HK1219804B - Hetero-ionic aromatic additives for electrochemical cells comprising a metal fuel - Google Patents

Description

Heteroionic aromatic additives for electrochemical cells comprising metal fuels

Cross-reference to prior applications

This application claims the benefit of U.S. Provisional Patent Application No. 61/780,662, filed March 13, 2013, which is hereby incorporated by reference herein in its entirety.

Technical Field

The present invention relates to an electrochemical cell for generating electricity, and more particularly to a cell using electrodeposition of fuels, wherein the ionically conductive medium of the cell comprises a heteroionic aromatic additive.

All publications, patents, and patent applications cited in this specification are hereby incorporated by reference in their entirety.

Background Art

Electrochemical cells are known to use metals as fuels. Electrochemical cells are also known to use an electrolyte (a solution of solvent molecules and solute ions) as an ion-conducting medium. Due to the thermodynamic interaction between the solvent molecules and the solute ions, the solvent molecules cause the solute ions to form a solvate, thereby maintaining the electrolyte's ion conductivity. Depending on the desired operating characteristics and chemical properties, electrochemical cells using metals as fuels can be "primary" (i.e., non-rechargeable) batteries or "storage" (i.e., rechargeable) batteries. In electrochemical cells using metals as fuels, the metal fuel is oxidized at the fuel electrode, which acts as an anode, during discharge. The oxidized metal fuel ions can be retained in the electrolyte solution in a reducible form (as solvated ions, or combined with other ions, such as in molecules or complexes).

During charging of the electrochemical cell, the reducible metal fuel ions are reduced to metal fuel at the interface between the electrolyte and the fuel electrode, which now acts as the cathode, thereby plating the metal fuel on the fuel electrode by a process known as electrodeposition.

A significant problem with electrochemical cells containing metal fuels is their tendency to corrode or self-discharge during idle mode (e.g., storage). This often manifests as a loss of usable capacity. In more extreme cases, self-discharge can lead to gas release, while excessive pressure can break the cell seal, ultimately causing cell failure. For example, in alkaline cells containing zinc metal fuel, the native oxide layer is insufficient to halt the corrosion process, which often leads to a loss of cell performance.

For batteries, a significant problem that arises during charge-discharge cycling is the formation of filaments or dendrites. These formations are typically uneven, dispersed deposits that may be due to mossy or dendritic growth and/or due to the growth of filaments, nodules, etc. Typically, this type of metal deposition can cause undesirable short circuits between electrodes, leading to battery failure. Ideally, the electrodeposited metal accumulates as a smooth layer across the entire fuel electrode surface, thereby maintaining the electrode surface morphology from one charge-discharge cycle to the next.

Another problem associated with conventional aqueous electrolyte batteries is water electrolysis during charging. During charging, current is passed through the cell to reduce the oxidized fuel at the fuel electrode. However, as represented by the following equation, in an aqueous alkaline solution, some of the current electrolyzes water, resulting in hydrogen evolution at the fuel electrode (i.e., reduction) and oxygen evolution at the oxidant electrode (i.e., oxidation):

2H ₂ O(1)+2e ^- →H ₂ (g)+2OH ^- (aq) and (1)

2OH ^- (aq)→1/2O ₂ (g)+H ₂ O(l)+2e ^- . (2)

In this way, the aqueous electrolyte is lost from the cell. Furthermore, the electrons consumed in reducing hydrogen are no longer available to reduce the fuel at the fuel electrode. Consequently, parasitic electrolysis of the aqueous electrolyte reduces the cycle efficiency of the battery (i.e., rechargeable).

To alleviate these problems, the electrolyte solution may contain additives. Electrochemical cells using additives are known. Examples of such devices are shown, for example, in U.S. Patents Nos. 3,945,849; 4,479,856; 6,027,827; and 6,395,422; 6,927,000; 7,169,504; and 7,563,537, which are incorporated herein in their entireties. Additives for various electrochemical systems can include surfactants, metal ions, organic compounds, and combinations thereof. The benefits of using additives in electrochemical cells can include, for example, enhancing electrochemical reactions by various means, such as forming an ion-conducting layer on the electrode, adsorbing to the metal surface and preventing corrosion, reducing electrode wettability issues, or acting as a chelating agent. However, additives can also hinder the function or efficiency of the electrochemical cell. For example, an electrolyte that promotes rapid electroplating in a regenerative cell may also promote less dense electroplating of a metal fuel on the electrode. For another example, strong adsorption of an additive may require a higher overpotential during battery charging, thereby reducing efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an electrochemical cell with a stack of permeable electrode bodies for generating electricity during discharge.

2 is a schematic diagram of an electrochemical cell with a stack of permeable electrode bodies for charging by electrodeposition fuel growth on the electrode bodies.

3 shows electrodeposition at the interface between an electrolyte containing 2.0 mM 1-benzyl-4-aza-1-azoniabicyclo[2,2,2]octane hydroxide and 0.25 mM indium chloride, InCl ₃ , and an electrode in a stack of permeable electrode bodies.

