Lithium-Ion vs LiFePo4
All you fellow lithium DIYers out there. We hear a lot of confusion out there about the best lithium chemistry for your DIY projects. So, let's try to clear up the nonsense.
Both chemistries offer advantages and disadvantages to the DIY project builder. Much of the confusion comes from the "18650 scavengers" community. Nothing wrong with that! But most of the time, no one tells you there are different cell chemistries, charging voltages, and even the number of cells in the pack, depending on the chemistry we use. Here are some useful tips about deploying lithium iron phosphate or lithium-ion, as well as some of the differences between each chemistry and lead acid.
This article stays with LiFePo4 and lithium-ion, as these two chemistries are the most common to recycle or refurbish here in Oz.
At no point in this article are we talking about LiPo batteries. Need info on other chemistries, see my links at the end of this article.
LiFePO4
Individual LiFePO4 cells have a nominal voltage of about 3.2V or 3.3V. We use multiple cells in series (usually 4) to make up a lithium iron phosphate battery pack.
- Using four lithium iron phosphate cells in series gives us roughly ~12.8-14.2 volts pack when full. This is the closest thing we're going to find to a traditional lead-acid or AGM battery.
- Lithium iron phosphate cells have greater cell density than lead acid, at a fraction of the weight.
- Lithium iron phosphate cells have less cell density than lithium-ion. This makes them less volatile, safer to use, and offers almost a one-to-one replacement for AGM packs.
- To reach the same density as lithium-ion cells, we need to stack lithium iron phosphate cells in parallel to increase their capacity. So, lithium iron phosphate battery packs with the same capacity as a lithium-ion cell will be larger, as it requires more cells in parallel to achieve the same capacity.
- Lithium iron phosphate cells can be used in high-temperature environments, whereas lithium-ion cells should never be used above +60 Celsius.
- The typical estimated life of a lithium iron phosphate battery is 1500-2000, charge cycles for up to 10 years.
- Typically, a lithium iron phosphate pack will hold its charge for 350 days +/- 20 or so.
- Lithium iron phosphate cells have four times (4x) the capacity of lead acid batteries.
Lithium-ion
Individual lithium-ion cells usually have a nominal voltage of 3.6V or 3.7 volts. We use multiple cells in series (usually 3) to make up a 12-volt lithium-ion battery pack.
- To use lithium-ion cells for a 12v power bank, we place them 3 in series to get a 12.6-volt pack. This is the closest we can get to the nominal voltage of a sealed lead acid battery using lithium-ion cells.
- Lithium-ion cells have a higher cell density than lithium iron phosphate, as mentioned above. This means we use fewer of them for the desired capacity. Higher cell density comes at the expense of greater volatility.
- As with lithium iron phosphate, we can also stack lithium-ion cells in parallel to increase the capacity of our packs.
- The typical estimated life of a lithium-ion battery is two to three years or 300 to 500 charge cycles.
- Typically, a lithium-Ion pack will hold its charge for 300 days +/- 25 or so.