WO2015104574A1

WO2015104574A1 - Rechargeable metal nitric oxide gas battery system

Info

Publication number: WO2015104574A1
Application number: PCT/IB2014/002809
Authority: WO
Inventors: Fuminori Mizuno; Paul T. Fanson; Charles A. ROBERTS; Nikhilendra Singh
Original assignee: Toyota Motor Engineering & Manufacturing North America, Inc.
Priority date: 2014-01-08
Filing date: 2014-09-29
Publication date: 2015-07-16
Also published as: JP6373389B2; CN105899280A; CN105899280B; JP2017504163A

Abstract

A metal-nitric oxide electrochemical cell which is fed a gas comprising nitric oxide (NO) and optionally, at least one gas selected from the group consisting of a nitrogen oxide of formula NxOy, oxygen, water vapor, a gaseous hydrocarbon, carbon monoxide and carbon dioxide is provided. The cell may contain a partition which inhibits diffusion of NxOy + active species from the cathode compartment to the anode compartment. Also provided is a rechargeable battery containing the metal- nitric oxide electrochemical cell. A vehicle system wherein NxOy from a combustion engine exhaust is fed to a metal-NxOy battery is additionally provided.

Description

TITLE OF THE INVENTION

RECHARGEABLE METAL NITRIC OXIDE GAS BATTERY SYSTEM CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Application No. 14/150,168, filed January 8, 2014, U.S. Application No. 14/221,814, filed March 21, 2014, and U.S. Application No. 14/222,989, filed March 24, 2014, the disclosures of which are incorporated herein by reference in their entireties.

BACKGROUND OF THE INVENTION

The present invention is directed to a metal-gas battery, specifically a metal-gas battery with a cathode comprising nitric oxide (NO) or a redox active N_xO_y gaseous compound as an active material.

Lithium ion batteries have been in commercial use since 1991 and have been conventionally used as power sources for portable electronic devices. The technology associated with the construction and composition of the lithium ion battery (LIB) has been the subject of investigation and improvement and has matured to an extent where a state of art LIB battery is reported to have up to 700 Wh/L of energy density. However, even the most advanced LIB technology is not considered to be viable as a power source capable to meet the demands for a commercial electric vehicle (EV) in the future. For example, for a 300 mile range EV to have a power train equivalent to current conventional internal combustion engine vehicles, an EV battery pack having an energy density of approximately 2000 Wh/L is required. As this energy density is close to the theoretical limit of a lithium ion active material, technologies which can offer battery systems of higher energy density are under investigation.

Metal-air batteries are one of the technologies under investigation as a potential advancement in energy technology to supplant and replace the lithium ion battery for several reasons. In a metal-air battery the positive electrode active material is oxygen gas which conceptually may be obtained from the air. As such, much of the mass of the battery associated with the cathode component is significantly reduced. Interest in metal-air batteries is also supported by the concept that 0₂ gas is continuously coming from outside of the battery, and therefore, the battery performance in terms of capacity and lifetime would be determined by the metal anode. Theoretically, such a battery would function until the metal anode is consumed and as a result, the metal-air battery may have higher energy density potential than other battery technologies presently under investigation.

Due to the known energy potential of lithium, a Li-0₂ battery is of interest as a candidate high energy density type rechargeable battery. Li-0₂ batteries based on a source of purified 0₂ have been demonstrated. However, when ambient air is employed as the oxygen source, the battery performance deteriorates and utility as a rechargeable battery is lost. This deterioration is believed to occur because the presence of H₂0 and C0₂ in air causes deactivation of lithium oxides such as Li₂0₂ and Li₂0, by formation of Li₂C0₃, which is an inactive material for recharging. Thus, a major challenge to the success of a Li-0₂ battery is the necessity for purification of 0₂ gas from ambient air or atmosphere. Generally, a battery consuming pure oxygen would not be practicable for conventional consumer utility.

However, with currently known technologies, the presence of H₂0 and C0₂ prevent successful development of a commercially useful battery.

One of the approaches to overcome this issue is removal of H₂0 and C0₂ through membrane technologies. Air management is necessary to implement the gas purification. However, the purification required seems to be quite difficult even using the state-of-art gas separation membrane technology. Further, it may be possible to eliminate H₂0 and C0₂ employing gas absorption, for example on a zeolite, however, such a gas absorption system would be too large to be considered a realistic solution in most battery applications.

In view of the problems associated with a metal-0₂ battery, effort is underway to develop alternative cathode systems for a metal-gas battery.

