METHOD FOR PRODUCING A LITHIUM BATTERY MATERIAL, MATERIALS AND LITHIUM BATTERY

Abstract

Some embodiments relate to a process of manufacturing a material for a lithium battery with enhanced or improved electrochemical characteristics, to the materials that can be obtained by the process of some embodiments, to an electrode incorporating a material of some embodiments, to a battery, in particular a lithium battery, incorporating a material of some embodiments, as well as to the devices incorporating a lithium battery according to some embodiments. Some embodiments can be applied in the manufacture of lithium batteries.

Claims

1. A method of manufacturing a material for an electrochemical cell, the process comprising: grinding fluorinated carbon nanofibers having the formula CFx with 0.2<x<1, the grinding being achieved by frictional impacts for a period of 2 to 100 hours, with a grinding pressure on the particles ranging from 0.2910.sup.6 Pa to 4.810.sup.6 Pa.

2. The method according to claim 1, wherein the grinding is performed under vacuum or under a neutral, or fluorinated atmosphere.

3. The method according to claim 1, wherein the grinding is performed at a temperature from 0 to 15 C. and from 55 to 60 C.

4. The method according to claim 1, wherein the fluorinated carbon nanofibres having the formula CFx with 0.2<x<1 have a diameter from 110 to 170 nm and a length from 5 to 9 m, the central non-fluorinated carbon part of which represents from 3 to 65% by volume of the volume of nanofibres, and whose .sup.13C MAS NMR spectrum has a chemical shift band of 120 to 135 ppm/tetramethylsilane (TMS).

5. The method according to claim 1, wherein the grinding includes an alternation of periods of grinding (B) and pausing (P) without grinding, with B being between 1 second and 100 hours and P also being between 1 second and 100 hours respectively.

6. A material for an electrochemical cell obtained according to the process of claim 1.

7. An electrode, comprising: the material according to claim 6.

8. A battery, comprising: the electrode according to claim 7.

9. The battery according to claim 8, the battery being a lithium battery.

10. The battery according to claim 8, the battery being a button battery, a laboratory battery, a cylindrical battery, or a spiral-wound battery.

11. A device, comprising: the battery according to claim 8.

12. The device according to claim 11, the device being one of a portable telephone, a meter, oil drilling communication equipment, a pressurized device, a low or high temperature device, a watch, a pacemaker, a drug or medication injector, or a neuro-stimulator.

13. The method according to claim 2, wherein the grinding is performed at a temperature from 0 to 15 C. and from 55 to 60 C.

14. The method according to claim 2, wherein the fluorinated carbon nanofibres having the formula CFx with 0.2<x<1 have a diameter from 110 to 170 nm and a length from 5 to 9 m, the central non-fluorinated carbon part of which represents from 3 to 65% by volume of the volume of nanotubes, and whose .sup.13C MAS NMR spectrum has a chemical shift band of 120 to 135 ppm/tetramethylsilane (TMS).

15. The method according to claim 3, wherein the fluorinated carbon nanofibres having the formula CFx with 0.2<x<1 have a diameter from 110 to 170 nm and a length from 5 to 9 m, the central non-fluorinated carbon part of which represents from 3 to 65% by volume of the volume of nanotubes, and whose .sup.13C MAS NMR spectrum has a chemical shift band of 120 to 135 ppm/tetramethylsilane (TMS).

16. The method according to claim 2, wherein the grinding includes an alternation of periods of grinding (B) and pausing (P) without grinding, with B being between 1 second and 100 hours and P also being between 1 second and 100 hours respectively.

17. The method according to claim 3, wherein the grinding includes an alternation of periods of grinding (B) and pausing (P) without grinding, with B being between 1 second and 100 hours and P also being between 1 second and 100 hours respectively.

18. The method according to claim 4, wherein the grinding includes an alternation of periods of grinding (B) and pausing (P) without grinding, with B being between 1 second and 100 hours and P also being between 1 second and 100 hours respectively.

19. A material for an electrochemical cell obtained according to the process of claim 2.

20. A material for an electrochemical cell obtained according to the process of claim 3.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0043] In these figures, Q.sub.exp represents the experimental capacity expressed in mAh/g; Q.sub.th represents the theoretical capacity in mAh/g calculated by considering the fluorination rate achieved by NMR, in the manner described in document F. Chamssedine, Marc Dubois, Katia Gurin, J. Giraudet, F. Masin, D. A. Ivanov, L. Vidal, R. Yazami, and A. Hamwi, Reactivity of Carbon Nanofibers with Fluorine Gas, Chem. Mater., 2007, 19 (2), pp 161-172 [7]; the theoretical capacity Qth is expressed in accordance with the following equation: Qth=(96500*x)/(3.6*(12+19*x), where x corresponds to the fluorination rate F/C for a compound CFx and 12 and 19 are the molar masses of carbon and fluorine respectively.

