Sb nanocrystals or Sb-alloy nanocrystals for fast charge/discharge Li- and Na-ion battery anodes

Abstract

A method for the production of SbM.sub.x nanoparticles is described that comprises the steps of reducing an antimony salt and optionally an alloying metal with a hydride in an anhydrous polar solvent, separating the solid product formed from the solution, preferably via centrifugation, and washing the product with water. M is an element selected from the group consisting of Sn, Ni, Cu, In, Al, Ge, Pb, Bi, Fe, Co, Ga, and 0x<2.

Claims

1. A method for the production of SbM.sub.x nanoparticles, wherein M is an element selected from the group consisting of Sn, Ni, Cu, In, Al, Ge, Pb, Bi, Fe, Co, Ga, and
0x<2, the method comprising: preparing a solution containing an antimony salt and one or more metal salts in an anhydrous polar solvent and at least one solution of hydride in an anhydrous polar solvent, heating the solution containing the one or more metal salts to a reaction temperature, then injecting the solution of hydride into the solution containing the one or more metal salts to generate a reaction mixture and start a reduction reaction, wherein said antimony salt and said one or more metal salts are reduced with said hydride and form a solid product; cooling said reaction mixture to room temperature immediately after the formation of the solid product; and separating the solid product formed from the solution reaction mixture, and washing the product with water.

2. The method of claim 1, wherein the solid product formed from the reaction mixture is separated via centrifugation.

3. The method of claim 1, wherein M is Sn.

4. The method of claim 1, wherein M is Sn and x is 1.

5. The method of claim 1, wherein the reduction reaction is performed after elevating the reaction temperature by heating.

6. The method of claim 5, wherein the reduction reaction is performed at a temperature of 6010 C.

7. The method of claim 1, wherein the hydride is selected from the group consisting of NaBH.sub.4, lithium hydride, sodium hydride, potassium hydride, magnesium hydride, calcium hydride, tributyltinhydride, diisobutyl aluminum hydride, lithium aluminum hydride, lithium triethylborohydride and mixtures thereof.

8. The method of claim 7, wherein the hydride is NaBH.sub.4.

9. The method of claim 1, wherein the anhydrous polar solvent is selected from the group consisting of 1-methyl-2-pyrrolidone (NW), hexamethylphosphoramide, 1,3-dimethyl-2-imidazolidinone,1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone, dimethylsulfoxide, sulfolane, glyme, diglyme, triethylene glycol dimethylether, and mixtures thereof.

10. The method of claim 9, wherein the anhydrous polar solvent is NMP.

11. The method of claim 1, wherein the antimony salt is selected from the group consisting of antimony chloride, antimony fluoride, antimony bromide, antimony iodide, antimony oxide or antimony sulfide, antimony sulfate, antimony acetate, potassium antimony tartrate hydrate, triphenylantimony, antimony ethoxide and mixtures thereof.

12. The method of claim 11, wherein the antimony salt is antimony chloride.

13. The method of claim 1, wherein the one or more metal salts include at least one salt selected from the group consisting of tin chloride (SnCl.sub.2), tin fluoride, tin bromide, tin iodide, tin oxide, tin sulfide, sodium stannate trihydrate, tetrabutyltin, chlorides of Ni, Cu, in, Al, Ge, Pb, Bi, Fe, Co, Ga and mixtures thereof.

14. The method of claim 13, wherein the one or more metal salts includes a mixture of tin salts.

15. The method of claim 13, wherein the one or more metal salts includes tin chloride.

16. The method of claim 1, wherein the reduction reaction is performed in inert gas.

17. The method of claim 16, wherein the reduction reaction is performed in argon.

18. The method of claim 1, wherein the reduction reaction is performed in air.

19. The method of claim 1, wherein the reaction mixture is cooled to room temperature immediately after injecting the solution of hydride.

20. The method of claim 1, wherein the product is dried in a vacuum oven at room temperature, optionally with a previous additional washing with a low boiling water miscible solvent.

21. The method of claim 20, wherein the low boiling water miscible solvent is acetone.

22. A method for producing an anode comprising performing the method of claim 1 for producing SbM.sub.x nanoparticles, mixing the such obtained SbM.sub.x nanoparticles, carbon black, carboxy methyl cellulose (CMC) and demineralized water, coating the aqueous slurry obtained on a current collector and drying.