Albertus et al. (U.S. 2012/0094193) describes an electrochemical metal-gas cell having a lithium negative electrode and an oxygen/carbon dioxide active cathode material. The oxygen/carbon dioxide mixture is based on ambient air and includes C0₂. According to Albertus, a specific ratio of C0₂/0₂, 2: 1 is necessary to achieve high energy density as a primary battery. However, except for the exhaust gas from a factory or other large stationary exhaust sources, it is difficult to concentrate the C0₂ gas to such ratio, because in ambient air, the quantity of C0₂ is approximately 0.03%. It may be possible to devise an air control system to meet this requirement in a fixed construction, although an air management system which maintains a constant C0₂ concentration is not conventionally available. However, for use in an automobile, such a battery would not be practical because the C0₂ concentration fluctuates and control to a specific ratio would be difficult. Takechi et al. (JP 201 1-070835) describes a metal air cell wherein the anode metal may be lithium, sodium, potassium, magnesium, calcium, aluminum or zinc. The oxidant supplied to the cathode is a combination of oxygen and carbon dioxide.

Hillhouse (U.S. 2013/0216924) describes a capacitor device for generating electrical power wherein a fuel is flowed over a working electrode of the capacitor, thus charging the capacitor. The flow is then reversed and an oxidant is flowed over the working electrode, thus generating current flow across the electrodes. Materials listed as fuels which can act as electron sources include hydrogen, carbon monoxide, NO, N0₂, S0₂ and volatile

hydrocarbons.

Hiraiwa et al. (U.S. 2013/0089810) describes an electrochemical reaction apparatus for fluid flow decomposition of an ammonia containing stream, wherein the NH₃ is converted to N₂ and water when air or oxygen is coupled as an oxidant. Electric power may be generated due to a potential difference between the apparatus anode and cathode. The apparatus is in the form of a membrane electrode assembly (MEA) and functions as a fuel cell, not as a battery.

Lee et al. (U.S. 2012/0141889) describes a lithium air battery containing an organic electrolyte which includes a metal-ligand complex. The negative electrode contains lithium and the positive electrode contains oxygen from an external supply. The metal-ligand complex has a charge/discharge voltage range which falls within the range of a lithium battery and may transfer electrons via formation of redox couples during the charging and discharging cycles. Air or oxygen are the only cathode active materials disclosed.

Huang (U.S. 2010/0247981) describes a system for energy management of a composite battery (fuel cell). The system includes a series of modules for collecting off-gas from the fuel cell, analyzing the content of the off-gas and then directing the off-gas to a point of further fuel consumption. For example, where the off-gas contains hydrogen it may be consumed in an internal combustion engine or a hydrogen fuel cell.

Limaye (U.S. 5,976,721) describes a chemical cogeneration process which is conducted in a specially constructed monolithic mass having sets of passageways. A fuel such as hydrogen sulfide, ammonia or a hydrocarbon is introduced into one passageway, and an oxidant such as air, a nitrogen oxide, carbon dioxide, sulfur dioxide, sulfur trioxide or steam is introduced to a second passageway. The passageways are constructed of electrically conducting materials which are connected to an external electrical circuit.

Langer et al. (U.S. 4,321,313) describes the electrogenerative reduction of nitric oxide by reaction with hydrogen in the presence of electrocatalytic electrodes and electrolyte. As described the electrogenerative cell is an electrochemical reactor which is similar to a fuel cell.

Smith et al. (U.S. 3,979,225) describes a fuel cell based on a cathodic reduction of nitrogen dioxide (N0₂) to nitric oxide (NO). Then NO is captured and reoxidized to nitrogen dioxide for recycle back to the cathode of the fuel cell. Hydrogen gas or reformed hydrocarbon gas stream are disclosed as the anode reactant, however, any other anode half reaction may be coupled with the cathodic reduction.

Liang et al. (CN102371888) (Abstract only) describes a plasma generator which is effective to remove nitric oxide from an exhaust gas of a gasoline engine. Although the NO is passed between electrodes, utility as a battery is not disclosed.

Wen et al. (CN 102208653) (Abstract only) describes a lithium air battery having an air electrode which contains a catalyst, a carrier and an adhesive.

Park (KR20090026589) describes fuel-cell based post processor to remove nitric oxides for an exhaust system of an engine.

Therefore, there is a need to find and develop alternative cathodic gases for a metal- gas battery which are safe, readily available and cost efficient. Further, there is a need for a battery and a battery system employing a readily available alternative gas that is

commercially viable. SUMMARY OF THE INVENTION

These and other objects are addressed by the present invention, the first embodiment of which includes an electrochemical cell comprising: an anode comprising a metal; a porous cathode supplied with a gas comprising nitric oxide (NO); a separator located between the anode and cathode; and an electrolyte; wherein the NO is the active cathode ingredient.

