EP2356070A1

EP2356070A1 - Method for manufacturing a sno2 composite material and carbon nanotubes and/or carbon nanofibres, material obtained by the method, and lithium battery electrode comprising said material

Info

Publication number: EP2356070A1
Application number: EP09803810A
Authority: EP
Inventors: Dominique Plee; Mohamed Chakir; Patrice Simon
Original assignee: Arkema France SA; Universite Toulouse III Paul Sabatier
Current assignee: Arkema France SA; Universite Toulouse III Paul Sabatier
Priority date: 2008-12-11
Filing date: 2009-12-04
Publication date: 2011-08-17
Also published as: JP2012511492A; FR2939786B1; WO2010066989A1; FR2939786A1; CN102307807A; KR20110094186A; US20110297889A1

Abstract

The invention relates to a method for manufacturing a composite material including tin oxide particles and a fibrillar carbon material, consisting of synthesising tin hydroxide particles obtained from a tin salt by precipitation/nucleation in a water-alcohol medium, in the presence of the fibrillar carbon material and an acid, the fibrillar carbon material being nanotubes, carbon nanofibres, or a mixture of the two. The invention can be used for the production of negative electrodes for lithium-ion batteries.

Description

PROCESS FOR MANUFACTURING COMPOSITE MATERIAL S _n O ₂ AND

NANOTUBES OF CARBON AND / OR NANOFIBRES OF CARBON,

MATERIAL OBTAINED BY THE PROCESS, BATTERY ELECTRODE FOR

LITHIUM COMPRISING SAID MATERIAL.

Technical field of the invention

The invention relates to a method for manufacturing a composite material comprising a fibrous carbon material and tin oxide. By fibrillar carbon material, one understands the carbon nanotubes NTC or the nanofibers of carbon NFC or a mixture of both. The invention also relates to electrodes made of said material and lithium batteries comprising such electrodes.

The invention applies to the field of storage of electrical energy in batteries and more particularly in lithium secondary batteries Li-ion type.

Tin, like silicon, is likely to form alloys with lithium and allow to obtain capacities much higher than those achieved with graphite.

It is known that the main difficulty in the development of these materials lies in the high volume expansion during lithiation, which causes loss of cohesion of the electrodes and electrical contact losses leading to a significant drop in performance. State of the art

The growth of portable electronic products has contributed to the growing expansion of the battery market, especially lithium-ion batteries. Indeed, by a few hundred thousand in 1995, the world production of lithium - ion batteries reached 500 million in 2000 (compared with the 1300 million Ni - MH batteries) then 1700 million in 2005.

In 2006, Japan, the world's largest producer, alone produced more than 1200 million lithium-ion batteries per year (ITE EXPRESS News, (2005).

Since the emergence of lithium and lithium-ion batteries, several generations of positive and negative electrodes have successively appeared. In the case of negative electrodes, the most commonly used material is carbon graphite due to a long life due to the formation of a protective layer during the first cycles of cycling. The reversible capacity of such anode is 372 mAh / g.

To improve this value, several studies are currently conducted on various materials such as carbon with high form factor (eg carbon nanotubes) or metals that can form alloys with lithium (silicon, antimony, tin, etc.). ..).

Some metal oxides can also be used as negative electrode for Li-ion batteries (SiO 2, SnO, SnO 2, ...). These materials have a capacity much greater than that of graphite carbon, but their lifetime is very limited because volume change during cycling during the alloy reaction. To overcome this problem, several ideas have been put forward, such as the use of nanoscale particles or the development of carbon-tin or carbon-tin oxide composites. In this regard, J. Xie et al, published an article entitled: "Synthesis and