[0044] The indications of time in hours (h) express the total grinding time when implementing the process of some embodiments; represents the ratio expressed as a percentage between the theoretical capacity and the capacity measured during the experiments; rpm expresses the number of rotations per minute on implementing some embodiments in a grinder as described in the examples below.

[0045] FIG. 1 shows two scanning electron microscope (SEM) photographs: (a) of non-fluorinated carbon nanofibers, and (b) of fluorinated carbon nanofibers having the formula CF.sub.0.31 that can be used in the process of some embodiments.

[0046] FIG. 2 is a schematic representation of the nanofibers similar to the multi-wall nanotubes in FIG. 1 (FIG. 1 (a) and FIG. 1 (b) respectively).

[0047] FIGS. 3 (a) and (b) show two photographs of a material according to some embodiments observed under a scanning electron microscope at different magnifications.

[0048] FIG. 4 is a schematic representation of a battery including a material of some embodiments and enabling the electrochemical behavior of the material of some embodiments to be measured.

[0049] FIG. 5 represents a series of comparative measurements of capacity of the overall electrochemical behavior between a material CF.sub.0.31 of the related art used to implement some embodiments and ground materials CF.sub.0.31 obtained thanks to the process of some embodiments, grinding being performed under air and argon. The theoretical and corrected capacities are shown.

[0050] FIGS. 6 (a) and (b) represent respectively the .sup.13C NMR characterization of nanofibers CF.sub.0.31 before and after grinding under air according to some embodiments, allowing the x of CFx to be measured before and after grinding according to the process of some embodiments. The deconvolution into three Lorentzian contributions is also shown with their attributions: C in CCF in the (C.sub.2F)n type structure (the underscored atom is responsible for resonance), C in a covalent CF bond (written CF), and sp.sup.2 carbon in weak interaction with a neighboring CF bond (written CF). x in CFx=S.sub.(CF)/(S.sub.CF+S.sub.CF+S.sub.CCF), S is the integrated surface of the resonances.

[0051] FIG. 7 shows respectively the .sup.13C NMR characterization of the nanofibers CF.sub.0.68 before (FIG. 7(a)) and after (FIG. 7 (b)) grinding, enabling the real quantity of fluorine x of CFx to be measured before and after grinding for 12 h under argon, according to the process of some embodiments. The deconvolution into two Lorentzian contributions is also shown with their attributions: C in a covalent CF bond (written CF) and sp.sup.2 carbon in weak interaction with a neighboring CF bond (written CF). x in CFx=S.sub.(CF)/(S.sub.CF+S.sub.CF); S is the integrated surface of the resonances. The theoretical and corrected capacities are shown.

[0052] FIG. 8 shows a graph of general comparison of the overall electrochemical behavior of material CF.sub.0.68 of the related art versus CF.sub.0.68 obtained by the process of some embodiments, after grinding for 12 h under air or argon.

[0053] FIG. 9 shows different experimental measurements made on button batteries and laboratory batteries including a material according to some embodiments.

[0054] FIG. 10 shows the discharge curves of fluorinated nanofibers by F.sub.2 () and by TbF.sub.4 (or controlled fluorination) with F/C 0.7. The theoretical capacity is 742 mAh/g for F/C=0.7.

[0055] FIG. 11 is an image of a scanning electron microscope observation of a material according to some embodiments.

[0056] FIG. 12 shows experimental results in the form of galvanostatic discharge curves at 10 mA/g of CF.sub.0.43 CNFs, unground (solid curve) and ground according to the process of some embodiments under different atmospheres for 12 h at 350 rpm under a pressure of 110.sup.6 Pa (under vacuum (solid triangle)), argon (solid circle), nitrogen (diamond), post-fluorination with XeF.sub.2 (solid square).

[0057] FIG. 13 shows experimental results in the form of galvanostatic discharge curves at 10 mA/g of CF.sub.0.71 CNFs, unground (solid curve) and ground, under different atmospheres for 6 h at 350 rpm under a pressure of 110.sup.6 Pa (under vacuum (solid circle)), argon (solid square), nitrogen (solid triangle).

