DESC:TECHNICAL FIELD
[0001] The disclosure generally relates to the field of electrochemical energy storage. In particular, the present disclosure relates to a process for substrate-integrated growth of nanostructured electroactive material on a substrate (current collector) for their utility in electrochemical energy storage devices.

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] Energy storage requirements continue to grow as the electronic, portable power, and energy infrastructure industries expand and transition away from more historic non-renewable energy supplies. For example, there has been a renewed interest in batteries and other energy storage devices for use in electric and hybrid automobiles, and this has been caused, in part, by volatile oil costs and the possibility of catastrophic climate change that has greatly drawn scientific attention toward the development of electrical and hybrid vehicles powered by rechargeable batteries, e.g., rechargeable lithium-ion (Li-ion) batteries that may be powered with electricity from renewable sources. Similarly, there is on-going research in ways to make lighter and more efficient batteries for electronic devices ranging from portable computers to cellular phones and other wireless communication devices.
[0004] General goals for battery manufacturers include providing long life and significant power levels with the least amount of weight while also providing a recharging functionality. More specifically, one of the most critical parameters for new energy storage technologies and designs is the demand for higher energy densities (i.e., energy storage per unit of battery or storage device weight). Additionally, there is growing concern over potential long term environmental impacts of product manufacture and use, and, the energy storage industry continues to search for storage devices that can make use of environmentally benign or green materials while still providing desirable energy densities. Unfortunately, many existing electrode materials that have high durable capacities and good rate capability are expensive and/or are toxic. Furthermore, improved energy density and rate capabilities are still demanded by the battery and other energy storage industries such as for battery designs facilitating a successful deployment of a fleet of electric vehicles. Hence, there remains a need for electrodes fabricated from abundant and nontoxic elements with durable high-reversible capacity and highly improved rate capability.
[0005] 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 based 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. The active materials are held in nickel-plated steel tubes or perforated pockets.
[0006] Iron-based batteries are both mechanically and electrically rugged as these batteries are tolerant tovariety of abuses (overcharge, overdischarge, 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 batteriesare often used in backup situations where they can be continuously charged.The ability of these batteries to survive frequent cycling is due to the low solubility of the reactants in the electrolyte. The formation of metallic iron during charge is slow because of the low solubility of the ferrous hydroxide. While the slow formation of iron crystals preserves the electrodes, it also limits the high rate performance. These cells charge slowly, and also able to discharge slowly which has limited their applications. Further, Nickel-iron cells should not be charged from a constant voltage supply since they can be damaged by thermal runaway. The cell internal voltage drops as gassing begins, raising the temperature, which increases current drawn and so further increases gassing and temperature.Due to its low specific energy, poor charge retention, and high cost of manufacture, other types of rechargeable batteries have displaced the nickel-iron battery in most applications.
[0007] Conventionally, electrodes have been fabricated by pasting slurry of electroactive materials prepared through mixing of active materials with binder and activated carbon, on appropriate mesh like structure or other substrate. However, such processes enhance internal resistance between electrode material and current collector, thus limiting overall power output, self-discharge and cycle life of the cell. A significant amount of research has been done in this technological domain to overcome one or more disadvantages associated with such processes and to improve their practical utility. However, to the best of our knowledge, none of the prior arts reportedmethod teaches preparation of electrodes for their utility in a battery,which can overcome the limitations of low power density of nickel-iron batteries apart from others mentioned above.
[0008] There is therefore an immediate need in the art for improved process for preparation of electrodes that facilitates electron/ion transfer from electrolyte to current collector and thus reduces internal resistance significantly and improvesthe power density of the cell (battery).

