Patent Grant
9843070
Due to the low cost, low flammability and 3-electron redox properties of aluminum (Al), rechargeable Al-based batteries could offer cost-effectiveness, high capacity and safety, leading to a breakthrough of energy storage technology. However, research over the past several years on rechargeable Al batteries have not been as successful as other types of batteries, plagued by problems of disintegration of cathode material, low cell discharge voltage, capacitive behavior without discharge voltage plateaus, and insufficient cycle life with fast battery capacity decay.
It is against this background that a need arose to develop embodiments of this disclosure.
In certain embodiments, a metal-ion battery includes: (1) an anode including aluminum; (2) a cathode including a layered, active material; and (3) an electrolyte disposed between the anode and the cathode to support reversible deposition and dissolution of aluminum at the anode and reversible intercalation and de-intercalation of anions at the cathode.
In some embodiments, the layered, active material is graphite. In some embodiments, the graphite is pyrolytic graphite.
In some embodiments, the layered, active material is a layered double hydroxide, a layered oxide, or a layered chalcogenide.
In some embodiments, the layered, active material has a porosity in the range of 0.05 to 0.95.
In some embodiments, the electrolyte corresponds to a mixture of an aluminum halide and an ionic liquid, and a molar ratio of the aluminum halide to the ionic liquid is greater than 1.1. In some embodiments, the aluminum halide is AlCl3, and the ionic liquid is 1-ethyl-3-methylimidazolium chloride. In some embodiments, the molar ratio of AlCl3 to 1-ethyl-3-methylimidazolium chloride is greater than 1.2. In some embodiments, a water content of the electrolyte is no greater than 1,000 ppm.
In additional embodiments, a metal-ion battery includes: (1) an aluminum anode; (2) a porous graphite cathode; and (3) an ionic liquid electrolyte disposed between the aluminum anode and the porous graphite cathode.
In some embodiments, the porous graphite cathode has a porosity in the range of 0.05 to 0.95. In some embodiments, the porosity is in the range of 0.3 to 0.9.
In some embodiments, the ionic liquid electrolyte corresponds to a mixture of an aluminum halide and an ionic liquid, and a molar ratio of the aluminum halide to the ionic liquid is greater than 1.1. In some embodiments, a water content of the ionic liquid electrolyte is no greater than 1,000 ppm. In some embodiments, the water content is no greater than 400 ppm.
In additional embodiments, a method of manufacturing a metal-ion battery includes: (1) providing an anode including aluminum; (2) providing a cathode including an active material capable of intercalating ions during charging and de-intercalating the ions during discharging, wherein the active material is selected from at least one of a carbon-containing material, a silicon-containing material, and a germanium-containing material; and (3) providing an electrolyte capable of supporting reversible deposition and dissolution of aluminum at the anode and reversible intercalation and de-intercalation of the ions at the cathode.
In some embodiments, providing the cathode includes providing a porous graphite material. In some embodiments, providing the porous graphite material includes forming a graphite foam through deposition on a porous, sacrificial template. In some embodiments, providing the porous graphite material includes expanding a graphite material through electrochemical hydrogen evolution.
In some embodiments, providing the electrolyte includes electrochemically drying the electrolyte, such that a water content of the electrolyte is no greater than 400 ppm.
In additional embodiments, a graphite foam for a metal-ion battery is formed by chemical vapor deposition on a sacrificial template, followed by etching removal of the sacrificial template.
In additional embodiments, a method of manufacturing includes electrochemically drying an electrolyte to reduce a water content of the electrolyte.
In further embodiments, a method of forming a porous graphite includes electrochemically exfoliating graphite, followed by hydrogen evolution reaction to expand the exfoliated graphite.
Other aspects and embodiments of this disclosure are also contemplated. The foregoing summary and the following detailed description are not meant to restrict this disclosure to any particular embodiment but are merely meant to describe some embodiments of this disclosure.
For a better understanding of the nature and objects of some embodiments of this disclosure, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.