Characterization of High Surface Area Tin Oxide / Functionized Carbon Composite Nanotubes as Anode Materials ", in Materials Chemistry and Physics, 91, (2005), 274-280. This article presents a synthetic route in which tin tetrachloride is reduced in the aqueous phase by means of urea in the presence of carbon nanotubes previously oxidized with permanganate at the surface. The suspension containing the nanotubes is stirred with ultrasound. Urea is then added. Several heat treatments follow one another, the last of which consists of placing the material in an oven at 600 ^° C. The resulting composites show the presence of small particles deposited on the nanotubes, of size between 10 and 20 nm. Many of these particles are not on the surface of the nanotubes, but in the form of aggregates and are therefore not very effective. In addition, the use as a negative electrode material is only suggested without experimental evidence to attest to the results produced in terms of cycling resistance and capacity. Another article by L. Yuan et al, titled "Nano-structured SnO 2 -carbon composite obtained by in-situ spray pyrolysis method as anodes in lithium batteries", J. of Power Sources, 146, (2005), 180-184, describes the preparation of 5-15 nm SnO ₂ nanoparticles, distributed in a carbon matrix synthesized by pyrolysis of an atomized solution of sucrose and SnCl ₂ .

Unlike the previous example, electrochemistry experiments were performed. The initial discharge capacity is 600 mAh / g, which shows that there is a strong irreversibility at the start.

However, the curve of discharge capacity as a function of the number of cycles, shows a decreasing all the less marked that the ratio carbon / carbon + SnO ₂ is high. Correlatively, it also means that the electrode has a lower overall capacity. This solution is not suitable because it does not combine both a good cycling performance and a strong capacity.

Other publications in which SnO ₂ and NTC have been combined have been described:

- The publication of Zhanhong Yang et al, titled "Lithium insertion into the composites of acid-oxidized carbon nanotubes and tin oxide" Materials Letters 61

(2007) 3103-3105 describes a mixture of 20% by weight of SnO ₂ and 80% by weight of carbon nanotubes used for the preparation of electrodes. The SnO ₂ used in this study was prepared at high temperature (1000 ^° C.). The capacity obtained for this material does not exceed 130 mAh / g. - The publication J. -H. Ahn, et al, entitled "Structural modification of carbon nanotubes by various lease milling", Journal of Alloys and Compounds 434-435 (2007) 428-432 describes the preparation of NTC-SnO ₂ composites. The synthesis method used consists of treating at high temperature (600 ^° C.) the NTC-SnO ₂ mixtures obtained by impregnating two types of CNTs (open-end CNTs and closed-ends CNTs) in an acid solution of tin. (SnCl ₂ + HCI). The discharge capacity obtained for the open-end CNT-based composite is less than 600 mAh / g.

- The publication of Zhenhai Wen, et al., Entitled "In Situ Growth of Mesoporous SnO2 on Multiwalled Carbon Nanotubes: A Novel Composite with Porous-Tube Structure as Anode for Lithium Batteries" Adv. Funct. Mater. 2007, 17, 2772-2778, describes a method for in-situ preparation of NTC-SnO ₂ composites by hydrothermal route. The capacity obtained is 350 mAh / g for 50 cycles. The publication Guimin An et al, entitled "Snθ ₂ / carbon nanotube nanocomposites synthesized in supercritical fluids: highly efficient materials for use as a chemical sensor and the anode of a lithium-ion battery", Nanotechnology 18 (2007) 435707, describes composites prepared by hydrothermal route. These materials comprise, by weight, 40% of SnO 2 and 60% of NTC. The capacity obtained after 30 cycles does not exceed 400 mAh / g.

It is understood that in all these publications, the authors always express the capacity relative to the tin contained in the composite, but it is the capacity of the electrode that matters in the battery application. Thus, the current state of the art shows that most studies do not respond to the technical problem of developing a process for manufacturing a composite material based on SnO 2 and NTC and more generally of an SnO2-based composite and a single fibrillar carbon material, leading to a composite material having good electrochemical performance.

In fact, besides the complexity of the processes described, it emerges that for the proposed SnO 2 -NTC composite materials, the cycling improves when the proportion of active compound, in this case tin oxide decreases in the composite, this accompanied by a decrease in the absolute capacity of the composite.

