Electrode active material and polymer electrolyte matrix...

Details Electrode active material and polymer electrolyte matrix... Electrode active material and polymer electrolyte matrix...

1999-08-09

2002-04-16

Kalafut, Stephen (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Electrode

C429S212000, C429S213000, C429S216000, C429S231900

Reexamination Certificate

active

06372386

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrode active material composition for a lithium (Li) ion polymer battery, a polymer electrolyte matrix composition and a method for preparing an Li ion polymer battery using the same, and more particularly, to an electrode active material composition for an Li ion polymer battery, a polymer electrolyte matrix composition, an Li ion polymer battery with improved high-rate charge and discharge characteristics while keeping a clean preparation process by obviating the need for a plasticizer extraction step using an organic solvent and a preparation method thereof using the same.
2. Description of the Related Art
A secondary lithium battery is classified into a lithium ion battery and a lithium ion polymer battery according to materials used as its anode and cathode materials.
In the lithium ion battery, electricity is generated such that lithium ions move between a cathode and an anode. The lithium ion battery has a higher discharge voltage and better charge/discharge cycle characteristics than a conventional nickel cadmium battery or nickel hydrogen battery, and there is no environmental pollution.
The lithium ion polymer battery uses a solid electrolyte such as a polymer, unlike the lithium ion battery using a liquid electrolyte. Thus, the lithium ion polymer battery is lighter and has a smaller volume than the lithium ion battery, and its discharge rate is very low.
In a conventional lithium ion battery, an electrode is fabricated by coating an active material composition on a metal thin film. However, a loss in the active material composition is generated during a fabrication process, resulting in unsatisfactory utilization efficiency of the active material composition.
A lithium ion polymer battery is fabricated by forming a film with an electrode active material composition containing an active material, a conductive agent, a binder and a solvent in a casting method, and then fusing the film onto a current collector at a predetermined temperature and pressure.
In the lithium ion polymer battery, a solid polymer electrolyte is generally used. The polymer electrolyte is divided into three types, a pure solid polymer electrolyte, a gel polymer electrolyte and a hybrid polymer electrolyte. Here, the hybrid polymer electrolyte is formed by filling an electrolytic solution into a porous polymer matrix, from which the electrolytic solution does not leak.
In the lithium ion polymer battery employing the above-described hybrid polymer electrolyte, to enhance the operational efficiency by forming pores for electrolytic solution injection and providing flexibility to an electrode plate, a method for adding a plasticizer to an electrode active material composition has been proposed. Dibutyl phthalate is generally used as the plasticizer, which must be removed prior to the step of battery assembly. The most widely used method for removing the plasticizer is an extraction method using an organic solvent such as ether.
However, the extraction method for removing the plasticizer is complicated, dangerous and environmentally harmful.
SUMMARY OF THE INVENTION
To solve the above problems, it is an objective of the present invention to provide an electrode active material composition for a lithium ion polymer battery using a pyrolytic plasticizer, in which a separate plasticizer extraction step using an organic solvent is not necessary, and by which high-rate charge and discharge characteristics are improved.
It is another objective of the present invention to provide a polymer electrolyte matrix composition using a pyrolytic plasticizer, in which a separate plasticizer extraction step using an organic solvent is not necessary, and by which high-rate charge and discharge characteristics are improved.
It is still another objective of the present invention to provide a preparation method of a lithium ion polymer battery using a pyrolytic plasticizer, in which a separate plasticizer extraction step using an organic solvent is not necessary, and by which high-rate charge and discharge characteristics are improved.
Accordingly, to achieve the first objective of the present invention, there is provided an electrode active material composition for a lithium ion polymer battery having an electrode active material, a conductive agent, a plasticizer and a binder, wherein the plasticizer is a pyrolytic plasticizer and the content thereof is in the range of 5 to 30% by weight based on the total weight of the electrode active material composition.
To achieve the second objective of the present invention, there is provided a polymer electrolyte matrix composition having a polymer resin and a plasticizer, wherein the plasticizer is a pyrolytic plasticizer and the content thereof is in the range of 10 to 60% by weight based on the total weight of the polymer electrolyte matrix composition.
To achieve the third objective of the present invention, there is provided a method for preparing a lithium ion polymer battery including the steps of (a) mixing an electrode active material, a conductive agent, a binder and a plasticizer to prepare an electrode active material composition, casting the same on a current collector, drying the resultant structure to form an electrode plate, (b) mixing a plasticizer with a polymer resin to form a polymer electrolyte matrix composition, casting the prepared composition and drying the same to form a polymer electrolyte, (c) laminating the electrode plates and the polymer electrolyte and thermally treating the same at a temperature of 60 to 150° C. to fabricate an electrode structure, and (d) injecting an electrolyte containing an organic non-aqueous solvent and a lithium salt into the electrode structure, wherein the plasticizer for the electrode active material composition in step (a) and/or the plasticizer for the polymer electrolyte matrix composition in step (b) are a pyrolytic plasticizer, the content of the pyrolytic plasticizer in step (a) is in the range of 5 to 30% by weight based on the total weight of the electrode active material composition, and content of the pyrolytic plasticizer in step (b) is in the range of 10 to 60% by weight based on the total weight of the polymer electrolyte matrix composition.
As the pyrolytic plasticizer, any material capable of increasing plasticity at a temperature in the range of 60 to 150° C. can be used. In particular, the pyrolytic plasticizer is preferably ammonium bicarbonate, an alkali metal carbonate or an alkali earth metal carbonate, and is preferably at least one selected from the group consisting of ammonium bicarbonate, sodium hydrogencarbonate (NaHCO
3
), potassium hydrogencarbonate (KHCO
3
), lithium hydrogencarbonate (LiHCO
3
), lithium carbonate (Li
2
CO
3
) and calcium carbonate (CaCO
3
).
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The feature of the present invention lies in that an electrode active material composition and/or a polymer electrolyte matrix composition include a pyrolytic plasticizer. The pyrolytic plasticizer is pyrolyzed at 80 to 150° C. to be removed. If the pyrolytic plasticizer is added to at least one of the electrode active material composition and/or a polymer electrolyte matrix composition, the flexibility and adhesiveness between the electrode and the polymer matrix are improved, thereby facilitating lamination of the electrode and electrolyte and enhancing the performance of the battery. Also, unlike the case of using the conventional plasticizer such as dibutyl phthalate, the extraction process using an organic solvent is not necessary, thereby keeping a clean preparation process.
The pyrolytic plasticizer is preferably ammonium bicarbonate, an alkali metal carbonate or an alkali earth metal carbonate and at least one of the following compounds: (KHCO
3
), sodium hydrogencarbonate (NaHCO
3
), potassium hydrogencarbonate (KHCO
3
), lithium hydrogencarbonate (LiHCO
3
), lithium carbonate (Li
2
CO
3
) and calcium carbonate (CaCO
3
).
In the case when the pyrolytic plasticizer of the present invention is

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