Method and apparatus for making positive electrode films for polymer batteries

Abstract

A method and an apparatus for manufacturing through an extruder a composite positive electrode film having a thickness of less than 50 μm and having a high solid content.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] The present application claims priority from U.S. provisional application No. 60 / 535,828 filed on Jan. 13, 2004.FIELD OF THE INVENTION [0002] The present invention relates generally to polymer batteries and, more specifically, to a method and an apparatus for making positive electrode films for polymer batteries. BACKGROUND [0003] Rechargeable batteries manufactured from laminates of polymer electrolytes and sheet-like electrodes display many advantages over conventional liquid electrolyte batteries. These advantages include lower overall battery weight, high power density, high specific energy, and longer service life. In addition, they are more environmentally friendly since the danger of spilling toxic liquid into the environment is eliminated. [0004] Polymer battery components generally include positive electrodes (also referred to as cathodes), negative electrodes (also referred to as anodes), and an insulating material capable of p...

AI Technical Summary

Benefits of technology

"The invention provides a method and apparatus for manufacturing a composite positive electrode film with a high solid content and a low thickness. The method involves compounding an active cathode material, an electronically conductive additive, and an ionically conductive polymer electrolyte in an extruder and extruding it through a sheet die to obtain a film with a thickness of more than 50 μm. The film is then reduced in thickness by using a pair of nip rollers or a series of at least two pairs of nip rollers. The apparatus includes a belt, a dispenser for lubricant, and a plurality of nip rollers with progressively smaller nip distance. The invention allows for the production of a thin and high-solid content positive electrode film with good adhesion and performance."

Problems solved by technology

This process is inefficient for the mass production of cathode films since it requires recycling the. solvent evaporated and the resulting cathode films have a relatively high porosity, and therefore decreased density.

However, the extrusion of positive electrode material into thin films is rendered extremely difficult by the high percentage of solids (active material and conductive filler) necessary to produce high energy density cathode films.

The difficulty increases dramatically when attempting to directly extrude cathode films of less than 50 μm.

The pressure required to extrude cathode material with over 40% solid content through a sheet die opening of less than 50 μm is such that the die itself may not resist and a gear pump capable of generating the required pressure may not be available on the market and therefore must be custom built.

Unfortunately, it is extremely difficult to process through an extruder cathode materials having a high solid content of active cathodic material and conductive filler (above 30%) to form a thin positive electrode composite film of less than 50 μm and preferably less than 30 μm.

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