BR102014006443A2 - compound si / c as anode materials for lithium ion batteries - Google Patents

Abstract

si / c compounds as anode materials for lithium ion batteries. The invention relates to a process for producing a si / c compound comprising providing a silicon-containing active material, providing lignin, contacting the active material with a lignin-containing c-precursor and carbonizing the active material by converting inorganic carbon lignin at a temperature of at least 400 ° C in an inert gas atmosphere. The invention further provides a si / c compound used as anode material in lithium ion batteries, an anode material for lithium ion batteries containing such an si / c compound, a process for producing an anode for a lithium ion battery. lithium-ion battery, where such anode material is used, and also a lithium-ion battery comprising an anode with an anode material according to the invention.

Description

deliberately. Typical surface functionalities may be: Si-H, Si-Cl, Si-OH, Si-O-alkyl, Si-O-aryl, Si-alkyl, Si-aryl, Si-O-silyl. Surface-bound groups may also contain functional groups and may be polymeric or monomeric. They may be attached only to the surface of Si in one or more chains of the molecule or may bridge with a plurality of Si particles.

In addition to the Si-based active material, other active materials may also be perfectly present in the Si / C composite materials of the invention.

They may consist of a modification of carbon (especially graphite, carbon black, amorphous carbon, pyrolytic carbon, soft carbon, hard carbon, carbon nanotubes (CNTs), fullerenes, graphene) or other active material such as modalities are not restricted to the mentioned examples) Li, Sn, Mg, Ag, Co, Ni, Zn, Cu, Ti, B, Sb, Al, Pb, Ge, Bi, rare earths or combinations thereof. In addition, other components based on an electrochemically inactive material based on metals (eg copper), oxides, carbides or nitrides may be present in the composition.

Lignin is a highly branched macromolecular polyphenol with a complex structure analogous to phenol or resorcinol formaldehyde resins.

For the purposes of the present invention, the term lignin encompasses all three-dimensional and amorphous polymeric networks composed of three basic aromatic building blocks of paracumaryl alcohol, coniferyl alcohol and synaphyl alcohol, which may bond together in various ways.

Natural lignin is a constituent of many plant organisms and can be obtained, for example, from coniferous woods, broadleaf trees, grasses or other plant raw materials.

Lignin may also have been chemically synthesized from suitable precursors.

Lignin from plant raw materials can be obtained by lignocellulose digestion processes.

Typical industrial digestion processes are the sulfate process, the sulfite process, wood or solvent saccharification methods (Organosolv or Aquasolv processes), which are practiced in various modifications.

Lignin may be used in pure form or as a derivative, for example, as lignosulfonate, or as metallic lignosulfonate.

In addition to lignin, other C precursors may also be introduced, mixed or separately, in succession, into the compound.

These possible precursors may be (but are not limited to the groups of materials mentioned): elemental carbon (especially carbon black, graphite, charcoal, coke, carbon fiber, fullerene, graphene, etc.) simple hydrocarbons (eg example methane, ethane, ethylene, acetylene, propane, propylene, butane, butene, pentane, isobutane, hexane, benzene, toluene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, pyridine, anthracene, phenanthrene, etc.), polyaromatic hydrocarbons and mixtures of hydrocarbons (especially brasses and tars: mesogenic pitch, mesophase pitch, petroleum pitch, hard coal tar pitch, etc.), organic acids (mainly citric acid), alcohols (especially ethanol, propanol, furfuryl alcohol, etc.), carbohydrates (especially glucose, sucrose, lactose, cellulose, starch including monosaccharides, oligosaccharides and polysaccharides), organic polymers (especially epoxy resins, phenol-formaldehyde resin, resorcinol-formaldehyde resin, polyethylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyvinyl oxide, polyethylene polyvinyl, polyvinyl , polydopamine, polypyrrol, polyparaphenylene) and silicones.

The C precursors may be present mixed in molecularly bound form (e.g. copolymers) or separately together in the structure of the compound.

The coating of the silicon-based active material with lignin and, optionally, other precursors of Cea incorporation of the silicon-based active material in a lignin-containing matrix can be done in a number of ways.

The silicon-based active material may be subjected to high energy milling together with lignin (dry or water or organic solvent) or may be physically mixed in any form with lignin.

In addition, the silicon-based active material may be dispersed in a lignin dispersion or solution, and coated with lignin or incorporated into lignin by subsequent evaporation of the solvent.

This can be accomplished by removing the solvent under reduced pressure or by Si / lignin precipitation and subsequent filtration or centrifugation.

Liquid phase processes are preferred as they allow the best distribution of silicon in lignin to be achieved.

In addition, the silicon-based active material can be processed directly into lignin solutions such as are obtained, for example, from the Organosolv process.

The silicon / lignin compounds obtained in this way may additionally react in wet form or after drying.

Intermediates may also be further milled prior to further processing or subjected to coating / incorporation with additional C precursors.

