Nonaqueous secondary battery containing silicic material

Details Nonaqueous secondary battery containing silicic material Nonaqueous secondary battery containing silicic material

1999-05-11

2001-05-22

Weiner, Laura (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Electrode

C429S231100, C429S223000, C429S224000, C429S209000, C029S623100

Reexamination Certificate

active

06235427

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a nonaqueous secondary battery and particularly a lithium secondary battery having a high capacity and a long cycle life.
1. Background of the Invention
A lithium secondary battery comprising a negative electrode material containing no metallic lithium and a positive electrode active material containing lithium is first subjected to a charging reaction, i.e., intercalation of lithium of the positive electrode active material into the negative electrode material to activate the negative electrode material. The reversal discharge reaction consists of intercalation of lithium ions from the negative electrode material to the positive electrode active material. Carbon has been used as a negative electrode material of this type of lithium batteries. The theoretical capacity of carbon in the form of C
6
Li is 372 mAh/g. A negative electrode material having a higher capacity has been awaited.
It has been known that the theoretical capacity of silicon which forms an intermetallic compound with lithium is higher than that of carbon, exceeding 400 mAh/g. For example, JP-A-5-74463 and JP-A-7-29602 disclose a single crystal of silicon and amorphous silicon, respectively. JP-A-63-66369, JP-A-63-174275, and JP-A-63-285865 teach Li—Al-based alloys containing 19 wt %, 0.05 to 1.0 wt % and 1 to 5 wt %, respectively, of silicon. In all these prior art references teaching silicon-containing alloys, compounds containing no lithium are used as a positive electrode active material because the alloys mainly comprise lithium. An alloy containing 0.05 to 1.0 wt % of silicon is proposed in JP-A-4-109562. JP-A-62-226563 teaches a method comprising mixing graphite powder with a powdered metal capable of forming an alloy with lithium. However, batteries obtained by using the conventional silicon-based negative electrode materials fail to have a sufficient cycle life for practical use.
The poor cycle life of lithium secondary batteries using a silicic material as a negative electrode material seems attributable to the low electron conductivity of silicon and volume expansion of the silicic negative electrode material on lithium intercalation, which would make the material finely powdered.
2. Summary of the Invention
An object of the present invention is to provide a lithium secondary battery having an increased energy quantity and a prolonged cycle life.
The object of the invention is accomplished by a nonaqueous secondary battery comprising a positive electrode having a positive electrode active material, a negative electrode having a negative electrode material, and a nonaqueous electrolyte, wherein the positive electrode active material is a transition metal oxide capable of intercalating and deintercalating lithium, and the negative electrode material comprises at least one silicic material capable of intercalating and deintercalating lithium selected from silicon, a silicon alloy and a silicide; and a process for producing the nonaqueous secondary battery.
According to the present invention, a nonaqueous secondary battery having an improved energy quantity and an improved cycle life is provided.


REFERENCES:
patent: 4820599 (1989-04-01), Furukawa et al.
patent: 5556721 (1996-09-01), Sasaki et al.
patent: 5624606 (1997-04-01), Wilson et al.
patent: 5869208 (1999-02-01), Miyasaka

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