CARBON MATERIAL, USE THEREOF IN BATTERIES, METHOD FOR PRODUCING SAID MATERIAL AND ELECTRODE COMPRISING SAME

Abstract

A carbon material comprising particles of hard, non-porous carbon having a spherical morphology, this material having an interlayer distance d002 of more than 3.6 Å and a total specific surface area, measured by the BET N2 method, of less than 75 m2/g, and a method for producing said material. The method further comprises a step of mixing an amine catalyst, an aromatic hydroxyl compound and an aldehyde compound.

Claims

1. A carbon material comprising particles of hard, non-porous carbon having a spherical morphology, this material having an interlayer distance d.sub.002 greater than 3.6 Å, a total specific surface area, measured by the BET N.sub.2 method, of less than 75 m.sup.2/g and a total specific surface area, measured by the BET CO2 method, of 1 to 100 m.sup.2/g .

2. The carbon material according to claim 1, wherein the interlayer distance is between 3.70 Å and 4.00 Å .

3. The carbon material according to claim 1, wherein said total specific surface area, measured by the BET CO.sub.2 method, is from 1 to 50 m.sup.2/g .

4. The carbon material according to claim 1 , wherein said material has a tapped density greater than 0.7 g/cm.sup.3 .

5. The carbon material according to claim 1 , said material having an active surface area (ASA) of less than 12 m.sup.2/g .

6. The carbon material according to claim 1 , said material having an oxygen-based functional group content of less than 0.5 mmol/g .

7. The carbon material according to claim 1 , wherein the particles have a size between 0 .Math.m and 15 .Math.m .

8. A method for manufacturing a non-porous carbon material comprising at least the following steps: a) mixing, in the presence of a polar protic solvent, at least: an amine catalyst selected from the group consisting of triethylenediamine, quinuclidine, triethylamine (TEA), HMTA (hexamethylenetetramine) and mixtures thereof; an aromatic hydroxyl compound selected from the group consisting of phenol, resorcinol and phloroglucinol, catechin, pyrogallol, hydroxyquinol, gallic acid, polyphenols, such as tannins, and mixtures thereof; and an aldehyde compound, selected from the group consisting of glyoxal, formaldehyde, acetaldehyde, a keto acid, glyoxylic acid, pyruvic acid, 2-methyl-3-oxopropanoic acid, and mixtures thereof; b) maturing the mixture obtained at the end of step a), at a temperature comprised between 20 and 35° C., for a period comprised between 0.5 and 5 days, making it possible to obtain a solid phase comprising spheres of phenolic resin and a liquid phase; c) controllably separating said solid phase from said liquid phase; d) polymerizing and/or drying the solid phase for a period of 1 to 48 hours resulting in the formation of a dry phenolic resin; e) carbonizing the dry phenolic resin in the presence of a flow of inert gas at a temperature between 1200° C. and 2000° C. to obtain a non-porous carbon material; and f) optionally a step of recovering the carbon material.

9. The method according to claim 8, wherein the polymerization step is a thermal step, comprising heating to a temperature of 70° C. to 150° C.

10. The method according to claim 9, wherein the amine catalyst is triethylenediamine, the aromatic hydroxyl compound is preferably phloroglucinol or a condensed tannin; and wherein the aldehyde compound is glyoxylic acid.

11. The method according to claim 8 , wherein the maturation step b) is carried out in the absence of stirring.

12. The method according to claim 8 , wherein the separation step c) is carried out without centrifugation.

13. A carbon material obtained according to claim 8 .

14. An electrode comprising a carbon material as described in claim 1 .

15. The carbon material of claim 1 wherein the total specific surface area measured by the BET CO2 method is 1 to 60 m.sup.2/g.

16. The carbon material of claim 2 wherein the interlayer distance is between 3.75 Å to 3.90 Å.

17. The carbon material of claim 3 wherein the total specific surface area, measured by the BET CO2, method is 1 to 10 m.sup.2/g.

18. The carbon material of claim 4 wherein the tapped density is within the range of 0.72 g/cm.sup.3 to 1.1 g/cm.sup.3.

19. The carbon material of claim 5 wherein the active surface area is less than 5 m.sup.2/g.

20. The carbon material of claim 6 wherein the content of the oxygen-based functional group is less than 0.1 mmol/g.

21. The carbon material of claim 6 wherein the size of the particles is between 0 .Math.m and 10 .Math.m.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0062] The invention will be better understood using the embodiments of the invention and the appended drawings, in which:

[0063] FIG. 1 is a diagram of a method according to the invention for manufacturing a carbon according to the invention.

[0064] FIG. 2 is an image obtained by SEM of a carbon according to the ABE 1300 invention (scale 20 .Math.m).

