Patent Description:
Lithium metal has an extremely high chemical reactivity, which poses critical challenges to its use in commercial batteries. It is naturally unstable in almost all electrolytes and spontaneously forms fragile, nonuniform and insulating solid-electrolyte interfaces (SEI). These result in uneven Li-ion flux which accelerates the growth of dendrites along with lithium metal corrosion and electrolyte decomposition. The stabilization of lithium metal has been under intensive study, and to date, most of the efforts have focused on the development of three-dimensional structural hosts that effectively reduce local current densities, surface protective or interfacial layers, and novel electrolytes or additives to promote stronger SEI. The application of physical layers including solid-state electrolytes and polymer electrolytes are also used to prevent detrimental side-reactions. Although these approaches assist in lithium metal electrodes with better stability, it is still very challenging to obtain stabilized cycling under high current densities and high cycling capacities. In addition, these methods rarely attempt to modulate the fundamental properties of metallic lithium, and therefore the performance improvements are still limited by its intrinsic reactivity.

<CIT> mentions an anode comprising a Li-Z alloy assembled onto a substrate, wherein Z is a metal or semiconductor. <CIT> mentions a Li-Al alloy for a battery anode. <CIT> mentions Li-Al tape for a battery anode.

The invention is defined according to the claims. Thus, the invention provides an anode, comprising: lithium metal, and a dopant, in the lithium metal, wherein the doped lithium is in the form of a foil having a thickness of at most <NUM>, the dopant is selected from the group consisting of aluminum, silver, gold, platinum, tin, bismuth, copper, indium, zinc, nickel and mixtures thereof, the dopant is present in an amount of <NUM> to <NUM> atomic percent, and the anode does not contain intermetallic compounds comprising lithium and the dopant.

In one embodiment, the dopant: (a) is present in an amount of at most <NUM> atomic percent; (b) is present in an amount of <NUM> to <NUM> atomic percent; (c) is a metal selected from the group consisting of: aluminum, silver, gold, platinum and tin; and/or (d) comprises aluminum or silver.

In one embodiment, the anode: (a) has a thickness of at most <NUM>; and/or (b) demonstrates stability in dry air.

In one embodiment, the anode passes the improved charge transport test.

In one embodiment, the dopant is present in an amount of <NUM> to <NUM> atomic percent, the anode has a thickness of at most <NUM>, and the dopant comprises silver.

The invention also provides a battery comprising: the anode of the invention, an anode charge collecting element in contact with the anode, a cathode, a cathode charge collecting element in contact with the cathode, and an electrolyte in contact with the anode and the cathode, and a housing, enclosing the anode, anode charge collecting element, cathode, cathode charge collecting element and electrolyte, wherein the anode comprises lithium metal doped with a dopant, and the dopant is present in an amount of <NUM> to <NUM> atomic percent.

In one embodiment, the battery further comprises a separator; optionally wherein the separator comprises a material selected from a group consisting of: cotton, nylon, polyesters, glass, polymer films, ceramic, rubber, asbestos and wood.

In one embodiment, (a) the electrolyte is liquid; (b) the cathode comprises a material selected from the group consisting of: sulfur compounds, cobalt compounds, graphite, nickel compounds, manganese compounds, oxides, iron compounds and mixtures thereof; and/or (c) the anode charge collecting element and the cathode charge collecting element comprise a material independently selected from the group consisting of: copper, aluminum, steel and combinations thereof.

In one embodiment, the electrolyte comprises: a salt, selected from the group consisting of: LiPF<NUM>, lithium bis(trifluoromethane)sulfonimide and mixtures thereof, and a solvent, selected from the group consisting of carbonates, ethers and mixtures thereof.

In one embodiment, the salt comprises LiPF<NUM>, the solvent comprises EC/DMC, and the cathode comprises NMC811.

The invention also provides a method of making the anode of the invention, the method comprising: melting lithium metal, introducing a dopant metal into the lithium metal to form molten doped lithium metal, solidifying the doped lithium metal, and forming the doped lithium metal into a foil having a thickness of at most <NUM>.

The invention also provides a method of generating electrical power with the battery of the invention, the method comprising: connecting the anode and cathode of the battery to an external load to complete a circuit.