[0058] FIG. 14 shows experimental results in the form of galvanostatic discharge curves at 10 mA/g of ground CF.sub.0.71 CNFs for 6 h at 350 rpm at 110.sup.6 Pa in small and large quantities (solid and dotted black curves, respectively).

EXAMPLES

Example 1: Examples of Implementation of the Process of Some Embodiments

[0059] In this first example, 200 mg of nanofibers (from the MER Corporation, under commercial reference MRCSD) were placed in a nickel basket positioned in the center of a one-liter passivated nickel reactor to be fluorinated by dynamic fluorination (flow of F.sub.2 gas in an open reactor).

[0060] Dynamic fluorination was performed under a flow of pure gaseous molecular fluorine F.sub.2 at a temperature Tf of 420 C., with a flow rate of F.sub.2 of 25-30 ml/min for 180 minutes.

[0061] The material obtained had an atomic ratio rate F/C of 0.31 determined by NMR.

[0062] This material had been ground by a Retsch PM100 (trademark) planetary ball mill in a 50 ml stainless steel bowl with four 10 mm-diameter stainless steel balls under an argon atmosphere for 6 hours at a grinding speed of 350 rpm with 1 min pauses in grinding every 9 min.

[0063] These experiments were repeated with different starter CFx materials, with x being between 0.2 and 1. For example, in order to obtain a CFx material where x=0.68, dynamic fluorination was performed under a flow of pure gaseous molecular fluorine F.sub.2 at a temperature Tf of 420 C., with a flow rate of F.sub.2 of 25-30 ml/min for 180 minutes.

[0064] The SEM photographs in the accompanying FIG. 1 and the diagrams in FIG. 2 show nanofibers before and after fluorination.

[0065] The photographs in FIGS. 3 (a) and (b) show a material of some embodiments after implementing the process of some embodiments, at different magnifications. Studies of these micrographs are under way, but the inventors of the presently disclosed subject matter have already noted: [0066] an altered 1D structure; [0067] nanofibers destroyed and reduced to small flakes; [0068] flaking of the external walls of the nanofibers in the form of isolated sheets and collections of particles; [0069] an opening up of fibers to tend towards a nanometric 2D structure.

Example 2: Example of the Make-Up of an Electrochemical Battery that can be Used to Implement the Material of Some Embodiments

[0070] The material obtained according to Example 1 was placed in suspension in a mixer with glass vessel by mixing with 10% by weight of polyvinylidene fluoride (PVDF) in a liquid medium of propylene carbonate.

[0071] The suspension was then deposited on the stainless steel electrode pads heated to 80 C. over a surface of around 1 cm.sup.2, then the pads were degassed under primary vacuum at 120 C. for 1 hour. 50 mg of cathode material, CFx/PVDF 90/10 was obtained.

[0072] The mass of the pads was then estimated to be between 2 and 5 mg. The pads were returned to the glove box and incorporated into a laboratory lithium battery consisting of or including metallic lithium, Celgard (registered trademark) microporous separators, wetted by LiPF.sub.6 PC/EC/3 DMC 1M electrolyte, as shown in the accompanying FIG. 4. This laboratory battery is a 304L stainless steel battery with an internal diameter of 12 mm consisting of or including a bored cylindrical body in which two 304L steel pistons slide that act as current collectors. Everything is assembled in a glove box and is perfectly sealed, adjustment screws being used to adjust the pistons in the cylindrical body.

[0073] In FIG. 4, the references correspond to the following elements of the electronic battery or cell: [0074] C: electrochemical battery; [0075] P: a stainless steel conductive pad; [0076] A: the active material CF.sub.x; [0077] S: separator elements which in this example are Celgard (registered trademark) membranes in the form of polymer films of polypropylene 12 mm in diameter, 25 m thick and with an average pore diameter of 0.064 m; and/or a Whatman (registered trademark) glass fiber disc 12 mm in diameter; [0078] E: the electrolyte LiPF.sub.6PC/EC/3DMC 1 M; [0079] Li: a lithium disc.

[0080] This electrochemical laboratory cell has two stainless steel electrodes consisting of or including a piston at each end.

