Over time, Lithium Polymer battery packs tend to puff up, causing them to take up more space and become more dangerous. This is not the case with Lithium Ion cells, which have a longer lifespan and can tolerate up to 1000 charge-discharge cycles before needing to be replaced.
Additionally, Lithium Ion cells are much more durable. A common mistake in RC aircraft design is placing sharp objects (such as nails) next to a Lithium Polymer battery. The packs can be easily punctured during a crash, causing them to catch on fire. The cylindrical shell of Lithium Ion batteries is much more durable, making it much less likely to be punctured during a crash.
Furthermore, Li Ion cells have been consistently on the forefront of new increases in battery energy density. Since the success of Tesla motors, much more focus has been put into developing Lithium Ion cells with greater energy density. The most advanced Lithium Ion battery available today is the NCR18650GA, a 3.7 Volt cell with a capacity of 3500 Mah, and a discharge rating of 10 Amps.
The batteries used in Tesla models are very similar to the GA series. Like the GA series, they have a max discharge of 10A. The only difference is that Tesla Li-Ions are much more durable because they are intended for automotives. Additionally, Tesla batteries can be supercharged from 0% to 80% in under an hour.
The more commonly referenced Li Ion battery is the NCR18650B developed by Panasonic.
Currently this battery model is being used in the Tesla model S, although Tesla is developing a new Lithium Ion battery with 18% more energy density that will be used in the Tesla model 3. Similarily, Tesla is working with the new NCR21700 battery, which will weigh 10% more than an 18650 Battery, but it will have 30% more energy density.
There are a few Lithium Ion cells similar to these that claim to have upwards of 5000-8000 Mah of capacity, but all of these batteries are Chinese ripoffs and should not be trusted.
There are a few disadvantages with Lithium Ion cells. The discharge rating high capacity Lithium Ion cells is low when compared to LiPo batteries. This is due in large part to the high internal resistance of a Lithium Ion cell. Unlike the NCR18650GA, lower capacity cells (with a capacity of around 2600 Mah or so) have a high discharge rating of 30 amps per cell. Once three of these batteries are put in parallel, a resultant 90 Amps of max discharge is achieved. This current draw is more than enough power for most commercially available RC planes. Even with the lower capacity rating, the Lithium Ion pack has 20-30% more energy density than a Lithium Polymer pack.
In more recent years, battery technology has improved even more than it has in the past. Many battery developers are hoping to achieve the equivalent of Moores Law — a theory developed by Robert Moore that transistor density will double every year.
As battery technology continues to improve, it makes more sense for the RC plane industry to make the switch to Lithium Ion batteries to double energy density and take advantage of the innovations in new Lithium Ion cells. Increases in cell capacity and smaller internal resistance will allow more RC planes to double their range by switching to Lithium Ion batteries.
DISCLAIMER: Like any battery, Lithium Ion batteries must be taken care of properly to avoid problems such as short circuits….etc. Please see our guide on How to Care for your Lithium Ion Batteries for more information.