RELATED APPLICATION

This application claims the benefit of Indian Provisional Patent Application No. 202211000395 filed on January 04, 2022, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The disclosure is generally related to electrochemical devices or batteries, particularly to an air electrode for an air battery and an air battery comprising the air electrode thereof, and an electrolyte for metal- air batteries.

BACKGROUND

Catalytic electrodes play a vital role in electrochemical devices. Examples of electrochemical cells that have catalytic electrodes include, but are not limited to, fuel cells, metal-air battery cells, gas (e.g., hydrogen) generating cells, and electrochemical sensor cells.

Selective catalysts containing electrodes generally consist of five materials: current collector, binder, a 'carbonaceous material such as activated carbon, graphite, graphene, carbon nanotubes, 3D carbon materials, and carbon quantum dots (to capture gas), conductive material and catalyst (as oxygen reduction reaction (ORR) is sluggish). Other than the current collector, all are powders so the uniform mixing and coating of these powders, especially catalyst is very important. If it is non uniform, it may result in low power density. That is why the cathode making process is sensitive and needs extra equipment and care thus increasing the total cost.

Also, the metals used at current collectors are required to have high electrical conductivity (to have lower internal resistance) and stability in the electrolyte (acidic or alkaline). This limits the choice of metals and thus it is needed to use expensive metals like Nickel.

SUMMARY

The present disclosure provides an air electrode comprising: (a) a current collector, wherein the current collector is coated with a catalyst such that the current collector performs the function of the catalyst as well; or (b) an electrically conducting catalyst which simultaneously acts as both a catalyst and a current collector.

In an aspect, the present disclosure provides an electrolyte for a metal-air battery, comprising an organic additive. In a further aspect, the present disclosure provides an electrolyte for a metal-air battery. The electrolyte comprises an aqueous alkaline electrolyte and at least an organic additive.

In yet another aspect, the present disclosure provides an electrochemical device comprising an air electrode as described in the preceding aspect.

In a further aspect, the present disclosure provides an electrochemical device comprising an electrolyte as described in the preceding aspect.

In yet another aspect, the present disclosure provides an electrochemical device comprising: an air electrode and an electrolyte; wherein the air electrode and the electrolyte are as described in the preceding aspects.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

In order that the present disclosure may be more readily understood, it will be described further with reference to the figures and to the specific examples hereinafter.

Figure 1 illustrates cross-sectional view of conventional air cathode. Figure 2 illustrates an air electrode (also referred to as “air cathode”) comprising gas diffusion layer (1), catalyst layer (2), current collector (3) having a catalyst coating (4) according to an embodiment.

Figure 3 illustrates an air cathode without a catalyst layer (2). This cathode comprises gas diffusion layer (1) and current collector (3) having a catalyst coating (4).

Figure 4 illustrates a galvanic cell (8) setup having an aluminum anode (5), an aqueous alkaline electrolyte (7), an air cathode shown in Figure 1 or Figure 2, and a conductive material (6) connecting anode and cathode.

DETAILED DESCRIPTION

Before the methods of the present disclosure are described in greater detail, it is to be understood that the methods are not limited to particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the methods will be limited only by the appended claims.

Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the methods. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges and are also encompassed within the methods, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the methods.

Certain ranges are presented herein with numerical values being preceded by the term “about.” The term “about” is used herein to provide literal support for the exact number that it precedes, as well as a number that is near to or approximately the number that the term precedes. In determining whether a number is near to or approximately a specifically recited number, the near or approximating unrecited number may be a number which, in the context in which it is presented, provides the substantial equivalent of the specifically recited number. For example, "about" can mean within one or more standard deviations, or within ± 30%, 25%, 20%, 15, 10% or 5% of the stated value.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure, preferred methods and materials are described. For the purposes of the present disclosure, the following terms are defined below.