Another possibility is to deposit silicon nanoparticles from the gas phase onto lignin by means of CVD or TVD processes, or to deposit C precursors from the gas phase onto the Si-based active material.

Conversion of lignin and, optionally, other C precursors to inorganic carbon to produce the Si / C compounds of the invention preferably occurs thermally by anaerobic carbonization; This process can occur, for example, in a tube furnace, a rotary tube furnace or a fluidized bed reactor.

The choice of reactor type will preferably depend on whether the carbonization is to be performed statically or with continuous mixing of the reaction medium.

The carbonization may be carried out at temperatures ranging from 400 to 1400 ° C, preferably from 500 to 1000 ° C and particularly preferably from 700 to 900 ° C.

The atmosphere used consists of an inert gas such as nitrogen or argon, preferably argon, so that new proportions of a reducing gas such as hydrogen can be optionally added.

The atmosphere may be static over the reaction medium or flow as a gas stream over the reaction mixture.

The flow rates used for this purpose may be (for example, in a reactor volume of ~ 2350 cm) in the range of 0 mL to 1 L per minute, preferably from 100 to 600 mL / min and particularly preferably 200 mL. mL / min.

Heating of the reaction mixture may be carried out at different heating rates in the range of 1 to 20 ° C per minute, preferably using heating rates of 1 to 10 ° C / min and particularly preferably from 3 to 5 ° C. C / min

In addition, a gradual carbonization process using various temperatures and intermediate heating rates can also be performed.

After the target temperature has been reached, the reaction mixture is kept at temperature for a specified period of time or immediately refrigerated.

Advantageous rest times are from 30 minutes to 24 hours, preferably from 2 to 10 hours and particularly from 2 to 3 hours.

Cooling can also be performed actively or passively as well as evenly or in stages.

Si / C compound powders obtained in this way can be characterized analytically directly and used for extra electrode preparation or can be further mechanically treated, for example by pre-milling or screening processes. In addition, it is also possible to use them for other surface modifications, for example by applying additional C coatings.

Si / C compound powders can be obtained as isolated particles, loose agglomerates or cohesive aggregates.

Si / C particles may be spherical, barbed or even linear, in the form of fibers, or may be present as tangled fibers of the ball.

The average primary particle size of the compounds may be <1 mm, preferably <20 pm and particularly preferably <10 pm.

The particle size distribution may be monomodal, bimodal or polymodal.

Amorphous carbon produced from lignin and, optionally, other C precursors may cover the silicon-based active material in the form of a thin layer or form a matrix of C, wherein the base-active material Silicon is internally incorporated or present outside the surface, as well as combinations of these configuration possibilities. The matrix of C may be very dense or otherwise porous.

Both the silicon-based active material and the carbon in the Si / C compound may be crystalline or amorphous, or contain mixtures of crystalline and amorphous constituents.

Si / C compounds may have low or very high specific surface areas (BET) which may be in the range 0.1 to 400 m2 / g (for purposes of the present invention, preferably from 100 to 200 m2 / g).

The Si / C compounds of the invention may have various chemical compositions.

In general, Si / C compounds may have Si contents from 10 to 90 wt%, C contents from 10 to 90 wt%, O contents from 0 to 20 wt% and N contents. from 0 to 10% by weight. Preference is given to compositions made up to 20 to 50 wt% Si, 50 to 80 wt% C, 0 to 10 wt% O, and 0 to 10 wt% N. Particular preference is given to compositions comprising up to 2040 wt% Si, 60 to 80 wt% C, 0 to 5 wt% O and 0 to 5 wt% N.

The carbon present may, depending on the composition of the compound, be pure amorphous carbon obtained by carbonization, conductive carbon black, graphite, carbon nanotubes (CNTs) and other carbon modifications.

In addition to the above-mentioned major constituents, other chemical elements may also be present in the form of an intentional addition or coincident impurity: Li, Fe, Al, Cu, Ca, K, Na, S, Cl, Zr, Ti, Pt, Ni, Cr, Sn, Mg, Ag, Co, Zn, B, Sb; their content is preferably <1 wt% and particularly preferably <100 ppm.

The present invention further provides the use of the Si compounds of the invention as electrode material for lithium ion batteries.

The electrode materials of the invention are preferably used to produce the negative electrode of a lithium ion battery.

In the present invention, the electrode materials of the invention are processed with other components and optionally with a solvent such as water, hexane, toluene, tetrahydrofuran, N-methylpyrrolidone, N-ethylpyrolidone, acetone, ethyl acetate, dimethyl sulfoxide, dimethylacetamide or ethanol, or solvent mixtures to produce a paint or electrode paste.

Processing of the material may be performed, for example, using rotor-stator machines, high energy mills, planetary kneading machines, agitated ball mills, stirring tables or ultrasonic devices.

For the purposes of the present invention, other components are storable materials such as graphite or lithium, polymeric binders or mixtures of binders, conductive materials such as conductive carbon black, carbon nanotubes (CNT) or post-metallic and other adjuvants, as dispersants or pore formers. Possible binders are polyvinylidene fluoride, polytetrafluoroethylene, polyolefins or thermoplastic elastomers, particularly ethylene propylene diene terpolymers.