Developing new types of rechargeable battery systems could fuel broad applications from personal electronics to grid storage. Some embodiments of this disclosure are directed to a high performance rechargeable metal-ion battery, such as an aluminum battery with high-rate capability using an Al metal anode and improved graphitic materials as a cathode. The improved graphitic cathode materials can afford rechargeable Al batteries operating in an ionic liquid with superior performance in terms of discharge voltage profile, cycling stability, and rate capability. The battery can operate by electrochemical redox deposition/dissolution of aluminum and graphite redox reactions through chloroaluminate anion intercalation/de-intercalation of graphite in a highly safe, non-flammable ionic liquid electrolyte. In some embodiments, the battery can exhibit well-defined discharge voltage plateaus near about 2 V, a specific capacity of about 70 mAh g−1, and about 98% Coulombic efficiency. More generally, (1) a voltage plateau can be in the range of about 2.25 V to about 1.5 V; (2) a specific (charge or discharge) capacity can be at least about 50 mAh g−1, at least about 60 mAh g−1, at least about 70 mAh g−1, at least about 80 mAh g−1, at least about 90 mAh g−1, at least about 100 mAh g−1, or at least about 110 mAh g−1, and up to about 127 mAh g−1 or more; (3) at least about 50% of an initial discharge capacity is retained after 300, 500, or 1,000 charge/discharge cycles, such as at least about 60%, at least about 70%, at least about 80%, at least about 85%, at least about 90%, at least about 93%, at least about 95%, or at least about 98%, and up to 99% or more; and (4) a Coulombic efficiency can be at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95%, or at least about 98%, and up to about 99% or more, where cycling is under a current density of C/10, C/5, C/4, C/2, 1C, 2C, or another higher or lower reference rate. In some embodiments, at least about 50% of a reference discharge capacity when cycling under a reference current density (e.g., 1C) is retained when cycling under 2 times, 5 times, 10 times, or 50 times the reference current density (e.g., 2C, 5C, 10C, or 50C), such as at least about 60%, at least about 70%, at least about 80%, at least about 85%, at least about 90%, at least about 93%, at least about 95%, or at least about 98%, and up to 99% or more. In some embodiments, an improved three-dimensional (3D) graphitic porous cathode can provide fast anion transport, infiltration and diffusion from electrolyte to cathode, affording unprecedented charging time of about 1 minute under high charging current densities of about 4,000 mA g−1 (about 3,000 W kg−1) impressively over about 7,500 cycles without noticeable capacity decay. The low cost, high safety, high stability and high speed Al battery opens a path for an improved energy storage system.
As shown in an embodiment of
In the illustrated embodiment, the battery 100 is an aluminum battery, although other types of metal-ion batteries are encompassed by this disclosure. The anode 104 includes aluminum, such as a non-alloyed form of aluminum or an aluminum alloy. More generally, a suitable anode material can include one or more of an alkali metal (e.g., lithium, potassium, sodium, and so forth), an alkaline earth metal (e.g., magnesium, calcium, and so forth), a transition metal (e.g., zinc, iron, nickel, cobalt, and so forth), a main group metal or metalloid (e.g., aluminum, silicon, tin, and so forth), and a metal alloy of two or more of the foregoing elements (e.g., an aluminum alloy).
The separator 106 mitigates against electrical shorting of the cathode 102 and the anode 104, and the electrolyte 108 supports reversible deposition and dissolution (or stripping) of aluminum at the anode 104, and reversible intercalation and de-intercalation of anions at the cathode 102. The electrolyte 108 can include an ionic liquid, which can support reversible redox reaction of a metal or a metal alloy included in the anode 104. Examples of ionic liquids include aluminates, such as alkylimidazolium aluminates, alkylpyridinium aluminates, alkylfluoropyrazolium aluminates, alkyltriazolium aluminates, aralkylammonium aluminates, alkylalkoxyammonium aluminates, aralkylphosphonium aluminates, aralkylsulfonium aluminates, alkylguanidinium aluminates, and mixtures thereof. For example, the electrolyte 108 can correspond to, or can include, a mixture of an aluminum halide and an ionic liquid, and a molar ratio of the aluminum halide and the ionic liquid is at least or greater than about 1.1 or at least or greater than about 1.2, and is up to about 1.5, up to about 1.8, or more, such as where the aluminum halide is AlCl3, the ionic liquid is 1-ethyl-3-methylimidazolium chloride, and the molar ratio of the aluminum chloride to 1-ethyl-3-methylimidazolium chloride is at least or greater than about 1.2. An ionic liquid electrolyte can be doped (or have additives added) to increase electrical conductivity and lower the viscosity, or can be otherwise altered to yield compositions that favor the reversible electrodeposition of metals.
Higher Coulombic efficiency and higher cycling stability can be attained by reducing a water content of the electrolyte 108, such as to a level no greater than about 7,500 parts per million (ppm), no greater than about 5,000 ppm, no greater than about 2,000 ppm, no greater than about 1,000 ppm, no greater than about 900 ppm, no greater than about 800 ppm, no greater than about 700 ppm, no greater than about 600 ppm, no greater than about 500 ppm, no greater than about 400 ppm, no greater than about 300 ppm, no greater than about 200 ppm, or no greater than about 100 ppm, and down to about 50 ppm, down to about 10 ppm, or less. In some implementations, a reduced water content can be attained by electrochemical drying of water, such as by cycling the battery 100 through one or more charge/discharge cycles, during which residual water in the electrolyte 108 can be consumed by decomposition into H2 gas that can be released from the battery 100.
The cathode 102 includes an active material that is capable of reversibly intercalating or otherwise incorporating metal anions from the electrolyte 108, such as intercalating chloroaluminate anions during charging and de-intercalating the chloroaluminate anions during discharging. Suitable cathode materials can include one or more of various two-dimensional (2D) layered materials or 3D materials. 2D materials can include multiple sheets or layers, with covalent bonding between atoms of a particular sheet or layer, and weaker interactions, such as Van der Waals bonding, between sheets or layers, although a single-layered material also can be a suitable 2D material. 3D materials can include 3D crystalline materials as well as layered materials in which at least some extent of covalent bonding occurs between sheets or layers of the layered materials. Examples of suitable cathode materials include (1) carbon-containing (or carbonaceous) materials, such as graphitic materials (e.g., graphitic foil, graphitic foam (or other porous structures), graphitic films, graphitic fibers, graphitic powders, or graphitic particles; graphene materials; and carbon nanotube materials), (2) a layered double hydroxide, (3) a layered oxide, (4) a layered chalcogenide, (5) silicon (or other silicon-containing materials), (6) germanium (or other germanium-containing materials), (7) other Group IV-containing materials, and (8) gallium arsenide (GaAs), among others.