[0081] The battery thus constituted is taken out of the glove box and connected to a VMP2 (commercial reference) potentiated/galvanostatic made by Bio-Logic Science Instruments SAS (France). After a relaxation period of 5 h, a 10 to 20 mA/g reduction current is applied with a cut-off voltage of 1.5 V vs. Li.sup.+/Li.

[0082] After the period of relaxation, the battery was discharged until the stopping potential of 1.5 V and a density of 10 mA/g (reduction) or 20 mA/g.

Example 3: Examples of Materials Obtained According to the Process of Some Embodiments and Comparisons with the Corresponding Materials of the Related Art

[0083] This example presents different experiments carried out on different materials obtained according to the process of some embodiments. In particular, the process of some embodiments used in order to obtain the materials tested in this example is that described in Example 1, and the measurements of electrochemical performance are made using a device as described in Example 2.

[0084] The variation in potential as a function of time is then measured. This duration multiplied by the current density allows the capacity to be determined. In 3 electrochemical tests performed on this material, the capacities 970, 1684 and 2339 mAh/g were obtained. The theoretical capacity of this material, corresponding to the capacity measured on the fluorinated carbon nanofibre material used to implement the process of some embodiments, i.e. before grinding, is 465 mAh/g. A marked phenomenon of extra capacity is therefore observed in these different experiments.

[0085] Tables I and II below summarize the experiments carried out in the context of some embodiments.

TABLE-US-00001 TABLE I Examples of experiments with CF.sub.0.31 Presentation .sup.13C NMR of Characterization Discharge of Fluorinated Material Measurements Nanofibers Observations on the electrochemical behavior of the materials CF.sub.0.31 nanofibers FIG. 5 FIG. 6 Discharge potential at 2.5 V of the related art Experimental capacity of 490 mAh/g (Qth at 465 mAh/g) CF.sub.0.31 material FIG. 5 Limited ohmic drop according to some Increase in the discharge potential up to 2.75 V embodiments Average capacity 585 mAh/g, i.e. an average experimental yield of 125% obtained according compared to the calculated capacity for the original composition CF.sub.0.31 and to the process of 150% compared to the calculated value for the corrected composition after Example 1, grinding CF.sub.0.24 (Q corr = 388 mAH/g) grinding for 6 Measured experimental capacity up to 610 mAh/g, i.e. an average hours under air experimental capacity of 131 and 157% of the theoretical capacity compared to the original (CF.sub.0.31) and the corrected composition after grinding (CF.sub.0.24) respectively CF.sub.0.31 material FIG. 5 FIG. 6 Limited ohmic drop according to some Increase in the discharge potential up to 2.7 V embodiments Average experimental capacity at 749 mAh/g for the materials of some obtained according embodiments, i.e. an average experimental yield of 161% compared to the to the process of original composition CF.sub.0.31 and 193% compared to the corrected Example 1, composition after grinding CF.sub.0.22 grinding for 6 Measured maximum capacity 1151 mAh/g, i.e. 247% of the theoretical hours under argon capacity Qth (CF.sub.0.31) Measured F/C for this material of some embodiments from NMR analyses at 0.24, which is equivalent to a corrected theoretical capacity value Qth of 388 mAh/g, to be compared with the measured extra-capacity of 1151 mAh/g for the material of some embodiments with this same F/C ratio, i.e. at 296% of the reference capacity Qth.sub.corrected

TABLE-US-00002 TABLE II Examples of experiments with CF.sub.0.68 Presentation .sup.13C NMR of Characterization Discharge of Fluorinated Material Measurements Nanofibers Observations on the electrochemical behavior of the materials CF.sub.0.68 nanofibers FIG. 8 FIG. 7 Discharge potential at 2.2 V of the related art Measured capacity at 788 mAh/g for a corrected theoretical capacity at 731 mAh/g CF.sub.0.68 material FIG. 8 Limited ohmic drop according to some Increase in the discharge potential up to 2.7 V embodiments Average capacity 792 mAh/g, i.e. an average yield of 108% compared to the obtained according theoretical capacity of a composition CF.sub.0.68 to the process of Measured experimental capacity up to 864 mAh/g, i.e. a yield of 118% Example 1, compared to the theoretical capacity of a composition CF.sub.0.68 grinding for 12 Considering the corrected composition after grinding CF.sub.0.31 and the hours under air corresponding theoretical capacity (464 mAh/g), the average yield is 170% and the maximum yield is 186% CF.sub.0.68 material FIG. 8 FIG. 7 Limited ohmic drop according to some Increase in the discharge potential up to 2.6 V embodiments Average experimental capacity at 927 mAh/g, i.e. a yield of 127% compared obtained according to the theoretical capacity of a composition CF.sub.0.68 to the process of Measured maximum capacity at 1329 mAh/g, i.e. a yield of 181% compared Example 1, to the theoretical capacity of a composition CF.sub.0.68 grinding for 6 Considering the corrected composition after grinding CF.sub.0.31 and the hours under argon corresponding theoretical capacity (464 mAh/g), the average yield is 200% and the maximum yield is 286%