DETAILED DESCRIPTION

Embodiments of the present invention provide an electrochemical cell comprising: a fuel electrode containing a metal fuel, a second electrode, and an ionically conductive medium communicating with the electrodes, the ionically conductive medium comprising a heteroionic aromatic additive. The fuel electrode and the second electrode can be operated in a discharge mode, wherein the metal fuel is oxidized at the fuel electrode, acting as an anode, thereby generating electrons that are conducted from the fuel electrode through a load to the second electrode.

Embodiments of the present invention also provide a method for discharging an electrochemical cell, wherein a metal fuel is oxidized at a fuel electrode serving as an anode, thereby generating electrons that are conducted from the fuel electrode through a load to a second electrode, and then the fuel electrode and the second electrode are disconnected from the load to interrupt discharge. Furthermore, embodiments of the present invention also provide a method for charging an electrochemical cell, wherein a current is applied between a charging electrode and a fuel electrode serving as a cathode, causing reducible metal fuel ions to be reduced and electrodeposited as an oxidizable form of the metal fuel on the first electrode, and then the current is cut off to interrupt charging.

Additionally, the present invention provides an ionically conductive medium for use in an electric current producing electrochemical cell comprising a heteroionic aromatic additive.

The accompanying drawings illustrate embodiments of various aspects of the claimed invention. These embodiments are not intended to be limiting, but are merely intended as examples to facilitate understanding of the principles of the claimed invention.

The principles of the presently described embodiments are broadly applicable to any electrochemical cell that includes a metal fuel. The electrochemical cell can be a primary cell (e.g., primary metal-air, alkaline zinc-manganese oxide, silver-zinc, etc.) or a secondary cell (e.g., rechargeable metal-air, nickel-cadmium, nickel metal hydride, etc.). Non-limiting examples of electrochemical cells in which the principles of the present invention may be used are disclosed in U.S. Patents or Patent Applications Nos. 8,168,337, 8,309,259, 11/962,803, 12/385,217, 12/549,617, 12/631,484, 12/776,962, 12/885,268, 12/901,410, 13/019,923, 13/028,496, 13/083,929, 13/085,714, 13/096,851, 13/105,794, 13/167,930, 13/185,658, 13/186,939, 13/190,13 ,864, 13/668,180, 13/668,185, 61/557,490, and 61/726,134; all of which are incorporated herein by reference.

According to embodiments of the present invention, the operation of an electrochemical cell comprising a metal fuel is now described, which may employ the heteroionic aromatic additives described herein. However, it should be understood that this description is provided merely as an example and is not intended to be limiting in any way. Numerous other cell chemistries and cell designs may employ heteroionic aromatic additives according to various embodiments of the present invention.

FIG1 illustrates an example of an electrochemical cell 10 according to an embodiment of the present invention. The electrochemical cell 10 has a fuel electrode 20 and a second electrode 30. In one embodiment, the fuel of the system can be oxidized at the fuel electrode 20 during discharge. The fuel electrode 20 can include a fuel in the form of a solid fuel electrodeposited on an electrically conductive electrode body, but can generally be referred to as a fuel electrode 20, even when no fuel is present. At the second electrode 30, the oxidant of the system is reduced during discharge. The second electrode 30 of each cell 10 can be provided as a smaller, separate, and single second electrode, rather than a larger single "cathode" or any other suitable configuration.

As shown in FIG1 , the fuel electrode 20 and the second electrode 30 can be spaced apart to define a gap 32 therebetween. The gap 32 can typically be a substantially empty gap to allow a fluid of the ion-conducting medium to flow from the fuel electrode 20 to the second electrode 30, or to flow between the two electrodes. Preferably, the width of the gap 32 is substantially constant along the vertical length of the electrode (as shown in FIG1 ), but in some configurations, it can be varied. In one embodiment, the gap 32 between the fuel electrode 20 and the second electrode 30 may have channels or other features that facilitate the flow of the ion-conducting medium and the oxidized fuel. In some embodiments, an ion exchange membrane or any other suitable separator may be present.

The ion-conducting medium, generally designated 22, is in communication with both the fuel electrode 20 and the second electrode 30. In some embodiments, the ion-conducting medium can flow in any suitable direction, while in other embodiments, the ion-conducting medium can be substantially static. For specific details of possible flow characteristics of the ion-conducting medium 22, reference is made to U.S. patent application Ser. Nos. 11/962,803, 12/631,484, 12/901,410, 13/019,923, 13/028,496, 13/362,775, 13/532,374, and 13/668,021, all of which have been incorporated herein by reference. The ion-conducting medium 22 can be an electrolyte solution. Hereinafter, the ion-conducting medium 22 may be referred to as the electrolyte 22. In one embodiment, the electrolyte 22 is an aqueous solution. Examples of suitable electrolytes include aqueous solutions containing sulfuric acid, phosphoric acid, trifluoromethanesulfonic acid, nitric acid, potassium hydroxide, sodium hydroxide, sodium chloride, potassium nitrate, or lithium chloride. As disclosed in U.S. Patent Application Nos. 12/776,962, 13/448,923, 13/526,058, 13/526,432, 13/526,342, 61/557,490, and 61/726,134 (all of which are incorporated herein by reference), the electrolyte may comprise a non-aqueous solvent, an ionic liquid, and/or an ion exchange material. Any ion-conductive medium may be used. In the non-limiting embodiment described herein, the electrolyte is an aqueous solution of potassium hydroxide.