In one embodiment, the battery retains at least <NUM>% capacity after <NUM> cycles.

The invention also provides a method of forming a battery, the method comprising: forming an anode by a method of the invention, and assembling the battery from the anode, wherein the assembling is carried out in air.

In one embodiment, the method of recharging the battery comprises connecting the battery to an electrical power source.

A "cell" is basic electrochemical unit that contains the electrodes, separator, and electrolyte.

A "battery" is defined as a collection of cells or cell assemblies, with housing, electrical connections, and optionally additional elements for protection or control.

A "dopant" refers to any metal additive that does not form intermetallic compounds with the primary metal in the amount used. As defined in the claims, the anodes of the invention comprise a dopant selected from the group consisting of aluminum, silver, gold, platinum, tin, bismuth, copper, indium, zinc, nickel and mixtures thereof.

"Anode" refers to the electrode where oxidation takes place during the discharge cycle. The anode may be one continuous body, or it may include more than one thin film attached to a current collecting element.

"Cathode" refers to the electrode where reduction takes place during the discharge cycle. The cathode may be one continuous body, or it may include more than one thin film attached to a current collecting element.

"Separator" refers to a barrier between the cathode and the anode to prevent them from coming into contact. If the electrolyte is solid, a separator is not necessary to avoid contact between the anode and cathode.

"Electrolyte" refers to a solution containing a solvent and ions, which conducts ions but is an insulator to electrons. An electrolyte may be a liquid, solid, or gel.

"Cycle" refers to the process of charging a rechargeable battery and discharging it as required into a load. The term is typically used to specify a battery's expected life, as the number of charge cycles affects life more than the mere passage of time.

The "rate of discharge" refers to the rate at which a battery would theoretically fully charge or discharge the battery in one hour. The rate of discharge is abbreviated as the "C rate" or "C". For example, trickle charging might be performed at C/<NUM> (or a "<NUM> hour" rate), while typical charging and discharging may occur at C/<NUM> (two hours for full capacity).

All percentages refer to atomic percentage, unless otherwise specified. Where the dopant percentage is not specified, the atomic percent of dopant is <NUM> percent.

The addition of dopants as trace impurities is a powerful approach for altering the electrical or optical properties of a substrate, and has been widely demonstrated in fields such as solid-state electronics and lasers. The present invention describes anodes of lithium metal doped with trace amounts of a dopant, selected from silver, aluminum, gold, platinum, tin, bismuth, copper, indium, zinc, nickel and mixtures thereof. The doped metal exhibits enhanced chemical stability and much better electrochemical reactivity. The introduction of dopants significantly increased its stability as the doped anode remained shiny with no degradation in electrochemical activity after exposure to dry air for months. The doped lithium metals as the anode exhibited more stable cycling compared to pristine lithium, with less change in battery capacity as the number of battery cycles increases. The doped lithium metals exhibited very fast electrochemical kinetics, with at least ten times higher exchange current densities at room temperature and become even faster at elevated temperatures. The doped metals also had substantially improved stability and enabled high-capacity and dendrite free battery cycling in both carbonate and ether electrolytes, demonstrating that these doped metals would be suitable for use in a variety of battery systems. The doped lithium anode also demonstrated success when paired with a sulfur cathode or a nickel-manganese-cobalt oxide (NMC811) cathode.

<FIG> illustrates a thin film anode, <NUM> comprising lithium metal and a dopant. <FIG> illustrates a diagram of the crystal structure of lithium, <NUM>, doped with a dopant, <NUM>.

The dopant in anodes of the invention is selected from aluminum, nickel, copper, zinc, silver, indium, tin, platinum, gold, bismuth, and mixtures thereof. Preferably the dopant is aluminum, silver, platinum, tin or gold. Most preferably the dopant is aluminum or silver.

The anode of the present invention includes lithium metal doped with a dopant. The dopant is present in an amount of <NUM> to <NUM> atomic percent, including <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. The dopant does not form intermetallic phases, and is present interstitially or replaces a lithium atom in the lithium crystal structure.

The doped lithium is in the form of a foil with a thickness of at most <NUM>. Preferably the foil has a thickness of less than <NUM>, including <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM>. Most preferably, the foil has a thickness of at most <NUM>.

