Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
  • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
  • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/02—Silicon
  • C01B33/021—Preparation
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
  • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
  • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/139—Processes of manufacture
  • H01M4/1393—Processes of manufacture of electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/139—Processes of manufacture
  • H01M4/1395—Processes of manufacture of electrodes based on metals, Si or alloys
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries

Definitions

• the present invention relates to an active material for the electrodes of an electrochemical element, a method for producing the active material and an electrode with such an active material and an electrochemical element having at least one such electrode.
• Rechargeable lithium batteries in which metallic lithium is used as the negative electrode material are known to have a very high energy density.
• cyclization (charging and discharging) of such batteries can cause a number of problems.
• unavoidable side reactions of metallic lithium with the electrolyte solution lead to an occupancy of the lithium surface with decomposition products, which can influence the processes of lithium deposition and dissolution.
• dendrites may also be formed, possibly damaging the electrode separator.
• SEI solid electrolyte interface
• SEI solid electrolyte interface
• a material that can intercalate comparatively large amounts of lithium ions is metallic silicon.
• an amount of lithium ions can be taken up which exceeds the comparable amount by more than ten times for a graphite electrode.
• the problem is that the inclusion of such a large amount of lithium ions can be accompanied by an extremely high volume change (up to 300%), which in turn can have a very negative impact on the mechanical integrity of electrodes with silicon as the active material.
• the intermetallic phases formed in the lithiation of silicon exhibit a potential that has a similar potential to reduce them as metallic lithium itself. Therefore, an SEI is formed here as well. Since the specific surface of an active material containing large amounts of nanoparticles is very large, the formation of the SEI consumes a correspondingly large amount of electrolyte and lithium. As a result, in turn, the positive electrode must always be oversized, which in the As a consequence, the energy density of a corresponding lithium-ion cell is considerably reduced and the advantage of the high energy density of the negative electrode is at least partially compensated.
• active materials can be obtained which are outstandingly suitable for use in electrodes, in particular in negative electrodes, of electrochemical elements.
• Preferred fields of application are, in particular, electrodes for rechargeable batteries with lithium-ion and lithium-polymer technology.
• active material should generally be understood as meaning a material which directly intervenes in the process of converting chemical energy into electrical energy in an electrochemical element
• lithium ions can be incorporated into the active material of a negative electrode are stored under the absorption of electrons and desorbed again with the release of electrons.
• the inventive method comprises at least three steps, namely
• the active material thus obtained is thus a composite material based on carbon particles, on the surface of which metallic silicon has been deposited.
• the carbon particles may in particular be graphite particles, CNTs (carbon nanotubes) or mixtures of both.
• graphite particles are basically not limited, so basically all graphite particles can be used, which can also be used in known from the prior art graphite electrodes.
• CNTs are known to be microscopic tubular structures made of carbon, in which lithium ions can also be incorporated.
• CNTs suitable for use as active materials are described, for example, in WO 2007/095013.
• silicon precursor is to be understood in principle to mean any substance or chemical compound which can be decomposed, in particular by heating, whereby metallic silicon is deposited.
• Such substances and compounds are known in principle to the person skilled in the art.
• the precursor from the gas phase on the carbon particles.
• a liquid or contained in a liquid silicon precursor to the Surface of the carbon particles applied, followed by the mentioned thermal decomposition.
• the silicon precursor may be both dissolved and dispersed in the liquid.
• the application of the silicon precursor to the surface of the carbon particles can basically be done in various ways. The most favorable procedure here depends fundamentally on the nature of the precursor, which will be discussed in more detail later.
• the carbon particles provided can be introduced, for example, into a solution in which the silicon precursor is contained. This can then settle on the surface of the carbon particles.
• solvent should be removed prior to subsequent thermal decomposition.
• the silicon precursor is particularly preferably at least one silane, very particularly preferably an oligomeric or polymeric silane.
