due to low solubility of reactants in the electrolyte. The formation of metallic iron during charge is slow because of the low solubility of ferrous hydroxide. While the slow formation of iron crystals preserves the electrodes, it also limits the high rate performance. These cells charge and discharge slowly. Due to its low specific energy, and poor charge retention, other types of rechargeable batteries have displaced the nickel-iron battery in most applications.
[0005] In hibernation for decades, the nickel-iron system has begun to catch the attention of researchers world over. The resurrection of the nickel-iron system rests heavily on its techno-economic feasibility in varying applications arising due to recent technological advances and introduction of nano-technology. A significant amount of research has already been done in this technological domain to overcome one or more disadvantages associated with such batteries and to improve their practical utility. However, to the best of our knowledge, none of the prior art reported Ni-Fe battery is devoid of the limitations of low power density apart from others mentioned above.
[0006] There is therefore a need in the art for improved nickel-iron battery with enhanced electron/ion transfer from electrolyte to current collector and consequently, reduced internal-resistance and improved power-density.

OBJECTS OF THE INVENTION
[0007] An object of the present disclosure is to overcome disadvantages associated with conventional nickel-iron cell (battery).
[0008] Another objective of the present disclosure is to provide a nickel-iron ultra-battery and electrodes thereof with significantly improved capacitive performance.
[0009] Another object of the present disclosure is to provide an electrode that completely avoids the use of any binder or carbon material to reduce internal resistance.
[0010] Another object of the present disclosure is to provide an electrode that employs nickel oxide (NiO) nano-flakes grown directly on to the current collector(s). Another object of the present disclosure is to provide an electrode that employs hematite (a-Fe2O3) nano-rods grown directly on the current collector(s).
[0011] Another object of the present disclosure is to provide an electrode that employs nickel oxide (NiO) nano-flakes grown directly on highly-conductive stainless steel substrate(s). Another object of the present disclosure is to provide an electrode that employs hematite (a-Fe2O3) nano-rods grown directly on highly-conductive stainless steel substrate(s).
[0012] Another object of the present disclosure is to provide a nickel-iron ultra-battery that employs nickel oxide (NiO) nano-flakes and hematite (a-Fe2O3) nano-rods as electroactive materials for its respective positive and negative electrodes.
[0013] Another object of the present disclosure is to provide a nickel-iron ultra-battery that employs electrodes with enhanced mechanical integrity of electro-active materials with the substrate.
[0014] Another object of the present disclosure is to provide nickel oxide (NiO) nano-flakes with narrow width grown directly on the substrate(s) to shorten the ion-diffusion path to facilitate ion and charge transfer.
[0015] Another objective of the present disclosure is to provide a nano-architectural design of positive and negative electroactive materials that can provide large number of interaction sites for electrolytic ions with electrode material(s) in conjunction with short ion-diffusion paths for efficient ion intercalation/deintercalation of ionic species from electrolyte(s).
[0016] Another objective of the present disclosure is to provide nano-rods of hematite with oxygen vacancies within the hematite lattice.
[0017] Another objective of the present disclosure is to provide highly dense vertical arrays of interconnected NiO nano-flakes that can essentially provide huge surface area for redox reactions.
[0018] Another objective of the present disclosure is to provide improved electrodes that can sustain enormous volume changes by repetitive ion intercalation/deintercalation process during long cycling test.
[0019] Another objective of the present disclosure is to provide a nickel-iron ultra-battery with improved cycle life/calendar life.

SUMMARY
[0020] The present disclosure relates to the field of electrochemical energy storage devices. In particular, the present disclosure relates to a substrate-integrated nanostructured nickel-iron ultra-battery.
[0021] In an aspect, the present disclosure relates to a nickel-iron battery including a positive electrode having a nickel oxide (NiO) nano-particle layer located over a first current collector and a negative electrode having a hematite (a-Fe2O3) nano-particle layer located over a second current collector, wherein at least one of the positive electrode and the negative electrode is substantially free from carbon and binder materials.