[0065] FIG. 3 is an SEM image of a known carbon, HC-water.

[0066] FIG. 4a is an image obtained by carbon SEM according to the ABE 1300 invention that also comprises a graph FIG. 4b showing the distribution of the particles.

[0067] FIG. 5b is an image obtained by SEM of a carbon according to the invention obtained using the same method as ABE 1300, but without a thermal step at 80° C., and which also comprises a graph FIG. 5a showing the distribution of the particles.

[0068] FIG. 6 is an exploded view of the assembly of a half-cell configuration according to the invention.

[0069] FIG. 7 is an exploded view of the assembly of a configuration of a battery according to the invention.

[0070] FIG. 8 shows the performance of the half-cell using the ABE 1400 material according to the invention, C/50 at 25° C.

[0071] FIG. 9 shows the performance of the half-cell using the ABE 1500 material according to the invention, C/50 at 25° C.

[0072] FIG. 10 shows the performance of the half-cell using the ABE 1600 material according to the invention, C/50 at 25° C.

[0073] FIG. 11 shows the performance of the half-cell using a hard carbon PAC2 C/50 at 25° C.

[0074] FIG. 12 shows the pace of the galvanostatic cycling of the complete cell produced with the ABE 1300 material during formation at C5 & D5

[0075] FIG. 13 shows the retention of the complete cell made with the ABE 1300 material in galvanostatic mode (C5 & D5 formation over 5 cycles then 1C & 1D over 100 cycles)

[0076] FIG. 14 shows the retention of the complete cell made with the ABE 1300 material in galvanostatic mode at different charging regimes and with a constant discharge regime

[0077] FIG. 15 shows the retention of the complete cell made with the ABE 1300 material in galvanostatic mode at different discharge regimes and with a constant charging regime.

[0078] FIG. 16 shows images obtained by SEM of carbons according to the invention, obtained using the method described in example 3bis.

[0079] FIG. 17 is an image obtained by SEM of the carbons according to the invention MC-00 and MC-01 and which also comprise a graph showing the distribution of the particles.

[0080] FIG. 18 is an image obtained by SEM of the carbons according to the invention MC-00, MC-04 and MC-05 and which also comprise a graph showing the distribution of the particles.

[0081] FIG. 19 is an image obtained by SEM of the carbons according to the invention MC-0524, MC-05, MC-0572 and MC-0597 and which also comprise a graph showing the distribution of the particles.

[0082] FIG. 20 shows the FT-IR spectra of different hydrolysable tannins (chestnut, myrobalan, tara) measured on a Jasco FT/IR-4100 spectrophotometer, using a “Jasco Spectra Manager” management program and a resolution at 0.4 cm.sup.-1.

EXAMPLES

Example 1: Syntheses of Carbon Materials According to the Invention

[0083] 4.1 g of phloroglucinol and 3.6 g of glyoxylic acid were dissolved in 200 mL (g) of water with mechanical stirring (~30 min -1 h) at ambient temperature (25° C.) in a flask. Then, 1.8 g of triethylenediamine (TEDA) was added to this mixture and stirred for about 5-10 min until completely dissolved. The addition of TEDA as a crosslinking agent/catalyst causes the formation of a turbid solution of phenolic resin spheres. The mixture is left to stand for an aging time of 24 hours. The spheres increase in size and weight and settle on the bottom of the flask. Two phases are observed: a solid phase (composed of polymer spheres) and a liquid phase. The latter is removed and the solid phase recovered (without centrifugation, by simple pouring) and dried in an oven at 80° C. for around 12 hours to evaporate the water and to better crosslink the resin spheres. A pyrolysis step was then carried out in an inert atmosphere (Ar), by heating 6.5 g of the obtained resin with a heating rate of 5° C./min up to 1300° C., 1400° C., 1500° C. or 1600° C.; once the desired temperature has been reached, a one-hour (1 hour) plateau is done, then a natural cooling step is carried out. The hard carbon is thus obtained (~ 2.5 g) and subsequently used without the need for a grinding step to standardize the particle size.

[0084] The obtained materials are called ABE 1300, ABE 1400, ABE 1500 and ABE 1600.

[0085] It is noted that the ABE 1300 hard carbon was synthesized in larger quantities (30 g) and that this change of scale did not produce any notable change in the structure or in the morphology of the hard carbon thus obtained.

[0086] Five other materials according to the invention were synthesized with condensed tannins of mimosa and cachou as precursors. The spectra in FIG. 20 highlight the structural differences between condensed tannins and hydrolysable tannins. Mimosa-G (MG) and Cachou (C) materials were purchased from GREEN’ING (France), while Mimosa-C (MC) material was obtained from Mimosa Extract Company Ltd.