23. The method according to claim 1, wherein the anhydrous polar solvent is not dimethyl formamide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. This description makes reference to the annexed drawings which show:

(2) FIG. 1. XRD pattern of Sb NPs synthesized by injection of SbCl.sub.3 into a solution of NaBH.sub.4 in NMP.

(3) FIG. 2. TEM images of Sb NPs synthesized with different amounts of NaBH.sub.4:

(4) A) 1 mmol, B) 2 mmol, C) 8 mmol

(5) FIG. 3. TEM images of Sb NPs synthesized according to the upscaled procedure.

(6) FIG. 4. TEM images of Sb NPs synthesized either at 60 C. (A) or 25 C. (B) using 4 mmol of NaBH.sub.4.

(7) FIG. 5. TEM image of Sb NPs synthesized according to the procedure described in Example 1-IV.

(8) FIG. 6. TEM images of Sb NPs synthesized in air.

(9) FIG. 7. XRD pattern of SnSb NPs synthesized by injection of SnCl.sub.2 and SbCl.sub.3 into a solution of NaBH.sub.4 in NMP.

(10) FIG. 8. TEM images of SnSb NPs.

(11) FIG. 9. Capacity retention for Sb-based anodes in Li-ion half-cells at a rate of 0.5 C.

(12) FIG. 10. Capacity retention for Sb-based anodes in Li-ion half-cells at a rate of 4 C with initial conditioning cycles (2 cycles at 0.1 C+8 cycles at 0.5 C).

(13) FIG. 11. Galvanic charge and discharge curves for Sb NPs from direct synthesis corresponding to FIG. 9.

(14) FIG. 12. Rate capability measurements for Sb-based anodes in Li-ion half cells.

(15) FIG. 13. Capacity retention for Sb-based anodes in Na-ion half-cells at a rate of 1 C.

(16) FIG. 14. Capacity retention for Sb-based anodes in Na-ion half-cells at a rate of 4 C.

(17) FIG. 15. Galvanic charge and discharge curves for Sb NPs from direct synthesis corresponding to FIG. 13.

(18) FIG. 16. Rate capability measurements for Sb-based anodes in Na-ion half cells.

(19) FIG. 17. Capacity retention for SnSb-based anodes in Li-ion half-cells at a current of 0.33 A g.sup.1 or 2.64 A g.sup.1. Before measurements at 2.64 A g.sup.1, batteries were cycled at 0.066 A g.sup.1 for two and afterwards at 0.33 A g.sup.1 for eight cycles. (Note: The electrochemical performance of 20 nm monodisperse was previously described in European patent application no. 13194946.3 and is shown here for comparison.)

(20) FIG. 18. Capacity retention for SnSb-based anodes in Na-ion half-cells at a current of 0.66 A g.sup.1 or 13.2 A g.sup.1. Before measurements batteries were cycled at 0.066 A g.sup.1 for two and afterwards at 0.33 A g.sup.1 for eight cycles. (Note: The electrochemical performance of 20 nm monodisperse was previously described in European patent application no.13194946.3 and is shown here for comparison.)

(21) FIG. 19. Galvanostatic charge and discharge curves for the 1st and 10th cycle for polydisperse SnSb NPs corresponding to cycling experiments at 0.33 A g.sup.1 (A) and 0.66 A g.sup.1 (B) shown in FIGS. 17 and 18, respectively.

MODES FOR CARRYING OUT THE INVENTION

(22) In a typical synthesis of SbM.sub.x NPs, in particular Sb NPs or SnSb NPs, a suitable amount of a hydride such as NaBH.sub.4 is dissolved in an appropriate amount of anhydrous polar solvent such as 1-methyl-2-pyrrolidone (NMP) and heated while stirred. Upon reaching the desired temperature, such as 60 C., a solution of an antimony salt such as SbCl.sub.3 in anhydrous solvent such as NMP is injected quickly. If alloy particles are desired, a solution of a suitable salt of an alloying metal, such as SnCl.sub.2, in anhydrous polar solvent such as NMP is injected prior to or simultaneously with or after the Sb containing solution. The reaction mixture turns black immediately, indicating the formation of SbM NPs. After the injection the suspension is cooled to room temperature, e.g. with a water-ice bath. The obtained material is separated from the solution by centrifugation and washed three times with 30 mL demineralized water to remove unreacted NaBH.sub.4 and water-soluble side-products such as NaCl. The reaction product is finally washed with 10 mL acetone for easier removal of residual water and dried in the vacuum oven at room temperature. Typically the reaction yields the desired product in amounts of 805%.

