Method for manufacturing an Sn:Sb intermetallic phase

Abstract

A method for preparing a material having an Sn:Sb intermetallic phase includes at least the steps of mixing chemical elements Sn and Sb, and treating the mixture with microwaves. An electrode is manufactured by using the material having an Sn:Sb intermetallic phase; forming the material in a form of powder; mixing the powder with carbon, a binder and a solvent to form an ink; coating a current collector with the ink; and drying the electrode.

Claims

1. Method for preparing a material having an Sn:Sb intermetallic phase, wherein the material comprises at most 5 wt % of impurities, relative to a total weight of the material and wherein the material comprises at most 10 wt % of Sn and/or of Sb not belonging to the intermetallic phase, relative to a total weight of the material, said method comprising at least the following steps: a/ mixing precursors consisting essentially of chemical elements Sn and Sb in solid form, and b/ treating the mixture from step a/ with microwaves, wherein the chemical elements Sn and Sb are in contract with a susceptor material for carrying out the treatment of step b/ with microwaves, and a specific energy of the treatment carried out in step b/ is greater than or equal to 24,000 J per g of susceptor, and wherein, with m.sub.(MP) denoting a total weight of the chemical elements Sn and Sb, and m.sub.(S) denoting a weight of susceptor, these weights satisfy the relation: 0.1 m.sub.(MP)≤m.sub.(S)≤3000 m.sub.(MP).

2. Method according to claim 1, wherein the chemical elements Sn and Sb are used in a molar proportion selected from the group consisting of 30/70, 40/60, 50/50, 60/40, and 70/30.

3. Method according to claim 1, wherein a duration of step b/ is greater than or equal to 60 s and less than or equal to 600 s.

4. Method according to claim 1, wherein the specific energy of the treatment carried out in step b/ is greater than or equal to 30,000 J per g of susceptor.

5. Method according to claim 1, wherein the susceptor material is a solid.

6. Method according to claim 5, wherein the susceptor material is selected from the group consisting of carbon and CuO.

7. Method according to claim 6, wherein the susceptor material is carbon and a duration of microwave treatment is from 90 s to 150 s.

8. Method according to claim 6, wherein the susceptor material is CuO and a duration of microwave treatment is from 300 s to 600 s.

9. Method according to claim 1, wherein the chemical elements Sn and Sb are used in a form of powder or pellets.

10. Method according to claim 1, wherein the method is carried out in a substrate made of one of the following materials: alumina (Al.sub.2O.sub.3), silica (SiO.sub.2).

11. Method according to claim 1, wherein the material having an Sn:Sb intermetallic phase corresponds to one selected from the group consisting of: Sn:Sb (3:7), Sn:Sb (2:3), Sn:Sb (1:1), Sn:Sb (3:2), and Sn:Sb (7:3).

12. Method for manufacturing an electrode, said method comprising at least: (1) manufacturing a material having an Sn:Sb intermetallic phase according to claim 1, (2) forming the material from step (1) in a form of powder, (3) mixing the powder from step (2) with carbon, a binder and a solvent to form an ink, (4) coating a current collector with the ink, and (5) drying the electrode.

Description

FIGURES

(1) FIGS. 1a, 1b, 1c, 1d, 1e, 1f, 1g: X-ray diffraction patterns of the material Sn:Sb (1:1) obtained in different synthesis conditions. FIGS. 1a, 1b, 1c, 1d: X-ray patterns of the material Sn:Sb (1:1) obtained using a fixed microwave oven power and a variable time. FIGS. 1e, 1f, 1g: X-ray patterns of the material Sn:Sb (1:1) obtained using fixed time and variable power.

(2) The ordinate represents the intensity in arbitrary units.

(3) The abscissa represents the angle between the incident beam (source) and the diffracted beam (detector) in degrees 2θ.

(4) FIG. 1a The synthesis time is 60 seconds with an applied power of 1000 W (i.e. a specific energy of 20 000 J/g).

(5) FIG. 1b The synthesis time is 70 seconds with an applied power of 1000 W (i.e. a specific energy of 23 333 J/g)

(6) FIG. 1c The synthesis time is 80 seconds with an applied power of 1000 W (i.e. a specific energy of 26 666 J/g)

(7) FIG. 1d The synthesis time is 90 seconds with an applied power of 1000 W (i.e. a specific energy of 30 000 J/g).

