Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1998-07-24
2001-01-09
Nuzzolillo, Maria (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S231800
Reexamination Certificate
active
06171725
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a non-aqueous secondary battery, and particularly, a negative electrode material for the non-aqueous secondary battery.
2. Prior Art
In recent years, the miniaturization and lightening of portable devices have been remarkable, and with this tendency, the miniaturization and lightening of the batteries which can be used as power sources of the portable devices have been required very strongly. In consequence, various non-aqueous secondary batteries such as the so-called lithium battery have been suggested.
In the lithium battery, it is desirable to use metal lithium as a negative electrode. However, particularly in the case that the lithium battery is used as the secondary battery, an irreversible change of lithium such as the production of dendrite-like lithium occurs by the repetition of charge and discharge, so that problems such as capacity loss and safety decrease take place. Thus, satisfactory results have not been obtained so far.
Hence, one usual strategy for solving these problems is to use a carbon material as the negative electrode. As the carbon materials, graphite (JP-A-62-23433), pitch cokes (e.g., JP-A-62-122066 and JP-A-2-66856) and the like have been suggested.
In the carbon materials, however, it is difficult to exceed a theoretical capacity of graphite (372 mAh/g), and hence various amorphous carbons have been suggested. In the cases of these amorphous carbons, a high capacity can be obtained only in a cycle of charging and discharging at a low current, (e.g., approximately 0.1 mA/cm
2
), but under actual use conditions, a low capacity (<270 mAh/g) can merely be obtained. The further improvement of the performance have been desired.
DISCLOSURE OF THE INVENTION
In view of the above-described problems, an object of the present invention is to provide a negative electrode material having a great discharge capacity.
The present inventors have discovered, by having made intense studies to solve the above-mentioned problems, that a negative electrode material obtained by heating silicon or a compound thereof at 600 to 1,500° C. under a non-oxidative atmosphere in the coexsistence with an organic material or a carbon material, is capable of solving the above-mentioned problems, and thus the present invention has been completed.
Namely, the invention is directed to a negative electrode material for a non-aqueous secondary battery, which has a silicon content in the range of 30 to 90% by weight and a carbon content in the range of 10 to 70% by weight and is obtainable by heating silicon or a compound thereof at 600 to 1,500° C. under a non-oxidative atmosphere in the coexsistence with an organic material or a carbon material.
In other words, the present invention provides a negative electrode material for a non-aqueous secondary battery, which has a silicon content in the range of 30 to 90% by weight and a carbon content in the range of 10 to 70% by weight and is obtainable by heating silicon or a compound thereof at 600 to 1,500° C. under a non-oxidative atmosphere in the coexsistence with an organic material or a carbon material.
A preferred silicon compound is selected from a silicon oxide, a silicone resin and a silicon-containing polymer. Silicon in the form of simple substance is more preferable.
A preferred organic material is a material which can be carbonized by a heat treatment.
The present invention further provides a method for preparing a negative electrode material for a non-aqueous secondary battery, having a silicon content in the range of 30 to 90% by weight and a carbon content in the range of 10 to 70% by weight, which comprises the step of heating silicon or a compound thereof at 600 to 1,500° C. under a non-oxidative atmosphere in the coexsistence with an organic material or a carbon material.
The present invention also relates to a non-aqueous secondary battery using the above-described negative electrode material for the non-aqueous secondary battery. It specifically comprises a positive electrode and a negative electrode, which can dope and undope lithium, and a non-aqueous electrolyte, said negative electrode including the negative electrode material. In general, a negative electrode includes a negative electrode material and a binder.
According to the present invention, silicon is used as the negative electrode and carbon is used as a conductive material and for this reason a high discharge capacity can be obtained.
Conventionally, use of silicon has been avoided because it reacts with lithium to lower the capacity, as described in JP-A-4-126374 and JP-A-6-310144.
JP-A-7-29602 (corresponding to U.S. Pat. No. 5,556,721) discloses a lithium-containing silicon shown by Li
x
Si (0≦x≦5), as a material for activating a negative electrode. However, where the silicon is used as it is, a great amount of conductive materials is required to impart conductivity. No satisfactory performance can be realized at a high current density. JP-A-7-315822 (corresponding to EP-A-685896) discloses a rechargeable battery comprising a carbonaceous negative electrode material containing a small amount of silicon. However, when such a negative material is used, battery properties are limited by the carbonaceous material, a battery having high capacity and high density cannot be obtained.
According to the present invention, it is discovered that silicon or a compound thereof is heated at 600 to 1,500° C. under a non-oxidative atmosphere in the coexsistence with an organic material or a carbon material to obtain a battery being capable of charging and discharging and having relatively higher capacity compared to that using only a carbon material.
DETAILED DESCRIPTION OF THE INVENTION
Next, the present invention will be described in detail.
In the present invention, the simple substance of silicon may be either crystalline or amorphous. An example of the silicon compound includes an inorganic silicon compound such as a silicon oxide and an organic silicon compound such as a silicone resin and a silicon-containing polymer, which can be changed to silicon by calcination. Among them, the simple substance of silicon is particularly preferred.
In the present invention, an organic material is any material which can be carbonized by a heat treatment, but has no more limitation. Typical examples of the organic material include thermosetting resins such as a phenol resin, an epoxy resin, an unsaturated polyester resin, a furan resin, a urea resin, a melamine resin, an alkyd resin and a xylene resin, blends thereof and modified resins thereof; and then condensed polycyclic hydrocarbon compounds such as naphthalene, acenaphthylene, phenanthrene, anthracene, triphenylene, pyrene, chrysene, naphtacene, picene, perylene, pentaphene, and pentacene, derivatives thereof, and pitches including a mixture thereof as the main component.
Alternatively, a carbon material can be used instead of or together with the above shown organic materials. Examples of the carbon material includes a carbonized substance obtained by heating the above shown organic materials, cokes, glass-like carbon, graphite and the like. The carbon material generally contains 70% by weight or more of carbon and mainly includes crystalline or amorphous carbon.
A content of silicon is preferably 30 to 90% by weight, more preferably 50 to 90% by weight, of the negative electrode material. If the silicon content is small, carbon becomes the main component which occupies the negative electrode material to a large extent, thereby reducing the capacity thereof. On the other hand, if the silicon content is too much, the capacity is also reduced similarly to the case of using the simple substance of silicon.
A content of carbon is preferably 10 to 70% by weight, more preferably 10 to 50% by weight, of the negative electrode material. If the carbon content exceeds 70% by weight, carbon becomes the main component, thereby reducing the capacity as described above. On the other hand, if the carbon content is less than 10% by weight, it reacts with
Isshiki Nobuyuki
Nakanishi Kuniyuki
Suzuki Atsushi
Birch & Stewart Kolasch & Birch, LLP
Kao Corporation
Nuzzolillo Maria
Wills M.
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