IMPROVED ANODE MATERIAL AND ANODE FOR A RECHARGEABLE BATTERY, A METHOD OF PRODUCTION THEREOF AND AN ELECTROCHEMICAL CELL MADE THEREFROM

Abstract

An anode material for an electrochemical cell comprises a matrix material:distributed material composite, which comprises one or more alkali metals and/or alkali earth metals. The distributed material may comprise a metal other than that of the matrix material, such as a transition and/or post transition metal. The anode material may be all or part of an anode for an electrochemical cell, which may further comprises a current collector and/or an SEI layer. The electrolyte may comprises an alkali metal and/or alkali earth metal and/or a transition metal and/or post transition metal containing electrolyte salt. The matrix material and/or the distributed material may comprise one or more of the metals of the electrolyte salt. All or part of the anode may be used as a substrate for electro-deposition of one or more matrix materials during charging and/or all or part of the anode may be used as a source of matrix material during discharging. The electrolyte may further comprise one or more electrolyte additives. The anode material may be produced by mixing a matrix material and distributed material and heating the mixture to selectively melt the matrix material to produce a matrix material:distributed material composite. The composite may be further chemically or mechanically processed to reduce the size of the distributed material and/or to increase the homogeneity of the matrix material:distributed material composite. The anode material, the anode or the electrochemical cell may be used in a device.

Claims

1.-25. (canceled)

26. An anode material for a rechargeable electrochemical cell, wherein the anode material comprises a matrix material:distributed material composite, and wherein, the matrix material comprises sodium metal and the distributed material comprises a metal and the distributed material metal that is different from the matrix material.

27. The anode material of claim 26, wherein the distributed material (3) comprises one or more transition metals and/or post transition metals, wherein the one or more post transition metals comprise aluminum, gallium, indium, tin and/or lead.

28. The anode material of claim 26, wherein the alkali metal comprises lithium, potassium and/or sodium.

29. The anode material of claim 26, wherein the distributed material comprises aluminum.

30. An anode for an electrochemical cell, wherein the anode comprises the anode material of claim 26.

31. The anode of claim 30, wherein the anode further comprises a current collector and/or an SEI layer.

32. An electrochemical cell comprising, a cathode, the anode of claim 30 and an electrolyte, at least in part, between the anode and the cathode.

33. The electrochemical cell of claim 32, wherein the electrolyte is an NH.sub.3, SO.sub.2, ether, carbonate, or nitrile solvent based electrolyte, or any mixture or combination thereof.

34. The electrochemical cell of claim 32, wherein the electrolyte comprises an alkali metal and/or alkali earth metal and/or a transition metal and/or post transition metal containing electrolyte salt.

35. The electrochemical cell of claim 32, wherein the matrix material and/or the distributed material comprise(s) one or more of the metals of the electrolyte salt.

36. The electrochemical cell of claim 32, wherein the metals of the electrolyte salt are Na and Al.

37. The electrochemical cell of claim 36, wherein the electrolyte salt is NaAlCl.sub.4.

38. The electrochemical cell of claim 32, wherein the electrolyte is NaAlCl.sub.4.xSO.sub.2.

39. The electrochemical cell of claim 32, wherein all or part of the anode is used as a substrate for electro-deposition of one or more matrix materials during charging and/or, wherein all or part of the anode is used as a source of matrix material during discharging.

40. The electrochemical cell of claim 32, wherein the electrolyte further comprises one or more electrolyte additives.

41. The electrochemical cell of claim 40, wherein the electrolyte additive comprises a halogenated electrolyte additive.

42. The electrochemical cell of claim 41, wherein the halogenated electrolyte additive comprises trifluoromethanesulfonyl-chloride (CF.sub.3SO.sub.2Cl), thionyl-chloride (SOCl.sub.2), SnCl.sub.4, and/or fluoro-ethylenecarbonate (4-fluoro-1,3-dioxolan-2-one) or any mixture or combination thereof.

43. The electrochemical cell of claim 42, wherein the cathode comprises a cation intercalation capable cathode material, a conversion reaction capable cathode material, a catholyte liquid or any mixture or combination thereof.

44. The electrochemical cell of claim 43, wherein the conversion reaction capable cathode material comprises a transition metal:halogen compound.

