Method and apparatus for making positive electrode films for polymer batteries
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.
1 . A method of making a positive electrode film having a thickness of less than 50 μm, said method comprising:
a) compounding in an extruder a composite positive electrode mixture of active cathode material, an electronically conductive additive, and an tonically conductive polymer electrolyte;
b) extruding the composite positive electrode mixture through a sheet die into a film having a thickness of more than 50 μm;
c) reducing the thickness of the extruded film through at least one pair of nip rollers to obtain a composite positive electrode film having a thickness of less than 50 μm.
2 . A method as defined in claim 1 , wherein the thickness of the composite positive electrode film is less than 40 μm.
3 . A method as defined in claim 1 , wherein the thickness of the composite positive electrode film is less than 30 μm.
4 . A method as defined in claim 1 , wherein the thickness of the extruded film is reduced through a series of at least two pairs of nip rollers.
5 . A method as defined in claim 1 , wherein, at step c), the extruded film is maintained at or above the melting point of its polymer electrolyte constituent.
6 . A method as defined in claim 4 , wherein the at least two pairs of nip rollers includes a first pair of nip rollers and a second pair of nip rollers, at least one nip roller of the first pair of nip rollers being heated at or above the melting point of the extruded film polymer electrolyte constituent, at least one nip roller of the second pair of nip rollers being maintained at a cool temperature such that when the extruded film of reduced thickness passes through said second pair of nip rollers, it is cooled down to a temperature that allows it to maintain its physical integrity.
7 . A method as defined in claim 4 , wherein the thickness of the extruded film is progressively reduced through the series of at least two pairs of nip rollers, the series of at least two pairs of nip rollers comprising a first pair of nip rollers including at least one heated nip roller, and a second pair of nip rollers including at least one heated nip roller.
8 . A method as defined in claim 7 , wherein both nip rollers of the first pair of nip rollers are heated and both nip rollers of the second pair of nip rollers are heated.
9 . A method as defined in claim 1 , wherein a lubricant is used on surfaces of the nip rollers in order to inhibit adhesion of the extruded film to the surfaces of the nip rollers.
10 . A method as defined in claim 9 , wherein the lubricant has the chemical formula of C 7 H 16 .
11 . A method as defined in claim 4 , wherein the series of at least two pairs of nip rollers comprises a first pair of nip rollers and a second pair of nip rollers, the first pair of nip rollers and the second pair of nip rollers being interconnected via a belt, the belt connecting one nip roller of the first pair of nip rollers to one nip roller of the second pair of nip rollers.
12 . A method as defined in claim 1 , wherein, at step c), the extruded film is separated from the nip rollers by a polypropylene film.
13 . A method as defined in claim 4 , wherein the series of at least two pairs of nip rollers comprises a first pair of nip rollers and a second pair of nip rollers, a rotational speed of the second pair of nip rollers exceeding a rotational speed of the first pair of nip rollers.
14 . An apparatus for reducing a thickness of an extruded positive electrode film to less than 50 μm, said apparatus comprising a series of at least two pairs of nip rollers including:
a first pair of nip rollers defining a first nip distance, at least one nip roller of said first pair of nip rollers being adapted to be heated; and
a second pair of nip rollers defining a second nip distance less than the first nip distance, at least one nip roller of said second pair of nip rollers being adapted to be heated.
15 . An apparatus as defined in claim 14 , further comprising a pair of cooling nip rollers positioned after said first and second pairs of nip rollers and adapted to solidify the extruded positive electrode film when the extruded positive electrode film reaches a desired thickness of less than 50 μm.
16 . An apparatus as defined in claim 14 , further comprising a belt interconnecting the first pair of nip rollers and the second pair of nip rollers, the belt connecting one nip roller of the first pair of nip rollers to one nip roller of the second pair of nip rollers.
17 . An apparatus as defined in claim 14 , further comprising a polypropylene film to separate the extruded positive electrode film from the nip rollers.
18 . An apparatus as defined in claim 14 , further comprising a dispenser for applying lubricant to a surface of at least one nip roller of at least one pair of nip rollers of the at least two-pairs of nip rollers.
19 . An apparatus as defined in claim 14 , wherein a rotational speed of the second pair of nip rollers exceeds a rotational speed of the first pair of nip rollers.
20 . An apparatus for reducing a thickness of an extruded positive electrode film to less than 50 μm, said apparatus comprising a pair of nip rollers defining a nip distance of less than 50 μm, at least one nip roller of said pair of nip rollers being adapted to be heated.