WO2015008093A1 - Procédé de formation de structures en silicium gravé - Google Patents

Procédé de formation de structures en silicium gravé Download PDF

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Publication number
WO2015008093A1
WO2015008093A1 PCT/GB2014/052219 GB2014052219W WO2015008093A1 WO 2015008093 A1 WO2015008093 A1 WO 2015008093A1 GB 2014052219 W GB2014052219 W GB 2014052219W WO 2015008093 A1 WO2015008093 A1 WO 2015008093A1
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silicon
metal
etching
etched
ions
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PCT/GB2014/052219
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Jonathon SPEED
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Nexeon Limited
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    • 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
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K13/00—Etching, surface-brightening or pickling compositions
    • C09K13/04—Etching, surface-brightening or pickling compositions containing an inorganic acid
    • C09K13/08—Etching, surface-brightening or pickling compositions containing an inorganic acid containing a fluorine compound
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
    • C23C18/18—Pretreatment of the material to be coated
    • C23C18/1851—Pretreatment of the material to be coated of surfaces of non-metallic or semiconducting in organic material
    • C23C18/1872—Pretreatment of the material to be coated of surfaces of non-metallic or semiconducting in organic material by chemical pretreatment
    • C23C18/1875—Pretreatment of the material to be coated of surfaces of non-metallic or semiconducting in organic material by chemical pretreatment only one step pretreatment
    • C23C18/1882—Use of organic or inorganic compounds other than metals, e.g. activation, sensitisation with polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02002—Preparing wafers
    • H01L21/02005—Preparing bulk and homogeneous wafers
    • H01L21/02008—Multistep processes
    • H01L21/0201—Specific process step
    • H01L21/02019—Chemical etching
    • 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
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
    • 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
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0416—Methods of deposition of the material involving impregnation with a solution, dispersion, paste or dry powder
    • 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
    • H01M4/386—Silicon or alloys based on silicon
    • 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 methods of etching silicon.
  • Etched silicon structures comprising pores or elongated pillar-like structures may be used in a wide range of applications including electrochemical cells, metal ion batteries such as lithium-ion batteries, lithium air batteries, flow cell batteries, other energy storage devices such as fuel cells, thermal batteries, photovoltaic devices such as solar cells, filters, sensors, electrical and thermal capacitors, microfluidic devices, gas/vapour sensors, thermal or dielectric insulating devices, devices for controlling or modifying the transmission, absorption or reflectance of light or other forms of electromagnetic radiation, chromatography or wound dressings.
  • electrochemical cells metal ion batteries such as lithium-ion batteries, lithium air batteries, flow cell batteries, other energy storage devices such as fuel cells, thermal batteries, photovoltaic devices such as solar cells, filters, sensors, electrical and thermal capacitors, microfluidic devices, gas/vapour sensors, thermal or dielectric insulating devices, devices for controlling or modifying the transmission, absorption or reflectance of light or other forms of electromagnetic radiation, chromatography or wound dressings.
  • Porous silicon particles may also be used for the storage, controlled delivery or timed release of ingredients or active agents in consumer care products including oral hygiene and cosmetic products, food or other nutritional products, or medical products including pharmaceutical products that deliver drugs internally or externally to humans or animals.
  • Etched silicon may also form architectured conducting or semiconducting components of electronic circuitry.
  • silicon has a substantially higher maximum capacity than graphite.
  • active graphite which remains substantially unchanged during insertion and release of metal ions
  • the process of insertion of metal ions into silicon results in substantial structural changes, accompanied by substantial expansion.
  • insertion of lithium ions into silicon results in formation of a Si-Li alloy.
  • the effect of Li ion insertion on the anode material is described in, for example, "Insertion Electrode Materials for Rechargeable Lithium Batteries", Winter et al, Adv. Mater. 1988, 10, No. 10, pages 725-763.
  • WO2009/010758 discloses the etching of silicon powder in order to make silicon material for use in lithium ion batteries.
  • the resulting etched particles contain pillars on their surface.
  • These structured silicon electrodes show good capacity retention when subjected to repeated charge/discharge cycles and this good capacity retention is believed to be due to the ability of the silicon pillars to absorb the volumetric expansion/contraction associated with lithium insertion/extraction from the host silicon without the pillars being broken up or destroyed.
  • Huang et al "Metal-Assisted Chemical Etching of Silicon: A Review", Advanced Materials 2010, 1 -24, discloses etching of silicon wherein elemental metal is deposited on the silicon surface by a process of electroless deposition followed by etching of silicon underlying the deposited silver.
  • the silicon is exposed to a solution of a metal salt, for example silver nitrate, and a source of fluoride ions, for example HF to reduce the metal ions and form elemental metal on the silicon surface.
