STITCHING TWO-DIMENSIONAL ATOMIC CRYSTALS BY ATOMIC LAYER DEPOSITION AS STABLE INTERFACES FOR BATTERIES
1. An anode comprising:
- a current collector; and
an interfacial layer disposed over the current collector,wherein the interfacial layer includes a film of a layered material and a reinforcing material selectively disposed over certain regions of the film, while other regions of the film remain exposed from the reinforcing material.
An anode includes: (1) a current collector; and (2) an interfacial layer disposed over the current collector. The interfacial layer includes a film of a layered material and a reinforcing material selectively disposed over certain regions of the film, while other regions of the film remain exposed from the reinforcing material.
- 1. An anode comprising:
a current collector; and an interfacial layer disposed over the current collector, wherein the interfacial layer includes a film of a layered material and a reinforcing material selectively disposed over certain regions of the film, while other regions of the film remain exposed from the reinforcing material.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
- 14. A method of forming an anode for a battery, comprising:
providing a current collector and a film of a layered material disposed over the current collector; and performing atomic layer deposition to deposit a reinforcing material selectively on certain regions of the film, while other regions of the film remain exposed from the reinforcing material.
- View Dependent Claims (15, 16, 17, 18, 19)
This application claims the benefit of U.S. Provisional Application No. 62/524,197, filed Jun. 23, 2017, the contents of which are incorporated herein by reference in their entirety.
This invention was made with Government support under contract DE-AC02-76SF00515 awarded by the Department of Energy. The Government has certain rights in the invention.
With the highest specific capacity of about 3860 mAh/g, lithium (Li) metal has long been considered the most promising candidate anode material to implement lithium-sulfur (Li—S) and lithium-air (Li—O2) battery technology, which can in turn provide about 5-10 times increased overall energy density as compared to Li-ion battery technology. However, the commercial application of Li metal anodes has been constrained by two fundamental challenges. First, Li metal is strongly reducing and tends to react with battery electrolytes to form a solid electrolyte interphase (SEI). The reaction at the electrode/electrolyte interface consumes both active Li and electrolyte. Second, due to the virtually infinite relative volume change in Li metal anodes, the naturally formed SEI layer is weak against mechanical deformation, and it undergoes continuous formation and breakdown upon battery cycling. Together, the chemical and mechanical instabilities cause dendritic Li plating/stripping with low Coulombic efficiencies, which can constrain the cycle life of batteries and lead to shorting and potentially severe safety events. The high-surface area Li also enhances the kinetics of thermal reactions, effectively lowering the temperature at which thermal runaway can occur. Therefore, engineering a stable interface is an important task to achieve a stable and safe Li metal anode.
It is against this background that a need arose to develop embodiments of this disclosure.
In some embodiments, an anode includes: (1) a current collector; and (2) an interfacial layer disposed over the current collector. The interfacial layer includes a film of a layered material and a reinforcing material selectively disposed over certain regions of the film, while other regions of the film remain exposed from the reinforcing material.
In some embodiments, a battery includes: (1) the anode of the foregoing embodiments; (2) a cathode; and (3) an electrolyte disposed between the anode and the cathode.
In some embodiments, a method of forming an anode for a battery includes: (1) providing a current collector and a film of a layered material disposed over the current collector; and (2) performing atomic layer deposition to deposit a reinforcing material selectively on certain regions of the film, while other regions of the film remain exposed from the reinforcing material.
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.
In some embodiments of the Li battery 100, the anode 104 is a lithium metal anode, and includes a current collector 108 and an interfacial layer 110 disposed over and covering at least a portion of a major surface (e.g., a top surface) of the current collector 108, as shown in a schematic of
In some embodiments of the Li battery 100, the interfacial layer 110 is formed as a flexible film having a largely flat or planar configuration. The interfacial layer 110 separates or isolates lithium metal deposition and dissolution beneath the interfacial layer 110 from formation of a stable, conformal SEI above the interfacial layer 110. The interfacial layer 110 is loosely or weakly bound to the current collector 108 and can move up and down to adjust the availability of spaces during cycling. A top surface of the interfacial layer 110 is relatively static and allows the formation of the stable, conformal SEI, while lithium metal deposition takes place underneath, on the current collector 108.
