# US 8,772,174 B2 · Method of fabricating structured particles composed of silicon or silicon-based material and their use in lithium rechargeable batteries

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- Number: US 8,772,174 B2
- Document ID: US8772174B2
- Status: Granted
- Kind: B2
- Application number: 13/639,395
- Filed: 2011-04-08
- Published: 2013-05-16
- Granted: 2014-07-08
- Earliest claimed: 2010-04-09
- Assignees: Nexeon Limited
- Applicants: Mino Green; Feng-Ming Liu; Yuxiong Jiang; Valerie Elizabeth Dawn Stevens; Benjamin Odarkwei Mills-Lamptey
- Inventors: Mino Green; Feng-Ming Liu; Yuxiong Jiang; Valerie Elizabeth Dawn Stevens; Benjamin Odarkwei Mills-Lamptey
- Web page: https://patentgrep.com/patent/US8772174B2

## CPC

- C23F 1/16: Acidic compositions (C23F1/42 takes precedence)
- C09K 13/08: containing a fluorine compound
- H10P 50/642: {Chemical etching}
- H01M 4/0492: {Chemical attack of the support material}
- H01M 4/38: of elements or alloys
- Y02E 60/10: Energy storage using batteries
- C23F: NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE (working metal by laser beams B23K26/00; desurfacing by applying flames B23K7/00; working of metal by electro-erosion B23H; producing decorative effects by removing surface material, e.g. by engraving, by etching, B44C1/22; electrolytic etching or polishing C25F); INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
- C09K: MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
- H01M: PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION

## Abstract

A method for treating silicon to form pillars, especially for use as the active anode material in Li-ion batteries, is disclosed. The process is simple to operate on a commercial scale since it uses a solution containing only a small number of ingredients whose concentration needs to be controlled and it can be cheaper to operate than previous processes. The solution includes: 0.01 to 5M HF 0.002 to 0.2M of metal ions capable of nucleating on and forming a porous layer comprising regions of elemental metal on the silicon surface; 0.001 to 0.7M of an oxidant selected from the group O2, O3, H2O2, the acid, ammonium or alkali metal salt of NO3−, S2O82−, NO2−, B4O72− and ClO4− or a mixture thereof. The treated silicon is suitably removed from the solution.

## Claims

### Claim 1

A method of treating silicon to form elongate structures on a treated surface, the method comprising a nucleation step in which metal is deposited on the silicon surface and an etching step in which silicon underlying the deposited metal is etched, wherein
a. the nucleation step comprises exposing a silicon containing material to a solution comprising HF at a concentration of less than 5M and
0.002 to 0.2M of metal ions capable of nucleating on and forming a porous layer comprising regions of elemental metal on the silicon surface; and
b. the etching step comprises
i. exposing the silicon surface comprising regions of elemental metal to a solution comprising HF at a concentration of greater than 5M and 0.001 to 0.70M of an oxidant selected from the group comprising O2, O3, H2O2, the acid, ammonium or alkali metal salt of NO3−, S2O82−, B4O72− and ClO4− or a mixture thereof; and
ii. adding oxidant to the solution during etching to maintain the concentration of oxidant within the above range.

### Claim 2 (depends on 1)

A method according to claim 1, wherein the concentration of HF used during the nucleation step is in the range 0.01 to 4M.

### Claim 3 (depends on 1)

A method according to claim 1, wherein the etching step is carried out at an HF concentration of no greater than 10M.

### Claim 4 (depends on 1)

A method according to claim 1, wherein the etching step is carried out at an HF concentration of 7.5M.

### Claim 5 (depends on 1)

A method according to claim 1, wherein further HF is added to the etching solution to maintain the concentration of HF within the stated range.

### Claim 6 (depends on 1)

A method according to claim 1, wherein the HF concentration in the etching solution is 0.5 to 2M greater than the HF concentration in the nucleating solution.

### Claim 7 (depends on 1)

A method according to claim 1, wherein the nucleation solution comprises 0.001 to 0.7M of an oxidant.