For example, the cathode 102 can include a 2D material that is graphitic.
As another example, the cathode 102 can include a 3D material in the form of pyrolytic graphite, in which covalent bonding occurs between adjacent graphene sheets.
As another example, the cathode 102 can include a 3D material in the form of graphite foam, which can be formed as graphite whiskers or other elongated structures on a sacrificial template by chemical vapor deposition, followed by etching removal of the sacrificial template. A width (e.g., an individual or average width, diameter, or other lateral dimension) of graphite whiskers in a graphite foam can be in the range of about 200 nm to about 2,000 μm, about 500 nm to about 1,500 μm, about 500 nm to about 1,000 μm, about 1 μm to about 1,000 μm, about 1 μm to about 900 μm, about 1 μm to about 800 μm, about 1 μm to about 700 μm, about 1 μm to about 600 μm, about 1 μm to about 500 μm, about 10 μm to about 500 μm, about 10 μm to about 400 μm, about 10 μm to about 300 μm, or about 10 μm to about 200 μm. A porous graphite structure also be formed by expanding a graphite material, such as thermal heating and exfoliating of pyrolytic graphite after one or more charge/discharge cycles and then electrochemical hydrogen evolution reaction in a basic solution, during which hydrogen gas can expand the pyrolytic graphite into a porous structure. In some implementations, a characteristic of a graphite or graphitic foam is its porosity, which is a measure of the extent of voids resulting from the presence of pores or any other open spaces in the foam. A porosity can be represented as a ratio of a volume of voids relative to a total volume, namely between 0 and 1, or as a percentage between 0% and 100%. In some implementations, a graphitic foam can have a porosity that is at least about 0.05 or at least about 0.1 and up to about 0.95, and, more particularly, a porosity can be in the range of about 0.1 to about 0.9, about 0.2 to about 0.9, about 0.3 to about 0.9, about 0.4 to about 0.9, about 0.5 to about 0.9, about 0.5 to about 0.8, or about 0.6 to about 0.8. Techniques for determining porosity include, for example, porosimetry and optical or scanning techniques.
As a further example, the cathode 102 can include a 3D material such as silicon or germanium.
The following examples describe specific aspects of some embodiments of this disclosure to illustrate and provide a description for those of ordinary skill in the art. The examples should not be construed as limiting this disclosure, as the examples merely provide specific methodology useful in understanding and practicing some embodiments of this disclosure.
Al batteries (schematic plot in
The Al/PG cell exhibited clear discharge voltage plateaus in the range of about 2.25 to about 2.0 V and about 1.9 to about 1.5 V (
Lowered Coulombic efficiency and cycling stability of the Al battery cell are observed when using electrolyte containing higher water content up to about 7,500 ppm (
The Al/pyrolytic graphite foil cell showed reduced rate capability with lowered specific capacity when charged and discharged at higher than 1C rate (
As high-rate and high-power batteries are highly desired for applications such as electrical grid storage, investigation was performed on flexible 3D graphitic foam (
Remarkably, the Al/3D graphite foam cell (in a pouch cell configuration) can be charged and discharged at a high current density up to about 5,000 mA g−1, about 75 times (e.g., at a 75C rate, <1 min charge/discharge time) higher than the Al/PG cell but with a similar voltage profile and discharge capacity (about 60 mAh g−1) (see
Investigation was performed of the Al-ion battery operation mechanism and electrode reactions in the mixed AlCl3/[EMIm]Cl ionic liquid electrolyte with an optimal mole ratio of AlCl3/[EMIm]Cl=about 1.3 (by mole). Cyclic voltammetry (CV) (
4Al2Cl7−+3e−Al+7AlCl4− (1)
and in line with Raman observation of both AlCl4 and Al2Cl7 anions in the electrolyte (
It is proposed that the following simplified cathode redox reactions during charging and discharging occur as
Cn+AlCl4−Cn[AlCl4]+e− (2)
where n is the mole ratio of carbon atom/anion in the intercalated graphite. Under an optimal electrolyte with AlCl3/[EMIm]Cl of about 1.3 (by mole), the Lewis acidity was relatively high and the AlCl4− concentration was about 2.3-fold higher than Al2Cl7− specified by
EMI+Cl−+AlCl3AlCl4−+EMI+ (3)
EMI++AlCl4−+AlCl3Al2Cl7+EMI+ (4)
The balanced AlCl4− and Al2Cl7− concentrations in the electrolyte favored an optimal charging capacity of the cathode with abundant AlCl4− for charging/intercalation on graphite (Eq. 2) and sufficient Al2Cl7− concentration for charging/electrodeposition on the anode (Eq. 1). During cell discharge, the local anion concentration near the anode side reduced (Eq. 1, AlCl4− ions were converted to fewer Al2Cl7− ions) while EMI+ ions migrated to the cathode side, accompanied by more AlCl4− anions released (Eq. 2) from the graphite layers to the cathode surrounding (
Ex situ XRD measurement of graphite foil (
In situ Raman spectroscopy is performed to probe chloroaluminate anions intercalation/de-intercalation into graphite during cell charge/discharge (
X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) also are performed to probe the chemical nature of the intercalated species in the graphitic cathodes (see Materials and Methods). To reduce trapped electrolyte, 3D graphite foam is used for this investigation and is thoroughly washed by anhydrous methanol. XPS revealed that upon charging pristine graphite, the about 284.8 eV C1s peak split to exhibit a shoulder peak at a higher energy of about 285.9 eV (
The Al battery was found to be mechanically bendable and foldable (
Materials and Methods
Preparation of Ionic Liquid Electrolytes.
