# US 2014/0193711 A1 · Combined electrochemical and chemical etching processes for generation of porous silicon particulates

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- Number: US 2014/0193711 A1
- Document ID: US20140193711A1
- Status: Published application
- Kind: A1
- Application number: 14/149,055
- Filed: 2014-01-07
- Published: 2014-07-10
- Earliest claimed: 2013-01-07
- Assignees: Lockheed Martin Corporation; William Marsh Rice University
- Inventors: Sibani Lisa Biswal; Michael S. Wong; Madhuri Thakur; Steven L. Sinsabaugh
- Web page: https://patentgrep.com/patent/US20140193711A1

## CPC

- H01M 4/134: Electrodes based on metals, Si or alloys
- C01B 33/02: Silicon (forming single crystals or homogeneous polycrystalline material with defined structure C30B)
- C25F 3/12: of semiconducting materials
- H01M 4/1395: of electrodes based on metals, Si or alloys
- H01M 4/386: {Silicon or alloys based on silicon}
- H01M 4/621: {Binders}
- H01M 4/622: {being polymers}
- H01M 4/626: {Metals}
- H01M 10/0525: Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
- C01P 2004/61: Micrometer sized, i.e. from 1-100 micrometer
- C01P 2006/16: Pore diameter
- H01M 4/366: {as layered products}
- H01M 10/052: Li-accumulators
- H01M 2004/021: {Physical characteristics, e.g. porosity, surface area}
- H01M 2004/027: {Negative electrodes}
- Y02E 60/10: Energy storage using batteries
- Y02P 20/133: Renewable energy sources, e.g. sunlight
- H01M: PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- C01B: NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; {METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C}
- C25F: PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
- C01P: INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS

## Abstract

Embodiments of the present disclosure pertain to methods of preparing porous silicon particulates by: (a) electrochemically etching a silicon substrate, where electrochemical etching comprises exposure of the silicon substrate to an electric current density, and where 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. Further embodiments of the present disclosure pertain to the formed porous silicon particulates and anode materials that contain them.

## Claims

### Claim 1

A method of preparing porous silicon particulates, wherein the method comprises:
(a) electrochemically etching a silicon substrate,
wherein the electrochemical etching comprises exposure of the silicon substrate to an electric current density, and
wherein the electrochemical etching produces a porous silicon film over the silicon substrate;
(b) separating the porous silicon film from the silicon substrate,
wherein 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.

### Claim 2 (depends on 1)

The method of claim 1, wherein the silicon substrate comprises a silicon wafer.

### Claim 3 (depends on 1)

The method of claim 1, wherein the electrochemical etching of the silicon substrate comprises use of an acid.

### Claim 4 (depends on 3)

The method of claim 3, wherein the acid comprises hydrofluoric acid.

### Claim 5 (depends on 1)

The method of claim 1, wherein the electrochemical etching comprises exposure of the silicon substrate to an electric current density of about 1 mA/cm2 to about 10 mA/cm2.

### Claim 6 (depends on 1)

The method of claim 1, wherein 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/cm2 per sequential increment.

### Claim 7 (depends on 1)

The method of claim 1, wherein steps (a) and (b) are repeated more than 5 times.

### Claim 8 (depends on 1)

The method of claim 1, wherein steps (a) and (b) are repeated until the porous silicon film becomes inseparable from the silicon substrate.

### Claim 9 (depends on 1)

The method of claim 1, wherein steps (a) and (b) are repeated until the silicon substrate develops one or more cracks.

### Claim 10 (depends on 1)

The method of claim 1, wherein the chemical etching occurs by exposure of the porous silicon film and the silicon substrate to a metal.

### Claim 11 (depends on 10)

The method of claim 10, wherein the metal is selected from the group consisting of silver, copper, chromium, gold, aluminum, tantalum, lead, zinc, silicon, and combinations thereof.

### Claim 12 (depends on 10)

The method of claim 10, wherein the metal is silver.

### Claim 13 (depends on 10)

The method of claim 10, wherein the exposure results in coating of the porous silicon film and the silicon substrate with the metal.

### Claim 14 (depends on 1)

The method of claim 1, wherein the splitting occurs by at least one of physical grinding, crushing, sonication, ultrasonication, ultrasonic fracture, pulverization, ultrasonic pulverization, and combinations thereof.

### Claim 15 (depends on 1)

The method of claim 1, wherein the splitting occurs by ultrasonication.

### Claim 16 (depends on 1)

The method of claim 1, further comprising a step of associating the porous silicon particulates with a binding material.

### Claim 17 (depends on 16)

The method of claim 16, wherein the binding material is selected from the group consisting of binders, carbon materials, polymers, metals, additives, carbohydrates, and combinations thereof.