TABLE-US-00001 Aromatic hydroxyl material Tannin type Constituents Main structural unit Mimosa-C (MC) (Acacia mearnsii) Condensed 66% condensed tannins Tannin[00004] Mimosa-G (MG) (Acacia mearnsii) Condensed 60 to 65% condensed tannins Tannin Cachou (C) (Acacia catechu) Condensed Condensed tannins + flavonols (quercitrin) Quercitrin[00005]

8 g of precursor, i.e. Mimosa-G, Mimosa-C or Cachou, and 9.6 g of glyoxylic acid were dissolved in 320 mL (g) of water with mechanical stirring (~ 30 min) at ambient temperature (25° C.) in a flask. The reaction between the phenolic (hydroxylated) precursor and the aldehyde (crosslinking agent) makes it possible to obtain a phenolic resin. Then, 4,992 g of hexamethylenetetramine (HMTA) was added to this mixture and stirred for about 5-10 min until completely dissolved. The addition of HMTA as a catalyst causes the formation of a turbid solution of phenolic resin spheres. The mixture is left to stand for an aging time of 48 h. The spheres increase in size and weight and settle on the bottom of the flask. Two phases are observed: a solid phase (composed of polymer spheres) and a liquid phase (composed of the solvent and the rest of the residual organic products). The latter is removed and the solid phase is recovered (without centrifugation), by simple pouring for syntheses using mimosa tannins as precursors. For the cachou tannin, centrifugation was necessary due to the small size of the particles (< 1 .Math.m). The solid phase was dried at 25° C., then in an oven at 80° C. for about 12 hours to evaporate the water and to better crosslink the resin spheres. A pyrolysis step was then carried out in an inert atmosphere (Ar), by heating ~ 7 g of the obtained resin with a heating rate of 5° C./min up to 1500° C.; once the desired temperature has been reached, a one-hour (1 hour) plateau is done, then a natural cooling step is carried out. The hard carbon is thus obtained (~ 2.6 g), and it is ground manually.

[0087] The carbons are called MG-00-1500 (from Mimosa-G), MC-00-1500 (from Mimosa-C) or C-00-1500 (from Cachou).

[0088] For the Mimosa G precursor, two syntheses with a higher quantity of glyoxylic acid (14.4 g) were carried out and the obtained polymer was pyrolyzed at 1500 and 1600° C. (sample names: MG-00-EG-1500 and MG-00-EG-1600).

Example 2: Characterization of New Carbon Materials According to the Invention and Comparison With Known Carbon Materials

1) Physicochemical Characterizations

N.SUB.2 and CO.SUB.2 Adsorption

[0089] The textural properties (porosity, specific surface area) of the hard carbons according to the invention were studied by the gas sorption technique with a Micromeritics ASAP 2420 device (Micromeritics France S.A.R.L., Merignac, France 33700) using nitrogen (N.sub.2) as adsorbent at 77K and with a Micromeritics ASAP 2020 using CO.sub.2 as adsorbent at 273K. Before the analysis, the materials were degassed at 300° C. for 12 h under vacuum on the degassing door to eliminate water molecules, and a second degassing was then carried out for an additional 2 h on the analysis door to eliminate the filling gas. A mass of between 150 and 300 mg was employed. The BET (Brunauer, Emmett and Teller) specific surface area was calculated in the relative pressure range of 0.05-0.3.

X-Ray Diffraction (XRD)

[0090] Diffraction data collection is provided by a Bruker D8 Advance A25 diffractometer with theta/theta geometry (goniometer radius: 280 mm), with Cu anode. The machine is equipped with an ultra-fast LynxEye XE-T high-resolution 1D detector with energy discrimination (< 380 eV, Cu Ka 1.2). A motorized anti-diffusion knife for effective suppression of low-angle air diffusion is present. The samples are prepared in a standard poly(methyl methacrylate)-(PMMA) sample holder by making a pyramid of powder that is flattened using a glass slide. The acquisition conditions were as follows: angular range 10-90°2theta, no counting: 0.01°, counting time per step: 0.5 s. The total acquisition time was 1h08. During this acquisition, the sample is rotated at 5 rpm. The DIFFRAC.SUITE, DIFFRAC.EVA software ensures the exploitation of the diffractograms and the calculation of the interlayer distance d(hkl) (distance between two consecutive planes of the same indices (hkl)) is obtained by simple application of Bragg’s law (2d(hkl) sinθ= nλ), where n is an integer (in the case of this work, n=1), λ is the wavelength, and θ is the angle of incidence of the X-ray beam on the plane in index diffraction condition (hkl).