  • a metal salt for example silver nitrate
  • a source of fluoride ions for example HF
  • Kato et al. "Metal-Assisted Chemical Etching Using Silica Nanoparticle for the Fabrication of a Silicon Nanowire Array", Japanese Journal of Applied Physics, Vol. 51 , 2012, pp. 02BP09-1 to 02BP09-4, discloses metal assisted chemical etching (MACE) of silicon, wherein the arrangement, spacing and diameter of silicon pillars formed is controlled by a mask of silica spheres.
  • the silica spheres are attached to the silicon surface via amines, which bond to the carboxylate groups on silica.
  • Silver metal is applied to the surface to assist etching in areas without silica.
  • US2013/0040412A1 discloses use of MACE to create silicon nanowires from a silicon layer.
  • Metal catalyst particles are applied directly to a polished silicon surface and the silicon is wet etched. An etch mask may be used.
  • the product is silicon nanowires, which do not themselves have a specific surface structure.
  • GB2492167A discloses pillared silicon particles fabricated using the MACE method of WO2010/040985. This method applies the metal catalyst particles directly to the silicon surface and etches using a wet etch solution. Using this method it is not possible to control the placement of catalyst particles and thus the size, spacing and arrangement of the surface features cannot be controlled.
  • US2011/0086165A1 discloses a method to metallise a porous silicon surface.
  • the pre-etched silicon surface is first functionalised with, preferably, a thiol chemical function and an ethylene diamine chemical function for reducing and chelating metal ions. It is then metallised. The aim is to achieve a complete metallic coating of the surface, including inside the pores.
  • the invention provides a method of etching silicon of a material comprising silicon at a surface thereof, the method comprising the steps of:
  • a functionalized surface comprising a functional group on the silicon surface wherein the functional group comprises a metal-binding group; binding a metal or metal ion to the metal-binding group;
  • Figure 1 is a schematic illustration of a method according to an embodiment of the invention wherein elemental metal is bound to a functionalized silicon surface;
  • Figure 2 is a schematic illustration of a method according to an embodiment of the invention wherein metal ions are bound to a functionalized silicon surface
  • Figure 3 is a schematic illustration of a functionalized silicon surface of a material used in combination with a capping layer in a method according to an embodiment of the invention
  • Figure 4 is a schematic illustration of a silicon surface having a functional group derived from APTS bound thereto;
  • Figure 5 is a schematic illustration of a metal ion battery according to an embodiment of the invention.
  • Figure 6A is a SEM image of a silicon particle after electroless metal deposition and etching.
  • Figure 6B is a SEM image of a silicon particle after etching by a method according to an embodiment of the invention.
  • Figure 1 illustrates an etching process according to an embodiment of the invention.
  • a silicon surface 103 of a material 101 which in this embodiment is a particulate material, is modified to form functional groups 105 bound to the silicon surface.
  • the functional groups 105 each have a metal-binding group 107 that is capable of binding to a metal.
  • the bond may be a dative bond.
  • particles 109 of elemental metal M are bound to the functional groups.
  • the source of the elemental metal may be metal particles, for example metal nanoparticles that are brought into contact with the functionalized silicon surface.
  • the bound metal nanoparticle may act as a nucleation point for the reduction of metal ions in a subsequent step, to form (grow) larger metal particles (or nucleates).
  • the functional group may be selected such that it binds strongly to the metal.
  • the functional group may have an amino group for binding to silver and may be a thiol group for gold.
  • the functionalized silicon surface carrying metal is then etched by metal- assisted chemical etching, which is an electroless etching process without the application of an external bias, to produce silicon pillars 11 1 extending from an etched surface 1 13.
  • the silicon may be etched to produce a porous surface.
  • metal-assisted chemical etching the metal forms an electrode of a local galvanic cell and the silicon surface is etched in the presence of a fluoride, for example HF or NH 4 F, and an oxidant. It is believed that the density and form of metal particles on the surface influences the type of etched structures that will be formed.
  • etching process may be as described in Huang et al, "Metal-Assisted Chemical Etching of Silicon: A Review", Advanced Materials 2010, 1-24, the contents of which are incorporated herein by reference.
  • Exemplary oxidants include 0 2 ; 0 3 ; hydrogen peroxide; the acid or salt of N0 3 " , S 2 0 8 2" , N0 2 " , B 4 0 7 2" or CI0 4 " ; and mixtures thereof.
  • Preferred oxidants include hydrogen peroxide and nitrates, for example alkali metal nitrates and ammonium nitrate.
  • the silicon-containing material may be irradiated during etching.
  • the etching process may be carried out in any suitable reaction vessel, for example a vessel formed from a HF-resistant material, such as polyethylene or polypropylene or a reaction vessel lined with a HF resistant material such as a HF resistant rubber. If the silicon is irradiated then the vessel may be light- transmissive.
  • a HF-resistant material such as polyethylene or polypropylene
  • a reaction vessel lined with a HF resistant material such as a HF resistant rubber. If the silicon is irradiated then the vessel may be light- transmissive.