(23) In the above indicated method the following chemicals in general are suitably applied to obtain Sb NPs or SbM NPs of comparable quality and quantity:

(24) I. As anhydrous solvent other than NMP:

(25) Any amide such as hexamethylphosphoramide, 1,3-dimethyl-2-imidazolidinone or 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone.

(26) II. As substitution for NaBH.sub.4:

(27) Any alkali or earth alkali hydride such as lithium hydride, sodium hydride, potasium hydride, magnesium hydride, calcium hydride or other metal hydrides such as tributyltinhydride, diisobutyl aluminum hydride, lithium aluminum hydride or lithium triethylborohydride.

(28) III. As Substitution for SbCl.sub.3:

(29) Any antimony halogenide such as antimony fluoride, antimony bromide, antimony iodide; any antimony oxide or chalcogenide such as antimony oxide or antimony sulfide; any other inorganic antimony salt such as antimony sulfate; any organic antimony salt such as antimony acetate or potassium antimony tartrate hydrate; any organic antimony compound such as triphenylantimony or antimony ethoxide.

(30) IV. To obtain SbM.sub.x NPs of a quality and quantity comparable to Sb NPs, the Sb salt may be partially substituted by a Sn salt, especially SnCl.sub.2, or any other tin halogenide such as tin fluoride, tin bromide, tin iodide; any tin chalcogenide such as tin oxide or tin sulfide; any other inorganic tin salt such as sodium stannate trihydrate, any other organic tin compound such as tetrabutyltin, or part of the Sb salt might be substituted by other metal chlorides, or generally metal compounds, to yield metal antimony alloy nanoparticles.

(31) The above indicated chemicals may be used alone or in combination with one or more other members of their respective group I to IV.

(32) The particles sizes may be influenced by several characteristics such as amount of hydride, reaction temperature and cooling speed.

(33) Depending on the amount of NaBH.sub.4 employed the size of the NPs can be varied, i.e. the higher the amount of NaBH.sub.4 the smaller the particles. In addition, to produce NPs of small sizes with high yield an excess of NaBH.sub.4 is necessary. Whereas for reactions using more than equimolar amounts of NaBH.sub.4 the reaction yield is at least 80%, it drops to 31% when employing only 1 mmol of NaBH.sub.4 per 1 mmol of Sb and optionally alloying metal salt.

(34) Sb NPs can also be produced at room temperature, however, the formation of smaller NPs is likely to be favored at elevated temperatures.

(35) Sb NPs with a diameter of approximately 10 nm can be obtained by employing a seven fold excess of NaBH.sub.4 as reducing agent and fast cooling down directly after the injection of the SbCl.sub.3 and optionally alloying salts. The fast cooling down can be achieved by any adequate cooling technique known to the person skilled in the art.

(36) In addition, it has been found that SbM.sub.x NPs of comparable quality and yield can be obtained by performing the synthesis in air which significantly reduces the costs (material as well as working hours). If working in air, the use of air sensitive reagents such as lithium triethylborohydride should be avoided.

(37) Besides of being easy to perform and comparatively cheap the method of the present invention has several advantages compared with methods described in literature. The advantages of this synthetic procedure compared to the two most similar publications are the following:

(38) I. No surfactant needs to be used: In Wang et al. [27], PVP is employed as surfactant to obtain Sb NPs. In Kieslich et al. [28] no surfactant is used, but in contrast to Kieslich et al. [28] with the herein described method also particles smaller than 20-50 nm can be obtained.

(39) II. Reaction can also be done in air: In Kieslich et al. the reaction is performed under inert conditions, as the employed reducing agent is sensitive to air and moisture.

(40) III. Inexpensive and safe chemicals: the herein preferably used NaBH.sub.4 is the least expensive metal hydride, unlike Kieslich et al. [28] that employed lithium triethylboronhydride. In Wang et al. [27] NaBH.sub.4 in dimethylformamide is used, however, this mixture is generally considered unsafe, unlike NaBH.sub.4 in NMP (see [29]). Thus, in the present case, dimethylformamide is excluded from the list of applicable solvents.

