DESC:
FIELD OF THE INVENTION
The present disclosure is related to electrochemical devices or metal-air battery. The disclosure typically relates to an electrolyte for the metal-air battery and more specifically towards additives in the electrolyte.

BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Metal-air batteries are being considered as a solution toward next-generation electrochemical energy storage for applications including electric vehicles or grid energy storage as have a theoretical energy density that is much higher than that of lithium-ion batteries. However, their full potential is not being realized because of challenges associated with the metal anode, air cathode, and electrolyte.
In general, the metal air battery is composed of a porous cathode, an electrolyte, and a metal anode. The fundamental working principle of a metal-air battery is to electrochemically reduce the oxygen from the air and oxidize the metal. During discharging, oxidation takes place at the metal anode and electrons are released to the external circuit. Oxygen reduction reaction takes place at the cathode, which generally requires catalyst, and produces hydroxide ions. Generally, side or parasitic reactions also occur besides oxidation and reduction reactions, which affects the efficiency of any metal-air battery.
The energy density of the metal-air batteries is 3 to 10 times greater than that of the conventional lithium-ion battery. Especially, aluminium has a high energy density (˜8,100 watt-hours per kilogram), easy availability, and low environmental impact. However, it is difficult to commercialize aluminium-air batteries due to some challenging issues where one of them is the redox reactions occurring in direct association of metal electrode in aqueous electrolyte.
A highly alkaline solution is generally used as an electrolyte in the metal-air battery to obtain a high energy density. However, in the alkaline solution, a parasitic side reaction at metal anode to produce hydrogen gas besides the main cell reaction also occurs, which reduces the battery performance. This reaction is called the hydrogen evolution reaction (HER). This side reactions can cause spontaneous degradation or self-corrosion of the metal anode which leads to poor efficiency, low energy density, short device longevity, and safety issues in metal-air batteries.
To reduce HER at the metal anode, the electrolyte is usually combined with an additive. The additive typically forms a protective layer upon the surface of the metal anode, which inhibits HER without compromising the performance of the metal anode.
Therefore, there is felt a need for metal air batteries that mitigates the aforesaid drawbacks.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
An object of the present disclosure is to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
Another object of the present disclosure is to provide an electrolyte for metal-air battery.
Still another object of the present disclosure is to provide metal-air battery with high energy density.
Yet another objective of the present disclosure is to provide a metal-air battery with reduced anode degradation.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
DETAILED DESCRIPTION OF THE INVENTION
At the very outset of the detailed description, it may be understood that the ensuing description only illustrates a particular form of this invention. However, such a particular form is only exemplary embodiment, and without intending to imply any limitation on the scope of this invention. Accordingly, the description is to be understood as an exemplary embodiment and teaching of invention and not intended to be taken restrictively.
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.
The terms and words used in the following description are not limited to the bibliographical meanings but are merely used by the inventor to enable a clear and consistent understanding of the disclosure, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present disclosure are provided for illustration purpose only and not for the purpose of limiting the disclosure.
Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.
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.
It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps, or components but does not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof.
As used herein, “combinations thereof” is inclusive of one or more of the recited elements, optionally together with a like element not recited, e.g., inclusive of a combination of one or more of the named components, optionally with one or more other components not specifically named that have essentially the same function. As used herein, the term “combination” is inclusive of blends, mixtures, alloys, reaction products, and the like.
As used herein, the term “metal-air battery” refers to an electrochemical cell that uses an anode made of a metal or a metal alloy and a cathode of ambient air (generally referred to as air cathode), with an electrolyte. The term “metal-air battery”, as used herein, may refer to a single electrochemical cell (that may be referred to as a metal-air cell) or a plurality of electrochemical cells connected in series and/or parallel configuration.
As used herein, the term hydrogen evolution reaction (HER) may refer to a reaction between a hydrogen ion and an electron at an anode of a metal-air battery to produce hydrogen. This is a parasitic reaction that reduces the performance of the metal-air battery.