OBJECTS OF THE INVENTION
[0009] An object of the present disclosure is to overcome disadvantages associated with conventionalprocesses for preparation of electrodes for their utility in electrochemical devices.
[0010] Another object of the present disclosure is to providea process for substrate-integrated growth of nanostructured electroactive material(s) on a substrate (current collectors).
[0011] Another object of the present disclosure is to provide a process of directly growing nanostructured electro-active materials on highly-conductive substrate(s) to enhance mechanical integrity of the electro-active materials with the substrate.
[0012] Another objective of the present disclosure is to provide an improved process for preparation of electrodes to completely avoid the use of any binder.
[0013] Another object of the present disclosure is to provide a process of growing nickel oxide (NiO) nano-flakes directly on highly-conductive stainless steel substrate(s).
[0014] Another object of the present disclosure is to provide a process of growing hematite (a-Fe2O3) nano-rods directly on highly-conductive stainless steel substrate(s).
[0015] Another object of the present disclosure is to provide a process of growing nickel oxide (NiO) nano-flakes with narrow width directly on the substrate(s) to shorten the ion-diffusion path to facilitate ion and charge transfer.
[0016] Another objective of the present disclosure is to provide an improved process for preparation of electrodes, utilization of which can significantly improve the capacitive performance of individual electrodesand hence, of the fabricated battery.
[0017] Another objective of the present disclosure is to provide a process of fabricating nano-rods of hematite with oxygen vacancies within the hematite lattice.
[0018] Another objective of the present disclosure is to provide a process of fabricating highly dense vertical arrays of interconnected NiOnano-flakes that can essentially provide huge surface area for the redox reactions.
[0019] Another objective of the present disclosure is to provide an improved process for preparation of electrodes that can sustain enormous volume change by repetitive ion intercalation/deintercalation process during long cycling test.
[0020] Another objective of the present disclosure is to provide an improved process for preparation of electrodes that can improve cycle life/calendar life of a battery fabricated therefrom.

SUMMARY
[0021] The present disclosure relates toelectrochemical energy storage batteries. In particular it pertains to improvement in internal resistance of these batteries by facilitating electron/ion transfer from electrolyte to current collector and concomitantly improving power density of these batteries.
[0022] In an aspect, electron/ion transfer from electrolyte to current collector is done through substrate integrated nanostructured electroactive materials grown directly on the current collectors. In an aspect,directly growing the nanostructures on the current collector 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, improving 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 battery.
[0023] In accordance with embodiments of the present invention, a substrate can be selected from the group including but not limited to a conductor substrate, a semiconductor substrate and a dielectric substrate (with provision of appropriate conductor layer lamination). In an embodiment, Stainless Steel (SS) can be used as a substrate to work as a 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.
[0024] In an embodiment, the anode and/or cathode can be grown directly on surface of current collectors/ substrate without using any additional binder(s) or carbon or carbonaceous material(s).
[0025] In an embodiment, the present disclosure provides an Iron-based alkaline rechargeable battery wherein nanostructures grown on the cathodes and the anodes are of iron based and nickel basedelectroactive materials respectively. In an embodiment, nickel oxide (NiO) is used as an active material for fabrication of anode of the cell, andhematite is used as an active material for fabrication of cathode of the cell.
[0026] To overcome limitations associated with conventional nickel oxide (NiO) electrodes, the advantageous method according to embodiments of the present disclosure allows for fabrication of highly dense vertical arrays of interconnected nickel oxide (NiO) nano-flakeswhich can provide huge surface area for the redox reactions. Further, 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.
[0027] In accordance with embodiments of the present invention, a method 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 SS substrate is disclosed. The method can be a Chemical Bath Deposition (CBD) method. The method can include steps of (i) preparing asolution for the CBD by mixing a nickel precursor or nickel salts such as nickel sulphate, an oxidizing agent such as potassium per-sulphate and aqueous solution of ammonia; (ii) keeping the solution under intermittent or continuous stirring at an appropriate temperature; (iii) suspending a cleaned piece of substrate into the CBD solution for a time period sufficient to generate a layerof nano-flakes of nickel hydroxide (a-3Ni (OH)2.2H2O)of desired thickness over the substrate; (iv) washingand drying the substrate after taking it out from the solution; and (v) annealing the deposited layer of nickel hydroxide (a-3Ni (OH)2.2H2O) by heating the substrate in an oven at 500o C for 1.5 h in air atmosphere to convert nickel hydroxide to NiO. In case of a need of provision of further layers, the abovementioned steps can be repeated one or more times.
[0028] In an embodiment, hematite used as an active material for fabrication of cathode of the cell provides advantage of high redox activity, abundance, high stability and being most environment friendly among all other transition metal oxides. However, low electronic conductivity and short hole diffusion length severely limit their electrochemical activity. These factors can be taken care of by following advantageous method of the present disclosure that allows fabrication of hematite nano-rods with introduction of oxygen vacancies within hematite lattice structure during their syntheses process. Further, advantageous method of the present disclosure allow for fabrication of hematite nano-rods, wherein each nano-rod can include several nano-strips with average width between 16 nm and 25 nm bunched together in a well-defined way to facilitates ion and electron transfer processes during electrochemical reactions.
[0029] In accordance with embodiments of the present invention, a method to deposit and/or grow one or more layers of high-density arrays of a-Fe2O3nano-rods or nano-particles with oxygen vacancies in the hematite lattice structureon the SS substrateis disclosed. The disclosed method uses a modified hydrothermal method and includes steps of (i) preparing a aqueous solution of an appropriate pH with required amounts of an iron precursor such as Ferric Chloride (FeCl3) and a sodium salt such as Sodium Nitrate (NaNO3); (ii) transferring the prepared solution to an autoclave such as a Teflon lined stainless steel autoclave; (iii) positioning a cleaned SS substrate within the solution; (iv)heating the autoclave at a suitable temperature for appropriate time, wherein a uniform yellow layer of iron oxy-hydroxide (FeOOH) shall be deposited/grownover the substrate; (v)washing the substrate with deionized water and acetone to remove any residual salts followed by drying at an elevated temperature preferably in an air oven; and (vi) sintering iron oxy-hydroxide in a furnace at an elevated temperature under N2 atmosphere during which FeOOH gets completely converted to iron oxide (a-Fe2O3) accompanied by change of color of the layer on the SS substrate from yellowish to brick red.
[0030] In an aspect, each nano-rod deposited over the substrate following the disclosed method can include several nano-strips having average width between 16 nm and 25 nm, which are bunched together in a well-defined way. The structure facilitates ion and electron transfer processes during electrochemical reactions.According to the advantageous method of the present disclosure, hematite nano-rods /nano-particles can be fabricated with introduction of oxygen vacancies within hematite lattice during the synthetises process.
[0031] In an aspect, a rechargeable battery (NiO//a-Fe2O3ultra-battery)realized using electrodes prepared in accordance with advantageous methods of the present disclosurecan exhibit aspecific 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 at least 55 % of its original value when the scan rate is increased 100 times. More importantly, energy and power density values achievable with such a battery can be at least 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.
[0032] 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 drawing figures in which like numerals represent like components