All publications cited in this specification are herein incorporated by reference as if each individual publication was specifically and individually indicated to be incorporated by reference and are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. The citation of any publication is for its disclosure prior to the filing date and should not be construed as an admission that the present methods are not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates, which may need to be independently confirmed.

It is appreciated that certain features of the methods, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the methods, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. All combinations of the embodiments are specifically embraced by the present disclosure and are disclosed herein just as if each and every combination was individually and explicitly disclosed, to the extent that such combinations embrace operable processes and/or composites/scaffolds. In addition, all sub-combinations listed in the embodiments describing such variables are also specifically embraced by the present methods and are disclosed herein just as if each and every such sub-combination was individually and explicitly disclosed herein.

As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present methods. Any recited method can be carried out in the order of events recited or in any other order which is logically possible.

The articles "a" and "an" are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, "an element" means one element or more than one element.

As used herein, the term "comprises", "comprising", or “comprising of’ is generally used in the sense of include, that is to say permitting the presence of one or more features or components.

As used herein, the term “invention” or “present invention” or “present disclosure” as used herein is a non-limiting term and is not intended to refer to any single embodiment of the particular invention but encompasses all possible embodiments as described in the specification and the claims.

Each embodiment is provided by way of explanation of the invention and not by way of limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to the compounds, compositions and methods described herein without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be applied to another embodiment to yield a still further embodiment. Thus, it is intended that the present disclosure includes such modifications and variations and their equivalents. Other objects, features and aspects of the present disclosure are disclosed in or are obvious from, the following detailed description. It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only and is not to be construed as limiting the broader aspects of the present disclosure.

In an embodiment, the present disclosure provides an air electrode comprising: (a) a current collector, wherein the current collector is coated with a catalyst such that the current collector performs the function of the catalyst as well; or (b) an electrically conducting catalyst which simultaneously acts as both a catalyst and a current collector.

In certain embodiments, the present disclosure provides an air electrode comprising: a current collector coated with a catalyst.

Catalyst containing electrode generally comprises catalyst layer (CL), current collector (CC), and Gas diffusion layer (GDL).

Catalyst layer ( CL):

The catalyst layer comprises large specific area materials like a 'carbonaceous material such as activated carbon, graphite, graphene, carbon nanotubes, 3D carbon materials, and carbon quantum dots, a binder, and a conductive material. Any suitable binder can be used. As the binder, conventionally known binder can be used. Examples of the binder include, but are not limited to, polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), nafion, and/or polyimide. As the conductive material, any suitable and conventional conductive material can be used. Examples of the conductive material include, but are not limited to, black carbon, metal powders, and the like.

The catalyst layer may further optionally comprise a catalyst. The catalyst is selected from a group comprising Pt, Pd, Au, Ag, Mn02, cobalt oxides, Ni, TiO2 or any other well-known catalysts.

In certain embodiments, the catalyst layer faces other electrode of the cell. Current collector ( CC ):

The current collector is used to make electrical connection from the battery. The current collector comprises a base material. As the base material, any suitable and conventional conductive material can be used. The base material structure can be a metal with porous structure such as mesh or fleece. Material can be a metal with high electrical conductivity like copper, aluminium, molybdenum, zinc, brass, nickel, steel, silver, and gold.

In certain embodiments of the present invention, the current collector is coated with a catalyst. This catalyst can be electroplated, dip coated, or the catalyst may be coated by electroless plating. In certain embodiments, the catalyst is selected from the group comprising Pt, Pd, Au, Ag, MnCh, cobalt oxides, Ni, TiCh, and any other well-known catalysts.

Gas diffusion layer ( GDL):

GDL provides gas for reduction or oxidation. The GDL comprises large specific area materials like activated carbon, and a binder. As the binder, any suitable and conventional binder can be used. Examples of the binder include, but are not limited to, polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), nafion, polyimide, and the like. In certain embodiments, the GDE may or may not contain other components such as in CE.