Reference may also be made to the state of the art consisting of the following documents D1, D2 and D3:

- D1 is a publication of WEI, R and AL entitled "Preparation of carbon fiber / SnO2" August 2008, page L2, § Experimental. This document describes a process for coating CFs carbon fibers with tin oxide. The carbon fibers are coated with a layer of SnO2 and are intended for producing microelectrodes. The process consists of cleaning the carbon fibers with acetone and then treating with HNO3 acid to obtain surface COOH or OH bonds. The process described consists in dissolving SnO2 in a mixture comprising 40 ml of ethanol for 60 ml of water in which 0.22 ml of HCl are added and then vigorous stirring at 40 ^° C. The solution continues to be stirred and the CFs cleaned are introduced into the mixture. Stirring of the mixture is continued and other stirring steps, addition of ammonia, washing with distilled water and then with ethanol and drying are chained.

Thus, document D1 relates to a process for depositing tin oxide particles on carbon fibers. It does not describe a process for depositing tin oxide on carbon nanofibers, or on carbon nanotubes. The carbon fibers have a diameter of about 10 micrometers. The SnO2 layer deposited on the surface of a fiber, according to this document, preferably has a thickness of 250 nm.

According to the present invention, the carbonaceous material consists of NTC or NFC or a mixture of NTC and NFC. The diameters of the CNTs and NFCs are not comparable to those of the fibers described in D1 since they are nanometers and not micrometers. In fact, for single-wall CNTs, at most a diameter of 2.2-2.3 nm is reached. Multi-wall CNTs have an external diameter ranging from 3 to 50 nm and NFCs have diameters of 50 to 200 nm. In addition, according to the present invention, multi-walled NTCs of external diameter ranging from 3 to 50 nm, preferably from 5 to 30 nm and better still from 8 to 20 nm, are preferably used. Indeed, the applicant has found that the use of multiwall NTC allows to obtain a higher conductivity, more homogeneous and more stable. In addition, the process described in D1 comprises a dissolving operation done with stirring at a temperature of 40 ^° C. and not at room temperature as in the present invention. The pressure under which this step is made is not given.

In addition, the process described in D1 is complex because of stirring times and additions of components, especially ammonia.

- This process involves a precipitation with ammonia, which corresponds to a chemical precipitation / nucleation.

In contrast, in the present invention, the method comprises a nucleation / crystallization phase which is a physical step since it corresponds to a drying step and then a heat treatment step. The drying step causes evaporation of the reaction medium (ie water) and thus, physical precipitation. One of the advantages of this physical nucleation step is its ease of industrial implementation (use of a simple evaporator or oven) and its non-production of liquid effluent (apart from the water of the reaction medium); which industrially is interesting because it leads to less effluent reprocessing.

Moreover, the problem that was sought to solve in the document D1 (WEIR et al), is not the same as that of the present invention. Indeed, the problem in D1 is that of obtaining a material having good optical and thermal performance.

In the present invention, the problem solved is the production of a composite material comprising a fibrous carbonaceous material (NTC and / or NFC) and tin oxide having good electronic conductivity, a moderate volume expansion during electrochemical cycling. and also a good reversible ability. In particular, the composite material has galvanostatic cycling, a capacity greater than 600 mAh / g after 60 cycles for the realization of electrodes. - D2 is a June 2, 2008 publication of Yu-Jin CHEN et al titled "High Capacity and Excellent Cycling Stability of Single-Walled Carbon Nanotubes / SnO2 Core-shell Structures as Li-insertion Matehal". The composite material described in this document consists of single wall nanotubes (SWNTs) and SnO2. Document D2 specifies that the initial discharge capacity of the "core-shell" structures is greater than 1399 mAh / g and that the reversible capacities of these structures are stabilized at about 900 mAh / g after 100 cycles. The document also states that the diameter of the tin particles deposited on the surface of the nanotubes is about 2 nm and that the length of the single wall carbon nanotubes (SWNTs) is about 20 microns. Thus SWNTs / SnO2 structures have a very large surface and a very long length / diameter ratio leading to their large capacity. Indeed, in this case, the reversible capacitance of the core-shell structures of nanotubes coated with tin oxide is high.