  • Figure 2 illustrates another embodiment of the invention.
  • a silicon surface is functionalized as described with reference to Figure 1 and is then brought into contact with a solution containing metal ions M n+ , wherein n is 1 , 2 or 3.
  • the metal ion is reduced to form elemental metal that provides a nucleation point for the metal ions remaining in the solution, or for metal ions in a further solution that the silicon surface is subsequently brought into contact with, enabling formation of a metal particle (or nucleate) that is formed (or grown) from multiple reduced metal ions. Etching may then be performed as described with reference to Figure 1.
  • the silicon surface carrying metal ions may be brought into contact with a fluoride, for example HF, to release electrons (Equation 1 ) to reduce the metal ions to elemental metal (Equation 2): Si° + 6F " SiF 6 2" + 4e " (Equation 1)
  • a fluoride for example HF
  • Fluoride ions both generate electrons for reduction of the metal ions and, upon addition of an oxidant, etch the silicon surface. Accordingly, reduction and etching steps may take place without separation of the silicon from the reaction mixture, and may take place in a single reaction vessel.
  • the metal ions may first be reduced before the silicon surface is brought into contact with a fluoride for etching of the silicon.
  • the metal may be reduced by heat treatment and / or by a reducing agent, for example sodium borohydride, trisodium citrate, citric acid, alkyl amines, ascorbic acid or ethylene glycol.
  • the functional group remains bound to the silicon surface during reduction of the metal ions, however some or all functional groups may detach from the silicon surface during reduction and / or during etching. Fluoride ions may cause detachment of functional groups from the silicon surface.
  • metal ions bound to the metal binding group are reduced, and remain bound to the metal binding group following reduction.
  • metal may detach from the metal binding group and deposit on the silicon surface during the reduction process.
  • Figure 3 illustrates one stage of a further embodiment of the invention, which follows the same process as described with reference to Figure 2, except that a capping agent is added before or during nucleation.
  • the capping agent is added before or during the process of growing the initially bound metal atom to form a larger metal particle (or nucleate).
  • the capping agent forms a capping layer 115 on the surface of the metal atom (and any nucleated metal ions if added during the nucleation process), and may halt further nucleation (or growth of the metal particle) or may constrain further nucleation to uncapped surface areas of the nucleated metal.
  • Figure 3 illustrates capping that prevents outward growth of the nucleate but allows lateral access to the nucleate for further lateral nucleation.
  • a capping agent may reduce the amount of metal needed in metal-assisted chemical etching, and may be used to control the shape of metal nucleates that are grown from the initial bound metal nanoparticle or reduced metal ion.
  • the capping agent prevents outward growth of the metal particle or nucleate away from the silicon surface and constrains growth sideways or laterally across the silicon surface.
  • Exemplary capping agents include metal citrates; polymers, for example polyvinylpyridine; and ascorbic acid. Controlled growth of capped nanoparticles may be as described in Bastus et al, Langmuir 2011 , 27, 1 1098-11 105, the contents of which are incorporated herein by reference.
  • Figures 1 , 2 and 3 illustrate etching of particles having silicon at a surface thereof, for example a silicon powder. It will be appreciated that other forms of material having a silicon surface may be used, such as bulk silicon, for example a silicon wafer or a polycrystalline or amorphous ribbon or sheet of silicon.
  • Figures 1 , 2 and 3 illustrate anisotropic etching of silicon to produce silicon pillars extending from a core. In other embodiments, anisotropic etching may produce porous silicon.
  • the etched material formed following etching may be used without further modification, or may be modified prior to use.
  • the pillars may be detached from the etched surface to form silicon fibres.
  • the functional group may be formed from a functionalizing material that is reacted with the silicon surface to form the functional group.
  • the functionalizing material may have a silicon-binding group capable of binding to the silicon surface and a metal-binding group capable of forming the bond with the metal or metal ion.
  • the functionalizing material used to form the functional group may have formula (I): (MBG) x -(Sp) y -(SBG)z (I) wherein MGB is a metal-binding group; SBG is a silicon-binding group; Sp is a spacer group; x and z are each at least 1 ; and y is 0 or 1
  • Exemplary groups MBG include amino groups
  • x is 1.
  • z is 1 , 2 or 3.
  • Exemplary groups SBG include groups capable of forming a Si-0 bond or a Si-C bond at the silicon surface.
  • Exemplary groups capable of forming a Si-0 bond include siloxy groups and siloxyl esters.
  • Exemplary groups capable of forming a Si-C bond include alkynes and alkenes.
  • the surface of the silicon may be activated prior to reaction with the functionalizing material to improve binding of the SBG.
  • the surface of the silicon may be activated by HF treatment before reaction with a SBG for formation of a Si-C bond.
  • the functionalizing material may be formed from a precursor material.
  • the or each MBG and / or SBG may be provided with protecting groups to prevent reaction of MBG and / or SBG prior to contact with the metal and / or silicon respectively.
