Solid State Cells
These are cells using solid electrolytes. They offer the advantages of no leakage or gassing, long shelf life, excellent packaging efficiency, no separators and miniature designs. they depend on electrolyte materials with high ionic conductivity and negligible electronic mobility. The former provides low internal resistance while the latter prevents self discharge providing long life. The Lithium Iodine primary cell used in heart pacemakers is an example of such a cell.Nanotechnology
Nanomaterials (nanocrystalline materials) are currently being used for electrodes and separator plates in experimental NiMH and Lithium ion batteries where their foam-like microstructure provides a very large porous active surface area which can hold and deliver considerably more energy than their conventional counterparts. C rates of 10 to 100 times higher have been claimed. (This implies charging the battery in one minute!)These cells are not yet commercially available.
Mercury Cells
The original technology for primary button cells was the mercury cell, which had a mercuric oxide cathode, an anode made of an amalgam of mercury and zinc, and an electrolyte consisting of potassium hydroxide mixed with zinc hydroxide. It is essentially an alkaline cell with a different and more efficient cathode. It provided an open circuit voltage of 1.35 Volts. Designed as a replacement for the carbon-zinc cell, this battery could not only resist high temperatures and high humidity, but also had better discharge characteristics, longer shelf life, and greater efficiency.As mercury is toxic, mercury cells are now banned in the US and some other countries and they are now only a curiosity.
Silver-Oxide or Zinc-Air cells make good or superior alternatives.
Metal Air Cells
A very practical way to obtain high energy density in a
galvanic cell is to utilize the oxygen in air as a "liquid" cathode. A
metal, such as zinc or aluminium, is used as the anode. (See below) The
oxygen cathode is reduced in a portion of the cell that is physically
isolated from the anode. By using a gaseous cathode, more room is
available for the anode and electrolyte, so the cell size can be very
small while providing good energy output.
Rechargeable Aluminium-Air Cells
They have long shelf-life and high energy density but are complex and have low efficiency.
Aluminium-air batteries obtain their energy from the
interaction of aluminium with air. The incoming air must be filtered,
scrubbed of CO2, and dehumidified; the water and electrolyte
must be pumped and maintained within a narrow temperature range - hence
the complexity of the battery.
The batteries are not electrically recharged but are "refueled" by replacing the aluminium anodes and the water supply.
Special versions which use seawater electrolytes have also been developed.
A new generation of Aluminium-Air cells recently
patented in Finland using nanotechnology have overcome the problems
associated with recharging aluminium cells and promise very high energy
and power densities.
Still under evaluation and not yet available in production quantities.
See also Zinc Air Cells and Lithium Air Cells