BRIEF DESCRIPTION OF THE DRAWINGS
[0033] 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.
[0034] FIG. 1(a) illustrates an exemplary Scanning Electron Microscope (SEM) image of hematite nano-rods prepared in accordance with embodiments to the present disclosure.
[0035] FIG. 1(b) illustrates an exemplary Transmission Electron Microscope (SEM) image of hematite nano-rods prepared in accordance with embodiments to the present disclosure.
[0036] FIG. 1(c) illustrates an exemplary Scanning Electron Microscope (SEM) image of Nickel oxide nano-flakes prepared in accordance with embodiments to the present disclosure.
[0037] FIG. 1(d) illustrates an exemplary Transmission Electron Microscope (SEM) image of Nickel oxide nano-flakes prepared in accordance with embodiments to the present disclosure.
[0038] FIG. 2 illustrates an exemplary flow diagram for method for growing substrate integrated nano-flakes of Nickel Oxide (NiO) on a substrate in accordance with embodiments of the present disclosure.
[0039] FIG. 3 illustrates an exemplary flow diagram for method for growingsubstrate integrated high-density arrays of a-Fe2O3nano-rods with oxygen vacancies in the hematite lattice structureon a substrate in accordance with embodiments to the present disclosure.
[0040] FIG. 4(a) 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.
[0041] FIG. 4(b) illustrates an exemplary constant current charge/discharge plots at different current densities with a potential window of 1.4Vin accordance with embodiments to the present disclosure.
[0042] FIG. 4(c) illustrates an exemplary variation in specific capacitance and capacity of the NiO//a-Fe2O3 ultra-battery as a function of current densityin accordance with embodiments to the present disclosure.
[0043] FIG. 4(d) illustrates an exemplary cycling performance of the assembled NiO//a-Fe2O3 ultra-batteryin accordance with embodiments to the present disclosure.
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DETAILED DESCRIPTION
[0044] 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 detail 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.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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.
[0049] Various terms as used herein are usedbelow. 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.
[0050] Substrate-integrated growth of individual nanostructures of electroactice materials on cathodes and anodes of cells of electrochemical storage batteries, 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 battery.
[0051] In accordance with embodiments of the present invention, a substrate working as current collector, can be selected from the group including but not limited to a conductor substrate, a semiconductor substrate and a dielectric substrate (with the provision of appropriate conductor layer lamination). In an embodiment, stainless steel can be used as a substrate 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 anodesand cathodes can be realized including a stainless steel substrate and one or more layers of nanostructures of electroactive materials substantially uniformly distributed about the stainless steel substrate. In an embodiment, the electroactive materials can be grown directly on the surface of the current collector/substrate without using any additional binder(s) or carbon or carbonaceous material(s).
[0052] In an embodiment, nickel oxide is used as an active material for fabrication of a positive electrode (anode) of the cell. To overcome limitations associated with conventional nickel oxide (NiO) electrodes, the advantageous method according to embodiments of the present disclosure allows for fabrication of highly dense vertical arrays of interconnected nickel oxide (NiO)nano-flakes,which can provide huge surface area for the redox reactions. Further, 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. In an embodiment, NiOnano-flakes (nano-particles) include highly dense vertical arrays of interconnected NiOnano-flakes.
[0053] 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.
[0054] In accordance with embodiments of the present invention,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.
[0055] FIG. 2 illustrates an exemplary flow diagram for method for growing substrate integrated nano-flakes of Nickel Oxide (NiO) on a substrate in accordance with embodiments of the present disclosure. The method can at step 202 involve preparing a solution for implementing Chemical Bath Deposition (CBD) methodby mixing a nickel precursor or nickel salts such as nickel sulphate, an oxidizing agent(s) such as potassium per-sulphate and ammonia (preferably an aqueous solution of ammonia). At step 204 the solution can be kept under intermittent or continuous stirring at an appropriate temperature. At step 206 a cleaned piece of substrate can be suspended into the CBD solution for a time period sufficient to generate anickel hydroxide (a-3Ni (OH)2.2H2O) 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 as shown at step 208. In case of a need of provision of further layers, the abovementioned steps can be repeated one or more times. At step 210 the deposited layer ofnickel hydroxide (a-3Ni (OH)2.2H2O)can be annealed by heating the substrate in an oven at 500o C for 1.5 h in air atmosphere to convert nickel hydroxide to NiO.