  • a siloxy SBG may be formed by reacting a silanol activated silicon surface with a tri-oxy silane.
  • the functionalizing material that is contacted with the silicon surface may be dissolved in one or more solvents, for example water, alcohols and mixtures thereof.
  • the precursor material may be converted into the functionalizing material before being brought into contact with the silicon surface, or may be converted in situ.
  • An exemplary precursor of a functionalizing material is (3- aminopropyl)triethoxysilane (APTS).
  • Figure 4 illustrates a silicon surface 103 having a functional group formed using APTS, and with silver bound to the amino metal-binding group of the functional group.
  • the functionalizing material, or a precursor thereof, may be dissolved in any suitable solvent including organic solvents, water, and mixtures thereof.
  • the extent to which the silicon surface is covered by the metal particles may be controlled by factors including, without limitation,
  • the concentration of functional groups on the silicon surface which may be controlled by one or more of concentration of the functionalizing material and duration of contact between the functionalizing material and the silicon surface;
  • the percentage of functional groups on the surface that bind to a metal or metal ion which may be controlled by one or more of: concentration of metal or metal ions brought into contact with the functionalized surface; duration of contact between the metal or metal ions and the functionalized surface; strength of the bond formed between the metal or metal ion and the metal-binding group; and temperature during chelation.
  • Exemplary metals that may be bound to the functional group and used in metal-assisted chemical etching, and metal ions thereof, include silver, gold, platinum and copper ions.
  • exemplary metal compounds containing these metal ions are AgN0 3 , AuCI 4 , silver acetate, copper sulphate pentahydrate, silver oxide, silver fluoride, silver tetrafluoroborate, silver trifluoroacetate, platinum chlorate and copper oxide.
  • the metal ions may be metal complex ions, for example [Ag(NH 3 ) 2 ] + ions, copper (II) tartrate ions and copper (II) citrate ions.
  • the metal compounds are preferably water soluble, and the solutions of metal ions are optionally aqueous solutions or a mixture of water and one or more water-miscible organic solvents.
  • Metal nanoparticles may have a width of less than 1 micron on average, optionally less than 500 nm, less than 250 nm, or less than 100 nm. Metal nanoparticles preferably have a width of at least 5 nm on average.
  • Silicon starting material The silicon surface to be etched may be undoped, n-doped, p-doped or a mixture thereof.
  • the silicon is n- or p-doped.
  • Examples of p-type dopants for silicon include B, Al, In, Mg, Zn, Cd and Hg.
  • Examples of n-type dopants for silicon include P, As, Sb and C. Dopants such as germanium and silver can also be used.
  • the silicon to be etched may be supported on a surface of another material.
  • the silicon may be pure silicon or may be an alloy or other mixture of silicon and one or more other materials.
  • the silicon may have a purity of at least 90.00 wt%, optionally at least 99 wt%, optionally at least 99.8 weight %.
  • the silicon purity may be less than 99.99 wt%.
  • the silicon may be metallurgical grade silicon.
  • the silicon may have a resistivity of between 0.0001 - 100 Q.cm, preferably less than 1 Q.cm, preferably less than 0.1 Q.cm.
  • the starting silicon material may be crystalline or amorphous. Etching may be carried out on, for example, bulk silicon or on a particulate material, for example a silicon powder.
  • Exemplary bulk silicon structures include silicon sheets such as silicon wafers or of metallurgical grade silicon, and silicon sheets or chips formed by breaking a silicon wafer into smaller pieces, or by breaking other forms of bulk silicon into sheets or flakes.
  • Powder particles of silicon may be formed from a silicon source such as metallurgical grade silicon by any process known to the skilled person, for example by grinding or jetmilling bulk silicon to a desired size. Suitable example silicon powders are available as "SilgrainTM " from Elkem of Norway.
  • bulk silicon such as a silicon wafer may have first and second opposing faces, the surface of each face having an area of at least 0.25 cm 2 , optionally at least 0.5 cm 2 , optionally at least 1 cm 2 . Each face may be substantially planar.
  • Bulk silicon may have a thickness of more than 0.5 micron, optionally more than 1 micron, optionally more than 10 microns, optionally more than 100 microns, optionally in the range of about 100 - 1000 microns.
  • particles may be in the form of flakes, wires, ribbons, cuboid, substantially spherical or spheroid particles. They may be multifaceted or may have substantially continuous curved surfaces.
  • Non-spherical core particles may have an aspect ratio of at least 1.5 : 1 , optionally at least 2 : 1.
  • the particles may have a size with a largest dimension up to about 100 pm, preferably less than 50 pm, more preferably less than 30 pm.
  • the starting material particles may have at least one smallest dimension less than one micron.
  • the smallest dimension may be at least 0.1 pm, preferably at least 0.5 pm.
  • Particle sizes may be measured using optical methods, for example scanning electron microscopy.