In an aspect of the first embodiment, the gas comprising nitric oxide (NO) further comprises at least one gas selected from the group consisting of a nitrogen oxide of formula N_xO_y, oxygen, water vapor, a gaseous hydrocarbon, carbon monoxide and carbon dioxide; wherein the active cathode ingredient is NO or the compound of formula N_xO_y, x is 1 or 2 and y is an integer of 1 to 4.

In one specific embodiment of the present invention, the metal of the anode comprises one selected from the group consisting of lithium, sodium, potassium, magnesium, calcium, aluminum and zinc.

In a further embodiment, the anode metal is lithium, sodium or magnesium. In aspects of each of these embodiments the electrochemical cell comprises: an anode compartment comprising a working electrode which comprises a metal; a cathode compartment comprising a porous cathode supplied with a gas comprising at least one of nitric oxide (NO) and a redox active N_xO_y gaseous compound; a partition located between and separating the anode compartment and the cathode compartment; and a mobile ion carrier; wherein the NO and the redox active N_xO_y is the active cathode ingredient, and the partition is conductive of the mobile ion carrier and nonconductive of a N_xO_y ⁺ ion.

In an aspect of this embodiment, the partition is a membrane comprising at least one of a gel, a polymer, a ceramic material and a composite of a polymer and a ceramic material. In a further special aspect of this embodiment, the partition is a membrane comprising a ceramic material and the ceramic material is a dense ceramic membrane.

The present invention further includes a rechargeable battery which contains the electrochemical cell of the previous embodiments.

In a further specialized embodiment the present invention includes a NO supply system which is attached to the battery and feeds NO to the cathode.

In a specialized aspect of this embodiment the present invention includes a N_xO_y supply system which is attached to the battery and feeds N_xO_y to the cathode.

In another embodiment, the present invention includes a vehicle having the rechargeable battery and the N_xO_y supply system wherein the N_xO_y supply system obtains N_xO_y from the exhaust of the vehicle combustion engine.

The foregoing paragraphs have been provided by way of general introduction, and are not intended to limit the scope of the following claims. The presently preferred

embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a comparison of cyclic voltammograms obtained with a Li-0₂ cell and cells according to the present invention.

Fig. 2 shows the charge-discharge profiles of NO gas in the 0.2mol kg PP13TFSI- LiTFSI solution.

Fig. 3 shows a schematic diagram of a NO electrochemical cell according to one embodiment of the present invention. Fig. 4 shows the cyclic voltammograms of Example 2 and Example 3 in the N- methyl-N-propylpiperidinium bis(trifluoromethansulfonyl)imide (PP13TFSI) based electrolyte solutions in Testing of NO mixed with Exhaust Components.

Fig. 5 shows the cyclic voltammograms of Example 4-1 and Example 4-2 in the N- methyl-N-propylpiperidinium bis(trifluoromethansulfonyl)imide (PP13TFSI) based electrolyte solutions in Testing of NO mixed with Exhaust Components.

Fig. 6 shows a schematic diagram of a metal N_xO_y battery according to one embodiment of the present invention.

Fig. 7 shows the charge-discharge profiles of the metal N_xO_y gas battery of the Example shown schematically in Fig. 6.

Fig. 8 shows a schematic diagram of a battery system for a vehicle according to an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The present inventors are conducting a wide scale study and evaluation of materials which may function as cathode active materials for a metal-gas battery. The object of this study is to discover a cathode active gas to function in a metal-gas battery having high capacity and high working potential and does not have the problems described above for oxygen. The cathodic gas should be readily available, safe, easy to handle and obtain and cost efficient.

Throughout this description all ranges described include all values and sub-ranges therein, unless otherwise specified. Additionally, the indefinite article "a" or "an" carries the meaning of "one or more" throughout the description, unless otherwise specified.

According to the present invention the term "vehicle" means any power driven device designed for transportation including an automobile, truck van, bus, golf cart and other utility forms of transportation.

In the course of study and evaluation of potential gas cathodic materials, the present inventors have surprisingly discovered that nitric oxide (NO) can function as a cathode gas for a metal-gas electrochemical cell. The experiments described in the Examples indicate that NO gas possesses higher working voltage as well as higher reversibility (rechargeability) than 0₂ gas. Moreover, the studies described also indicate that when NO is employed as the cathode gas, the charged and discharged states are kept on the cathode, thus showing redox performance. In addition, the working voltage as well as voltage hysteresis of the cell may be significantly improved by introducing NO gas into a metal-gas battery.