As used herein, the term “energy density” can be defined as the amount of energy that can be generated for a given unit weight of a metal-air battery. It is expressed as Watt hours per kilogram (Wh/kg).
As used herein, the term “electrolyte additive” refers to a chemical compound which when added to an electrolyte minimizes hydrogen evolution reaction at an anode of the metal-air battery, and may also improve a discharge potential by activating the surface of the anode for the electrochemical reaction. The electrolyte additive, hereinafter, is also otherwise termed as “corrosion inhibitor”, “inhibitor”, or “additive”.
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 invention includes such modifications and variations and their equivalents. Other objects, features and aspects of the present invention 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 invention.
The present disclosure envisages an electrolyte solution that overcomes the drawbacks of the conventional electrolyte solution for metal-air battery.
In accordance with an aspect of the present disclosure, an electrolyte solution is disclosed.
The present disclosure discloses the electrolyte solution for metal-air battery wherein the electrolyte solution comprises an aqueous alkaline solution and at least one metal additive.
Typically, the aqueous alkaline solution comprises an alkaline hydroxide. Examples of alkaline hydroxide include sodium hydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide, and cesium hydroxide.
In accordance with an aspect of the present disclosure, the alkaline hydroxide can be sodium hydroxide or potassium hydroxide. Typically, alkaline hydroxide is potassium hydroxide.
In an embodiment, the alkaline electrolyte may include an aqueous solution of sodium hydroxide, potassium hydroxide, or a combination thereof.
In accordance with an aspect of the present disclosure, the metal additive can be a metal carbonate. Typically, the metal carbonate can be zinc carbonate.
Such electrolyte additives may form a protective layer on the surface of an anode to inhibit or reduce hydrogen evolution reaction.
The inventors of the present disclosure found that when the metal carbonate additive is added to the alkaline solution forming an electrolyte, the performance of the metal-air battery is improved in comparison to conventional metal air battery where no such additives have been used. The energy density and durability of anode improved due to suppression of parasitic reactions.
In accordance with an aspect of the present disclosure, the metal carbonate additive in the electrolyte may be present in an amount from 0.1 to 200 g/L. Typically, the metal carbonate additive in the electrolyte solution may be present in an amount from about 0.2 g/L to about 180 g/L, or from about 0.3 g/L to about 180 g/L, or from about 0.3 g/L to about 170 g/L, or from about 0.5 g/L to about 150 g/L, or from 0.5 to 100 g/L.
In accordance with an aspect of the present disclosure, the concentration of the alkaline hydroxide in the electrolyte solution is about 1 to 15 M, about 1 to 10 M, about 2 M, about 3 M, about 4 M, about 5 M or about 6 M.
In an embodiment of the present disclosure, the invention is not just limited to a metal-air battery but may be a flow-type battery where the electrolyte is constantly circulated.
In an embodiment of the present disclosure, the metal-air battery has a single electrochemical cell. In another embodiment of the present disclosure, the metal-air battery may have a plurality of electrochemical cells in a series configuration, a parallel configuration or a combination of a series and parallel configuration.
In an embodiment of the present disclosure, the invention also includes a metal-air battery. A typical air battery comprises an anode, a cathode, and an electrolyte.
In accordance with another aspect of the present disclosure, the cathode may be an air cathode. In an embodiment, the air electrode may comprise a current collector and gas diffusion layer (GDL). In another embodiment, the cathode may include a catalyst. The catalyst may comprise large specific area materials like carbonaceous materials such as activated carbon, graphite, graphene, carbon nanotubes, 3D carbon materials, and carbon quantum dots. In another embodiment, the catalyst may be selected from the group comprising platinum, palladium, gold, silver, manganese oxide, cobalt oxides, nickel, titanium dioxide or any other well-known catalysts and their combination thereof.
In another embodiment, the cathode may include a binder and a conductive material. Any suitable binder can be used. Examples of the binder include, but not limited to, polymers such as polyvinylidene fluoride (PVDF), polytetrafluorethylene (PTFE), Nafion®, Fumion®, and/ or polyamide. Any suitable and conventional conductive materials can be used. Examples of the conductive material include, but are not limited to, black carbon, metal powders, and the like.