SEM (Scanning Electron Microscopy)

[0091] The morphology of the carbon material was analyzed with an FEI Quanta 400 Scanning Electron Microscope instrument, high-resolution low-vacuum field emission gun (FEG). The samples were analyzed with a resolution between 1 mm and 10 .Math.m and a magnification up to 10,000X. ImageJ software was used to determine the average particle size. Several images were analyzed and approximately 700 to 1000 particles counted in order to produce a particle size distribution histogram.

TPD-MS (Temperature Programmed Desorption Coupled With Mass Spectrometry)

[0092] Temperature-programmed desorption coupled with mass spectrometry (TPD-MS) is an analysis method allowing the study of structural changes in the mass of a material subjected to a temperature-controlled variation. More specifically, TPD-MS measures the desorption rate of molecules as a function of temperature, providing valuable information regarding desorption kinetics, surface concentrations, adsorption sites, etc. With regard to carbon materials, TPD-MS is mainly used to identify oxygenated surface functions, functions which, on decomposing, release CO, CO.sub.2, H.sub.2O and H.sub.2 at the specific thermal stability temperature of the corresponding functional group. The thermodesorption measurements were carried out using a “homemade” assembly operating under vacuum, equipped with a mass spectrometer (maximum pressure 10.sup.-4 Torr).

[0093] Before performing the analyses, the mass spectrometer is calibrated with the following gases: H.sub.2 (m/z=2), H.sub.2O (m/z=18), CO (m/z=28), N.sub.2 (m/z=28), O.sub.2 (m/z=32) and CO.sub.2 (m/z=44).

[0094] About 15-60 mg HC is placed in a quartz boat, then in an oven and degassed for 12 hours under secondary vacuum in order to eliminate the physisorbed water. The TPD-MS is carried out up to 950° C. (with a heating rate of 5° C./min followed by a one-hour plateau), and the released gaseous phase is analyzed quantitatively, throughout the duration of the analysis, by the mass spectrometer.

Another Important Parameter That Can Be Determined by Tpd-Ms is the Active Surface Area (ASA)

[0095] The active surface of a carbon material corresponds to all the different types of defects present in the carbon: stacking faults, single and multiple vacancies, as well as dislocations. The presence of such active sites is important because they can interact with other species (i.e. Li.sup.+, Na.sup.+). The ASA consists in carrying out an oxygen chemisorption followed by a TPD-MS measurement. After a first TPD-MS measurement, the vacuum sample is brought into contact with oxygen at 300° C. (oxygen pressure: 66.5 Pa), which is chemisorbed for 10 hours, leading to the formation of oxygenated complexes on the surface of the material. After these 10 hours, the oxygen is eliminated from the system and a second TPD-MS is carried out (up to 950° C. with a heating rate of 10° C./min), and the oxygenated groups formed are decomposed into CO and CO.sub.2, their amounts then being determined by mass spectrometry. Finally, the ASA value is calculated by taking into account the number of moles of each of the desorbed gases, considering that the surface of an active site of the carbon material that adsorbs an atom of oxygen is 0.083 nm.sup.2.

Tapped Density

[0096] This value is measured using a jolting volumeter, such as the STAV II from J. Engelsmann, Ludwigshafen (DE). The procedure is as follows: [0097] Addition of approximately 2 g of material in a 10 mL graduated cylinder [0098] Initial volume measurement (bulk density) [0099] Launching of 12,000 shots (3 cycles of 4,000 shots) by measuring the volume at each end of the cycle (final tapped density at 12,000 shots).

[0100] To distinguish new materials from known ones, the properties of known materials were also studied and measured. These known carbons are: [0101] Commercial hard carbon reference PAC2* (AEKYUNG PETROCHEMICAL, K, South Korea); [0102] Hard carbon PR 600 obtained according to the method described in Maetz et al. Green Chemistry 19 (2017) p. 2266; [0103] Hard carbon PR 1200 and 1500 described in E. Irisarri et al. (Journal of The Electrochemical Society, 165 (16) A4058-A4066 (2018)) [0104] HC-water hard carbon obtained according to the method described in Beda et al., Carbon 139 (2018) 248-257, with water as solvent (see table 1, row 3).

[0105] The results of these measurements are compiled in particular in the comparative table below as well as in FIGS. 2 and 3.