### Claim 8 (depends on 1)

A method according to claim 1, wherein the oxidant is added to the etching solution in one or more discrete steps or continuously over the duration of the etching period to maintain the concentration of oxidant and/or HF within the specified concentration ranges.

### Claim 9 (depends on 1)

A method according to claim 1, wherein the nucleation step and the etching step are carried out in separate baths.

### Claim 10 (depends on 1)

A method according to claim 1, wherein the nucleation step and the etching step are carried out simultaneously.

### Claim 11 (depends on 1)

A method according to claim 1, wherein the oxidant is added at the end of the nucleation step.

### Claim 12 (depends on 1)

A method according to claim 1, which comprises the steps of:
a. Exposing silicon-containing material to a solution comprising
i. 0.01 to 4 MHF
ii. 0.002 to 0.2 M Ag+ to form a silver-coated silicon product; and
b. Mixing the silver-coated silicon product of step (a) with HF to give a solution comprising no greater than 10M HF, with the proviso that the concentration of HF in the solution at the end of step (b) is greater than the concentration of HF in the solution in step (a);
c. Adding NO3− to the solution formed in (b) to maintain the concentration of NO3− within the concentration range 0.003 to 0.7M, wherein the NO3− ions are in the form of an alkali metal nitrate salt, ammonium nitrate or nitric acid.

### Claim 13 (depends on 1)

A method according to claim 1, wherein the solution contains less than 0.5 wt % ferric ions.

### Claim 14 (depends on 1)

A method according to claim 1, wherein the solution contains less than 0.5 wt % alcohol.

### Claim 15 (depends on 1)

A method according to claim 1, wherein the metal ions are selected from the group silver, gold, platinum, copper, nickel, lead, cobalt, cadmium, chromium, zinc and tin.

### Claim 16 (depends on 15)

A method according to claim 15, wherein the metal ion is a silver ion used at a concentration of 0.01 to 0.15M.

### Claim 17 (depends on 1)

A method according to claim 1, wherein the oxidant is selected from the group comprising O2, O3, H2O2 and the acid, ammonium or alkali metal salt of NO3−.

### Claim 18 (depends on 1)

A method according to claim 1, wherein the silicon comprises undoped silicon, doped silicon of either p-type or n-type or a mixture thereof.

### Claim 19 (depends on 1)

A method according to claim 1, wherein the elongate structures formed on a treated surface have a diameter in the range 0.02 to 0.7 μm.

### Claim 20 (depends on 1)

A method according to claim 1, wherein the elongate structures formed on a treated surface have an aspect ratio in the range 5:1 to 100:1.

### Claim 21 (depends on 1)

A method according to claim 1, wherein the concentration of NO3− is maintained by continuous addition of NO3− ions to the solution.

### Claim 22 (depends on 1)

A method according to claim 1, wherein the concentration of NO3− is maintained by adding NO3− ions to the solution in one or more steps.

### Claim 23 (depends on 1)

A method according to claim 1, wherein at least one of the nucleation step and the etching step is conducted at a temperature of 0 to 70° C.

### Claim 24 (depends on 1)

A method according to claim 1, wherein the silicon loading in the treatment solution is in the range 2 to 60 g/l.

### Claim 25 (depends on 24)

A method according to claim 24, wherein the silicon is in granular form, the granules having a particle size in the range 1 μm to 1.5 mm.

### Claim 26 (depends on 25)

A method according to claim 25, wherein when the silicon granule has a diameter of the order of 25 μm, the silicon loading is in the range 15 to 40 g/l.

### Claim 27 (depends on 25)

A method according to claim 25, wherein when the silicon granule has a diameter of the order of 200 to 800 μm, the silicon loading is in the range 2 to 8 g/l.

### Claim 28 (depends on 1)

A method according to claim 1 wherein the elongate structures are selected from pillars, rods, columns, nanowires, tubes, fibers, ribbons and flakes.