In a particular embodiment, modified cellulose is used as a binder.

The solids content of the paint or paste is in the range of 5 wt% to 95 wt%, particularly preferably from 10 wt% to 50 wt%.

The paint or electrode paste comprising the compound materials of the invention is applied by means of a doctor blade under a dry layer thickness of 2 pm to 500 pm, preferably 10 pm to 300 pm, to a copper foil. or other current collector.

Other coating methods such as spin coating, dipping, painting or spraying can likewise be used.

Prior to coating the copper foil with the electrode material of the invention, the copper foil may be treated with a commercial brush, for example one based on polymeric resins. This increases copper adhesion, but has virtually no electrochemical activity per se.

The electrode coating is dried to constant weight.

The drying temperature depends on the materials used and the solvent used.

It is in the range of from 20 ° C to 300 ° C, particularly preferably from 50 ° C to 150 ° C.

The proportion of the composite material according to the invention based on the dry weight of the electrode coating is in the range of 5 wt.% To 98 wt.%, Particularly preferably from 60 wt.% To 95. % by weight.

[0088] The present invention further provides a lithium-ion battery with a first electrode as a first cathode, a second electrode as an anode, a membrane disposed between the two electrodes as a separator, two connections on the electrodes, a housing that accommodates the components. and a lithium-containing electrolyte with which the two electrodes are impregnated, where part of the second electrode contains the Si-containing composite material according to the invention.

As cathode material it is possible to use lithium and cobalt oxide, lithium and nickel oxide, lithium oxide, nickel and cobalt (doped and undoped), lithium and manganese oxide (spinel), lithium oxides, nickel , cobalt and manganese, lithium oxide, nickel and manganese oxide, lithium iron phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium vanadium phosphate or lithium vanadium oxides.

[0090] The separator is a membrane that is permeable to ions only, as is known in the production of batteries. The separator separates the first electrode from the second electrode.

Electrolyte is a solution of a lithium salt (= electrolyte salt) in an aprotic solvent. Electrolyte salts that may be used include, for example, lithium hexafluorophosphate, lithium hexafluorarsenate, lithium perchlorate, lithium tetrafluorborate, LICF3SO3, LiN (CF3SO2) or lithium borates.

The concentration of the electrolyte salt is preferably 0.5 mol / l up to the solubility limit of the respective salt, but is preferably 1 mol / l.

As solvents, cyclic carbonates, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, dimethoxyethane, diethoxyethane, tetrahydrofuran, gamma-butyrolactone, dioxolane, acetonitrile may be used. organic carbonic esters or nitriles, either individually or as mixtures thereof.

Even more preference is given to the electrolyte containing an old film such as vinylene carbonate, fluoroethylene carbonate, etc., as a result of which a significant improvement in cycle stability of the Si composite electrode can be achieved. This is mainly attributed to the formation of an intermediate solid electrolyte phase on the surface of active particles.

The proportion of the film former in the electrolyte is in the range of 0.1 wt% to 20.0 wt%, preferably in the range of 0.2 wt% to 15.0 wt%, and even more. preferably from 0.5 wt% to 10 wt%.

In addition to the above-described liquid electrolyte systems, it is also possible to use solid electrolytes or gel electrolytes comprising a solid phase, for example, polyvinylidene fluoride, hexafluorpropylene, polyvinylidenehexafluorpropylene fluoride copolymer, polyacrylonitrile, methacrylate. polymethyl or polyethylene oxide, and also mixtures of these solid electrolytes with the above mentioned liquid electrolyte phases.

The lithium-ion battery of the invention can be produced in all common forms, in rolled, folded or stacked form.

All substances and materials used to produce the lithium-ion battery of the invention as described above are known.

[0099] The production of the battery parts of the invention and their assembly to form the battery of the invention are carried out by known processes in the field of battery production.

The invention is illustrated below with the examples.

Examples Unless otherwise indicated, the examples below were performed under a dry argon 5.0 atmosphere and under local atmospheric pressure, ie about 101.3 kPa (1013 mbar), and at room temperature, ie at about 23 ° C.

The solvents used for the synthesis were dried by standard methods and stored under a dry argon atmosphere.

The following methods and materials were used in the examples: Carbonization: All carbonizations performed in the examples were performed using a three zone tube oven at 1200 ° C (TFZ 12/65/550 / E301) available. from Carbolite GmbH using cascade adjustment including an N-type thermocouple.

The temperatures indicated are the internal temperature of the tube furnace at the thermocouple position.

The starting material to be charred in each case was weighed into one or more combustion crucibles made of fused silica (QCS GmbH) and inserted into a working tube made of fused silica (6 cm in diameter; 83 cm in diameter). length).

[00107] The process settings and parameters used for carbonizations are given in the respective examples.

Post-treatment / grinding mechanics: The Si / C powders obtained after carbonization were further comminuted by grinding using a PM1000 planetary ball mill available from Retsch.