- In D2 (Yu-Jin Chen), the SnO2 content is not taught; therefore, the given charge / discharge results can not be compared with those of the present invention.

According to the present invention, the results are given with respect to the SnO2-NTC composite which contains about 71% by weight of SnO2. Document D2 does not explicitly describe a deposit method but indicates that the method used is that described in the publication corresponding to document D3. However, the process described in document D3 is different from the process of the invention as described hereinafter. - D3 is a March 2003 issue of Wei-Qiang Han et al, entitled "Coating single-walled carbon nanotubes with tin oxide". This document describes a method for depositing tin oxide on single-walled carbon nanotubes. The method described consists in cleaning the surfaces of the carbon nanotubes in a 40% acid bath and at a temperature of 120 ^° C. for 1 hour.

The nanotubes are then rinsed with distilled water. 1 g of tin chloride is placed in a container containing 40 ml of distilled water and then 0.7 ml of 38% hydrochloric acid is added. 10mg of previously cleaned mono-walled carbon nanotubes are put into the prepared solution. Ultrasound is applied to the solution for 3 to 5 minutes and then stirred for 30 to 60 minutes at room temperature.

The nanotubes thus treated are rinsed with distilled water. Then these carbon nanotubes covered with tin oxide are filtered.

The process described in this document D3 is different from the process of the present invention because there is no nucleation / crystallization phase carried out at a temperature above room temperature nor a heat treatment phase. There is also no use of alcohol.

In addition, the process described in D3 comprises a step of filtering the nanotubes coated with tin oxide. Filtration is an operation which results in loss of tin, so the method described therein has a lower tin yield than that of the present invention.

The Applicant has reproduced the experimental conditions described in this document. The curve of discharge capacity as a function of the number of cycles, obtained under these conditions, is illustrated in FIG. 4 and shows that at the end of the second cycle the capacity drops to 790 mAh / g and that after 12 cycles this capacity drops to 620mAh / g. With the method of the present invention, as seen in Figure 1, the capacity is greater than 800 mAh / g after 12 cycles. And the poor tin yield has been confirmed, this yield being 1, 1%, the process used using a large amount of tin.

The state of the art which has just been described furthermore consists of theoretical articles without industrial vision and in particular of an industrial implementation method.

Description of the invention

The problem which the Applicant has sought to solve by the present invention is to propose a method of manufacturing a composite material comprising a fibrillar carbon material and tin oxide without the disadvantages of the deposition processes which have just been described.

The fibrillar carbon / tin oxide composites thus produced according to the present invention have a good electronic conductivity, a moderate volume expansion during the electrochemical cycling and also a good reversible capacity.

The Applicant proposes a method which makes it possible to control the effects of volume expansion during cycling so as not to cause excessive performance losses.

In addition, the proposed method is simple to implement because it uses low temperature conditions and atmospheric pressure for the attachment of tin oxide particles on the surfaces of the carbonaceous fibrillar material. This method is more efficient than the solutions known to date because the composite material obtained has a capacity in charge and discharge after several cycles, greater than that of composite materials in carbon nanotubes and tin oxide of the state of the technical.

In addition, the method does not use any technique likely to deteriorate the performance of the fibrillar carbon material used as is the case in the techniques using ultrasound. The method makes it possible to use a fibrous carbon material such as carbon nanotubes but also carbon nanofibers or a mixture of carbon nanotubes and nanofibers.

The present invention more particularly relates to a method of manufacturing a composite material comprising tin oxide particles and a fibrillated carbonaceous material, mainly characterized in that it comprises a synthesis by precipitation / nucleation in a water-alcohol medium of tin hydroxide particles derived from a tin salt, in the presence of the fibrillar carbonaceous material and of an acid, in that the fibrous carbonaceous material consists of carbon nanotubes or carbon nanofibers or a mixture of carbon nanotubes and carbon nanofibers and in that the synthesis comprises a dissolution / contact phase , carried out at ambient temperature and at atmospheric pressure, then a nucleation / chstallization phase carried out at a temperature above ambient temperature and finally a heat treatment phase.