  • composition containing a plurality of particles for example a powder, preferably at least 20%, more preferably at least 50% of the particles have smallest dimensions in the ranges described above.
  • Particle size distribution may be measured using laser diffraction methods or optical digital imaging methods.
  • a distribution of the particle sizes of a powder of starting particles used to form etched particles may be measured by laser diffraction, in which the particles being measured are typically assumed to be spherical, and in which particle size is expressed as a spherical equivalent volume diameter, for example using the MastersizerTM particle size analyzer available from Malvern Instruments Ltd.
  • a spherical equivalent volume diameter is the diameter of a sphere with the same volume as that of the particle being measured. If all particles in the powder being measured have the same density then the spherical equivalent volume diameter is equal to the spherical equivalent mass diameter which is the diameter of a sphere that has the same mass as the mass of the particle being measured.
  • the powder is typically dispersed in a medium with a refractive index that is different to the refractive index of the powder material.
  • a suitable dispersant for powders of the present invention is water.
  • a particle size analyser provides a spherical equivalent volume diameter distribution curve. Size distribution of particles in a powder measured in this way may be expressed as a diameter value Dn in which at least n % of the volume of the powder is formed from particles that have a measured spherical equivalent volume diameter equal to or less than D.
  • the D50 values referred to herein mean that particles forming 50% of the measured powder sample volume have a spherical equivalent volume diameter of D50 or less, as measured by laser diffraction in a water dispersant (using the aforementioned Malvern MastersizerTM).
  • Preferred size distributions for a powder of starting silicon particles include a smallest dimension of D50 > 0.1 pm, and a largest dimension of D50 ⁇ 25 pm, optionally ⁇ 15 pm, optionally ⁇ 10 ⁇
  • BET Brunauer, Emmett and Teller surface area per unit mass of a starting material may be at least 0.5 m 2 /g, preferably at least 1 , 2 or 3 m 2 /g. All BET values cited herein are as measured using a standard gas adsorption method using a QuantachromeTM NOVA 2200E system.
  • etching a starting material particle to produce a pillared particle for example as described with reference to Figures 1 -3, then the resultant pillared particle will have a pillared particle core that is smaller than the starting material particle.
  • a porous particle produced by etching a starting material may be substantially the same size as, or smaller than, the starting material.
  • the material to be etched may consist essentially of silicon as described above, for example silicon having a purity of at least 90%, such as metallurgical grade silicon as described above, or it may contain one or more further materials.
  • the material to be etched may have a non-silicon core, for example a core of graphite, and a silicon shell wherein the shell is etched.
  • the material to be etched may comprise or essentially consist of silicon oxide SiO x , where 0 ⁇ x ⁇ 2 , including silicon monoxide.
  • the shell thickness may be greater than 0.5 microns, optionally in the range of 1-10 microns or 1 -5 microns.
  • the material having a non-silicon core may be a powder, and the non-silicon core of this material may have a diameter greater than 5 microns.
  • the starting silicon to be etched may have a surface layer of a silicon compound, for example a silicon oxide layer.
  • Silicon may have a native silicon oxide surface layer which may have a thickness of about 1-2 nm. This may be increased by heating to a thickness of no more than 20 nm.
  • the surface of the silicon-containing material may include non-silicon materials.
  • the etched silicon structure may comprise pillars, pores, or both pillars and pores.
  • the BET value of the etched material may be > 5 m 2 g "1 , preferably >
  • Pillars formed by etching of the silicon surface may have any shape.
  • Pillars may be branched or unbranched; substantially straight or bent; and of a substantially constant thickness or tapering. Pillars may contain steps.
  • Pillars extend outwardly from, and may be spaced apart on, an etched silicon surface. In one arrangement, substantially all pillars may be spaced apart. In another arrangement, some or substantially all of the pillars may be clustered together.
  • the cross-sections of the pillars may form regular shapes (e.g. circular, square or triangular) or be irregular in shape (e.g. may contain one or more concave or convex curved sides or branches or spurs extending outwards or combinations thereof). It will be appreciated that the shape of the pillars is at least partly determined by the shape of the exposed surface areas of silicon after metal deposition.
  • the PMF may be determined by measuring mass of the particles before and after separation of pillars from the core. Pillars may be separated from the core by sonication.
  • Pillar volume fraction (volume of pillars / volume of pillared particles) is the same as PMF if the densities of the core and the pillars are the same.
  • the particle core of a pillared particle is not silicon then the PVF and PMF values may be different.
  • a PMF value may be converted to a PVF value using the densities of the pillars and the core.
  • the pillars may have a diameter or thickness in the range of about 0.02 to 0.70 pm, e.g. 0.1 to 0.5pm, for example 0.1 to 0.25pm, preferably in the range 0.04 to 0.50 ⁇ m.