[0086] These different experiments show that the ohmic drop is limited or non-existent with the materials of some embodiments. Thus, batteries made using a material according to some embodiments are immediately operational. The potential has been increased to 2.75 V with the materials of some embodiments.

[0087] The NMR analyses show a defluorination during grinding. However, the electrochemical properties of the materials are markedly enhanced or improved thanks to the process of some embodiments.

[0088] A limitation of heating of the battery is also observed thanks to the materials of some embodiments, as well as enhanced or improved battery life and power, which allows them to be the material of choice for the manufacture of a new generation of batteries, including batteries that must operate at high temperatures, for example at temperatures ranging from 150 to 180 C., or at a low temperature, for example at 20 C.

Example 4: Analysis by SEM Imaging of a Material Obtained According to the Process of Some Embodiments

[0089] During grinding, the grains of powder are highly stressed: they deform and some break, while others stick together. The combined action of this plastic deformation, breakage and sticking together leads to the formation of very homogenous powders consisting of or including agglomerates.

[0090] In the case of the materials obtained by the process of some embodiments, for example a material CF.sub.0.51, the fluorinated carbon nanofibers are still visible, despite the presence of some agglomerates, as shown by the scanning electron microscope (SEM) image in the accompanying FIG. 11.

[0091] These agglomerates have an average size of 1.65 m. In FIG. 11, it will be noted that the fibers are badly damaged: they are broken, cracked and some are open and reduced to small pieces. For this material of some embodiments, three main classes of fibers are identified after grinding: i) those smaller than 1 m ii) those between 1 and 3 m and iii) those larger than 3 m. The most numerous are the fibers smaller than 1 m accounting for 50 to 70%, i.e. about 60% in all of the SEM images analyzed, and those between 1 and 3 m constitute 20 to 40%, i.e. around 30% of the populations represented, and those larger than 3 m represent from 5 to 15% in general, i.e. around 10% of the populations represented.

Example 5: Effect of Variations in Certain Grinding Conditions when Implementing the Process of Some Embodiments

[0092] According to the protocol described in Example 1, other materials according to some embodiments are made by varying the degree of fluorination and/or the grinding time and/or the grinding speed and/or the grinding cycles and/or the grinding temperature in order to obtain different fluorinated materials according to some embodiments, having a degree of fluorination CFx where x ranges from 0.2 to less than 1.

[0093] For example, the experiments with the following parameters are implemented, without being vertically related to each other:

TABLE-US-00003 Variation of grinding speed Examples: 350 rpm 450 rpm Grinding Grinding times 6 hours 12 hours parameters Examples: Quantities of 0.2 g 2 g materials ground Examples: Atmospheres Air Argon Examples:

[0094] Measurements on the materials are made using a device such as that described in Example 2: [0095] CF.sub.0.51 Q.sub.theo 1=630 mAh/g [0096] LiPF.sub.6 PC-EC-3DMC 1M [0097] Relaxation: 5 h [0098] Current Density: 10 mA/g

[0099] The following observations are made regarding the materials currently obtained: [0100] Importance of the grinding atmosphere: the best performance in terms of capacity is achieved when grinding is performed under an argon atmosphere, possibly fluorinated or under a fluorinated atmosphere; [0101] The grinding time must be longer in the case of fluorinated nanofibers that have a higher fluorination rate; [0102] An enhancement or improvement is observed in discharge potential, limitation of ohmic drop and increase in capacity under air and in argon, for ground fibers; [0103] Grinding times from 5 to 10 hours are advantageous, even more so with grinding cycles such as those defined in some embodiments; [0104] Advantageous grinding speeds of 300 to 500 rpm (rotations per minute).

Example 6: Laboratory Battery/Button Battery Comparative Experiments

[0105] The material obtained according to Example 1 was placed in suspension as described in Example 2, except that the battery used differed because button batteries were used.