45. The electrochemical cell of claim 44, wherein the transition metal of the transition metal:halogen compound is Cu and/or the halogen of the transition metal:halogen compound is F and/or wherein the transition metal of the transition metal:halogen compound is CuF.sub.2.

46. A method of manufacturing the anode material of claim 26 comprising the steps of mixing a matrix material and distributed material and heating the mixture to selectively melt the matrix material to produce a matrix material:distributed material composite.

47. The method of claim 46, wherein the matrix material:distributed material composite is an intermediate matrix material:distributed material composite and, wherein the intermediate matrix material:distributed material composite is chemically or mechanically processed to reduce the size of the distributed material and/or to increase the homogeneity of the matrix material:distributed material composite.

48. The use of the anode material of claim 26, in the manufacture of a device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1: Anode material according to one embodiment of the invention.

[0020] FIG. 2: An electrochemical cell according to the invention, wherein the anode comprises, at least in part, the anode material of the invention.

[0021] FIG. 3: Exemplary anodes according to several embodiments of the invention.

[0022] FIG. 4: Exemplary means of producing anodes and freestanding anode material films according to several embodiments of the invention.

[0023] FIG. 5: Exemplary means of producing anodes from freestanding anode material films according to several embodiments of the invention.

[0024] FIG. 6: A photograph of the exemplary preferred anode material, with 1:1 mass ratio of Na:Al

[0025] FIG. 7: A photograph of the electrode produced from the exemplary preferred anode material, with 1:1 mass ratio of Na:Al

[0026] FIG. 8: The comparative Coulombic efficiency evolution of a battery cell containing CuCl.sub.2.Math.CuCl+NaCl conversion cathode, NaAlCl.sub.4.2SO.sub.2 electrolyte, and two versions of the anode:pure metallic sodium versus Na:Al composite material, with 1:1 mass ratio of Na:Al. The horizontal scale shows the cycle number, and the vertical scale shows the efficiency %. Charts A and B show full efficiency scale and the scale near to 100%, respectively.

[0027] FIG. 9: The comparative discharge time/discharge capacity evolution of a battery cell containing CuCl.sub.2.Math.CuCl+NaCl conversion cathode, NaAlCl.sub.4.2SO.sub.2 electrolyte, and two versions of the anode:pure metallic sodium versus Na:Al composite material, with 1:1 mass ratio of Na:Al. The horizontal scale shows the cycle number, and the vertical scale has s/μAh units.

[0028] FIG. 10: The comparative Internal Resistance evolution of a battery cell containing CuCl.sub.2.Math.CuCl+NaCl conversion cathode, NaAlCl.sub.4.2SO.sub.2 electrolyte, and two versions of the anode:pure metallic sodium versus Na:Al composite material, with 1:1 mass ratio of Na:Al. The horizontal scale shows the cycle number, and the vertical scale has Ω units.

[0029] FIG. 11: The comparative average discharge voltage evolution of a battery cell containing CuCl.sub.2.Math.CuCl+NaCl conversion cathode, NaAlCl.sub.4.2SO.sub.2 electrolyte, and two versions of the anode:pure metallic sodium versus Na:Al composite material, with 1:1 mass ratio of Na:Al. The horizontal scale shows the cycle number, and the vertical scale has V units.

[0030] FIG. 12: The comparative Coulombic efficiency evolution of a battery cell containing CuCl.sub.2.Math.CuCl+NaCl conversion cathode, Na:Al composite anode with 1:1 mass ratio of Na:Al, and two versions of the NaAlCl.sub.4.2SO.sub.2 electrolyte: without additives versus 2 weight % CF.sub.3SO.sub.2Cl additive containing. The horizontal scale shows the cycle number, and the vertical scale shows the efficiency %. Charts A and B show full efficiency scale and the scale near to 100%, respectively.

[0031] FIG. 13: The comparative discharge time/discharge capacity evolution of a battery cell containing CuCl.sub.2.Math.CuCl+NaCl conversion cathode, Na:Al composite anode with 1:1 mass ratio of Na:Al, and two versions of the NaAlCl.sub.4.2SO.sub.2 electrolyte: without additives versus 2 weight % CF.sub.3SO.sub.2Cl additive containing. The horizontal scale shows the cycle number, and the vertical scale has s/μAh units.

