Bipolar battery cells, batteries and methods

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS General The two most difficult aspects of bipolar battery technology have been the bipolar plate and the seal of the individual cells.
Needed or desired properties are not found in readily available plate or seal materials.
Lead metal has previously been used as a bipolar plate material.
Lead has the advantages of inertness with respect to both oxygen evolution at the positive electrode and hydrogen evolution at the negative electrode, as well as most other undesirable battery reactions.
It forms an excellent interface with the active material.
The disadvantages include softness, high specific gravity and most serious of all, inadequate corrosion resistance over extended charge/discharge cycling.
Attempts have been made to use other metals, such as titanium, in the construction of a bipolar battery.
Titanium is of low specific gravity, is mechanically strong, and can be made in ultrathin layers.
Unfortunately, titanium is partially soluble in sulfuric acid electrolyte, and promotes the evolution of oxygen at the positive electrode.
Further, adhesion of the active material to the plate can be difficult.
The use of tin dioxide as a protective coating for a bipolar plate has also been proposed.
Most other metals either promote oxygen evolution at the positive electrode, or are not stable in sulfuric acid.
Titanium suboxides have also been considered.
Titanium suboxides are semiconductive.
There is a range of these compositions (grouped in phases), some of which have quite high conductivity.
Further, they are virtually inert, chemically and electrochemically.
The main difficulty, which has caused titanium suboxides to be rejected for bipolar battery use, is in creating thin material which is not brittle, and in causing adhesion with the electrode active materials to the substrate.
Several composite materials have been proposed, which to one extent or another, combine desirable properties of two or more materials.
Most are mixtures of carbon powder and a polymer