  • the pillars may have an aspect ratio (defined as the height of the pillar divided by the average thickness or diameter of the pillar at its base) in the range 5:1 to 100:1 , preferably in the range 10:1 to 100: 1.
  • the pillars may be substantially circular in cross-section but they need not be. Where the pillars have irregular cross-sections comprising a plurality of extended sections with changing direction and/or with branches or spurs then the average thickness of the plurality of such section is used in the calculation of the aspect ratio.
  • the pillars may extend outwards from the silicon in any direction and may comprise kinks or changes in direction along their length.
  • Pillars may be formed by etching the silicon surface to a depth of more than 0.25 microns, more than 0.5 microns, optionally at least 1 micron, optionally at least 2 microns, optionally more than 10 microns.
  • the pillars are formed by etching the silicon surface to a depth in the range of 1 -10 microns.
  • Silicon may be etched silicon to produce porous silicon, eg mesoporous silicon (pores ⁇ 50nm) or macroporous silicon (i.e. silicon with pores of diameter > 50nm).
  • the process of etching silicon to form porous silicon may be substantially the same as described with reference to Figures 1 -3, except that etching results in formation of pores on the surface of the silicon to be etched and extending downwards into the silicon material, rather than pillars extending from an etched surface of the etched silicon.
  • Porous silicon may have a substantially continuous connected network of silicon walls at the outer surface of the silicon that has been etched.
  • the surface of the etched silicon may comprise both regions of porous silicon and regions with pillars.
  • the etched silicon may also combine regions of porous and pillared silicon in an inward extending direction. That is, an outer shell region of the etched silicon may comprise pillared silicon whilst the inner region comprises porous silicon and vice versa.
  • Pores may extend at least 100 nm, optionally at least 0.5 microns into the silicon from silicon surface, optionally at least 1 micron, optionally at least 2 microns.
  • the pores may have a diameter of at least 10 nm, 20 nm, or 100 nm, optionally at least 300nm, optionally at least 0.5 microns.
  • the pores may extend inwards perpendicular to the silicon surface or may extend inwards at any intermediate angle. Not all pores may extend in the same direction, instead the plurality of pores may extend in a plurality of directions. The direction in which the pores extend inwards may change partway down. Two or more pores may join to form an irregular network of pores below the surface of the silicon.
  • the walls between adjacent pores may be greater than 2 nm, preferably greater than 10 nm, and may be less than 1 pm, preferably less than 250 nm.
  • the surfaces of pores or pillars may be relatively smooth or they may be rough.
  • the surfaces may be pitted or comprise pores or voids with diameters less than 50nm.
  • the pillar structures may be solid; mesoporous; microporous or a combination thereof.
  • the pillar structures may have a solid core with a mesoporous outer shell.
  • the porosity of the etched silicon may be defined as the percentage ratio of the total volume of the void space or pores introduced into the etched silicon to the volume of the silicon before etching. This may be calculated as [(pore volume)/(pore volume + solid volume)] x 100%.
  • a higher porosity may provide a higher surface area which may increase the reactivity of the silicon in a device, for example in electrochemical cells, sensors, detectors, filters etc. or it may provide a larger volume for containing ingredients or active agents in medical or consumer product compositions.
  • the porosity is too large the structural integrity (or mechanical strength) of the silicon may be reduced and for example, in devices such as a lithium ion battery, the volume of electrochemically active silicon material is reduced.
  • the porosity of the etched silicon may be at least 5%, optionally at least 10%. Preferably it is at least 20%, at least 40 %, at least 50 % or at least 50 %. The porosity may be less than 95%, less than 90%, optionally less than 80%. The porosity of the etched material may be 10-90%. Alternatively, it may have a substantially solid core with a porous outer region of 10-90% porosity.
  • pores and pillars may be measured using optical methods, for example scanning electron microscopy.
  • Porosity may be measured using known gas or mercury porosimetry techniques or by measuring the mass of the silicon material before and after etching.
  • Etched silicon formed as described herein may be used as an active material in an anode of a rechargeable metal ion battery
  • active material or "electroactive material” as used herein means a material which is able to insert into its structure, and release therefrom, metal ions such as lithium, sodium, potassium, calcium or magnesium during the respective charging phase and discharging phase of a battery.
  • metal ions such as lithium, sodium, potassium, calcium or magnesium during the respective charging phase and discharging phase of a battery.
  • the material is able to insert and release lithium.
  • the structure of an exemplary rechargeable metal-ion battery is shown in Fig. 5.
  • the battery cell includes a single cell but may also include more than one cell.
  • Batteries of other metal ions are also known, for example sodium ion and magnesium ion batteries, and have essentially the same cell structure.
  • the battery cell comprises a current collector for the anode 10, for example copper, and a current collector for the cathode 12, for example aluminium, which are both externally connectable to a load or to a recharging source as appropriate.
