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Lithium Iron Phosphate Battery (LiFePO4)

Features and Benefits When Compared To SLA
This information will cover the features and benefits of Lithium Iron Phosphate (LiFePO4) batteries when compared to traditional Sealed Lead Acid (SLA) battery technology. Since the discussion is around LiFePO4 and SLA, the article concentrates on 12VDC and 24VDC applications.
 
Different Lithium Technologies
It is important to note that there are many types of “Lithium Ion” batteries. The point to note in this definition refers to a “family of batteries”.
There are several different “Lithium Ion” batteries within this family which utilize different materials for their cathode and anode. As a result, they exhibit very different characteristics and therefore are suitable for different applications.
 
Lithium Iron Phosphate (LiFePO4)
Lithium Iron Phosphate (LiFePO4) is a well-known lithium technology in Australia due to its wide use and suitability to a wide range of applications.
Characteristics of low price, high safety and good specific energy, make this a strong option for many applications.
LiFePO4 cell voltage of 3.2V/cell also makes it the lithium technology of choice for sealed lead acid replacement in a number of key applications.
 
Why LiFePO4
Of all the lithium options available, there are several reasons why LiFePO4 has been selected as the ideal lithium technology for replacement of SLA. The main reasons come down to its favourable characteristics when looking at the main applications where SLA currently exist. These include:

• Similar voltage to SLA (3.2V per cell x 4 = 12.8V) making them ideal for SLA replacement.
• Safest form of the lithium technologies.
• Environmentally friendly –phosphate is not hazardous and so is friendly both to the environment and not a health risk.
• Wide temperature range

Features and benefits of LiFePO4 when compared to SLA
Below are some key features LiFePO4 batteries which give some significant advantages of SLA in a range of applications. This is not a complete list, however it does cover the key items. A 100AH AGM battery has been selected as the SLA, as this is one of the most commonly used sizes in deep cycle applications. This 100AH AGM has been compared to a 100AH LiFePO4 in order to compare a like for like as close as possible.

Feature – Weight:
Comparison

• LifePO4 is less than half the weight of SLA
• AGM Deep cycle – 27.5Kg
• LiFePO4 – 12.2Kg

Benefits

• Increases fuel efficiency
• In caravan and boat applications, towing weight is reduced.
• Increases speed
• In boat applications water speed can be increased
• Reduction in overall weight
• Longer runtime

Weight has a large bearing on many applications, especially where towing or speed in involved, such and caravan and boating. Other applications including portable lighting and camera applications where the batteries need to be carried.
 
Feature – Greater Cycle Life:
Comparison

• Up to 6 time the cycle life
• AGM Deep cycle – 300 cycles @ 100% DoD
• LiFePO4 – 2000 cycles @ 100% DoD

Benefits

• Lower total cost of ownership (cost per kWh much lower over life of battery for LiFePO4)
• Reduction in replacement costs – replace the AGM up to 6 times before the LiFePO4 needs replacing

The greater cycle life means that the extra upfront cost of a LiFePO4 battery is more than made up for over the life use of the battery. If being used daily, an AGM will need to be replaced approx. 6 times before the LiFePO4 needs replacing.
 
Feature – Flat Discharge Curve:
Comparison

• At 0.2C (20A) discharge
• AGM – drops below 12V after
• 1.5 hrs of runtime
• LiFePO4 – drops below 12V after approximately 4 hrs of runtime

Benefits

• More efficient use of battery capacity
• Power = Volts x Amps
• Once voltage starts to drop off, battery will need to supply higher amps to provide same amount of power.
• Higher voltage is better for electronics
• Longer run time for equipment
• Full use of capacity even at high discharge rate
• AGM @ 1C discharge = 50% Capacity
• LiFePO4 @ 1C discharge = 100% capacity

This feature is not common knowledge but is a strong advantage and it gives multiple benefits. With the flat discharge curve of LiFePO4, the terminal voltage holds above 12V for up to 85-90% capacity usage. Because of this, less amps are required in order to supply the same amount of power (P=VxA) and therefore the more efficient use of the capacity leads to longer run time. The user will also not notice the slowing down of the device (golf cart for example) earlier.
Along with this the effect of Peukert’s law is much less significant with lithium than that of AGM. This results in having available a large percentage of the capacity of the battery no matter what the discharge rate. At 1C (or 100A discharge for 100AH battery) the LiFePO4 option will still give you 100AH vs only 50AH for AGM.
 
Feature – Increased Use of Capacity:
Comparison

• AGM recommended DoD = 50%
• LiFePO4 recommended DoD = 80%
• AGM Deep cycle – 100AH x 50% = 50Ah usable
• LiFePO4 – 100Ah x 80% = 80Ah
• Difference = 30Ah or 60% more capacity usage

Benefits

• Increased run time or smaller capacity battery for replacement

The increased use of the available capacity means the user can either obtain up to 60% more runtime from the same capacity option in LiFePO4, or alternatively opt for a smaller capacity LiFePO4 battery while still achieving the same runtime as the larger capacity AGM.
 
Feature – Greater Charge Efficiency:
Comparison

• AGM – Full charge takes approx. 8 hours
• LiFePO4 – Full charge can be as low as 2 hrs

Benefits
Battery charged and ready to be used again more quickly
Another strong benefit in many applications. Due to the lower internal resistance among other factors, LiFePO4 can accept charge at a much great rate than AGM. This allows them to be charged and ready to use much faster, leading to many benefits.
 
Feature – Low Self Discharge Rate:
Comparison

• AGM – Discharge to 80% SOC after 4 months
• LiFePO4 – Discharge to 80% after 8 months

Benefits

• Can be left in storage for a longer period

This feature can be very useful for recreational vehicle users who may only use the vehicle for a couple of months a year before going into storage for the rest of the year, products such as caravans, boats, motorcycles and Jet Skis etc. LiFePO4 do not calcify and so even after being left for extended periods of time, the battery is less likely to be permanently damaged. A LiFePO4 battery is not harmed by not being left in storage in a fully charged state. If your applications warrant any of the above features, then you will be sure to get your monies worth for the extra spend on a LiFePO4 battery. 

 

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