A room temperature ionic liquid electrolyte was made by mixing 1-ethyl-3-methylimidazolium chloride ([EMIm]Cl, 97%, Acros Chemicals) and anhydrous aluminum chloride (AlCl3, 99.999%, Sigma Aldrich). [EMIm]Cl was baked at about 130° C. under vacuum for about 16-32 hours to remove residual water. ([EMIm]AlxCly) ionic liquid electrolytes were prepared in an argon-atmosphere glove box (both [EMIm]Cl and AlCl3 are highly hygroscopic) by mixing anhydrous AlCl3 with [EMIm]Cl, and the resulting light-yellow, transparent liquid was stirred at room temperature for about 10 minutes. The mole ratio of AlCl3 to [EMIm]Cl was varied from about 1.1 to about 1.8. The water content of the ionic liquid was determined (about 500-700 ppm) using a coulometric Karl Fischer titrator, DL 39 (MettlerToledo). The predominant anions in basic melts (AlCl3/[EMIm]Cl mole ratio<1) are Cl− and AlCl4−, while in acidic melts (AlCl3/[EMIm]Cl mole ratio>1) chloroaluminate anions such as Al2Cl7−, Al3Cl10−, and Al4Cl13− are formed. The ratio of anions to cations in the AlCl3/[EMIm]Cl electrolyte was determined using a glass filterpaper (Whatman GF/D) loaded with an about 4-8 μm Au-coated SiO2 bead in a cuvette cell (0.35 mL, Starna Cells) with random orientation quartz windows. Then, in the glove box, the cuvette cell was filled with AlCl3/[EMIm]Cl=about 1.3 (by mole). Raman spectra (200 to 650 cm−1) were obtained using a 785-nm laser with 2 cm−1 resolution. Raman data were collected from the surface of the Au-coated SiO2 bead to benefit from surface enhanced Raman (
Preparation of 3D Graphite Foam.
Nickel foams (Alantum Advanced Technology Materials (Shenyang, China)) were used as 3D scaffold templates for the CVD growth of 3D graphite. The nickel foams were heated to about 1000° C. in a horizontal tube furnace (Lindberg Blue M, TF55030C) under Ar (about 500 sccm) and H2 (about 200 sccm) and annealed for about 10 min to clean their surfaces and to eliminate a thin surface oxide layer. Then, CH4 was introduced into the reaction tube at ambient pressure at a flow rate of about 10 sccm, corresponding to a concentration of about 1.4 vol. % in the total gas flow. After about 10 minutes of reaction gas mixture flow, the samples were rapidly cooled to room temperature at a rate of about 300° C. min−1 under Ar (about 500 sccm) and H2 (about 200 sccm). The Ni foams covered with graphite were drop-coated with a poly(methyl methacrylate) (PMMA) solution (about 4.5% in ethyl acetate), and then baked at about 110° C. for about 0.5 hours. The PMMA/graphene/Ni foam structure was obtained after solidification. Afterwards, these samples were put into an about 3 M HCl solution for about 3 hours to substantially completely dissolve the Ni foam to obtain the PMMA/graphite at about 80° C. Finally, the pure 3D graphite was obtained by removing PMMA in hot acetone at about 55° C. and annealing in NH3 (about 80 sccm) at about 600° C. for about 2 hours, and then annealing in air at about 450° C. for about 2 hours. The microstructure of 3D graphite was examined by SEM analysis using a FEI XL30 Sirion scanning electron microscope (
Preparation of Glassy Carbon (GC).
GC was used as the current collector in the Swagelok-type cell. About 72 g phenol (Sigma-Aldrich) and about 4.5 mL ammonium hydroxide (30%, Fisher Scientific) were dissolved in about 100 mL formaldehyde solution (37%, Fisher Scientific) under reflux while stirring rapidly. The solution was stirred at about 90° C. until the solution turned a milk-white color. Rotary evaporation was used to remove the water and get the phenolic resin. The phenolic resin was solidified at about 100° C. in a mold (½ inch glass tube), and then carbonized at about 850° C. under Ar atmosphere for about four hours to obtain the glassy carbon rod. The resulting GC rod contributed negligible capacity to the cathode.
Electrochemical Measurements.
