# Patent

## Title
High energy density aluminum battery

## Abstract

Compositions and methods of making are provided for a high energy density aluminum battery. The battery comprises an anode comprising aluminum metal. The battery further comprises a cathode comprising a material capable of intercalating aluminum or lithium ions during a discharge cycle and deintercalating the aluminum or lithium ions during a charge cycle. The battery further comprises an electrolyte capable of supporting reversible deposition and stripping of aluminum at the anode, and reversible intercalation and deintercalation of aluminum or lithium at the cathode.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
The invention is a continuation-in-part of U.S. patent application Ser. No. 12/895,487, filed Sep. 30, 2010, the disclosure of which is incorporated by reference herein.


STATEMENT OF GOVERNMENT INTEREST
The invention was made with government support under contract number DE-FOA-0000207 by the Department of Energy. The Government has certain rights in the invention.


BACKGROUND
There is great interest and motivation to make a transition from fossil energy based electricity to the generation from renewable sources such as solar or wind. These sources offer enormous potential for meeting future energy demands. However, the use of electricity generated from these intermittent sources requires efficient electrical energy storage. For large-scale, solar- or wind-based electrical generation to be practical, the development of new electrical energy storage systems are critical to meeting continuous energy demands and effectively leveling the cyclic nature of these energy sources. Transformational developments in electrical energy storage are needed. In particular, there are needs for secondary batteries (or secondary batteries assembled in a charged state) made from novel materials that would increase the level of energy storage per unit volume and decrease dead weight while maintaining stable electrode-electrolyte interfaces. There is potential for increases in charge density by utilizing multielectron redox couples, such as in an aluminum battery.
The currently available electric energy storage technologies fall far short of the requirements for efficiently providing electrical energy for transportation vehicles, commercial and residential electrical and heating applications, and even for many electrically powered consumer devices. In particular, electrical storage devices with high energy and power densities are needed to power electric vehicles with performance comparable to that of vehicles powered by petroleum-fueled internal combustion engines.
Previous attempts to utilize aluminum anodes in secondary batteries have been plagued by high corrosion rates, parasitic hydrogen evolution, and a decrease in the reversible electrode potential (i.e., cell voltage is considerably lower than the theoretical value) due to formation of an oxide film on the anode surface.
SUMMARY
Compositions and methods of making are disclosed for high energy density aluminum batteries.
In one embodiment, the battery comprises an anode comprising aluminum metal. The battery further comprises a cathode comprising a material capable of intercalating aluminum or lithium ions during a discharge cycle and deintercalating the aluminum or lithium ions during a charge cycle. The battery further comprises an electrolyte capable of supporting reversible deposition and stripping of aluminum at the anode, and reversible intercalation and deintercalation of aluminum or lithium at the cathode.
In certain embodiments, the battery is a primary battery. In some embodiments, the primary battery comprises a cathode material selected from the group consisting of Ti(AlCl4)2, MnCl(AlCl4), Co(AlCl4)2.
In certain embodiments, the battery is a secondary battery. In one embodiment, the secondary battery maintains a discharge capacity of at least 50% of an initial discharge capacity after 50 cycles. In certain embodiments, the battery is a secondary battery that is assembled in charged state.
In some embodiments, the anode is an aluminum metal alloy. In certain embodiments, the aluminum metal alloy comprises an element selected from the group consisting of: copper, magnesium, manganese, silicon, titanium, zinc, or mixtures thereof.
In certain embodiments, the cathode material in the battery is selected from the group consisting of Mn2O4, Ti(AlCl4)2, MnCl(AlCl4), Co(AlCl4)2, and V2O5. In some embodiments, the cathode is “LiMxOy” [any lithium ion cathode material comprising a metal (M) and oxide (O)]. In one particular embodiment, the cathode material comprises spinel-Mn2O4. In another particular embodiment, the cathode material comprises V2O5.
In certain embodiments, the electrolyte in the battery comprises an ionic liquid. In some embodiments, the ionic liquid is an aluminate selected from the group consisting of alkylimidazolium aluminates, alkylpyridinium aluminates, alkylfluoropyrazolium aluminates, alkyltriazolium aluminates, dialkylpiperidinium aluminates, aralkylammonium aluminates, alkylalkoxyammonium aluminates, aralkylphosphonium aluminates, aralkylsulfonium aluminates, and mixtures thereof. In additional embodiments, the electrolyte further comprises aluminum chloride, and the ratio of aluminum chloride to the aluminate is greater than 1:1. In yet additional embodiments, the electrolyte in the battery further comprises an alkali metal halide additive. In some embodiments, the alkali metal halide additive is selected from the group consisting of: LiCl, lithium chloroaluminate, NaCl, KCl, NH4Cl, and mixtures thereof.
In one embodiment, the electrolyte in the battery comprises ethylmethylimidazolium tetrachloroaluminate and aluminum chloride. In another embodiment, the molar ratio of aluminum chloride to ethylmethylimidazolium tetrachloroaluminate is greater than 1:1. In yet another embodiment, the electrolyte further comprises an alkali metal halide additive. In some embodiments, the alkali metal halide additive is selected from the group consisting of: LiCl, lithium chloroaluminate, NaCl, KCl, NH4Cl, and mixtures thereof.
In yet another embodiment, the electrolyte in the battery is an ionic liquid electrolyte comprising a cation having one of the following structures:




wherein R1, R2, R3, and R4 each independently comprise a non-ionizable substituent. The electrolyte further comprises an anion having one of the following structures: AlCl4−, CF3SO3−, B(CO2)4−, N(SO2CF2CF3)2−, N(SO2CF3)2−, N(SO2F)2−, PF6−, BF4−, and BF4-x(CnF2n+1)x−, wherein x=1, 2, or 3, and n=1, 2, 3, 4, 5, 6, 7, 8, 9, or 10.