For this purpose Si / C powder was introduced into a 50 mL grinding cup (special steel or zirconium oxide) together with a grinding medium (especially steel or zirconium oxide; 10 or 20 µm). mm in diameter) and bite for a set time at a predefined speed of rotation (200 or 300 rpm).

The following analytical methods and instruments were used to characterize the Si / C compound obtained: Scanning Electron Microscopy / Energy Dispersive X-ray Spectroscopy (EDX / SEM): The microscopic studies were performed using a Zeiss Ultra 55 scanning electron microscope and an INCA x-sight energy dispersion X-ray spectrometer.

A carbon coating was applied to the vapor phase samples by means of an SCD500 Baltec sputtering / carbon coating prior to examination to avoid charge accumulation phenomena.

Inorganic Analysis / Elemental Analysis: The C levels and, where appropriate, the S levels given in the examples were determined by means of a Leco CS 230 analyzer; A Leco TCH-600 analyzer was used to determine O and, where appropriate, N and H contents.

Qualitative and quantitative determination of the other indicated elements in the obtained Si / C compounds was performed after digestion using HNO3 / HF by inductively coupled plasma emission spectrometry (ICP) using the Perkin Elmer Optima 7300 DV instrument.

The indicated chlorine contents were determined by ion chromatography.

Particle Size Determination Particle size distribution indicated in the examples was determined by static laser light scattering on a LA-950 instrument available from Horiba.

Si / C compounds were, for this purpose, dispersed in water with the addition of octylphenoxypolyethoxyethanol (IGEPAL). BET-specific surface area: [00118] Determination of the specific surface area of the Si / C compounds obtained was performed by the BET method using the Sorptomatic 1990 instrument available from Thermo Fisher Scientific, Inc.

Thermogravimetric Analysis (TGA): The ratio of various carbon modifications in a compound (especially graphite (G) in addition to amorphous carbon (a-C)) was determined by thermogravimetric analysis using a Mettler TGA 851 thermobalance.

The measurement was performed under oxygen as the measurement gas in the temperature range 25 to 1000 ° C and at a heating rate of 10 ° C / min.

In the presence of G and C, the mass loss caused by the combustion of total carbon occurs in two stages, in the temperature range 400 to 800 ° C, from the reason that an aC: G ratio indicated in the relevant examples. has been determined.

Materials Used: The following materials were purchased from commercial sources or internally synthesized and used directly without further purification: Silicon Nanopowder Powder (20 to 30 nm; nanostructured and amorphous materials), Silicon Nanopowder Dispersion (23%, by weight, in ethanol, D50 = 180 nm) Graphite KS6L-C (Timcal), Carbon Nanotubes (Baytubes C70P; Bayer Material Science), Polyacrylonitrile (Sigma-Aldrich), Dimethyl Sulfoxide (Acros Organics), Sodium Dodecyl Sulfate (SDS; Sigma Aldrich).

Lignin was produced as an aqueous-organic solvent from beech chips in an Organosolv process.

Digestion (at 180 ° C for 4 h) was performed in 50% strength (v / v) aqueous-ethanolic solution using a 4: 1 liquid ratio (solvent: flakes).

The lignin solution was separated from the fibrous fraction by filtration.

The dark brown lignin solution obtained had a solids content of 4 to 7% by weight.

Alternatively, the corresponding digestion (170 ° C for 2 h) was performed in 50% (v / v) strength aqueous-ethanolic solution with an additional 1% by weight of H2 SO4 - unless otherwise indicated. , the H2SO4 free lignin solution was used in the following examples.

Example 1 1.50 g of silicon nanopowder (20 to 30 nm;

Nanostructured & Amorphous Materials) was added in 150 mL of lignin solution (7 wt.% In H2 O / EtH) and treated in an ultrasonic bath for 1 hour. The volatile constituents were removed under reduced pressure and the brown residue was partitioned between two molten silica crucibles and charred under argon in a tube furnace: under heating rate of 10 ° C / min, temperature 800 ° C, holding time 2 h and 200 mL / min Ar flow. After cooling, 4.70 g of a powdery black solid (36% carbonization yield) was obtained. The product was later bite in a planetary ball mill: the grinding cup and the grinding medium made of special steel; 1st milling: 3 balls (20 mm), 200 rpm, 1 h; 2nd milling: 12 balls (10 mm), 200 rpm, 1 h.

Elemental composition: 27 wt% Si, 56 wt% C, 15 wt% O, Li <10 ppm, 0.34 wt% Fe, Al <10ppm, Cu <10 ppm, 0.31 wt% Ca, 0.60 wt% K, 250 ppm Na, S <0.1 wt%.

Particle size distribution: monomodal; D10: 3.83 µm, D50: 6.87 µm, D90: 10.7 µm.

Specific surface area (BET): 106 m2 / g.