The present inventors have found that instead of coated CC, a direct thin porous layer of catalyst (electrically conductive type) can be used which can function as catalyst and current collector both by itself. As such, in certain embodiments, instead of using three parts (GDE, CC, CL) in an air electrode, only GDL and CC coated with a catalyst may be used directly. Place of the coated or uncoated current collector can be changed and moved to front (of CL) or back (of GDL) or middle (of CL or GDL). Thus, in certain embodiments, the present disclosure provides improvement of power and energy density for electrodes which require a catalyst. Also, provides for simplifying the electrode making process, decreasing the internal resistance and cost.

In certain embodiments, any known catalyst may be used for coating the current collector (CC). In certain embodiments, the catalyst is selected from the group comprising nickel (Ni), platinum (Pt), palladium (Pd), gold (Au), silver (Ag), MnC , cobalt oxides, Ni, TiCh, and any combination thereof.

In certain embodiments, coating the current collector with a catalyst ensures uniform presence of catalyst on the electrode thus decreasing the sensitivity, time, and cost of process. The coating additionally gives the advantage of using highly conductive current collectors such as Cu. In certain embodiments, the coating protects it in electrolyte (basic and acidic solution) which in turn decreases internal resistance, cost and improves power of a cell. In certain embodiments, the coating can be of any thickness. In some instances, the coating is of a predetermined thickness. In certain embodiments, the thickness of the coated catalyst is about 0.01 microns or more. In certain embodiments, the thickness of the coated catalyst is about 0.01 microns or more and less than 35 microns. In further embodiments, the thickness of the coated catalyst is from about 0.01 microns to about 30 microns.

In some instances, the thickness of the coated catalyst is about 0.1 microns, about 0.5 microns, about 1 micron, about 1.5 microns, about 2 microns, about 2.5 microns, about 3 microns, about 3.5 microns, about 4 microns, about 4.5 microns, about 5 microns, about

5.5 microns, about 6 microns, about 6.5 microns, about 7 microns, about 7.5 microns, about 8 microns, about 8.5 microns, about 9 microns, about 9.5 microns, about 10 microns, about

10.5 microns, about 11 microns, about 11.5 microns, about 12 microns, about 12.5 microns, about 13 microns, about 13.5 microns, about 14 microns, about 14.5 microns, about 15 microns, about 15.5 microns, about 16 microns, about 16.5 microns, about 17 microns, about 17.5 microns, about 18 microns, about 18.5 microns, about 19 microns, about 19.5 microns, about 20 microns, about 20.5 microns, about 21 microns, about 21.5 microns, about 22 microns, about 22.5 microns, about 23 microns, about 23.5 microns, about 24 microns, about 24.5 microns, about 25 microns, about 25.5 microns, about 26 microns, about 26.5 microns, about 27 microns, about 27.5 microns, about 28 microns, about 28.5 microns, about 29 microns, about 29.5 microns, about 30 microns, about 30.5 microns, about 31 microns, about 31.5 microns, about 32 microns, about 32.5 microns, 33 microns, about 33.5 microns, about 34 microns, about 34.5 microns, about 34 microns, or about 35 microns.

In certain embodiments, the present disclosure provides an air electrode comprising: a current collector coated with a catalyst; wherein the catalyst is coated by electroplating or electroless plating on the current collector. In some instances, the air electrode comprises a current collector coated with a catalyst; wherein the catalyst is coated by electroplating on the current collector. In certain embodiments, the catalyst is selected from the group comprising Pt, Pd, Au, Ag, MnC , cobalt oxides, Ni, TiCh, and any other well-known catalysts. In certain embodiments, the electroplating is done at a temperature of about 40 °C or more. In some embodiments, the electroplating is done at a temperature from about 40 °C to about 90 °C. In some instances, the electroplating is done at about 60 °C to about 70 °C. In certain embodiments, the electroless plating is done at a temperature of about 40 °C or more. In some embodiments, the electroless plating is done at a temperature from about 40 °C to about 90 °C. In some embodiments, the electroless plating is done at about 60 °C to about 70 °C. The electroplating or electroless plating is carried out for about 30 to 70 minutes.

