Methods for forming porous materials

1. A method for forming a porous material, the method comprising:

combining SiO x (0<x<2) particles with a lithium metal;

causing the SiO x (0<x<2) particles and the lithium metal to react to form lithium oxide nanoparticles in a silicon matrix; and

removing at least some of the lithium oxide nanoparticles from the silicon matrix, thereby forming porous silicon particles.

2. The method as defined in claim 1 wherein the causing results in lithium silicate nanoparticles to form in the silicon matrix;

and the removing further includes removing at least some of the lithium silicate nanoparticles from the silicon matrix.

3. The method as defined in claim 2 wherein the removing of at least some of the lithium oxide nanoparticles and the removing of at least some of the lithium silicate nanoparticles includes any of:

i) exposing the silicon matrix to deionized water, ethanol, or a combination thereof, thereby leaching at least some of the lithium oxide nanoparticles from the silicon matrix; and

exposing the silicon matrix to a diluted acid, thereby etching at least some of the lithium silicate nanoparticles from the silicon matrix and forming a dispersion containing the porous silicon particles, wherein the diluted acid is selected from the group consisting of HCl, H 2 SO 4 , HNO 3 , H 3 PO 4 , and combinations thereof; or

ii) exposing the silicon matrix to a diluted acid, thereby etching at least some of the lithium oxide nanoparticles and at least some of the lithium silicate nanoparticles from the silicon matrix and forming a dispersion containing the porous silicon particles, wherein the diluted acid is selected from the group consisting of HCl, H 2 SO 4 , HNO 3 , H 3 PO 4 , and combinations thereof;

and wherein the method further comprises isolating the porous silicon particles using centrifugation or ultrasonic waves.

4. The method as defined in claim 1 wherein the causing includes applying a voltage, ranging from about 0.2 volts to 0.8 volts versus a Li/Li + reference electrode, to an electrochemical cell including an electrolyte solution, the lithium metal as a counter electrode, and a current collector, wherein the SiO x (0<x<2) particles and the current collector are in electrical contact to form a working electrode, thereby lithiating the SiO x (0<x<2) particles to form the lithium oxide nanoparticles in the silicon matrix.

5. The method as defined in claim 4 wherein:

the current collector is selected from the group consisting of a metal container, metal foil, and a metal cup, wherein the metal of the container, the foil, or the cup is selected from the group consisting of copper, nickel, titanium, platinum, gold, silver, magnesium, aluminum, vanadium, and alloys thereof; and

the current collector includes the electrolyte solution, the lithium metal as the counter electrode, the reference electrode, and the SiO x (0<x<2) particles therein.

6. The method as defined in claim 4 wherein:

the current collector is a porous structure selected from the group consisting of copper, nickel, titanium, platinum, gold, silver, aluminum, magnesium, vanadium, and alloys thereof; and

the working electrode is formed by introducing the SiO x (0<x<2) particles into the porous structure;

and the method further comprises placing the working electrode into the electrolyte solution with the lithium metal as the counter electrode.

7. The method as defined in claim 4 wherein the electrochemical cell further includes a separator positioned between the working electrode and the counter electrode.

8. The method as defined in claim 4 wherein the voltage is applied for a time ranging from about 1 minute to about 100 hours.

9. The method as defined in claim 4 wherein the Li/Li + reference electrode and the counter electrode are a single counter/reference electrode.

10. The method as defined in claim 1 wherein the combining includes mixing the SiO x (0<x<2) particles with the lithium metal at a ratio of the SiO x (0<x<2) particles to the lithium metal being 1:2X where X is equal to x of the SiO x (0<x<2) particles; and wherein the causing includes heating the SiO x (0<x<2) particles and the lithium metal to a temperature greater than 100° C.

