# Which is better



## Zemmo (Sep 13, 2007)

From what I have read/heard. Li-Ion can handle the high amp draw for quick acceleration where LiFePo4 doesn't handle the high Amp draws as well. The Li-Ion has a ton more cells involved so that is a lot of connections to make sure that they are correct. LiFePo4 is a large format battery so it has fewer connections. Both batteries really need a Battery Management System. I believe the Ah/$ (or Kwh/$) is cheaper with LiFePo4 batteries. This is just a few of the general differences between those two types of batteries.


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## ZeroGasoline (Jul 30, 2008)

ziggds said:


> Trying to work out which is better li-ion or lipo batteries. Tesla uses the small li-ion along with the volt. Yet most people on here rave about lipo. Which is more compact and lighter?
> 
> Zippy


I believe the biggest concern with lion is their instability. Lion batteries were the ones known to catch fire and otherwise not function properly.

LiFePO4 batteries solve the stability problem, thus being more suitable for EV's.


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## Jason Lattimer (Dec 27, 2008)

After talking to several people on here it is plainly obvious Lithium Iron's are the best to use today. Some on here have been using sites to directly import from China "I.E. Thundersky Batteries" and have been paying about what you would pay for some good high dollar agm or gel cell batteries.


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## JRP3 (Mar 7, 2008)

Just to be clear, LiFePo4 batteries are lithium ion batteries, just a different chemistry. The classic lithium ion cells that Tesla uses are Lithium Cobalt. Lithium Cobalt has higher energy density than other types, but are more prone to thermal runaway. Nanophosphate cells such as A123 can have higher discharge rates than Lithium Cobalt but lower energy density.
The Volt is not using the small cylindrical cells but larger prismatic cells from LG Chem.


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## Madmac (Mar 14, 2008)

In a simple description there are two voltages for rechargeable lithium cells. Around 3.7, 3.8 for the lithium cobalt used in the Tesla, Volt and other vehicles like the Tzero. And the lower voltage 3.2, 3.3 covering most of the other chemistries including LiFePo cells. Both types are available in cylindrical cells and rectangular format used for most prismatic cells. The higher voltage are considered to be more dangerous than petrol by many!!!

Most of the lower cost lithium’s are limited in discharge currents. The max for continuous use is 2C or twice the listed AmpHour rating. The short time discharge varies widely between manufacturers and has a significant effect on battery life or the number of charge discharge cycles before the capacity drops away.

Some cells, for example Thundersky, package a version that can take greater discharge better by limiting the heating of the electrodes. The cell is the same in both versions. Discharging at 10C (the improved rating) for significant time will decrease the battery life.

As to which is lighter and smaller for the same power then lithium cobalt wins hands down. 
Taking an example of 160AmpHour Thundersky’s

160AHr at 3.2Volts = 512WattHr weight = 5.6Kg size = 182x279x71mm 

Using 2.4AmpHour 3.7 volt 18650 cells as used in the Tesla. (2.6 and 3AHr versions are also available at quite a price premium )

2.4 x 3.7 = 8.88 WattHr per cell, for 512 WattHr 58 cells needed.

Weight for one 18650 is 45gm so for 58 = 2.6Kg about half the Thundersky.

As for size look at the following photos with 58 18650’s along side a cardboard mock up of the Thundersky.


The parallel set of 54 is one of 96 that I am using in the battery system for my AC conversion. 12 sets of 54 paralleled batteries are in one assembly with its own BMS control PCB. The full pack is 355 Volts, at 129AHr giving 46KWattHours and weighing approx 280Kg. The battery will supply 3C continuous, so max of approx 390Amps.

If you need the max power in the smallest size and lightest weight you cannot beat the 18650 approach. A lot of people have concerns about these batteries catching fire. It is about two years since any of the major manufacturers have had a problem and before that it was limited to a few dozen cells in an annual production of over one billion. The last few years have seen problems with low cost prismatic cells only.

Most problems with battery packs are poor assembly or bad connections. Both types of litium batteries burn well. Take a look at

http://www.batteryvehiclesociety.org.uk/forums/viewtopic.php?t=1825
http://www.go-ev.co.uk/images/fire/index.html
http://wikileaks.org/wiki/Toyota_Prius_A123_car_fire_investigation_report_2008
http://www.youtube.com/watch?v=tw4RHdPHq0s&feature=related


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## aeroscott (Jan 5, 2008)

You gone done it again Madmac . Great work!I am comparing my 1.25 Amp x 3.6V 18650 Panasonic , they are 2x heavier then yours .120 cells = 500w


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## ziggds (May 11, 2009)

Have been reading a lot about batterys and it seems for high power the best is either 18650 cells or Lipo packs. What is the down side to these options?

Thanks.

Zig


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## JRP3 (Mar 7, 2008)

ziggds said:


> What is the down side to these options?
> 
> 
> Zig


Money  What application are you going to be using them in? That depends a lot on what makes the most sense.


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