LiFePO4 battery

Date:Dec 09, 2020

The lithium iron phosphate battery (LiFePO
4 battery) or LFP battery (lithium ferrophosphate), is a type of lithium-ion battery using  LiFePO
4 as the cathode material (on a battery this is the positive side), and a graphitic carbon electrode with a metallic backing as the anode. The energy density of LiFePO
4 is lower than that of lithium cobalt oxide (LiCoO
2) chemistry, and also has a lower operating voltage. The main drawback of LiFePO
4 is its low electrical conductivity. Therefore, all the LiFePO
4 cathodes under consideration are actually LiFePO
4/C. Because of low cost, low toxicity, well-defined performance, long-term stability, etc. LiFePO
4 is finding a number of roles in vehicle use, utility scale stationary applications, and backup power.

Batteries are booming business. In the energy world, the Lithium-Iron Battery (LFP) still has a lot of advantages. Because of its low energy density, this battery is pre-eminently suited for Energy buffers (stationary storage). 

However, we see that NMC batteries are slowly taken the position of the LFP because of their higher energy density and because prices are leveling. 

Lithium Iron Phosphate (LFP)

In 1996, the University of Texas (and other contributors) discovered phosphate as cathode material for rechargeable lithium batteries. Li-phosphate offers good electrochemical performance with low resistance. This is made possible with nano-scale phosphate cathode material. The key benefits are high current rating and long cycle life, besides good thermal stability, enhanced safety and tolerance if abused.

Li-phosphate is more tolerant to full charge conditions and is less stressed than other lithium-ion systems if kept at high voltage for a prolonged time. As a trade-off, the lower voltage of 3.2V/cell reduces the specific energy to less than that of Li-manganese. With most batteries, cold temperature reduces performance and elevated storage temperature shortens the service life, and Li-phosphate is no exception.

Li-phosphate has a higher self-discharge than other Li-ion batteries, which can cause balancing issues with aging. Figure 9 summarizes the attributes of Li-phosphate.

Li-phosphate is often used to replace the lead acid starter battery.

Four cells in series produce 12.80V, a similar voltage to six 2V lead acid cells in series.

Vehicles charge lead acid to 14.40V (2.40V/cell) and maintain a topping charge.

With four Li-phosphate cells in series, each cell tops at 3.60V, which is the correct full-charge voltage.

At this point, the charge should be disconnected but the topping charge continues while driving.

Li-phosphate is tolerant to some overcharge; however, keeping the voltage at 14.40V for a prolonged time, as most vehicles do on a long drive, could stress Li-phosphate.

Cold temperature operation starting could also be an issue with Li-phosphate as a starter battery.

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