11. The method as defined in claim 1 wherein the removing of the lithium oxide nanoparticles includes any of:

i) exposing the silicon matrix to deionized water, ethanol, or a combination thereof, thereby leaching at least some of the lithium oxide nanoparticles from the silicon matrix and forming a dispersion containing the porous silicon particles; or

ii) exposing the silicon matrix to a diluted acid, thereby etching at least some of the lithium oxide nanoparticles from the silicon matrix and forming the dispersion containing the porous silicon particles, wherein the diluted acid is selected from the group consisting of HCl, H— 2 SO 4 , HNO 3 , H 3 PO 4 , and combinations thereof;

and wherein the method further comprises isolating the porous silicon particles using centrifugation or ultrasonic waves.

12. The method as defined in claim 1 , further comprising applying an electrically conductive coating to the porous silicon particles, wherein the electrically conductive coating is selected from the group consisting of a graphitic carbon coating and a nitride based coating.

13. The method as defined in claim 12 wherein the electrically conductive coating is applied using chemical vapor deposition or atomic layer deposition.

14. The method as defined in claim 1 , further comprising:

forming a lithium battery negative electrode including:

the porous silicon particles as a negative electrode active material of the lithium battery negative electrode;

a binder; and

a conductive material; and

applying a conductive coating to a surface of the lithium battery negative electrode.

15. The method as defined in claim 1 wherein no hydrofluoric acid is used during the method of forming the porous material.

16. The method as defined in claim 1 , further comprising adding the porous silicon particles as a negative electrode active material to a negative electrode dispersion.

17. The method as defined in claim 16 , further comprising:

applying the negative electrode dispersion to a current collector; and

removing any solvent from the negative electrode dispersion to form a lithium battery negative electrode on the current collector.

18. The method as defined in claim 17 , further comprising incorporating the lithium battery negative electrode into a lithium ion battery or a lithium-sulfur battery.

19. The method as defined in claim 18 wherein the lithium-sulfur battery further includes:

a sulfur-based positive electrode; and

an other electrolyte solution, the other electrolyte solution including an ether based solvent and a lithium salt dissolved in the ether based solvent, the ether based solvent being selected from the group consisting of 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,2-dimethoxyethane, 1-2-diethoxyethane, ethoxymethoxyethane, tetraethylene glycol dimethyl ether (TEGDME), polyethylene glycol dimethyl ether (PEGDME), and combinations thereof; and the lithium salt being selected from the group consisting of LiClO 4 , LiAlCl 4 , LiI, LiBr, LiB(C 2 O 4 ) 2 (LiBOB), LiBF 2 (C 2 O 4 ) (LiODFB), LiSCN, LiBF 4 , LiB(C 6 H 5 ) 4 , LiAsF 6 , LiCF 3 SO 3 , LiN(FSO 2 ) 2 (LIFSI), LiN(CF 3 SO 2 ) 2 (LITFSI), LiPF 6 , LiPF 4 (C 2 O 4 ) (LiFOP), LiNO 3 , and mixtures thereof.

20. The method as defined in claim 18 wherein the lithium ion battery further includes:

a lithium-based positive electrode; and

an other electrolyte solution, the other electrolyte solution including an organic based solvent and a lithium salt dissolved in the organic based solvent, the organic based solvent being selected from the group consisting of carbonates, linear carbonates, aliphatic carboxylic esters, γ-lactones, chain structure ethers, cyclic ethers, and combinations thereof, and the lithium salt being selected from the group consisting of LiClO 4 , LiAlCl 4 , LiI, LiBr, LiSCN, LiBF 4 , LiB(C 6 H 5 ) 4 , LiCF 3 SO 3 , LiN(FSO 2 ) 2 , LiN(CF 3 SO 2 ) 2 , LiAsF 6 , LiPF 6 , LITFSI, LiB(C 2 O 4 ) 2 (LiBOB), LiBF 2 (C 2 O 4 ) (LiODFB), LiPF 4 (C 2 O 4 ) (LiFOP), LiNO 3 , and combinations thereof.