TABLE-US-00002 Names TT (°C) d.sub.002 (Å) S.sub.BET N.sub.2 (m2/g) S.sub.BET CO.sub.2 (m2/g) COx (mmol/ g) ASA (M21g) Morphol ogy Particle size (.Math.m) ABE 1300 1300 3.90 2.7 60.0 0.36 11.9 spheres 3.5/7.5 ABE 1400 1400 3.88 7.0 20.4 0.11 3.3 spheres 3.9/7.5 ABE 1500 1500 3.80 3.5 6.4 0.046 1.2 spheres 3.4/7.0 ABE 1600 1600 3.77 6.1 9.1 0.044 1.3 spheres 3.5/7.7 MC-00-1500 1500 3.73 8.5 9.2 0.15 5.8 spheres 2.3 MG-00-1500 1500 3.75 6.0 14.6 0.13 4.3 spheres 4.2 C-00-1500 1500 3.67 11.2 17.4 0.22 6.5 spheres 0.45 MG-00-EG-1500 1500 3.75 6.5 10.5 0.12 4.8 spheres 3.7 MG-00-EG-1600 1600 3.72 6.8 13.3- 0.09 3.2 spheres 3.8 PAC2 3.75 3.8 3.6 0.07 6.4 random 9 HC-water 1300 4.00 72 220 0.21 8.4 random 5-200 PR-600 600 4.00 450 5.66 spheres 2-6 PR-1200 1200 3.88 30 394 0.86 24 random 30-200 PR-1500 1500 3.72 58 139 0.64 17 random 30-200

[0106] TT - Heat treatment temperature; d.sub.002 - interlayer distance determined by XRD; S.sub.BET N.sub.2 and S.sub.BET CO.sub.2 - BET surfaces determined by N.sub.2 and CO.sub.2 adsorption; COx -quantity of oxygen-based functional groups assessed by TPD-MS; ASA - active surface area obtained by oxygen chemisorption and TPD-MS; Size of the particles obtained by the SEM technique.

[0107] The hard carbon according to the invention has a spherical and relatively uniform morphology, which allows it to be distinguished from the hard carbons currently available. As is clear when comparing the morphologies of a hard carbon according to the invention and a known hard carbon, which are respectively shown in FIGS. 2 and 3, a hard carbon of known type (Beda et al., and Irisarri et al.) exhibits heterogeneous and random, non-spherical particle morphology with very large sizes (up to 200 .Math.m). The hard carbon according to the invention not only has a spherical and uniform morphology of these particles, but also preferably a uniformity of size. Finally, this mean particle size is advantageously smaller (<10 .Math.m).

[0108] The hard carbon according to the invention is also very different from known spherical amorphous carbons such as PR 600 carbon (Maetz et al.). The hard carbon according to the invention is also a non-porous carbon, that is to say, a carbon having a small total pore volume, or even a low specific surface area, and in particular having a BET N.sub.2 specific surface area of less than 100 m.sup.2/g. Another advantageous characteristic is a small quantity of oxygenated functions (COx) at the surface of the material.

[0109] Table 2 below highlights other differences between the type of hard carbon according to the invention ABE 1300 and the porous carbon PR600.

TABLE-US-00003 *-measured by XPS: Parameter PR600 ABE 1300 Surface chemistry composition* Nitrogen-doped carbon (3-4% N, 8% O, 88% C) Carbon without nitrogen (97% C and 3% O) Density** 1.6 g/cm.sup.3 2.1 g/cm.sup.3

[0110] X-ray photoelectron spectroscopy (XPS) was performed with a VG SCIENTA SES-2002 spectrometer equipped with a concentric hemispherical analyzer. The incident radiation used was generated by a monochromatic Al Ka (1486.6 eV) X-ray source operating at 420 W (14 kV; 30 mA). The broad sweep spectrum signal was recorded with a pass energy of 500 eV.

[0111] **Measured by gas pycnometer: Model: Accupyc 1330™ from Micromeritics, under He. Procedure: 20 purges with 5 repetitions on a 1 mL cell filled to ¾.

Example 3: Effect of the Thermopolymerization Step

[0112] Using a thermopolymerization step makes it possible to obtain different distributions in terms of average particle sizes. A carbon material according to the invention was obtained by carrying out a synthesis identical to those of example 1 having a thermal step at 1300° C., but where the thermopolymerization step was replaced by a drying step (or simple polymerization by standing) at 25° C. The results are shown in FIGS. 4a and 4b and 5a and 5b, which show a typical distribution for the material without a thermal step (FIGS. 5a and 5b) with a peak for an average size at around 3.5 .Math.m,6.5 .Math.m and a more complex distribution with two distinct peaks of average particle sizes at 3.5 .Math.m and 7.4 .Math.m. Such a heterogeneous distribution can be advantageous for the porosity of the electrode. The particle size of these materials was measured using the SEM images and the ImageJ software, which was used to determine the average particle size. Several SEM images were analyzed and approximately 700 to 1000 particles counted in order to produce a particle size distribution histogram.