The air electrode as provided herein can be used wherever catalyst is required. Examples include, but are not limited to, hydrogen fuel cells, metal air batteries to reduce oxygen or oxidize hydrogen. The air electrode can also be used in cells which require catalysts like redox flow batteries etc.

In certain embodiments, the present disclosure provides an air electrode for a metalair battery, wherein the air electrode comprises a current collector coated with a catalyst. In some instances, the catalyst is coated by electroplating on the current collector. In certain embodiments, the air electrode provided by the present disclosure is for a metal-air battery comprising at least one gas diffusion layer configured to supply oxygen to the air electrode. In certain embodiments, the air electrode of the present disclosure comprises catalyst coated current collector along with conventional catalyst layer. Figure 2 shows an air cathode comprising gas diffusion layer (1), catalyst layer (2), current collector (3) having a catalyst coating (4) according to an embodiment of the present disclosure.

In certain embodiments, the air electrode of the present disclosure may not comprise a conventional catalyst layer as shown in figure 3. Figure 3 shows an air cathode having no catalyst layer (2). As shown in figure 3, the air cathode comprises a gas diffusion layer (1) and current collector (3) having a catalyst coating (4).

In certain embodiments, catalyst coating on the current collector gives better power density compared to conventional current collector, in an electrolyte flooded battery having gas diffusion layer. In some instances, catalyst coated current collector along with catalyst layer gives 2.6 times the power density compared to conventional current collector, in an electrolyte flooded battery having gas diffusion layer.

Thus, in certain embodiments, the air electrode as provided herein is for a metal-air battery comprising at least one gas diffusion layer configured to supply oxygen to the air electrode; and an electrolyte. As electrolyte, any suitable and conventional electrolyte may be used. Examples of electrolyte include, but are not limited to, aqueous (neutral, acidic, basic) and non-aqueous (ionic, organic). In certain embodiments, the electrolyte is a flooded electrolyte.

In certain embodiments, the air electrode as provided herein is for a metal-air battery comprising (i) at least one gas diffusion layer configured to supply oxygen to the air electrode; and (ii) a flooded electrolyte. In certain embodiments, the electrolyte is an aqueous alkaline electrolyte. In certain embodiments, the aqueous alkaline electrolyte comprises an alkaline hydroxide. Examples of alkaline hydroxide include, but are not limited to, sodium hydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide, and cesium hydroxide. In certain embodiments, the alkaline hydroxide is sodium hydroxide or potassium hydroxide. In certain embodiments, the concentration of the electrolyte is from about 0.01 M to about 30 M. In further embodiments, the concentration of the electrolyte is from about 0.01 M to about 20 M or from about 0.01 M to about 15 M or about 0.1 M to about 15 M or from about 1 M to about 15 M or from about 4 M to about 12 M. In some instances, the concentration of the electrolyte is from about 4 M to about 12 M.

Thus, in certain embodiments, the present disclosure provides a metal-air battery comprising: an air electrode comprising a current collector coated with a catalyst; an anode comprising a metal; at least one gas diffusion layer configured to supply oxygen to the air electrode; and an electrolyte; wherein the air electrode; gas diffusion layer and electrolyte are same as described above.

As anode, any suitable and/or conventionally known anode may be used in the metal-air battery of the present disclosure.

In a metal-air battery of the present disclosure, the anode comprises at least an anode active material. As the anode active material, general anode active materials for metal-air batteries can be used and the anode active material is not particularly limited. Examples of anode active materials include, but are not limited to, Fe, Si, Ti, V, Mn, Mg, Zn, Cu, Zr, Ga, B, Ni, Sr, Li, Na and any combination thereof. In certain embodiments any anode comprising a metal may be used as the anode. Examples of metal include, but are not limited to, Fe, Mg, Zn, Li, Na and any combination thereof.