(8) FIG. 1e The synthesis time is 90 seconds with an applied power of 800 W (i.e. a specific energy of 24 000 J/g)

(9) FIG. 1f The synthesis time is 90 seconds with an applied power of 900 W (i.e. a specific energy of 27 000 J/g)

(10) FIG. 1g The synthesis time is 90 seconds with an applied power of 1000 W (i.e. a specific energy of 30 000 J/g)

(11) FIGS. 2a and 2b: Images from scanning electron microscopy. FIG. 2a: material from mechanosynthesis; FIG. 2b: material from microwave synthesis.

(12) FIG. 3: Mössbauer .sup.119Sn spectrum of the product Sn:Sb (1:1) made at room temperature. The abscissa represents the speed in mm/s and the ordinate represents the transmission (scale from 0 to 1).

(13) The circles are associated with the experimental points obtained during acquisition.

(14) The solid line represents the spectrum calculated after refinement. An isomeric shift of 2.815 (relative to the source BaSnO.sub.3) corresponds to the material SnSb.

(15) FIG. 4: X-ray diffraction pattern of Sn:Sb (1:1) prepared by microwave synthesis (in black) and by mechanosynthesis (in grey).

EXPERIMENTAL SECTION

(16) I—Materials and Methods:

(17) Raw Materials

(18) Tin: the tin used was that marketed by the company Sigma under reference 14509, of 99% purity, or the tin marketed by the company Alfa Aesar under reference 10378, of 99.5% purity, with particle diameter of 149 μm.

(19) Antimony: the antimony used was that marketed by the company Alfa Aesar under reference 7440-36-0, of 99.5% purity, with particle diameter of 44 μm.

(20) Susceptor: In some examples, the carbon C-Nergy Super C45 Timcal (˜3 g) was used. In other examples, CuO marketed by the company Labosi (Fischer Scientific/Acros Organics) under reference 405862500 was used.

(21) Crucible: a crucible made of alumina (Al.sub.2O.sub.3) was used. The weight of the crucible is 123 grams, with an internal volume of about 60 cm.sup.3.

(22) Rock wool: The upper part of the crucible is heat-insulated with rock wool, which is deposited on the carbon surface directly exposed to the air. The upper part of the crucible is therefore covered with rock wool.

(23) Microwave oven: in some examples, a laboratory microwave oven was used (designated P) (Milestone, StartSynth®, 1200 W); in other examples, a domestic microwave oven was used (designated D) (Panasonic, NN-SD459 W, 1000 W).

(24) The StartSynth, Milestone® microwave oven consists of a single magnetron provided with a rotating diffuser (stirrer) allowing uniform scattering of the waves within the housing. The waves are reflected and then focused (characteristic of multimode operation) on the central zone of the microwave oven in order to irradiate the sample(s) uniformly. Focusing the waves on a defined zone makes it possible to reduce the synthesis time and the energy losses. The maximum useful power supplied is 1200 W. Monomode operation of a microwave oven focuses all of the waves on the sample (restricted zone) via a waveguide. The energy density in monomode is higher than in multimode (at equal power).

(25) —Protocol

(26) The (metallic) precursors in the form of powder in 50/50 molar amount are placed directly in the carbon (susceptor) contained in a crucible, then covered with a thickness of 1-2 cm of this same susceptor and placed in a microwave oven.

(27) Air cooling is used. However, if synthesis is carried out with a container (precursors covered with carbon inside a silica tube for example; the whole is embedded in the carbon), it is possible to perform a water quench. The products are collected in the form of ingots, and are then ground in a mortar for characterization (XRD, Mössbauer, electrochemistry).

Examples 1 to 4: According to the Invention

(28) The details of the parameters of the protocol are stated in Table 1.

(29) TABLE-US-00001 TABLE 1 Synthesis conditions for SnSb Ex1 Ex 2 Ex3 Ex 4 Susceptor CuO C C C Susceptor weight (g) 7 3 3 3 Precursor weight (g) 0.4 0.4 0.5 2.5 Oven D D P P Power (W) 1000 1000 1000 1000 Time (s) 600 420 90 150 Specific energy (J/g of susceptor) 85714 140 000 30 000 50 000

Counter-Examples

(30) Tests following the same protocol are carried out with other starting materials. The conditions are summarized in Table 2.