In the dissolution / contacting phase, a) the tin salt is dissolved in a mixture of water, alcohol and acid and stirred, water is added while stirring is maintained; b) the fibrous carbonaceous material is added and the mixture is stirred, whereby steps a) and b) can be carried out in this order or in the reverse order.

The nucleation / crystallization phase comprises dry evaporation. The drying consists in fact in bringing the reaction mixture to a temperature higher than the ambient temperature (typically 25 ° C under 1atms) but lower than the boiling temperature of the mixture (typically less than 100 ⁰ C). This dry evaporation is, for example, carried out at a temperature of between 25 and 80 ^° C., or better still of 40 ° C. at 70 ^° C.

The heat treatment phase consists of heating the product obtained at a temperature much higher than the boiling temperature of the reaction mixture. This heat treatment phase is carried out in an oven, under nitrogen or in air, for about ten minutes, at a temperature of between 300 ° and 500 ° C.

Drying ensures nucleation while heat treatment provides crystallization.

Nucleation is carried out according to the invention by a physical step. The fibrillar carbonaceous material may be added during the dissolving / contacting phase in powder form or in pre-dispersion.

Previous predispersion can be achieved by milling in planetary ball mill type water or the like. In the case where the fibrillar carbonaceous material is added in powder form, the agitation is vigorous stirring, which may be identical to that practiced in the case of predispersion. This energetic agitation breaks down the aggregates and increases the density of the material. In other cases of agitation, stirring can be carried out by means of a blade (non-energetic agitation).

According to another characteristic of the invention, the fibrous carbonaceous material consists of carbon nanotubes or carbon nanofibers or a mixture of carbon nanotubes and carbon nanofibers. By carbon nanotubes is meant hollow tubes with one or more graphitic plane walls, concentric from 2 to 50 nm in outer diameter. By carbon nanofibers is meant solid fibers of graphitic carbon, with a diameter of 50 to 200 nm, but which may often have a thin hollow central channel. For nanotubes as for nanofibres, the length / diameter ratio is much greater than 1, typically greater than 100.

The Applicant has found that it is preferable to obtain the best results of treating the fibrillar carbon material at the output of manufacture (synthesis). This material is treated so as to remove the catalytic residues present. Thus, the tin oxide particles adhere better to the surfaces. This purification treatment consists of carrying out an oxidation which enables the fibrillar carbonaceous material to exhibit OH and / or COOH type surface polar functions.

The purification is obtained for example by means of a strong mineral acid such as HNO ₃ or H ₂ SO ₄ . The acid treatment is followed by a surface oxidation operation by means of sodium hypochlorite (NaOCl) or hydrogen peroxide (H2O2) or ozone (O _3), when the selected acid to purify is not enough oxidizing (for example H ₂ SO ₄ ).

The invention also relates to the composite material obtained by the process as described, the material being mainly characterized in that it consists of a homogeneous distribution of tin particles on the surfaces of the fibrillar carbonaceous material with a virtual absence of tin particles not supported by said material. The material consists of 20 to 35% by weight of fibrous carbonaceous material and 65 to 80% by weight of tin oxide particles.

In the case where the fibrous carbonaceous material is a mixture of carbon nanotubes and carbon nanofibers, this mixture is preferably composed of 50% by weight of each of the two constituents.

In the case where the composite material described consists of carbon nanotubes and tin oxide particles, it has galvanostatic cycling, a capacity greater than 600 mAh / g after 60 cycles.

In the case where the composite material consists of carbon nanotubes, carbon nanofibers and tin oxide particles, it has, in galvanostatic cycling, a capacity greater than 750 mAh / g after 60 cycles.

The carbon nanotubes are preferably multi-wall CNTs.

