US20140193711A1 - Combined electrochemical and chemical etching processes for generation of porous silicon particulates - Google Patents

Combined electrochemical and chemical etching processes for generation of porous silicon particulates Download PDF

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US20140193711A1
US20140193711A1 US14/149,055 US201414149055A US2014193711A1 US 20140193711 A1 US20140193711 A1 US 20140193711A1 US 201414149055 A US201414149055 A US 201414149055A US 2014193711 A1 US2014193711 A1 US 2014193711A1
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porous silicon
particulates
silicon substrate
silicon
anode material
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Sibani Lisa Biswal
Michael S. Wong
Madhuri Thakur
Steven L. Sinsabaugh
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William Marsh Rice University
Lockheed Martin Corp
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William Marsh Rice University
Lockheed Martin Corp
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Assigned to WILLIAM MARSH RICE UNIVERSITY reassignment WILLIAM MARSH RICE UNIVERSITY ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: BISWAL, SIBANI LISA, THAKUR, MADHURI, WONG, MICHAEL S.
Assigned to LOCKHEED MARTIN CORPORATION reassignment LOCKHEED MARTIN CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: SINSABAUGH, STEVEN L.
Publication of US20140193711A1 publication Critical patent/US20140193711A1/en
Priority to US15/147,567 priority patent/US9947918B2/en
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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
    • H01M4/134—Electrodes based on metals, Si 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
    • H01M4/04—Processes of manufacture in general
    • H01M4/0438—Processes of manufacture in general by electrochemical processing
    • H01M4/044—Activating, forming or electrochemical attack of the supporting material
    • 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
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
    • C25F3/00—Electrolytic etching or polishing
    • C25F3/02—Etching
    • C25F3/12—Etching of semiconducting materials
    • 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
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    • 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
    • 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
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/626—Metals
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/16—Pore diameter
    • H—ELECTRICITY
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    • 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
    • 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
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
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    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
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    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • 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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/10—Process efficiency
    • Y02P20/133—Renewable energy sources, e.g. sunlight

Definitions

  • the present disclosure pertains to methods of preparing porous silicon particulates.
  • the methods comprise: (a) electrochemically etching a silicon substrate, where the electrochemical etching comprises exposure of the silicon substrate to an electric current density, and where the electrochemical etching produces a porous silicon film over the silicon substrate; (b) separating the porous silicon film from the silicon substrate, where the separating comprises a gradual increase of the electric current density in sequential increments; (c) repeating steps (a) and (b) a plurality of times; (d) electrochemically etching the silicon substrate in accordance with step (a) to produce a porous silicon film over the silicon substrate; (e) chemically etching the porous silicon film and the silicon substrate; and (f) splitting the porous silicon film and the silicon substrate to form porous silicon particulates.
  • the electrochemical etching comprises the use of an acid, such as hydrofluoric acid. In some embodiments, the electrochemical etching comprises exposure of the silicon substrate to an electric current density of about 1 mA/cm 2 to about 10 mA/cm 2 . In some embodiments, the gradual increase of the electric current density during the separating step comprises an increase of the electric current density by about 1-2 mA/cm 2 per sequential increment.
  • the chemical etching occurs by exposure of the porous silicon film and the silicon substrate to a metal (including transition metals and metalloids).
  • the metal is selected from the group consisting of silver, copper, chromium, gold, aluminum, tantalum, lead, zinc, silicon, and combinations thereof.
  • the exposure results in coating of the porous silicon film and the silicon substrate with the metal.
  • the splitting occurs by at least one of physical grinding, crushing, sonication, ultrasonication, ultrasonic fracture, pulverization, ultrasonic pulverization, and combinations thereof. In some embodiments, the splitting occurs by ultrasonication.
  • the methods of the present disclosure further comprise a step of associating the formed porous silicon particulates with a binding material.
  • the binding material is selected from the group consisting of binders, carbon materials, polymers, metals, additives, carbohydrates, and combinations thereof.
  • the binding material comprises a carbonized polyacrylonitrile.
  • the methods of the present disclosure also include a step of controlling a thickness of the porous silicon film used to form the porous silicon particulates.
  • the thickness of the porous silicon film is controlled by adjusting one or more parameters selected from the group consisting of electric current density during electrochemical etching, resistivity of the silicon substrate during electrochemical etching, concentration of electrolyte etchants used during electrochemical or chemical etching, temperature during electrochemical or chemical etching, and combinations thereof.
