NANO SILICON-CARBON COMPOSITE MATERIAL AND PREPARATION METHOD THEREOF

• US 20140302396A1
• Filed: 11/09/2012
• Published: 10/09/2014
• Est. Priority Date: 11/10/2011
• Status: Active Grant

• Current Assignee: China Automotive Battery Research Institute Co., Ltd.
• Original Assignee: General Research Institute For Non-Ferrous Metals
• Inventors: Lu, Shigang, Yang, Juanyu, Wang, Xingming, Ding, Haiyang, Gao, Zhefeng
• Granted Patent: US 9,666,863 B2
• Time in Patent Office: Days
• US Class Current: 429/231.8
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: C01B 32/956 Silicon carbide
• CPC Class Codes: C01B 32/984 Preparation from elemental silicon
• CPC Class Codes: C25B 1/33 Silicon
• CPC Class Codes: H01M 10/052 Li-accumulators
• CPC Class Codes: H01M 4/0438 by electrochemical processing electroless electrochemical plating C23C18/54
• CPC Class Codes: H01M 4/1393 of electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
• CPC Class Codes: H01M 4/1395 of electrodes based on metals, Si or alloys
• CPC Class Codes: H01M 4/364 as mixtures
• CPC Class Codes: H01M 4/386 Silicon or alloys based on silicon
• CPC Class Codes: H01M 4/483 for non-aqueous cells H01M4/485 takes precedence
• CPC Class Codes: H01M 4/58 of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
• CPC Class Codes: H01M 4/587 for inserting or intercalating light metals
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

The invention relates to a nano silicon-carbon composite negative material for lithium ion batteries and a preparation method thereof. A porous electrode composed of silica and carbon is taken as a raw material, and a nano silicon-carbon composite material of carbon-loaded nano silicon is formed by a molten salt electrolysis method in a manner of silica in-situ electrochemical reduction. Silicon and carbon of the material are connected by nano silicon carbide, and are metallurgical-grade combination, so that the electrochemical cycle stability of the nano silicon-carbon composite material is improved. The preparation method of the nano silicon-carbon composite material provided by the invention comprises the following steps: compounding a porous block composed of carbon and silica powder with a conductive cathode collector as a cathode; using graphite or an inert anode as an anode, and putting the cathode and anode into CaCl₂ electrolyte or mixed salt melt electrolyte containing CaCl₂ to form an electrolytic cell; applying voltage between the cathode and the anode; controlling the electrolytic voltage, the electrolytic current density and the electrolytic quantity, so that silica in the porous block is deoxidized into nano silicon by electrolytic reduction, and the nano silicon-carbon composite material for lithium ion batteries is prepared at the cathode.

Claims

1. A nano silicon-carbon composite material for lithium ion batteries, characterized by comprising carbon matrix, nano silicon dispersed on the carbon matrix, nano silicon carbide SiC dispersed on the interface of the carbon matrix and the nano silicon, and silicon oxide SiOx coated on the surface of the nano silicon except for the interface connected with the carbon matrix, wherein 0<

x≦

2.

2. The nano silicon-carbon composite material for lithium ion batteries of claim 1, wherein the mass percent of the components is as follows:

2-40% of nano silicon, 55-90% of carbon, 0.1-3% of nano SiC and 1-5% of silicon oxide SiOx.

3. The nano silicon-carbon composite material for lithium ion batteries of claim 1, wherein the mass percent of the nano silicon is 5-35%.

4. The nano silicon-carbon composite cathode material for lithium ion batteries of claim 1, wherein the mass percent of the carbon is 60-85%.

5. The nano silicon-carbon composite material for lithium ion batteries of claim 1, wherein the carbon is in at least one selected from the group consisting of a spherical shape, a similar spherical shape, a flake shape, a linear shape and a tubular shape.

6. The nano silicon-carbon composite material for lithium ion batteries of claim 1, wherein the nano silicon is at least one selected from the group consisting of a nano silicon line, a nano silicon spherical particle, a nano silicon tube and a nano silicon sheet.