In one embodiment, the second electrode 30 comprises a porous body covered on its outer side with a gas permeable layer through which the oxidant can diffuse, but the ion conductive medium 22 cannot pass. In some embodiments, the oxidant can be arranged as a contained oxidizer. In other embodiments, the oxidant can be delivered as a passivation or activation system to deliver oxygen from ambient air to the second electrode 30. For further specific details related to the second electrode 30 according to various embodiments, reference can be made to U.S. patent application Nos. 13/531,962, 13/668,180, and 13/668,185, which have been cited above. During discharge, when the first electrode 20 and the second electrode 30 are connected to the external load 40, a reaction between at least the oxidant and the electrons flowing to the second electrode 30 can occur at the second electrode 30, thereby reducing the oxidant. The reduced oxidant ions can react with the oxidized fuel ions to complete the electrochemical cell reaction.

As illustrated in FIG1 , the fuel electrode 20 may include a plurality of electrode bodies, described as electrode bodies 20 a, 20 b, and 20 c, respectively. Each body may be configured to allow electrolyte 22 to flow through the body while simultaneously enabling fuel to be electrodeposited onto the body during charging, as described in U.S. Patents or Patent Applications Nos. 12/885,268, 13/230,549, 13/299,167, and 8,309,259. The combination of one or more bodies and fuel particles constitutes the first electrode 20. As shown in FIG1 , the first electrode 20 has a substantially rectangular configuration, however, this configuration is not intended to be limiting, and any other shape or configuration is possible.

1 , the fuel is oxidized at the fuel electrode 20, providing oxidized fuel ions that are ionically conducted through the electrolyte 22. Fuel oxidation occurs such that the fuel is oxidized into at least oxidized fuel ions that can remain in the electrolyte 22, and electrons that are conducted from the fuel electrode 20 to the second electrode 30 through the external load 40.

In the simplified and non-limiting schematic diagram of Figure 1, the external load 40 is generally described as being connected to the first electrode body 20a. However, it should be understood that many other connection configurations are possible based on the desired operating conditions. For example, the metal fuel electrodeposition may establish an electrical connection between some or all of the electrode bodies 20 (for example, due to a prior charging operation). Such a connection may exist between the end electrode body 20a and the subsequent permeable electrode body 20b. In addition, the electrode body 20b may be further connected to the electrode body 20c through such a metal fuel electrodeposition. In the case where the end electrode body 20a is connected to the external load 40, due to such an internal connection, oxidation of the metal fuel can begin at the electrode body 20c adjacent to the second electrode 30. In some embodiments, it is also desirable to establish an external circuit connection between the electrode body 20c and the external load 40 through a switch. In addition to the internal connection due to the metal fuel electrodeposition, or in the absence of such an internal connection, the external connection may be established based on the desired operating conditions. The connection can be selectively and programmatically established based on sensed conditions, based on or not based on elapsed time. For specific details concerning connection schemes and their control, reference may be made to U.S. Patent or Patent Application Nos. 12/885,268, 13/083,929, 13/230,549, 13/277,031, 13/299,167, and 8,309,259; all of which are incorporated herein by reference.

The fuel can be a metal, for example, iron, zinc, aluminum, magnesium, or lithium. With respect to metal, the term is intended to include all elements that are considered metals or semimetals in the periodic table when aggregated on the electrode body in atomic form, alloy form, or molecular form, including but not limited to alkali metals, alkaline earth metals, lanthanides, actinides, transition metals, and post-transition metals, and the metal fuel can have any form. However, the present invention is not intended to be limited to any particular fuel, and therefore, any other fuel may be used. To illustrate the operating principles of the present invention, an example is described herein in which zinc is the metal fuel; however, this is not intended to be a limiting embodiment.

For a specific reaction in one non-limiting embodiment, potassium hydroxide is used as the electrolyte 22. Zinc particles are used as the fuel and oxygen from the ambient air is used as the oxidant. During discharge, zinc is oxidized at the first electrode 20 to produce zinc cations Zn2+, which are supported by four hydroxide ions to produce zincate complex anions according to equation (3):

During discharge, oxygen is reduced at the second electrode 30 according to equation (4):

O ₂ +2H ₂ O+4e ^- ——→4OH ^- (4)

In the electrolyte solution 22, the following reaction represented by equation (5) occurs:

The hydroxide ion concentration in the electrolyte 22 can be maintained by the reduction reaction of the oxidant at the second electrode 20 (Equation 4) and the hydroxide ions released from the chemical reaction of the zincate anions (Equation 5). The flow of the electrolyte 22 can transport the relatively unstable zincate anions away from the first electrode 20, thereby preventing the zinc ions from being reduced back to zinc at the first electrode 20, which in turn improves efficiency because electrons are free to flow through the external load 40 rather than being consumed by the reduction of the zincate ions. In some embodiments, depending on various factors related to the composition of the electrolyte 22, zinc can remain dissolved rather than precipitated as ZnO.