  • porous silicon particulates formed by the methods of the present disclosure Further embodiments of the present disclosure pertain to porous silicon particulates formed by the methods of the present disclosure. Additional embodiments of the present disclosure pertain to anode materials that contain the porous silicon particulates of the present disclosure. In some embodiments, the anode materials of the present disclosure have discharge capacities of at least about 600 mAh/g over at least 50 cycles. In some embodiments, the anode materials of the present disclosure have discharge capacities of at least about 1000 mAh/g over at least 50 cycles. In some embodiments, the anode materials of the present disclosure have Coulombic efficiencies of at least about 90% over at least 50 cycles.
  • the anode materials of the present disclosure are utilized as components of energy storage devices, such as batteries. In more specific embodiments, the anode materials of the present disclosure are utilized as components of lithium ion batteries.
  • FIG. 1 provides a scheme of a method for making porous silicon particulates (PSPs).
  • FIG. 2 provides illustrations of methods of making porous silicon particulates.
  • FIG. 2A provides an illustration of porous silicon film formation from a silicon wafer at a current density of 1-10 mA/cm 2 for 1-4 hours.
  • FIGS. 2B-2C provide scanning electron microscope (SEM) images for the top view ( FIG. 2B ) and the side view of porous silicon films ( FIG. 2C ).
  • FIG. 3 provides SEM images of electrochemically and chemically etched porous silicon particulates ( FIG. 3A ) and chemically etched porous silicon particulates ( FIG. 3B ). Additional images of electrochemically and chemically etched porous silicon particulates are shown in FIGS. 3C-E .
  • FIG. 4 shows discharge capacity and efficiency vs. cycle number of the porous silicon particulates of FIG. 3 during galvanostatic charge/discharge studies. Discharge capacity (red square, A) and coulombic efficiency (blue square, C) for electrochemically and chemically etched porous silicon particulates and discharge capacity (red triangle, B) and coulombic efficiency (blue triangle, D) for chemically etched porous silicon particulates are shown.
  • FIG. 5 provides discharge capacity and efficiency vs. cycle number of porous silicon particulates when used as anodes along with cathode materials (i.e., lithium cobalt oxide (LiCoO 2 )) during galvanostatic charge/discharge between 2.8-4V at a constant charge capacity of 1000 mAhg ⁇ 1 .
  • cathode materials i.e., lithium cobalt oxide (LiCoO 2 )
  • Rechargeable batteries continue to draw attention because energy storage devices with higher energy storage capabilities are required for numerous applications.
  • researchers continue to focus on the development of new electrode materials with higher capacities and longer lifetimes for the major components of Li-ion batteries: cathode and anode. Therefore, developing new electrode materials with higher energy capacities can lead to significant improvements in the performance and lifetimes of the rechargeable batteries.
  • lithium ion batteries e.g., lithium ion batteries
  • the capacity of lithium ion batteries generally depends on the amount of lithium (Li) ion an anode material can hold.
  • a material that reacts with lithium at low potential is silicon.
  • carbon-based materials e.g. graphite are utilized as anode materials in most rechargeable batteries.
  • the highest achievable specific capacity for silicon is 3579 mAhg ⁇ 1 , far greater than the theoretical capacity of graphite (372 mAhg ⁇ 1 ).
  • silicon when silicon is lithiated, it undergoes a large volume expansion ( ⁇ 300%). This in turn causes severe cracking of the silicon and leads to electrode failure.
  • silicon-based nanostructures such as nanosized particles, thin film, silicon nanowires, silicon nanotubes, core-cell nanowires, porous silicon (PSi), and interconnected silicon hollow nanospheres. Many of these structures have shown success in addressing the mechanical breaking issues associated with silicon.
  • the first patent application describes in some embodiments an electrochemically etched porous silicon with metal coatings and a freestanding macroporous silicon with pyrolyzed polyacrylonitrile (PPAN) infiltration (International Application No. PCT/US2010/054577, filed on Oct. 28, 2010).
  • the second patent application describes in some embodiments a macroporous silicon micro-particulate with PPAN composite as an anode material for lithium ion batteries (U.S. patent application Ser. No. 13/589,588, filed on Aug. 20, 2012).
  • binder free metal-coated porous silicon with bulk silicon exhibits a higher capacity and good cycle life than other forms of binder free silicon materials, such as silicon nanowires.
  • metal coatings may add to the cost of the materials.
  • porous silicon films with bulk silicon adds to the overall weight of the materials without adding to the specific capacity.
  • the bulk silicon substrate can be removed by backside chemical etching processes. However, such processes usually result in waste of useful silicon materials.
  • Applicants have developed a method of producing porous silicon films from a silicon substrate by etching the silicon substrate through the application of current densities (U.S. patent application Ser. No. 13/589,588). This results in the formation of a porous silicon film over the silicon substrate.
  • the porous silicon film can then be separated from the silicon substrate through a multi-step lift-off process that applies higher current densities during etching. As such, multiple films can be removed from a single wafer, thereby leading to less silicon waste.