[0056] In an embodiment, hematite is used as an active material for fabrication of a negative electrode of the cell because of its high redox activity, abundance, high stability and being most environment friendly among all other transition metal oxides. However, low electronic conductivity and short hole diffusion length severely limit their electrochemical activity. These factors can be taken care of by following advantageous method(s) of the present disclosure that allows fabrication of hematite nano-rods with introduction of oxygen vacancies within hematite lattice structure during their synthetic process. Further, advantageous method of the present disclosure allows fabrication of hematite nano-rods, wherein each nano-rod can include several nano-strips with average width between 16 nm and 25 nm bunched together in a well-defined way to facilitates ion and electron transfer processes during electrochemical reactions.
[0057] In an embodiment, the cathodecan include a stainless steel (SS) substrate working as a current collector and substrate integrated hematite (a-Fe2O3) nano-structuresover surface of the current collector. 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 the current collector. 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. 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.
[0058] FIG. 3 illustrates an exemplary flow diagram for method for growingsubstrate integrated high-density arrays of a-Fe2O3nano-rods with oxygen vacancies in the hematite lattice structureon a SS substrate in accordance with embodiments to the present disclosure.In accordance with embodiments of the present disclosure, one or more layers of high-density arrays of a-Fe2O3nano-rods (nano-particles) with oxygen vacancies in the hematite lattice structure can be synthesized on the SS substrate using a modified hydrothermal method. The method can include steps 302 of preparing an aqueous solution of an iron precursor or salts thereof such as iron (III) chloride (FeCl3), and an appropriate amount of a nitrate salt such as sodium nitrate (NaNO3). At step 304 the preparedsolution can be transferred to an autoclave (preferably a Teflon lined stainless steel autoclave). At step 306 a cleaned SS substrate can bepositioned within the solution and the autoclave can be heated at a suitable temperature (preferably in an air oven) for appropriate time as at step 308. A uniform yellow layer of iron oxy-hydroxide (FeOOH) can be observed on the substrate, which can at step 310be washed (preferably with deionized water and acetone) to remove any residual salts followed by drying at an elevated temperature (preferably in an air oven). At step 312 the substrate can be subjected to sintering in a furnace at an elevated temperature under N2 atmosphere for appropriate time period for convertingthe layer of iron oxy-hydroxide (FeOOH)to iron oxide (a-Fe2O3) which shall be evident by change of yellowish color of the layer on the SS substrate to brick red.
[0059] In an aspect, the electrodes constructed using concept of the present disclosure 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.
[0060] 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.
[0061] 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.
[0062] In an embodiment, a battery is realized utilizing an electrode, prepared in accordance with advantageous method(s) of the present disclosure, 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 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.
[0063] In an embodiment, a battery is realized utilizing an electrode, prepared in accordance with advantageous method(s) of the present disclosure, 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 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 nickel–iron ultra-battery (NiO//a-Fe2O3 ultra-battery) is realized utilizing nickel oxide (NiO) nano-flakes as electroactive materials for its positive electrode and hematite (a-Fe2O3) nano-rods as electroactive materials for its negative electrode, which are prepared in accordance with advantageous methods of the present disclosure. The battery can include a container, a negative electrode including a stainless steel (SS) substrate with one or more layers of hematite (a-Fe2O3) nano-particles disposed over its surface, a positive electrode including a stainless steel (SS) substrate with nickel oxide (NiO) nano-flakes 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.
[0065] The nanostructures grown directly on highly-conductive stainless steel substrate (substrate integrated growth), 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.