(41) IV. Washing procedure: In the inventive procedure SbM.sub.x NPs are simply washed with water in air, whereas in Kieslich et al. [29] particles are washed with THF in a glovebox.

(42) V. High yield: Per batch (60 mL of solvent) 1.2 g of SbM.sub.x NPs can be produced corresponding to 82% yield with the herein described procedure. In Wang et al. [27] the maximal yield per batch (50 mL of solvent) is limited to 6.1 mg Sb NPs. In Kieslich et al. [28] no reaction yield is mentioned.

(43) VI. Depending on the excess of NaBH.sub.4 used and the reaction temperature, the size of the particles can be tuned: In Wang et al. particles with an average size of 4 nm are reported. In Kieslich et al. [28] particles in the range 20-50 nm are synthesized. In both cases no variation of the size with the reaction conditions is described.

(44) Although the method of this invention is preferred for synthesizing metal nanoparticles, it may also be used together with a subsequent oxidizing step resulting in SbO.sub.y NPs or SbM.sub.xO.sub.y NPs with the oxygen content (y) varying up to at most about 3. Depending on the alloying metal also such oxides can be suitable as electrochemically active materials.

(45) An anode may be prepared by mixing SbM.sub.x NPs, carbon black, CMC and demineralized water, preferably by using a ball-mill for e.g. 1 h. The aqueous slurry obtained is then coated on a current collector like a Cu current collector, and subsequently dried, e.g. overnight at 80 C. under vacuum.

(46) Experimental Part

(47) I. Materials Used

(48) Chemicals and solvents: Acetone (99.5%, Sigma Aldrich), antimony (III) chloride (99.9%, ABCR), 1-methyl-2-pyrrolidone (NMP, anhydrous, 99.5%, Acros Organics), sodium borohydride (99%, Sigma Aldrich).

(49) Battery components: Carbon black (Super C65, provided by TIMCAL), 1 M solution of LiPF.sub.6 in ethylene carbonate/dimethyl carbonate (EC/DMC, Novolyte), NaClO.sub.4 (98%, Alfa Aesar), propylene carbonate (PC, BASF), ethylene carbonate (Novolyte), diethyl carbonate (>99%, Aldrich), 4-Fluoro-1,3-dioxolan-2-one (FEC, >98.0%, TCI), Celgard separator (Celgard 2320, 20 m microporous trilayer membrane (PP/PE/PP), Celgard Inc. USA) and glass-fiber separator (EUJ-grade, Hollingsworth & Vose Company Ltd., United Kingdom), carboxymethyl cellulose (CMC, Grade: 2200, Lot No. B1118282, Daicel Fine Chem Ltd).

(50) II. Methods

(51) Synthesis of SbM.sub.x NPs

Example 1: Synthesis of Sb NPs

(52) In a typical synthesis of Sb NPs, 8 mmol of NaBH.sub.4 were dissolved in 17 mL anhydrous NMP and heated to 60 C. under Ar, while stirred mechanically. Upon reaching 60 C. 3 mL of a solution of 2 mmol SbCl.sub.3 in anhydrous NMP were injected quickly. The solution of metal salts could be heated first and then the hydride solution could be injected into it. However, this alternative is not preferred because of the higher solubility of metal salts in NMP and because of the larger volume to inject. The reaction mixture turned black immediately, indicating the formation of Sb NPs. After the injection the suspension was cooled to room temperature by with a water-ice bath. The obtained material was separated from the solution by centrifugation and washed three times with 30 mL demineralized water to remove unreacted NaBH.sub.4 and water-soluble side-products such as NaCl. The reaction product was finally washed with 10 mL acetone for easier removal of residual water and dried in the vacuum oven at room temperature. Typically the reaction yield was 200 mg (83%). The XRD pattern of the obtained product showed only peaks corresponding to crystalline Sb (FIG. 1). No traces of crystalline Sb oxide could be detected. Further, by XRD no other species that might be present such as NaBH.sub.4, NaCl or borates were observed, indicating the successful washing of the NPs. Analysis of the reaction product by TEM showed that particles were polydisperse with sizes in the 20 nm range (FIG. 2C). In accordance, the crystallite size calculated with the Scherrer equation was 27 nm.