  • porous silicon films produced by Applicants' lift-off processes are that they may have limited processability in various circumstances.
  • Applicants changed from a film structure to a particulate structure that can be combined with PAN (or any other binders) to form slurries that can be processed with standard coating technologies.
  • PAN or any other binders
  • the lift-off processes can lead to cracking of the silicon substrate due to its brittle nature before the lift-off of the layer. Therefore, the cracked silicon substrate cannot be reused. This in turn leads to waste of the silicon materials.
  • the present disclosure pertains to novel methods of preparing porous silicon particulates. In some embodiments, the present disclosure pertains to anode materials that include such porous silicon particulates.
  • the present disclosure pertains to methods of preparing porous silicon particulates.
  • the methods of the present disclosure include: electrochemically etching a silicon substrate to produce a porous silicon film over the silicon substrate (step 10 ); separating the porous silicon film from the silicon substrate (step 12 ); repeating steps 10 and 12 a plurality of times; electrochemically etching the silicon substrate in accordance with step 10 to produce a porous silicon film over the silicon substrate (step 14 ); chemically etching the porous silicon film and the silicon substrate (step 16 ); and splitting the porous silicon film and the silicon substrate to form porous silicon particulates (step 18 ).
  • the methods of the present disclosure also include a step of associating the porous silicon particulates with a binding material (step 20 ). In some embodiments, the methods of the present disclosure also include a step of controlling the thickness of the porous silicon films that are used to make the porous silicon particulates.
  • the methods of the present dislcosure can have numerous embodiments.
  • various silicon substrates, binding materials, electrochemical etching techniques, porous film separation techniques, chemical etching techniques, and splitting techniques may be utilized to form various types of porous silicon particulates.
  • the methods of the present disclosure may utilize various types of silicon substrates.
  • the silicon substrates may include bulk silicon substrates.
  • the silicon substrates include crystalline silicon, semicrystalline silicon, amorphous silicon, doped silicon, coated silicon, silicon pre-coated with silicon nanoparticles, and combinations thereof.
  • the silicon substrate is a silicon wafer. In some embodiments, the silicon substrate is a crystalline silicon wafer. In some embodiments, the silicon substrate is a doped silicon wafer. In some embodiments, the silicon substrate is a silicon wafer doped with boron, phosphorous, arsenic, antimony, other dopants, and combinations thereof. In some embodiments, the silicon substrate is a p-type silicon wafer, an n-type silicon wafer, and combinations thereof. In some embodiments, the silicon substrate may be an n-doped or a boron doped silicon wafer. The use of additional silicon substrates can also be envisioned.
  • the electrochemical etching produces a porous silicon film over the silicon substrate.
  • the electrochemical etching may include the use of one or more strong acids, such as nitric acid (HNO 3 ), hydrofluoric acid (HF), sulfuric acid (H 2 SO 4 ), hydrochloric acid (HCl), and combinations thereof.
  • HNO 3 nitric acid
  • HF hydrofluoric acid
  • HCl hydrochloric acid
  • the electrochemical etching of the silicon substrate occurs in the presence of hydrofluoric acid.
  • the electrochemical etching of the silicon substrate occurs in the presence of hydrofluoric acid in dimethylformamide (DMF).
  • DMF dimethylformamide
  • the electrochemical etching occurs in the presence of an applied electric field, such as an electric field with a constant electric current density.
  • electrochemical etching includes exposure of the silicon substrate to an electric current density.
  • the etching occurs by the use of a strong acid (e.g., HF) in the presence of an applied electric field.
  • a strong acid e.g., HF
  • the applied electric field may contain various levels of electric current densities.
  • the electric current density is from about 0.5 mA/cm 2 to about 50 mA/cm 2 . In some embodiments, the electric current density is from about 1 mA/cm 2 to about 10 mA/cm 2 . In some embodiments, the maximum electric current density is about 20 mA/cm 2 . In some embodiments, the electric current density is applied to a silicon substrate in an electrochemical cell.
  • an electric current density may be applied to silicon substrates in one or more increments.
  • the etching process may include from 1 increment to about 10 increments.
  • the electric current density may be from about 1 mA/cm 2 to about 20 mA/cm 2 per increment.
  • each increment may last from about 30 seconds to about 60 minutes.
  • each increment may last for about 10 minutes.
  • the increments may be separated by intervals. In some embodiments, the intervals may be from about 30 seconds to about 30 minutes.
  • silicon substrates may be exposed to various current densities for various periods of time. For instance, in some embodiments, electrochemical etching occurs for about 3 hours to about 5 hours. In more specific embodiments, electrochemical etching occurs by exposure of silicon substrates to electric current densities of 1 mA/cm 2 to 10 mA/cm 2 for about 1 hour to about 4 hours.