Multi-walled NTCs of external diameter ranging from 3 to 50 nm, preferably from 5 to 30 nm and better still from 8 to 20 nm, are preferably used because the multi-wall CNTs make it possible to obtain a higher, more homogeneous conductivity and more stable.

The invention applies to the production of electrodes comprising a composite material as described above and particularly to the production of negative lithium-ion battery electrodes. In particular, an electrode comprises a composite material consisting of a mixture of at least 80% by weight of active material (NTC-SnO 2) and at most 20% by weight of binder.

The binder can consist of any liquid, or molecular or polymeric paste, chemically inert, generally used to adhere together powder particles, such as polyvinylidenedifluoride (PVDF), polyvinylpyrrolidone (PVP), CMC (carboxymethylcellulose) .

The invention applies to the production of lithium-ion batteries comprising a negative electrode comprising a composite material as described above. Brief description of the drawings

Other features and advantages of the invention will become clear from reading the description which is given below and which is given by way of illustrative and nonlimiting example and with reference to the figures in which: FIG. 1 represents the load capacitance and discharge curves of a composite material consisting of NTC-SnO 2 as a function of the number of cycles.

FIG. 2 represents a scanning electron microscope photograph of the composite material according to the invention with a magnification of

150000.

FIG. 3 represents a diagram of an exploded view of an elementary lithium battery cell according to the invention.

FIG. 4 represents the discharge capacity curve as a function of the number of cycles obtained under the experimental conditions reproduced by FIG.

Applicant, of document D3 of the prior art.

Detailed examples and characterization of the results.

The following examples will better understand the scope of the invention. Example 1

Particular example of implementation of the method of manufacturing the composite material. In this example, purified CNTs are used as fibrous carbonaceous material to obtain better adhesion of the tin particles as previously described. The Applicant has found that the carbon nanotubes at the output of synthesis are not adapted to the process. In order for the tin oxide particles to adhere, the surface of the nanotubes must have surface polar functions of the OH and / or COOH type. These functions are obtained by treating the nanotubes in a strong acid such as HNO3 (oxidizing acid) or H ₂ SO ₄ (weakly oxidizing acid), followed by surface oxidation by means of sodium hypochlorite if acid used to purify is not enough oxidizing.

Other oxidants, such as H ₂ O ₂ or O ₃ can also be used without compromising the scope of the invention.

This finding is also true when it is desired to incorporate carbon nanofibers into the composition.

In addition, the Applicant has found that tin oxide particles of the order of a few nanometers provided better results. The particles used are advantageously nanoparticles of tin oxide. This first example is carried out in the following steps:

Dissolution of 3.8 g of SnCl ₂ , 2H ₂ O in a mixture of C ₂ H ₅ OH (15 ml) + HCl (37%, 0.1 ml).

- Agitation for a few hours (1 to 3 hours) by means of a blade or a magnetic bar.

- Add 90ml of distilled water and keep stirring for a few hours (1 to 2 hours).

- Addition of 1g of carbon nanotubes previously purified by means of H ₂ SO ₄ and oxidized on the surface with NaClO then vigorous stirring if the nanotubes are in powder form and not already predispersed, for 2 hours.

- Evaporation to dryness (in an oven for example at 60 ⁰ C).

Heat treatment at 400 ^° C. for 15 minutes under nitrogen or in air.

It is clear that the opposite order can be followed: first, a predispersion of nanotubes is prepared by vigorous stirring, to which nanofibres are optionally added, and then the tin salt solution is added. Example 2 Figure 3 The electrochemical performances were characterized in lithium batteries, that is to say that the positive electrode K consists of lithium metal and the electrolyte E is a lithium salt in an organic solvent of composition

EC / DMC 1/1 by volume (ethylene carbonate / DiMethyl carbonate), with a concentration of LiPF ₆ equal to 1 M.