[0022] In an embodiment, wherein the first current collector and the second current collector are made of the same material. In another embodiment, the first current collector and the second current collector are made of different materials.
[0023] In another aspect, the present disclosure relates to a nickel-iron battery that exhibits a specific capacity value of at least 40 mAh/g at a scan rate of 2 mV/s in a potential window between 0 V and 1.4 V.
[0024] In an embodiment, the nickel oxide (NiO) nano-particle layer includes a nickel oxide (NiO) nano-flake layer and the hematite (a-Fe2O3) nano-particle layer includes a hematite (a-Fe2O3) nano-rod layer.
[0025] In an embodiment, the nickel oxide (NiO) nano-particle layer is directly grown on the first current collector. In another embodiment, the hematite (a-Fe2O3) nanoparticle layer is directly grown on the second current collector.
[0026] In an embodiment, the nickel oxide (NiO) nano-particle layer includes arrays of interconnected NiO nano-particles and the hematite (a-Fe2O3) nano-particle layer includes hematite nano-particles with oxygen vacancies within hematite lattice structure.
[0027] In still another aspect, the present disclosure relates to a battery having an electrode comprising a substrate and a hematite (a-Fe2O3) nano-particle layer located over the substrate, wherein the electrode is substantially free of carbon and binder material and wherein the hematite (a-Fe2O3) nano-particle layer includes hematite nano-particles with oxygen vacancies within hematite lattice structure.
[0028] In still another aspect, the present disclosure relates to a battery having an electrode including a substrate and a nickel oxide (NiO) nano-particle layer located over the substrate, wherein the electrode is substantially free of carbon and binder material and wherein the nickel oxide (NiO) nano-particle layer includes arrays of interconnected NiO nano-particles.
[0029] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawings/figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0031] FIG. 1A illustrates an exemplary Scanning Electron Microscope (SEM) image of hematite nano-rods prepared in accordance with embodiments to the present disclosure.
[0032] FIG. 1B illustrates an exemplary Transmission Electron Microscope (TEM) image of hematite nano-rods prepared in accordance with embodiments to the present disclosure.
[0033] FIG. 1C illustrates an exemplary Scanning Electron Microscope (SEM) image of Nickel oxide nano-flakes prepared in accordance with embodiments to the present disclosure.
[0034] FIG. 1D illustrates an exemplary Transmission Electron Microscope (TEM) image of Nickel oxide nano-flakes prepared in accordance with embodiments to the present disclosure.
[0035] FIG. 2A illustrates an exemplary cyclic voltammetry data for the assembled cell at different potential scan rates within 0V to 1.4V in accordance with embodiments to the present disclosure.
[0036] FIG. 2B illustrates an exemplary constant current charge/discharge plots at different current densities with a potential window of 1.4V in accordance with embodiments to the present disclosure.
[0037] FIG. 2C illustrates an exemplary variation in specific capacitance and capacity of the NiO//a-Fe2O3 ultra-battery as a function of current density in accordance with embodiments to the present disclosure.
[0038] FIG. 2D illustrates an exemplary cycling performance of the assembled NiO//a-Fe2O3 ultra-battery in accordance with embodiments to the present disclosure.

DETAILED DESCRIPTION
[0039] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of details offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0040] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the “invention” may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the “invention” will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[0041] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0042] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0043] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.
[0044] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0045] The present disclosure relates to the field of electrochemical energy storage devices. In particular, the present disclosure relates to a substrate-integrated nanostructured nickel-iron ultra-battery.
[0046] In an aspect, the present disclosure relates to a nickel-iron battery that can include a positive electrode having a nickel oxide (NiO) nano-particle layer located over a first current collector and a negative electrode having a hematite (a-Fe2O3) nano-particle layer located over a second current collector, wherein at least one of the positive electrode and the negative electrode can be substantially free of carbon and binder material.
[0047] In an embodiment, the first current collector can include a material similar to that of the second current collector. In another embodiment, the first current collector can include a material different than that of the second current collector.