As shown in the Examples and Fig. 1 , the inventors have determined that NO gas exhibits a redox reaction with narrow peak separation during oxidation/reduction. Compared with other gases, NO gas shows an improved rechargeability.

Regarding working voltage, NO also has a high operation voltage. Its working voltage is estimated at 4.2V vs. Li/Li+, which is extremely high when compared to that of the oxygen redox reaction (ORR) (2.2-2.7V), as also shown in Fig. 1.

Therefore, the first embodiment of the present invention is an electrochemical cell comprising: an anode comprising a metal; a porous cathode supplied with a gas comprising nitric oxide (NO); a separator located between the anode and cathode; and an electrolyte; wherein the NO is the active cathode ingredient.

In an embodiment of the present invention, the positive electrode may be a porous unit construction comprising an oxidation reduction catalyst, a conductive material and a binder. The cathode may be constructed by mixing the redox catalyst, conductive material and optionally the binder and applying the mixture to a current collector of appropriate shape. The oxidation reduction catalyst may be any material which promotes the NO redox reaction. The NO absorbing catalyst may contain as its active component any material which promotes NO absorption. Examples of a suitable catalyst active component include but are not limited to an alkali or alkali earth metal in the form of its oxide (Li₂0, Na₂0, K₂0, MgO, CaO, SrO, BaO), hydroxide (LiOH, NaOH, KOH, Mg(OH)₂, Ca(OH)₂, Sr(OH)₂, Ba(OH)₂), carbonate (Li₂C0₃, Na₂C0₃, K₂C0₃, MgC0₃, CaC0₃, SrC0₃, BaC0₃), or any combination thereof. The active component is typically impregnated on a high surface area oxide support such as A1₂0₃, Zr0₂, Ti0₂, Ce0₂, or any mixed oxide thereof. The rate of NO absorption may be increased by the addition of a precious metal such as Pt, Pd, Rh, or any combination thereof.

The positive electrode may contain an electrically-conductive material which is chemically stable in the potential window of use of the cell. Preferably the conductive material is porous and has a large specific surface area to provide high output. An example of such material may include but is not limited to a carbonaceous material such as Ketjen black, acetylene black, vapor grown carbon fiber, graphene, natural graphite, artificial graphite and activated carbon. Other suitable conductive materials may be conductive fibers, such as a metal fiber, metal powder, such as nickel and aluminum, and organic conductive materials, such as a polyphenylene derivative. In some embodiments mixtures of these materials may be employed. Other suitable conductive materials may be conductive ceramics such as titanium nitride and titanium carbide.

Suitable binders known to one of ordinary skill which are chemically stable in the potential window of use of the cell may include thermoplastics and thermosetting resins. For example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), Polyvinylidene fluoride (PVDF), styrene butadiene rubber, a tetrafluoroethylene hexafluoro ethylenic copolymer, a tetrafluoroethylene hexafluoropropylene copolymer (FEP), a

tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE resin), polychlorotrifluoroethylene resin (PCTFE), a propylene- tetrafluoroethylene copolymer, an ethylene-chlorotrifluoroethylene copolymer (ECTFE) and an ethylene-acrylic acid copolymer. These binders may be used independently, or mixtures may be used.

The components may be wet blended in the presence of a suitable solvent or dry blended using a mortar or other conventionally known mixing equipment. The mixture may then be applied to a charge collector by conventionally known methods. Any suitable charge collector may be employed. Preferred charge collectors may be any of carbon, stainless steel, nickel, aluminum and copper. In order to assist diffusion of the NO, it may be preferable that the collector is a porous body, such as mesh. In certain embodiments the charge collector may comprise a protective coating of an oxidation-resistant metal or alloy to protect the collector from oxidation.

In one specific embodiment of the present invention, the metal of the negative electrode comprises one selected from the group consisting of lithium, sodium, potassium, magnesium, calcium, aluminum and zinc and in a specific embodiment the metal of the negative electrode is one of lithium and magnesium.