  • a composite anode layer 14 overlays the current collector 10 and a lithium containing metal oxide-based composite cathode layer 16 overlays the current collector 12 (for the avoidance of any doubt, the terms "anode” and "cathode” as used herein are used in the sense that the battery is placed across a load - in this sense the negative electrode is referred to as the anode and the positive electrode is referred to as the cathode).
  • the cathode comprises a material capable of releasing and reabsorbing urn ions for example a lithium-based metal oxide or phosphate, LiCo0 2 , LiNio.8Coo.15Alo.05O2, LiMn x NixCo 1 -2 xO2 or LiFePO 4 .
  • a lithium-based metal oxide or phosphate LiCo0 2 , LiNio.8Coo.15Alo.05O2, LiMn x NixCo 1 -2 xO2 or LiFePO 4 .
  • a porous plastic spacer or separator 20 is provided between the graphite- based composite anode layer 14 and the lithium containing metal oxide-based composite cathode layer 16.
  • An electrolyte material is dispersed within the porous plastic spacer or separator 20, the composite anode layer 14 and the composite cathode layer 16.
  • the porous plastic spacer or separator 20 may be replaced by a polymer electrolyte material and in such cases the polymer electrolyte material is present within both the composite anode layer 14 and the composite cathode layer 16.
  • the polymer electrolyte material can be a solid polymer electrolyte or a gel-type polymer electrolyte and can incorporate a separator.
  • lithium has been transported from the lithium containing metal oxide cathode layer 16 via the electrolyte into the anode layer 14.
  • an anode current collector may be formed on one side of the bulk silicon and another side of the bulk silicon having an etched surface may come into contact with the electrolyte of the battery.
  • the current collector may be a metal foil, for example copper, nickel or aluminium, or a non-metallic current collector such as carbon paper
  • a slurry comprising the etched powder and one or more solvents may be deposited over an anode current collector to form an anode layer.
  • the slurry may further comprise a binder material, for example polyimide, polyacrylic acid (PAA) and alkali metal salts thereof, polyvinylalchol (PVA) and polyvinylidene fluoride (PVDF), sodium carboxymethylcellulose (Na-CMC) and optionally, non-active conductive additives, for example carbon black, carbon fibres, ketjen black or carbon nanotubes.
  • PAA polyacrylic acid
  • PVDF polyvinylalchol
  • Na-CMC sodium carboxymethylcellulose
  • non-active conductive additives for example carbon black, carbon fibres, ketjen black or carbon nanotubes.
  • one or more further active materials may also be provided in the slurry.
  • Exemplary further active materials include active forms of carbon such as graphite or graphene.
  • Active graphite may provide for a larger number of charge / discharge cycles without significant loss of capacity than active silicon, whereas silicon may provide for a higher capacity than graphite.
  • an electrode composition comprising a silicon-containing active material and a graphite active material may provide a lithium ion battery with the advantages of both high capacity and a large number of charge / discharge cycles.
  • the slurry may be deposited on a current collector, which may be as described above. Further treatments may be done as required, for example to directly bond the silicon particles to each other and/or to the current collector. Binder material or other coatings may also be applied to the surface of the composite electrode layer after initial formation.
  • cathode materials examples include LiCo0 2 , LiCoo.99Alo.01 O2, LiNiO 2 , LiMnO 2 , LiCoo.5Nio.5O2, LiCoo. 7 Nio. 3 O 2 , LiCoo.8Nio.2O2, LiCoo.82Nio.i8O2, LiCoo.8Nio.15Alo.05O2, LiNi 0 . 4 Coo.3Mno.3O 2 and LiNi 0 .33Coo.33Mno.3 4 O 2 .
  • the cathode current collector is generally of a thickness of between 3 to 500 pm. Examples of materials that can be used as the cathode current collector include aluminium, stainless steel, nickel, titanium and sintered carbon.
  • the electrolyte is suitably a non-aqueous electrolyte containing a lithium salt and may include, without limitation, non-aqueous electrolytic solutions, solid electrolytes and inorganic solid electrolytes.
  • non-aqueous electrolyte solutions that can be used include non-protic organic solvents such as propylene carbonate, ethylene carbonate, butylenes carbonate, dimethyl carbonate, diethyl carbonate, gamma butyro lactone, 1 ,2-dimethoxy ethane, 2- methyl tetrahydrofuran, dimethylsulphoxide, 1 ,3- dioxolane, formamide, dimethylformamide, acetonitrile, nitromethane, methylformate, methyl acetate, phosphoric acid trimester, trimethoxy methane, sulpholane, methyl sulpholane and 1 ,3-dimethyl-2-imidazolidione.
  • organic solid electrolytes examples include polyethylene derivatives polyethyleneoxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, polyester sulphide, polyvinyl alcohols, polyvinylidine fluoride and polymers containing ionic dissociation groups.
  • inorganic solid electrolytes examples include nitrides, halides and sulphides of lithium salts such as Li 5 NI 2 , Li 3 N, Lil, LiSiO 4 , Li 2 SiS 3 , Li 4 SiO 4 , LiOH and Li 3 PO 4 .