[0048] In another aspect, the present disclosure relates to a nickel-iron battery that can exhibit a specific capacity value of at least 40 mAh/g at a scan rate of 2 mV/s in a potential window between 0 V and 1.4 V.
[0049] In an embodiment, the nickel oxide (NiO) nano-particle layer can include a nickel oxide (NiO) nano-flake layer and the hematite (a-Fe2O3) nano-particle layer can include a hematite (a-Fe2O3) nano-rod layer.
[0050] In an embodiment, the nickel oxide (NiO) nano-particle layer can be directly grown on the first current collector. In another embodiment, the hematite (a-Fe2O3) nano-particle layer can be directly grown on the second current collector.
[0051] In an embodiment, the nickel oxide (NiO) nano-particle layer can include arrays of interconnected NiO nano-particles and the hematite (a-Fe2O3) nano-particle layer can include hematite nano-particles with oxygen vacancy within hematite lattice structure.
[0052] In still another aspect, the present disclosure relates to a battery having an electrode including a substrate and a hematite (a-Fe2O3) nanoparticle layer located over the substrate, wherein the electrode can be substantially free of carbon and binder material and wherein the hematite (a-Fe2O3) nanoparticle layer can include hematite nano-particles with oxygen vacancy within hematite lattice structure.
[0053] In still another aspect, the present disclosure relates to a battery having an electrode including a substrate and a nickel oxide (NiO) nano-particle layer located over the substrate, wherein the electrode can be substantially free of carbon and binder material and wherein the nickel oxide (NiO) nano-particle layer can include arrays of interconnected NiO nano-particles.
[0054] The electrodes taught in this description may be utilized in nearly any electrochemical device including electrodes/layers in batteries, ultra capacitors, fuel cells, water-splitting electrodes, and other energy storage/discharge devices and in electrochromic devices such as smart windows and the like.
[0055] In an embodiment, an electrochemical device is provided that may be in the form of a stack or otherwise includes a number of layers of materials that provide particular functions. For example, the device may be an energy storage device with a pair of electrodes (an anode and a cathode) separated by an electrolyte layer. The device includes a layer of electrode material or electrode that may be configured to be binder-free. By contrast, a conventional electrode for a battery or storage device may have an active material (e.g., about 80 percent by weight), a conductive additive (e.g., 10 percent by weight of carbon black or the like), and a binder (e.g., 10 percent by weight of a polymer) that holds the active material and conductive additive together and assists in binding with adjoining layers/substrates.
[0056] In an embodiment, a particular device, e.g. a battery is provided. The battery can include a container, an anode, a cathode, an electrolyte, and a separator (optional and may be a polyethylene or the like component). The anode, the cathode, the electrolyte, and the separator are positioned within the container, and a negative terminal and a positive terminal can be disposed on or electrically connected to the negative current collector layer of the anode and the positive current collector layer of the cathode to allow connection of the battery to an electrical circuit/power use or storage circuit.
[0057] In accordance with embodiments of the present invention, a substrate (current collector) can be selected from the group including but not limited to a conductor substrate, a semiconductor substrate and a dielectric substrate (provided with appropriate conductor layer lamination). In an embodiment, stainless steel can be used as a substrate (current collector) over which one or more layers of nano-particles of active material of appropriate thickness can be directly deposited and/or grown to realize an electrode. In an embodiment, an anode can be realized including a stainless steel substrate (current collector) and one or more layers of material(s) including a nano-particle active material portion substantially uniformly distributed about the stainless steel substrate (current collector). In an embodiment, a cathode can be realized including a stainless steel substrate (current collector) and one or more layers of material(s) including a nano-particle active material portion substantially uniformly distributed about the stainless steel substrate (current collector). In an embodiment, the anode or cathode can be grown directly on the surface of the current collector (substrate) without using any additional binder(s) or carbon or carbonaceous material(s).