The electrolyte ion conducting medium which is interposed between the positive electrode and the anode may comprise as an electrolyte, one or more of LiPF₆, LiC10₄, LiAsF₆, LiBF₄, Li(CF₃S0₂) ₂N, Li (CF₃S0₃) and LiN(C₂F₅S0₂) ₂. A nonaqueous solvent is preferred and may be selected from organic solvents including cyclic carbonates, chain carbonates, cyclic esters, cyclic ethers and chain ethers. Examples of a cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate and vinylene carbonate. Examples of a chain carbonate include dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate. Examples of a cyclic ester carbonate include gamma butyrolactone and gamma valerolactone. Examples of a cyclic ether include tetrahydrofuran and 2- methyltetrahydrofuran. Examples of a chain ether include dimethoxyethane and ethylene glycol dimethyl ether. In some preferred embodiments the solvent may be a nitrile system solvent such as acetonitrile or an ionic liquid. Ionic liquids comprises any of cations such as imidazolium cation, piperidinium cation, pyrrolidinium cation and ammonium cation and any of anions such as bis(trifluoromethansulfonyl)imide anion, bis(fluorosulfonyl)imide anion, tetrafluoroborate anion and hexafluorophosphate anion. In one preferred embodiment the solvent is an ionic liquid such as N-methyl-N-propylpiperidinium bis

(trifluoromethylsulfonyl)imide (PP 13TFSI).

An example of an electrochemical cell according to the present invention is shown in Fig. 3. The negative electrode 25 is placed in a casing 21 and the positive electrode is placed to oppose the negative electrode 25 via separator 27. The electrolyte 28 is between the positive electrode 23 and the negative electrode 25. A porous board 22 is on the positive electrode 23, and NO supply inlet 29 is in communication with the positive electrode across the porous board.

Moreover, the present inventors have discovered that a gas containing NO and components typically found in an exhaust of a combustion engine may effectively serve as the source of active material to be fed to the cathode. Such unexpected discovery may allow for the development of an energy system in a vehicle composed of a metal NO gas battery wherein the exhaust gas of a combustion engine is the source of the gas fed to the cathode of the battery.

The inventors have further shown in Figs. 4 and 5 that even when NO is mixed with nitrogen oxides such as N0₂, the N_xO_y gas redox reaction was observed, and the redox performance was quite similar to that of the pure NO gas reaction. Even under exhaust gas condition, the N_xO_y gas redox reaction was observed, and then it was quite similar in performance to that of pure NO gas reaction. Other species such as hydrocarbons and carbon monoxide do not show any influence on the N_xO_y redox reaction.

Therefore, a further embodiment of the present invention is an electrochemical cell comprising: an anode comprising a metal; a porous cathode supplied with a gas comprising nitric oxide (NO) and at least one gas selected from the group consisting of a nitrogen oxide of formula N_xO_y, oxygen, water vapor, a gaseous hydrocarbon, carbon monoxide and carbon dioxide; a separator located between the anode and cathode; and an electrolyte; wherein the active cathode ingredient is NO or the compound of formula N_xO_y, wherein x is 1 or 2 and y is an integer of 1 to 4.

Without being limited by theory, the inventors believe an element of the present invention includes a N_xO_y gas having an unpaired electron as a reactive gas, i.e., active cathode material, wherein the N_xO_y gas defines NO, N0₂ and N₂0₄. This N_xO_y gas is included in the exhaust gas.

However, in the model cell previously described, the discharge capacity was typically only about 33% of the charge capacity. The inventors believe that in the model cell, NO⁺ as the charged state may easily diffuse in the electrolyte media to the anode where it would be reduced back to NO even during charging. As a result of this migration and reduction, the concentration of charged species near the working electrode just after charging is

significantly depleted and therefore, upon discharge the concentration of the NO⁺ is quite low in comparison to the charge capacity, and thus the coulombic efficiency is also very low.

Therefore, in a further embodiment, the present invention includes an electrochemical cell comprising: an anode compartment comprising a working electrode which comprises a metal; a cathode compartment comprising a porous cathode supplied with a gas comprising N_xO_y; a partition located between and separating the anode compartment and the cathode compartment; and a mobile ion carrier; wherein the N_xO_y is the active cathode ingredient, and the partition is conductive of the mobile ion carrier and nonconductive of a N_xO_y ⁺ ion.

The inventors have determined that by insertion of a partition which does not allow passage of a N_xO_y ⁺ specie between the anode and cathode, the charged species are maintained only near the cathode. The purpose of this partition is to hinder the diffusion of the charged species from cathode to anode, and ultimately to shut off the diffusion. The partition must allow passage of the mobile carrier in the overall battery system. Therefore, the structure of the partition must be varied to correspond with the ion conducting property depending on the mobile carrier. For example, in a Li electrochemical system, a partition which efficiently conducts Li ions is employed. Likewise, in a Mg electrochemical system, a magnesium ion conducting partition is employed. The partition may be in the form of a membrane which is constructed of polymer, ceramics or a composite thereof. To reduce any detrimental effect of gas on performance of the anode, an effective partition will be fully impermeable or substantially impermeable to gas, thus preventing gas admitted to the cathode compartment from entrance to the anode compartment. A preferable partition is a dense ceramic membrane. For example, the partition may be a lithium-ion conducting ceramics plate in the Li system, and more concretely, Li-La-Ti-0 based perovskite, Li-Al-Ti-P-0 based

NASICON, Li-La-Zr-0 based garnet, Li-P-S based solid electrolyte and Li-Ge-P-S based solid electrolyte are examples of the lithium-ion conducting ceramics.