  • the lithium salt is suitably soluble in the chosen solvent or mixture of solvents.
  • suitable lithium salts include LiCI, LiBr, Lil, LiCIO 4 , LiBF 4 , LiBC 4 O 8 , LiPF 6 , LiCF 3 SO 3 , LiAsF 6 , LiSbF 6 , LiAICI 4 , CH 3 SO 3 Li and CF 3 SO 3 Li.
  • the battery is provided with a separator interposed between the anode and the cathode.
  • the separator is typically formed of an insulating material having high ion permeability and high mechanical strength.
  • the separator typically has a pore diameter of between 0.01 and 100pm and a thickness of between 5 and 300pm.
  • suitable electrode separators include a micro-porous polyethylene film.
  • APTS (2 g) was added to water (5 mL) and ethanol (95 mL). 50 mL of 10% v/v acetic acid was added to give a pH in the range of 4.5 - 5.5. The solution was stirred and set aside for at least 5 min to form the silanol.
  • Silver was deposited onto the surface of the silicon starting particles described in Example 1 by electroless deposition as described in WO2009/010758 followed by metal- assisted chemical etching of the silicon to form pillared silicon particles.
  • Figure 6A is a SEM image of etched silicon formed by the process of Comparative Example 1
  • Figure 6B is a SEM image of etched silicon formed by the process of Example 1.
  • the PMF of Example 1 is significantly higher than that of Comparative Example 1. This may be partly explained by a denser coverage of pillars on some particle surfaces.
  • the pillars may also be thicker, making them more robust but it is also believed that a more uniform etching of the particles surfaces has been achieved, reducing the number of unetched or poorly etched surfaces in the powder on Comparative Example 1.
  • the higher PMF provides a higher capacity electrode material.
  • etched silicon structures as described herein may be applicable to other metal ion batteries, for example sodium or magnesium ion batteries.
  • etched silicon as described herein may be used in devices other than metal ion batteries, for example filters, other energy storage devices such as fuel cells, photovoltaic devices such as solar cells, sensors, and capacitors.
  • Etched silicon as described herein may also form conducting or semiconducting components of electronic circuitry.

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Abstract

La présente invention concerne un procédé de gravure du silicium par attaque chimique assistée par métal (MACE). Selon le mode de réalisation de l'invention, une surface de silicium est fonctionnalisée; un métal ou un ion métallique est lié à la surface fonctionnalisée; l'ion métal, s'il est utilisé, est réduit à un métal élémentaire; puis l'attaque chimique assistée par métal (MACE) est réalisée. Les structures en silicium gravé produites selon ce procédé comprennent des particules poreuses et en colonne.
PCT/GB2014/052219 2013-07-19 2014-07-21 Procédé de formation de structures en silicium gravé WO2015008093A1 (fr)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2319956A1 (fr) * 2009-10-08 2011-05-11 Commissariat à l'Énergie Atomique et aux Énergies Alternatives Métallisation d'une zone en silicium poreux par réduction in situ et application à une pile à combustible
GB2492167A (en) * 2011-06-24 2012-12-26 Nexeon Ltd Pillared particles for metal ion battery
US20130040412A1 (en) * 2010-05-07 2013-02-14 Unist Academy-Industry Research Corporation Method of forming silicon nanowires and method of fabricating lithium secondary battery using the same

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2319956A1 (fr) * 2009-10-08 2011-05-11 Commissariat à l'Énergie Atomique et aux Énergies Alternatives Métallisation d'une zone en silicium poreux par réduction in situ et application à une pile à combustible
US20130040412A1 (en) * 2010-05-07 2013-02-14 Unist Academy-Industry Research Corporation Method of forming silicon nanowires and method of fabricating lithium secondary battery using the same
GB2492167A (en) * 2011-06-24 2012-12-26 Nexeon Ltd Pillared particles for metal ion battery

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
S. KATO, Y. WANATABE, Y. KUROKAWA, A. YAMADA, Y. OHTA, Y. NIWA, M. HIROTA: "Metal-Assisted Chemical Etching Using Silica Nanoparticle for the Fabrication of a Silicon Nanowire Array", JAPANESE JOURNAL OF APPLIED PHYSICS, vol. 51, no. 02BP09, 20 February 2012 (2012-02-20), pages 1 - 4, XP002730477, DOI: 10.1143/JJAP.51.02BP09 *
SHIU S C ET AL: "Influence of pre-surface treatment on the morphology of silicon nanowires fabricated by metal-assisted etching", APPLIED SURFACE SCIENCE, ELSEVIER, vol. 257, no. 6, 2011, online: 20-10-2010, pages 1829 - 1834, XP027562439, ISSN: 0169-4332, [retrieved on 20101020], DOI: 10.1016/j.apsusc.2010.08.086 *

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