Example 2 2.00 g silicon nanopowder (20 to 30 nm;

Nanostructured & Amorphous Materials) were added in 200 mL of lignin solution (7 wt.% In H2 O / EtH) and the resulting dispersion was sonicated for 10 minutes. Water (200 mL), which was previously free of dissolved oxygen by passing argon through it, was added dropwise to the stirring dispersion. The precipitated Si / lignin compound, as filtered off, was washed several times with water and dried at 60 ° C under reduced pressure (3.5 h). The increased residue was divided between two molten silica crucibles and carbonized under argon in a tube furnace; heating rate 0 ° C / min, temperature 800 ° C, standby time 2 h, air flow 200 irtL / min. After cooling, 3.95 g of a black powdery solid was obtained (57% carbonization yield). The product was later bite in a planetary ball mill: the grinding cup and the grinding medium made of special steel; 3 balls (20 mm, 200 rpm, h.

Elemental composition: 44 wt% Si, 48 wt% C, 7 wt% 0, Li <10 ppm, 0.10 wt% Fe, 120 ppm Al, Cu <10 ppm, 32 ppm Ca, 21 ppm K, 46 ppm Na, S <0.1 wt.%.

Particle size distribution: monomodal; D10: 0.65 µm, D50: 7.09 µm, D90: 14.2 µm.

Specific surface area (BET): 254 m2 / g.

Example 3 4.00 g silicon nanopowder (20 to 30 nm;

Nanostructured & Amorphous Materials) were added in 400 mL of lignin solution (7 wt% in H2 O / EtOH) and the resulting dispersion was sonicated for 10 minutes. Water (400 mL), which was previously free of dissolved oxygen by passing argon through it, was added dropwise to the stirring dispersion. The precipitated Si / lignin compound, as filtered off, was washed several times with water and dried at 60 ° C under reduced pressure (4.5 h). The increased residue was divided between two molten silica crucibles and carbonized in two stages under argon in a tube furnace: 1) Heating rate 2 ° C / min, temperature 300 ° C, standby time 2 h, flow rate 200 ml / min. Carbonization yield at stage 1: 70%. 2) Heating rate of 10 ° C / min, temperature of 800 ° C, standby time of 2 h, air flow rate of 200 mL / min. Carbonization yield at stage 2: 89%.

After cooling, 6.25 g of a black powdery solid (63% total carbonization yield) was obtained. The product was subsequently ground in a planetary ball mill: the grinding cup and the grinding medium made of special steel; 3 balls (20 mm, 200 rpm, 3 h.

Elemental composition: 53 wt% Si, 41 wt% C, 5 wt% O, Li <10 ppm, 143 ppm Fe, 48 ppm Al, Cu <10 ppm, 70 ppm Ca, 98 ppm K 110 ppm Na, S <0.1 wt%.

Particle size distribution: monomodal; D10: 0.75 µm, D50: 2.54 µm, D90: 5.56 µm.

Specific surface area (BET): 201 m2 / g.

Example 4 2.00 g of silicon nanopowder (20 to 30 nm;

Nanostructured & Amorphous Materials) and 3 g of graphite (Timcal) were added in 180 mL of lignin solution (7 wt% in H 2 O / EtOH) and the resulting dispersion was sonicated for 15 minutes. Water (180 mL) that was previously free of dissolved oxygen by passing argon through it was added dropwise to the stirring dispersion. The precipitated Si / graphite / lignin compound was filtered off, washed several times with water and dried at 60 ° C under reduced pressure (4 h). The black-brown residue was placed in a molten silica crucible and charred under argon in a tube furnace; first, at a heating rate of 2 ° C / min, a temperature of 300 ° C, a standby time of 2 h and an air flow rate of 200 mL / min; then immediately thereafter at a heating rate of 10 ° C / min, temperature 800 ° C, standby time 2 h, air flow rate 200 mL / min. After cooling, 6.00 g of a black powdery solid was obtained (76% carbonization yield). The product was manually comminuted to a grail.

Elemental composition: 30 wt% Si, 66 wt% C (44 wt% G; 22 wt% BC), 3 wt% O, Li <10 ppm, 15 ppm de Fe, 17 ppm Al, Cu <10ppm, 17 ppm Ca, 19 ppm K, 20 ppm Na, S <0.1 wt.%.

Particle size distribution: monomodal; D10: 3.04 ym, D50: 5.31 ym, D90: 8.72 ym.

[00145] Specific Surface Area (BET): 101 m2 / g.

Example 5 18.0 g of silicon nanopowder dispersion (23 wt% in ethanol, D50 = 180 nm) and 400 ml lignin solution (7 wt% in H2 O / EtOH) were mixed together. under agitation. Water (450 mL), which was previously free of dissolved oxygen by passing argon through it, was added dropwise to the stirring dispersion. The precipitated Si / lignin compound was filtered off, washed several times with water and dried at 60 ° C under reduced pressure (4.5 h). The brown residue was divided between two molten silica crucibles and carbonized under argon in a tube furnace: first, at a heating rate of 3 ° C / min, temperature 300 ° C, waiting time for air flow to 200 mL / min; then immediately thereafter at a heating rate of 10 ° C / min, temperature 800 ° C, standby time 2 h and air flow rate of 200 mL / min. After cooling, 5.04 g of a black powdery solid was obtained (49% carbonization yield). The product was first comminuted manually in a gral and then ground in a planetary ball mill: the grinding cup and grinding medium made of special steel; 3 balls (20 mm, 200 rpm, 2 h.

