Battery using light weight electrodes

This invention discloses a method to make a light-weight and flexible electrode for electrochemical application especially for nickel hydride batteries. The method uses a conductive polymer as the substrate of an electrode. The conductive polymer can be an acidic or a basic type polymer. In the preparation of an electrode, the monomers of the conductive polymer can be used as the starting material. The electrode of this invention has about 20% more capacity than the electrode using nickel metal substrate.

BACKGROUND OF THE INVENTION 
1. Field of the invention 
This invention relates to light weight electrodes and a battery using same. 
More particularly, this invention relates to the rechargeable battery, 
especially a metal oxide-hydride battery using a novel light weight 
substrate current collector in the anode and/or cathode electrodes. 
2. Description of Prior Art 
The market size of batteries especially rechargeable batteries such as 
nickel hydride batteries is increasing with the expansion of electronic 
products in this Information Age. The direction of the electronic products 
is totowards the reduction of the size and the weight of the products. 
Accordingly, it is very important for batteries to move in the same 
direction. This is one of the reasons that nickel hydride batteries are 
begining to replace the nickel cadmium batteries. The energy density of a 
hydride battery is much higher than that of a cadmium battery. 
At present, the substrate current collector used in a nickel positive 
electrode, cadmium or hydride negative electrode is made of nickel or 
nickel-plated steel in the form of mesh, fiber, sponge, expanded or 
perforated foil. Depending on the type of the battery made, the weight 
and/or the volume of the metal-type substrate is about 20 to 30 wt. % of 
the electrode. This is one of the liming factors in the development of 
battery technology. It would be better to have a lighter material to 
replace the metal used in the substrate current collector, thus reducing 
the weight and/or volume of the electrode. Types of substrate such us 
carbon fiber and nickel-coated plastic mesh have been mentioned in some 
articles. However, carbon fiber is not strong, and is also expensive. A 
nickel-coated plastic mesh is not easy to coat and of high cost as well. 
To solve the weight and the thickness problems, this invention provides a 
method to make a thin and light weight electrode, especially a 
light-weight nickel positive electrode and/or a light-weight hydride 
negative electrode using a novel substrate current collector, and to make 
a battery using same. 
SUMMARY OF THE INVENTION 
This invention discloses a method to make a thin and light weight electrode 
using a novel conductive polymer as the substrate current collector. The 
method includes the following steps: 
1. Provide the active material of an electrode. 
2. Dissolve a conductive polymer in a solvent to make a solution of 
suitable viscosity. 
3. Mix the active material of the electrode with the conductive polymer 
solution to make a slurry. 
4. Let the slurry solidify at an ambient or a mild warm temperature to form 
a positive or a negative electrode using the conductive polymer as the 
substrate current collector. 
Alternatively, the monomers of the conductive polymer can be used to 
replace the conductive polymer as the staffing raw material. In this ease, 
a catalyst such as an oxidant generally is added to speed up the 
polymerization. 
Thus a rechargeable battery such as a metal oxide-hydride battery, 
especially, a rechargeable sealed nickel-hydride battery using thin and 
light weight electrodes can be made. The battery, according to this 
invention, is composed of a container, thin and light weight positive and 
negative electrodes, a separator positioned between the positive and 
negative electrodes, and an electrolyte in the container and in contact 
with the positive and negative electrodes and the separator. In the ease 
of a rechargeable nickel-hydride battery, the negative electrode is a 
hydrogen storage electrode comprising at least one hydrogen storage 
material (alloy) and/or its hydride. 
The advantages, features and other objects of the present invention will 
become clear in the following detailed description. 
DETAILED DESCRIPTION OF THE INVENTION 
The purpose of this invention is to provide a method to make a thin and 
light weight electrode using a novel conductive polymer as the substrate 
current collector, and therefore make a high capacity battery especially a 
rechargeable hydride battery using same. The advantages of this novel 
method are: 
1. The heavy and bulky metal substrate is eliminated and replaced by a very 
light-weight and low-volume conductive polymer. 
2. The preparation process is simple. 
3. The electrode made can be thin like paper. 
4. The electrode made is very flexible and durable. 
5. The electrode made has a very high energy density. 
The method of this invention uses a conductive polymer as the substrate 
current collector of an electrode. The polymer itself is a conductor, as 
opposed to a plastic fiber coated with a layer of nickel metal. 
Furthermore, it is not necessary to make the conductive polymer in a 
fibrous form before using. 
The method includes the following steps: 
1. Provide the active material of an electrode. 
2. Dissolve a conductive polymer in a solvent to make a solution of 
suitable viscosity. 
3. Mix the active material of the electrode with the conductive polymer 
solution to make a slurry. 
4. Let the slurry solidify at an ambient or mild warm temperature to form a 
positive or negative electrode using the conductive polymer as the 
substrate current collector. 
The size, thickness, and the shape of the electrode made can be controlled 
with various methods like fabric or paper. 
Alternatively, the monomers of the conductive polymer can be used to 
replace the conductive polymer as the staring raw material. In this case, 
a catalyst such as an oxidant generally is added to speed up the 
polymerization. The use of monomers as the starting raw material has some 
advantages. The monomers are much easier to dissolve in the solvent and to 
mix with the active material to make a homogeneous slurry. In the presence 
of a catalyst such as an oxidant, the monomers will polymerize to form the 
conductive polymer in the solvent. During the solidification the 
conductive polymer then binds the active material homogeneously to form 
the electrode. 
In this invention, one or more conductive polymers can be used as the 
substrate current collector. Also, the conductive polymer can be a basic 
or an acidic type. The basic type conductive polymer is suitable for a 
battery which uses an alkaline solution as the electrolyte such as a 
nickel hydride battery. The acidic type conductive polymer is useful for 
an acidic battery such as a lead acid battery. 
In an alkaline battery such as a nickel cadmium battery or a nickel hydride 
battery, the conductive polymer is a basic type polymer such as 
polythiophene, polyorthotoluidine, polyoctylthiophene. In making an 
electrode using a conductive polymer as the substrate, a conductive 
polymer can be dissolved in a solvent such as toluene to make a solution 
of suitable viscosity. Then a suitable mount of the active material of the 
positive or negative electrode is added to the solution to make a slurry. 
Alternatively, a suitable amount of the monomers of a conductive polymer 
such as thiophene, 3-n-octylthiophene, plus an oxidant such as ferric 
chloride, nitromethane, nitrobenzene, is mixed with a solvent such as 
toluene to form a homogeneous solution. A suitable amount of the active 
material for the positive or negative electrode is added to the solution 
to make a slurry. With the help of the oxidant, the monomers in the 
solvent will polymerize to form the conductive polymer. The conductive 
polymer itseft serves as a substrate current collector as well us a binder 
to the active material. At an ambient temperature, the solvent will 
evaporate and the slurry will solidify to form an electrode. A slightly 
warm temperature up to 120.degree. C. will speed up the solidification 
process. In this invention, the conductive polymer is the substrate. 
Therefore, the pasting of the active material onto other substrate is not 
needed. Consequently, the weight and the thickness of the electrode in 
this invention is lighter than the electrode using the metal substrate. 
The electrode made is very flexible and can be very thin like a paper. 
Thus, the electrode of this invention has a very high energy density. 
It is noted that the conductive polymer can replace wholly or partially the 
typical binder such as PTFE, CMC, PVA (polyvinyl alcohol), polyox, 
methylcellulose and hydroxylmethyl cellulose to enhance the binding and 
conductivity of the current sintered or pasted electrode. Also, the 
conductive polymer can be coated on a hydride or nickel electrode to 
improve the performance of the battery. 
Thus a rechargeable battery such as an oxide-hydride battery, and in 
particular, a rechargeable sealed nickel-hydride battery using the thin 
and light weight electrodes of this invention can be made. The battery, 
according to this invention, is composed of a container, thin and light 
weight positive and negative electrodes, a separator positioned between 
the positive and negative electrodes, and an electrolyte in the container 
and in contact with the positive and negative electrodes and the 
separator. In the case of a rechargeable nickel-hydride battery, the 
negative electrode is a hydrogen storage electrode comprising at least one 
or more multicomponent hydrogen storage material (alloy) and/or its 
hydride chosen from the group of AB.sub.5 -, AB.sub.2 -, AB.sub.x -type 
alloys and combinations thereof. Some of the AB.sub.x -type multicomponent 
alloys are disclosed by Hong in U.S. Pat. Nos. 4,849,205, 5,006,328, 
5,501,917, 5,541,017, 5,552,246, and 5,556,719. The positive electrode 
active material comprises at least a metal oxide, preferably a nickel 
oxide plus 1-15 wt. % cobalt oxide. To ensure high efficiency, 0.5-15 wt. 
% of fine powder selected from the group consisting of Ni, Cu, Zn, C, Mg, 
Al, Mn, iodine, iodide (LiI, NaI, KI, etc.), hydride, and combinations 
thereof, is added during the preparation of a nickel positive electrode.