In some embodiments of the Li battery 100, the interfacial layer 110 is formed as a hybrid or a composite of a film 112 of a 2D material having defect sites, and a coating 114 of a stitching or reinforcing material selectively or preferentially disposed over certain regions of the 2D material corresponding to the defect sites, while other regions of the 2D material remain exposed from the stitching material. As shown in
The presence of the stitching material selectively on defects sites is beneficial in improving overall physical and chemical stability of the hybrid film. Examples of suitable 2D materials include hexagonal boron nitride (h-BN), graphene, layered transition metal oxides and chalcogenides (e.g., MoS2), and other layered materials. A combination of different 2D materials is also contemplated. Suitable 2D materials can be single layered, or can include two or more stacked layers. In some embodiments, the film 112 of the 2D material is polycrystalline including crystalline domains or grains, and having defect sites corresponding to point defects (e.g., pinholes within one or more crystalline domains or grains) and line defects (e.g., boundaries between crystalline domains or grains). In some embodiments, the stitching material is selectively or preferentially disposed over regions of the 2D material corresponding to the defect sites, and can be in the form of nanostructures having at least one dimension in a range of about 1 nm to about 1000 nm, about 1 nm to about 500 nm, about 1 nm to about 300 nm, or about 1 nm to about 100 nm, such as nanoparticles having aspect ratios of about 3 or less, and nanowires having aspect ratios of greater than about 3. Examples of suitable stitching materials include compounds including at least one metal and at least one non-metal, such as metal halides (e.g., metal fluorides including alkali metal fluorides like lithium fluoride (LiF) and post-transition metal fluorides like aluminum fluoride (AlF3)), metal oxides (e.g., alkali metal oxides like lithium oxide (Li2O) and post-transition metal oxides like aluminum oxide (Al2O3)), and metal nitrides (e.g., alkali metal nitrides like lithium nitride (Li3N)). Mixed metal compounds including two or more different metals and at least one non-metal and mixed non-metal compounds including at least one metal and two or more different non-metals (e.g., lithium phosphorus oxynitride (LiPON)) are also encompassed by this disclosure. Other embodiments of the interfacial layer 110 having three-dimensional (3D) configurations are contemplated. For instance, instead of a planar configuration, 2D materials can be formed into 3D materials having 3D morphologies to attain enhanced specific areas for high current applications, and a stitching material can be disposed between boundaries of constituents of a 3D material and on defect sites within the constituents of the 3D material.
Other types of batteries are encompassed by this disclosure. For instance, some embodiments are directed to a sodium (Na) battery, which includes a cathode, an anode, and an electrolyte disposed between and in contact with the cathode and the anode. In some embodiments of the Na battery, the anode is a sodium metal anode, and includes a current collector and an interfacial layer disposed over and covering at least a portion of a major surface (e.g., a top surface) of the current collector. An anode material, which corresponds to sodium metal in some embodiments, is disposed between the current collector and the interfacial layer, and is deposited on the current collector during cycling.
Other embodiments are directed to a method of forming an electrode for a battery, such as an anode. In some embodiments, the method includes providing a current collector and a film of a 2D material disposed over and covering at least a portion of a major surface (e.g., a top surface) of the current collector. The film of the 2D material has defect sites. The method also includes performing atomic layer deposition to deposit a stitching or reinforcing material selectively or preferentially on certain regions of the 2D material corresponding to the defect sites, while other regions of the 2D material remain exposed from the stitching material.
In some embodiments of the method, providing the current collector and the film of the 2D material includes growing or forming the film of the 2D material, such as via chemical vapor deposition, on a substrate, and transferring the film of the 2D material from the substrate to the current collector.
In some embodiments of the method, the stitching material includes a compound including at least one metal and at least one non-metal, and performing atomic layer deposition includes sequentially performing a first atomic layer deposition cycle to introduce deposition gases including a chemical precursor or reactant including the metal, followed by performing a second atomic layer deposition cycle to introduce deposition gases including a chemical precursor or reactant including the non-metal. The first deposition cycle and the second deposition cycle can be repeated sequentially to deposit a desired amount of the stitching material. It is noted that the first deposition cycle can be repeated multiple times before the second deposition cycle, and that the second deposition cycle can be repeated multiple times before the first deposition cycle. It is also noted that either deposition cycle can be performed first.
Other embodiments are directed to a method of forming a metal layer. In some embodiments, the method includes providing a substrate and a hybrid film of a 2D material and a stitching material disposed over and covering at least a portion of a major surface (e.g., a top surface) of the substrate. The method also includes electrochemically depositing a metal (e.g., lithium, sodium, zinc, copper, or another metal) underneath the hybrid film to the form the metal layer between the hybrid film and the substrate.