EXAMPLES
[0066] Example 1: 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 NiOnano-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 layerof nickel hydroxide (a-3Ni(OH)2. 2H2O) on the SS substrate was annealed in air at 5000C for 1.5 hfor complete conversion of nickel hydroxide into NiO. By carefully weighing the substrate prior and after the deposition process, the mass loading of the NiOnano-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.
[0067] Example 2: 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-Fe2O3nano-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.
[0068] Example 3: Fabrication of a battery utilizing nickel oxide (NiO) nano-flakes directly grown over the surface of stainless steel substrate as the positive electrode and hematite (a-Fe2O3) nano-rods directly grown over the surface of stainless steel substrate as the negative electrode

A battery was realized employing a stainless steel substrate with a layer of NiOnano-flakes directly grown over its surface as the positive electrode, a stainless steel substrate with a layer of a-Fe2O3nano-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 4A, 4B, 4C and 4D. FIG. 4A illustrates an exemplary cyclic voltammetry data for the assembled cell at different potential scan rates within 0V to 1.4V. FIG 4B illustrates an exemplary constant current charge/discharge plots at different current densities with a potential window of 1.4 V. FIG 4C illustrates an exemplary variation in specific capacitance and capacity of the NiO//a-Fe2O3 ultra-battery as a function of current density. FIG 4D 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

[0069] As evident from Table 1 above, a battery (NiO//a-Fe2O3ultra-battery) realized using electrodes, prepared in accordance with advantageous methods of the present disclosure,can exhibit 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 such a battery can be ~ 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.
[0070] 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.