In another embodiment, the electrolyte in the battery comprises an ionic constituent dissolved in an organic solvent having a high dielectric constant. In some embodiments, the organic solvent is selected from the group consisting of propylene carbonate, ethylmethylsulfone, ethylmethoxyethylsulfone, and methoxyethylmethylsulfone. In certain embodiments, the cathode material in the battery is selected from the group consisting of spinel-Mn2O4, Ti(AlCl4)2, MnCl(AlCl4), Co(AlCl4)2, and V2O5.
In certain embodiments, the battery is used in a grid storage application, vehicle battery application, portable electronic device application, or standard cell size battery application.
In another embodiment, the battery comprises an aluminum metal anode. The battery further comprises a λ-MnO2 cathode capable of intercalating lithium ions during a discharge cycle and deintercalating the lithium ions during a charge cycle. The battery further comprises an ionic liquid electrolyte comprising lithium chloroaluminate dissolved in aluminum chloride and ethylmethylimidazolium tetrachloroaluminate, having a molar ratio of aluminum chloride to ethylmethylimidazolium tetrachloroaluminate greater than 1:1, wherein the electrolyte is capable of supporting reversible deposition and stripping of aluminum at the anode, and reversible intercalation and deintercalation of lithium at the cathode. In one embodiment, the battery maintains a discharge capacity of at least 50% of an initial discharge capacity after 50 cycles.
In another embodiment, a method of making a battery comprises providing an anode comprising aluminum metal. The method further comprises providing a cathode comprising a material capable of intercalating aluminum or lithium ions during a discharge cycle and deintercalating the aluminum or lithium ions during a charge cycle. The method further comprises providing an electrolyte capable of supporting reversible deposition and stripping of aluminum at the anode, and reversible intercalation and deintercalation of aluminum or lithium at the cathode.
In certain embodiments, the method of making a battery comprises providing a cathode material selected from the group consisting of Mn2O4, Ti(AlCl4)2, MnCl(AlCl4), Co(AlCl4)2, and V2O5.
In certain embodiments, the method of making a battery comprises providing an electrolyte having aluminum chloride and an ionic liquid aluminate selected from the group consisting of alkylimidazolium aluminates, alkylpyridinium aluminates, alkylfluoropyrazolium aluminates, alkyltriazolium aluminates, dialkylpiperidinium aluminates, aralkylammonium aluminates, alkylalkoxyammonium aluminates, aralkylphosphonium aluminates, aralkylsulfonium aluminates, and mixtures thereof. In some embodiments, the ratio of aluminum chloride to the aluminate in the electrolyte provided is greater than 1:1.
In certain embodiments, the method of making a battery comprises providing an electrolyte having aluminum chloride, an ionic liquid aluminate, and an alkali metal halide additive. In some embodiments, the alkali metal halide additive is lithium chloroaluminate.
In one particular embodiment, the method of making a battery comprises providing an electrolyte comprising aluminum chloride and ethylmethylimidazolium tetrachloroaluminate; wherein the molar ratio of aluminum chloride to ethylmethylimidazolium tetrachloroaluminate is greater than 1:1. In another embodiment, the method further comprises providing an alkali metal halide additive in the electrolyte. In certain embodiments, the alkali metal halide additive is lithium chloroaluminate.
In other embodiments, the method of making a battery comprises providing an ionic liquid electrolyte having a cation having one of the following structures:




wherein R1, R2, R3, and R4 each independently comprise a non-ionizable substituent; and

an anion having one of the following structures: AlCl4−, CF3SO3−, B(CO2)4−, N(SO2CF2CF3)2−, N(SO2CF3)2−, N(SO2F)2−, PF6−, BF4−, and BF4-x(CnF2n+1)x−, wherein x=1, 2, or 3, and n=1, 2, 3, 4, 5, 6, 7, 8, 9, or 10.
In yet other embodiments, the method of making a battery comprises providing an organic solvent electrolyte selected from the group consisting of propylene carbonate, ethylmethylsulfone, ethylmethoxyethylsulfone, and methoxyethylmethylsulfone.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts a comparison of the theoretical energy density of an aluminum battery with other batteries.
FIGS. 2A and 2B depict aluminum dissolution and deposition as a function of the electrolyte composition (acidic, basic, or neutral).
FIGS. 3A and 3B depicts aluminum dissolution and deposition for an acidic electrolyte mixture of 2:1 AlCl3:EMIC for a number of cycles.
FIGS. 4A and 4B depict aluminum anode electrochemical behavior in an acidic electrolyte mixture of 2:1 AlCl3:EMIC for a number of cycles.
FIGS. 5A and 5B depict electrochemical responses for MnO2 and AlMn2O4 cathodes in an acidic electrolyte mixture of 2:1 AlCl3:EMIC.
FIGS. 6A and 6B depict cyclic voltammograms of (a) Al and (b) λ-MnO2 in three electrode Swagelok cells with electrolyte of lithium chloroaluminate (3.0 mol/kg) dissolved in 1-ethyl-3-methyl imidazolium chloroaluminate (1.1:1).
FIGS. 7A and 7B depict battery performance of Al—MnO2 coin cells with electrolyte of lithium chloroaluminate (3.0 mol/kg) disolved in 1-ethyl-3-methyl imidazolium chloroaluminate (1.1:1), showing (a) a typical charge-discharge curve and (b) discharge capacity vs. Cycle numbers at a C/10 (15 mA/g) current rate.