[0032] FIG. 14: The comparative Internal Resistance evolution of a battery cell containing CuCl.sub.2.Math.CuCl+NaCl conversion cathode, Na:Al composite anode with 1:1 mass ratio of Na:Al, and two versions of the NaAlCl.sub.4.2SO.sub.2 electrolyte: without additives versus 2 weight % CF.sub.3SO.sub.2Cl additive containing. The horizontal scale shows the cycle number, and the vertical scale has Ω units.

[0033] FIG. 15: The discharge capacity versus cycle number of a rechargeable battery, built with Na:Al composite anode having 1:1 mass ratio of Na:Al, CuF.sub.2 cathode, and NaAlCl.sub.4.1.5SO.sub.2 electrolyte. The horizontal scale shows the cycle number, and the vertical scale has mAh units.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] Detailed embodiments of the present invention are disclosed herein with the reference to accompanying drawings.

[0035] An electrochemical cell, according to the invention, may comprise an anode according to the invention, a cathode and an electrolyte at least partially between the anode and cathode. An electrochemical cell may further comprise a separator between the anode and cathode. An electrochemical cell may further comprise one or more charge carriers (current collectors). The anode and/or the cathode may also act as current collectors. An electrochemical cell may further comprise a housing. The electrochemical cell of the invention may be a rechargeable electrochemical cell. The electrolyte may be in any state of matter. The electrolyte may be, for instance, a solid, liquid, glass or gel.

[0036] The anode of an electrochemical cell, according to the invention, may comprise a composite. The composite may in the form of a matrix material and a distributed material. The matrix material may be continuous (i.e., continuously connected throughout the material). The distributed material may be discontinuous (i.e. dispersed or not continuously connected throughout the material). The matrix material may be a metal or an alloy of two or more metals. The distributed material may a metal or an alloy of metals. The metals may be metallic metals. The metals may be essentially pure metals. The alloys may be alloys of metallic or essentially pure metals. The distributed material may be in the form spheroids, flakes, rods, polyhedrons or any other form or combination of forms (here termed “particle” or “particles”). The distributed material may be distributed or dispersed in the matrix material. The distributed material may be essentially evenly distributed in the matrix material or may be unevenly distributed in the matrix material. The size of the particles may be essentially uniform or have a size distribution. The size of the particles may be preferably between 0.1 and 1000 microns, and preferably between 0.1 and 100 microns and more preferably between 0.1 and 50 microns and most preferably between 0.1 and 10 microns.

[0037] Here metallic metals means metals in their elemental or atomic state or otherwise unbound in a molecule with one or more non-metal atoms. Examples of metallic metals include metals that have electrons in 3-dimensional delocalized state. A pure metal here means a material comprising metallic metal or an alloy of metallic metals in a high concentration. Here high concentration means having a mass fraction of metallic metals preferably greater than 90% and more preferably greater than 95% and more preferably greater than 98% and more preferably greater than 99% and more preferably greater than 99.5% and more preferably greater than 99.8% and most preferably greater than 99.9%. Metals, according to the invention, may include alkali metals, alkali earth metals, transition metals and/or post transition metals. Alkali metals include, but are not limited to, Li, Na and K. Other alkali metals are possible according to the invention. Alkali earth metals include, but are not limited to, Be, Mg, Ca and Sr. Other alkali earth metals are possible according to the invention. Transition metals include, but are not limited to, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag and Cd. Other transition metals are possible according to the invention. Post transition metals include Al, Ga, In or Sn. Other transition metals are possible according to the invention.

[0038] According to one embodiment of the invention, the composite may comprise sodium and aluminum (a sodium:aluminum composite). The matrix metal may be sodium metal. The distributed material may be aluminum metal. The distributed material may be in the form or particles. The aluminum particles may be distributed in the sodium matrix material. The particles may be in the form of flakes. The average size of the aluminum particles, in this embodiment, in the form of flakes, may be between 1 and 100 microns. The average flake size may be below 20 microns. Other particle forms and sizes are possible according to the invention.

[0039] The matrix material distributed material composite may be formed by any means known in the art. According to one method according to the invention, a matrix material:distributed material composite is prepared by mixing matrix material and distributed material and heating the mixture above the melting point of the matrix material but below the melting point of the distributed material so as to form a composite of continuous matrix material and dispersed distributed material particles. One or both of the matrix material and the distributed material may be in the form of a powder (i.e. a collection of particles). The composite material may be subsequently further processed, e.g. chemical or physical means, e.g. by mortaring, e.g., in a mortar mill.