ADVANTAGES OF THE PRESENT INVENTION
[0071] The present disclosure overcomes disadvantages associated with conventional process(es) for preparation of electrodes for their utility in electrochemical device(s).
[0072] The present disclosure provides a process of substrate-integrated growth of nanostructured electroactive materials on current collectors.
[0073] The present disclosure provides a process of directly growing nanostructured electro-active materials on highly-conductive substrate(s) to enhance mechanical integrity of the electro-active materials with the substrate.
[0074] The present disclosure provides an improved process for preparation of electrodes to completely avoid the use of any binder.
[0075] The present disclosure provides a process of growing nickel oxide (NiO) nano-flakes directly on highly-conductive stainless steel substrate(s).
[0076] The present disclosure provides a process of growing hematite (a-Fe2O3) nano-rods directly on highly-conductive stainless steel substrate(s).
[0077] The present disclosure provides a process of growing nickel oxide (NiO) nano-flakes with narrow width directly on the substrate(s) to shorten the ion-diffusion path to facilitate ion and charge transfer.
[0078] The present disclosure provides an improved process for preparation of electrodes, utilization of which can significantly improve the capacitive performance of individual electrodes and hence, of the fabricated battery.
[0079] The present disclosure provides a process of fabricating nano-rods of hematite with oxygen vacancies within the hematite lattice.
[0080] The present disclosure provides a process of fabricating highly dense vertical arrays of interconnected NiOnano-flakes that can essentially provide huge surface area for the redox reactions.
[0081] The present disclosure provides an improved process for preparation of electrodes that can sustain enormous volume change by repetitive ion intercalation/deintercalation process during long cycling test.
[0082] The present disclosure provides an improved process for preparation of electrodes that can improve cycle life/calendar life of a battery fabricated therefrom.
,CLAIMS:1. An electrochemical energy storage battery comprising one or more cells, each of the one or more cells having cathodes and anodes, wherein the cathodes and the anodes are made up of a substrate working as a current collector and substrate integrated nanostructures of electroactive materials.

2. The battery as claimed in claim 1, wherein the substrate integrated nanostructures of electroactive materials are grown over the substrates.

3. The battery as claimed in claim 1, wherein the substrate isof Stainless Steel.

4. The battery as claimed in claim 2, wherein the battery is an iron based alkaline battery, and the nanostructures grown on the cathodes and the anodes are of iron based and nickel basedelectroactive materials respectively,and wherein the nanostructures work to lower internal resistance and self-discharge of the cells.

5. The battery as claimed in claim 4, wherein the iron based and nickel based electroactive materials grown on the cathodes and the anodes are hematite (a-Fe2O3) and nickel oxide (NiO) respectively.

6. The battery as claimed in claim 5, wherein shape of nanostructures of hematite (a-Fe2O3) and nickel oxide (NiO) is nano-rods and nano-flakes respectively.

7. The battery as claimed in claim 5, wherein specific capacity value of the cells is at least 44 mAh/g at a scan rate of 2 mV/s in a potential window between 0.0 V - 1.4 V, with capacitance retention of at least 55 % of its original value when the scan rate is increased 100 times.

8. The battery as claimed in claim 5, wherein energy and power density values of the cells are at least 25 Wh/kg and 7 kW/kg respectively.

9. A method for growing nanostructures of an nickel based electroactive material on a substrate, the method comprising steps of:
preparing a solution of a nickel precursor, an oxidizing agent and aqueous solution of ammonia;
keeping solution under intermittent or continuous stirring at an appropriate temperature;
suspending the substrate for growth of layer of nanostructures ofNickel hydroxide of desired thickness over the substrate;
washing and drying the substrate: and
annealing in a furnace at elevated temperature in air atmosphere for complete conversion of nickel hydroxide into NiO.

10. The method of claim 9, wherein the substrate is Stainless Steel current collector and the current collector with grown nanostructures of nickel based electroactive material is used as anodes in cells of an iron based alkaline battery.

11. The method of claim 9, wherein the nanostructures ofnickel based electroactive material are nano-flakes, wherein the nano-flakes form highly dense vertical arrays of interconnected network on the substratefor fast electron transfer to the current collector during electrochemical reactions..

12. A method for growing nanostructures of an iron based electroactive material on a substrate, the method comprising steps of:
preparing an aqueous solution of appropriate pH of an iron precursor and a sodium salt;
transferring the prepared solution to an autoclave;
positioning the substrate within the solution;
heating the autoclave for growth of a layer of iron oxy-hydroxide (FeOOH) over the substrate;
washing the substrate with deionized water and acetone followed by drying at an elevated temperature; and
sintering in a furnace at elevated temperature under N2 atmosphere to convert FeOOH to iron oxide (a-Fe2O3).

13. The method of claim 12, wherein the substrate is Stainless Steel current collector and the current collector with grown nanostructures of ironbased electroactive material is used as cathodes in cells of an iron based alkaline battery.

14. The method of claim 12, wherein the nanostructures of the ironbased electroactive material are nano-rods, wherein each nano-rod includes several nano-strips with average width between 16 nm and 25 nm bunched together in a well-defined way to facilitates ion and electron transfer processes during electrochemical reactions.