The anode demonstrates stability in dry air. To demonstrate stability in dry air, an anode must show less than <NUM>% surface tarnish after <NUM> days of exposure to dry air (relative humidity <<NUM>%).

The doped anode also demonstrates improved charge transport at the anode/electrolyte interface, compared to an anode of pristine lithium. The diffusion coefficient of the doped anode may be <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> times greater than the diffusion coefficient of a pristine lithium anode. The doped anode shows an increasing diffusion coefficient, compared to pristine lithium, as the temperature increases, as shown in <FIG>. The temperature of the anode may be <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>. Preferably the doped anode demonstrates a diffusion coefficient that is at least ten times greater than the diffusion coefficient of pristine lithium. The doped anode preferably passes the improved charge transport test, which requires the doped anode to have a diffusion coefficient that is at least ten times greater than the diffusion coefficient of a pristine lithium anode, when the diffusion coefficients of the two anodes are tested with <NUM> LiPF<NUM> in ethylene carbonate/diethyl carbonate (EC/DEC) as the electrolyte.

Optionally, the anode may be incorporated into a battery, having a cathode, electrolytes and a housing. The battery may also include charge collecting elements on the anode and cathode to gather or distribute the electrons. The charge collecting elements may be connected to an external circuit that is optionally connected to a load or to a recharging source.

<FIG> illustrates a battery, <NUM>. The battery has an anode, <NUM> and a cathode, <NUM>. The anode and cathode are rolled up, and a separator, <NUM>, is between the cathode and anode. The battery has a positive terminal, <NUM> and a negative terminal <NUM>. The battery is enclosed in a housing, <NUM>.

<FIG> illustrates a schematic of a battery, <NUM>. The battery has a cathode, <NUM>, illustrated as thin film strips, attached to a cathode charge collecting element, <NUM>. The anode, <NUM> is attached to an anode charge collecting element, <NUM>. A separator, <NUM> is positioned between the anode and cathode. The electrolyte, <NUM> is in contact with the anode and cathode, and allow for the movement of ions, <NUM> between the anode and cathode.

In a lithium-ion battery, the lithium ions move from the anode to the cathode during discharge and in the opposite direction during recharge. The electrolyte carries positively charged lithium ions from the anode to the cathode and vice versa through the separator. The movement of the lithium ions creates free electrons in the anode which creates a charge at the anode current collecting element. The electrical current then flows from the current collector on the cathode, through a load (device being powered), to the current collecting element on the anode. When the battery is being recharged the electrons and ions flow in the opposite directions.

Preferably the battery maintains a capacity of at least <NUM>% of the battery's initial capacity after <NUM> cycles. The battery may retain a capacity of <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>% and <NUM>% of the battery's initial capacity after <NUM> cycles. Most preferably the battery maintains a capacity of at least <NUM>% of the initial capacity. Preferably the battery maintains a capacity of at least <NUM>% of the battery's initial capacity for <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM> cycles.

The cathode of the battery preferably comprises sulfides, cobalt compounds, graphite, nickel compounds, manganese compounds, oxides, and iron compounds, in combination or alone. LiCoO<NUM> and LiMn<NUM>O<NUM> are two of the most common cathode materials used in lithium ion batteries. The cobalt material has a high theoretical specific heat capacity, high volumetric capacity, low self-discharge, high discharge voltage, and good cycling performance. The manganese cathodes are attractive because manganese is cheaper than cobalt. The cathode may also be made of nickel manganese cobalt (NMC), nickel cobalt aluminum (NCA), or lithium iron phosphorus (LiFePO or LFP). One skilled in the art would appreciate that the ratios of the cathode component elements may be optimized to improve the desired characteristics. An example of a high capacity cathode is NMC811, which means a cathode made of <NUM>% nickel, <NUM>% manganese, and <NUM>% cobalt. Cathodes and cathode materials are described in Bensalah N, Dawood H (<NUM>) Review on Synthesis, Characterizations, and Electrochemical Properties of Cathode Materials for Lithium Ion Batteries. J Material Sci Eng <NUM>: <NUM>.