• oligomeric or polymeric silanes are used which can be described by the general formula - [SiHa] n - with n> 10, ie have a minimum chain length of at least 10 silicon atoms.
• Such silanes are usually liquid or can be processed in solution. So there is no need to use gaseous precursors, the corresponding expenditure on equipment is accordingly relatively low.
• a silane mixture which is particularly suitable as a silicon precursor can be obtained, for example, by oligomerization or polymerization starting from cyclic silanes.
• the oligomerization or the polymerization can - O -
• the average molecular weight M w of a silane mixture which is particularly preferred according to the invention is preferably in particular between 500 and 5,000.
• the decomposition of the silicon precursor is usually carried out by a heat treatment, in particular at a temperature> 300 ° C.
• a temperature> 300 ° C At such a temperature, oligomeric and polymeric silanes decompose usually with elimination of hydrogen.
• metallic silicon in particular into amorphous metallic silicon.
• Particularly preferred temperatures between 300 0 C and 1200 0 C are selected. For energetic reasons, usually the aim is to carry out the conversion at the lowest possible temperatures. In particular, temperatures between 300 0 C and 600 0 C are therefore preferred. At such temperatures, a substantially complete conversion of the oligosiloxane or polysilane can take place.
• Silanes or silane mixtures which are suitable according to the invention and suitable conditions for the decomposition of such silanes and silane mixtures are also described in Shimoda et al.'S scientific paper "Solution-processed Silicone Films and Transistors" (NATURE Vol. 440, April 06, 2006, pages 783 In particular the corresponding experimental statements in this publication are hereby incorporated by reference in their entirety.
• the active material preparable by a process according to the invention is also an object of the present invention.
• it comprises carbon particles whose surface is at least partially coated with a layer of silicon, in particular one Layer of amorphous silicon, at least partially covered.
• the active material according to the invention particularly preferably consists of such particles.
• the layer of silicon on the surface of the carbon particles may form a substantially closed shell.
• the composite particles of carbon and silicon have a core (formed by the carbon particle) and a shell of silicon arranged around it.
• the layer of silicon can surface-oxidize.
• the resulting layer of silicon oxide usually has a passivating effect, it counteracts oxidation of deeper-lying silicon layers.
• the result is particles with a core of carbon, a middle layer of particular amorphous silicon and an outer layer of silicon oxide.
• the conditions in the decomposition of the silicon precursor can be selected so that in the resulting layer or shell of silicon optionally still a small amount of hydrogen is contained. As a rule, however, it is present in a proportion of less than 5% by weight (based on the total weight of the layer or shell), preferably in a proportion of between 0.001% by weight and 5% by weight, in particular in one proportion between 0.01 and 3 wt .-%.
• the carbon particles preferably have an average particle size between 1 ⁇ m and 200 ⁇ m, in particular between 1 ⁇ m and 100 ⁇ m, in particular between 10 ⁇ m and 30 ⁇ m.
• the sheath of silicon is usually not thicker than 15 microns. This shows that the total size of the particles (mean particle size) in - O -
• 215 microns in particular 115 microns does not exceed. It is particularly preferably between 10 .mu.m and 100 .mu.m, in particular between 15 .mu.m and 50 .mu.m.
• the active material according to the invention is substantially free of particles with particle sizes in the nanoscale range.
• the active material preferably contains no carbon-silicon particles with sizes ⁇ 1 ⁇ m.
• the weight ratio of carbon to silicon in the active material according to the invention is preferably in the range between 1:10 and 10: 1. Values in the range between 1: 1 and 3: 1 are particularly preferred here.
• the active material according to the invention electrodes, which have up to three times higher lithium-ion storage capacity than comparative electrodes with classic active material made of graphite.
• the active material according to the invention showed a cyclic stability similar to the nanoparticulate silicon mentioned at the beginning in cyclization tests, but without the disadvantages described.
• An electrode according to the invention is characterized in that it has an active material according to the invention.
• the active material is incorporated in an electrode according to the invention in a binder matrix.