[0058] In an embodiment, the electrode can include a stainless steel (SS) substrate and Nickel Oxide (NiO) nano-particles disposed over its surface. In an embodiment, Nickel Oxide (NiO) nano-particles can include Nickel Oxide (NiO) nano-flakes. In another embodiment, Nickel Oxide (NiO) nano-particles are directly grown over the surface of current collector. In still another embodiment, Nickel Oxide (NiO) nano-particles are directly grown over the surface of stainless steel substrate. In still further embodiment, Nickel Oxide (NiO) nano-flakes are directly grown over the surface of stainless steel substrate. In an embodiment, NiO nano-flakes (nano-particles) include highly dense vertical arrays of interconnected NiO nano-flakes.
[0059] In an embodiment, chemical bath deposition (CBD) method can be used to deposit and/or grow one or more layers of highly dense vertical arrays of interconnected Nickel Oxide (NiO) nano-flakes or nano-particles on a stainless steel (SS) substrate (current collector). Solution for the CBD can be prepared by mixing nickel sulphate or any other nickel precursor or nickel salts known to a person skilled in the art, potassium per-sulphate or any other oxidizing agent(s) known to a person skilled in the art and ammonia (preferably aqueous solution). The solution can then be kept under intermittent or continuous stirring at an appropriate temperature. A cleaned piece of substrate can be suspended into the CBD solution for a time period sufficient to generate a film (layer) of desired thickness over the substrate. After formation of uniform layer (film) over the substrate, the substrate can be taken out from the solution, washed with water and dried. In case of a need of provision of further layers, the abovementioned steps can be repeated one or more times. Exemplary Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) images of Nickel oxide nano-flakes prepared in accordance with embodiments of the present disclosure are illustrated in Figure 1C and Figure 1D.
[0060] In an embodiment, a battery is provided utilizing an electrode that includes a stainless steel (SS) substrate and one or more layers of Nickel Oxide (NiO) nano-particles disposed over its surface. The battery can include a container, a negative electrode, a positive electrode prepared in accordance with embodiments of the present disclosure including a stainless steel (SS) substrate with one or more layers of Nickel Oxide (NiO) nano-particles disposed over its surface, an electrolyte, and a separator (optional and may be a polyethylene or the like component). The positive electrode, the negative electrode, the electrolyte, and the separator are positioned within the container, and a negative terminal and a positive terminal can be disposed on or electrically connected to the negative current collector layer of the anode and the positive current collector layer of the cathode to allow connection of the battery to an electrical circuit/power use or storage circuit.
[0061] In an embodiment, the electrode can include a stainless steel (SS) substrate and hematite (a-Fe2O3) nano-particles disposed over its surface. In an embodiment, hematite (a-Fe2O3) nano-particles can include hematite (a-Fe2O3) nano-rods. In another embodiment, hematite (a-Fe2O3) nano-particles are directly grown over the surface of current collector. In still another embodiment, hematite (a-Fe2O3) nano-particles are directly grown over the surface of stainless steel substrate. In still further embodiment, hematite (a-Fe2O3) nano-rods are directly grown over the surface of stainless steel substrate.
[0062] In an embodiment, one or more layers of high-density arrays of a-Fe2O3 nano-rods (nano-particles) with oxygen vacancies in the hematite lattice can be synthesized on the SS substrate using a modified hydrothermal method. An appropriate amount of iron (III) chloride (FeCl3) or any other precursor or salts thereof as known to a person skilled in the art, and an appropriate amount of sodium nitrate (NaNO3) or any other nitrate salts known to a person skilled in the art can be mixed in water at an appropriate pH. The resultant solution can be transferred to an autoclave (preferably a Teflon lined stainless steel autoclave) containing a cleaned SS substrate. The autoclave can then be heated at a suitable temperature (preferably in an air oven) for appropriate time. A uniform yellow layer of iron oxy-hydroxide (FeOOH) can be observed on the substrate, which can then be washed (preferably with deionized water and acetone) to remove any residual salts followed by drying at an elevated temperature (preferably in an air oven). Subsequently, iron oxy-hydroxide sample can be sintered in a furnace at an elevated temperature under N2 atmosphere for appropriate time period. During this process, FeOOH completely gets converted to iron oxide (a-Fe2O3) accompanied by the change of yellowish color of the layer on the SS substrate to brick red. Exemplary Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) images of hematite (a-Fe2O3) nano-rods prepared in accordance with embodiments of the present disclosure are illustrated in Figure 1A and Figure 1B. According to the advantageous method(s) of the present disclosure, hematite nano-rods (nano-particles) can be fabricated with introduction of oxygen vacancies within hematite lattice during the synthetic process. As can be observed from Figure 1A and Figure 1B, each nano-rod can include several nano-strips having average width between 16 nm and 25 nm, which are bunched together in a well-defined way. Such structure facilitates ion and electron transfer processes during electrochemical reactions.