DETAILED DESCRIPTION
As used herein, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. For example, reference to “a substituent” encompasses a single substituent as well as two or more substituents, and the like.
As used herein, the terms “for example,” “for instance,” “such as,” or “including” are meant to introduce examples that further clarify more general subject matter. Unless otherwise specified, these examples are provided only as an aid for understanding the applications illustrated in the present disclosure, and are not meant to be limiting in any fashion.
As used herein, the following terms have the following meanings unless expressly stated to the contrary. It is understood that any term in the singular may include its plural counterpart and vice versa.
As used herein, the term “aluminum battery” refers to an aluminum metal anode battery, unless specified otherwise.
As used herein, the term “lithium battery” refers to an lithium metal anode battery, unless specified otherwise.
As used herein, the term “aluminum metal” includes aluminum metal, aluminum metal alloys, or any other anode composition that includes aluminum metal, or combinations thereof, unless specified otherwise. In certain embodiments, an aluminum metal alloy may comprise at least one of the following alloying elements: copper, magnesium, manganese, silicon, titanium, or zinc. In other embodiments, the aluminum metal may include at least one insertion compound such as graphite, silicon nanowires, or titanium oxide.
As used herein, the term “aluminum ion” may refer to any ion comprising aluminum, including but not limited to Al3+, AlCl4−, and Al2Cl7−.
As used herein, the term “lithium ion” may refer to any ion comprising lithium, including but not limited to Li+.
As used herein, the terms “primary” and “primary battery” refer to any kind of battery in which the electrochemical reaction is generally not reversible (i.e., the reaction cannot be reversed by running a current into the cell to restore the capacity of the battery). Unless otherwise specified, the terms “primary” or “primary battery” refer to batteries that are assembled in a charged state wherein the electrochemical reactions are generally not reversible.
As used herein, the terms “secondary” and “secondary battery” refer to rechargeable batteries wherein the electrochemical reactions are electrically reversible (i.e., the reaction can be reversed by running a current into the cell to restore the capacity of the battery). In certain embodiments, the secondary battery can achieve a number of “cycles” (discharge and charge) while maintaining a “functional discharge capacity” (i.e., the discharge capacity is more than 50%, 60%, 70%, 80%, or 90% of the initial discharge capacity). Unless otherwise specified, the terms “secondary” or “secondary battery” may also refer to batteries that are assembled in a charged state wherein the electrochemical reactions are electrically reversible. In other words, the term may refer to a battery that does not need to be charged prior to its first use (like a typical primary battery), but is still capable of being recharged. For example, in one embodiment, an Al—MnO2 battery with a lithium ion containing electrolyte constitutes a secondary, rechargeable battery that is assembled in a charged state.
As used herein, the term “room temperature ionic liquid” may refer to an ionic liquid electrolyte that is in its liquid state at room temperature (i.e., approximately 20-25° C.). In certain embodiments, the room temperature ionic liquid electrolyte remains in liquid state over a wide composition range. In one non-limiting example, an electrolyte comprising ethylmethylimidazolium tetrachloroaluminate is in a liquid state as low as approximately 8° C. at approximately a 1:2 molar ratio of aluminum chloride: EMIC. Additionally, the electrolyte remains in a liquid state as low as −98° C. for a 2:1 molar ratio of aluminum chloride: EMIC. Such ionic liquids have the potential to deposit highly reactive metals such as aluminum that cannot be deposited by an aqueous solution.
As used herein, the term “high dielectric constant” may refer to an electrolyte that is electrically insulating and ionically conducting by virtue of dissolved ions.
In one embodiment, the battery may be formed with an aluminum anode. Aluminum is an attractive anode material for energy storage and conversion. Its relatively low atomic weight of 26.98 g/mol along with its trivalence gives a gram-equivalent weight of 8.99 and a corresponding electrochemical equivalent weight of 2.98 amp-hours per gram (Ah/g), compared with 3.86 Ah/g for lithium, 2.20 Ah/g for magnesium and 0.82 Ah/g for zinc. From a volume standpoint, aluminum should yield 8.04 Ah/cm3, compared with 2.06 Ah/cm3 for lithium, 5.85 Ah/cm3 for zinc and 3.83 Ah/cm3 for magnesium.
In comparison with a lithium battery, the theoretical voltage for aluminum is similar to lithium (2.86 volts v. 3.4 volts, respectively), and due to the mass of aluminum and its trivalency, the aluminum battery has the potential to yield 8-9 times better storage capacity than a lithium battery. If a cathode of approximately the same mass is used in each battery, the aluminum battery can provide approximately 4 times higher energy than the lithium battery. FIG. 1 provides a comparison of the theoretical energy density for various batteries, including aluminum and lithium batteries. Furthermore, an aluminum battery does not necessarily develop a solid electrolyte interface (SEI) layer between electrolyte and electrode. Also, the aluminum anode can be the protective containment (i.e., it is self-supporting). Additionally, aluminum is both an abundant and relatively inexpensive metal, and the use of a nonflammable ionic liquid electrolyte may provide an increased margin of safety.
Overall, an aluminum battery has the capability of achieving a much higher energy density than a lithium battery. Aluminum batteries have the potential for providing energy densities exceeding 200 Wh/kg (mass density) and 300 Wh/liter (volumetric density) at system-level costs below $250/kWh for various applications. In certain embodiments, the aluminum battery can be used in grid storage applications, vehicle battery applications, portable electronic device application, or standard cell size battery applications. In one particular embodiment, the aluminum battery is used for a grid storage application. In another particular embodiment, the aluminum battery is used in a vehicle battery application.
In one embodiment, the aluminum battery is a primary battery. In another embodiment, the aluminum battery is a secondary battery. In certain embodiments, the secondary battery is capable of having at least 50, 100, 150, 200, or 500 cycles prior to battery failure. In some embodiments, battery failure is related to the functional discharge capacity becoming only 50%, 60%, 70%, 80%, or 90% of the initial discharge capacity after a number of cycles. In other embodiments, battery failure is related to the inability to recharge the battery due to dendrite formation, oxide film formation, or other buildup on the anode or cathode. In one particular embodiment, the secondary battery is capable of having a functional discharge capacity greater than 50% of the initial discharge capacity after 50 cycles. In another embodiment, the secondary battery is capable of having a functional discharge capacity greater than 50% of the initial discharge capacity after 150 cycles.
In certain embodiments, the aluminum battery comprises: (1) an anode comprising aluminum metal, (2) a cathode comprising a material capable of intercalating aluminum or lithium ions during a discharge cycle and deintercalating the aluminum or lithium ions during a charge cycle, and (3) an electrolyte capable of supporting reversible deposition and stripping of aluminum at the anode, and reversible intercalation and deintercalation of aluminum or lithium at the cathode.
Anode
In certain embodiments, the anode material comprises aluminum metal. In other embodiments, the anode material comprises an aluminum metal alloy. Non-limiting examples of aluminum metal alloys include an alloying element selected from the group consisting of copper, magnesium, manganese, silicon, titanium, zinc, and mixtures thereof. In yet other embodiments, the anode material comprises an insertion compound. Non-limiting examples of insertion compounds include graphite, silicon nanowires, titanium oxide, and mixtures thereof.
In some embodiments, high purity aluminum foils and wires (99.999%, Aldrich) may be used as anodes and reference electrodes, respectively. In other embodiments, aluminum alloys (with Al as the predominant metal, at least 50%) could also be used as the anodes.
In certain embodiments, during the manufacture of the battery, the anode material is subjected to a pretreatment step to remove oxides from the material. In one embodiment, oxides are removed from the aluminum anode material through an electrochemical reduction step known to one of ordinary skill in the art.
Electrolyte
Suitable electrolytes for an aluminum battery are electrochemically stable within the operation window of the electrodes. In other words, in certain embodiments, the electrolyte is capable of supporting reversible deposition and stripping of aluminum at the anode, and reversible intercalation and deintercalation of aluminum at the cathode. In other embodiments, the electrolyte is capable of supporting reversible deposition and stripping of aluminum at the anode, and reversible intercalation and deintercalation of lithium at the cathode. Suitable electrolytes may include materials that assist in achieving a wide electrochemical window, good ionic conductivity, improved rate capability, long cycle ability, good capacity retention, and compatibility with the anode and cathode materials.
In certain embodiments, the electrolyte materials may be optimized through the addition of suitable co-solvents that may assist in reducing viscosity (increasing mobility) and/or increasing charge transfer number (increasing salt dissociation).
In certain embodiments, the electrolyte comprises an ionic liquid. In some embodiments, the ionic liquid is a room temperature ionic liquid. In certain embodiments, the room temperature ionic liquid comprises an aluminate material selected from the group consisting of alkylimidazolium aluminates, alkylpyridinium aluminates, alkylfluoropyrazolium aluminates, alkyltriazolium aluminates, aralkylammonium aluminates, alkylalkoxyammonium aluminates, aralkylphosphonium aluminates, and aralkylsulfonium aluminates.
In certain embodiments, the electrolyte includes a compound that is capable of assisting in dissociating Al3+ or Li+ for intercalation. In certain embodiments, the compound is selected from the group consisting of: aluminum chloride (AlCl3), lithium trifluoromethane sulfonate, aluminum trifluoromethane sulfonate (aluminum triflate), butylpyridium chloride, 1-methyl-3-propylimidizolium chloride, a triazolium chloride, or an aluminum bis(trifluoromethanesulfonyl)imide salt. In particular, aluminum triflate and aluminum bis(trifluoromethanesulfonyl)imide salts may provide electron delocalization of the anions so that Al3+ will not be tightly bonded.
In one embodiment, the molar ratio of the compound (e.g., aluminum chloride) to the aluminate in the ionic liquid is greater than 1:1, which forms an acidic electrolyte. In other embodiments, the molar ratio of the compound to aluminate in the electrolyte is greater than 1.5:1, 2:1, 3:1, 4:1, 5:1, or 10:1. In yet other embodiments, the molar ratio of the compound to aluminate is approximately 1.5:1, 2:1, 3:1, 4:1, 5:1, or 10:1.
In certain compositions comprising excess aluminum chloride to aluminate, the predominant aluminum species in solution is an anion such as AlCl4− or Al2Cl7−. These electrolyte compositions can prevent the formation of oxides on the aluminum anode surface as well as eliminate hydrogen gas evolution. Additionally, acidic electrolyte compositions can minimize the evolution of Cl2, which can be prevalent in basic electrolyte compositions.
In one particular embodiment, the ionic liquid comprises ethylmethylimidazolium trifluoromethane sulfonate. In another particular embodiment, the ionic liquid comprises ethylmethylimidazolium tetrachloroaluminate. In another embodiment, the ionic liquid comprises aluminum chloride added to the EMIC. The molar ratio of aluminum chloride to EMIC in the electrolyte material is greater than 1:1in certain embodiments, wherein such combination creates an acidic solution. In other embodiments, the molar ratio of aluminum chloride to EMIC is greater than 1.5:1, 2:1, 3:1, 4:1, 5:1, or 10:1. In yet other embodiments, the molar ratio of aluminum chloride to EMIC is approximately 1.5:1, 2:1, 3:1, 4:1, 5:1, or 10:1.
Adjustment of the molar ratio of aluminum chloride to the aluminate can affect the Lewis acidity of the ionic liquid. At AlCl3 mole fractions less than 0.5 in the electrolyte, the anions present are the Lewis bases Cl− and AlCl4−; hence these melts are regarded as basic. On the other hand, at AlCl3 mole fractions greater than 0.5, the stable anions are AlCl4− and Al2Cl7−. Since Al2Cl7− is a potential source of the Lewis acid AlCl3, these melts are regarded as acidic. Adjustment of the molar ratio of AlCl3 changes the Lewis acidity of the AlCl3-EMIC ionic liquid. This is expected to be a consideration in the design of the battery because it has been demonstrated that the deposition of aluminum occurs from the acidic medium.
In such a reaction, excess AlCl3 dimerizes in the medium to form Al2Cl6, and the equilibrium occurs when AlCl3 is dissolved in the aluminate (EMIC, for example) to form AlCl4− and Al2Cl7−, as shown below in equations (1) and (2):

