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LITHIUM TECHNOLOGY
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Lithium is an excellent material for making storage cell anodes, as it gives up electrons very easily and is very light. Lithium cells can provide an order of magnitude better energy density than lead-acid cells.
One of the big problems with lithium is that reacts violently with moisture, and manufacturing lithium cells requires a moisture-free environment. Lithium cells also require venting and other safety systems to keep them from exploding if moisture does infiltrate the case, or if such cells are heated. This delayed their use for a very long time. There are a bewildering range of lithium cell technologies. They can be basically divided into non-rechargeable lithium cells, and rechargeable "lithium-ion" cells.
* The conceptually simplest and most common nonrechargeable lithium cell is the "lithium-manganese" cell. This has a lithium anode, a manganese dioxide cathode, and a carbonate electrolyte. The anode reaction is:
Li --> Li + e-
The cathode reaction is:
MnO2 and Li+ and e- --> MnO2(Li)
The cell voltage is about 3 volts. Such cells are are constructed in a jelly roll configuration, with a sheet of lithium foil, a separator sheet containing electrolytic salts, and a sheet of manganese dioxide rolled up together. They have an indefinite shelf life.
There are many other nonrechargeable lithium cell configurations, such as "lithium sulfur dioxide", "lithium thionyl chloride", and "lithium polycarbonate monofluoride", with complicated constructions and chemistries that are substantially more capable than lithium-manganese but not as cheap, and so not in as widespread use.
The latest generation of nonrechargeable lithium cells uses a polymeric electrolyte. Such "lithium polymer" cells of course have electrical characteristics similar to those of the predecessors, but they can be more easily built in flat or rectangular configurations that are very useful for lightweight portable equipment.
* The high cell voltage of the lithium ion cell means that it is not interchangeable with standard zinc-carbon or alkaline cells. A nonrechargeable "lithium disulfide" cell or "voltage compatible lithium cell" has been introduced that does provide a cell voltage of 1.5 volts. Lithium disulfide cells are also built in a jelly roll configuration, with a lithium anode, an electrolytic separator sheet, an iron disulfide (FeS2) cathode, and an aluminum cathode collector. It is lighter than an alkaline cell, has high capacity, and has a very long shelf life.
* Lithium is easier to handle in its ionized form, and so rechargeable lithium cells, which have to deal with the hazards of being recharged, have been traditionally based on lithium compounds. Again, there are many variations, but a typical "lithium ion" cell has a carbon anode, a lithium cobalt dioxide or manganese dioxide cathode, and an electrolyte consisting of a lithium salt in solution.
Lithium-ion cells have a cell voltage of about 3.6 volts. They have high internal resistance and are not suited to high current applications. They have very long cycle lives, up to a thousand cycles for single cells, and their storage capacity does not degrade significantly with cycling. They are increasingly becoming the rechargeable battery of choice for portable consumer electronics equipment, though they are expensive.
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