The foregoing description of metal fuel cells is provided for reference only and is not intended to be limiting. The present invention can be applied to a variety of electrochemical cells having various chemistries and arrangements. In some embodiments, the electrochemical cell may be a primary cell, and the following description of the charging operation is therefore not relevant thereto.

In some embodiments, the electrochemical cell can be a storage (i.e., rechargeable) electrochemical cell. The following exemplary description relates to an electrochemical cell operable in a charging mode when an electric current is applied between a charging electrode and a fuel electrode. According to an embodiment of the present invention, reducible metal fuel ions can be reduced and electrodeposited as an oxidizable form of metal fuel on a fuel electrode acting as a cathode. The technology of electrodeposition on the fuel electrode 20 can be used in the above-mentioned battery or any other type of battery, including an embodiment in which the first electrode is a single body. However, as previously mentioned, in some embodiments, the electrochemical cell can be a primary cell, and thus the electrodeposition method can be unrelated thereto. Therefore, the description of the storage battery provided herein is not intended to be limiting.

In FIG2 , electrochemical cell 10 is schematically depicted and somewhat exaggerated in the same manner as in FIG1 to facilitate a better understanding of various operational modes. This is not intended to be limiting, but rather for illustrative purposes only. As shown in FIG2 , electrochemical cell 10 further includes a charging electrode spaced apart from first electrode 20. In the illustrated embodiment, the charging electrode is a third electrode 50 spaced apart from first electrode 20 on the same side as second electrode 30, for example, within gap 32. In some embodiments, third electrode 50 may be disposed on the opposite side of first electrode 20 (i.e., adjacent electrode body 20a), or in any other suitable arrangement. Third electrode 50 may be spaced apart from first electrode 20, forming gap 52 that includes ionically conductive medium 22. In some embodiments, second electrode 30 may function as the charging electrode during charging, obviating the need for a separate electrode (e.g., third electrode 50) for charging. While not intended to be limiting, it is possible to select a second electrode 30 that is "dual-functional," meaning that it may simultaneously function as an air-breathing cathode during current generation and as an anode charging electrode during charging. Therefore, any reference to a charging electrode herein may be considered to be the second electrode 30 or the third electrode 50 that is used or acts as an anode during the charging process. More specifically, although the illustrated embodiment is described with reference to the case where the charging electrode is the third electrode 50, it should be understood that the same description can also be applied to the case where the second electrode 30 is the charging electrode.

Thus, it can be appreciated that, from the fact that the same physical component or parts thereof can, in some embodiments, perform different electrode functions, that when electrodes are referred to herein, it should be understood that, depending on the operating mode of the device, various structures in the same embodiment can act as one or more electrodes in different ways. For example, in some embodiments in which the oxidant electrode has a dual function and serves as a charging electrode, the same electrode structure acts as an oxidant electrode during the discharge process and as a charging electrode during the discharge process. For another example, during the discharge process, all bodies of the fuel electrode can act as fuel electrodes, but during the charging process, one or more of these bodies acts as a fuel electrode by receiving the electrodeposited fuel, and the other one or more bodies act as charging electrodes to release the oxidant (e.g., oxygen), and the fuel electrode grows as the electrodeposited growth connects to more bodies. Thus, the electrodes referred to are clearly defined as the functional roles that a unique electrode structure or a structure having multiple electrode functions can play during different battery operating modes, and therefore the same multifunctional structure can be considered to meet the requirements of multiple electrodes for this reason.

In one embodiment, the permeable body of the first electrode 20 may be separated by an inert non-conductive separator and/or an ion exchange membrane. Alternatively, the separator may also include structures within the interior region that help maintain the separation of the permeable electrode body without significantly impeding the flow of electrolyte 22 therethrough. As another non-limiting option, the separator may also include structures within the interior region that help and guide the growth morphology of the metal fuel deposit, such as a grid-like arrangement.

While three electrode bodies (i.e., 20a, 20b, and 20c) are described in the illustrated embodiment, any suitable number of electrode bodies is possible. Furthermore, any suitable electrode body configuration is also possible. For example, in one embodiment, the first electrode 20 may include electrode bodies arranged in a symmetrical configuration, wherein the central electrode body 20a is the axis of symmetry and is thus located as the innermost electrode between electrode body 20b and electrode body 20b' (not depicted, but generally a mirror image of electrode body 20b). In such an embodiment, the configuration may further include any suitable number of additional first electrode bodies, second electrodes 30, and third electrodes 50.

For further specific details concerning battery construction, reference may be made to U.S. Patent or Patent Application Nos. 13/019,923, 13/167,930, 13/185,658, 13/531,962, 13/532,374, 13/566,011, 13/666,948, and 8,309,259; all of which are incorporated herein by reference above.