The following example describes specific aspects of some embodiments of this disclosure to illustrate and provide a description for those of ordinary skill in the art. The example should not be construed as limiting this disclosure, as the example merely provides specific methodology useful in understanding and practicing some embodiments of this disclosure.
Defects are features in two-dimensional (2D) materials that can have a strong influence on their chemical and physical properties. With enhanced chemical reactivity at defect sites (e.g., point defects, line defects, and so forth), 2D materials can be selectively functionalized via chemical reactions to tune their properties. In this example, the selective atomic layer deposition of lithium fluoride (LiF) is performed on defect sites of hexagonal boron nitride (h-BN) prepared by chemical vapor deposition. The LiF deposited primarily on the line defects and point defects of h-BN, creating seams that hold h-BN crystallites together. The chemically and mechanically stable hybrid LiF/h-BN film successfully suppressed lithium dendrite formation during initial electrochemical deposition onto a copper foil and during subsequent cycling. The protected lithium electrodes were cycled more than 300 times with high Coulombic efficiency, in an additive-free carbonate electrolyte.
h-BN, a 2D atomic crystal, has emerged as an attractive material for various applications in electronics and optoelectronics, due to its unusual electrical and optical properties. In addition, it has superior chemical inertness, making it stable against most chemicals such as oxygen and Li metal. Perfect single atomic layer of h-BN has very strong mechanical strength with a predicted in-plane Young'"'"'s modulus approaching about 1.0 TPa. Due to these advantages, h-BN can be used as a stable coating that prevents metal oxidation at high temperature and suppresses lithium dendrite formation during electrochemical lithium metal plating. Many of the above-mentioned applications involve large-area and high-quality h-BN. While chemical vapor deposition (CVD) has emerged as one of the most powerful methods to prepare high-quality h-BN, CVD h-BN still has numerous defects intrinsic to the synthesis and transfer processes. H—BN prepared by CVD is typically polycrystalline and has a grain size on the order of a few hundred nanometers to a few tens of micrometers with a high density of point defects. Moreover, the transfer processes of 2D materials also introduce different kinds of defects such as cracks and wrinkles. These defects serve as a double-edged sword. On the one hand, their existence may compromise the effectiveness of h-BN as a stable interfacial layer in the above-mentioned applications. On the other hand, due to the strong B—N bonds, the pristine h-BN lattice is rather chemically inert; however, defects surrounded by dangling bonds provide possible anchoring sites for selective chemical modification to take place on h-BN. The defects can provide rich chemistry to tune the properties of h-BN.
Enhanced chemical reactivity can occur at the edge and defect sites in graphene, but such a case study of h-BN remains to be performed. The chemical functionalization at defect sites can greatly improve the chemical and mechanical stability of h-BN, which is especially important for h-BN when applications such as surface protection is of interest. For instance, grain boundaries can present mechanically weakened points, and therefore a single layer h-BN with small grain sizes has smaller elastic modulus and tensile strength compared to a defect-free, single crystalline, single layer h-BN. For multilayer and bulk 2D materials, degradation through chemical and electrochemical exfoliation also can occur.
With respect to using CVD h-BN as an interfacial layer, the weak bonding at the domain boundaries can present issues for maintaining the stable interface over long cycling. In this example, the selective atomic layer deposition (ALD) of LiF is performed on CVD h-BN and its application is proposed as a chemically and mechanically stable interfacial layer for stable Li metal cycling. The selective deposition, via ALD, allows deposition of LiF onto defect sites of CVD h-BN and void space where there is little or no h-BN coverage. The selectivity was confirmed by atomic force microscopy (AFM), Auger spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). LiF is a main component in SEI in Li-ion batteries and it has a wide electrochemical stability window, which makes it stable against Li metal. The addition of LiF can improve the stability of Li metal anode during cycling. Therefore, LiF is a desirable candidate to serve as molecular stiches that hold polycrystalline CVD h-BN domains strongly together using selective ALD. The chemically and mechanically stable hybrid LiF/h-BN film successfully suppressed lithium dendrite formation during initial electrochemical deposition onto a copper foil and during subsequent cycling. The protected lithium electrodes were cycled more than 300 times with high Columbic efficiency, in an additive-free carbonate electrolyte.
Polycrystalline h-BN was prepared in a custom-built CVD system using heated ammonia borane as the precursor at a growth temperature of about 1000° C. on copper (Cu) foils (see additional growth details in the methods section). The morphology and coverage of CVD h-BN on Cu can be carefully controlled by adjusting precursor feeding rates and growth durations. Single layer h-BN exhibited the typical triangular shape with short growth durations and h-BN triangle domains then merged to form a continuous film with longer growth durations (see supporting information). As-grown CVD h-BN was then transferred onto Si substrates with a poly(methyl methacrylate) (PMMA) support for further characterization.