[0040] FIG. 1 describes the anode material (1) according to one embodiment of the invention. The anode material (1) may comprise a matrix material (2) distributed material (3) composite. As shown in cross-section in FIG. 2, the anode material (1) may comprise all or part of the anode (4) of an electrochemical cell stack (5) according to the invention. The electrochemical cell stack (5) may further comprise a cathode (6). The electrochemical cell stack (5) may further comprise a separator or spacer (7) between the anode (1) and the cathode (6). The anode (4) and/or cathode (6) may further comprise one or more solid electrolyte interface (SEI) layers (8) on the anode (4) and/or the cathode (6). The cell stack (5) may further comprise an electrolyte (not shown) at least partially between the anode (4) and the cathode (6).

[0041] The cathode (6) may comprise any compatible cathode material, included but not limited to cation intercalation capable cathode materials, conversion reaction capable cathode material and/or catholyte liquids. Other cathode materials are possible according to the invention. Here a cation intercalation capable cathode material means a material in which the concentration of infused and departing cations and electrons is varied without a change in the host material's molecular crystal structure, Here a conversion reaction capable cathode material means a material in which the concentration of infused and departing cations and electrons is varied along with a change in the host material's molecular crystal structure, Here a catholyte liquid mean a reversible conversion reaction capable cathode material in the liquid state.

[0042] A suitable cathode according to the invention may comprise a transition metal:halogen compound. The transition metal:halogen compound may be an active material in the cathode. The transition metal:halogen compound may be the active material in the cathode. The transition metal of the transition metal:halogen compound may be, for instance, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, O, Ir, Pt, Au, Hg, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg and/or Cn and/or any combination thereof. The halogen of the transition metal:halogen compound may be, for instance, F, Cl, Br, and/or I and/or any combination thereof. The transition metal may comprise Cu and the halogen may comprise F. The transition metal:halogen compound may comprise Cu and F as a transition metal and a halogen respectively. The Cu and F containing transition metal:halogen compound may comprise CuF.sub.2 active material. The cathode and/or cathode material may further comprise a conductive additive. The conductive additive may comprise a conductive material. The conductive material may be a metal or a metallic material. The metallic and/or conductive material may comprise carbon. The carbon comprising additive may be a carbon additive. The metallic conductive additive may be a nanomaterial. The conductive additive may be in in the form of a tube, wire, ball or flake. The conductive additive may comprises carbon or an allotrope thereof and/or a metal. The conductive additive may be in the form of a conductive high aspect ratio particle. The metallic and/or carbon comprising conductive additive may be a nanotube (e.g. a carbon nanotube), nanowire (e.g. a metal nanowire), nanoball (e.g. a fullerene) a nanoflake (e.g. a graphene or graphite) or a hybrid or combination thereof (e.g. a carbon nanobud), ketjen black, hard carbon, nanofibers, activated carbon, reduced graphene oxide and any combination thereof.

[0043] The (transition metal:halogen compound) (conductive additive) mass ratio in the cathode and/or cathode material, e.g. CuF.sub.2 conductive carbon additive, may be between 20:1 and 1:10 and more preferably between 15:1 and 1:4, and more preferably between 10:1 and 1:2 and more preferably between 7:1 and 1:1 and more preferably between 5:1 and 3:1 or any combination thereof and most preferably be approximately 4:1.

[0044] Other cathodes, cathode materials, active materials, conductive additives, carbons and mass ratios are possible according to the invention.

[0045] FIG. 3 describes in cross-section various exemplary embodiments of the anode (4) according to the invention. As shown in embodiment 3A, the anode (4) may be made solely of the anode material (1), comprising the matrix material (2) and the distributed material (3). In this case, the anode material may also act as an anodic current collector (9). As shown in embodiments 3B-3E, the anode material (1) may be deposited on and/or or in a separate anodic current collector (9). The current collector (9) may comprise any appropriate conductive material compatible with, for instance, the anode material (1) and/or the electrolyte (not shown) under the charging and/or discharging and or storage voltage and/or current of the electrochemical cell (5). The current collector (9) may be in the form of, for instance a foil or film of current collector material, as shown in FIGS. 3B and 3C. The anode material (1) may be on one side of the current collector (9), as shown in FIG. 3B, or may be on both sides of the current collector (9), as shown in FIG. 3C. The anodic current collector (9) may be in the form of, for instance, an open structure such as, for instance, a mesh, perforated foil, weave or other topology containing voids or open spaces, of anodic current collector material, as shown in FIGS. 3D and 3E. The anode material (1), in such a case, may be placed so as to fully or partially fill the void spaces of the open structure of the anodic current collector (9). The anode material (1) may be on one side of the current collector (9), as shown in FIG. 3D, or may be on both sides of the current collector (9), as shown in FIG. 3E.