(31) TABLE-US-00002 TABLE 2 Testing Conditions Ta.sub.2Sn.sub.3 Precursor 1 (P1) Ta Precursor 2 (P2) Sn Molar ratio P1/P2 2/3 Susceptor Carbon Susceptor weight (g) 3 Precursor weight (g) 0.5 Oven P Power (W) 1000 Time (s) 210 Specific energy (J/g of susceptor) 70 000

(32) Tantalum-Tin Alloy

(33) The tantalum-tin phase diagram consists of two phases, Ta.sub.3Sn and Ta.sub.2Sn.sub.3. These alloys are essentially considered for their properties of superconductivity.

(34) Microwave synthesis does not allow the binary Ta:Sn (2:3) to be obtained. No reaction is detected between the two precursors.

(35) —Determination of the Optimum Specific Energy:

(36) The specific energy defines the amount of energy transferred to a gram of susceptor (carbon) and is expressed in joules per gram of susceptor.

(37) We tried to evaluate the minimum specific energy necessary for complete synthesis of the material Sn:Sb (1:1). This determination is carried out according to two methods. According to a first protocol, the time varies while the power is fixed and according to the second protocol the inverse is used, fixing the time and varying the power. All the syntheses are performed with a weight of precursors of 0.5 grams and a weight of susceptor of about 3 grams.

(38) FIGS. 1a, 1 b, 1c, and 1d represent the variation of the X-ray diffraction patterns for synthesis of the material Sn:Sb (1:1) using fixed power and variable time. FIGS. 1e, 1f, and 1g represent the variation of the X-ray patterns for synthesis of the material Sn:Sb (1:1) using fixed time and variable power.

(39) It can be seen that complete synthesis of the material SnSb is possible with a minimum specific energy of 27 000 J/g. Taking into account the uncertainty of the parameters (of the order of 10 seconds or 100 W), a margin of error must be applied; on this basis the minimum specific energy necessary for complete synthesis of the material SnSb can be estimated at 27 000±3000 J/g.

(40) —Determination of the Optimum Synthesis Time:

(41) A value of specific energy of 30 000 J/g is adopted and the parameters (power or time) are selected in order to reach this value.

(42) A power of 400 W with a time set at 225 seconds allows SnSb to be synthesized.

(43) When the maximum power of the microwave oven (1200 W) is used without focusing the waves on the sample, with a synthesis time of 75 seconds, it is found that the synthesis of SnSb is incomplete: both tin and antimony are still present. These two last-mentioned tests demonstrate that a minimum synthesis time is necessary for obtaining complete synthesis. All of the syntheses carried out in the laboratory show that a synthesis time greater than or equal to 90 s with a power of 1200 W makes it possible to obtain complete synthesis. If higher power were to be used, or if the microwave oven focuses the waves on the sample (monomode), the synthesis time could be reduced.

(44) —Methods of Characterization:

(45) X-ray diffraction (XRD): A Panalytical Empyrean® instrument was used (Cu Kα radiation, θ-θ diffractometer).

(46) Mössbauer .sup.119Sn spectrometry (γ-ray source: Ba.sup.119mSnO.sub.3, transmission spectrometer): it is verified whether an amorphous oxide, SbO.sub.x, not detected by XRD, is present. A shoulder around an isomeric shift of 0 is indicative of the presence of a tin oxide. FIG. 3 does not show any shoulder and confirms the absence of SbO.sub.x.

(47) —Electrochemistry:

(48) Step 1: making the ink: Sn:Sb (1:1) synthesized by microwave is formed in order to be tested in electrochemistry. An ink is made and then is spread on a copper sheet serving as current collector. The details of the composition of the ink and its preparation are given in Table 3. The four products are mixed in a mortar and then placed in an agate jar (internal volume: 13 cm.sup.3) with 4 balls with a diameter of 6 mm.

(49) The ink is formulated with 0.82 ml of ultrapure water, to a weight of active material of 200 mg. Mechanical grinding for one hour at 500 rev/min is applied.

(50) The carbon black is marketed by the company SN2A under reference Y50A.