Elemental composition: 48 wt% Si, 43 wt% C, 8 wt% O, 0.2 wt% N, 0.5 wt% H, Li <10 ppm, 440 ppm Fe, Al <100 ppm, Cu <10ppm, 240 ppm Ca and 34 ppm K.

Particle size distribution: monomodal; D10: 0.62 µm, D50: 2.56 µm, D90: 5.53 µm.

Specific surface area (BET): 206 m2 / g.

Example 6 1.70 g of silicon nanopowder (20 to 30 nm;

Nanostructured & Amorphous Materials) and 2.60 g of carbon nanotubes were introduced into 155 ml of lignin solution (7 wt.% In H20 / EtOH) and the resulting dispersion was first mixed with a small amount (spatula tip ) sodium dodecyl sulfate (SDS) and was subsequently ultrasonically treated for 25 minutes. Water (200 mL), which was previously free of dissolved oxygen by passing argon through it, was added dropwise to the stirring dispersion. The precipitated Si / lignin compound was filtered off, washed several times with water and dried at 60 ° C under reduced pressure (4.5 h). The black-brown residue was placed in a molten silica crucible and charred under argon in a tube furnace; first, at a heating rate of 2 ° C / min, a temperature of 300 ° C, a standby time of 2 h and an air flow rate of 200 mL / min; then immediately thereafter at a heating rate of 10 ° C / min, temperature 800 ° C, standby time 2 h, air flow rate 200 mL / min. After cooling, 5.72 g of a black powdery solid from carbonization yield (25% was obtained). The product was subsequently ground in a planetary ball mill; the grinding cup and grinding medium made of zirconium oxide; 3 balls (20 mm), 300 rpm, 2 h.

Elemental composition: 29 wt% Si, 54 wt% C (44 wt% CNT; 10 wt% BC), 17 wt% O, Li <10ppm, 20 ppm Fe 0.13 wt% Al, 15 ppm Cu, 130 ppm Ca, 70 ppm K, 40 ppm Zr, S <0.1 wt%.

Particle size distribution: bimodal; D10: 0.14 pm, D50: 0.45 pm, D90: 2.19 pm.

Specific surface area (BET): 231 m2 / g.

Example 7 A) 4.00 g of silicon nanopowder (20 to 30 nm;

Nanostructured & Amorphous Materials) were added in 400 mL of lignin solution (7 wt.% In H2 O / EtH) and the resulting dispersion was sonicated for 15 minutes. Water (400 mL), which was previously oxygen-free by passing argon through it, was added dropwise to the stirring dispersion. The precipitated Si / lignin compound was filtered off, washed several times with water and dried at 60 ° C under reduced pressure (4.5 h). The brown residue was placed in a molten silica crucible and charred under argon in a tube furnace; first, at a heating rate of 3 ° C / min, a temperature of 300 ° C, a standby time of 2 h and an air flow rate of 200 mL / min; then immediately thereafter at a heating rate of 10 ° C / min, temperature 800 ° C, standby time 2 h and air flow rate of 200 mL / min. After cooling, 6.33 g of a black powdery solid was obtained (51% carbonization yield). The product was subsequently milled in a planetary ball mill: the grinding cup and grinding medium made of special steel; 12 balls (10 mm), 200 rpm, 2 h. Particle size distribution: bimodal; D10: 0.14 pm, D50: 0.91 pm, D90: 5.75 pm.

B) 4.00 g of polyacrylonitrile (PAN) was dissolved in 60 mL of water-free dimethyl sulfoxide by stirring at room temperature. The Si / C compound produced in a) (6.05 g) was introduced into the stirring PAN solution, and the resulting dispersion was treated in an ultrasonic bath for 1 hour. Volatile constituents were removed at 80 to 90 ° C under reduced pressure. The rubber-like residue was comminuted, split between two molten silica crucibles and charred under argon in a tube furnace: first, at a heating rate of 3 ° C / min, temperature 280 ° C, holding time 1, 5 h and 200 mL / min Ar flow rate; then immediately thereafter at a heating rate of 10 ° C / min, temperature 800 ° C, standby time 2 h and air flow rate of 200 mL / min. After cooling, 7.29 g of a black powdery solid was obtained (72% carbonization yield). The product was subsequently ground in a planetary ball mill; the grinding cup and grinding medium made of zirconium oxide; 3 balls (20 mm), 300 rpm, 2 h.

Elemental composition: 38 wt% Si, 51 wt% C, 7 wt% 0, 4 wt% N, Li <10 ppm, 670 ppm Fe, 61 ppm Al, 35 ppm Cu, 90 ppm Ca, 54 ppm K, 400 ppm Zr.