[Al2Cl6]+Cl−[Al2Cl7]−  (1)

2[AlCl4]−[Al2Cl7]+Cl−  (2)

In acidic electrolytes, the Al2Cl7− species is the electrochemically active species for deposition of aluminum metal according to the following net reaction (3):

4Al2Cl7−+3 e →Al+7AlCl4−  (3)

A neutral ionic liquid electrolyte possesses the widest electrochemical window for electrolyte solutions such as AlCl3-EMIC. Therefore, in certain embodiments, it may be beneficial to have a neutral electrolyte solution. However, there are difficulties maintaining a neutral electrolyte composition comprising AlCl3-EMIC, for example. Therefore, in certain embodiments, an alkali metal halide additive (i.e., neutralizing compound) can be added to the originally acidic electrolyte. In certain embodiments, the neutralizing compound is selected from the group consisting of NaCl, LiCl, lithium chloroaluminate, KCl, NH4Cl, and mixtures thereof.
In one embodiment, the neutralizing compound is NaCl. In other embodiments, the neutralizing compound is KCl or, NH4Cl. The salt neutralizes the Al2Cl7− anions via the reaction in equation (4) (wherein the neutralizing compound is NaCl in this non-limiting example):

NaCl(s)+[Al2Cl7−]Na++2[AlCl4]−  (4)

In certain embodiments, lithium chloroaluminate is dissolved in the ionic liquid. In one embodiment, the ionic liquid is ethylmethylimidazolium tetrachloroaluminate. In these embodiments, the electrolyte works as a reservoir to provide and store lithium cations and chloroaluminate anions. The imidazolium cations in the electrolyte serve as charge carriers to neutralize the charge balance. The reactions are described as the following:

