Lithium battery

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W84
An electrochemical device which stores energy in the form of lithium ions.

edit Purpose

A device which stores electrical energy for use in mobile computing devices, cameras and music players, enabling these devices to work in locations without mains power. Sometimes.

edit Alternatives

Zinc-carbon

Alkaline

Lead-Acid

Nickel-Cadmium

Nickel-Metal Hydride

edit Underlying Technology

Lithium battery technology is a direct spin-off from the work of the Lawrence Livermore Laboratory, in particular of the innovations which led to the W84 and B61 prototypes. The active component of the battery is in fact a hydride of lithium rather than lithium metal itself. This compound is chosen for its ability to release high-enegy fast neutrons under the conditions of extreme pressure and temperature typically found inside the can of an activated lithium battery.

These fast neutrons form a key component in the chain-reaction which takes place, with each successive lithium-cell heating the adjacent cells in the pack to a critical temperature of around 100,000,000K at which casing-rupture occurs.

Whilst the internal features are typically classified, we have been able to deduce that the most common arrangement is that of a cylindrical cell with a central, hollow rod of plutonium which serves as the cathode. Surrounding this is the lithium hydride compound which serves as the main energy-source. Ouside of this will be a uranium or lead casing, which doubles as the anode. In the prototypes, high-density polystyrene foam held these components in-place inside the can, however in production models this is replaced by plenty of double-sided gaffertape and a few dobs of superglue.

It is reported that the use of an depleted-plutonium anode roughly doubles the energy output, albeit at the expense of considerably more atmospheric pollution.

edit Design Considerations

Whilst other technologies are able to fulfil the role of powering portable IT equipment, manufacturers had realised as long ago as 1952 that the other battery chemistries have several shortcomings. Not least of these is a low sensitivity to impact, as determined by way of the standard Picatinny (weight-drop) test apparatus. Long shelf-life is also a key concern with alkaline cells, plus the ability of metal-hydride chemistry to be recharged many times without loss of capacity has an adverse effect on the profitability of the replacement-battery market.

An associated concern is that the operational life of solid-state electronic devices tends to be very long, often in fact far exceeding the obsolescene, or end of usefulness of the device. This contrasts with earlier valve (faucet for you yanks) technology which had an inbuilt tendency to self-burnout, leading tho a healthy replacement market. To overcome this, manufacurers urgently wished to build a self-destruct mechanism into consumer electronics, and the lithium battery is an ideal choice in that its ordnance-like nature allows it to double as that role.

Owing to the unstable nature of lithium batteries, several precautions are incorporated into the more modern versions. Typically these will include at least five microprocessors inside the battery case, plus temperature, voltage and current sensors. These safety devices operate on the 'strong link/weak link' principle, and ensure that even in the event of major structural damage to the casing which disables the control circuit, the battery will still explode.

edit Advantages

We have already mentioned the equipment self-destruct capability. A further advantage is that while other technologies such as metal-hydride cells tend to come in standardised packages such as the AA, AAA and D cells, the wide range of package styles, plus the multiplicity of special connector-types on lithium packs prevent batteries being interchanged between equipment. This ensures that the enthusiast will have to carry multiple spare battery-packs for each piece of equipment in his/her possession, instead of just one spare to fit all. Potentially this can mean a doubling or even a trebling of battery-sales, as compared to battery technologies which fail to take steps to prevent interchangeability of spare packs.

A further advantage, often not realised by consumers, is that while other technologies may eventually 'wear out' after many charge-discharge cycles, lithium-technology packs wear out even if the battery is not being used. This is of key importance for the notebook-computer replacement battery market, where a typical notebook will be used on mains (house current) most of the time, and when taken on location will be found to give only 5.2 minutes running on the until-then unused battery. In order to hasten this automatic wearing-out of the lithium pack, the computer may be designed with an internal heater to raise the temperature of the pack to around 80C.

edit Limitations

Along with alkaline technologies, Lithium cells exhibit little or no natural self-discharge tendency. In the commercial battery-pack this is however overcome by ensuring that the internal microprocessor-bank will gradually drain the cells even when not in use.

There have been a number of well-publicised manufacturer's recalls of lithium packs, owing to concerns over the reliability of the self-destruct feature.

Lithium packs do not have the corrosive capabilities of the zinc-carbon or lead-acid varieties. That said, their pyrotechnic qualities far outweigh that disadvantage.


References:

Self-destruct in action

Phone kills chinese man

Charging lithium packs

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