Example 3bis

[0113] The effect of the TEDA vs. HMTA catalyst was analyzed using Mimosa-C as precursor or aromatic hydroxyl compound. The method according to the invention described in Example 1 for Mimosa-C was replicated the use; either of 0.5 g of TEDA or of 0.624 g of HMTA. 1 g of precursor, i.e. Mimosa-C, and 1.2 g of glyoxylic acid were dissolved in 40 mL (g) of water with mechanical stirring (~30 min) at ambient temperature (25° C.) in a flask. Then, TEDA or HMTA was added to this mixture and it was stirred for about 5-10 min until completely dissolved. It has been observed that the polymer yield recovered after the solid/liquid separation phase is substantially improved (from 33% to 82%) when HTMA is used instead of TEDA. Moreover, as shown in FIG. 16, the morphology obtained in the presence of HMTA is better defined and the particle size is larger. Finally, using a larger quantity of HMTA (0.624 g vs. 0.468 g) makes it possible to obtain better uniformity.

[0114] Using the synthesis described in this example with 0.624 g of HDTMA, the impact of varying the amount of water and glycolic acid as well as the resting time, or maturation, was studied. These data are presented in Tables A, B and C and in FIGS. 17, 18 and 19.

TABLE-US-00004 Sample MC-00 MC-01 Mimosa-C 1 g 1 g Glyoxylic acid 1.2 g 1.2 g H.sub.2O 40 mL 20 mL HMTA 0.624 g 0.624 g Mixing during the maturation phase No No Maturation time 48 hours 48 hours Polymer mass 0.82 g 1.02 g Morphology Spheres (2.3 .Math.m) Spheres (1.8 .Math.m) Carbon yield 30% 45%

[0115] Reducing the amount of water has an advantageous effect on the carbon yield according to the invention. It is also noted that the particle size decreases (cf. FIG. 17).

TABLE-US-00005 Sample MC-04 MC-00 MC-05 Mimosa-C 1 g 1 g 1 g Glyoxylic acid 0.6 g 1-2 g 1.8 g H.sub.2O 40 mL 40 mL 40 mL HMTA 0.624 g 0.624 g 0.624 g Mixing during the maturation phase No No No Maturation time 48 hours 48 hours 48 hours Polymer mass 0.8201 g 0.9809 Morphology Spheres (1.5 .Math.m) Spheres (2.3 .Math.m) Spheres (1.9 .Math.m) Carbon yield 34% 30% 43%

[0116] A decrease in the amount of glyoxylic acid appears to reduce the particle size (cf. FIG. 18).

TABLE-US-00006 Sample MC-0524 MC-05 MC-0572 MC-0597 Precursor Mimosa-C Mimosa-C Mimosa-C Mimosa-C Mass 1 g 1 g 1 g 1 g Glyoxylic acid 1.8 g 1.8 g 1.8 g 1.8 g H.sub.2O 40 mL 40 mL 40 mL 40 mL HMTA 0.624 g 0.624 g 0.624 g 0.624 g Mixture No No No No Maturation time 24 h 48 h 72 h 97 h Morphology Spheres (1.8 gm) Spheres (1.9 .Math.m) Spheres (2.4 .Math.m) Spheres (2.2 .Math.m) Carbon yield 26.0% 44.0% 47.0% 51.0%

[0117] The rest time appears to be optimized around 48 hours, as an increase in this duration only allows a small increase in the size of the spheres (see FIG. 19).

Example 4: Examples of Electrochemical Devices According to the Invention and Comparative Data With a Material of the Prior Art (PAC2)

[0118] Button-type electrochemical cells were assembled according to the diagram in FIG. 6.

[0119] Electrodes according to the invention are manufactured by mixing: [0120] 94% by mass of a hard carbon according to the invention ABE 1300, ABE 1400, ABE 1500 and ABE 1600; [0121] 3% by mass carbon black as conductive additive (C45 from the company Imerys, Paris, FR); and [0122] 3% by weight poly(vinylidene fluoride) (PVdF), PVDF 5130 or SOLEF from SOLVAY, as polymer binder; in the mortar for 5 minutes.

