NON-AQUEOUS ELECTROLYTE SECONDARY BATTERY, NEGATIVE ELECTRODE MATERIAL, AND MAKING METHOD

• US 20090239151A1
• Filed: 03/16/2009
• Published: 09/24/2009
• Est. Priority Date: 03/17/2008
• Status: Active Grant

• Current Assignee: Shin-Etsu Chemical Company Limited
• Original Assignee: Shin-Etsu Chemical Company Limited
• Inventors: Fukuoka, Hirofumi, NAKANISHI, Tetsuo, Watanabe, Koichiro
• Granted Patent: US 8,105,718 B2
• Time in Patent Office: Days
• US Class Current: 429/231.950
• CPC Class Codes: H01M 10/0525 Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
• CPC Class Codes: H01M 4/0428 Chemical vapour deposition
• CPC Class Codes: H01M 4/134 Electrodes based on metals, Si or alloys
• 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 4/366 as layered products
• 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 4/622 being polymers
• CPC Class Codes: H01M 4/625 Carbon or graphite
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A negative electrode material comprising an active material and 1-20 wt % of a polyimide resin binder is suitable for use in non-aqueous electrolyte secondary batteries. The active material comprises silicon oxide particles and 1-50 wt % of silicon particles. The negative electrode exhibits improved cycle performance while maintaining the high battery capacity and low volume expansion of silicon oxide. The non-aqueous electrolyte secondary battery has a high initial efficiency and maintains improved performance and efficiency over repeated charge/discharge cycles by virtue of mitigated volumetric changes during charge/discharge cycles.

Claims

1. A negative electrode material for non-aqueous electrolyte secondary batteries, comprising an active material and 1 to 20% by weight of a binder, wherein said active material comprises silicon oxide particles and silicon particles, and the silicon particles are present in an amount of not more than 50% by weight based on the active material.

2. The negative electrode material of claim 1 wherein said silicon particles are polycrystalline silicon particles.

3. The negative electrode material of claim 2 wherein said silicon oxide particles and/or said polycrystalline silicon particles are coated with carbon.

4. The negative electrode material of claim 2 wherein said polycrystalline silicon particles have a crystallite size of 20 nm to 34 nm as determined, on X-ray diffraction analysis, by the Scherrer equation from the FWHM (full width at half maximum) of a diffraction curve assigned to Si(111) around 2θ

=28.40.

5. The negative electrode material of claim 2 wherein said polycrystalline silicon particles have a true specific gravity of 2.300 to 2.320.

6. The negative electrode material of claim 2 wherein said polycrystalline silicon particles have been prepared by pyrolysis of a silane gas at a temperature of up to 1,000°

C.

7. The negative electrode material of claim 6 wherein said polycrystalline silicon particles are particulate polycrystalline silicon which has been prepared by pyrolysis of a silane gas in a fluidized bed.

8. The negative electrode material of claim 6 wherein the silane gas is a silane or chlorosilane.

9. The negative electrode material of claim 2 wherein said polycrystalline silicon particles have a median diameter D₅₀ of 0.1 to 20 μ

m.

10. The negative electrode material of claim 1 wherein said silicon oxide particles are silicon oxide particles coated on their surface with a graphite coating,

said graphite coating, on Raman spectroscopy, exhibits scattering peaks having an intensity I₁₃₃₀ and I₁₅₈₀ at 1330 cm⁻

1 and 1580 cm<sup>−

1</sup>, an intensity being in the range;

1.5<

I₁₃₃₀/I₁₅₈₀<

3.0, and

the coated silicon oxide particles, on solid NMR (²⁹Si-DDMAS) analysis, exhibit a signal area S<sub>−

84</sub> around −

84 ppm and a broad signal area S<sub>−

110</sub> centering around −

110 ppm, an area ratio S<sub>−

84</sub>/S<sub>−

110</sub> being in the range;

0.5<

S<sub>−

84</sub>/S<sub>−

110</sub><

1.1.

11. The negative electrode material of claim 10 wherein said silicon oxide particles have been prepared by heating a mixture of silicon dioxide and metallic silicon under vacuum at a temperature of 1,000 to 1,500°

C. to produce a silicon oxide gas and letting the silicon oxide gas to precipitate at a temperature of 500 to 1,100°

C.

12. The negative electrode material of claim 10 wherein said silicon particles are polycrystalline silicon particles.

13. The negative electrode material of claim 10 wherein said silicon particles are silicon particles coated on their surface with a graphite coating.

14. The negative electrode material of claim 1 wherein said binder comprises a polyimide resin.

15. A negative electrode for non-aqueous electrolyte secondary batteries, comprising the negative electrode material of claim 1 and experiencing a volumetric change by a factor of less than 2 before and after charging.

16. A non-aqueous electrolyte secondary battery comprising a negative electrode of claim 15, a positive electrode, a separator, and a non-aqueous electrolyte.

17. The non-aqueous electrolyte secondary battery of claim 16 which is a lithium ion secondary battery.

18. A method for preparing the negative electrode material of claim 10, comprising the steps of:

(I) effecting chemical vapor deposition of an organic gas and/or vapor on silicon oxide particles under a vacuum of 50 to 30,000 Pa at 600 to 1,100°

C. to coat surfaces of the silicon oxide particles with a graphite coating, and

(II) combining the coated silicon oxide particles resulting from step (I) with silicon particles and a binder.

19. The method of claim 18 wherein throughout the steps, the silicon oxide particles and the coated silicon oxide particles are kept in an atmosphere which is up to 1,100°

C.