Chemistry: electrical current producing apparatus – product – and – Plural concentric or single coiled electrode
Reexamination Certificate
1999-04-08
2001-08-28
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Plural concentric or single coiled electrode
C429S210000, C429S231900
Reexamination Certificate
active
06280873
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to small, high energy density batteries and how to make them. It relates to using thin sheets of plastic material coated with thin layers of dissimilar metals, which act as cathode and anode, so as to form a bipolar battery element. Also, it relates to coating the cathode and anode layers with thin layers of cathode-active and anode active material, respectively. It relates to tightly winding these layers; together with a separator plastic layer so as to have a high energy density battery.
2. Prior Art
Secondary lithium batteries have a much higher energy density than conventional batteries, such as lead-acid or Ni—Cd batteries, because of a high electrode potential and the lightweight of the lithium. Lithium, however, shows poor rechargeability in an organic electrolyte. The charge-discharge cycling efficiency of lithium is low. Although lithium can be used to make a high-energy battery, the high activity of lithium can also make the battery unsafe.
Xie et al., as part of the active cathode material (U.S. Pat. No. 5,750,288), used a transition metal nickel together with a non-transition metal selected from the group consisting of aluminum, gallium, tin and zinc. Instead of LiNiO
2
, the combination Li
x
M
y
O
z
was used. The purpose was to increase the number of rechargeable cycles and to improve safety. Saidi et al. (U.S. Pat. No. 5,851,696) used a vanadium oxide nonmetal negative electrode (anode) instead of a solid lithium metal anode. This was done for manufacturing ease and to achieve a large discharge capability while maintaining integrity of the anode over a prolonged life cycle. Li et al. (U.S. Pat. No. 5,733,681) used a lithium manganese oxide cathode for a non-aqueous battery. Lithium manganese oxides are less of a toxicity concern and are relatively inexpensive.
Secondary lithium batteries using polymer electrolytes offer advantages over lithium ion batteries with liquid electrolytes, such as enhanced safety, long-cycle life, high energy density and flexibility. Composite electrodes for secondary lithium polymer batteries typically contain an electrode material providing active mass and a polymer electrolyte providing mechanical integrity and ionic conductivity. High conductivity for ions and electrons is needed for a high rate operation of the lithium battery. Good mechanical strength is necessary for processing and manufacturing. Prior art examples include Gozdz, et al. (U.S. Pat. No. 5,620,811) who used polyvinylidene fluoride; other polymers included in this survey are polyethylene oxide and polyacrylonitrile. Scrosati et al. (U.S. Pat. No. 5,645,960) formulated a thin film polymer battery having a flat discharge curve with either Li—Ag
2
WO
4
or Li—Cu
2
WO
4
.
SUMMARY OF THE INVENTION
This invention utilizes a layered battery where a layer of plastic such as polyimide forms the divide between the positive electrode and the negative electrode so as to form a bipolar element. The polyimide layer thickness is in the range 0.3 &mgr;m to 50 &mgr;m, with a typical value of 9 &mgr;m. Gold or aluminum is deposited or plated or sputtered in a thin layer to form the metal conductive part of the positive electrode. The function of the metal deposited is to form a conductive layer. The positive electrode metal is then coated with a mixture of three substances, namely, a lithium transition metal oxide compound, a powder AB, and a compound PVDF. The lithium transition metal oxide compound is selected from the group consisting of LiCoO
2
, LiNiO
2
, and LiMn
2
O
4
. The powder AB is acetylene black powder. This is a form of carbon black, any form of which may be used. However, AB is a preferred embodiment. Graphite powder or any carbon black may be substituted for the AB component. PVDF is polyvinyldifluoride and is used with the solvent NMP (n methyl pyrrolidone).
The thickness of the metal layer may be about 0.3 &mgr;m to 3 &mgr;m for gold and for aluminum. The positive electrode active material layer may be in the range 20 to 100 &mgr;m thick with a preferred embodiment range of 30 &mgr;m to 80 &mgr;m. Plating or depositing or sputtering a metal layer on the side of the polyimide layer other than the positive electrode side is a first step in making the negative electrode. The metal is selected from a group consisting of gold, copper, nickel, titanium, and iron. The metal's function is to act as a conductor, primarily. The metal layer thickness is in the range 0.3 &mgr;m to 3 &mgr;m for gold, copper, nickel, titanium, and iron. The negative electrode metal is then coated with a mixture of graphite powder and PVDF. The negative electrode active material layer may be in the range 20 &mgr;m to 100 &mgr;m thick with a preferred embodiment range of 30 &mgr;m to 80 &mgr;m.
A separator sheet of a microporous film such as polyethylene may be placed over the mixture of the negative electrode. The layers can all be wound into a tight cylinder. Contacts are provided such that the negative and positive electrodes are attachable to feedthroughs in the case so there is a convenient way of accessing the power of the battery. Because there is only one sheet of material as the support for the positive and negative electrodes, and that sheet of polyimide is in the range of 0.3 &mgr;m to 50 &mgr;m, with a typical value of about 9 &mgr;m, the two thin layers of metal, are in the range 0.3 &mgr;m to 3 &mgr;m thick, while the active material layers are in the range 20 &mgr;m to 100 &mgr;m, with a thin polyethylene separating layer of about 27 &mgr;m, therefore the battery can be wound very tightly and a relatively higher energy density achieved. This is because the polyimide layer has a high tensile strength compared to a similar thickness of aluminum or copper. It is also because the thickness dimensions are all relatively small.
Arsenic, lead, platinum and zinc cannot be used as a metal plate in this invention because they react destructively with the active materials in the active layers.
Methods of getting the active materials onto the respective underlying metal layers include screen printing, where the “screen printing ink” is the active material, in a small amount of liquid vehicle, coating on the active material, and spraying on the active material.
A variation of the battery is using gold as the underlying metal for both positive and negative electrodes.
REFERENCES:
patent: 5162172 (1992-11-01), Kaun
patent: 5582931 (1996-12-01), Kawakami
patent: 5620811 (1997-04-01), Zhang et al.
patent: 5645960 (1997-07-01), Scrosati et al.
patent: 5658684 (1997-08-01), Lake
patent: 5733681 (1998-03-01), Li et al.
patent: 5750288 (1998-05-01), Xie et al.
patent: 5851696 (1998-12-01), Saidi et al.
Chaney Carol
Freilich Hornbaker & Rosen
Quallion LLC
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