[0123] ≈1 g of dispersed powder is placed in a vial with a magnetic bar. ≈1 g of solvent /V-methyl-2-pyrrolidone (NMP) (CAS No. 872-50-4) is added and the mixture is dispersed for 12 hours at 300 rpm at 25° C. The liquid, or ink, thus obtained is deposited by coating on an aluminum collector (from RJC HOLDINGS CORPORATION in Incheon City, South Korea). The ink layer is dried for 2 hours at 60° C. under air flow. The films thus obtained have a thickness comprised between 130 .Math.m and 160 .Math.m (collector included) and a mass varying between 7.5-10.2 mg/cm.sup.2 of active material. The films are then calendered by successive passage between 2 remote rollers of increasingly smaller size until a film is obtained, the thickness of which remains unchanged regardless of the pressure applied to the film. The films are then pelleted to obtain circular electrodes of 1 cm.sup.2 for the batteries cycling vs. Na and of 1.327 cm.sup.2 for those cycling vs. NVPF. The electrodes are then dried in an oven at 70° C. for 2 hours, as are the various parts of the button cell assembly.

[0124] For full-cell devices, the NVPF electrodes are obtained by mixing:

[0125] 92% by mass NVPF produced by the LRCS in Amiens 4% by mass carbon black as conductive additive (C45 from Imerys, Paris, FR); and

[0126] 4% by mass poly(vinylidene fluoride) (PVDF), PVDF 5130 or SOLEF from SOLVAY, as polymer binder; in the mortar for 5 minutes.

[0127] ≈1 g of dispersed powder is placed in a vial with a magnetic bar. ≈1 g of N-methyl-2-pyrrolidone (NMP) (CAS No. 872-50-4) is added and the mixture is dispersed for 12 hours at 300 rpm at 25° C. The liquid, or ink, thus obtained is deposited by coating on a 22 .Math.m aluminum collector (from RJC HOLDINGS CORPORATION in Incheon City, South Korea). The ink layer is dried for 2 hours at 60° C. under air flow. The films thus obtained have a thickness comprised between 140 .Math.m and 200 .Math.m (collector included) and a mass varying between 15-20 mg/cm.sup.2 of active material.

[0128] The films are then calendered by successive passage between 2 remote rollers of increasingly smaller size until a film is obtained, the thickness of which remains unchanged regardless of the pressure applied to the film. The films are pelleted to obtain circular electrodes of 1.327 cm.sup.2. The electrodes are then dried in an oven at 70° C. for 2 hours, as are the various parts of the button cell assembly. The electrodes comprising ABE 1400, 1500 and 1600 material were combined with sodium metal (to form a half-element or half-cell configuration). The electrode comprising ABE 1300 material was associated with an electrode based on sodium vanadium (III) fluorophosphate (NVPF), to constitute a full-cell configuration.

[0129] The elements of the half-element device are shown in FIG. 6. With the exception of the electrodes, they come from the company INNOV' METOR, FERRIERES EN GATINAIS, FR. A stainless steel spring 6 is positioned in a lower part 2 of a steel cover and inside an insulating ring 4. A current collector 8 made of 316L stainless steel and 0.5 mm thick is positioned on the circular spring. This collector 8 is a disc with a diameter of about 15 mm covered with sodium metal. Sodium metal was spread over the entire upper surface of collector 8, then scraped off with a spatula in order to obtain a clean surface, free of metal oxides. A separator disc 10 made of fiberglass, 1 mm thick and 16 mm in diameter, is positioned on the metal sodium surface. 200 .Math.L of electrolyte is then added. This electrolyte is a mixture of ethyl carbonate (EC) and dimethyl carbonate (DMC) in proportions (1:1% mass mixture, to which the NaPF.sub.6 salt is added in proportions of 1 mol/L. Then an electrode 12 made from hard carbon as described above is positioned on the separator 10. Finally, the upper part 14 of the stainless steel cover is positioned to encapsulate the electrode 12, and the two parts of the cover 2 and 14 are secured together (for example, crimped). In this device, the electrode 12 is in the cathode position and the sodium metal is in the anode position. This device is produced under argon in a glove box. The electrochemical cell is left to rest for 2 hours before the first cycle. The characteristics of the device are then measured by galvanostatic cycling at C/50 in discharge and in charge with a rest of 1 min between 2 modes. Two half-cells (CELL 1 and CELL 2) were studied, and as the results show in FIGS. 8 to 10, the curves obtained are identical. Specific capacity values were acquired when the variation in potential reached 10 mV compared to the previous acquisition and/or every 5 seconds. In this way, it is possible to know the specific capacity with precision.