ALD of LiF was carried out using lithium tert-butoxide and titanium fluoride (TiF4) as precursors at a growth temperature of about 250° C. (see additional deposition details in the methods section). It was performed on various substrates including pristine Si, Cu and stainless steel (SS). ALD has an ability to achieve a conformal coating. For instance, the ALD LiF film developed was highly uniform on pristine Si, Cu and SS substrates with just 50 ALD cycles (see supporting information). Conversely, the ALD LiF deposition on h-BN is selective and does not cover the entire substrate. For comparison, h-BN/Si before and after ALD LiF deposition was characterized by SEM (
To further analyze the LiF/h-BN hybrid film, morphologies and height profiles of single layer h-BN with and without ALD LiF deposition were examined by using AFM. Single layer h-BN film was about 1 nm higher than the Si substrate itself (
Nevertheless, observation is made of height gain on defect sites (highlighted by arrows in
To further verify the enhanced nucleation at the grain boundaries of h-BN, TEM characterization is employed to provide direct evidence. H—BN was suspended on a gold (Au) TEM grid with about 2 μm openings using a PMMA-assisted transfer method (see methods section). After annealing in Ar/H2 environment at about 380° C., the TEM grid with suspended h-BN was subjected to ALD LiF deposition directly. Consistent with SEM characterization, TEM confirmed the scattered LiF nucleation and preferred LiF nucleation along certain lines (highlighted by arrows). Here it is noted that the nucleation density of LiF on suspended h-BN observed in TEM was higher than the nucleation density of LiF on h-BN/Si observed in SEM. Such difference might be because LiF can nucleate on both sides of the suspended h-BN on the TEM grid compared to one side of h-BN on Si. The nucleation density of ALD LiF particles on suspended h-BN was about 3500 per μm2, indicating a high density of point defects. The nucleation density of LiF particles along grain boundaries was about two times higher (
With a Gibbs formation energy of about −587.7 kJ/mol, the thermodynamically stable electrochemical window of LiF is as wide as 0 to about 6.1 V vs. Li+/Li. Being a main component in SEI, LiF is also chemically stable against various reactive species in a battery including Li metal and HF. Therefore, LiF is a potential candidate to function as a stable interfacial layer. A possible concern of using LiF as a protection layer lies mainly in its poor Li ion conductivity. Nevertheless, such concern can be alleviated if an ultrathin layer or a composite layer can be obtained. Here, ALD provides a way to fine-tune a coating thickness of LiF thin films or a size of LiF nanoparticles to address the poor ionic conductivity of LiF.
Evaluation is made of the morphology of Li plating in additive-free carbonate electrolyte on various substrates using SEM. The Li plated on Cu exhibited the typical dendritic growth (
Compared to the nature of strong chemical binding between LiF and Cu, the physical interaction between h-BN and Cu is considerably weaker. For instance, 2D materials such as graphene can be lifted from a substrate via hydrogen generation. h-BN can be lifted by Li plated underneath. However, in spite of a high theoretical in-plane Young'"'"'s modulus, the grain boundaries are predicted to be the weak points of h-BN when tensile stress is applied. While starting with a seemingly continuous CVD h-BN film, holes appeared after Li plating (
Using the LiF/h-BN hybrid film as the interfacial layer combines the advantages of both components. First, the weak physical interaction between h-BN and Cu allows Li to be plated in between h-BN and Cu. Second, with the addition of chemically stable LiF linkers, the overall mechanical strength of LiF/h-BN was improved. It also helps to seal any pinholes or cracks induced in the CVD synthesis and transfer. The superior chemical and mechanical stability of the LiF/h-BN combination effectively suppressed the Li dendrite formation. The resulting electrochemical plating of Li is smooth and uniform (
Long-term Li plating/stripping experiments were also conducted on Cu, h-BN/Cu, LiF/Cu and LiF/h-BN/Cu substrates in an ethylene carbonate (EC)/diethyl carbonate (DEC) electrolyte with about 1 M LiPF6 containing no additives (
Among the three types of modified substrates, LiF/Cu had the poorest cycling performance, which was even worse than pristine Cu. As discussed above, the electrochemical Li plating on LiF/Cu was non-uniform across the substrate. Due to the poor conductivity of LiF and strong adhesion between LiF and Cu, the initial Li nucleation is difficult, leading to a high overpotential even though just a few nm of LiF was deposited (
In contrast, Li plating/stripping on h-BN/Cu was considerably more stable than on pristine Cu with both lower overpotentials and higher Coulombic efficiencies over long cycles. At the 2nd cycle, the initial nucleation barrier on h-BN/Cu was about 64 mV and the average Li plating overpotential was about 42 mV. The average Coulombic efficiency during the first 100 cycles was about 92.2%, which then dropped to about 70% after about 150 total cycles. As plating/stripping cycles progressed, h-BN layer may have slowly broken apart starting from defective sites and became exfoliated from the substrate, eventually losing its ability to reduce the side reactions between Li and the electrolyte.