[0106] FIG. 9 shows the discharge curves obtained with a laboratory battery (square .square-solid.) and a button battery (solid black line).

[0107] A high discharge potential of around 2.8 V was observed in the button battery, with a very limited ohmic drop, which confirms the enhanced or improved electrochemical properties of the materials of some embodiments.

[0108] The .sup.13C NMR analyses show a defluorination of the fluorinated nanofibers during grinding, which implies a reduction in the fluorination rate F/C and theoretical capacity of the material.

[0109] An increased extra-capacity and enhanced or improved electrochemical performance are achieved for laboratory batteries and an extra-capacity is for this reason observed in the button battery.

Example 7: Study of Mechanical Grinding Parameters: Modeling of Grinding and Forces Exerted Using the Process of Some Embodiments

[0110] The grinder used in this example is a planetary ball mill, which produces mechanical stresses of the frictional impact type. The starting materials are comparable to those of Example 3 above, namely CF.sub.0.43 and CF.sub.0.76 versus CF.sub.0.31 and CF.sub.0.68 in Example 3.

[0111] The balls exert a centrifugal force that is determined on the one hand from characteristics specific to the latter, namely their mass, density, diameter, etc., and on the other hand from grinding conditions and accessories, in particular rotation speed and diameter of the bowl, and lastly taking account of the physicochemical characteristics of the material to be ground, in particular the diameter of the particles or fluorinated nanofibers and their stiffness.

[0112] From this force, and using the mechanical formula described below, the pressure of a ball on a particle to be ground can be determined in order to model what happens during the implementation of some embodiments.

[00001]$\mathrm{contact}.Math..Math.\mathrm{surface}=\mathrm{circle}.Math..Math.\mathrm{with}.Math..Math.\mathrm{radius}.Math..Math.a$$a=0.88.\sqrt[3]{\frac{P}{2}.Math.\frac{\frac{1}{E_1}+\frac{1}{E_2}}{\frac{1}{d_1}+\frac{1}{d_2}}}$$\mathrm{maximum}.Math..Math.\mathrm{pressure}.Math..Math.P_{\max }=1.5.\frac{P}{.Math..Math.a^2}$$\mathrm{matching}.Math..Math.\mathrm{of}.Math..Math.\mathrm{the}.Math..Math.\mathrm{centers}.Math..Math.\mathrm{of}.Math..Math.\mathrm{the}.Math..Math.\mathrm{spheres}$$=0.77.\sqrt[3]{2..Math.P^2.{\left(\frac{1}{E_1}+\frac{1}{E_2}\right)}^2.\left(\frac{1}{d_1}+\frac{1}{d_2}\right)}$ [0113] a [m]: radius of the contact disc between the 2 spheres [0114] P [N]: pressure exerted on the sphere [0115] E [MPa]: the Young's moduli of the materials making up the spheres [0116] d [m]: diameters of the spheres [0117] (lambda) [m]: crushing/sinking/matching of the centers of the spheres during contact

[0118] Three ball diameters were studied: 10 mm-15 mm-20 mm, which corresponds to respective pressures of about 110.sup.6 Pa, 210.sup.6 Pa and 410.sup.6 Pa.

[0119] Four different grinding durations were studied: 3 h, 6 h, 12 h and 18 h.

[0120] A speed of 350 rpm was set for all of the experiments.

[0121] In light of the electrochemical performance obtained in this example, optimal grinding conditions for fluorinated nanofibers with a fluorination rate F/C0.4 were determined in the context of this example: [0122] Duration: 12 h [0123] Pressure (ball diameter): 110.sup.6 Pa (10 mm).

[0124] For fluorinated nanofibers with a fluorination level F/C0.8, the optimal grinding conditions were: [0125] Duration: 6 h [0126] Pressure (ball diameter): 110.sup.6 Pa (10 mm).

Example 8: Characterization of a Product Obtained Using the Process of Some Embodiments, from Photos as Shown in FIGS. 3 and 4: Statistical Analysis of the Obtained Materials: % of Each of the Essential Component Elements of these Materials Obtained by Grinding (Sizes, Shapes, % s)

[0127] During grinding, the grains of powder are highly stressed: they deform, and some break, while others stick to each other. The combined action of this plastic deformation, breakage and sticking together leads to the formation of very non-homogenous powders consisting of or including agglomerates.

[0128] In the case of the materials obtained by the process of some embodiments, for example a material CF.sub.0.51, the fluorinated carbon nanofibers are still visible, despite the presence of some agglomerates, as shown by the scanning electron microscope (SEM) image in the accompanying FIG. 11.