[0130] The full-cell elements of the device are shown in FIG. 7. With the exception of the electrodes, they come from the company INNOV' METOR, FERRIERES EN GATINAIS, FR. A stainless steel spring 106 is positioned in a lower part 102 of a steel cover and inside an insulating ring 104. A current collector 108 made of 316L stainless steel and 0.5 mm thick is positioned on the circular spring. This collector 108 is a disc with a diameter of approximately 15 mm on which an electrode 112 is positioned comprising a material according to the ABE 1300 invention. The electrode 112 adopts the form of a disc 1.3 cm in diameter and about 110 .Math.m (collector included) thick. A separator disc 110 made of fiberglass, 1 mm thick and 6 mm in diameter, is positioned on the electrode 112. 200 .Math.L of electrolyte is then added. This electrolyte is a mixture of ethyl carbonate (EC) and dimethyl carbonate (DMC) in proportions (1:1 % by mass), mixture to which NaPF6 is added in proportions of 1 mol/L. Then, an NVPF electrode 109 with a diameter of 1.3 cm as described above is positioned on the separator 110. Finally, the upper part 114 of the stainless steel cover is positioned to encapsulate the electrodes 112 and 109 and the two parts of the cover 102 and 114 are secured together (for example, crimped). In this device, the electrode 112 constitutes the anode and the electrode 109 constitutes the cathode. This device is produced under argon in a glove box. The electrochemical cell is left to rest for 2 hours before the first cycle. The mass ratio between the mass of NVPF and the material ABE 1300, NVPF/ABE1300 varies between 2 and 2.5.

[0131] The variation of specific capacity as a function of voltage is shown in FIGS. 12 and 13 and was measured as follows:

[0132] Retention cycle: [0133] Formation: galvanostatic cycling over 5 cycles at C/5 & D/5 at 25° C. with a 5 min rest [0134] Retention: galvanostatic cycling at 1C & 1D at 25° C. with a 5 min rest.

[0135] The specific capacities of the cell were measured as follows:

[0136] The specific capacities as a function of the applied speed (at different currents) make it possible to obtain important information on the performance of the cells in power, for example with a view to addressing certain industrial applications shown in FIGS. 14 and 15.

[0137] Power cycling: [0138] Formation: galvanostatic cycling over 5 cycles at C/5 & D/5 at 25° C. with a 5 min rest [0139] Crate: galvanostatic cycling at variable charge over 5 cycles: from C/5 to 4C and at constant discharge: D/5 at 25° C. with a 5 min rest [0140] Drate: galvanostatic cycling at constant charge: C/5 & at variable charge over 5 cycles: from D/5 to 4D at 25° C. with a 5 min rest

[0141] The specific capacity of the cell is high (about 125 mAh*g.sup.-1). The specific discharge capacity corresponds to 80% of the charge capacity, which corresponds to an initial irreversible capacity of 25 mAh g.sup.-1, when it is cycled at a rate C/5. This loss of capacity is due to the irreversibility of the electrode with the greatest irreversibility, i.e. hard carbon (irreversibility of NVPF: 10%). The capacity decreases to ~75 mAh g.sup.-1 when cycled at 1C/1D. When evaluating the rate (current variation) on the capacity, it was found that the cycling rate used during the charge/discharge step (insertion/extraction of Na+ into/from the hard carbon anode) is essential for good performance. If a low enough current is used to charge the cell, even high discharge rates (3D) end up giving good performance (∼80% retention capacity). On the contrary, when a fast charge rate is used (i.e. 1C), low efficiency is obtained even if the discharge current applied is low (i.e. D/5).

[0142] Porosity, COx functional groups and structural defects quantified by ASA have a significant impact on the initial irreversible capacity. The irreversible capacity decreases with decreasing structural defects (ASA) and with decreasing COx groups. Moreover, the irreversible capacity decreases with the increase in the tapped density.

[0143] Table 3 below compiles the characteristics of carbon materials according to the invention and those of the cells comprising them, as well as the characteristics of a prior art material PAC2 and of a cell comprising it as described above.

TABLE-US-00007 Carbon material Density He (g/cm3) Tapped density g/cm3) Porosity after pelleting (%) Cirrev (%) QiD (mAh g.sup.-1) Qic (mAh g.sup.-1) PAC2* 1.954 0.96 46 14 323 278 ABE 1300 2.107 0.71 62 11 341 303 ABE 1400 2.163 0.74 54 11 346 307 ABE 1500 1.875 0.84 46 8 320 294 ABE 1600 1.633 0.72 41 8 337 309 MC-00-1500 2.10 0.73 58 15 374 315 MG-00-1500 2.05 0.73 56 15 385 329 C-00-1500 1.97 0.71 58 18 354 286 MG-00-EG-1500 2.12 0.67 64 17 403 334 MG-00-EG-1600 1.85 0.70 49 13 366 317 PR1200 0.7 PR1500 0.7 Cirrev = irreversible capacity; Q.sub.ID = initial discharge capacity, Q.sub.ic = initial charge capacity.

[0144] The materials according to the invention have a significant advantage in terms of initial irreversible capacity, which capacity is lower compared to other similar hard carbon materials.