Of note, LiF/h-BN/Cu stood out among the three types of modified substrates in the long-term cycle stability test. Benefiting from the weak interaction between h-BN and Cu, the Li plating readily took place underneath LiF/h-BN. At the 2nd cycle, the initial nucleation barrier on LiF/h-BN/Cu was about 60 mV and the average Li plating overpotential was about 47 mV (
To further analyze the Li deposition morphology, cross section SEM images were acquired after ten repeated plating/stripping cycles (
To summarize, demonstration is made of the selective atomic layer deposition of LiF at defect sites of h-BN with enhanced chemical reactivities. The selective deposition allows visualization of the location of defects in h-BN. The chemically and electrochemically stable LiF served as molecular stitches to seal the polycrystalline CVD h-BN. With its superior chemical and mechanical properties, the LiF/h-BN hybrid film effectively suppressed Li dendrite formation and improved the Coulombic efficiency of Li metal cycling during long cycles.
Materials Synthesis and Preparation
ALD LiF deposition was performed on different types of substrates including Si, SS, Cu, BN/Si, and BN/Cu using a Savannah S100 ALD system (Cambridge Nanotech). The deposition included alternating pulse and purge of lithium tert-butoxide (about 97%, Sigma Aldrich) and TiF4 (Sigma Aldrich) as precursors. TiF4 was subjected to gentle grinding in an argon (Ar) glove box prior to use. The typical pulse and purge durations for lithium tert-butoxide sub-cycle are about 1 s and about 25 s, respectively. The typical pulse and purge durations for TiF4 sub-cycle are about 0.1 s and about 25 s, respectively. Lithium tert-butoxide was heated to about 160-170° C. and TiF4 was kept at about 115-125° C. High purity Ar was used as the carrier gas and purging gas. LiF thin films were obtained at a deposition temperature of about 250° C.
h-BN was synthesized in a custom-built CVD system. Prior to the deposition, Cu foil (about 99.8% Alfa Aesar) was electrochemically polished by holding about 1.5 V vs. Cu counter electrode for about 60 minutes in a mixture of phosphoric acid (about 70 wt. %) and ethylene glycol (about 30 wt. %) electrolyte. After rinsing and blowing dry, Cu foil was annealed under about 35 Standard Cubic Centimeters per Minute (sccm) H2 and about 50 sccm Ar flow for about 30 minutes at about 1000° C. For the growth of h-BN, about 50 mg ammonia borane (H3N—BH3, about 97%, Sigma Aldrich) precursor was loaded into a glass tube attached to the deposition chamber. The precursor vapor was delivered to the deposition chamber when heated by a heating tape wrapping around the glass tube. The h-BN growth was carried out at about 1000° C. under about 35 sccm H2 and about 50 sccm Ar flow.
h-BN was transferred to various substrates including Si, SiO2 coated Si, Cu and TEM grid (Ted Pella, about 2 μm hole size) with PMMA support. A PMMA solution was spin-coated on the surface of the as-grown h-BN/Cu at the speed of about 500 rpm for about 60 s and about 4000 rpm for about 30 s. The backside of Cu foil was cleaned using 02 plasma and gently wiped with an isopropyl alcohol (IPA) soaked cotton stick. The sample was then placed into a solution of iron chloride to etch the underlying Cu foil. The PMMA/h-BN films were rinsed with a diluted hydrochloric acid solution and deionized water for three times each. The PMMA/h-BN films were picked up by desired substrates and dried at about 60° C. PMMA was removed by soaking in acetone and then in IPA. Finally, samples were annealed in about 10 sccm H2 and about 40 sccm Ar flow at about 380° C. for about 2 h to remove residual PMMA to obtain a clean h-BN surface.