Due to the presence of the partition, the electrochemical cell is divided into an anode compartment and a cathode compartment. The electrolyte ion or mobile ion carrier is selected to be compatible with the metal of the electrode. Such materials are conventionally known to one of skill in the art. For example, when the anode comprises lithium, the electrolyte salt may comprise one or more of LiPF₆, LiC10 , LiAsF₆, LiBF , LiN(CF₃S0₂)₂, Li(CF₃S0₃) and LiN(C₂F₅S0₂)₂.

An example of a lithium electrochemical cell according to this embodiment is schematically shown in Fig. 6. In Fig. 6 the partition is labeled as ceramic electrolyte and the cathode compartment contains the 2^nd liquid electrolyte and the carbon cathode while the anode compartment contains the 1^st electrolyte and the lithium anode. The cell is housed in a container which is charged with a gas comprising the cathode active gas (NO or equilibrium oxides N0₂ and/or N₂0₄). The gas enters the cathode compartment through the opening of a poly(ether ether ketone) (PEEK) resin which contains the Cathode line.

The inventors have surprisingly discovered that even though the NO gas is exposed to ambient air, forming the N0₂ gas, almost the same redox activity was observed (Fig. 4). The N_xO_y gas mixture is a highly reactive gas group which provides superior properties as a cathode active material in a metal-gas battery.

Thus in a further embodiment, the present invention provides a rechargeable battery equipped with a NO gas feed and in a special embodiment the gas feed is a component of a system wherein the NO is obtained from the exhaust of a combustion engine. One example of such a system is schematically shown in Fig. 8 where the NO gas is collected from the gas mainstream out of the combustion engine by using, for example, a NO gas absorber. Next, the collected NO gas is released from the absorber into a battery where electrical energy is produced. After cycling, the NO gas used for the battery reaction may be released from the battery and then new NO gas from the absorber introduced into the battery. Release from the battery may be accomplished by vacuum draw or other conventional methods. The released gas may be mixed with fresh exhaust and directed to a catalytic reactor for conventional treatment before vented to the environment. Of course, as indicated in Fig. 8, the normal flow of the engine exhaust may be conducted from 1 1 through 12 to 15. In other

embodiments, the NO fed to the metal-NO battery may be enriched within the feed system. In order to protect the battery, the NO feed may be cooled before entry into the battery. The feed of the NO may be either continuous or of intermittent flow.

As NOx gases are components of the exhaust of combustion engines, this discovery may have significant environmental and energy ramifications because as shown in Fig. 8, a system wherein NO is obtained from the exhaust gas of the combustion engine and fed to a metal-NO battery may be constructed. Such system would eliminate at least NO from the exhaust and convert it to electrical energy.

In a further aspect of this embodiment, the present invention provides a rechargeable battery equipped with a NO or N_xO_y gas feed and the gas feed is a component of a system wherein the exhaust of a combustion engine serves as the active material feed source. In another embodiment, the exhaust fed to the metal- N_xO_y battery may be enriched with NO within the feed system. In order to protect the battery, the exhaust feed may be cooled before entry into the battery. The feed of the gas may be either continuous or of intermittent flow.

Having generally described this invention, a further understanding can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only and are not intended to be limiting unless otherwise specified.

EXAMPLES

Test cells containing working, counter and reference electrodes were constructed to compare 0₂ and NO as cathodic active materials.

The test gas was obtained from respective high grade gas cylinders. The working, counter and reference electrodes were glassy carbon as rod, Pt wire and Ag wire in the acetonitrile solution containing tetrabutyl ammonium perchlorate (TBAP) and AgN0₃ as supporting salt, respectively. The scan rate was 50mV/sec and the operation temperature was room temperature.

Fig. 1 shows the cyclic voltammograms in the N-methyl-N-propylpiperidinium bis(trifluoromethansulfonyl)imide (PP13TFSI) based electrolyte solutions;

Comparative example 1

under pure 02 gas in the 0.2mol/kg PP13TFSI-LiTFSI solution

Example 1

under NO/Ar/He mixed gas (l%/l%/98% in vol) in the 0.2mol/kg PP13TFSI-LiTFSI solution Example 2

under NO/Ar/He mixed gas (l%/l%/98% in vol) in the O. lmol/kg PP13TFSI-Mg(TFSI)2 solution As can be seen, a cathodic peak due to 0₂ reduction was observed at around -1.0V vs.