Particle size distribution: monomodal; D10: 1.24 pm, D50: 4.34 pm, D90: 8.61 pm.

Specific surface area (BET): 105 m2 / g.

Example 8 1.18 g of the compound material of example 4 and 0.18 g of conductive carbon black (Timcal, Super P Li) was dispersed in 11.4 g of 1.0 wt% strength solution. of sodium carboxymethylcellulose (Daicel, grade 1380) in water by means of a high speed mixer at a circumferential speed of 12 m / s. After degassing, the dispersion was applied by means of a film pulling frame with a gap height of 0.25 mm (Erichsen model 360) to a copper sheet (Schlenk Metallfolien, SE-Cu58) with a thickness of 0.030 mm The electrode coating produced in this way was subsequently dried at 80 ° C for 60 minutes. The average weight per unit area of the electrode coating is 2.35 mg / cm2.

Example 9 Electrochemical studies were performed on a half cell in a three-electrode array (zero current potential measurement). The electrode sheath of example 8 was used as the working electrode, the lithium foil (0.5 mm thick Rockwood Lithium) was used as the reference electrode and counter electrode. A 6-layer nonwoven stack (Freudenberg Vliesstoffe, FS2226E) impregnated with 100 µl of electrolyte served as a separator. The electrolyte used consisted of a 1 molar solution of lithium hexafluorophosphate in a 3: 7 (v / v) mixture of ethylene carbonate and diethyl carbonate, which was mixed with 2% by weight of vinylene carbonate. The cell was constructed in a glove box (<1 ppm H2 O2), and the dry matter water content of all components used was less than 20 ppm.

The electrochemical test was performed at 20 ° C. The potential limits used were 40 mV and 1.0 V vs. Li / Li +. Electrode charging or lithium was performed by the cc / cv (constant current / alternating voltage) method under constant current and then reached the voltage limit under constant voltage until the current was below 50 mA / g. Electrode discharge or slippage was performed by the dc method (constant current) using a constant current until the voltage limit is reached. The specific current selected was based on the weight of the electrode coating.

[00162] Reference is made below to Figures 1 and 2.

[00163] Figure 1 shows the charging (dashed line) and discharge capacity (continuous line) of the electrode sheath of example 8 as a function of the number of cycles in a current of 100 mA / g.

The electrode coating of example 8 exhibits a reversible capacity of about 700 mAh / g, which corresponds to a capacity of the composite material of example 4 of 875 mAh / g.

[00165] Figure 2 shows the discharge capacity of the electrode coating as a function of discharge current at a constant load current of 100 mA / g.

[00166] The reversible electrode sheath capacity according to example 8 is practically independent of the prescribed specific current of up to 1000 mA / g.

Comparative Example 1 (not according to the invention) 2.00 g silicon nanopowder (20 to 30 nm;

Nanostructured & Amorphous Materials) were introduced into a solution of 16 mL ethanol and 160 mL water under vigorous stirring and treated in an ultrasonic bath for 30 minutes. Ammonia solution (32%, 625 µl) and resorcinol (1.60 g) were added and the dispersion was stirred at room temperature for 30 minutes until all resorcinol was eliminated in solution. The formaldehyde solution (37 wt% in stabilized water with 10 wt% methanol; 2.36 g) was added and the reaction mixture was first stirred at 30 ° C for 30 minutes and then heated to 60 ° C for 10 hours. After cooling to room temperature, the silicon-containing particles were separated from the dispersion medium by centrifugation (5000 rpm, 30 min, 23 ° C), redispersed in 125 mL of ethanol, centrifuged again and washed with 4 x 25 mL of ethanol. The solvent was removed from the combined particles at 80 ° C under reduced pressure (3.5 x 10 mbar) and the obtained solid residue was dried for 2 hours under vacuum. The brown residue was placed in a molten silica crucible and charred under argon in a tube furnace; heating rate 5 ° C / min, temperature 650 ° C, standby time 3 h, air flow 200 mL / min. After cooling, 1.78 g of a black powdery solid was obtained (63% carbonization yield).

Elemental composition: 36 wt% Si, 42 wt% C, 22 wt% O, Li <10 ppm, 15 ppm Fe, 39 ppm Al, Cu <10 ppm, 15 ppm Ca , 17 ppm K, Cl <3 ppm.

[00169] Specific Surface Area (BET): 322 m2 / g.

The Si / C material of comparative example 1 exhibits a significantly higher O content (> 20% by weight) compared to examples 1 to 7 according to the invention.

[00171] The present invention makes it possible to obtain Si / C compounds as anode active materials for lithium batteries, which compared to the prior art have a carbon matrix with higher strength and elasticity and thus exhibit better cycle stability, especially compared to a physical mixture of silicon and carbon of comparable composition.