(53) Remarks on the Synthetic Procedure

(54) I. Depending on the amount of NaBH.sub.4 employed the size of the NPs could be varied. To produce NPs of small sizes with high yield an excess of NaBH.sub.4 was necessary (FIG. 2). Whereas for reactions using 2 mmol of NaBH.sub.4 or more the reaction yield was at least 80%, it dropped to 31% when employing only 1 mmol of NaBH.sub.4.

(55) II. Sb NPs on a gram-scale could be synthesized by performing the exact same procedure, but using 46 mmol of NaBH.sub.4 in 51 mL of anhydrous NMP and a solution of 12 mmol SbCl.sub.3 in 9 mL anhydrous NMP. Sb NPs with similar sizes according to TEM and XRD were obtained with typically 1.2 g (82%) yield (FIG. 3).

(56) III. Sb NPs could also be produced at room temperature, however, the direct comparison with the synthesis at 60 C. showed the formation of smaller NPs was favored at elevated temperatures (FIG. 4).

(57) IV. Sb NPs with a diameter of approximately 10 nm could be obtained by employing 16 mmol of NaBH.sub.4 as reducing agent and adding directly after the injection of the SbCl.sub.3 10 mL of acetonitrile for fast cooling down (FIG. 5).

(58) V. Sb NPs of comparable quality and yield could be obtained by performing the synthesis in air (FIG. 6).

(59) Variation of chemicals. The following chemicals may be applied to obtain Sb NPs of comparable quality and quantity:

(60) I. As Substitution for NMP:

(61) Any amide such as hexamethylphosphoramide, 1,3-dimethyl-2-imidazolidinone or 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone, and excluding N,N-dimethylformamide for safety reasons, any linear ether such as glyme, diglyme, triethylene glycol dimethyl ether, any sulfoxide such as dimethylsulfoxide, sulfolane.

(62) II. As Substitution for NaBH.sub.4:

(63) Any alkali or earth alkali hydride such as lithium hydride, sodium hydride, potasium hydride, magnesium hydride, calcium hydride or other metal hydrides such as tributyltinhydride, diisobutyl aluminum hydride, lithium aluminum hydride or lithium triethylborohydride.

(64) III. As Substitution for SbCl.sub.3:

(65) Any antimony halogenide such as antimony fluoride, antimony bromide, antimony iodide; any antimony chalcogenide such as antimony oxide or antimony sulfide; any other inorganic antimony salt such as antimony sulfate; any organic antimony salt such as antimony acetate or potassium antimony tartrate hydrate; any organic antimony compound such as triphenylantimony or antimony ethoxide.

Example 2: Synthesis of SnSb NPs

(66) In a typical synthesis of SnSb NPs, 16 mmol NaBH.sub.4 were dissolved in 17 mL anhydrous NMP and heated to 60 C. under Ar, while stirred mechanically. Upon reaching 60 C. 1.5 mL of a solution of 1 mmol SnCl.sub.2 in anhydrous NMP were injected. Afterwards 1.5 mL of a solution of 1 mmol of SbCl.sub.3 in anhydrous NMP were added. The reaction mixture is cooled down immediately to room temperature using a water-ice bath. The obtained material was separated from the solution by centrifugation and washed three times with 30 mL demineralized water to remove unreacted NaBH.sub.4 and water-soluble side-products such as NaCl. The reaction product was finally washed with 10 mL acetone for easier removal of residual water and dried in the vacuum oven at room temperature. Typically SnSb NPs with 194 mg (80%) yield were obtained. The XRD pattern of the obtained product showed only peaks corresponding to crystalline SnSb (FIG. 7). No traces of pure crystalline Sb or Sn could be detected. Further, by XRD no other species that might be present such as NaBH.sub.4, NaCl or borates were observed, indicating the successful washing of the NPs. Using the Scherrer equation an average size of 41 nm was determined from the XRD pattern. In accordance analysis of the reaction product by TEM showed that the particles were polydisperse with sizes in the 40 nm range (FIG. 8).

(67) Variation of chemicals. To obtain SnSb NPs of comparable quality and quantity SnCl.sub.2 may be substituted by the following chemicals: Any tin halogenide such as tin fluoride, tin bromide, tin iodide; any tin chalcogenide such as tin oxide or tin sulfide; any other inorganic tin salt such as sodium stannate trihydrate, any other organic tin compound such as tetrabutyltin.

