Lithium battery technology is based on the material characteristics of lithium - the lightest metal with the highest electrochemical potential of any solid material. The technology has not yet fully matured and is still being improved continuously as new metal and chemical combinations are being tried to increase energy density and prolong service life.
In many ways, lithium is superior to nickel and lead-based chemistries and the applications for a lithium battery are growing as a result. One of the most exciting applications of course is in the radio control hobby field.
A lithium battery prefers a partial rather than a full discharge and frequent full discharges should be avoided when possible. Instead, charge the battery more often (they are good for 300-500 discharge/charge cycles) or use a larger battery. There is no concern of memory when applying unscheduled charges.
Aging of lithium-ion is an issue that is often ignored and a lithium battery has a lifetime of 2-3 years. The clock starts ticking as soon as the battery comes off the manufacturing line and the capacity loss is the result of increased internal resistance caused by oxidation. Eventually, the cell resistance will reach a point where the pack can no longer deliver the stored energy, although the battery may still contain ample charge.
With lithium cells, there is always the risk of fire which can result from shorting, improper charging or crash damage to the batteries. And because a lithium battery fire is very hot (several thousand degrees) it often starts other fires which can result in burning down the house!
Now the reason fire occurs is due to contact between the lithium and oxygen in the air. It doesn’t need any other source of ignition or fuel to start, and burns almost explosively.
Please follow these simple safety rules:
- Store and charge in a fireproof container, never in your model. You can buy fireproof charging bags.
- Never leave the charging process unattended, especially overnight. Charge in a protected area away from any combustibles. Always stand watch over the charging process.
- Never attempt to charge a lithium battery that has been damaged and if it has been damaged, carefully remove it to a safe place for at least a half hour to observe. After sufficient time to ensure safety, damaged cells should be discarded at a recycling depot, not in the household rubbish.
- Always use a dedicated lithium charger, never a Ni-Cd/NiMh charger.
- Use charging systems that monitor and control the charge state of each cell in the pack because unbalanced cells can lead to the overcharge of a single cell in the pack resulting in swelling. If swelling occurs, discontinue charging immediately and remove to a safe place outside. Swelling means air has leaked into the usually airtight battery and there is a danger of explosion if charged.
Lithium ion Polymer Batteries
Superior lithium ion polymer batteries (LiPol or LiPo) use a polymer electrolyte that can be packaged in flexible material and designed to prevent explosion making them safe to handle as an RC battery.
These cells offer working voltages in the range of 3.0~4.2V compared to 1.2V~1.5V for lead acid, NiCd, and NiMh rechargeable batteries so it takes only half the number of cells to achieve the same voltage.
LiPoly Battery Features:
- Overlander, Thunder Power and E-Flight are some of the best lithium batteries on the market, but other good brands are appearing all the time.
- Up to 1000 cycles (more than twice lion)
- Extremely lightweight & compact
- Provides 5X the operating time of same-sized NiCds
- No memory effect
- 3.7 volt cell output provides 3X the reliability of NiCds
- Cell chemistry is non-toxic and contains no carcinogens
- will burn furiously if punctured when charged
On a final note, I would recommend deliberatly damaging a lipo battery so you know what can happen. Put a fully charged LIpo of decent size, say 2200 mah 1 cell, 2 cell, 3 cell or whatever you have (1 cell would be better), into a fireproof container (say a metal bin) and take it to a wide open space away from any dangers. Also take with you a pair of goggles and a garden cane with a sharp nail or spike attached to one end. Stab your fully charged battery while wearing safety goggles and see what happens. Believe me, it's much less stressful to see it for the first time this way than in some kind of accident. However, if you do burst a battery cell in an accident, just keep away from it and wait for it to burn itself out, unless it's on something that will catch fire - in which case you may have to quickly disconnect it and get it somewhere where it won't set anything on fire, but if you decide to do this goggles are highly recommended as the battery can spit out sparks and bits of soot like a Roman Candle.
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