Ag/Ag+, while the peaks attributed to NO+ reduction were observed at 1.0V vs. Ag/Ag+. Furthermore, a large peak separation (1.2V) between reduction and oxidation was observed under 0₂ atmosphere, while a small separation was observed under NO atmosphere. This result indicates that NO gas possesses higher working voltage as well as higher reversibility (rechargeability) than 0₂ gas.

A cell of the same construction described above having NO gas as cathodic material and 0.2mol/kg PP13TFSI-LiTFSI solution as electrolyte was maintained at a current density of 700nA/cm² and the charge-discharge profiles measured as shown in Fig. 2. The charge and discharge plateaus were observed at around 1.05V and 0.95V, respectively. Also, when the cell was held at open circuit potential, the flat potential after charging and discharging was observed slightly above 1.0V and below 1.0V, respectively. Thus, the charged and discharged states were maintained on the cathode and provided evidence of a NO redox reaction. The working voltage as well as voltage hysteresis was significantly improved by introducing NO gas into a metal-gas battery.

Testinfi of NO mixed with Exhaust Components

Test cells containing working, counter and reference electrodes were constructed to compare different NO containing gases as cathodic active materials. Cyclic voltammograms were then obtained. Fig 4 shows the cyclic voltammograms in the N-methyl-N- propylpiperidinium bis(trifluoromethansulfonyl)imide (PP13TFSI) based electrolyte solutions:

Example 2 was run under pure NO/Ar/He(l%/l%/98%) gas condition in the 0.1 mol/kg PP13TFSI-Mg(TFSI)₂ solution. The color of the gas atmosphere of the cell is always transparent.

Example 3 was run under NO/Ar/He(l %/l %/98%) gas exposed to ambient air for 5 min in the 0.1 mol/kg PP13TFSI-Mg(TFSI)₂ solution. The color of gas atmosphere is slightly medium brown. Fig. 5 shows the cyclic voltammograms in the N-methyl-N-propylpiperidinium bis(trifluoromethansulfonyl)imide (PP13TFSI) based electrolyte solutions:

Example 4-1 and 4-2 were run under pure 0₂/NO/CO/C₃H₆/Ar/He

(2%/0.4%/0.1%/0.13%/97.5%) gas condition in the 0.1 mol/kg PP13TFSI-Mg(TFSI)₂ solution with different scanning ranges. The color of the gas atmosphere is slightly medium brown.

Example 5

A lithium/N_xO_y gas battery was constructed according to the structure schematically shown in Fig. 6. The N_xO_y reaction gas supplied to the cathode was a mixture of NO/Ar/He (l%/l%/98%) gas which had been exposed to ambient air for 5 minutes prior to admission to the battery. The cathode was 2 sheets of Carbon paper (To ray, TGP-H-120) and the catholyte (2^nd electrolyte) was N,N-Diethyl-N-Methyl-N-(2-methoxyethyl)ammonium

bis(trifluoromethansulfonyl)imide (DEMETFSI, Kanto corporation) with 0.35mol/kg LiTFSI (3M) and glass fiber was used as a separator (Whattman) and the ceramic partition

(electrolyte) was a Li-Al-Ti-P-0 based NASICON ceramic made by OHARA Inc. The anolyte was: 1M lithium bis(trifluoromethansulfonyl)imide LiTFSI (3M) in propylene carbonate (PC, Kishida Chemical).

Figure 7 shows the initial charge-discharge profiles of the Li/N_yO_x gas battery shown schematically in Fig. 6 and described in the previous paragraph. By introducing a Li-ion conducting ceramic membrane as a partition between cathode and anode, as according to the present invention, the reversibility (coulombic efficiency) of the N_xO_y redox reaction was almost 100% and highly reversible. The discharge voltage was maintained at higher voltage. As a result, the voltage hysteresis difference during charge and discharge was also narrow as indicated in Fig. 7.

Numerous modifications and variations on the present invention are possible in light of the above description and examples. It is therefore to be understood that within the scope of the following Claims, the invention may be practiced otherwise than as specifically described herein. Any such embodiments are intended to be within the scope of the present invention.

Claims

1. An electrochemical cell comprising:

an anode comprising a metal;

a porous cathode supplied with a gas comprising nitric oxide (NO);

a separator located between the anode and cathode; and

an electrolyte;

wherein the NO is the active cathode ingredient.

