Real cycle life for lithium LiFePO4 cells

Fonte: http://gwl-power.tumblr.com/post/97128890296/faq-what-is-the-real-cycle-life-for-lithium

FAQ: What is the real cycle life for lithium LiFePO4 cells?

Question: I study the specifications of the LiFePO4 (LFP) cells and I see that the information about the cycle life of the cells is changing. For example in some older technical sheets the cycle life is only 2000 cycles. In the new ones there is 5000 cycles.  Some manufacturers give 2000 cycles, other give 3000, 5000 or even more. What is the real cycle life and how to compare the values given by various manufacturers?

Answer: GWL/Power has been doing the business with LFP cells since 2008. The 7 years have proved that the LFP technology is very stable, lasting and reliable. The manufacturers have the same results and feedback from their battery applications and customers. In addition to this, the technology, production methods and the purity of the raw materials keep improving over the years. Based on these real results the manufacturers are updating the estimated life span in the official datasheets. That is why the new datasheets publish higher cycle number data. 

Simply said: all of the manufacturers, GWL is working with, give the same basic specification of the cycle life: at 2000 cycles at standard discharge conditions. This kind of cycle life is defined as an irreversible drop of the capacity from 100% to 80%.

However, the real life of the cells in much higher. It means the cell can be used even after the 2000 cycles. This information is given not as guaranteed warranty information, but as an estimation reference of the future life expectancy. Somemanufactures give 3000, 5000, 8000 or even more cycles.

This is the same as with a car: How many kilometers can a car drive until a serious breakdown? The manufacturer may give the basic warranty of 100 000 kilometers, but everybody knows the car will of cause drive much longer. Depending on the driving style, driving conditions, the maintenance and the behaviors towards the car, the car may drive 300 000, 500 000 or even 1 million kilometers without a serious defect. However this cannot be provided as official “guaranteed information”.  Everybody knows this, everybody understands it, but it is never given by the car manufacturer as some official data.

And the lithium battery life span is the same. The manufacturers give the basic warranty of usually 2000 cycles, but what is beyond this is only an approximate estimation.

Some manufacturers can be rather conservative, giving the “safeway” estimation, some may give the higher “nominal” estimation. Other manufacturers are veryoptimistic about their products and can give more far reaching results.  This is seen from the attached graph. 

Keep in mind that the life span of the LFP cells is really very long. Making the thousands of cycles means many years of continuous service.  It is again the same logic as with a car: the investment in purchase will return in some 5 to 7 years and beyond that the car (LFP cells) will keep serving many additional years, as if free of charge. 

The functional service life of the LFP cells is given as 10, 20, 30 or even more years. When the cells are stored in a stable environment and charged and discharged properly, they will keep serving years after years. 

Final note: the very long life- span for LFP cells is a completely different approach from other types of battery technology (like Ni-Cd, Lead-Acid, Sodium-sulfate, etc): all these types of cells need a complex maintenance and service cycles - this keep increasing the operational costs. There is nothing like this for LFP cells.

We encourage to start using the LFP technology for all new installations.  Get your DC power now!