Anode: Al+7AlCl4−4Al2Cl7−+3e−  (5)

Cathode: 2MnO2+Li++e−LiMn2O4  (6)

Overall: Al+7AlCl4−+6MnO2+3Li+4Al2Cl7−+3LiMn2O4  (7)

In other embodiments, the electrolyte comprises an ionic liquid electrolyte having:
a cation with one of the following structures:




wherein R1, R2, R3, and R4 each independently comprise a non-ionizable substituent such as, for example, various hydrocarbons, alkyls, fluoro-alkyls, aryls, and ethers; and

an anion having one of the following structures: AlCl4−, CF3SO3−, B(CO2)4−, N(SO2CF2CF3)2−, N(SO2CF3)2−, N(SO2F)2−, PF6−, BF4−, and BF4-x(CnF2n+1)x−, wherein x=1, 2, or 3, and n=1, 2, 3, 4, 5, 6, 7, 8, 9, or 10.
In certain embodiments, the cation in the ionic liquid is selected from the group consisting of: imidazolium, pyrrolidinium, piperidinium, triazolium, and tetraalkylammonium.
In yet another embodiment, the electrolyte comprises an organic solvent having a wide electrochemical window (e.g., similar or wider than the neutral melt window between −2 V and 2.5 V as shown in FIG. 2A) and a high dielectric constant. In certain embodiments, the organic solvent is selected from the group consisting of propylene carbonate, ethylmethylsulfone, ethylmethoxyethylsulfone, and methoxyethylmethylsulfone.
Cathode
In certain embodiments, the cathode comprises a material capable of intercalating aluminum or lithium ions during a discharge cycle and deintercalating the aluminum or lithium ions during a charge cycle. The cathode must readily incorporate Al(III) or Li, either as an anion or as the Al(III) or Li cation after shedding the Cl− ligands.
In certain embodiments, for each equivalent of Al which is plated on the anode, three equivalents of AlCl4− will need to be incorporated in the cathode. In some embodiments, the electrolyte will tend to become more basic as Al is plated on the anode, but part of this problem will be alleviated by incorporation of the AlCl4− anions in the cathode.
In certain embodiments, the cathode comprises an active material selected from the group consisting of: λ-MnO2 (or λ-Mn2O4), Ti(AlCl4)2, MnCl(AlCl4), Co(AlCl4)2, and V2O5. In some embodiments, the cathode is “LiMxOy” [herein defined as any lithium ion cathode material comprising a metal (M) and oxide (O)]. Nonlimiting examples of LiMxOy cathodes include lithium cobalt oxide, lithium iron phosphate, and lithium manganese oxide. In certain embodiments, the battery is a primary battery and the cathode is a material selected from the group consisting of Ti(AlCl4)2, MnCl(AlCl4), Co(AlCl4)2, and LiMxOy.
In certain embodiments, aluminum is inserted into the cathode material lattice. In one particular embodiment, aluminum is inserted into spinel-Mn2O4 to form spinel AlMn2O4. In another embodiment, the cathode material may comprise layered structures of V2O5 aerogels and Al3+. Hence, AlxV2O5 material can be used as a possible cathode material for Al(III) insertion.
In certain embodiments, these active components can be mixed with a carbon material (such as carbon black, for example) to make them conducting, and mixed with a binder (such as PVDF binder in N-methylpyrrolidinole, for example) to hold the material together. In some embodiments, the cathode comprises between approximately 50-90% of AlMn2O4, Ti(AlCl4)2, MnCl(AlCl4), Co(AlCl4)2, and/or AlxV2O5, 1-20% of binder, and 1-40% of carbon material. In one particular embodiment, the cathode comprises approximately 80% of MnO2 or AlMn2O4, approximately 10% of PVDF binder in N-methylpyrrolidinole, and approximately 10% of carbon black.
In yet another embodiment, the cathode may be an air cathode, thereby forming an aluminum-air battery.
In one non-limiting example, the cathode is prepared from Co(AlCl4)2 mixed with powdered graphite to make it conducting (and a binder to hold the material together). In this example, the net reaction during charging will be oxidation of Co(II) to Co(III). During this process, the AlCl4− anion will be incorporated in the cathode for charge balance. The structure of Co(II) complexed by AlCl4− anions in an ionic liquid has been shown to be discrete ions with the composition [Co(AlCl4)3]− in which the tetrachloroaluminate ions are bidentate and the Co(II) center is octahedrally coordinated. The structure of Co(AlCl4)2 in the solid state has four tetrachloroaluminate centers bound to each Co(II), two with bidentate coordination and two that are monodentate but bridging. Co(III) will always be octahedrally coordinated. Thus, oxidation of Co(II) to Co(III) is not expected to cause a large change in the coordination environment of the Co center.
In other non-limiting examples, Ti(II) and Mn(II) complexes may also be considered as a transition element for the cathode material.
In another embodiment, the cathode material is λ-MnO2. In one example, during the cycle, Al dissolves in the electrolyte from the anode and AlCl4− anions are formed, consuming the Cl− anions generated when Al(III) or Li+ cations are incorporated in the cathode. During discharge, manganese in oxidation state IV will be reduced to a lower oxidation state at the cathode and the Al(III) or Li+ ions enter the solid to compensate for the charge. In certain embodiments, the cathode material can be prepared in a “reduced” or uncharged state by reacting MnO2 with triethylaluminum in a similar manner that butyllithium is used to incorporate Li in cathodes for Li-ion batteries. The cathode may then be “charged” by oxidation of the Mn oxide resulting in expulsion of Al(III) or Li+ ions, which are subsequently complexed by chloride ions and then plated at the anode.
Spinel-type MnO2 may be made by treating LiMn2O4 with aqueous acid. This λ-MnO2 has the same structural framework of spinel, but with most of the lithium removed from the tetrahedral sites of the spinel lattice. The mechanism for the conversion of LiMn2O4 to λ-MnO2 involves a disproportionation of the Mn3+ ions into Mn4+ (remains in the solid) and Mn2+ (leaches out into the aqueous solution).
In certain embodiments, it is possible to insert Al3+ into spinel λ-Mn2O4 to form spinel AlMn2O4. In one embodiment, the following discharge reactions can occur in an aluminum battery (the reverse reactions will occur during charge), as shown in equations (8), (9), and (10):

