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Silicon composite, making method, and non-aqueous electrolyte secondary cell negative electrode material

a secondary cell and electrode material technology, applied in the field of silicon composite powder, can solve the problems of poor cycle performance, low initial efficiency, low initial efficiency, etc., and achieve excellent cycle performance, alleviate a substantial volume change, and high initial efficiency inherent in silicon

Inactive Publication Date: 2006-01-05
SHIN ETSU CHEM IND CO LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0006] An object of the present invention is to provide a silicon composite which maintains the high initial efficiency inherent to silicon, has excellent cycle performance, and has alleviated a substantial volume change during charge / discharge cycles so that it is effective as active material for lithium ion secondary cell negative electrodes; a method for preparing the same; and a non-aqueous electrolyte secondary cell negative electrode material comprising the silicon composite.
[0007] The inventor has discovered a silicon composite which maintains the high initial efficiency inherent to silicon, has excellent cycle performance, and has alleviated a substantial volume change during charge / discharge cycles and which is thus effective as the active material for lithium ion secondary cell negative electrodes.
[0011] Making extensive investigations from this standpoint on a material which undergoes a less volume change upon occlusion and release of lithium even during full charge / discharge operation and has highly adhesive surfaces, the inventor has found that the above problems of lithium ion secondary cell negative electrode active material are overcome by coating silicon particles or micro-particles with an inert robust material, that is, silicon carbide. The resulting material has an initial efficiency comparable to or surpassing the existing carbonaceous materials and an extremely greater charge / discharge capacity than the carbonaceous materials and achieves drastic improvements in cyclic charge / discharge operation and efficiency thereof.
[0016] The silicon composite of the present invention maintains the high initial efficiency inherent to silicon, has excellent cycle performance, and alleviates a substantial volume change during charge / discharge cycles so that it is effective as the active material for lithium ion secondary cell negative electrodes. When the silicon composite is used as the active material for a lithium ion secondary cell negative electrode, the resulting lithium ion secondary cell negative electrode material is adherent to a binder, has a high initial efficiency, alleviates a volume change during charge / discharge cycles, and is improved in repeated cyclic operation and efficiency thereof.

Problems solved by technology

Only few of them have been used in practice because of their shortcomings including substantial degradation upon repeated charge / discharge cycles, that is, poor cycle performance and in particular, low initial efficiency.
However, this approach starting with silicon oxide left the problem of low initial efficiency due to the presence of oxygen atoms.
These solutions, however, invited side issues that the cell manufacture process becomes complex and unnecessary materials are left within the cell.

Method used

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  • Silicon composite, making method, and non-aqueous electrolyte secondary cell negative electrode material
  • Silicon composite, making method, and non-aqueous electrolyte secondary cell negative electrode material

Examples

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Effect test

example 1

[0047] To illustrate the structure of the silicon composite of the invention, a silicon composite was prepared using a milled powder of industrial metallic silicon.

[0048] A metallic silicon mass of industrial grade was crushed on a crusher, and milled on a ball mill and then a bead mill using hexane as a dispersing medium until fine particles having a predetermined average particle size (about 4 μm) were obtained. A vertical reactor was charged with the silicon fine powder, and thermal CVD was conducted in a stream of a methane-argon mixture at 1,150° C. for an average residence time of about 4 hours. The black mass thus obtained was heated in air at 800° C. for one hour for removing free carbon from the surface. After the oxidizing treatment, the mass was disintegrated on an automated mortar into a fine powder having an average particle size of about 4 μm.

[0049] The silicon composite powder was analyzed by x-ray diffractometry (Cu—Kα). FIG. 2 illustrates an x-ray diffraction patt...

example 2

[0053] A metallic silicon mass of industrial grade (low Al silicon available from SIMCOA Operations Pty. Ltd., Australia, Al 0.4%, Fe 0.21%, etc.) was crushed on a jaw crusher and atomized on a jet mill, obtaining fine silicon particles having an average particle size of about 4 μm. The silicon fine powder was fed to a rotary kiln reactor, and thermal CVD was conducted in a stream of a methane-argon mixture at 1,200° C. for an average residence time of about 2 hours. The black mass thus obtained was disintegrated on an automated mortar. The powder was fed to the rotary kiln reactor again, and thermal CVD was conducted in a stream of a methane-argon mixture at 1,200° C. for an average residence time of about 2 hours. The black mass thus obtained was similarly disintegrated on the automated mortar again. There was obtained a black powder having a total carbon content of 47% and a free carbon content of 36%. The black powder was then placed in an alumina bowl, and heated in air at 800°...

example 3

[0060] The metallic silicon powder with an average particle size of about 4 μm obtained through the pulverization in Example 2 was milled on a bead mill using hexane as a dispersing medium to a predetermined particle size (the target average particle size below 1 μm). A milled silicon powder having an average particle size of about 0.8 μm was obtained. The resulting slurry was passed through a filter for removing hexane, leaving a cake-like mass containing hexane, which was placed in an alumina bowl. The bowl was set in a lateral reactor, and thermal CVD was conducted in a stream of a methane-argon mixture at 1,150° C. for about 2 hours. The black mass thus obtained was disintegrated on an automated mortar. The powder was placed in the alumina bowl and the reactor again, and thermal CVD was conducted under the same conditions. The black mass thus obtained was similarly disintegrated on the automated mortar again. There was obtained a black powder having a total carbon content of 59%...

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Abstract

A silicon composite comprises silicon particles whose surface is at least partially coated with a silicon carbide layer. It is prepared by subjecting a silicon powder to thermal CVD with an organic hydrocarbon gas and / or vapor at 900-1,400° C., and heating the powder for removing an excess free carbon layer from the surface through oxidative decomposition.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] This non-provisional application claims priority under 35 U.S.C. §119(a) on patent application No. 2004-195586 filed in Japan on Jul. 1, 2004, the entire contents of which are hereby incorporated by reference. TECHNICAL FIELD [0002] This invention relates to a silicon composite powder having a capacity controlled to compensate for the drawback of silicon which is believed useful as lithium ion secondary cell negative electrode active material; a method for preparing the same; and a non-aqueous electrolyte secondary cell negative electrode material comprising the powder. BACKGROUND ART [0003] With the recent remarkable development of potable electronic equipment, communications equipment and the like, a strong demand for high energy density secondary batteries exists from the standpoints of economy and size and weight reductions. One prior art method for increasing the capacity of secondary batteries is to use oxides as the negative elect...

Claims

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Application Information

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IPC IPC(8): H01M4/58B32B5/16C23C16/26H01M4/02H01M4/36H01M4/38H01M10/05H01M10/052
CPCH01M4/0421H01M4/13H01M4/139H01M4/366Y10T428/2993H01M4/58H01M10/052H01M2004/027Y02E60/122H01M4/38H01M4/386Y02E60/10H01M4/36H01M4/134H01M10/44Y02P70/50
Inventor ARAMATA, MIKIOMIYAWAKI, SATORUFUKUOKA, HIROFUMIMOMII, KAZUMAURANO, KOUICHI
Owner SHIN ETSU CHEM IND CO LTD
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