AFM was performed using Park XE-70 system with ACTA tips. SEM images of LiF, h-BN and LiF/h-BN on various substrates were captured in a FEI XL30 Sirion. A Woollam M2000 Spectroscopic Ellipsometer was used for measuring and fitting optical properties and thicknesses of ALD LiF films on Si substrates. TEM characterization was performed at about 80 kV using a FEI Titan. After Li plating/stripping cycling, samples were rinsed in 1,3-dioxolane (DOL) to remove residual electrolyte and salt for SEM imaging. The morphology of plated Li was observed with a focused ion beam (Nova 600i Dual Beam, FEI). The cycled electrodes were cross-sectioned with a Ga+ ion beam and observed with SEM (JSM-6700F, JEOL).
Battery cycling performance was evaluated by galvanostatic cycling of coin cells (CR 2032) with Cu, LiF/Cu, h-BN/Cu and Li/h-BN/Cu as the working electrodes and Li foils (Alfa Aesar) as the counter electrodes. The working electrodes and the counter electrodes were cut into round disks with a diameter of about 1 cm and separated by two layers of Celgard separators. About 30 μL solution of about 1 M LiPF6 in about 1:1 (v:v) ethylene carbonate (EC) and diethyl carbonate (DEC) (BASF) was added as the electrolyte. No additional additive was added into the electrolyte. Battery cycling data was collected using a LAND 8-channel battery tester at room temperature. After assembly, coin cells were galvanostatically cycled between 0 V and about 2 V at about 50 μA/cm2 for five cycles. Battery cycling was then performed by controlling about 1 mAh/cm2 areal capacity for Li plating and a cut off potential of about 2 V vs. Li+/Li for Li stripping during each cycle. The Coulombic efficiency was specified as the Li stripping capacity divided by the Li plating capacity.
The morphology of h-BN films can be controlled by adjusting precursor feeding rates and growth durations. Using ammonia borane (H3N—BH3) as the precursor, its feeding rate is a function of precursor heating temperature. At a low precursor heating temperature, the slow feeding of precursor leads to h-BN with large domain sizes, or vice versa (
ALD of LiF was carried out using lithium tert-butoxide and titanium fluoride (TiF4) as precursors at a growth temperature of about 250° C. ALD can achieve a conformal coating. For instance, the ALD LiF film developed was highly uniform on the pristine Si substrate (
The amount of LiF deposition can be controlled by varying ALD cycle numbers.
50 ALD cycles of LiF deposition were performed on both SS and Cu substrates with high uniformity across large areas. As shown in
Li metal is highly reactive and changes color when it reacts with H2O, CO2 and N2 in the ambient air. A perfect LiF/h-BN film coverage could in-principle prevent Li from reacting with air, and therefore keep Li metal'"'"'s original metallic color. As shown in
As used herein, the singular terms “a,” “an,” and “the” may include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to an object may include multiple objects unless the context clearly dictates otherwise.
As used herein, the terms “substantially,” “substantial,” 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, when used in conjunction with a numerical value, the terms can encompass a range of variation of less than or equal to ±10% of that numerical value, 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%.
As used herein, the term “size” refers to a characteristic dimension of an object. Thus, for example, a size of an object that is circular or spherical can refer to a diameter of the object. In the case of an object that is non-circular or non-spherical, a size of the object can refer to a diameter of a corresponding circular or spherical object, where the corresponding circular or spherical object exhibits or has a particular set of derivable or measurable characteristics that are substantially the same as those of the non-circular or non-spherical object. When referring to a set of objects as having a particular size, it is contemplated that the objects can have a distribution of sizes around the particular size. Thus, as used herein, a size of a set of objects can refer to a typical size of a distribution of sizes, such as an average size, a median size, or a peak size.
As used herein, an “alkali metal” refers to an element from Group 1 of the Periodic Table, encompassing lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).
As used herein, a “post-transition metal” refers to an element from a set encompassing aluminum (Al), gallium (Ga), indium (In), tin (Sn), thallium (Tl), lead (Pb), bismuth (Bi), and polonium (Po).
Additionally, amounts, ratios, and other numerical values are sometimes presented herein in a range format. It is to be understood that such range format is used for convenience and brevity and should be understood flexibly to include numerical values explicitly specified as limits of a range, but also to include all individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly specified. For example, a range of about 1 to about 200 should be understood to include the explicitly recited limits of about 1 and about 200, but also to include individual values such as about 2, about 3, and about 4, and sub-ranges such as about 10 to about 50, about 20 to about 100, and so forth.
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 are not a limitation of this disclosure.