The metal-air battery of the present disclosure may further comprise a separator between the air electrode and the anode. As separator, any suitable and/or conventionally known separator may be used in the metal-air battery of the present disclosure. Examples of the separator include, but are not limited to, an anion exchange membrane (AEM) such as Fumion, polysulfonium-cation-based AEM, Zirforn, QAFC, PPO-TMA, Versogen, Sustanion, and Selemion.

In certain embodiments, a typical illustration of a metal-air battery of the present disclosure is shown in figure 4. Figure 4 illustrates an overall galvanic cell (8) setup, having an aluminum anode (5), an aqueous alkaline electrolyte (7), an air cathode shown in figure 1 or figure 2, and a conductive material (6) connecting the anode and the cathode.

In certain embodiments, the present disclosure provides an electrochemical device comprising: an air electrode, and an electrolyte; wherein the air electrode and the electrolyte are same as described above.

The electrolyte may prevent or limit the metal dissolution in a battery. Use of an aqueous alkaline electrolyte in a metal-air batter causes a parasitic side reaction at metal anode. Water reacts with the metal anode to produce H2. The side reaction is given as:

M + xH20 — > M(OH) _S + x/2H ₂

M = Al, Zn, Mg, Na, Li, Fe

The side reaction causes spontaneous degradation of aluminum or self-corrosion of aluminum, hence leading to fuel loss. Ultimately, the consequences are poor coulombic efficiency, low energy density, short device longevity, and safety issues.

Present inventors have found that adding at least an organic additive to an aqueous alkaline electrolyte may overcome one or more said problems in the metal-air battery. Accordingly, in certain embodiments, the present disclosure provides an electrolyte for a metal-air battery, comprising at least an organic additive.

Thus, the present disclosure also provides an electrolyte for a metal-air battery, and a metal-air battery comprising said electrolyte.

In certain embodiments, the present disclosure provides an electrolyte for a metalair battery, wherein the electrolyte comprises an aqueous alkaline electrolyte and at least an organic additive. In certain embodiments, the aqueous alkaline electrolyte comprises an alkaline hydroxide. Examples of alkaline hydroxide include, but are not limited to, sodium hydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide, and cesium hydroxide. In certain embodiments, the alkaline hydroxide is sodium hydroxide or potassium hydroxide. In certain embodiments, the alkaline hydroxide is potassium hydroxide. In certain embodiments, concentration of the electrolyte is from about 0.01 M to about 30 M. In further embodiments, the concentration of the electrolyte is from about 0.01 M to about 20 M or from about 0.01 M to about 15 M or about 0.1 M to about 1 M or from about 1 M to about 15 M or from about 4 M to about 12 M. In some instances, the concentration of the electrolyte is from about 0.1 M to about 10 M. In some instances, the concentration of the electrolyte is about 0.1-10 M. In some instances, the concentration of the electrolyte is about 1-10 M, about 1-6 M, including about 2 M, about 3 M, about 4M, about 5M and about 6M.

The organic additive is selected from the group comprising carboxymethyl cellulose (CMC), cetyltrimethylammonium bromide (CTAB), cetrimonium chloride (CTAC), and any combination thereof.

In certain embodiments, the electrolyte comprises an aqueous alkaline electrolyte and a combination of organic additives selected from the group comprising carboxymethyl cellulose (CMC), cetyltrimethylammonium bromide (CTAB), and cetrimonium chloride (CTAC). In some embodiments, the electrolyte comprises an aqueous alkaline electrolyte, CMC, and CTAB. In certain embodiments, the electrolyte comprises an aqueous alkaline electrolyte, CMC, and CTAC. In certain embodiments, the electrolyte comprises an aqueous alkaline electrolyte, CTAB, and CTAC. In some instances, the electrolyte comprises an aqueous alkaline electrolyte, CMC, CTAB and CTAC.