Electrolyte: AlCl3+[EMI]+Cl−[EMI]+AlCl4−  (8)

Anode: Al+7[AlCl4]−4[Al2Cl7]−+3e−  (9)

Cathode: λ-Mn2O4+4[Al2Cl7]−+3e−AlMn2O4+7[AlCl4]−  (10)

Net reaction: λ-Mn2O4+Al→AlMn2O4  (11)

where:
λ-Mn2O4≡(□)tet[Mn2]octO4;
AlMn2O4≡(Al)tet[Mn2]octO4; and
wherein the subscripts “tet” and “oct” refer, respectively, to 8a tetrahedral and 16d octahedral sites in the spinel lattice.
The edge-shared Mn2O4 spinel framework into/from which Al3+ ions could be reversibly inserted/extracted is stable. The 3-dimensional diffusion of Al3+ ions from one 8a tetrahedral site to another 8a tetrahedral site via the neighboring empty 16c octahedral site can support fast aluminum-ion diffusion through the lattice. Additionally, the edge-shared Mn2O4 framework with direct Mn—Mn interaction can provide good electronic conduction. The fast aluminum-ion diffusion together with the good electronic conduction can support high rate capability. The electrochemical cell can be represented as:

λ-Mn2O4|AlCl3+[EMI]+Cl−|Al  Theoretical voltage: 2.65 V

The theoretical capacities for the aluminum battery including a λ-Mn2O4 cathode are calculated and shown in Table 1 below. From these theoretical calculations, the aluminum battery has a distinct edge in capacity and energy density over the state-of-the-art lithium batteries.







TABLE 1







Calculated Theoretical Capacity for Aluminum Battery














Cell Energy
Cell




Cell Capacity
Density
Voltage



System
(mAh/g)
(Wh/kg)
(V)
