As described in the illustrative embodiment of Figure 2, current from an external power source 60 is applied between the third electrode 50 and the first electrode 20 during the charging mode. In this case, the third electrode 50 acts as an anode and the end permeable electrode body 20a acts as a cathode. It should be recognized that the general connection to the end electrode body 20a in the illustrative example is only one possible configuration among many other connection configurations that can be selected based on the desired operating characteristics. For specific details related to the charge/discharge process, switches and their control, reference may be made to U.S. Patents or Patent Application Nos. 12/885,268, 13/083,929, 13/230,549, 13/277,031, 13/299,167, and 8,309,259; all of which are incorporated herein by reference.

In one non-limiting example, the metal fuel is zinc and the electrolyte 22 is an aqueous solution containing potassium hydroxide, which can be the same fuel and electrolyte 22 used in the embodiment of Figure 1 described above. In the electrolyte 22, the zinc ions can be provided in any suitable reducible form, preferably in the form of zinc oxide ZnO. This is advantageous because zinc oxide is a byproduct of the current generating operation described above in the previous embodiment, and therefore the electrochemical cell 10 can be charged using the reversible byproduct of its own current generating operation. Since the current generating operation has already produced reducible zinc oxide in the electrolyte 22, this can minimize the need to supply fresh source fuel for each charge. In such an embodiment, according to equation (6), a reduction reaction occurs at the reduction site:

wherein the corresponding oxidation occurs at the third electrode 50, which in the illustrated embodiment acts as a charging electrode and as an anode, according to equation (7),

4OH ^- ——→O ₂ +2H ₂ O+4e ^- (7)

According to equation (7), the charging electrode may also be referred to as the oxygen evolution electrode. The generation of oxygen may optionally be vented in any suitable manner. For example, oxygen generation may be conveniently managed as described in U.S. patent application Ser. Nos. 12/549,617, 13/532,374, 13/566,948, and 13/666,864 (incorporated herein in their entireties).

The fuel need not be limited to zinc, and any other metal fuel, including any of the above-mentioned metal fuels in this application, may also be used. Similarly, in various embodiments, the electrolyte 22 may be different and may be alkaline or acidic. Likewise, the reducible metal fuel ions are not necessarily provided by byproducts of the current generating operation, and it is within the scope of the present invention to use fuels produced from products that are not easily reversible in some embodiments. Therefore, it is within the scope of the present invention to supply the electrolyte 22 for charging from a separate fuel source having fuel ions in a suitable form for reduction and electrodeposition, which fuel source is separate from the electrolyte 22 that is used in the current generating process and accumulates byproducts. Similarly, the same electrolyte 22 may be used for both processes simultaneously, but the fuel may be provided separately from its own source during the charging operation.

During the charging operation, electrodeposition can cause or promote the growth of the metal fuel in a flowing, permeable form within the permeable electrode body 20, such that the electrodeposited metal fuel establishes an electrical connection between the end permeable body 20a and each subsequent permeable electrode body (e.g., connected to electrode body 20b and then to electrode body 20c). Due to this continuous growth, each subsequent permeable electrode body 20 undergoes reduction and electrodeposition as the electrical connection is established by the metal fuel growth. In some embodiments, as growth occurs on each subsequent permeable electrode body 20, an external connection can also be established via a switch on a circuit including an external power source 60. This connection can be selectively established over time, either programmatically or non-programmatically, based on a sensed condition. For specific details concerning continuous or progressive fuel growth methods, connection schemes and their control, reference may be made to U.S. Patent or Patent Application Nos. 12/885,268, 13/083,929, 13/230,549, 13/277,031, 13/299,167, and 8,309,259; all of which are incorporated herein by reference.

In one embodiment, the growth of the electrodeposit can be controlled in a manner that produces an overall uniform coating growth with a flow-permeable morphology. The term flow-permeable morphology refers to the morphology of the metal growth in the electrode body 20 being constructed so that the electrolyte 22 is still able to flow through the electrode body 20. Therefore, in some embodiments, flow is allowed to continue, and the growth does not exhibit major lateral characteristics that would cause the holes or openings of the permeable electrode body 20 to be completely blocked or blocked. The allowed flow can be in any direction. Although flow is preferred, growth may also occur without any flow. In a preferred embodiment, electrodeposition can be stopped before the lateral growth closes the holes or openings of the first electrode 20 substrate. The preferred morphology of the deposition may or may not change based on the application, battery configuration, desired operating characteristics. Therefore, the morphology of the embodiments is not intended to be limiting, but rather the invention described herein provides a system and method for adjusting the morphology using the heteroionic aromatic additives described below.

In a preferred embodiment, growth occurs as an overall uniform coating. The fuel electrodeposition morphology can be controlled by the composition of the additives in the ionically conductive medium 22. Properties that can be affected by the additive composition include growth density, particle size, edge effects, and electrodeposition coating potential and current density.

It can be appreciated that additives may be intended to be introduced into the electrodeposit at a substantially constant rate, thereby facilitating partial cycles (i.e., short charge/discharge cycles). If the additive is introduced into the electrodeposit at a gradually decreasing rate, an uneven electrodeposit will form, and the effective additive concentration in the electrolyte will decrease. Under partial cycle conditions, the reduced concentration of the additive may undesirably change the morphology of the electrodeposit, and each additional partial cycle may exacerbate the adverse effects, ultimately leading to short circuits or other failures.