The organic additive in the electrolyte may present in an amount from about 0.001 wt% to about 10 wt%. In certain embodiments, the organic additive in the electrolyte may present in an amount from about 0.001 wt% to about 5 wt%, or from about 0.001 wt% to about 4 wt%, or from about 0.001 wt% to about 3 wt%, or from about 0.001 wt% to about 2 wt%, or form about 0.001 wt% to about 1 wt%, or from about 0.001 wt% to about 0.5 wt%, or from about 0.01 wt% to about 3 wt%.

In certain embodiments, the organic additive is CMC, in an amount from about 0.01 wt% to about 3 wt%. In some instances, the CMC is present in an amount of about 0.01 wt%, about 0.02 wt%, about 0.03 wt%, about 0.04 wt%, about 0.05 wt%, about 0.06 wt%, about 0.07 wt%, about 0.08 wt%, 0.09 wt%, about 0.1 wt%, about 0.11 wt%, about 0.12 wt%, about 0.13 wt%, about 0.14 wt%, about 0.15 wt%, about 0.16 wt%, about 0.17 wt%, about 0.18 wt%, about 0.19 wt%, about 0.2 wt%, about 0.21 wt%, about 0.22 wt%, about 0.23 wt%, about 0.24 wt%, about 0.25 wt%, about 0.26 wt%, about 0.27 wt%, about 0.28 wt%, about 0.29 wt%, about 0.3 wt%, about 0.4 wt%, about 0.5 wt%, about 1 wt%, about 1.5 wt%, about 2 wt%, about 2.5 wt%, about 3 wt%.

In certain embodiments, the organic additive is CTAB, in an amount from about 0.001 wt% to about 3 wt%. In some instances, the CTAB is present in an amount of about 0.001 wt%, about 0.002 wt%, about 0.003 wt%, about 0.004 wt%, about 0.005 wt%, about 0.006 wt%, about 0.007 wt%, about 0.008 wt%, about 0.009 wt%, about 0.01 wt%, about 0.02 wt%, about 0.03 wt%, about 0.04 wt%, about 0.05 wt%, about 0.06 wt%, about 0.07 wt%, about 0.08 wt%, 0.09 wt%, about 0.1 wt%, about 0.11 wt%, about 0.12 wt%, about 0.13 wt%, about 0.14 wt%, about 0.15 wt%, about 0.16 wt%, about 0.17 wt%, about 0.18 wt%, about 0.19 wt%, about 0.2 wt%, about 0.21 wt%, about 0.22 wt%, about 0.23 wt%, about 0.24 wt%, about 0.25 wt%, about 0.26 wt%, about 0.27 wt%, about 0.28 wt%, about 0.29 wt%, about 0.3 wt%, about 0.4 wt%, about 0.5 wt%, about 1 wt%, about 1.5 wt%, about 2 wt%, about 2.5 wt%, about 3 wt%.

In certain embodiments, the organic additive is CTAC, in an amount from about 0.001 wt% to about 3 wt%. In some instances, the CTAC is present in an amount of about 0.001 wt%, about 0.002 wt%, about 0.003 wt%, about 0.004 wt%, about 0.005 wt%, about 0.006 wt%, about 0.007 wt%, about 0.008 wt%, about 0.009 wt%, about 0.01 wt%, about 0.02 wt%, about 0.03 wt%, about 0.04 wt%, about 0.05 wt%, about 0.06 wt%, about 0.07 wt%, about 0.08 wt%, 0.09 wt%, about 0.1 wt%, about 0.11 wt%, about 0.12 wt%, about 0.13 wt%, about 0.14 wt%, about 0.15 wt%, about 0.16 wt%, about 0.17 wt%, about 0.18 wt%, about 0.19 wt%, about 0.2 wt%, about 0.21 wt%, about 0.22 wt%, about 0.23 wt%, about 0.24 wt%, about 0.25 wt%, about 0.26 wt%, about 0.27 wt%, about 0.28 wt%, about 0.29 wt%, about 0.3 wt%, about 0.4 wt%, about 0.5 wt%, about 1 wt%, about 1.5 wt%, about 2 wt%, about 2.5 wt%, about 3 wt%.