EXAMPLE 1 
According to the method of this invention, a hydride electrode using a 
hydrogen storage alloy having a composition: Ti.sub.8.97 Zr.sub.21.94 
Cr.sub.2.50 Mn.sub.8.48 V.sub.23.95 Ni.sub.33.92 Si.sub.0.15 as the active 
material and a conductive polymer: polyoctylthiophene as the substrate 
current collector is made. The capacity of this electrode including the 
substrate is up to 347 mAH/g of electrode. For comparison, a similar 
electrode using a nickel mesh as the substrate current collector is made. 
The capacity is 287 mAH/g of electrode. Clearly, the electrode using the 
conductive polymer polyoctylthiophene as the substrate has about 20% more 
capacity than the one using nickel mesh as the substrate. 
EXAMPLE 2 
According to the method of this invention, a hydride electrode using a 
hydrogen storage alloy having a composition: Ti.sub.21.25 Zr.sub.18.01 
Cr.sub.2.53 Mn.sub.9.34 V.sub.7.95 Ni.sub.40.92 as the active material and 
a conductive polymer: polyoctylthiophene as the substrate current 
collector is made. However, the starting raw material is the 
3-octythiophene monomer, toluene the solvent and ferric chloride the 
oxidant. The capacity of this electrode made is up to 335 mAH/g of 
electrode. For comparison, a similar sintered electrode using a nickel 
mesh as the substrate current collector is made. The capacity is 272 mAH/g 
of electrode. Clearly, the electrode using the conductive polymer 
polyoctylthiophene as the substrate has about 23% more capacity than the 
one using nickel mesh as the substrate.