Another cathode material of interest is sulfur. Lithium-sulfur batteries have advantages over lithium-ion cells because of their higher energy density and reduced cost from the use of sulfur. Sulfur has low conductivity, so the sulfur cathodes may also be paired with a highly conductive material to improve the conductivity. A carbon coating may be used to provide the missing electroconductivity. Sulfur based electrodes include copolymerized sulfur, sulfur-graphene oxide, and sulfur/lithium-sulfide. Preferably the sulfur cathode comprises a dimethylformamide (DMF) slurry containing Ketjen-Black carbon/sulfur composite (<NUM> wt% of sulfur), carbon black (SUPER-P®) and polyvinylidene fluoride (PVDF) in a mass ratio of <NUM>:<NUM>:<NUM>. Preferably the cathode is formed on aluminum foils as the cathode current collector.

Separators are preferred components in liquid electrolyte batteries. In the case of a liquid electrolyte, the separator is a foam material that is soaked with the electrolyte and holds it in place. The separator needs to be an electronic insulator while having minimal electrolyte resistance, maximum mechanical stability, and chemical resistance to degradation in the highly electrochemically active environment. In addition, the separator often has a safety feature, called "thermal shutdown;" at elevated temperatures, it melts or closes its pores to shut down the lithium-ion transport without losing its mechanical stability. Separators are either synthesized in sheets and assembled with the electrodes or deposited onto one electrode in situ. A separator generally includes a polymeric membrane forming a microporous layer. The separator may be made from nonwoven fibers, such as cotton, nylon, polyesters, glass; polymer films, such as polyethylene, polypropylene, poly (tetrafluoroethylene), polyvinyl chloride; ceramic; and naturally occurring substances, such as rubber, asbestos, or wood. Separator materials are described in <NPL>.

The electrolyte provides a medium for the transport of the lithium ions from the cathode to the anode and vice versa. Types of electrolytes include liquid, polymer, and solid-state electrolytes. Liquid electrolytes in lithium-ion batteries include salts, such as LiPF<NUM>, LiBF<NUM>, and LiClO<NUM>, and a solvent, such as ethylene carbonate, dimethyl carbonate, and diethyl carbonate. The selection of the electrolyte may be influenced by the selection of the cathode material. One skilled in the art would select an appropriate electrolyte, an appropriate electrolyte volume, and an appropriate electrolyte concentration based on the cathode material, separator material, anode material, and cell design. The concentration of the electrolyte may be <NUM> to <NUM>, including <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. Preferably the concentration of the electrolyte is <NUM>-<NUM>. Preferably the electrolyte is LiPF<NUM> in ethylene carbonate/dimethyl carbonate (EC/DMC) or LiPF<NUM> in ethylene carbonate/diethyl carbonate (EC/DEC). The ratio of the ethylene carbonate to dimethyl carbonate or diethyl carbonate is preferably <NUM>:<NUM> by volume. Another preferred electrolyte in batteries having a sulfur cathode is lithium bis(trifluoromethane)sulfonimide (LiTFSI) in dioxolane/dimethoxyethane (DOL/DME); around <NUM>% LiNOs may be added to improve coulombic efficiency.

The electrolyte may be a solid, such as a ceramic. Solid electrolytes avoid the risk of leaks, and a separator is not necessary as the solid electrolyte prevents contact between the anode and the cathode. Solid ceramic electrolytes are mostly lithium metal oxides. Ceramic solid electrolytes are highly ordered compounds with crystal structures that usually have ion transport channels. Common ceramic electrolytes are lithium super ion conductors (LISICON) and perovskites. Solid electrolytes are described in <NPL>.

The current collecting element collects the electrons from the anode during discharge, prior to the electrons entering the external circuit. The current collecting element on the cathode will distribute the electrons to the cathode material. During recharging the electrons move in the opposite direction. The current collecting elements may comprise aluminum, copper, steel, or other conductive materials.

The housing encloses the battery and prevents the electrolyte for leaking. The housing may comprise metal or plastics. The housing may be rigid or flexible. Flexible housing materials allows for expansion of the cell during recharging, or for expansion caused by gas formation inside the battery. Battery structures and manufacturing techniques are described in <NPL>).

The battery shape and design may be selected from various shapes to optimize the battery and avoid overheating, increase energy density, or reduce self-discharge. Common battery designs include small cylindrical (solid body without terminals, such as those used in older laptop batteries), button cells, prismatic cells, large cylindrical (solid body with large threaded terminals), pouch (soft, flat body, such as those used in cell phones and newer laptops; also referred to as Li-ion polymer or lithium polymer batteries), and rigid plastic case with large threaded terminals (such as in electric vehicles).