In certain embodiments, the present disclosure provides a process for preparing an electrolyte for a metal-air battery. The process comprises adding an alkane hydroxide to an aqueous solution of at least an organic additive. The process comprises stirring the alkane hydroxide with aqueous solution of the organic additive. The alkane hydroxide and the organic additive are the same as described above. In certain embodiments, the stirring is continued until a solution is obtained. In some instances, the stirring is continued for about 30-60 minutes. In certain embodiments, concentration of the electrolyte solution is from about 1 M to about 12 M. The electrolyte solution is allowed to room temperature and then used in a metal-air battery.

Thus, in certain embodiments, the present disclosure provides a metal-air battery comprising: an air electrode; an anode comprising a metal; and an electrolyte; wherein the electrolyte comprises an aqueous alkaline electrolyte and at least an organic additive; wherein the anode, the aqueous alkaline electrolyte and the organic additive are the same as defined above.

As an air electrode any suitable and/or conventionally known air electrode may be used in the metal-air battery of the present disclosure. In certain embodiments, an air electrode comprising a catalyst coated current collector of the present disclosure is used in the metal-air battery.

The metal-air battery of the present disclosure may further comprise a separator between the air electrode and the anode. As separator, any suitable and/or conventionally known separator may be used in the metal-air battery of the present disclosure. Eexamples of the separator include, but are not limited to, an anion exchange membrane (AEM) such as Fumion, polysulfonium-cation-based AEM, Zirforn, QAFC, PPO-TMA, Versogen, Sustanion, and Selemion.

In certain embodiments, the present disclosure provides an electrolyte which may be used in a metal-air battery comprising: an air electrode comprising a current collector coated with a catalyst; an anode comprising a metal; at least one gas diffusion layer configured to supply oxygen to the air electrode; and an electrolyte; wherein the electrolyte comprises an aqueous alkaline electrolyte and at least an organic additive.

In certain embodiments, the present disclosure provides an electrochemical device comprising: an air electrode; and an electrolyte; wherein the electrolyte comprises an aqueous alkaline electrolyte and at least an organic additive of the present disclosure. As an air electrode, any suitable and/or conventionally known air electrode may be used in the metal-air battery. In certain embodiments, an air electrode comprising a catalyst coated current collector of the present disclosure is used in the electrochemical device.

The present disclosure is further described with reference to the following examples, which are only illustrative in nature and should not be construed to limit the scope of the present disclosure in any manner.

EXAMPLES

EXAMPLE 1:

ELECTROLYTE

KOH or NaOH was added to the distilled water and mixed for 30-60 minutes to make a solution in the range of 4M-12M. The electrolyte was allowed to room temperature before using it in a battery.

CURRENT COLLECTOR

A commercially available copper mesh of 0.35 mm wire diameter was used as current collector. CATALYST COATED CURRENT COLLECTOR

METHOD 1:

For catalyst coated current collector, copper mesh of 0.35 mm wire diameter and 1 mm knit size was taken. Nickel (99.5% purity) was coated onto the copper mesh via electroplating at a temperature of 60-70 °C for 45 minutes. The coating thickness ranges from 5 to 30 microns. The loading of Ni was in the range 0.2- 1.4 gram per square meter of Cu mesh.

METHOD 2:

For catalyst coated current collector, copper mesh of 0.35 mm wire diameter and 1 mm knit size was taken. Nickel (99.5% purity) was coated onto the copper mesh via electroless plating at 60-70 °C for 55 minutes. The coating thickness ranges from 5 to 30 microns. The loading of Ni was in the range 0.2- 1.4 gram per square meter of Cu mesh.

The coating thickness and its effect on the battery power are shown in Table 1.

Table 1 AIR CATHODE

Cathode constitutes three layers: catalyst layer (CL); catalyst coated current collector; and gas diffusion layer (GDL).