  • Various methods may also be utilized to separate the formed porous silicon films from silicon substrates (also referred to as a “lift-off” procedure). In various embodiments, such separation steps can occur during or after electrochemical etching.
  • the separating includes a gradual increase of the electric current density in sequential increments until the porous silicon film has been separated from the silicon substrate.
  • a gradual increase in electric current density generally refers to a stepwise increase in electric current density over several sequential increments.
  • the electric current density may increase gradually in at least 5-10 sequential increments that may last from about 30 seconds to 60 minutes per increment.
  • the gradual increase in electrical current density may occur through at least 5 to 10 sequential increments that may be separated by intervals of about 30 seconds to 60 minutes per increment.
  • the applied electric current density may be from about 0.5 mA/cm 2 to about 50 mA/cm 2 . In some embodiments, the electric current density may gradually increase from about 1 mA/cm 2 to about 2 mA/cm 2 per increment. In some embodiments, the maximum electric current density may be about 15 mA/cm 2 . In some embodiments, the electric current density may gradually increase in small increments of 1 mA/cm 2 at 10-60 minutes per increment for up to 15 mA/cm 2 . In some embodiments, the electric current density may gradually increase in 13 sequential increments by at least about 1 mA/cm 2 per increment for up to 15 mA/cm 2 . In some embodiments, the electric current density may gradually increase in small increments of 0.5 mA/cm 2 at 1-2 hours per increment for up to 20 mA/cm 2 .
  • the aforementioned “lift off” procedures may occur through various mechanisms.
  • HF as an electrochemical etchant
  • the availability of fluoride ions at the pore tip decreases.
  • Such a decrease may in turn lead to isotropic etching at the tip of the pores, thereby resulting in a layer of silicon that is more porous at the point of contact with the silicon substrate. See, e.g., FIG. 2A .
  • the hydrogen byproduct accumulates and starts to exert a hydrodynamic pressure onto the walls of the pores. At some point, the pore walls may not be able to withstand this hydrodynamic pressure. This in turn may lead to separation of the porous silicon film from the silicon substrate.
  • separation steps may also include additional steps.
  • separation steps may also include a step of physically removing the formed porous silicon film from the silicon substrate.
  • the physical removal may occur by the use of a razor blade, a tweezer, or other objects.
  • the physical removal may occur by a rinsing step or a washing step.
  • the electrochemical etching and separation steps are repeated a plurality of times. For instance, in some embodiments, the electrochemical etching and separation steps are repeated more than 5 times. In some embodiments, the electrochemical etching and separation steps are repeated more than 10 times. In some embodiments, the electrochemical etching and separation steps are repeated until the porous silicon film becomes inseparable from the silicon substrate. In some embodiments, the electrochemical etching and separation steps are repeated until the silicon substrate develops one or more cracks.
  • the methods of the present disclosure can include a final step of electrochemically etching the silicon substrate to produce a porous silicon film over the silicon substrate. Thereafter, the porous silicon film and the silicon substrate may be chemically etched.
  • the chemical etching occurs by exposure of the porous silicon film and the silicon substrate to a metal (including transition metals and metalloids).
  • the metal includes at least one of silver, copper, chromium, gold, aluminum, tantalum, lead, zinc, silicon and combinations thereof.
  • the metal is silver.
  • the metal includes silicon, such as silicon nitride, silicon oxide, and combinations thereof.
  • the exposure of the porous silicon films and the silicon substrates of the present disclosure to a metal can have various effects.
  • the exposure results in coating of the porous silicon film and the silicon substrate with metals.
  • the coating may be uniform and homogenous.
  • the exposure may result in the partial coating of the porous silicon film and the silicon substrate with metals.
  • the exposure may result in the full coating of the porous silicon film and the silicon substrate with metals.
  • the porous silicon film and the silicon substrate may become infiltrated with or embedded with the metals.
  • a chemical etching step is followed by splitting the porous silicon film and the silicon substrate to form porous silicon particulates.
  • Various splitting methods may be utilized for such purposes.
  • the splitting occurs by at least one of physical grinding, crushing, sonication, ultrasonication, ultrasonic fracture, pulverization, ultrasonic pulverization, and combinations thereof.
  • the splitting occurs by ultrasonication.
  • the porous silicon particulates may also be associated with one or more binding materials. In various embodiments, the association may occur prior to, during, or after porous silicon particulate formation.
  • Binding materials generally refer to materials that may enhance the electric conductivity or stability of porous silicon films.
  • the binding materials may include at least one of binders, carbon materials, polymers, metals, additives, carbohydrates, and combinations thereof.
  • the binding materials may include a polymer.
  • the polymer may include at least one of polyacrylonitrile (PAN), pyrolyzed polyacrylonitrile (PPAN), polyvinylidene difluoride (PVDF), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), and combinations thereof.