The negative electrode A consists of a mixture of 80% by weight of active material (NTC-SnO ₂ ) and 20% by weight of PVDF (PolyVinylidene difluoride), which is a binder for ensuring good mechanical strength. of the electrode. These different constituents are introduced into N-methyl pyrrolidone in order to obtain a very homogeneous mixture. This mixture is then coated on a glass plate by "Doctor BLADE" enducous plate.

The coating is at a thickness of 150 microns. Electrodes 11 mm in diameter are then cut from this film and dried for several hours (6 to 8 hours) at 80 ° C under vacuum.

Once in a cell (button cell), the negative electrode A is covered successively with a separator S (polypropylene impregnated electrolyte) and the positive electrode K which is a lithium metal pellet. The electrolyte used is a lithium salt (LJPF6, 1M) dissolved in the organic solvent mixture EC / DMC (ethylene carbonate / DiMethyl carbonate) in the proportions by volume 1/1. Different elementary cells thus constituted assembled in glove box under controlled atmosphere to form a battery.

The various electrochemical tests are carried out on VMP3 (Biology SAS). The electrochemical behavior of NTC-SnO2 composites was studied in C / 10 constant mode galvanostatic mode in the potential window [0.02-1.2] V (vs. LiVLi).

FIG. 1 represents the electrochemical performances in charge-discharge of the carbon nanotube-SnO 2 composite used as negative electrodes (anode) for Li-ion batteries.

This negative electrode consists of the material synthesized by the process just described. The reversible capacity drops at the end of the first cycle but remains at about 700 mAh / g for more than 30 cycles. After 60 cycles, the composite capacity remains above 600mAh / g.

Figure 2 is an electron microscope view of the NTC-SnO2 composite. In this figure, we can see the homogeneous distribution of tin nanoparticles on the walls of carbon nanotubes and a virtual absence of unsupported particles. Example 3

This example reproduces the test conditions of Example 2 but replacing in the synthesis half of the carbon nanotubes, ie 0.5 g per 0.5 g of carbon nanofibers (for example, it is nanofibers of carbons sold by the company Showa Denko and whose diameter is 150 nm).

Before preparation of the composite, these nanofibers were treated in the presence of sodium hypochlorite. A negative electrode A is then manufactured with this new composite. The reversible capacity drops at the end of the first cycle but remains at about 870 mAh / g for more than 30 cycles. After 60 cycles, the composite capacity remains above 750 mAh / g. Nanofibers are able to provide electrical connections over long distances and carbon nanotubes act more locally.

Indeed, nanotubes seem to play the role of "elastomeric" material to accommodate volumic variations, as well as short-distance electrical connectors between particles and nanofibers seem to play the role of long-distance connector.

In all cases, the nanotubes used are purified so that the ash content is less than 2.5% by weight loss at 900 ⁰ C in air and the nature of the surface, because at the output of synthesis, the nanotubes contain catalytic residues which can reach up to 10% by weight.

The invention presented here makes it possible for a tin oxide SnO 2 to obtain a reversible capacity of the order of 850 mAh / g after 50 cycles without unfavorable volume expansion. The composite material obtained by the process (SnO 2 with a fibrillar carbon material) also provides the following results:

an increase in the specific surface area thanks to the nanometric size of the SnO 2 particles, making it possible to reduce the diffusion length of lithium during the deintercalation / intercalation of lithium,

an increase in the electronic conductivity thanks to the addition of the fibrillar carbon material.

Claims

1. A method of manufacturing a composite material comprising tin oxide particles and a fibrillar carbon material, characterized in that it comprises a synthesis by precipitation / nucleation in water-alcohol medium of hydroxide particles. tin from a tin salt in the presence of the fibrillated carbonaceous material and an acid, in that the fibrillar carbon material is carbon nanotubes or carbon nanofibers or a mixture of carbon nanotubes and carbon nanotubes; carbon nanofibers and in that the synthesis comprises a dissolution / contacting phase carried out at ambient temperature and at atmospheric pressure and then a nucleation / crystallization phase carried out at a temperature above room temperature and a heat treatment phase.

