Lithium polymer secondary cell

Details Lithium polymer secondary cell Lithium polymer secondary cell

2002-01-07

2003-12-30

Chaney, Carol (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Electrode

C429S212000, C429S300000, C429S303000, C429S304000

Reexamination Certificate

active

06670075

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a lithium polymer secondary battery comprising: a positive electrode comprising a lithium-containing complex oxide; a negative electrode comprising a material capable of intercalating and deintercalating lithium ions; and a separator interposed between the positive electrode and the negative electrode; wherein the respective positive electrode, the negative electrode and the separator contain a polymer electrolyte.
BACKGROUND ART
Lithium ion secondary batteries which use a lithium-containing complex oxide as a positive electrode material, a carbon material as a negative electrode material, and which contain a liquid non-aqueous electrolyte have a high voltage, a high energy density and an excellent low temperature characteristic as compared with aqueous solution type secondary batteries. Further, lithium ion secondary batteries are excellent in cycle life and safety because they use no metallic lithium in the negative electrode, and therefore they have rapidly been put into practical use.
In recent years, in order to meet the demand for thinner and lighter-weight batteries than conventional ones, lithium polymer batteries containing a polymer electrolyte in which a liquid non-aqueous electrolyte is retained in a polymer material have been developed.
However, lithium polymer secondary batteries containing a gel-like polymer electrolyte have a problem of being inferior in the cycle stability as compared with lithium ion secondary batteries containing a liquid non-aqueous electrolyte.
For example, when a lithium polymer secondary battery is charged and discharged at room temperature at 1C. (one hour rate), the capacity at the 100th cycle happens to be decreased to around 80% of the initial capacity. This decrease is larger than that of a lithium ion secondary battery.
On the other hand, as a polymer material constituting a polymer electrolyte, for example, materials described in the following have been proposed.
In Japanese Laid-Open Patent Publication No. Hei 3-171567, an ethylene oxide type polymer which has an excellent solubility with a non-aqueous electrolyte has been disclosed. However, the ethylene oxide type polymer has a problem in the thermal stability because it causes sol/gel transition at high temperatures.
In Japanese Laid-Open Patent Publication No. Hei 4-306560, a polyacrylonitrile type material which is flame-retardant and which exhibits a high ionic conductivity is disclosed. However, limited numbers of non-aqueous solvents are soluble with the polyacrylonitrile type material; there is also a problem of the thermal stability in a resultant gel.
In U.S. Pat. No. 5,296,318, a vinylidene fluoride type polymer which is electrochemically stable and excellent in the flame-retardancy. However, the vinylidene fluoride type polymer has a problem of having a low affinity with a non-aqueous solvent at high temperatures.
In Japanese Laid-Open Patent Publication No. Sho 55-35420, a polyacrylate type material which is excellent in retaining a non-aqueous solvent. However, the polyacrylate type material is considered to be electrochemically unstable.
In each of the materials, improvements in view of the respective problems have been proposed; however, remarkable improvements have not been achieved yet.
DISCLOSURE OF INVENTION
The present invention improves the cycle stability in the lithium polymer secondary battery by optimizing the distribution of the polymer material contained in the positive electrode, the negative electrode and the separator.
Specifically, the present invention relates to a lithium polymer secondary battery comprising: a positive electrode comprising a lithium-containing complex oxide; a negative electrode comprising a material capable of intercalating and deintercalating lithium ions; and a separator interposed between the positive electrode and the negative electrode;
wherein the positive electrode, the negative electrode and the separator contain a polymer electrolyte comprising a polymer material, a non-aqueous solvent and a solute;
and wherein, the weight Wp of the polymer material contained in the positive electrode, the weight Wn of the polymer material contained in the negative electrode, and the weight Ws of the polymer material contained in the separator, satisfy all of the following:
Ws<Wn<Wp  (1)
20≦100
Wp
/(
Wp+Wn+Ws
)≦50  (2)
20≦100
Wn
/(
Wp+Wn+Ws
)≦50  (3)
20≦100
Ws
/(
Wp+Wn+Ws
)≦50  (4)
In the negative electrode, the material capable of intercalating and deintercalating lithium ions preferably comprises at least one selected from the group consisting of a carbon material, an alloy, an oxide and a nitride.
The above polymer material preferably comprises a polymer comprising at least one of an acrylate unit and a methacrylate unit as well as an alkylene oxide unit, a polyurethane having a carbonate group or a polymer comprising a vinylidene fluoride unit. These may be used singly or in combination of two or more kinds.
The polymer electrolyte contained in the positive electrode, the negative electrode and the separator preferably comprises the same or similar polymer material. For example, when a copolymer of vinylidene fluoride and hexafluoropropylene is used as the polymer material, the respective positive electrode, negative electrode and separator preferably contain the copolymer of vinylidene fluoride and hexafluoropropylene or a polymer having a very similar structure thereto.
Hereinafter, the polymer material refers to the polymer material constituting the polymer electrolyte, and it is distinguished with a material having other functions. However, the polymer material constituting the polymer electrolyte and also serving as a binder for the active material at the same time is treated as the polymer material constituting the polymer electrolyte.


REFERENCES:
patent: 5296318 (1994-03-01), Gozdz et al.
patent: 5952126 (1999-09-01), Lee et al.
patent: 6090504 (2000-07-01), Sung et al.
patent: 6579649 (2003-06-01), Tsutsue et al.
patent: 0822608 (1998-02-01), None
patent: 938150 (1999-08-01), None
patent: 1001477 (2000-05-01), None
patent: 55-35420 (1980-03-01), None
patent: 3-171567 (1991-07-01), None
patent: 4-306560 (1992-10-01), None
patent: 2001-68158 (2001-03-01), None

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