  • PAN polyacrylonitrile
  • PPAN pyrolyzed polyacrylonitrile
  • PVDF polyvinylidene difluoride
  • PAA polyacrylic acid
  • CMC carboxymethyl cellulose
  • the polymers may be in polymerized form prior to association with porous silicon particulates.
  • the polymers may polymerize during or after association with porous silicon particulates.
  • the binding material is an additive.
  • the additive is sodium alginate.
  • the binding materials may include one or more metals.
  • the metals may include, without limitation, gold, copper, silver, titanium, iron, and combinations thereof.
  • the binding materials may include one or more carbon materials.
  • suitable carbon materials include carbon nanotubes, carbon black, graphite, carbon fibers, carbon nanofibers, graphene sheets, fullerenes, graphene platelets, sodium alginate binders associated with carbon black, carbohydrates, and combinations thereof.
  • the binding material includes a carbohydrate. In some embodiments, the carbohydrate is glucose.
  • association may occur by sputtering, spraying, or physically applying the one or more binding materials onto the porous silicon particulates. In some embodiments, the association may occur by dipping the porous silicon particulates into a solution containing one or more binding materials.
  • the association may result in the partial coating of the porous silicon particulates with a binding material. In some embodiments, the association may result in the full coating of the porous silicon particulates with a binding material. In some embodiments, the porous silicon particulates may become infiltrated with, embedded with or dispersed in the binding materials.
  • the binding materials that are associated with porous silicon particulates may be in carbonized form. In some embodiments, the binding materials may become carbonized before, during, or after association with the porous silicon particulates. In some embodiments, the binding materials may become carbonized by pyrolysis before, during or after association with porous silicon particulates. In more specific embodiments, the binding materials may include PAN that has been carbonized by pyrolysis after association with porous silicon particulates. In some embodiments, pyrolysis may occur by heating porous silicon particulates at high temperatures (e.g., 550° C.) in the presence of an inert gas (e.g., Argon).
  • an inert gas e.g., Argon
  • the binding material includes a carbonized polyacrylonitrile.
  • An advantage of using carbonized PAN as a binding material is that it forms conjugated carbon chains upon carbonization. This in turn can enhance the electrical properties of the porous silicon particulates.
  • the methods of the present disclosure also include a step of controlling a thickness of the porous silicon films that are used to form the porous silicon particulates.
  • Various methods may also be utilized to control the thickness of the porous silicon films.
  • the thickness of the porous silicon films is controlled by adjusting one or more parameters.
  • the controllable parameters include at least one of electric current density during electrochemical etching, resistivity of the silicon substrate during electrochemical etching, concentration of electrolyte etchants used during electrochemical or chemical etching, placement of the electrode, process temperature, temperature during electrochemical or chemical etching, and combinations thereof.
  • the formed porous silicon particulates include a plurality of pores.
  • the pores include various diameters.
  • the pores of the porous silicon particulates include diameters between about 1 nanometer to about 5 micrometers.
  • the pores include macropores with diameters of at least about 50 nm.
  • the pores include macropores with diameters between about 50 nanometers to about 3 micrometers.
  • the pores include macropores with diameters between about 500 nanometers to about 2 micrometers.
  • the pores include mesopores with diameters of less than about 50 nm.
  • the pores include micropores with diameters of less than about 2 nm.
  • porous materials have been classified according to their pore diameters.
  • micropores are those with diameters less than 2 nm.
  • Mesopores have diameters that range from 2 nm to 50 nm.
  • Macropores have diameters that are greater than 50 nm.
  • the pores in the formed porous silicon particulates may include various combinations of micropores, mesopores and macropores.
  • the porous silicon particulates include hierarchical pores.
  • the hierarchical pores include micropores and mesopores within macropores.
  • the pores in the formed porous silicon particulates can also have various arrangements.
  • the formed porous silicon particulates include pores that span at least 50% of a thickness of the porous silicon particulates.
  • the formed porous silicon particulates include pores that span an entire thickness of the porous silicon particulates.
  • the formed porous silicon particulates can also have various thicknesses. For instance, in some embodiments, the formed porous silicon particulates have thicknesses ranging from about 10 micrometers to about 200 micrometers. In more specific embodiments, the formed porous silicon particulates have thicknesses ranging from about 10 micrometers to about 50 micrometers.
  • the formed porous silicon particulates can also have various diameters.
  • the porous silicon particulates include diameters from about 1 ⁇ m to about 50 ⁇ m. In some embodiments, the porous silicon particulates include diameters from about 10 ⁇ m to about 20 ⁇ m.
  • the porous silicon particulates of the present disclosure can also have various electrical properties.