[0063] In an embodiment, a battery is provided utilizing an electrode that includes a stainless steel (SS) substrate and hematite (a-Fe2O3) nano-particles disposed over its surface. The battery can include a container, a negative electrode prepared in accordance with embodiments of the present disclosure including a stainless steel (SS) substrate with one or more layers of hematite (a-Fe2O3) nano-particles disposed over its surface, a positive electrode, an electrolyte, and a separator (optional and may be a polyethylene or the like component). The positive electrode, the negative electrode, the electrolyte, and the separator are positioned within the container, and a negative terminal and a positive terminal can be disposed on or electrically connected to the negative current collector layer of the anode and the positive current collector layer of the cathode to allow connection of the battery to an electrical circuit/power use or storage circuit.
[0064] In an embodiment, a substrate-integrated nickel–iron ultra-battery (NiO//a-Fe2O3 ultra-battery) is provided utilizing nickel oxide (NiO) nano-flakes and hematite (a-Fe2O3) nano-rods as electroactive materials for its positive and negative electrodes, respectively. These nanostructures can be grown directly on highly-conductive stainless steel substrate (substrate integrated growth) so as to enhance mechanical integrity of the electro-active materials with the substrate. Further, directly growing nanostructures onto the substrate (current collector) completely avoids the use of any binder that could add to the internal resistance of the electrodes. This special nano-architectural design of positive and negative electroactive materials can provide large number of interaction sites for the electrolytic ions with the electrode materials in conjunction with short ion-diffusion paths for efficient ion intercalation/deintercalation of ionic species from electrolyte, which significantly improve the capacitive performance of individual electrodes and hence of the fabricated ultra-battery.
[0065] Negative electrode of the cell can comprise hematite nano-rods because of its high redox activity, abundance, high stability and most environment friendly among all other transition metal oxides. However, low electronic conductivity and short hole diffusion length limit their electrochemical activity significantly. In accordance with embodiments of the present disclosure, these factors can be taken care of by fabricating nano-rods of hematite and through the introduction of oxygen vacancies within hematite lattice during synthetic process. Each nano-rod can include several nano-strips having average width between 16 nm and 25 nm, which are bunched together in a well-defined way. Such structure facilitates ion and electron transfer processes during electrochemical reactions. Similarly, highly dense vertical arrays of interconnected NiO nano-flakes can provide huge surface area for the redox reactions. Besides, the narrow width of the flakes shortens the ion-diffusion path significantly, thus facilitating ion and charge transfer. Furthermore, the interconnecting nature of the nano-flakes among themselves improves charge-transfer kinetics and helps free movement of electrons to the current collector during the redox reactions.
[0066] Substrate-integrated growth of individual nanostructures in ultra-battery, in accordance with embodiments of the present disclosure, can improve contact resistance of electrodes. In the present invention, nanostructures have been grown directly on current collector which not only improves mechanical integrity of the system, but also facilitates the electron transfer from electrolyte to current collector thus improving power density limit and reduces self-discharge loss, thus improves cell voltage. Moreover, higher mechanical stability and structural integrity of these substrate integrated nanostructures can help them to sustain enormous volume changes during repetitive ion intercalation/deintercalation processes during long cycling, thus improving cycle life/calendar life of fabricated nickel-iron ultra-battery.
[0067] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.