[0046] The herein disclosed anode material may be used either as current collector substrate for metallic metal electro-deposition in discharged state assembled electrochemical cells, or as charged state metallic metal electrode in charged state assembled electrochemical cells.

[0047] The material of the separate anodic current collector (9) may be any suitable electrically conductive material. Here electrically conductive material means material having electric conductivity greater than approximately 1×10.sup.5 σ(S/m) at 20° C. Examples of electrically conductive materials include metallic materials. Metallic materials include materials that have electrons in 3-dimensional delocalized state. Examples of metallic materials may include metals. Examples of metals may include Hg, Dy, Eu, Ce, Er, Ho, La, Pr, Tm, Nd, Y, Sc, Lu, Po, Am, Ti, Zr, Sb, Fr, Ba, Hf, As, Yb, U, Pb, Cs, V, Pa, Re, Tl, Th, Tc, Ga, Nb, Ta, Sr, Cr, Rb, Sn, Pd, Pt, Fe, Li, Os, In, Ru, Cd, K, Ni, Zn, Co, Mo, W, Ir, Na, Rh, Mg, Ca, Be, Al, Au, Cu, Ag and any mixtures, alloys or combinations thereof. Metallic materials may include allotropes of carbon. Allotropes of carbon include diamond, graphite, graphene, amorphous carbon, fullerenes, carbon nanotubes, carbon nanobuds and glassy carbon, carbon nanofoam, lonsdaleite, linear acetylenic carbon or any other allotrope of carbon and/or any combination thereof. Other metallic materials are possible according to the invention. The choice of suitable current collector material is dependent on the specifics of, for instance, the battery composition, chemical and electrochemical stability with regards to the electrolyte, charging voltage and/or charge and/or discharge current.

[0048] The matrix material:distributed material composite anode material may be prepared by any means known in the art. One method of preparation is to heat a mixture of matrix material and distributed material particles above the melting point of matrix material but below the melting point of distributed material to create a matrix material distributed material composite matirial. The composite material can then subsequently processed to improve the material properties, such as particle size or composite homogenaity. This can be by any means known in the art, for instance, by being mortared, for instance, in a mortar mill. Any heating and/or processing time is possible according to the invention. Preferably, the processing time is between 1 and 1000 minutes, and more preferably, between 2 and 100 minutes and most preferably between 5 and 50 minutes. The heating and/or mortaring processes can be carried out under any appropriate atmosphere. Preferably the atmosphere is inert to one or both of the matrix material and distributed material. Examples include, but are not limited to argon and nitrogen atmospheres. The matrix material distributed material mass ratio of the mixture may be any defined ration. Preferably the ratio is between 100:1 and 1:100, and more preferably between 50:1 and 1:50 and more preferably between 20:1 and 1:20 and more preferably between 10:1 and 1:10 and more preferably between 5:1 and 1:5, and more preferably between 3:1 and 1:3, and more preferably between 2:1 and 1:2, and most preferably between 1.1:1 and 1:1.1.

[0049] The anode material (1) may be processed by any means known in the art to create the anode (4). Examples include rolling, e.g. through a nip, dip coating, calandering, hydraulic pressing. An exemplary means of forming the anode (1) according to the invention are shown in FIG. 4. As shown in FIG. 4A, anode material (1) may be drawn through a nip (10) to form, either a an anode (4), wherein the anode (4) is also the current collector (9) or a freestanding anode material film (12). As shown in FIG. 4B, anode material (1) may be drawn through a nip (10) to form, together with a current collector (9), an anode (4) comprising separate anode material (1) and current collector substrate (9). As shown in FIG. 4C, anode material (1) may be drawn through a nip (10) to form, together with a current collector (9), an anode (4) comprising separate anode material (1) in two layers on both sides of a current collector substrate (9). FIG. 5 shows how a freestanding anode material film (12), produce by the method of FIG. 4 or otherwise, can be combined with a current collector (9) substrate to form a one-sided (FIG. 5A) or two-sided (FIG. 5B) anode (4) by passing one or two freestanding anode material films (12) through a lamination nip (11).