Prior to assembling the Al/graphite cell in the glove box, all components were heated under vacuum at about 60° C. for over about 12 hours to remove residual water. All electrochemical tests were performed at 25±1° C. A Swagelok-type cell (½ inch diameter) was constructed using an about 4 mg pyrolytic graphite (PG) foil (0.017 mm, Suzhou Dasen Electronics Materials) cathode and an about 90 mg aluminum foil (0.25 mm, Alfa Aesar) anode. A ½ inch glassy carbon (GC) rod (10 mm) was used as the current collector for the PG cathode, and a ½ inch graphite rod (10 mm) was used for the Al anode. Six layers of ½ inch glass filter paper (Whatman 934-AH) were placed between the anode and cathode. Then, about 1.0 mL of ionic liquid electrolyte (prepared with AlCl3/[EMIm]Cl mole ratios of about 1.1, about 1.3, about 1.5 and about 1.8) was injected and the cell sealed. The Al/PG cell was then charged (to about 2.45 V) and discharged (to about 0.01 V) at a current density of about 66 mA g−1 with a MTI battery analyzer (BST8-WA) to identify the ideal AlCl3/[EMIm]Cl mole ratio (
Pyrolytic graphite foil was synthesized by pyrolysis of polyimide at high temperature, in which some covalent bonding is generated. Natural graphite foil was produced by compressing expanded graphite flakes, leading to stacking of natural graphite flakes by Van der Waals bonding in-between. Similar battery characteristics were observed with pyrolitic graphite and graphite foil electrodes, indicating that the battery behavior was derived from the graphitic property of the electrodes (
Pouch cells were assembled in the glove box using a 3D graphite foam (about 3 mg) cathode and an Al foil (about 70 mg) anode, which were separated by two layers of glass filter paper to prevent shorting. Nickel foils (0.09×3×60 mm3 in size) were used as current collectors for both anode and cathode. The electrolyte (about 2 mL prepared using AlCl3/[EMIm]Cl=about 1.3 by mole) was injected and the cell was closed using a heat sealer. The cell was removed from the glove box for long-term cycling stability tests, in which the cell was charged/discharged at a current density of 4,000 mA g−1 (
Cyclic voltammetry (CV) measurements were performed using a potentiostat/galvanostat model CHI 760D (CH Instrument) in three-electrode mode. The working electrode was an Al foil or a PG foil, the auxiliary electrode included an Al foil, and an Al foil was used as the reference electrode. Copper tape was attached to these electrodes as the current collector. All three electrodes were placed in a plastic (1.5 mL) cuvette cell (containing electrolyte AlCl3/[EMIm]Cl=about 1.3 by mole) in the glove box, which was then sealed with a rubber cap using a clamp. The scanning voltage range was set from about −1.0 to about 1.0 V (vs. Al) for Al foil and about 0 to about 2.5 V (vs. Al) for graphitic material, and the scan rate was about 10 mV s−1 (
To demonstrate the high flexibility of the Al/graphitic cell, a pouch cell was assembled in the glove box by sandwiching a glass filter paper between a thin Al foil anode (about 20-50 mg) and a pyrolytic graphite foil (about 20-30 mg) cathode with a suitable amount (about 0.05 mL per mg of graphite foil) of ionic liquid electrolyte (AlCl3/[EMIm]Cl=about 1.3 by mole). The Al-graphite cell was capable of powering a red LED light under both non-bending and bending conditions (
Ex-Situ X-Ray Diffraction and In-Situ Raman Spectroscopy Studies of Graphite Cathode During Charge and Discharge.
For ex-situ X-ray diffraction (XRD) study, an Al/graphitic materials (PG) cell (in a Swagelok configuration) was charged and discharged at a constant current density of about 66 mA g−1. The reactions were stopped after 30 mAh g−1 charged, fully charged (about 62 mAh g−1), and about 40 mAh g−1 discharged capacities after charge/discharge capacities were in a stable state. The fully charged (about 62 mAh g−1) 3D graphite was also prepared. After either charge or discharge reaction, the graphitic cathode was removed from the cell in the glove box. To avoid the reaction between the cathode and air/moisture in the ambient atmosphere, the cathode was placed onto a glass slide and then wrapped in a Scotch tape. The wrapped samples were immediately removed from the glove box for ex-situ XRD measurement, which were performed on a PANalyticalX′Pert instrument (
During the charging/anion-intercalation process, the graphite (002) peak substantially completely vanished and two new peaks arose. The intensity pattern is an example for a stage n GIC, where the most dominant peak is the (00n+1) and the second most dominant peak is the (00n+2). By increasing the charging state from about 48-60% charged (about 30 mAh g−1) to the fully charged state (about 62 mAh g−1), the distance between the (00n+1) and (00n+2) peaks gradually increased, as more AlxCly− anions intercalated. By determining the ratio of the d(n+2)/d(n+1) peak position and correlating these to the ratios of stage pure GICs, the most dominant stage phase of the observed GIC can be assigned. After assigning the (00l) indices, the periodic repeat distance (k), the intercalant gallery height (di) and the gallery expansion (Ad) can be calculated using
Ic=di+3.35 Å·(n−1)=Δd+3.35 Å·n=l·dobs[1]
where l is the index of (00l) planes oriented in the stacking direction, and dobs is the observed value of the spacing between two adjacent planes.