The doping of lithium metal was performed inside an argon-filled glovebox, and as a general procedure, <NUM> of lithium was slowly melted at <NUM> in a nickel crucible. Then the dopant metal (in the form of bulk wire) was immersed to the molten lithium where it dissolves in a few seconds. The mixture was kept at <NUM> for <NUM> hours to ensure complete homogenization. The doped molten lithium was then quenched to room temperature and a piece of doped lithium lump was obtained, which was pressed into foils with a thickness of <NUM> or <NUM> using a rolling press for battery assembly. These foils were cut into <NUM> discs for investigation of their properties and electrochemical behavior. To ensure proper comparison, the identical procedure was used to process the undoped lithium electrodes.

Lithium based binary phase diagrams were used to rationally select the dopant and the molar ratio (<FIG>), and focused on the use of silver as the dopant as it has a similar atomic radius as Li (<NUM>Å for Ag vs <NUM>Å for Li) and they both commonly assume the +<NUM> oxidation state. The molar ratio was varied from <NUM>% to <NUM>% to ensure complete solvation of silver atoms without forming alloy phases. In addition to silver, lithium metals doped with aluminum, tin, platinum, gold and palladium were also prepared and studied.

Electrochemical studies were performed using <NUM>-coin cells. Cyclic voltammograms were recorded using a CH Instruments potentiostat. Battery cycling and rate behavior were evaluated using Neware CT-<NUM> battery analyzers. Electrochemical impedance measurements were conducted at room temperature using a Gamry Reference <NUM> potentiostat with a frequency range of <NUM> to <NUM>. The symmetric cells were assembled using lithium metal anodes of identical composition using either <NUM> lithium bis(trifluoromethane)sulfonimide (LiTFSI) in dioxolane/dimethoxyethane (DOL/DME; <NUM>:<NUM> vol) or <NUM> LiPF<NUM> in ethylene carbonate/diethyl carbonate (EC/DEC, <NUM>:<NUM> vol). The electrolyte volume was <NUM>µl. Two types of cathodes were used to evaluate prototype lithium metal batteries. The NCM-<NUM> electrodes (~ <NUM> cm-<NUM>) were supplied by the Cell Analysis, Modeling, and Prototyping Facility at Argonne National Laboratory. The electrodes were punched into <NUM> discs and dried at <NUM> under vacuum overnight before use. The batteries were cycled initially <NUM> C for <NUM> cycles at and then cycled at <NUM> C for <NUM> cycles, with a voltage window of <NUM> to <NUM> V. A combination of constant current and constant voltage charging protocol was used for the cycling at <NUM> C, and when the voltage reached <NUM>. 3V, the battery was held at <NUM> V until the charging current decreased to the value equivalent to <NUM> C (<NUM> C = <NUM> mA/cm<NUM>). The sulfur electrodes (~ <NUM>/cm<NUM> loading) were prepared by casting a dimethylformamide (DMF) slurry containing Ketjen-Black carbon/sulfur composite (<NUM> wt% of sulfur), SUPER-P® and PVDF in a mass ratio of <NUM>:<NUM>:<NUM> on aluminum foils. The sulfur electrodes were also dried under vacuum and cut to <NUM> discs. The batteries were cycled at room temperature between <NUM> and <NUM> V.

The X-ray diffraction (XRD) of doped lithium metals electrodes with silver and aluminum at different molar ratios all exhibited peaks that can be indexed to the body-centered cubic structure of lithium crystals (lm-<NUM>) and no alloy phases were identified (<FIG>), which reveals the dopant is incorporated uniformly in the lithium crystal structure. XRD measurements were carried out on a Rigaku MiniFlex X-ray diffractometer operating at <NUM> kV and <NUM> mA, using Cu Ko radiation (λ=<NUM>). SEM images were collected using a Tescan Vega II microscope and the EDX spectra were collected using a INCAx-act Analytical EDS detector (Oxford Instruments). The electrodes were washed inside a glovebox and vacuum dried prior to analysis. The XPS spectra were collected using a Kratos AXIS Ultra DLD spectrometer. The binding energies were calibrated using the C <NUM> peak at <NUM> eV.