EXAMPLES
[0068] Example 1: Fabrication of NiO//a-Fe2O3 ultra-battery
Fabrication of an electrode including a stainless steel substrate (current collector) with one or more layers of nickel oxide (NiO) nano-particles directly grown over its surface
In accordance with embodiments of the present disclosure, high-density vertical arrays of interconnected NiO nano-flakes (nano-particles) were prepared on stainless steel (SS) substrate following a chemical bath deposition (CBD) method. Solution for the CBD was prepared by mixing 40 mL of 1M nickel sulphate, 30 mL of 0.25M potassium per-sulphate and 10 mL of aqueous ammonia (25-28%) in a beaker. The solution was then kept under continuous stirring at 200 rpm at room temperature. A cleaned piece of SS substrate (5.5×2.1 cm2 in size) was suspended vertically into the CBD solution to deposit the precursor film. After about 30 minutes, the substrate was taken out from the solution, washed copiously with distilled water and kept in an air oven at 800C for drying. The film deposited on the substrate was found to be uniform and grey in color. Finally, the grey colored layer on the SS substrate was annealed in air at 5000C for 1.5 h. By carefully weighing the substrate prior and after the deposition process, the mass loading of the NiO nano-flakes grown on SS substrate was found to be 0.2 mg/cm2. Exemplary Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) images of Nickel oxide nano-flakes prepared in accordance with embodiments of the present disclosure are illustrated in Figure 1C and Figure 1D. Stainless steel substrate with a layer of NiO nano-flakes directly grown over its surface was employed as the positive electrode for realizing an ultra-battery in accordance with embodiments of the present disclosure.
Fabrication of an electrode including a stainless steel substrate (current collector) with one or more layers of hematite (a-Fe2O3) nano-particles directly grown over its surface
In accordance with embodiments of the present disclosure, one or more layers of high-density arrays of nitrogenated a-Fe2O3 nano-rods (nano-particles) were synthesized on the SS substrate using a modified hydrothermal method. 0.15 M of iron (III) chloride (FeCl3) and 1M of sodium nitrate (NaNO3) were mixed in water at a pH 1.5 in a beaker at room temperature. The resultant solution was transferred to a 60 ml Teflon lined stainless steel autoclave containing SS substrate of size 5.75×2.85 cm2. Prior to this, SS substrate was cleaned adequately with alcohol, acetone and finally with deionized water in an ultrasonicator. The autoclave was then heated at 950C in an air oven for 20 hours. A uniform yellow layer of iron oxy-hydroxide (FeOOH) was formed on the substrate, which was then washed copiously with deionized water and acetone to remove any residual salts followed by drying at 800C in an air oven. Subsequently, iron oxy-hydroxide sample was sintered in a tubular furnace at 4000C under N2 atmosphere for 1 hour. During this process, FeOOH was completely converted to iron oxide (a-Fe2O3) accompanied with the change in yellowish color of the layer on the SS substrate to brick red. In this case, the loading density of hematite nano-rods was found to be 0.18 mg/cm2. Exemplary Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) images of hematite (a-Fe2O3) nano-rods prepared in accordance with embodiments of the present disclosure are illustrated in Figure 1A and Figure 1B. Stainless steel substrate with a layer of a-Fe2O3 nano-rods directly grown over its surface was employed as the negative electrode for realizing an ultra-battery in accordance with embodiments of the present disclosure.
[0069] A battery was realized employing a stainless steel substrate with a layer of NiO nano-flakes directly grown over its surface as the positive electrode, a stainless steel substrate with a layer of a-Fe2O3 nano-rods directly grown over its surface as the negative electrode, aqueous electrolytes and a separator. Exemplary performance parameters of the assembled battery are illustrated in Figures 2A, 2B, 2C and 2D. Figure 2A illustrates an exemplary cyclic voltammetry data for the assembled cell at different potential scan rates within 0V to 1.4V. Figure 2B illustrates an exemplary constant current charge/discharge plots at different current densities with a potential window of 1.4 V. Figure 2C illustrates an exemplary variation in specific capacitance and capacity of the NiO//a-Fe2O3 ultra-battery as a function of current density. Figure 2D illustrates an exemplary cycling performance of the assembled NiO//a-Fe2O3 ultra-battery. Table 1 below highlights exemplary performance parameters for the NiO//a-Fe2O3 ultra-battery realized in accordance with embodiments of the present disclosure.