This has been made possible by the use of naturally occurring biopolymeric lignin as a precursor to the production of a carbon coating or matrix rather than established C-precursors based on hydrocarbons, carbohydrates or organic polymers to immerse silicon-containing particles. active in carbon and thus effect electrochemical stabilization.

It has been surprisingly found that the production of Si / C compounds from lignin as a precursor of Ceo and the use of the materials obtained as anode active materials in ion lithium batteries have several advantages over other Si / C compounds. , based on the established C precursors.

Compared to hydrocarbon precursors, which are mainly used in the form of highly toxic polyaromatic compounds based on turkeys or tars, lignin is as a natural, non-toxic material and unrelated to a source of petrochemical raw materials.

In addition, lignin is readily soluble in polar solvents such as water / alcohol mixtures, whereas established pitch precursors often contain insoluble components and can be processed only in molten state or in non-polar solvents, can often be a complication and therefore undesirable in production processes.

Compared to carbohydrate-based C precursors such as sugars and cellulose, which is also readily soluble and processable in polar protic solvents, lignin and carbon materials obtained from lignin have a significantly higher oxygen content. smaller, as a result of which oxidation of the silicon surface in the compound can be largely minimized.

Advantages over polymer and thermoplastic C precursors (e.g. vinyl polymers such as PVC) are provided, in particular, by the highly significant carbon yields from lignin in carbonization.

Although lignin has, as a highly branched polyphenol, many structural analogies with phenolic and resorcinol resins, that is, unlike the mentioned resins, it is not produced from petrochemical starting materials but is based on renewable plant raw materials and therefore offers a sustainable alternative that is not oil based and therefore conserves the resources of the established thermoset and polymeric C precursors.

The low oxygen, crosslinked solid carbon produced by lignin carbonization serves as a stabilizing matrix to structurally accommodate the extreme volumetric expansion of silicon during loading and thus minimize the mechanical destruction of the active material and structure. loss of electrode over a plurality of charge and discharge cycles.

In addition, carbon protects the surface of the silicon-based active material against reactions with other electrode or battery cell constituents and thus further minimizes lithium losses.

This provides a Si / C composite material that exhibits significantly improved electrochemical behavior compared to a physical mixture of silicon and carbon with a comparable composition.

Claims (15)

A process for producing a Si / C compound, characterized in that it comprises providing a silicon containing active material, providing lignin, contacting the active material with a C precursor-containing lignin and converting lignin to inorganic carbon at a temperature of at least 400 ° C under an inert gas atmosphere. Process according to Claim 1, characterized in that the active material comprises elemental silicon, silicon oxide or silicon metal alloy. Process according to either claim 1 or claim 2, characterized in that the active material comprises silicon micro or nanoparticles, preferably Si nanoparticles with an average particle size of less than 500 nm. Process according to any one of Claims 1 to 3, characterized in that the active material and the C precursor are brought into contact by grinding or physical mixing. Process according to any one of Claims 1 to 3, characterized in that the contact of the active material and the C precursor is effected by dispersing the active material in a lignin dispersion or solution and coating it with lignin. or incorporation thereof into lignin by subsequent removal of the solvent. Process according to Claim 3, characterized in that the contact of the active material and the C precursor is effected by depositing the silicon particles on the C precursor or depositing the C precursor on the silicon particles. by chemical or thermal vapor deposition. Process according to any one of Claims 1 to 6, characterized in that the carbonization is carried out by heating to a final temperature of 400 to 1400 ° C, heat treatment at that final temperature for at least 30 minutes and subsequent cooling. . 8. Si / C compound containing from 10 to 90% by weight of silicon and from 10 to 90% by weight of carbon and having an average size of less than 1 mm, CHARACTERIZED by the fact that carbon originates at least partially from lignin. Si / C compound produced by a process defined in any one of claims 1 to 7, characterized in that it contains from 10 to 90% by weight of silicon and from 10 to 90% by weight of carbon, 0 and with a average size less than 1 mm. Si / C compound according to claim 8 or 9, characterized in that it comprises carbon-coated silicon particles. Si / C compound according to any one of claims 8 to 10, characterized in that it contains a carbon matrix in which silicon particles are incorporated. Anode material for a lithium ion battery, characterized in that it contains a Si / C compound as defined in any one of claims 8 to 11. A process for producing an anode for an lithium ion battery, characterized in that it comprises processing anode material as defined in claim 12 to form a paint or paste having a solids content of 5 to 95% by weight, applying the paint or paste in a dry layer 2 to 500 pm thick to a current collector, dry the paint or paste over the current collector at a temperature of 20 to 300 ° C, where the anode based material ratio The dry weight of the paint or paste is 5 to 98% by weight. Process according to claim 13, characterized in that the anode material is processed with one or more constituents selected from the group consisting of graphite, lithium, binders, conductive carbon black, carbon nanotubes, metallic powder, dispersant, pore former and solvent to form a paint or paste. Lithium-ion battery, characterized in that it comprises a cathode, anode, a membrane separating cathode from anode, a lithium ion-containing electrolyte, wherein the anode contains an anode material as defined in claim 12.