[0129] These agglomerates have an average size of 1.65 m. In FIG. 11, it will be noted that the fibers are badly damaged: they are broken, cracked and some are open and reduced to small pieces. For this material of some embodiments, three main classes of fibers are identified after grinding: i) those smaller than 1 m; ii) those between 1 and 3 m; and iii) those larger than 3 m.

[0130] The most numerous are the fibers smaller than 1 m accounting for 50 to 70%, i.e. about 60% in all of the SEM images analyzed, and those between 1 and 3 m constitute 20 to 40%, i.e. around 30% of the populations represented, and those larger than 3 m represent from 5 to 15% in general, i.e. around 10% of the populations represented.

Example 9: Additional Grinding Experiments Under Fluorinated Atmosphere=Grinding Under Fluorine of the Material Dynamically Sub-Fluorinated According to the Process of Some Embodiments

[0131] Post-fluorination experiments were conducted on materials comparable to those of Example 3, and the electrochemical performance of the materials was studied.

[0132] The appended FIG. 12 shows the performance for CF.sub.0.43 ground for 12 h at a pressure of 110.sup.6 Pa under different atmospheres. In particular, galvanostatic discharge curves are shown at 10 mA/g of the CF.sub.0.43 fluorinated nanofibers, not ground (solid curve) and ground under different atmospheres for 12 h at 350 rpm under a pressure of 110.sup.6 Pa (under vacuum (solid triangle), argon (solid circle), nitrogen (diamond), post-fluorination with XeF.sub.2 (solid square)).

[0133] The best performance observed in these experiments was under argon atmospheres.

[0134] The inventors of the presently disclosed subject matter have observed that post-fluorination enhances or improves the performance in terms of the experimental capacity obtained, the fluorination level having slightly increased. Indeed, fluorination by XeF.sub.2 done after grinding induces a surface fluorination of the nanofibers that have been broken or been reduced to small pieces. The intrinsic carbon (not fluorinated) initially located in the core of the fiber is brought back to the surface during grinding and is more accessible to the atomic fluorine derived from the XeF.sub.2 fluorinating agent. This surface re-fluorination, slight but nevertheless present, makes it possible to increase the fluorination level of the ground material and thus explains how a higher capacity is obtained. The ohmic drop remains limited relative to the non-ground fibers (black curve) of the related art but is more pronounced than for the grinding done under argon, vacuum or nitrogen according to the process of some embodiments.

[0135] For the ground CF.sub.0.71 (comparable to the CF.sub.0.8) CNFs (6 h at 110.sup.6 Pa, speed 350 rpm), the same tendencies were observed, as shown in the appended FIG. 13. In this figure, the galvanostatic discharge curves at 10 mA.Math.g.sup.1 of the CF.sub.0.71 CNFs, not ground (solid curve) and ground under different atmospheres for 6 h at 350 rpm under a pressure of 110.sup.6 Pa (under vacuum (solid circle), argon (solid square), nitrogen (solid triangle)).

Example 10: Reproducibility of the Performance Enhancements or Improvements

[0136] The observed extra capacity was visible and repeated on batteries of the Swagelok type, i.e. laboratory batteries and button batteries (industrial batteries).

[0137] The inventors of the presently disclosed subject matter reproduce the experimental results in a button battery, since the performance in general is more reproducible, but above all because these are industrial batteries.

[0138] A study seeking to study the performance of the material on a larger volume was carried out. Thus, a first batch of ground fluorinated CNFs F/C0.8 was synthesized in a 50 ml (1.5 g) bowl, then a second batch in a 250 ml (10 g) bowl.

[0139] The electrochemical performance is comparable to that observed in all of the experiments done relative to some embodiments, including those described above, for the two aforementioned batches, as shown in the appended FIG. 14.

[0140] On average, the discharge potential is 2.6 V for both batches. The average capacity for the small batch (50 ml) is 730 mAh/g and 732 mAh/g for the large batch (250 ml). The results are therefore comparable when the volumes are increased.

[0141] The extra capacity phenomenon was not observed on the selected materials, but they nevertheless have a good experimental capacity, equal or close to the theoretical capacity of the non-ground material, a smaller or non-existent ohmic drop, and a high discharge potential compared to the non-ground fluorinated nanofibers of the related art.

LIST OF REFERENCES

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