2. A method of manufacturing a composite material according to claim 1, characterized in that in the dissolution / contacting phase, a) the dissolution of the tin salt in an alcohol and acidic water mixture is carried out and stirred. then adding water while maintaining agitation, b) adding fibrous carbonaceous material and stirring the mixture; the "steps a) and b) can be operated in this order or in the reverse order.

3. Process for manufacturing a composite material according to claim

1, characterized in that the nucleation / crystallization phase comprises dry evaporation.

4. A method of manufacturing a composite material according to claim 3, characterized in that the dry evaporation is carried out in an oven at a temperature between 25 and 70 ⁰ C.

5. A method of manufacturing a composite material according to claim 1, characterized in that the heat treatment phase is carried out under nitrogen or air for about ten minutes at a temperature between 300 ⁰ C and 500 ° C .

6. A method of manufacturing a composite material according to any one of the preceding claims characterized in that the fibrillar material is added in powder form or in pre-dispersion beforehand.

7. A method of manufacturing a composite material according to claim 6, characterized in that, in the case where the material is added in powder form, stirring is vigorous stirring.

8. A method of manufacturing a composite material according to claim 6, characterized in that the predispersion is carried out by grinding in water, the grinding being planetary ball milling type.

9. A method of manufacturing a composite material according to any one of the preceding claims, characterized in that the fibrillar carbon material consists of carbon nanotubes or carbon nanofibers or a mixture of carbon nanotubes and nanofibers of carbon.

10. A method of manufacturing a composite material according to claim 9, characterized in that the carbon nanotubes are multi-walled NTC of external diameter ranging from 3 to 50 nm, preferably NTC multi walls of external diameter ranging from at 30 nm and better from 8 to 20 nm.

11. A method of manufacturing a composite material according to any one of the preceding claims, characterized in that the fibrillar carbonaceous material is treated beforehand so as to be purified by oxidation to have OH-type surface polar functions and / or COOH.

12. A method of manufacturing a composite material according to claim 11, characterized in that the polar surface functions are obtained by a treatment of the fibrillar carbon material in an acid such as HNO3 or H ₂ SO ₄ .

13. A method of manufacturing a composite material according to claim 12, characterized in that the treatment with an acid is followed by a surface oxidation operation by means of sodium hypochlorite (NaOCI) or hydrogen peroxide (H ₂ O ₂ ) or ozone (O3), when the acid chosen for purification is not enough oxidizing (for example H ₂ SO ₄ ).

14. Composite material obtained by the method according to any one of the preceding claims, characterized in that it consists of a homogeneous distribution of tin particles on the walls of the fibrillar carbonaceous material with a virtual absence of particles of tin not supported by said material.

15. Composite material according to claim 14, characterized in that it consists of 20 to 35% by weight of fibrillar carbon material and 65 to 80% by weight of tin oxide particles.

16. Composite material according to claim 14 or 15, characterized in that in the case where the fibrillar carbon material is a mixture of carbon nanotubes and carbon nanofibres, this mixture is preferably composed of 50% by each of the two constituents. .

17. Composite material consisting of carbon nanotubes and tin oxide particles, according to claim 14, characterized in that it has galvanostatic cycling, a capacity greater than 600 mAh / g after 60 cycles.

18. Composite material consisting of carbon nanotubes, carbon nanofibers and tin oxide particles, according to claim 16, characterized in that it has galvanostatic cycling, a capacity greater than 750 mAh / g after 60 cycles.

An electrode comprising a composite material according to any one of claims 14 to 18.

20. Negative electrode lithium-ion battery according to claim 19, characterized in that it comprises a mixture of at least 80% by weight of active material (NTC-SnO2) and at most 20% by weight of binder .

21. Negative electrode according to claim 20, characterized in that the binder consists for example of polyvinylidenedifluoril (PVDF), polyvinylpyrrolidone (PVP) or carboxymethylcellumose (CMC).

22. Lithium-ion battery comprising a negative electrode according to claim 19, 20 or 21.