Li-ion battery;
140
404
4



C6—LiCoO2



Al battery;
400
1,060
2.65



Al-λ-Mn2O4



Al battery;
329
872
2.65



C6-λ-Mn2O4



Al-ion battery;
274
315
1.15



TiO2-λ-Mn2O4










In certain embodiments, methods of making an aluminum battery comprise providing an anode comprising aluminum metal. In certain embodiments, the methods further comprise providing a cathode comprising a material capable of intercalating aluminum or lithium ions during a discharge cycle and deintercalating the aluminum or lithium ions during a charge cycle. In certain embodiments, the methods further comprise providing an electrolyte capable of supporting reversible deposition and stripping of aluminum at the anode, and reversible intercalation and deintercalation of aluminum or lithium at the cathode. In some embodiments, the electrolyte comprises an ionic liquid. In other embodiments, the electrolyte comprises an organic solvent having a high dielectric constant.
In some embodiments, batteries for grid storage applications may be formed. In other embodiments, batteries for vehicle applications may be formed. In yet other embodiments, batteries for portable electronic devices may be formed.
In another example, a coin cell battery may be formed. In such an example, a cathode slurry for the battery may be made by homogenizing the active components of the cathode with the carbon material (such as carbon black, for example) and the binder (such as PVDF binder in N-methylpyrrolidinole, for example). In certain embodiments, the cathode slurry is dried at an elevated temperature (>100° C.) and then pressed under a load (e.g., 1 ton load) for a certain length of time before cutting into a disk (e.g., 1.3 cm diameter disk). In some embodiments, the cathode disks are further dried at an elevated temperature (>100° C.) under a vacuum before assembling into the coin cell battery. In certain embodiments, the coin cell battery is assembled with an aluminum anode, MnO2 cathode, and an electrolyte capable of supporting reversible deposition and stripping of aluminum at the anode and reversible intercalation and deintercalation of aluminum or lithium at the cathode, wherein the coin cell battery comprises either Celgard or carbon fiber filter paper as the separator. In certain embodiments, the cells may be cycled under different current densities on Arbin instruments.
While the invention as described may have modifications and alternative forms, various embodiments thereof have been described in detail. It should be understood, however, that the description herein of these various embodiments is not intended to limit the invention, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the claims. Further, while the invention will also be described with reference to the following non-limiting examples, it will be understood, of course, that the invention is not limited thereto since modifications may be made by those skilled in the art, particularly in light of the foregoing teachings.
EXAMPLES
Example 1
In this example, the salt of EMIC was synthesized and purified, and three electrolyte mixture AlCl3 and EMIC were made. The ratios of AlCl3:EMIC were approximately 1:1.5 (basic), 1:1 (neutral), and 2:1 (acidic). All three electrolytes were tested for their electrochemical potential using a platinum and aluminum coin cell disks for the cathode and anode, with the electrolyte coupled with aluminum wire. The results are shown in FIGS. 2A and 2B.
It was observed that the neutral ionic liquid electrolyte (1:1 AlCl3:EMIC) had the widest electrochemical potential window (FIG. 2A). However, the aluminum reaction only proceeded in the acidic electrolyte (2:1 AlCl3:EMIC). In the acidic electrolyte, the current efficiency of the aluminum reaction (Cdissolution/Cdeposition) was observed to be close to 100% (FIG. 2B).
Example 2
Aluminum deposition and dissolution were studied using similar test parameters as Example 1 for an acidic electrolyte mixture of 2:1 AlCl3:EMIC. Sixty-five charge/discharge cycles were carried out at 5 mV/s. The results are shown in FIGS. 3A and 3B.
It was observed that the acidic electrolyte mixture was capable of intercalating aluminum ions during the discharge cycles and deintercalating the aluminum ions during the charge cycles before perceived failure in the 65th cycle.
Example 3
Aluminum anode electrochemical behavior was studied using similar test parameters as Example 1 for an acidic electrolyte mixture of 2:1 AlCl3:EMIC. Tests were carried out at 100 mV/s for 50 cycles and 10 mV/s for 150 cycles. The results are shown in FIGS. 4A and 4B.
It was observed that the aluminum anode showed good cyclability and high current density in the acidic electrolyte mixture for 150 cycles.
Example 4
MnO2 and AlMn2O4 cathode materials were studied for their electrochemical response using similar test parameters as Example 1 for an acidic electrolyte mixture of 2:1 AlCl3:EMIC. Tests were carried out at 1 mV/s. The results are shown in FIGS. 5A and 5B.
It was observed that both MnO2 and AlMn2O4 showed redox activity in the acidic electrolyte mixture.
Example 5
In this example, a coin cell battery was prepared. The cathode slurry was prepared with 80 wt % of active materials (MnO2 or AlMn2O4), 10 wt % carbon black and 10 wt % PVDF binder in N-Methylpyrrolidinole. The slurry was homogenized for about 5 min before casting on stainless steel foil with a doctor blade. After drying at approximately 120° C., the electrode was pressed under 1 ton load for about 1 min before cutting into discs with diameter of approximately 1.3 cm. The electrode discs were further dried at approximately 120° C. under vacuum for 24 hrs before assembling coin cells. The coin cells were assembled inside a well-controlled Argon filled glove box with both moisture and oxygen levels below 1 ppm. The coin cells were assembled with aluminum as the anode, MnO2 as the cathode, and an acidic electrolyte mixture of 2:1 AlCl3:EMIC as the electrolyte with either Celgard or carbon fiber filter paper as the separator. The cells were cycled under different current densities on Arbin instruments.
Example 6
High purity aluminum foils and wires (99.999%, Aldrich) were used as anodes and reference electrodes, respectively. Al foils were cut into disks with diameters of 1.0 cm and 1.6 cm to fit the electrochemical cells. These Al disks were mechanically polishing by sandpaper. Nylon cloth with 5.0 μm alumina and microcloth with 0.05 μm alumina (polishing kit, Pine Instrument), following chemically polishing in an acid mixture of 25% (by volume) H2SO4 (98%), 70% H3PO4 (85%) and 5% HNO3 (52.5%). Al wires were cleaned by chemical polishing. After washing using by acetone and drying, they were placed in a glove box (VAC, moisture <1 ppm, oxygen <4 ppm) in inert atmosphere for later use.
λ-MnO2 was synthesized following Hunter's method. The precursor LiMn2O4 was prepared by ball-milling the mixture of 10 g Mn2O3 and 2.34 g Li2CO3 and sintering the mixture at 850° C. in air for 1 hour. 2 g LiMn2O4 was added into 100 ml DI water to form a slurry solution. 2M H2SO4 was dropped into this slurry under stirring, till until the pH was stable at 1. After washing with distilled water and drying in vacuum oven at 100° C. overnight, λ-MnO2 powder was obtained.
The cathodes were fabricated by a conventional coating method. A slurry consisting of the as-synthesized λ-MnO2 (80 wt. %), Super-S carbon black (10 wt. %), and polyvinylidene fluoride (PVDF, 10 wt. %) in N-methyl-2-pyrrolidone (NMP) was uniformly spread onto a tungsten (W) foil. The active material loading was 1-2 mg/cm2. The electrodes were pressed under 1 ton/cm2 and dried in a vacuum oven at 120° C. overnight.
Ionic liquid, slightly acidic 1-ethyl-3-methyl imidazolium chloroaluminate, was prepared by mixing aluminum trichloride (homemade) and 1-ethyl-3-methyl imidazolium chloride (homemade) with a molar ration of 1.1:1.0 in the glove box. The acidicity of the ionic liquid can be adjusted by changing the molar ratio. A metal halide additive, lithium chloroaluminate (nonhydrate, Aldrich), was dissolved in the ionic liquid to form the electrolyte. Up to 4.0 mol/Kg lithium chloroaluminate is able to dissolve in the acidic (1.1:1.0) ionic liquid.
Three-electrode Swagelok cells were used to study the electrochemical behavior of Al and λ-MnO2 in the ionic liquid electrolyte. An Al disk and a MnO2/W disk were used as working electrodes, W disk as a counter electrode, and Al wire as a reference electrode. Two pieces of filter paper clamping the Al wire were used as a separator. The electrolyte, acidic 1-ethyl-3-methyl imidazolium chloroaluminate, has a wide electrochemical window on W electrode, along with reversible Al deposition and dissolution. This makes a W disk a good candidate for counter electrode and current collector of MnO2 electrodes. Cyclic voltammetry (CV) was conducted using a Princeton Applied Research Model 263 potentiostat. For the Al working electrode, CVs were recorded at 1 mV/s sweep rate between −0.3 V and +0.3 V vs. Al/Al3+. For the MnO2 electrode, CVs were recorded at 1 mV/s between 1.5 V and 2.4 V vs. Al/Al3+.
FIGS. 6A and 6B show the cyclic voltammograms of Al and λ-MnO2 in an electrolyte of lithium chloroaluminate (4.0 mol/Kg) dissolved in 1-ethyl-3-methyl imidazolium chloroaluminate (1.1:1.0). It can be seen that AI dissolution and deposition start at 40 mV and 120 mV, respectively, indicating the ease of Al deposition in this electrolyte. The CV cycle with a nearly equivalent of cathodic and anodic charges can repeat for 100 times, which validates the reversibility of this reaction and is in agreement with previous report. It is found that the oxide thin film on Al surface, which is inevitably formed even after mechanical and chemical polishing, is important to sustain the cyclability. If this thin film is mechanically removed in the glove box, the currents abruptly change during CV cycles and the cell failed by short circuit after several cycles. It is believed that removal of the oxide film is incomplete or that the oxide film reacts with chloroaluminate anions to form a kind of solid electrolyte interface (SEI) layer on Al surface, which slow-downs the reaction between Al and the electrolyte and mitigates the formation of dendrites. Because Al does not react with the electrolyte to produce new oxides, this oxide layer effectively sustains the steady cycling of Al dissolution and deposition, in contrast with the negative role of an oxide film in aqueous Al batteries.
In FIG. 6B, λ-MnO2 shows a dual-peak redox behavior in the ionic liquid electrolyte, which is identical to the lithium intercalation behavior in traditional organic electrolytes. The two pairs of peaks between 1.5 V and 2.5 V indicate a two-stage process of lithium insertion and extraction in the spinel structure, which is associated with the structure ordering when lithium ions occupy one half of the tetrahedral 8a sites. The increase of anodic current at potential >2.3V is attributed to the evolution of chlorine in this ionic liquid electrolyte. This is the anodic limit that hinders other materials with higher oxidation potential as cathode in chloroaluminate-based electrolyte. We also study the possibility of Al ion intercalation in λ-MnO2 contributing the redox reaction. Without adding lithium chloroaluminate, λ-MnO2 shows none of the redox peaks in the CV cycling in the pure ionic liquid electrolyte. This confirms that the redox response in FIG. 1(b) only comes from lithium insertion and extraction.
Example 7
Coin cells (CR2032) were used as prototype to evaluate Al—MnO2 battery. An Al disk was used as the anode, a MnO2/W disk as the cathode, Celgard 3014 as the separator, and lithium chloroaluminate dissolved in 1-ethyl-3-methyl imidazolium chloroaluminate as the electrolyte. The cells were tested using a MTI battery charger. Two charge-discharge regimes, constant current (CC) and constant current-constant voltage (CC-CV) were used. In a CC regime, the cells were charged at a C/10 (15 μA/g) current to 2.5 V and discharged at the same current to 1.3 V. In a CC-CV regime, the cells were charged at a C/10 (15 μA/g) current to 2.4 V, held at 2.4 V until the current was less than 1 μA/g, and then discharged at the same current to 1.0 V. The current rate was defined as per the theoretical specific capacity of λ-MnO2(1 C is equal to 148 mA/g).
The open circuit voltage (OCV) of the battery is 2.12 V, which is quite stable in an observation at open circuit condition for 24 hours. This implies that both Al and MnO2 do not react with the electrolyte at open circuit condition. FIG. 7A shows a typical charge-discharge curve with a constant current (CC) regime at C/10 (15 mA/g) current rate between 1.3 V-2.5 V. Both of charge and discharge curves appear a two-stage process, which is corresponding to the dual-peak redox behavior in the CV. The first discharge plateau is around 2.15 V and the second around 1.95 V. The specific charge and discharge capacity are 65 mAh/g and 74 mAh/g based on MnO2 weight. The larger discharge capacity than charge capacity could be attributed to inadequate charge due to the intervention of chlorine evolution. This results in rapid capacity fading under CC charge-discharge regime. In order to mitigate this effect, constant current-constant voltage (CC-CV) regime was adopted to charge this battery. FIG. 7B shows the plot of discharge capacity vs. cycle numbers with a regime that the cell is charged to 2.4 V by a C/10 (15 μA/mg) current and kept at 2.4 V until the current is less than 1 μA/mg. The discharge capacity is 94 mAh/g at the first cycle, while decreases to 54 mAh/g after 50 cycles. The capacity fading mostly occurs in the first 10 cycles. It is known that in a lithium ion battery, the capacity fading of LiMn2O4 cathode largely originates from the dissolution of Mn in the electrolyte. In the case of Al—MnO2 battery, it appears that the dissolution of Mn is also the major cause of capacity fading. In the discharged state, the electrolyte becomes a more acidic chloroaluminate ionic liquid where low-valence Mn ions may dissolve. The approaches to improving LiMn2O4 cathode in lithium ion batteries maybe also work for MnO2 cathode in rechargeable Al batteries.