These experiments study the changes to the physiochemical properties of lithium metal via heteroatom doping, without introducing alloy phases. One significant feature of these results is the dramatic changes in the relative intensity of the (<NUM>) and (<NUM>) peaks. Curve fitting of the changes in the X-ray diffraction suggest the dopants occupy vacant face-centered sites in the body centered cubic crystal structure of metallic lithium. Importantly, this effect is most pronounced for the electrodes with <NUM>% Ag and the peak ratio was <NUM>:<NUM>, as opposed to the <NUM>:<NUM> of pristine lithium electrodes. Similar results were obtained with aluminum doped electrodes.

The silver doped lithium (at <NUM> atomic percent) electrodes have significantly improved stability in dry air (relative humidity <<NUM>%), which is in strong contrast to the case of pristine lithium electrodes where they react readily and form insulating nitride/oxide surface layers. The comparison of surface tarnishing percentage estimated from optical analysis reveals that the Ag doped lithium remained shiny without black tarnish for weeks whereas the pristine lithium metal is completely covered with black tarnish within a few days (<FIG>). The changes in Li+/Li transport properties of doped and pristine lithium electrodes after various days of exposure was compared via electrochemical impedance spectroscopy (EIS) using symmetric coin cells (<FIG>). The charge-transfer resistance (Rct) of the silver doped lithium electrodes only increased slightly after <NUM> days of exposure (<NUM> to <NUM>Ω cm-<NUM>), as opposed to the at least <NUM> times increase in pristine lithium electrodes within only two days. As expected, the SEM analysis confirms the surface of doped lithium remained dense without evident corrosion pits while pristine lithium become very porous (<FIG>). Importantly, the substantially enhanced dry-air stability as a result of silver doping would enable the integration of doped lithium electrodes in conventional manufacturing process without additional surface protection.

The effect of the dopants on the fundamental electrochemical behavior of lithium metal was examined using EIS, and the charge transport properties at the metallic Li/electrolyte interphases was quantified. <FIG> compares the Nyquist plot of symmetric coin cells composed of identical electrodes (doped or pristine lithium) and the <NUM> LiPF<NUM> in EC/DMC electrolytes. These spectra were fitted using the equivalent circuit model to decouple the Rct and DLi+ (Li+ ions diffusion coefficient). All of the doped Li electrodes exhibited smaller Rct and higher DLi+ compared with pristine lithium electrodes (<FIG>), implying that the doping effectively promoted charge transport at the electrode interface. Notably, the <NUM> percent silver doped lithium electrode has the fastest kinetics, evidenced with the lowest Rct and highest Du+ (<NUM> ×<NUM>-<NUM> cm<NUM> s-<NUM>) that are approximately <NUM> and <NUM> times compared with pristine lithium electrodes, respectively. The interfacial transport of doped lithium electrodes become even faster as the temperature was increased, and the DLi+ was more than <NUM> times higher than pristine lithium at <NUM>. These results demonstrate that the doped lithium electrodes have promoted ion transport and suggesting intrinsic higher electrochemical activity due to the incorporation of dopant.

The electrochemical behavior of the symmetric <NUM> atomic percent Ag doped lithium electrodes were further evaluated using cyclic voltammetry (CV) in the voltage range of -<NUM> to <NUM> V. They show typical Li+/Li polarization curves and no redox peaks attributable to side-reactions were observed, confirming the silver dopants didn't affect the redox properties of metallic lithium. The polarization curves from the doped electrodes have markedly higher slopes, which indicates promoted redox kinetics that agree with EIS results discussed above. The current-overpotential data of these CV results were analyzed using the Tafel relationship and the exchange current densities were estimated. The Li+/Li exchange current for the pristine and doped lithium electrodes with <NUM>, <NUM> and <NUM> percent of silver were <NUM>, <NUM>, <NUM> and <NUM> mA cm-<NUM>, respectively, which confirms that the lithium doped with <NUM> percent silver has the best kinetics. Such differences were more pronounced at elevated temperatures, and the exchange current at <NUM> for <NUM> percent silver doped lithium was more than twenty times higher than pristine lithium (<NUM> vs. <NUM> mA cm-<NUM>). Since the most pronounced results were obtained from electrodes with <NUM> percent silver doping, this sample was studied in detail as discussed below and will be referred as Ag-Li hereafter.