  • the porous silicon particulates of the present disclosure have discharge capacities of at least about 600 mAh/g over numerous cycles, such as at least 20 cycles, at least 40 cycles, at least 50 cycles, at least 60 cycles, at least 80 cycles, at least 100 cycles, at least 120 cycles, at least 140 cycles, at least 160 cycles, at least 180 cycles, at least 200 cycles, or at least 220 cycles.
  • the porous silicon particulates of the present disclosure have discharge capacities of at least about 1,000 mAh/g over numerous cycles, such as at least 20 cycles, at least 40 cycles, at least 50 cycles, at least 60 cycles, at least 80 cycles, at least 100 cycles, at least 120 cycles, at least 140 cycles, at least 160 cycles, at least 180 cycles, at least 200 cycles, or at least 220 cycles.
  • the porous silicon particulates of the present disclosure have Coulombic efficiencies of at least about 90% over numerous cycles, such as at least 20 cycles, at least 40 cycles, at least 50 cycles, at least 60 cycles, at least 80 cycles, at least 100 cycles, at least 120 cycles, at least 140 cycles, at least 160 cycles, at least 180 cycles, at least 200 cycles, or at least 220 cycles.
  • anode materials include the porous silicon particulates of the present disclosure.
  • the anode materials of the present disclosure include: (1) porous silicon particulates with a plurality of pores; (2) a coating associated with the porous silicon particulates; and (3) a binding material associated with the porous silicon particulates.
  • the porous silicon particulates in the anode materials of the present disclosure can have various types of pores.
  • the pores include diameters between about 1 nanometer to about 5 micrometers.
  • the pores include diameters of at least about 50 nm.
  • the pores include diameters of less than about 50 nm.
  • the pores include diameters of less than about 2 nm.
  • the porous silicon particulates in the anode materials include hierarchical pores.
  • the hierarchical pores include micropores and mesopores within macropores.
  • the porous silicon particulates include pores that span at least 50% of a thickness of the porous silicon particulates. In some embodiments, the porous silicon particulates include pores that span an entire thickness of the porous silicon particulates. In some embodiments, the porous silicon particulates have thicknesses ranging from about 10 micrometers to about 200 micrometers.
  • porous silicon particulates in the anode materials of the present disclosure may also be associated with various types of coatings.
  • the porous silicon particulates may be associated with metal coatings.
  • the metal coatings may include, without limitation, silver, copper, chromium, gold, aluminum, tantalum, lead, zinc, silicon, and combinations thereof.
  • the metal coating is silver.
  • the porous silicon particulates in the anode materials of the present disclosure may also be associated with various types of binding materials.
  • the binding materials may include at least one of binders, carbon materials, polymers, metals, additives, carbohydrates, and combinations thereof.
  • the binding materials may include polymers.
  • the polymers may include at least one of polyacrylonitrile (PAN), pyrolyzed polyacrylonitrile (PPAN), polyvinylidene difluoride (PVDF), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), and combinations thereof.
  • the binding materials may include carbonized polyacrylonitriles, carbohydrate (e.g., glucose), additives (e.g., sodium alignate), and combinations thereof.
  • porous silicon particulates in the anode materials of the present disclosure may also have various diameters.
  • the porous silicon particulates include diameters from about 1 ⁇ m to about 50 ⁇ m.
  • the anode materials of the present disclosure can also have various electrical properties.
  • the anode materials of the present disclosure have discharge capacities of at least about 600 mAh/g over numerous cycles, such as at least 20 cycles, at least 40 cycles, at least 50 cycles, at least 60 cycles, at least 80 cycles, at least 100 cycles, at least 120 cycles, at least 140 cycles, at least 160 cycles, at least 180 cycles, at least 200 cycles, or at least 220 cycles.
  • the anode materials of the present disclosure have discharge capacities of at least about 1,000 mAh/g over numerous cycles, such as at least 20 cycles, at least 40 cycles, at least 50 cycles, at least 60 cycles, at least 80 cycles, at least 100 cycles, at least 120 cycles, at least 140 cycles, at least 160 cycles, at least 180 cycles, at least 200 cycles, or at least 220 cycles.
  • the anode materials of the present disclosure have Coulombic efficiencies of at least about 90% over numerous cycles, such as at least 20 cycles, at least 40 cycles, at least 50 cycles, at least 60 cycles, at least 80 cycles, at least 100 cycles, at least 120 cycles, at least 140 cycles, at least 160 cycles, at least 180 cycles, at least 200 cycles, or at least 220 cycles.
  • the anode materials of the present disclosure may also be associated with various types of energy storage devices.
  • the anode materials of the present disclosure may be associated with batteries.
  • the anode materials of the present disclosure may be associated with lithium ion batteries.