(68) Further, SnCl.sub.2 may also be substituted by other metal chlorides, or generally metal compounds, to yield metal antimony alloy nanoparticles.

(69) Preparation of Sb-Based Electrodes and Electrochemical Testing

(70) In a typical electrode preparation, Sb NPs or SnSb NPs, carbon black, CMC and demineralized water were mixed by ball-milling for 1 h using a Fritsch Pulverisette 7 classic planetary mill (composition: 63.75 wt % Sb or SnSb, 21.25 wt % CB and 15 wt % CMC). The aqueous slurries were coated on Cu current collectors, which were subsequently dried overnight at 80 C. under vacuum prior to use. All electrochemical measurements were conducted in homemade, reusable and air-tight coin-type cells. Batteries were assembled in an Ar-filled glove box (O.sub.2<0.1 ppm, H.sub.2O<0.1 ppm). Elemental lithium or sodium was employed as both reference and counter electrode. For Li-ion half cells, both Celgard and glass fiber separator were employed, whereas for Na-ion half cells only glass fiber separator was used. 1 M LiPF.sub.6 in EC:DMC (1:1 by wt.) with 3% FEC served as electrolyte for Li-ion and 1 M NaClO.sub.4 in PC with 10% FEC (Sb) or 3% FEC (SnSb) served as electrolyte for Na-ion half-cells. All galvanostatic measurements were conducted on MPG2 multi-channel workstation (BioLogic) with between 0.02 and 1.5 V. The obtained capacities were normalized by the mass of employed Sb NPs or SnSb NPs.

(71) III. Characterization

(72) Transmission Electron Microscopy (TEM) images were obtained with a Philips CM30 TEM microscope at 300 kV using carbon-coated TEM grids (Ted-Pella). Powder X-ray diffraction (XRD) was measured on a STOE STADI P powder X-ray diffractometer. The crystallite size x was estimated using the Scherrer equation:

(73) $x=\frac{K.Math.}{.Math.\cos }$

(74) K is the shape factor. is the X-ray wavelength (CuK 1=1.540598 ). is the full width at half the maximum intensity and is the Bragg angle.

(75) IV. Electrochemical Results

(76) Sb NPs Based Anodes

(77) FIG. 9 and FIG. 10 show the electrochemical performance of Sb NPs synthesized by the herein described procedure (in the following denoted as Sb NPs from direct synthesis) in comparison to monodisperse 10/20 nm Sb NPs and bulk Sb as published in He et al. [26]. In He et al. also a more detailed discussion of the performance of nanometer sized particles in comparison to bulk Sb can be found. Due to the similar average size of Sb NPs synthesized by direct synthesis compared to monodisperse Sb NPs, similar results in terms of cycling stability and rate capability were obtained for both Li-ion and Na-ion batteries. This might be explained by the fact, that washing the NPs with water is more efficient in removing all contaminations. Additionally, the absence of any surfactants, which can insulate particles, possibly gives rise to the observed enhanced capacities.

(78) SnSb-Based Anodes

(79) FIG. 17 and FIG. 19 show the electrochemical performance of SnSb NPs synthesized by the herein described procedure in comparison to monodisperse 20 nm SnSb NPs. The as-synthesized SnSb NPs showed the same cycling stability compared to monodisperse 20 nm Sb NPs for both Li-ion and Na-ion half cells, despite their polydispersity and larger average size. Moreover, these SnSb NPs show also in all cases higher capacity levels, most likely due to the removal of all residual contaminations by the washing procedure with water. In particular, such polydisperse SnSb NPs achieved stable capacities of 770 mAh g.sup.1 at 0.33 A g.sup.1 and 700 mAh g.sup.1 at 2.64 A g.sup.1 in Li-ion half cells. In comparison monodisperse 20 nm SnSb NCs showed capacities of 700 and 610 mAh g.sup.1 respectively. FIG. 19 shows the galvanostatic charge and discharge curves for SnSb NPs in Li-ion and Na-ion half cells. In contrast to pure Sb NPs [26], SnSb NPs show lower potentials for the delithiation/desodiation reaction. Therefore, SnSb NPs can even provide higher power compared to pure Sb NPs in a full cell.

(80) In conclusion, SnSb NPs synthesized by the above described procedure showed excellent cycling stability and capacity retention for both Li-ion and Na-ion batteries.

(81) While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

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