• Suitable materials for such a binder matrix are known to the person skilled in the art.
• copolymers of PVDF-HFP polyvinylidene difluoride-hexafluoropropylene
• a possible alternative binder based on carboxymethylcellulose is disclosed in German Patent Application No. 10 2007 036 653.3, which has not yet been disclosed. - -
• the active material is usually contained in an electrode according to the invention in an amount of at least 85% by weight. Further shares are attributable to the binder already mentioned and optionally to one or more conductivity additives (eg carbon black).
• conductivity additives eg carbon black
• An electrochemical element according to the invention is characterized in that it has at least one electrode according to the invention.
• An electrochemical element according to the invention may, for example, be a stacked cell in which a plurality of electrodes and separators are stacked one above the other.
• the fields of application for the active material according to the invention and thus the electrodes according to the invention are, however, in principle not limited, so that numerous other types (for example winding electrodes) are also conceivable.
• FIG. 1 shows a comparison of the cycle stability of an electrode according to the invention with silicon-carbon composite particles with a comparable electrode with graphite as active material as a function of the charging or discharging cycles.
• FIG. 2 shows a comparison of the cycle stability of an electrode according to the invention with silicon-carbon composite particles a comparable electrode already known from the prior art with a mixture of graphite and SiIi- zium nanoparticles as active material.
• cyclopentasilane was polymerized under an argon atmosphere (water content and oxygen content ⁇ 1 ppm) by photo-induced ultraviolet light at a wavelength of 405 nm. It was polymerized until the resulting polysilane mixture had a gel-like consistency. This was blended with graphite particles having an average particle size of 15 ⁇ m, to give a paste which was subsequently heat-treated at a temperature of 823 K. The heat treatment was carried out until no more hydrogen evolution was observed. The material thus obtained was then ground in a ball mill and adjusted to an average particle size of about 20 microns.
• the electrode paste thus obtained was knife-coated onto a copper foil in the thickness of 200 ⁇ m.
• a comparative electrode wt .-% sodium umcarboxymethylzellulose (Walocell® ® CRT2000PPA12) added to water and to swell fully accommodated. 8
• 20% nanoparticulate silicon (Nanostructured and Amorphous Materials Los Alamos) and 5% carbon nanofibers (Electrovac AG, LHT-XT) were sequentially introduced and highly energetically dispersed.
• 5% conductive black (Super P) and 62% graphite (natural graphite, potato shaped) are finally introduced and dispersed.
• the electrode paste thus obtained was knife-coated onto a copper foil in the thickness of 200 ⁇ m.
• FIG. 1 shows a comparison of the cycle stability of an inventive electrode produced according to (2) with a comparable electrode with graphite as the active material (instead of the silicon-carbon composite particles) as a function of the charging or discharging cycles. It can be clearly seen that the electrode according to the invention has a significantly higher capacity.
• FIG. 2 shows a comparison of an inventive electrode produced according to (2) with silicon-carbon composite particles with a comparison electrode produced in accordance with (3) as a function of the charge or charge. Unloading cycles shown. In the case of the electrode according to the invention (upper curve, triangles), the capacitance remains essentially constant even after more than 40 cycles, whereas in the case of the comparative electrode (lower curve, squares), a clear decrease in the capacitance is measurable.

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• 2008
  • 2008-12-05 DE DE102008063552A patent/DE102008063552A1/de not_active Withdrawn
• 2009
  • 2009-12-04 US US13/132,213 patent/US20110309310A1/en not_active Abandoned
  • 2009-12-04 JP JP2011538901A patent/JP5779101B2/ja active Active
  • 2009-12-04 WO PCT/EP2009/008673 patent/WO2010063480A1/de not_active Ceased
  • 2009-12-04 CN CN200980148623.0A patent/CN102239585B/zh active Active
  • 2009-12-04 KR KR1020117013003A patent/KR101625252B1/ko active Active
  • 2009-12-04 EP EP09807494.1A patent/EP2364511B1/de active Active

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