## Claims

1. A battery comprising:
an anode comprising aluminum metal;
a cathode comprising spinel AIMn2O4; and
an electrolyte, wherein the electrolyte is an ionic liquid comprising an aluminate selected from the group consisting of alkylimidazolium aluminates, alkylpyridinium aluminates, alkylfluoropyrazolium aluminates, alkyltriazolium aluminates, aralkylammonium aluminates, alkylalkoxyammonium aluminates, aralkylphosphonium aluminates, aralkylsulfonium aluminates, and mixtures thereof.

2. The battery of claim 1, wherein the battery is a secondary battery.

3. The battery of claim 2, wherein the secondary battery maintains a discharge capacity of at least 50% of an initial discharge capacity after 50 discharge cycles.

4. The battery of claim 1, wherein the anode is an aluminum metal alloy.

5. The battery of claim 4, wherein the aluminum metal alloy comprises an element selected from the group consisting of: copper, magnesium, manganese, silicon, titanium, zinc, and mixtures thereof.

6. The battery of claim 1, wherein the aluminate is ethylmethylimidazolium tetrachloroaluminate having a molar ratio of aluminum chloride to EMIC greater than 1:1.

7. The battery of claim 6, wherein the electrolyte further comprises an alkali metal halide additive.

8. The battery of claim 7, wherein the alkali metal halide additive is selected from the group consisting of: NaCl, KCl, NH4Cl, and mixtures thereof.

9. The battery of claim 1, wherein the ionic liquid comprises ethylmethylimidazolium tetrachloroaluminate.

10. A method of making a battery comprising:
providing an anode comprising aluminum metal;
providing a cathode comprising spinel AIMn2O4; and
providing an electrolyte, wherein the electrolyte is an ionic liquid comprising an aluminate selected from the group consisting of alkylimidazolium aluminates, alkylpyridinium aluminates, alkylfluoropyrazolium aluminates, alkyltriazolium aluminates, aralkylammonium aluminates, alkylalkoxyammonium aluminates, aralkylphosphonium aluminates, aralkylsulfonium aluminates, and mixtures thereof.

11. The method of claim 10, wherein the aluminate is ethylmethylimidazolium tetrachloroaluminate having a molar ratio of aluminum chloride to EMIC of greater than 1:1.

12. The method of claim 10, wherein the electrolyte further comprises an alkali metal halide additive.

13. The method of claim 11, wherein the electrolyte further comprises an alkali metal halide additive.

14. The battery of claim 1, wherein the cathode further comprises a carbon material and a binder.

15. The battery of claim 14, wherein the cathode comprises:
approximately 50-90% of the spinel AlMn2O4;
approximately 1-20% of the binder; and
approximately 1-40% of the carbon material.

16. The battery of claim 15, wherein the carbon material is carbon black.

17. The battery of claim 1, wherein the cathode comprises an active material, the active material being the spinel AlMn2O4.

18. The battery of claim 17, wherein the cathode further comprises a carbon material and a binder.

19. The battery of claim 18, wherein the cathode comprises:
approximately 50-90% of the spinel AlMn2O4 as the active material of the cathode;
approximately 1-20% of the binder; and
approximately 1-40% of the carbon material.

20. The battery of claim 19, wherein the carbon material is carbon black.