### Claim 18 (depends on 16)

The method of claim 16, wherein the binding material comprises a polymer selected from the group consisting of polyacrylonitrile (PAN), pyrolyzed polyacrylonitrile (PPAN), polyvinyldiene difluoride (PVDF), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), and combinations thereof.

### Claim 19 (depends on 16)

The method of claim 16, wherein the binding material is carbonized.

### Claim 20 (depends on 19)

The method of claim 19, wherein the binding material comprises a carbonized polyacrylonitrile.

### Claim 21 (depends on 1)

The method of claim 1, wherein the formed porous silicon particulates comprise a plurality of pores, wherein the plurality of pores comprise diameters between about 1 nanometer to about 5 micrometers.

### Claim 22 (depends on 1)

The method of claim 1, wherein the plurality of pores comprise diameters of at least about 50 nm, less than about 50 nm, less than about 2 nm, and combinations thereof.

### Claim 23 (depends on 1)

The method of claim 1, wherein the plurality of pores comprise hierarchical pores.

### Claim 24 (depends on 23)

The method of claim 23, wherein the hierarchical pores comprise micropores and mesopores within macropores.

### Claim 25 (depends on 1)

The method of claim 1, wherein the formed porous silicon particulates have thicknesses ranging from about 10 micrometers to about 200 micrometers.

### Claim 26 (depends on 1)

The method of claim 1, wherein the formed porous silicon particulates comprise pores that span at least 50% of a thickness of the porous silicon particulates.

### Claim 27 (depends on 1)

The method of claim 1, wherein the formed porous silicon particulates comprise pores that span an entire thickness of the porous silicon particulates.

### Claim 28 (depends on 1)

The method of claim 1, wherein the porous silicon particulates comprise diameters from about 1 μm to about 50 μm.

### Claim 29 (depends on 1)

The method of claim 1, further comprising a step of controlling a thickness of the porous silicon film.

### Claim 30 (depends on 29)

The method of claim 29, wherein 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.

### Claim 31

An anode material comprising:
porous silicon particulates,
wherein the porous silicon particulates comprise a plurality of pores, wherein the plurality of pores comprise diameters between about 1 nanometer to about 5 micrometers;
a coating associated with the porous silicon particulates; and
a binding material associated with the porous silicon particulates, wherein the binding material is selected from the group consisting of binders, carbon materials, polymers, metals, additives, carbohydrates, and combinations thereof.

### Claim 32 (depends on 31)

The anode material of claim 31, wherein the coating comprises a metal coating.

### Claim 33 (depends on 32)

The anode material of claim 32, wherein the metal is selected from the group consisting of silver, copper, chromium, gold, aluminum, tantalum, lead, zinc, silicon, and combinations thereof.

### Claim 34 (depends on 32)

The anode material of claim 32, wherein the metal is silver.

### Claim 35 (depends on 31)

The anode material of claim 31, wherein the binding material comprises a polymer selected from the group consisting of polyacrylonitrile (PAN), pyrolyzed polyacrylonitrile (PPAN), polyvinylidene difluoride (PVDF), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), and combinations thereof.

### Claim 36 (depends on 31)

The anode material of claim 31, wherein the binding material comprises carbonized polyacrylonitrile.

### Claim 37 (depends on 31)

The anode material of claim 31, wherein the plurality of pores comprise diameters of at least about 50 nm, less than about 50 nm, less than about 2 nm, and combinations thereof.

### Claim 38 (depends on 31)

The anode material of claim 31, wherein the plurality of pores comprise hierarchical pores.

### Claim 39 (depends on 31)

The anode material of claim 31, wherein the hierarchical pores comprise micropores and mesopores within macropores.

### Claim 40 (depends on 31)

The anode material of claim 31, wherein the porous silicon particulates have thicknesses ranging from about 10 micrometers to about 200 micrometers.

### Claim 41 (depends on 31)

The anode material of claim 31, wherein the porous silicon particulates comprise pores that span at least 50% of a thickness of the porous silicon particulates.

### Claim 42 (depends on 31)

The anode material of claim 31, wherein the porous silicon particulates comprise pores that span an entire thickness of the porous silicon particulates.

### Claim 43 (depends on 31)

The anode material of claim 31, wherein the porous silicon particulates comprise diameters from about 1 μm to about 50 μm.

### Claim 44 (depends on 31)

The anode material of claim 31, wherein the anode material has a discharge capacity of at least about 600 mAh/g over at least 50 cycles.

### Claim 45 (depends on 31)

The anode material of claim 31, wherein the anode material has a discharge capacity of at least about 1000 mAh/g over at least 50 cycles.

### Claim 46 (depends on 31)

The anode material of claim 31, wherein the anode material has a Coulombic efficiency of at least about 90% over at least 50 cycles.

### Claim 47 (depends on 31)

The anode material of claim 31, wherein the anode material is utilized as part of a lithium ion battery.