CL and GDL were made according to the conventional method. Wen, H, Liu, Z, Qiao, J, et al., Int J Energy Res. 2020; 44 7568 7579 can be considered as a reference.

An air cathode comprising a gas diffusion layer (1), a catalyst layer (2), a current collector (3) having a catalyst coating (4) is shown in Eigure 1.

An air cathode having no separate catalyst layer (2) is shown in figure 2. As shown in figure 2, the air cathode comprises a gas diffusion layer (1) and a current collector (3) having a catalyst coating (4).

ELECTROLYTIC CELL SETUP

Aluminum anode and air cathode were set up with a 4 mm separation between them. Electrolyte was circulated between the two electrodes in the range of 0.8 LPM to 1.2 LPM using a diaphragm pump. The test condition was 0.62-0.72 V and 1.76 A.

A galvanic cell (8) setup, having an aluminum anode (5), an aqueous alkaline electrolyte (7), an air cathode of figure 1 or figure 2, and a conductive material such as copper (6) connecting the anode and the cathode are shown in figure 3.

EXAMPLE 2:

A metal-air battery was made under the same conditions as those in Example 1 except that conventional catalyst layer (CL) is absent in preparing an air cathode.

EXAMPLE 3:

A metal-air battery was made under the same conditions as those in Example 1 except that Ag catalyst was used instead of Ni in preparing an air cathode. EXAMPLE 4:

A metal-air battery was made under the same conditions as those in Example 3 except that conventional catalyst layer (CL) is absent in preparing an air cathode.

COMPARTIVE EXAMPLE 1: A metal-air battery was made under the same conditions as those in Example 1 except that there is no catalyst coating on current collector in preparing an air cathode.

COMPARTIVE EXAMPLE 2:

A metal-air battery was made under the same conditions as those in comparative example 1 except that conventional catalyst layer (CL) is absent in preparing an air cathode. EVALUATION OF BATTERY POWER

The power of batteries was determined using a batter tester (of Neware). The results are shown in Table 2 below.

Table 2 As shown in Table 2, metal-air batteries made according to Examples 1-4 have high power compared to that of Comparative Examples 1 and 2.

EXAMPLE 5: PREPARATION OF ELECTROLYTE HAVING ADDITIVE

10 g CMC was added continuously for 30-40 minutes to 1000 ml of distilled water in vigorous stirring condition (1000-1500 rpm). Then, KOH or NaOH was added to the above solution and stirred for 30-60 minutes to create a colorless solution in the range of IM - 12M. The electrolyte was allowed to room temperature.

Electrolyte having CMC with different concentration was prepared using the procedure depicted in Example 5. The flow of electrolyte is shown in Table 3.

Table 3 EXAMPLE 6: ELECTROLYTIC CELL SETUP

Aluminum anode and air cathode are set up with a 4 mm separation between them. The exposed surface area of anode and cathode is 40 mm*40 mm. Aqueous alkaline electrolyte having additive(s) is circulated between the two electrodes in the range of 0.8 LPM to 1.2 LPM using a diaphragm pump. The test condition was 0.62-0.72 V and 1.76 A.

EXAMPLE 7: HYDROGEN EVOLUTION STUDY:

Electrolytes having different concentrations of one or more organic additives selected from CMS, CTAB, and CTAC were prepared using the procedure depicted in Example 7 with appropriate variations in quantities of components in the electrolyte. These were used in electrolytic cells according to Example 8 and studied for hydrogen evolution. The results were shown in Tables 4-7. In a comparative example, KOH was added to make a 4M electrolyte solution. Volume of hydrogen evolved was measured after 20 minutes of the start of cell reaction. The hydrogen evolution was determined by gas chromatography.

Table 4

Table 5

Table 6

Table 7

As shown in Tables 4-7, metal-air batteries having electrolytes of Examples 5 and 8-44 have less hydrogen evolution compared to that of Comparative Examples 3-6.