Without being bound by any particular theory, heteroionic aromatic additives can have physicochemical properties that lead to adsorption at the fuel electrode surface, thereby inhibiting corrosion. This is particularly useful for primary cells, which are generally harmed by high self-discharge rates. The physicochemical properties of the additive can be selected based on aromaticity, functional groups, electron density, steric effects, etc. Again, without being bound by any particular theory, aromatic functional groups that provide delocalized π electrons can provide effective corrosion inhibition through interactions with d orbitals of the metal electrode surface. For example, heteroionic compounds containing unpaired electrons attached to nitrogen atoms can provide desirable interactions with the metal electrode surface.

In one embodiment, the heteroionic aromatic additive may have a structure according to the following formula:

wherein A represents a charge center selected from the group consisting of quaternary ammonium, cyclic ammonium, polycyclic ammonium, quaternary phosphonium, cyclic phosphonium, polycyclic phosphonium, phosphazene, cyclic phosphazene, polycyclic phosphazene, and derivatives thereof;

wherein R represents an organic linker selected from the group consisting of (C ₁ -C ₂₀ ) linear alkyl, branched alkyl, aryl, alkylamino, pyridyl, pyrrolyl, imino, pyridylpyrazinyl, pyrimidinyl, thienyl, thiazolyl, and derivatives thereof; and

wherein B represents an aromatic group which may be selected from the group consisting of benzene, azirine, diazirine, azete, pyrrole, imidazole, pyrazole, triazole, pyridine, pyrazine, diazine, triazine, azepine, diazepine, azocine, 1-phosphole, phosphinine, oxazole, thiophene, and derivatives thereof.

In one embodiment, the heteroionic aromatic additive may have a structure according to the following formula:

In one embodiment, the heteroionic aromatic additive structure can be designed to avoid electrochemical reductive cleavage by ensuring a base-stable linkage without β-protons. It can be recognized that the base-stable linkage can prevent the electrochemical reductive cleavage of the heteroionic aromatic additive. For example, benzyltrimethylammonium containing β-protons is less stable against electrochemical reductive cleavage than trimethyl-2-phenyl-2-propylammonium (propanaminium) containing a base-stable linkage without β-protons. In some embodiments, the linkage adjacent to the aromatic group can be designed to have more than one carbon to suppress resonance connected to the aromatic ring, thereby further providing stability.

According to one embodiment, the heteroionic aromatic additive may have a structure according to the following formula:

wherein A represents a charge center selected from the group consisting of quaternary ammonium, cyclic ammonium, polycyclic ammonium, quaternary phosphonium, cyclic phosphonium, polycyclic phosphonium, phosphazene, cyclic phosphazene, polycyclic phosphazene, and derivatives thereof;

wherein R ₁ represents a branched link providing a beta carbon atom relative to the charge center A which may be selected from the group consisting of a branched alkyl group, an aryl group, a neopentyl group, tert-butyl alcohol, and derivatives thereof;

wherein R ₂ represents an organic linker comprising at least two carbon atoms which may be selected from the group consisting of (C ₁ -C ₂₀ ) linear alkyl, branched alkyl, aryl, alkylamino, pyridyl, pyrrolyl, imino, pyridylpyrazinyl, pyrimidinyl, thienyl, thiazolyl, and derivatives thereof; and

wherein B represents an aromatic group selected from the group consisting of benzene, azepine, diazepine, azetidine, pyrrole, imidazole, pyrazole, triazole, pyridine, pyrazine, diazine, triazine, azepine, diazepine, azecin, 1-phosphol-2,4-diene, phosphine, oxazole, thiophene, and derivatives thereof.

In one embodiment, the heteroionic aromatic additive may have a structure selected from the group consisting of:

and its derivatives.

In one embodiment, the anion associated with a particular heteroionic aromatic cation can be selected based on solubility, chemical stability, electrochemical stability, or any other suitable properties. Non-limiting examples of anions include hydroxide, methyl carbonate, tetrafluoroborate (BF ^4- ), hexafluorophosphate (PF ^6- ), halides, phosphates, sulfates, and combinations thereof.

In one embodiment, the heteroionic aromatic additives described herein may be combined with other additives disclosed in the aforementioned patents or patent applications. It will be appreciated that the absence of synergistic effects observed with individual additives may be advantageous for operating electrochemical cells comprising metal fuels.

In some embodiments, ionically conductive medium 22 may include poly(ethylene glycol) tetrahydrofurfuryl (PEG-THF) and/or indium, tin, lead, germanium, copper, mercury, bismuth, tartrate, phosphate, citrate, succinate, ammonium, or other hydrogen evolution reaction (HER) suppressing additives, as described in U.S. Patent Application No. 13/028,496, which has been incorporated by reference above. These are optional and may be omitted. In some embodiments, ionically conductive medium 22 may include a metal salt of a metal other than the metal fuel. For example, ionically conductive medium 22 may include a metal salt of indium, tin, lead, germanium, copper, mercury, or other suitable metal or semimetal. PEG-THF and the metal salt are optional and may be omitted.