7. The nano silicon-carbon composite material for lithium ion batteries of claim 6, wherein the particle size of the nano silicon spherical particle is smaller than 100 nm;

the diameter of the nano silicon line is smaller than 100 nm;

the diameter of the nano silicon tube is smaller than 100 nm;

the thickness of the nano silicon sheet is smaller than 100 nm.

8. The nano silicon-carbon composite material for lithium ion batteries of claim 1, wherein the nano silicon carbide SiC is in at least one selected from the group consisting of a granular shape, a linear shape and a flake shape.

9. The nano silicon-carbon composite material for lithium ion batteries of claim 8, wherein the particle size of the granular nano SiC is smaller than 100 nm;

the diameter of the linear nano SiC is smaller than 100 nm;

the thickness of the flake nano SiC is smaller than 100 nm.

10. A preparation method of the nano silicon-carbon composite material for lithium ion batteries of claim 1, comprising the following steps:

firstly, preparing silica sol from silica powder, and then adding a carbon particle feed to the silica sol, wherein the mass percent of the silica powder is 10-90 wt %, the mass percent of the carbon particle is 90-10 wt %, and the total mass of the silica powder and the carbon particle material is 100 wt %;

evenly mixing, and forming a mixture of carbon and silica by drying and crushing;

foaming a porous block from the mixture in a hot-pressing manner, or sintering the mixture into a porous block after mold pressing or mold filling;

controlling the porosity, the density and the resistivity of the porous block;

compounding the porous block composed of the carbon and the silica with a conductive cathode collector as a cathode;

using graphite or an inert anode as an anode, and putting the cathode and anode into CaCl₂ electrolyte or mixed salt melt electrolyte containing CaCl₂ to form an electrolytic cell;

applying voltage between the cathode and the anode;

controlling the electrolytic voltage, the electrolytic current density and the electrolytic quantity, so that the silica in the porous block is deoxidized into the nano silicon by electrolytic reduction, and the nano silicon-carbon composite material for lithium ion batteries is prepared at the cathode.

11. The preparation method of claim 10, wherein the particle size of the silica powder is from 10 nm to 1 μ

m.

12. The preparation method of claim 10, wherein the carbon particle material is at least one selected from the group consisting of natural graphite, artificial graphite, amorphous carbon and carbon nano tube.

13. The preparation method of claim 10, wherein the particle size of the carbon particle material is from 10 nm to 50 μ

m.

14. The preparation method of claim 10, wherein the hot-pressing temperature is 900-1400°

C.;

the hot-pressing pressure is 8-40 MPa;

the heat preservation time is 1-8 hours;

the sintering temperature is 800-1500°

C.;

the sintering time is 1-8 hours.

15. The preparation method of claim 10, wherein the porosity of the porous block is 5-65 vol %.

16. The preparation method of claim 10, wherein the density of the porous block is 0.80-2.10 g/cm³.

17. The preparation method of claim 10, wherein the resistivity of the porous block is 0.001-100 Ω

·

cm.

18. The preparation method of claim 10, wherein the mixed salt melt electrolyte containing CaCl₂ is CaCl₂+MY¹, wherein the mole percent of the CaCl₂ is 40-95%;

the allowance is MY¹;

M is Ba, Li, Al, Cs, Na, K, Mg, Rb, Be or Sr;

Y¹ is Cl or F.

19. The preparation method of claim 10, wherein the electrolyte comprises calcium oxide CaO, and the mole percent of the calcium oxide in the total mass of the electrolyte is 0.001-20%.

20. The preparation method of claim 10, wherein electrolysis is carried out at the temperature of 500-1,000°

C.

21. The preparation method of claim 10, wherein the electrolytic voltage is lower than the theoretical decomposition potential of the electrolyte;

the electrolytic current density is greater than the background current density of the electrolytic cell;

the electrolytic time is the time required for achieving the required theoretical electrolytic quantity or more by the required theoretical electrolytic quantity.

22. A lithium ion battery, comprising a positive electrode, a negative electrode and non-aqueous electrolyte, wherein the negative electrode comprises the nano silicon-carbon composite material of claim 1.