(51) The carbon fibres are marketed by the company Showa Denko under reference VGCF type H.

(52) The carboxymethylcellulose (carboxymethylcellulose sodium with a degree of substitution of 0.7) is marketed by the company Sigma Aldrich under reference 419311.

(53) TABLE-US-00003 TABLE 3 composition of the ink Active material Carbon Carbon CMC (SnSb) black fibres (carboxymethylcellulose) wt % 70 9 9 12 Weight (mg) 200 25.71 25.71 34.29

(54) Step 2: Preparation of the Electrodes

(55) The SnSb ink is deposited using a knife (height of the deposit: 132.5 μm) on a copper sheet with a thickness of 17.5 μm. The film is air-dried for 24 h at room temperature followed by drying at 120° C. under vacuum for 12 h. The thickness of the dried electrode (copper sheet plus ink) is about 40 μm. Electrodes with diameter of 15 mm are cut out using a punch.

(56) Step 3: Assembly of a Button Cell

(57) The SnSb MO electrodes thus prepared are tested in a button cell. The separator is Whatman paper (Ref: GF/D 1823070). Details of the constituents of the electrolyte are shown in Table 4.

(58) TABLE-US-00004 TABLE 4 Composition of the electrolyte Additives Solvents FEC EC PC DMC VC (fluoro- Li salt (ethylene (propylene (dimethyl (vinylene ethylene LiPF.sub.6 carbonate) carbonate) carbonate) carbonate) carbonate) Concen- 1 1 3 1 vol % 5 vol % tration 1 mol/L

(59) Step 4: Electrochemical Performance

(60) The electrochemical results for the electrode made from SnSb produced according to example 4 are shown in Table 5.

(61) TABLE-US-00005 TABLE 5 electrochemical performance of SnSb obtained according to example 4 Theoretical capacity 825 mAh/g Comments Synthesis extremely easy and quick, aqueous electrode formulation Low irreversible capacity in the 1st cycle Reversible specific capacity 865/755 1st cycle (mAh/g) *Calculated relative to SnSb Irreversible exp. capacity in the 13% 1st cycle (%) Specific capacity (≈100 mA/g) 400 mAh/g after 300 cycles Volume capacity after 100 cycles 3600 mAh/cm.sup.3 Coulombic efficiency 1st cycle (%) 87 Coulombic efficiency 300th ≈100 cycle (%)

(62) —Comparison with a Material from Mechanosynthesis:

(63) Preparation of SnSb by mechanosynthesis: this synthesis is carried out following the protocol described by Darwiche, A., Sougrati, M. T., Fraisse, B., Stievano, L. & Monconduit, L. Easy synthesis and long cycle life of SnSb as negative electrode material for Na-ion batteries. Electrochem. commun. 32, 18-21 (2013).

(64) The material from example 3 and the material obtained by mechanosynthesis were analysed by scanning electron microscopy and by X-ray diffraction.

(65) Scanning Electron Microscopy:

(66) The images obtained by SEM are shown in FIGS. 2a and 2b. FIG. 2a corresponds to the material obtained by mechanosynthesis and FIG. 2b corresponds to the material of the invention, example 3. The particles resulting from mechanosynthesis have pronounced surface roughness. However, the SnSb material of the invention is obtained in the form of ingots after microwave synthesis. When these are broken up, we discover highly faceted fragments. The surface is smooth and reveals organization similar to superposition of planes.

(67) X-Ray Diffraction (FIG. 4):

(68) The diffraction pattern of the SnSb from example 3 shows an excess of tin, in contrast to that of SnSb prepared by mechanosynthesis. The presence of a peak of Sn on a diffraction pattern was thought to be due to the presence of 5% of residual Sn, possibly less. A small proportion of antimony is probably in amorphous form (and therefore not detectable by X-ray diffraction) or will potentially enrich the SnSb phase.

(69) The work by Withers, R. L. et al., Old friends in a new light: “SnSb” revisited, 179, 404-412 (2006), describes an SnSb intermetallic phase prepared in an oven for 3 months at 270° C. followed by recasting and then quenching. The diffraction pattern from this work is identical to the SnSb obtained by the method of the invention (example 3). The method of synthesis described in this prior art is not industrially applicable.