Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2002-03-01
2004-05-11
Weiner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S231400, C429S232000, C428S367000, C428S408000, C428S357000, C427S122000, C427S215000, C252S182100
Reexamination Certificate
active
06733922
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority of Japanese application Nos. 2001-058397, 2001-058398 and 2001-058399. filed in the Japanese Patent Office on Mar. 2, 2001, and Korean application No. 2001-068302, filed with the Korean Industrial Patent Office on Nov. 2, 2001, the disclosures of which are incorporated herein by reference.
FIELD OF THE INVENTION
The present invention relates to a carbonaceous material and a lithium secondary battery comprising the same, and particularly to a carbonaceous material having a high charge-discharge capacity and improved cycle-life characteristics and a lithium secondary battery comprising the same.
BACKGROUND OF THE INVENTION
As electronic products have become smaller, lighter in weight, and higher in quality and performance, demands for development of lithium secondary batteries exhibiting higher capacity have rapidly increased.
Although graphite, one candidate for a negative active material for a lithium secondary battery, has a theoretical capacity of 372 mAh/g, many efforts have been made to find an alternative material having a higher capacity.
Silicon or a compound thereof has already been proposed as an alternative to graphite since it is known to be capable of forming an alloy with lithium and providing a higher electro-capacity than that of graphite.
There are three recently suggested kinds of silicon material, namely: (1) a simple mixture material in which a silicon compound powder is added to graphite, (2) a graphite material in which a silicon compound particulate is chemically immobilized on the surface of the graphite by means of a silane coupling agent, and (3) a material in which a graphite-based carbon material and a metal material such as Si are bound and coated with an amorphous carbon material.
However, since the silicon compound is not firmly adhered to the graphite in the aforementioned simple mixture material (1), there is concern that the silicon compound may separate from the graphite due to the expansion and contraction of the graphite during the charge-discharge cycle. In addition, since the silicon compound has low electro-conductivity, it is not a sufficient negative active material because it degenerates the cycle characteristics of the lithium secondary battery.
Further, in the silicon compound particulate-immobilizing-graphite material (2), while adhesion of the silicon compound on the graphite is preserved in the early cycles of charge and discharge, rendering the silicon capable of acting as a negative active material, upon repeated charge and discharge cycles the silicon compound expands as a result of forming an alloy with the lithium so as to dissociate the bond and separate the silicon compound from the graphite. Also, the silicon compound is not a sufficient negative active material because it degenerates the cycle characteristics of the lithium secondary battery. Further, unless the silane-coupling agent is uniformly treated while preparing the negative electrode material, a negative electrode material having uniform quality cannot be obtained.
Lastly, the amorphous carbon material coated or bound on a graphite-based carbon material and a metal material such as Si (3) has the same problems as those of the (2) material. That is, upon repeated charge and discharge cycles, the bonding strength between the silicon compound and the amorphous carbon material becomes weaker so that the metal material is segregated from the graphite-based carbon material. Accordingly, the metal material is not a sufficient negative active material because it degenerates the cycle-life characteristics of the lithium secondary battery.
Japanese unexamined patent publication No. P5-74463 discloses a single-crystalline silicon being used as a negative active material, but the silicon has a low capacity at a low temperature. Further, the charge-discharge efficiency thereof at each cycle is relatively low, and the cycle characteristics degenerate in the case of adopting a Lewis acid base electrolyte such as LiBF
4
.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve the above-mentioned problems, and to provide a carbonaceous material having a high C-rate capacity and improved cycle-life characteristics.
Further, it is another object of the present invention to provide a lithium secondary battery comprising the carbonaceous material.
In order to fulfill the objects, the present invention provides a carbonaceous material in which silicon and carbon are disposed in the vicinity of a graphite particle having a 002 plane interval d002 of less than 0.337 nm as measured by an X-ray wide angle diffraction method. In the carbonaceous material, complex particles having a particle size smaller than that of the graphite particle are also disposed and distributed. Both the graphite and the complex particles are coated with an amorphous carbon layer having a plane interval d002 of more than 0.37 nm, the amorphous carbon layer being a polymer layer. In the complex particles, a conductive carbon material is further disposed and distributed in the vicinity of the surface of the Si particulate, the Si 5 particulate being composed of crystalline silicon, and the Si particulate and the conductive carbon material are coated with a rigid carbon material layer. The Si particulate is characterized in that SiO
2
, SiC, and SiB
4
phases are deposited on the crystalline Si phase.
The term “vicinity” herein is intended to express the positional relationship between the graphite particle and the complex particles, whereby the complex particles are located in contact with or adjacent to and marginally apart from the surface of the graphite particle.
The term “vicinity” is also intended to express the positional relationship between the Si particulate and the conductive carbon material, whereby the conductive carbon material is located in contact with or adjacent to and marginally apart from the surface of the Si particulate.
The term “dispose and distribute” is intended to describe the state of distributing a plurality of complex particles without aggregating them with each other, and positioning the complex particles in contact with or adjacent to and marginally apart from the surface of the graphite particle.
The term “coat” means the state of covering the subject particles to be coated, and binding the subject particles to be coated. In this case, the particles do not need to be in contact with each other.
Particularly, to coat the graphite particle and the complex particles with an amorphous carbon layer is to thoroughly cover both the graphite particle and the complex particles with the amorphous carbon layer rendering them bound together, or to locate the complex particles adjacent to the surface of the graphite particle within an amorphous carbon layer.
The amorphous carbon layer is obtained by heat-treating at least one polymer material selected from the group consisting of thermoplastic resins, thermosetting resins, vinyl-based resins, cellulose-based resins, phenol-based resins, coal-based pitch materials, petroleum-based pitch materials, and tar-based materials. The carbon layer is amorphous and is not relatively overly grown, and it preferably has a plane interval d002 of more than 0.37 nm.
Preferably, to coat the Si particulate and the conductive carbon material with a rigid carbon layer is to thoroughly cover both the Si particulate and the conductive carbon material with the rigid carbon layer rendering them bound together, and to locate the conductive carbon material adjacent to the surface of the Si particulate in the rigid carbon layer.
Further, “deposit” describes the state in which other deposited phases having compositions differing from that of the mother phase are incorporated in the mother phase. That is, SiO
2
, SiC, and/or SiB
4
phases are deposited in the Si mother phase in an incorporated form, but it does not mean that the SiO
2
, SiC, and/or SiB
4
phases are physically separated from each other.
The charge-discharge capacity is improved in the carbonaceous material of the pr
Matsubara Keiko
Sheem Kyou-Yoon
Tsuno Toshiaki
Samsung SDI & Co., Ltd.
Weiner Laura
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