In some embodiments, ionically conductive medium 22 may comprise a metal oxide of a metal other than the metal fuel. For example, ionically conductive medium 22 may comprise a metal salt of indium, tin, lead, germanium, copper, mercury, or other suitable metals or semimetals. The metal oxide is optional and may be omitted.

In some embodiments, the ionically conductive medium may include a heteroionic compound as disclosed in U.S. Patent Application No. 13/526,432, which has been incorporated by reference above. For example, the heteroionic compound cation may be selected from 1-methyl-4-aza-1-azoniabicyclo[2,2,2]octane, methyl-3-quinuclidinolium, derivatives thereof, and combinations thereof. The heteroionic compound is optional and may be omitted.

In some embodiments, the ionically conductive medium may include additives described in co-pending application "Synergistic additives for electrochemical cells with electrodeposited fuel," filed on the same date as this application and commonly assigned to Fluidic, Inc. For example, the ionically conductive medium may further include a macroheterocyclic compound, a quaternary phosphonium salt, an aminophosphonium salt, and derivatives and combinations thereof. However, any of the additives mentioned herein may be used alone.

The concentration of the heteroionic aromatic additive may be in the range of 0.0001 mol/L to 0.4 mol/L. The current density may be in the range of 110 mA/cm ² or below. In a preferred embodiment, the current density may be in ^{the range of 5-100 mA/cm 2. These} ranges are examples and are not intended to be limiting.

To maintain a desired or target level of additives in the electrolyte solution, additive modifiers as disclosed in US Patent Application No. 13/220,349, which is incorporated herein by reference in its entirety, may be used.

Example

In an exemplary embodiment of the present invention, a current density of 50 mA/cm ² was applied to the first electrode 20 in an 8.0 M KOH and 1.25 M ZnO electrolyte solution. The images in FIG3 at different magnifications show electrodeposition at the interface between the electrolyte and the electrode in a stack of permeable electrode bodies, wherein the electrolyte contains 2.0 mM 1-benzyl-4-aza-1-azoniabicyclo[2,2,2]octane hydroxide and 0.25 mM indium chloride (InCl ₃₎ . The smooth electrodeposition shows that the electrodeposited metal accumulates as a generally smooth, slightly rough layer over the entire fuel electrode surface. Negligible dendrites are formed, thereby maintaining the electrode surface morphology from one charge-discharge cycle to the next.

The embodiments described above are provided solely to illustrate the structural and functional principles of the present invention and are not intended to be limiting. For example, the present invention may be implemented using different fuels, different oxidants, different electrolytes, and/or different overall structural configurations or materials. Therefore, the present invention is intended to encompass all modifications, substitutions, variations, and equivalents.

Claims (27)