[0050] It has been surprisingly discovered that employing halogenated electrolyte additives may further improve the electrochemical performance of the herein disclosed matrix mateiral distributed material composite anode. Here, halogenated electrolyte additives are defined as halogen-containing molecules, which are soluble in the electrolyte and chemically react at the anode or cathode surface. Any halogenated electrolyte additive can be used according to the invention. Halogenated here means having a halogen in the molecule. Halogens include, but are not limited to Fl, Cl, Br and I.

EXAMPLES

[0051] In one embodiment of the method, sodium aluminum composite anode material has been prepared by first mixing sodium metal and a powder of aluminum flakes and heating the mixture of sodium and aluminum flakes above the melting point of sodium (98° C.) but below the melting point of aluminum (660° C.). In this example the temperature was approximately 120° C. The sodium:aluminum mass ratio of the mixture according to this embodiment was approximately 1:1. For this embodiment of the invention, the ratio is preferably between 5:1 and 1:5, and more preferably between 3:1 and 1:3, and more preferably between 2:1 and 1:2, and most preferably between 1.1:1 and 1:1.1. The resulting Na:Al intermediate composite material was then subsequently further processed by being mortared in a mortar mill for 10 minutes during its cooling to create the final composite material. This heating and mortaring process was carried out under an argon atmosphere, which is inert to metallic sodium.

[0052] It has been surprisingly discovered that, as the sodium cools below its melting point, mortaring action produces a homogeneous composite from the sodium:aluminum mixture, with a flaky appearance. The visual appearance of the resulting material is shown in FIG. 6. This homogeneous composite formation is surprising, since sodium is known to poorly wet other materials, i.e. sodium has a generally poor affinity for dispersion. As the resulting sodium:aluminum composite was transferred out into ambient air, it has been surprisingly discovered that its air stability is significantly higher than the stability of plain sodium metal, and the composite retained its shiny metallic appearance. In a dry-room environment, the sodium aluminum composite was found to be sufficiently stable to allow the production of battery electrodes. The sodium:aluminum composite was found to be sufficiently soft for being press-rolled into a continuous film and/or for lamination onto a current collector film or into a current collector mesh. Upon warming the composite to higher temperature than room temperature, but still below the sodium melting point, its softness was found to increase further. This mechanical property allows simple and cost effective electrode production from the herein disclosed sodium aluminum composite material. FIG. 7 shows an anodic electrode, produced by pressing the sodium:aluminum composite into an aluminum mesh current collector.

[0053] The herein disclosed anode material may be used either as current collector substrate for metallic sodium electro-deposition in discharged state assembled battery cells, or as charged state sodium electrode in charged state assembled battery cells.

[0054] The electrochemical properties of the resulting anode were evaluated in battery cells comprising NaAlCl.sub.4.2SO.sub.2 electrolyte formulation. This electrolyte was selected for evaluation because it supports the reversible cycling of a metallic sodium anode, and therefore, allows electrochemical comparison against a plain metallic sodium anode. The employed cathode was a discharged state cathode comprising a Cu+2NaCl active material formulation. After charging the cathode to CuCl.sub.2 state, the cathode was cycled according to the CuCl.sub.2.Math.CuCl+NaCl conversion reaction. The electrochemical performance of 1:1 mass ratio Na:Al composite anode versus plain metallic Na anode was evaluated by measuring three parameters during battery cycling: i) Coulombic Efficiency; ii) discharge time/discharge capacity ratio; and iii) Internal Resistance of the cell. FIGS. 8-10 show the measured data. As seen from FIG. 8, the average Coulombic Efficiency is similar in both cases. However, the fluctuation of Coulombic Efficiency is smaller for the Na:Al composite anode, indicating a more stable electrode-electrolyte interface. The discharge program is composed of a sequence of decreasing discharge currents, each step ending at the cut-off voltage of 3.2 V. The duration of discharge under such discharge program is related to the resistance of the electrode-electrolyte interface, since longer discharge time means the shifting of the discharge towards lower currents. The discharge time is divided by the discharge capacity of the cathode, in order to eliminate cathode capacity evolution effects. As seen from FIG. 9, the discharge time is significantly shorter for the Na:Al composite anode, indicating a significantly lower resistance of the electrode-electrolyte interface. The Internal Resistance of the cell is estimated from the voltage data evolution at the charging start and stop events. As seen from FIG. 10, the Internal Resistance is significantly smaller for the Na:Al composite anode, again indicating a significantly lower resistance of the electrode-electrolyte interface. As seen from FIG. 11, the average discharge voltage is approximately the same for the Na:Al composite anode as for the metallic Na anode. Therefore the herein described performance improvements have no disadvantage in terms of cell voltage. Altogether, these data prove the improved cell performance of the herein disclosed Na:Al composite anode campared to cell comprising a pure metallic Na anode.