The doped lithium electrodes enabled more robust lithium metal batteries as observed with substantially improved interphasical stability in both carbonate and ether electrolytes and prototype metal batteries. <FIG> demonstrates that the Ag-Li electrodes have sustained stable cycling in a symmetric configuration at a practical current density of <NUM> mA cm-<NUM> and a capacity of <NUM> mAh cm-<NUM> (<NUM><NUM> electrode). The cell exhibited very stable profiles with no sudden voltage drops or spikes during the <NUM> hours of cycling, which is in sharp contrast of pristine lithium electrodes that exhibit clear failure within <NUM> hours. Similar stability was also observed with the cycling of symmetric cells at <NUM> and <NUM> mA cm-<NUM>. <FIG> illustrate the behavior of lithium metal batteries in which the lithium anodes were paired with the state-of-the art intercalation cathode LiNi<NUM>Mn<NUM>Co<NUM>O<NUM> (NMC <NUM>) with a loading of <NUM> mAh cm-<NUM> (<NUM> mAh per electrode). As expected, the Ag-Li anode afforded significantly improved stability and a capacity retention of <NUM>% is observed over <NUM> cycles at <NUM> C and the coulombic efficiency (CE) maintained at nearly unity. In contrast, the control battery with pristine lithium electrode only had <NUM>% of retention and rapid capacity decays after ~ <NUM> cycles were commonly observed, which is now widely accepted as lithium metal failure.

The impedance analysis of these batteries during cycling (<FIG>) reveals that the Ag-Li anode maintained stabilized interface, and the increases in Rct was only ~ <NUM>% (<NUM> to <NUM>Ω cm-<NUM>) whereas the pristine lithium anode increased to a much higher value of <NUM>Ω cm-<NUM> during the <NUM> cycles. Post-mortem XRD analysis of the lithium electrodes reveals that the cycled Ag-Li anode only has diffraction peaks from crystalline Li (<FIG>), as opposed with the strong peaks from crystalline Li<NUM>O and LiF generated on the pristine lithium electrode. The SEI layers formed on Ag-Li electrode have a flat surface morphology and were much thinner compared to the pristine lithium (<FIG>). The SEI layers formed on Ag-Li electrode appeared very dense, did not have a porous structure, and adhered to the underlying metallic lithium strongly. These results agree with the stable Rct observed with EIS. The XPS analysis of the SEI layers (<FIG>) reveals substantial levels of silver compounds that includes AgF, AgO and AgPx, and likely these compounds contributed to the formation of stabilized SEI.

In addition to lithium electrodes with ~ <NUM> thickness, we explored the possibility of using ~ <NUM> electrodes that are required to implement a high-energy Li metal battery (anode/cathode capacity ratio is ~ <NUM>:<NUM>). The Ag-LiINMC cells in this case were able to cycle stably for over <NUM> cycles, whereas the control cell with pristine lithium quickly failed within <NUM> cycles.

The Ag-Li electrodes also exhibited substantially improved stability in the ether electrolyte for Li-S batteries (<NUM> LiTFSI in DOUDME). <FIG> shows the voltage profile of Ag-Li and lithium symmetric cells with <NUM><NUM> electrodes that were cycled at <NUM> mA cm-<NUM> for a high capacity of <NUM> mAh cm-<NUM> each cycle. The Ag-Li electrodes show very stable voltage profile along with nearly no voltage fluctuations, as opposed to the pristine lithium electrodes that failed within <NUM> hours as signaled by sharp increases in overpotential. <FIG> shows the performance of Ag-Li anodes cycled with conventional sulfur cathodes prepared with sulfur impregnated in KB carbon black (<NUM> cm-<NUM> sulfur loading). These cathodes were used because they slowly release soluble lithium polysulfide to the electrolyte and create harsh conditions at the lithium metal anode, and therefore are a better system for examining lithium metal stability. These cells were cycled at a rate of <NUM> C, and the cell with Ag-Li anode delivered much better cyclic stability, with an overall retention of <NUM>% while the cell with pristine lithium electrode only retained <NUM>% under the same condition (<FIG>). Post-mortem SEM analysis of the cycled lithium electrode confirms the outstanding cyclic stability of the Ag-Li, and its surface remained dense without formation of porous or dendritic structures (<FIG> compares the voltage profiles of the doped and pristine lithium anodes in this system. While initially the doped and pristine lithium have identical profiles, after <NUM> cycles the voltage profiles differ greatly, with the doped lithium voltage profile being more similar to the initial voltage profiles than the pristine lithium.