For the simultaneous use of in-situ Raman and galvanostatic charge/discharge reaction measurements, a cuvette cell (0.35 mL, Starna Cells) with random orientation quartz windows was used. An aluminum foil and a graphitic material (PG or 3D graphite) were used as the anode and cathode, respectively. The electrolyte was mixed AlCl3/[EMIm]Cl=about 1.3 (by mole). The electrochemical cell was assembled in the glove box following the process mentioned above. Raman spectra were obtained (1500-1700 cm−1) using a HeNe laser (633 nm) with 2 cm−1 resolution. The spectral data were collected after a few successive charge/discharge scans between about 2.45 to about 0.01 V at a current density of about 66 mA g−1 (PG) (
X-Ray Photoelectron Spectra (XPS) and Auger Electron Spectroscopy (AES) Measurements.
Al/3D graphite cells were fully charged/discharged at a current density of about 4,000 mA g−1. Then, the Al/3D graphite cells were transferred to the glove box for preparation for XPS and AES analysis. Fully charged/discharged 3D graphite foams were collected from the pouch cell and washed with anhydrous methanol to remove the residual AlCl3/EMIC ionic liquid electrolyte. The as-rinsed 3D graphite foams were attached to a Si wafer and baked at about 90° C. for about 10 minutes to remove residual methanol. The samples were sealed in a plastic pouch to avoid contamination by reaction with moisture and oxygen prior to XPS and AES characterization. Auger electron spectra were taken by PHI 700 Scanning Auger Nanoprobe operating at 10 kV and 10 nA. XPS spectra were collected on a PHI VersaProbe Scanning XPS Microprobe (
TGA Measurements.
Fully charged PG cathodes were washed with methanol for about 24 hours to remove the residual AlCl3/EMIC ionic liquid electrolyte. The as-washed PG samples were calcined at about 850° C. for about 3 hours in air. The as-calcined samples (white foam) were collected, weighed, and analyzed by SEM-EDX to study the chemical composition (
Al batteries were constructed in pouch cells, using an aluminum foil (thickness of about 15-250 μm) anode and pyrolytic graphite (PG) foil (about 17 μm) cathode, in an AlCl3/1-ethyl-3-methylimidazolium chloride ([EMIm]Cl) ionic liquid electrolyte (residual water of about 400 ppm). The Al/PG cell was then charged under a constant voltage at about 2.5 V for about 24 h. The cathode PG was taken out of the pouch after charge and washed by ethanol and water to remove the residual ionic liquid electrolyte. The PG foil was expanded by rapid thermal heating after intercalation/charging in the Al ion cell and then electrochemical hydrogen evolution reaction in a basic solution (about 10 M NaOH, with saturated sodium acetate (NaAc)) (
Pouch cells were assembled in the glove box using PG (about 57 mg) cathode and an Al foil anode, which were separated by two layers of glass filter paper to prevent shorting. Carbon Fiber paper (CFP) was used as back contact of the PG with Ni bar as current collector for the cathode, and Ni bar was used as current collector for the anode. The electrolyte (about 2.8 g prepared using AlCl3/[EMIm]Cl=about 1.3 by mole) was injected, and the cell was sealed upon heating. The Al/PG cell was then charged under a constant voltage at about 2.45 V for about 1 h, and discharged (to about 0.5 V) at a current density of about 66 mA g−1, showing good capacity and high stability (
Pouch cells were assembled in the glove box using an aluminum foil (thickness of about 15-250 μm) anode and pyrolytic graphite (PG) foil cathode, which were separated by two layers of glass filter paper. The pre-dried electrolyte (residual water of about 400 ppm, prepared using AlCl3/[EMIm]Cl=about 1.3 by mole) was injected, and the cell was closed using a heat sealer. The Al/PG cell was then charged (to about 2.45 V) and discharged (to about 0.5 V) at a current density of about 66 mA g−1. The H2 gas from the hydrogen evolution reaction of the residual water filled the pouch after several cycles. The pouch was then punctured by a needle to release the gas and re-sealed. This was repeated until the pouch cell did not inflate any more after three times of the gas releasing. It is proposed that the residual water in the electrolyte was consumed by decomposition into H2 gas electrochemically during battery charging, providing a way to electrochemically dry the battery electrolyte to a high degree.
This example describes an improved Al-ion battery system using a flexible graphite foil as a cathode combined with a flexible aluminum anode in a non-flammable ionic liquid electrolyte of AlCl3-[EMIm]Cl with an optimal composition. The Al/graphite battery (Al/GF battery) shows a discharge plateau ranging from about 2.25 V to about 1.5 V and delivers a specific capacity up to about 127 mAh g−1, or more, based on the mass of the graphite foil cathode. Intercalation and de-intercalation processes of anions of the ionic liquid in the graphite cathode were investigated, revealing a large expansion of graphite interlayer spacing due to electrochemical intercalation of AlxCly− anions. The charge-discharge cycling stability of the Al/GF battery shows an about 100% capacity retention over at least 300 cycles with a Coulombic efficiency of about 98-100%. The Al/graphite battery with high cost-effectiveness, safety and high voltage represents an improved energy storage system.
