Lithium-Ion technology, as used in rechargeable cells, possesses a fantastic power-to-weight ratio, and this makes it particularly attractive to our industry. It is for this reason that it is especially well suited to the latest portable broadcast equipment, because, while cameras have become more compact, the current required to power them has steadily increased. The expectations of the user to access this reserve of power safely, is behind many of the problems being experienced today.
In the 1970s and 1980s, cell manufacturers introduced commercial rechargeable cells based on metallic Lithium. Unfortunately, some of these batteries quickly earned a dubious reputation for safety.
Metallic Lithium in rechargeable batteries was replaced by Lithium kept in its ionic state. In this way most of the electrochemical benefits of Lithium-based cells can be reaped without the safety issues associated with the volatile pure metal.
In order to maintain safety, the present Lithium-Ion technology must still be treated responsibly and with respect. It appears that many users of this “safe” technology are being lulled into a false sense of security, for it is perfectly possible to implement this technology poorly, resulting in a potentially dangerous battery.
For this reason the International Civil Aviation Organisation (ICAO) has introduced stringent regulations that preclude the transportation of Lithium-Ion batteries without a Manufacturer’s Air Transportation Certificate. The certificate attests that the product being transported meets those regulations (false declarations incur severe penalties).
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Potential Dangers
Despite the aforementioned advances in electrochemical structure, Lithium-Ion batteries remain inherently intolerant of overcharge, over-discharge and high current abuse, and all reputable batteries contain electronic protection circuits that are designed to protect both the battery and the user if these conditions are brought about.
Overcharge
The target charging voltage of a Lithium-Ion cell is 4.2V +/- 0.05V per cell, and the protection circuits should prevent charging above the specified safe voltage. Consistent overcharging can cause the plating of metallic Lithium within the cell. Bringing metallic Lithium back into the equation will cause instability, especially if the cell is of lower manufactured quality, and especially if any moisture has been introduced inadvertently during the production stage.
Over-discharge
Over discharging can cause copper plating that leads to internal shorting within the cell. The protection circuits should stop discharge well before the battery gets below 2.5V per cell. A well-designed battery would permanently disconnect if a voltage below 1.5V is observed by the protection circuit.
High current abuse
If the battery is discharged at an excessive rate, the excessive transition of Ions can bring about a breakdown in the crystalline-layered structure of the plates of a cobalt oxide Lithium-Ion cell. This can lead to a sudden rise in temperature that could possibly ignite the organic solvent of the electrolyte (which will not self extinguish).
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