[0055] As an anode for charged state assembled cells, the preferred embodiment of 1:1 mass ratio between Na:Al composite is a dense anode with 550 mAh/g gravimetric capacity, which can be operated at the potential of −2.7 V vs. SHE. As an anodic substrate for discharged state assembled cells, the preferred embodiment of 1:1 mass ratio between Na:Al composite anode supports highly efficient and durable anodic cycling of metallic sodium deposition and stripping. In both cases, the electrochemical performance is better than the performance of pure metallic Na anodes. Battery cells employing the herein disclosed anode may be assembled in a dry room environment.

[0056] It has been surprisingly discovered that employing halogenated electrolyte additives may further improve the electrochemical performance of the herein disclosed Na:Al composite anode. The anodic performance of the Na:Al composite is compared in two versions of the NaAlCl.sub.4.2SO.sub.2 electrolyte: additive-free versus 2 weight % CF.sub.3SO.sub.2Cl additive containing. The anodic performance was evaluated by measuring three parameters during battery cycling: i) Coulombic Efficiency; ii) discharge time/discharge capacity ratio; and iii) Internal Resistance of the cell. FIGS. 12-14 show the measured data. As seen from FIG. 12, the Coulombic Efficiency is initially higher than 100% for the cell with CF.sub.3SO.sub.2Cl additive containing electrolyte, indicating the consumption of the electrolyte additive. However, after about 50 cycles, the Coulombic Efficiency of the cell with CF.sub.3SO.sub.2Cl additive containing electrolyte converges very close to 100%, demonstrating better Coulombic Efficiency than the additive-free electrolyte. As seen from FIGS. 13-14, the discharge time is slightly shorter and the Internal Resistance is slightly lower for the cell with CF.sub.3SO.sub.2Cl additive containing electrolyte, indicating a slightly lower resistance of the electrode-electrolyte interface. It is also seen from FIGS. 13-14 that resistance fluctuation is smaller with the CF.sub.3SO.sub.2Cl additive containing electrolyte, indicating a more stable electrode-electrolyte interface. Altogether, these data show that the anodic performance of the herein disclosed Na:Al composite anode may be further enhanced by employing one or more halogenated electrolyte additives. The long-term cycling stability is also demonstrated by this data.

[0057] An exemplary rechargeable cell was produced according to one embodiment of the invention, employing the following cell structure. The anodic electrode comprised Na:Al composite with 1:1 mass ratio between Na and Al metals. The cathodic electrode comprised CuF.sub.2 active material with 4:1 mass ratio between CuF.sub.2 and the conductive carbon additive, though other cathodes, cathode materials, active materials, conductive additives, carbons and mass ratios are possible according to the invention. The electrodes had 2.5 cm.sup.2 surface area. The electrolyte had NaAlCl.sub.4.1.5SO.sub.2 composition, and we used glass fiber separator, though other electrolytes, electrolyte compositions and separator materials are possible according to the invention. FIG. 15 shows the cell's discharge capacity versus cycle number for said example. Cycles 1-70 show increasing discharge capacity, due to the gradual activation of the larger CuF.sub.2 particles in the cathode. The cell was rested for 5 days at cycle 70. Starting from approximately cycle 70, the cell demonstrated stable discharge capacity. The average cell voltage was 3.35 V during the discharge. This cell demonstrates the stable operation of the herein disclosed anode structure in a rechargeable cell.

[0058] While the foregoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.