Components in Al/Graphite Battery.
Through systematic investigation of full battery characteristics, identification was made of aluminum foil (thickness of about 15-250 μm) as a desirable anode, graphite foil as a desirable cathode among different forms of carbon materials including, for example, graphite foil (GF), carbon fiber paper (CFP), carbon black (CB) films, and various forms of graphitic materials, and an optimal ionic liquid electrolyte with AlCl3/[EMIm]Cl molar ratio of about 1.3 (e.g., greater than about 1.1). The cathode material is varied, and the Al/GF cells are tested under slow charge/discharge current density of about 6.6 mA g−1 (about C/10) to maximize the specific capacity. Al/GF cell exhibited significantly higher specific capacity (about 74 mAh g−1) than Al/CFP (about 27 mAh g−1) and Al/CB (about 36 mAh g−1) cells but with similar voltage plateaus at about 2.25-1.5 V (See
The Al-ion battery performance depended on the composition of the electrolyte and identifying an optimal composition of AlCl3-[EMIm]Cl ionic liquid electrolyte is a desirable for a rechargeable Al-ion battery with high performance. Charge/discharge characteristics of an Al/GF cell were studied in various molar ratios of AlCl3 to [EMIm]Cl (from about 1.1 to about 2.7) for optimization, as indicated in
An optimal AlCl4− and Al2Cl7− ion ratio under a specific AlCl3 to [EMIm]Cl ratio could give rise to a maximized battery capacity by balancing the ions involved in electrochemical reactions involving AlCl4−/Al2Cl7− intercalation into graphite in the cathode and Al2Cl7− reduction to Al on the anode. The Al/GF battery exhibited a highest specific capacity up to about 47 mAh g−1 or more at a discharge voltage cut-off of about 1.5 V in AlCl3/[EMIm]Cl electrolyte of molar ratio of about 1.3-1.5 (
Cycling Properties of Al/Graphite Battery.
Most of the graphite expansion occurred during the first cycles of the battery in an activation stage of the battery. Once a steady state is reached, the long-term cycling measurement shows that the Al/GF battery still retained about 100% of the specific capacity (about 66 mAhg−1) after 300 cycles or more under a current density of about 33 mA g−1(about C/2) with about 98-100% Coulombic efficiency (see
Charge-Discharge Mechanism of Al-Graphite Battery.
To further glean the mechanism of intercalation/de-intercalation process, ex situ XRD measurement and in situ Raman spectroscopy of the graphite cathode were performed.
Flexible Al-Graphite Battery.
In summary, this examples describes an improved Al-ion battery system using a flexible graphite foil as a cathode combined with an aluminum anode in an ionic liquid electrolyte of AlCl3-[EMIm]Cl. The Al/graphite battery displayed excellent electrochemical features with stable cycling behavior over 200 charge-discharge cycles with a high discharge plateau in the voltage range of about 2.25 V to about 1.5 V. The estimated energy density of Al-ion battery with a graphite foil as a cathode against an aluminum anode is about 662 Wh kg−1, which is comparable to that of Li-ion battery. The theoretical capacities and energy cost for the aluminum-ion battery including graphite cathode are calculated and shown in Table 1 of
Methods
Preparation of Ionic Liquid Electrolytes.
A room temperature ionic liquid electrolyte was made of 1-ethyl-3-methylimidazolium chloride ([EMIm]Cl, 97%, Acros chemicals) and anhydrous aluminum chloride (AlCl3, 98.5%, Acros chemicals). The preparation of AlCl3-([EMIm]Cl) ionic liquid electrolytes was conducted in an argon-filled glove box (AlCl3 is highly reactive). The electrolytes were prepared by dissolving anhydrous AlCl3 into [EMIm]Cl and stirring at room temperature for about 10 minutes, which resulted in a clear light yellow solution. The molar ratio of AlCl3 to [EMIm]Cl was varied from about 0.8 to about 2.7. The dominant anions in basic melts (AlCl3/[EMIm]Cl molar ratio<1) are Cl− and AlCl4−. On adding excess of AlCl3 to the acidic melts (AlCl3/[EMIm]Cl molar ratio>1), chloroaluminate anions such as Al2Cl7−, Al3Cl10−, and Al4Cl13− are formed.
Electrochemical Measurements.