Table 1
Parameters Positive electrode
(NiO) Negative electrode
(a-Fe2O3) NiO//a-Fe2O3 ultra-battery
Operating voltage (V) 0V to 0.5V 0V to -0.85V 0V to 1.4V
Specific capacitance
@ 2mV/s 500 F/g 215.6 F/g 112 F/g
Capacity @ 2mV/s 69.4 mAh/g 50.9 mAh/g 44 mAh/g
Cycling performance 83% after 1000 cycles 99% after 1000 cycles ~ 80% after 1000 cycles
Response time - - ~ 0.77s
Maximum energy and power density - - 25Wh/kg and 7kW/kg

[0070] As evident from Table 1 above, nickel-iron ultra-battery prepared according to embodiments of the present disclosure exhibits the specific capacity value of at least 40 mAh/g (specific capacitance ~ 112 F/g and volumetric capacitance ~ 0.92 F/cm3) at a scan rate of 2 mV/s in a potential window between 0 V and 1.4 V, with capacitance retention of ~ 55 % of its original value when the scan rate is increased 100 times. More importantly, maximum energy and power density values achievable with the ultra-battery of the present disclosure are ~ 25 Wh/kg and ~ 7 kW/kg respectively, which are superior to other reported pristine nickel, iron and other transition metal/metal oxide-based energy storage devices.

ADVANTAGES OF THE PRESENT INVENTION
[0071] The present disclosure overcomes disadvantages associated with conventional nickel-iron cell (battery).
[0072] The present disclosure provides a nickel-iron ultra-battery with significantly improved capacitive performance.
[0073] The present disclosure provides a nickel-iron ultra-battery that completely avoids use of carbon or binder material to reduce internal resistance.
[0074] The present disclosure provides a nickel-iron ultra-battery that employs nickel oxide (NiO) nano-flakes grown directly on current collector(s). The present disclosure provides a nickel-iron ultra-battery that employs hematite (a-Fe2O3) nano-rods grown directly on current collector(s).
[0075] The present disclosure provides a nickel-iron ultra-battery that employs nickel oxide (NiO) nano-flakes grown directly on highly-conductive stainless steel substrate(s). The present disclosure provides a nickel-iron ultra-battery that employs hematite (a-Fe2O3) nano-rods grown directly on highly-conductive stainless steel substrate(s).
[0076] The present disclosure provides a nickel-iron ultra-battery that employs nickel oxide (NiO) nano-flakes and hematite (a-Fe2O3) nano-rods as electroactive materials for its respective positive and negative electrodes.
[0077] The present disclosure provides a nickel-iron ultra-battery that employs electrodes with enhanced mechanical integrity of electro-active materials with the substrate.
[0078] The present disclosure provides nickel oxide (NiO) nano-flakes with narrow width grown directly on the substrate(s) to shorten the ion-diffusion path to facilitate ion and charge transfer.
[0079] The present disclosure provides a nano-architectural design of positive and negative electroactive materials that can provide large number of interaction sites for electrolytic ions with electrode material(s) in conjunction with short ion-diffusion paths for efficient ion intercalation/deintercalation of ionic species from electrolyte(s).
[0080] The present disclosure provides nano-rods of hematite with oxygen vacancies within the hematite lattice.
[0081] The present disclosure provides highly dense vertical arrays of interconnected NiO nano-flakes that can essentially provide huge surface area for the redox reactions.
[0082] The present disclosure provides improved electrodes that can sustain enormous volume change by repetitive ion intercalation/deintercalation process during long cycling test.
[0083] The present disclosure provides a nickel-iron ultra-battery with improved cycle life/calendar life.