1. An electrochemical battery, comprising: i. Fuel electrode containing metallic fuel, ii. Second electrode, iii. An ion-conducting medium connected to the electrode, the ion-conducting medium comprising a heteroionic aromatic additive having aromatic functional groups, wherein the ion-conducting medium is an aqueous electrolyte solution; The fuel electrode and the second electrode are operable in discharge mode, wherein the metallic fuel is oxidized at the fuel electrode, which acts as the anode, thereby generating electrons that are conducted from the fuel electrode to the second electrode through a load. 2. The electrochemical battery according to claim 1 is a galvanic cell. 3. The electrochemical battery according to claim 1 is a storage battery. 4. The electrochemical cell according to claim 3, further comprising a charging electrode and reducible metal fuel ions within the ion-conducting medium; wherein the fuel electrode and the charging electrode are operable in a charging mode, wherein when a current is applied between the charging electrode and the fuel electrode, the reducible metal fuel ions are reduced and electrodeposited on the fuel electrode, which acts as a cathode, as an oxidizable form of metal fuel. 5. The electrochemical cell according to claim 4, wherein the fuel electrode comprises a series of spaced-apart permeable electrode bodies; wherein during the charging process of the electrochemical cell: when the charging electrode acts as the anode and at least one of the permeable electrode bodies acts as the cathode, an electrochemical current is applied between the charging electrode and at least one of the permeable electrode bodies, such that the reducible metal fuel ions are reduced and electrodeposited on at least one of the permeable electrode bodies as an oxidizable form of metal fuel. The electrodeposition causes growth between the permeable electrode bodies, thereby establishing an electrical connection between the electrodeposited metal fuel and the permeable electrode bodies. 6. The electrochemical cell of claim 3, wherein the fuel electrode comprises a plurality of spaced-apart permeable electrode bodies for receiving metal fuel by electrodeposition, wherein the electrodeposition causes growth between the permeable electrode bodies such that the electrodeposited metal fuel establishes an electrical connection between the permeable electrode bodies. 7. The electrochemical battery according to claim 1, wherein the electrolyte aqueous solution is alkaline. 8. The electrochemical battery according to claim 7, wherein the electrolyte aqueous solution contains potassium hydroxide. 9. The electrochemical battery according to claim 1, wherein the heteroionic aromatic additive is added to the electrolyte aqueous solution and has a structure according to the following formula: Where A represents a charge center that can be selected from the following group: quaternary ammonium, cyclic ammonium, polycyclic ammonium, quaternary phosphorus, cyclic phosphorus, polycyclic phosphorus, phosphonazine, cyclic phosphonazine, polycyclic phosphonazine, and their derivatives; Where R represents an organic linking bond selected from the following group: ( _C1 - _C20 ) straight-chain alkyl, branched-chain alkyl, aryl, alkylamino, pyridyl, pyrroloyl, imino, pyridylpyrazinyl, pyrimidinyl, thiophenyl, thiazolyl, and their derivatives; and Wherein B represents an aromatic group selected from the following group: benzene, acrylonitrile, diacylonitrile, azacyclobutadiene, pyrrole, imidazole, pyrazole, triazole, pyridine, pyrazine, diazine, triazine, acrylonitrile, diacylonitrile, acrylonitrile, 1-phosphacyclopent-2,4-diene, phosphabenzene, oxazole, thiophene, and their derivatives. 10. The electrochemical battery according to claim 1, wherein the heteroionic aromatic additive has a structure according to the following formula: Where A represents a charge center that can be selected from the following group: quaternary ammonium, cyclic ammonium, polycyclic ammonium, quaternary phosphorus, cyclic phosphorus, polycyclic phosphorus, phosphonazine, cyclic phosphonazine, polycyclic phosphonazine, and their derivatives; Where R ₁ represents a branched bond that provides a β carbon atom relative to the charge center A without a β proton, and can be selected from: branched alkyl, aryl, neopentyl, tert-butanol, and their derivatives; Wherein _R2 represents an organic linker bond containing at least two carbon atoms, which may be selected from: ( _C1 - _C20 ) straight-chain alkyl, branched-chain alkyl, aryl, alkylamino, pyridyl, pyrroloyl, imino, pyridylpyrazinyl, pyrimidinyl, thiophenyl, thiazolyl, and their derivatives; and Where B represents an aromatic group selected from the following group: benzene, acrylonitrile, diacylonitrile, aziridine, imidazole, pyrazole, triazole, pyridine, pyrazine, diazine, triazine, acrylonitrile, diacylonitrile, acrylonitrile, 1-phosphacyclopent-2,4-diene, phosphabenzene, oxazole, thiophene and its derivatives. 11. The electrochemical battery according to claim 1, wherein the heteroionic aromatic additive has a structure according to the following formula: 12. The electrochemical battery according to claim 1, wherein the heteroionic aromatic additive has a structure according to the following formula: 13. The electrochemical battery according to claim 1, wherein the heteroionic aromatic additive has a structure according to the following formula: 14. The electrochemical battery according to claim 1, wherein the heteroionic aromatic additive has a structure according to the following formula: 15. The electrochemical battery according to claim 1, wherein the heteroionic aromatic additive has a structure according to the following formula: 16. The electrochemical battery according to claim 1, wherein the heteroionic aromatic additive has a structure according to the following formula: 17. The electrochemical battery according to claim 1, wherein the heteroionic aromatic additive has a structure according to the following formula: 18. The electrochemical cell according to claim 1, wherein the concentration of the heteroionic aromatic additive is from 0.0001 mol/L to 0.4 mol/L. 19. The electrochemical battery according to claim 1, wherein the metal fuel is zinc. 20. The electrochemical cell of claim 1, wherein the heteroionic aromatic additive is firmly adsorbed onto the fuel electrode comprising the metal fuel. 21. The electrochemical battery according to claim 1, wherein the heteroionic aromatic additive inhibits the corrosion of the metal fuel. 22. The electrochemical cell according to claim 3, wherein the heteroionic aromatic additive controls the morphology of the metal fuel electrodeposit. 23. The electrochemical cell of claim 3, wherein the heteroionic aromatic additive minimizes the preferential coating of metal fuel electrodeposit at edges or corners. 24. The electrochemical battery according to any one of the preceding claims, wherein the metal fuel is zinc and the ion-conducting medium further comprises an indium salt additive. 25. The electrochemical battery according to claim 24, wherein the heteroionic aromatic additive is 1-benzyl-4-aza-1-azaonium bicyclo[2,2,2]octane hydroxide and the indium salt additive is indium chloride. 26. A method for operating the electrochemical cell according to any one of the preceding claims, The method includes discharging the electrochemical cell by the following steps: i. Oxidizing the metallic fuel at the fuel electrode, which acts as the anode, thereby generating electrons that are conducted from the fuel electrode to the second electrode through a load; and ii. Disconnect the fuel electrode and the second electrode from the load to interrupt the discharge. 27. The method of claim 26, wherein the electrochemical cell further comprises a charging electrode and reducible metal fuel ions in the ion-conducting medium; The method further includes charging the electrochemical cell by the following steps: i. Applying a current between the charging electrode and the fuel electrode, which acts as the cathode, such that reducible metal fuel ions are reduced and electrodeposited on the fuel electrode as an oxidizable form of metal fuel; and ii. Disconnect the current to interrupt the charging.