Preliminary two-electrode cell tests were carried out in both of a 1.4 mL plastic cuvette cell and a ½-inch Swagelok-type cell with a MTI battery analyzer (BST8-WA, Richmond). An aluminum foil (thickness of about 0.015 mm, MTI Corporation) was selected as anode, and a graphite foil (thickness of about 0.13 mm, GTA Flexible Graphite) cathode was obtained from GrafTech International, Ltd. For comparison, carbon fiber paper (GDL10 AA, SGL Carbon) and carbon black (Black Pearl 2000, Cabot) were also used as cathode material. A Whatman 934-AH glass fiber filter was used as the separator membrane. An Al anode, one of those cathodes, and a separator were sealed into the plastic cuvette cell containing AlCl3:[EMIm]Cl molar ratio of about 1.3:1 electrolyte with a flat rubber in an argon-filled glove box. A galvanostatic discharge/charge reaction was performed at the cell voltage of about 2.3 to about 0.01 V at different current densities (about 6.6 or about 33 mA g−1). The Swagelok cell was constructed using a graphite foil (GF) (about 0.018 g) as cathode, four layers of the glass separator membrane, and an aluminum foil (about 0.006 g) as anode. Then, few drops of ionic liquid electrolyte (AlCl3/[EMIm]Cl ratios from about 1.1, about 1.2, about 1.3, about 1.5, about 1.8 and about 2.7) were filled and sealed in the glove box. The Swagelok cell was charged and discharged at the cell voltage of about 2.5 to about 0.01 V at a constant current density of about 33 mA g−1. Short-term charge-discharge test of the Al/graphite battery (in Swagelok cell) was carried out at current densities from about 16.5 to about 198 mA g−1 in the AlCl3/[EMIm]Cl (about 1.3 in molar ratio) ionic liquid electrolyte. In the case of long-term charge-discharge, the current density was set at about 33 mA g−1. The cyclic voltammetry measurement was carried out using a potentiostat/galvanostat model VMP3 (Bio-Logic) in both three-electrode and two-electrode modes. The working electrode was an aluminum foil or a GF, the auxiliary electrode included a platinum foil, and an Al foil was used as the reference electrode. All three electrodes were sealed into a plastic cuvette cell containing AlCl3:[EMIm]Cl molar ratio of about 1.3:1 electrolyte following the same sealing procedure as above. The CV measurements were carried out in the laboratory at the ambient environment. The scanning range was set from about −1 to about 0.85 V (vs. Al) for Al foil and about 0 to about 2.5 V (vs. Al) for the GF, and the scan rate was 10 mV s−1. For the two electrode mode (Swagelok cell), an Al/GF battery were charged and discharged in AlCl3:[EMIm]Cl molar ratio of about 1.3:1 electrolyte. The Swagelok cell assembly was performed following the same procedure mentioned above. All electrochemical measurement were performed in the laboratory in the ambient environment at 25±1° C.
In-Situ Raman Spectroscopy and Ex-Situ X-Ray Diffraction Studies of Graphite Cathode During Charge and Discharge.
For the simultaneous use of in-situ Raman and galvanostatic charge/discharge reaction measurements, a cuvette cell (0.35 mL, Starna Cells) with random orientation quartz windows was used. An aluminum foil and a GF were used as anode and cathode, respectively. The electrolyte was AlCl3:[EMIm]Cl about 1.3:1 by molar mixture. The electrochemical cell was assembled in the glove box. Raman spectra were excited by a HeNe laser (633 nm) at a resolution of 2 cm−1 in the range between 1400 and 1800 cm−1. The spectra data were collected after few successive charge/discharge scans of the Al/GF battery between about 2.3 to about 0.01 V at a current density of about 33 mA g−1. For ex-situ X-ray diffraction (XRD) study, an Al/GF battery (in Swagelok configuration) was charged and discharged at a constant current density of about 33 mA g−1, the reactions were stopped after about 60% charge, fully charged, and about 60% discharge capacities after 10 charge-discharge cycles. In addition, the fully charged samples were obtained after 25 and 100 charge-discharge cycles, respectively. After either charge or discharge reaction, the GF cathode was removed from the cell in the glove box. To avoid the reaction between the cathode and air/moisture in the ambient atmosphere, the cathode was placed onto a glass slide, then the sample was wrapped in a Scotch tape. The wrapped samples were removed from the glove box to air to perform ex-situ XRD measurement immediately. Ex-situ XRD measurement was carried out on a PANalytical X'Pert instrument.
As used herein, the singular terms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to an object can include multiple objects unless the context clearly dictates otherwise.
As used herein, the terms “connect,” “connected,” “connecting,” and “connection” refer to an operational coupling or linking Connected objects can be directly coupled to one another or can be indirectly coupled to one another, such as through another set of objects.
As used herein, the terms “substantially” and “about” are used to describe and account for small variations. When used in conjunction with an event or circumstance, the terms can refer to instances in which the event or circumstance occurs precisely as well as instances in which the event or circumstance occurs to a close approximation. For example, the terms can refer to less than or equal to ±10%, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%.
While this disclosure has been described with reference to the specific embodiments thereof, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of this disclosure as defined by the appended claims. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, method, operation or operations, to the objective, spirit and scope of this disclosure. All such modifications are intended to be within the scope of the claims appended hereto. In particular, while certain methods may have been described with reference to particular operations performed in a particular order, it will be understood that these operations may be combined, sub-divided, or re-ordered to form an equivalent method without departing from the teachings of this disclosure. Accordingly, unless specifically indicated herein, the order and grouping of the operations is not a limitation of this disclosure.
This application claims the benefit of U.S. Provisional Application No. 61/946,618, filed on Feb. 28, 2014, and the benefit of U.S. Provisional Application No. 62/076,420, filed on Nov. 6, 2014, the disclosures of which are incorporated herein by reference in their entireties.
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| Number | Date | Country | |
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