  • porous silicon particulates of the present disclosure have various advantageous properties, such as enhanced discharge capacities and enhanced Coulombic efficiencies over numerous cycles. As such, the methods and porous silicon particulates of the present disclosure can find numerous applications.
  • the porous silicon particulates of the present disclosure can be utilized as anode materials for various types of energy storage devices in numerous fields, including the defense industry, the automotive industry, the renewable energy industry, the aerospace industry, the telecommunication industry, information technology, consumer electronics, implantable devices, and electric vehicles.
  • the porous silicon particulates of the present disclosure can be utilized as anode materials in batteries, such as lithium ion batteries.
  • porous silicon particulates of the present disclosure can improve the performance and lower the cost of high performance anode materials in many energy storage devices, such as lithium ion batteries.
  • batteries that contain the porous silicon particulates of the present disclosure have potential discharge capacities up to an order of magnitude higher than today's lithium ion batteries.
  • batteries containing the porous silicon particulates of the present disclosure can provide optimal cycleability and capacities of 1000 mAhg ⁇ 1 for hundreds of cycles.
  • the methods and porous silicon particulates of the present disclosure can provide additional advantages and applications, including use as improved anode materials for lithium ion batteries; use for development of lithium ion batteries with improved cycling behavior and high capacity, which can be 1000 mAhg ⁇ 1 for more than 200 cycles; use as low cost methods for manufacturing anodes for lithium ion batteries; use as reproducible methods for making anode battery materials; and use for development of lithium ion batteries with substantially higher discharge capacities than current batteries.
  • This Example illustrates a combined electrochemical/chemical etching process to generate porous silicon micron size particulates as an anode for lithium ion batteries.
  • the silicon wafer is first electrochemically etched to a depth of a few hundreds of microns.
  • the porous film is electrochemically lifted-off. This process is repeated until the remaining wafer is thinned and begins cracking. Once the wafer starts cracking, the wafer is chemically etched and crushed.
  • Applicants have tested these electrochemically/chemically etched porous silicon particulates as anode materials for lithium ion batteries. To compare the results, Applicants have done controlled experiments. Initially, a porous silicon film is formed by electrochemically etching at room temperature with constant current density of 1-5 mA/cm 2 for 3-5 hour, resulting in a wafer composed of a porous silicon layer with a thickness of 10-200 ⁇ m. Next, chemical etching is performed by placing the previously electrochemically etched wafer into solution silver nitrate/hydrofluoric acid solution that is in a 1:10 ratio by volume for 1-10 minutes.
  • FIGS. 3A-B show the scanning electron microscopic (SEM) images for electrochemically/chemically etched ( FIG. 3A ) and chemically etched ( FIG. 3B ) porous silicon particulates. Additional images of the electrochemically/chemically etched porous silicon particulates are shown in FIGS. 3C-E .
  • FIG. 4 shows the cycle performance of the electrochemically/chemically etched porous silicon particulates in comparison to the chemically etched porous silicon particulates (PSP) (controlled).
  • the mass of the anode materials was 1.5 mg/cm 2 .
  • the anode materials are mixed with the Polyacrylonitrile (PAN) in a ratio of 7:3 and coated on the stainless steel foil.
  • the coated porous silicon particulates/PAN composite are pyrolyzed at 550° C. at argon atmosphere. Both the materials are charged/discharged at 500 mAcm ⁇ 2 between 0-1 V at a constant charge capacity of 1000 mAhg ⁇ 1 .
  • PAN Polyacrylonitrile
  • the volume expansion of the silicon can be control by limiting the intercalation of the lithium into the silicon.
  • Cui et al. Nano Letters, 2009, 9:491-495 also found that limiting the intercalation of the silicon between 30-50% of the maximum specific capacity resulted in extended life cycle, and that charging silicon microparticles and nanoparticles at constant charge capacity increased the life cycle of the anode.
  • the increase in the capacity of the electrochemically/chemically etched porous silicon particulates in comparison to the chemically etched porous silicon particulates is also due to different pore geometries on the silicon particulates, such as macropores (>50 nm), mesopores ( ⁇ 50 nm) and micropores ( ⁇ 2 nm). See, e.g., FIG. 2A .
  • the electrochemically/chemically etched porous silicon particulates were also tested in the full cell by using lithium cobalt oxide (LiCoO 2 ) as a cathode material.
  • the mass of the anode is 0.001 g/cm 2
  • the mass of the cathode material LiCoO 2 with carbon black and Polyvinylidene fluoride (PVDF)
  • the capacity of the full cell was calculated based on the mass of the anode materials.
  • FIG. 5 shows the cycle performance of the full cell.
  • the porous silicon was synthesized via electrochemical etching of silicon wafer using a multistep lift-off process.