In accordance with another aspect of the present disclosure, the anode comprises at least a metal. The anode metal may be, but are not limited to, Fe, Si, Ti, V, Mn, Mg, Al, Zn, Cu, Zr, Ga, B, Ni, Sr, Li, Na, and any combination thereof.
In accordance with as aspect of the present disclosure, the electrolyte solution may be employed in, but not limited to, electrochemical cell, metal-air cell and metal-air battery.
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.
EXPERIMENTS
Potassium hydroxide pellets were kept inside an oven at 90 - 130°C for 1-3 hours to remove moisture. The dried KOH pellets were then added to distilled water and stirred for 30 minutes to 2 hours at a temperature of 20°C to 40°C in a fume hood to obtain an alkaline solution. To the alkaline solution, zinc carbonate was added and stirred to obtain the electrolyte solution. The electrolyte solution was kept at room temperature and then employed in the metal-air battery for experiments.
Hydrogen evolution test:
The hydrogen evolution test was performed by a conventional method using a measuring cylinder. The coin shaped Al sample of 1XXX series (Thickness = 2 mm, Radius = 10 mm) is soaked in various electrolytes as mentioned in Table 1 inside the measuring cylinder. As soon as the coin is immersed in the electrolyte, the data is collected for 20 minutes based on the amount of electrolyte (in mL) coming out from the measuring cylinder per minute. Thus, the rate of hydrogen evolution is calculated in mL/ min.
Energy Density measurements:
The energy density tests were carried out on an electrochemical workstation (AMEL Electrochemistry, Model 2550) having current capacity of 1A. Porous carbon as cathode and Al metal as anode were used. The active area of the cathode and anode was 16 cm2. The energy tests were performed at 1V for 3 hours with different additive concentration as mentioned in the Table 1. The energy density values achieved with different concentration of ZnCO3 in aq. KOH solution is mentioned in the table 1.
Table 1 – Effect of zinc carbonate additive in the electrolyte
S. No. ZnCO3 in aq. KOH solution
(g/L) H2 evolution rate
(mL/min) Energy Density
(Wh/kg)
1 0 2.6 2847
2 10 0.5 3523
3 20 0.6 3711
4 30 0.3 3300

Metal-air battery having electrolyte solution of the present invention shows reduced hydrogen evolution and thereby prevents anode degradation. This also results in high energy density of the metal-air battery.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of an electrolyte, wherein the electrolyte improves the overall efficiency of the metal-air battery by preventing hydrogen evolution due to parasitic reactions and degradation of anode, thereby providing high energy density of the metal-air battery.
Certain embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Of course, variations on these described embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
Furthermore, numerous references have been made to patents and printed publications throughout this specification. Each of the above-cited references and printed publications are individually incorporated herein by reference in their entirety.
While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.
,CLAIMS:1. An electrolyte for a metal air battery comprising aqueous alkaline solution and zinc carbonate.
2. An electrolyte as claimed in claim 1, wherein the aqueous alkaline solution comprises sodium hydroxide or potassium hydroxide.
3. An electrolyte as claimed in claim 1, wherein the concentration of the aqueous alkaline solution is 1M to 15M.
4. An electrolyte as claimed in claim 1, wherein the concentration of the aqueous alkaline solution is 1M to 10M.
5. An electrolyte as claimed in claim 1, wherein the zinc carbonate is present in the range of 0.1 to 200 g/L.
6. An electrolyte as claimed in claim 1, wherein the zinc carbonate is present in the range of 0.3 to170 g/L.
7. An electrolyte as claimed in claim 1, wherein the zinc carbonate is present in the range of 0.5 to 150 g/L.
8. An electrolyte as claimed in claim 1, wherein the zinc carbonate is present in the range of 0.5 to 100 g/L.
9. A metal air battery comprising:
an air cathode;
a metal anode; and
an electrolyte as claimed in claim 1.

10. A metal air battery as claimed in claim 8, wherein the metal anode is formed of aluminium metal.