<FIG> demonstrates that dopants of silver, gold, and aluminum each improve the stability of a lithium anode. The anodes of <FIG> were paired with a cathode of NMC-<NUM> (<NUM> mAh per electrode) and the electrolyte was LiPFs in EC/DEC. As the number of cycles increased, lithium doped with aluminum, silver and gold all display a greater retention of their specific capacity compared to pristine lithium.

<FIG> demonstrates that doped lithium anodes improve stability in Li-S batteries. Li-S batteries using anodes of lithium doped with aluminum or silver maintained their capacity more than pristine lithium. After <NUM> cycles the Li-S battery with pristine lithium only retained <NUM>% of its initial capacity. In comparison, Li-Ag and Li-Al retained <NUM>% and <NUM>%, respectively, after <NUM> cycles.

<FIG> shows the initial voltage profiles of lithium metal batteries that use a S@Fe<NUM>O<NUM>-NC cathode paired with an aluminum doped lithium anode, a silver doped lithium anode, and a pristine lithium anode. The S@Fe<NUM>O<NUM>-NC cathode includes sulfur, nitrogen doped carbon, and Fe<NUM>O<NUM> (see, citation [<NUM>] to Lu et al. <FIG> also shows the initial voltage profile of a battery with a pristine lithium anode and a Ketjen black carbon (KBC) cathode. <FIG> demonstrates that cells using the doped lithium metal retained a much greater percentage of their initial capacity compared to the batteries using pristine lithium metal as the anode. The batteries using the S@Fe<NUM>O<NUM>-NC cathode also exhibited improved capacity retention compared to the KBC cathode.

The cells using doped lithium metal as the anode also have less resistance change after the battery is cycled. <FIG> show that aluminum doped lithium anode cells have nearly no change in the resistance after <NUM> cycles. <FIG> also show that aluminum doped lithium anode cells have nearly no change in the resistance, as the profile of pristine lithium has a drastic change after <NUM> cycles, while the profile of the aluminum doped lithium shows only a small change after <NUM> cycles. These observations are similar in batteries tested with flooded electrolyte levels. The term flooded electrolyte refers to the use of substantially higher volume of electrolytes than industrial standards, which is usually quantified using a term called EIS ratio (electrolyte/cathode ratio).

<FIG> demonstrate that the aluminum doped lithium anode cells have great stability over time as well. <NUM>, <NUM>, <NUM>, and <NUM> percent aluminum doped lithium anodes were tested. All the dopant percentages exhibited excellent stability over time, with <NUM> percent aluminum showing the greatest stability.

<FIG> demonstrates doped lithium anodes improve the battery stability over time. Dopants, such as aluminum, gold, platinum, and silver, all exhibited improved stability, compared to pristine lithium. <FIG> shows that batteries using the doped lithium anodes also exhibited improved capacity retention.

<FIG> demonstrates the initial voltage profiles of aluminum doped lithium, silver doped lithium, and pristine lithium. The doped lithium anodes exhibit better kinetics (smaller polarization), and the doped lithium anodes enable the battery to have higher capacity and an increased efficiency. <FIG> demonstrates the initial impedance profiles of the batteries. The initial impedance profiles show that the doped lithium anodes have better kinetics (smaller charge-transfer resistance).

Claim 1:
An anode, comprising:
lithium metal, and
a dopant, in the lithium metal,
wherein the doped lithium is in the form of a foil having a thickness of at most <NUM>,
the dopant is selected from the group consisting of aluminum, silver, gold, platinum, tin, bismuth, copper, indium, zinc, nickel and mixtures thereof,
the dopant is present in an amount of <NUM> to <NUM> atomic percent, and
the anode does not contain intermetallic compounds comprising lithium and the dopant.