2. The electrochemical cell according to claim 1 wherein the metal of the anode comprises one selected from the group consisting of lithium, sodium, potassium, magnesium, calcium, aluminum and zinc.

3. The electrochemical cell according to claim 2, wherein the metal comprises lithium.

4. The electrochemical cell according to claim 2, wherein the metal comprises magnesium.

5. A rechargeable battery comprising the electrochemical cell according to claim 1.

6. The rechargeable battery according to claim 5, wherein the anode of the electrochemical cell comprises lithium.

7. The rechargeable battery according to claim 5, wherein the anode of the electrochemical cell comprises magnesiun.

8. The rechargeable battery according to claim 5, wherein the battery comprises a gas inlet for introduction of a gas feed comprising NO.

9. A vehicle comprising:

an internal combustion engine having an exhaust comprising NO;

a battery according to claim 5; and

a NO absorber attached to an exhaust system of the engine; wherein the NO absorber is in communication with the gas inlet of the battery and NO from the exhaust is fed to the battery through the gas inlet.

10. An electrochemical cell comprising:

an anode comprising a metal;

a porous cathode supplied with a gas comprising nitric oxide (NO) and at least one gas selected from the group consisting of a nitrogen oxide of formula N_xO_y, oxygen, water vapor, a gaseous hydrocarbon, carbon monoxide and carbon dioxide;

a separator located between the anode and cathode; and

an electrolyte;

wherein the active cathode ingredient is NO or the compound of formula N_xO_y, wherein x is 1 or 2 and y is an integer of 1 to 4.

1 1. The electrochemical cell according to claim 10, wherein the metal of the anode comprises one selected from the group consisting of lithium, sodium, potassium, magnesium, calcium, aluminum and zinc.

12. The electrochemical cell according to claim 1 1 wherein the metal comprises lithium.

13. The electrochemical cell according to claim 1 1 , wherein the metal comprises magnesium.

14. A rechargeable battery comprising the electrochemical cell according to claim 1.

15. The rechargeable battery according to claim 14, wherein the battery comprises a gas inlet for introduction of a gas feed comprising NO or N_xO_y which is an exhaust stream from a combustion engine.

16. A vehicle comprising:

an internal combustion engine having an exhaust comprising NO and at least one gas selected from the group consisting of a nitrogen oxide of formula N_xO_y, oxygen, water vapor, a gaseous hydrocarbon, carbon monoxide and carbon dioxide; and

a battery according to claim 15.

17. An electrochemical cell comprising:

an anode compartment comprising a working electrode which comprises a metal; a cathode compartment comprising a porous cathode supplied with a gas comprising a redox active N_xO_y gaseous compound;

a partition located between and separating the anode compartment and the cathode compartment; and

a mobile ion carrier;

wherein

x is 1 or 2 and y is 1 , 2 or 4,

the N_xO_y is the active cathode ingredient, and

the partition is conductive of the mobile ion carrier and nonconductive of a N_xO_y ⁺ ion.

18. The electrochemical cell according to claim 17, wherein

the partition is a membrane comprising at least one of a gel, a polymer, a ceramic material and a composite of a polymer and a ceramic material.

19. The electrochemical cell according to claim 18, wherein

the partition is a membrane comprising a ceramic material and the ceramic material is a dense ceramic membrane.

20. The electrochemical cell according to claim 17 wherein the metal of the anode comprises one metal selected from the group consisting of lithium, sodium, magnesium, aluminum, silver and copper.

21. The electrochemical cell according to claim 17, wherein

the metal of the anode comprises lithium,

the partition is a dense ceramic membrane, and

the dense ceramic membrane is a lithium ion conducting membrane comprising at least one ceramic selected from the group consisting of a Li-La-Ti-0 perovskite, a Li-Al-Ti- P-0 NASICON, a Li-La-Zr-0 garnet, a Li-P-S solid electrolyte and a Li-Ge-P-S solid electrolyte.

22. A rechargeable battery comprising the electrochemical cell according to claim 17.

23. The rechargeable battery according to claim 22, wherein the battery comprises a gas inlet for introduction of a gas feed comprising the redox active N_xO_y gaseous compound.

24. A vehicle comprising:

an internal combustion engine having an exhaust comprising a redox active N_xO_y gaseous compound;

a battery according to claim 23; and

a N_xO_y absorber attached to an exhaust system of the engine;

wherein the N_xO_y absorber is in communication with the gas inlet of the battery and N_xO_y from the exhaust is fed to the battery through the gas inlet.