  • the thickness of the porous silicon films can be modified by controlling the etching parameters such as applied current, wafer resistivity, concentration of electrolyte and doping of the wafer.
  • etching parameters such as applied current, wafer resistivity, concentration of electrolyte and doping of the wafer.
  • prime grade, boron doped, p-type (100) silicon wafers (Siltronix Corp, silicon sense and silicon quest) were used.
  • the wafer presented has a thickness of 275 ⁇ 25 ⁇ m with an average resistivity between 14-22 ohm-cm and 10-30 ohm-cm.
  • pores are etched into the wafers at a constant current density delivered by an Agilent power supply (E3612A) at room temperature.
  • the etching solution is composed of 20-30 mL dimethylformamide (DMF, Sigma Aldrich) and 2-4 mL 49% HF (Fisher Scientific) solution.
  • the formation of the pores takes place when the number of fluoride ions was greater than the number of holes ([F ⁇ ]>[h+]).
  • the porous silicon etched can have an average diameter of 500 nm-2 ⁇ m and a depth between 10 ⁇ m-200 ⁇ m depending on etching time.
  • a porous silicon film is formed by etching at room temperature with constant current density of 1-5 mA/cm 2 for 3-5 hours. This results in the formation of a porous silicon layer with a thickness of 10 ⁇ m-200 ⁇ m.
  • FIG. 2A (right panel).
  • FIGS. 2B and 2C The SEM images for the top and side views of the porous silicon films are shown in FIGS. 2B and 2C , respectively.
  • the formed porous silicon films were lifted off from the silicon substrate multiple times by increasing the current density during the electrochemical etching process.
  • the silicon wafers used have a thickness of 275 ⁇ 25 ⁇ m with an average resistivity between 1-20 ohm-cm.
  • the etching solution is composed of dimethylformamide/49% HF solution in a ratio of 10:1.
  • a porous silicon film is formed by etching the wafers at room temperature with constant current density of 1-5 mA/cm 2 for 3-5 hours. Once the silicon substrate started cracking during the electrochemical etching, Applicants were not able to lift-off the porous silicon film layer.
  • Chemical etching was performed on the cracked silicon substrate containing porous silicon film by putting the porous substrate into 1-10 ml of hydrofluoric acid (HF) and 0.1-1 ml of silver nitrate (AgNO 3 ) at room temperature for 1-10 minutes. This resulted in the coating of the silicon substrate and the porous silicon film on the silicon substrate with silver particles. After the silver coating, the porous silicon film and the cracked silicon substrate were kept in a chemical etchant (10 ml of HF and 0.1 ml of 30% hydrogen peroxide (H 2 O 2 )) for 10-120 minutes.
  • a chemical etchant 10 ml of HF and 0.1 ml of 30% hydrogen peroxide (H 2 O 2 )
  • FIGS. 3C-E shows the SEM images of the electrochemically/chemically etched porous silicon particulates.
  • Two electrodes and three electrode cells were used for all electrochemical measurements.
  • a working electrode was prepared by drop casting PAN and electrochemically/chemically etched porous silicon particulates on stainless steel. The composition was pyrolyzed at 550° C. in an Argon atmosphere. Lithium foil (0.75 mm thick, Alfa Aesar) was used as a counter-electrode in half cell configurations. Lithium cobalt oxide (LiCoO 2 ) was used in full cell configurations. A trilayer polypropylene membrane (Celgard 2325) wetted with an electrolyte was used as a separator.
  • the electrolyte used was 1 M LiPF 6 in a 1:1 ratio w/w ethylene carbonate: diethyl carbonate (Ferro Corporation) or a 1:1 ratio w/w FEC (Ferro Corporation): dimethyl carbonate (Sigma Aldrich).
  • the anode material was not exposed to air before assembling into the cell. All the cells were assembled in an argon-filled glove box ( ⁇ 5 ppm of oxygen and water, Vacuum Atmospheres Co.).
  • the electrochemical testing is performed using an Arbin Instruments BT2000. Applicants' anode material is charged and discharged between 0-1 V versus Li/Li+ at C/3 and C/2 rates for constant charge capacity (CCC) of 1000 mAhg ⁇ 1 .
  • CCC constant charge capacity

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RU2795525C1 (ru) * 2022-11-01 2023-05-04 федеральное государственное автономное образовательное учреждение высшего образования "Национальный исследовательский ядерный университет МИФИ" (НИЯУ МИФИ) Способ получения наночастиц кремния для инактивации коронавирусной инфекции

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EP2941783A4 (en) 2016-07-13
EP2941783A1 (en) 2015-11-11
US9947918B2 (en) 2018-04-17
KR20150104590A (ko) 2015-09-15
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WO2014107704A1 (en) 2014-07-10
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