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| Li-Poly Advantages & Disadvantages |
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Li-ions have very high energy density, Lithium ion batteries can hold between 5 and 12 times the energy - hence greater ‘energy density’ than similar weight Nicad or NiMH batteries, i.e. a HUGE amount of energy! Therefore, if a battery is accidentally short circuited, 5-12 times the energy of a nicad will try and escape from the battery AT ONCE!! the battery may EXPLODE if not disconnected quickly! Lithium ion batteries are unlike Nicad or Nimh batteries in that they hold FAR MORE energy than those batteries and are therefore more dangerous. Please re-read this if you are unclear about any of the above and you plan to use Li-ion batteries in you models.
LITHIUM ION - DIFFERENT FROM NICADS
- Different chemistry to Nicads/NiMHs, Lithium reacts rapidly with oxygen, will burn skin and is strongly corrosive. If things go wrong inside a Li-ion battery, elemental Lithium can be deposited internally - and if the battery case becomes ruptured Lithium can be ejected from the battery! Further, elemental Lithium is highly reactive when exposed to water, producing flammable hydrogen gas and corrosive fumes. Please note that Li-ion batteries contain no elemental Lithium and that Lithium metal is only created when the battery goes seriously wrong. Make sure nothing goes wrong!
- Charging and discharging Li-ion's in model applications. Were you told any of the above bits of info when you bought your Li-ion powered mobile phone and laptop computer? Probably not. However, your phone and laptop are probably only ever charged at ‘low’ charge rates, and discharged at similarly ‘low’ discharge rates. Plus, they are most likely equipped with voltage and current regulators/monitors. Very few model Li-ion cells are equipped with regulators/monitors. On the discharge front, its a fact that most model flight applications demand relatively high (and variable) discharge rates from Li-ion batteries, and worse still modellers will often demand faster charge times and hence sometime overcharge their batteries!
- In summary you must use the right Li-ion charger and charge at the correct rate. You MUST NOT OVERCHARGE or over-discharge Li-ions. Overcharging and over-discharging can be DISASTROUS. Li-ions could catch fire or explode if overcharged! Lithium ions are relatively new for the model community and do represent a potentially great future for electric modelling but only if used carefully and responsibly.
ADVANTAGES
- Huge duration improvements, Lithium ion batteries in model aircraft and helicopters can give 15 minute to half hour flights where previously 5 to 10 minute flights using nickel cadmium (nicad) or Nickel metal hydride NiMH batteries had been the norm. Lithium ion batteries (Li-ion) are therefore said to have a very high ‘energy density’ compared with Nicad or NiMH batteries around 5-12 times, approximately.
- Much lighter batteries. The high energy density means that, for example, a Li-ion battery might weigh just a quarter of the weight of the same capacity nicad. You can see that small models that once flew for just a few minutes last week can now fly for considerably longer with Li-ions this week.
- No Cadmium, As most people know, Cadmium is highly toxic and is known to accumulate in biological systems, which is why nicad batteries must be disposed of carefully and in the right place.
DISADVANTAGES
- Much greater care needed. The plusses for modelers come at the expense of the MUCH greater care required in use.
- More precise equipment and monitoring required. A more rigorous approach plus a profound awareness of the difference between nicads and Li-ions is vital to the well being and SAFETY of users, homes, bystanders and equipment. Many of these points also apply to nicad/NiMH cells - it’s important to remember that these batteries too will explode if abused! Li-ions, however, have additional characteristics, of which all model users should be aware. See chemistry and energy density above.
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