Lithium-ion cell suppliers for automotive brands such as Mercedes and Voyah, Farasis Energy conducted tests to reassure on the longevity of electric vehicle batteries.
Conditions
Available since 2018, it is its P73 and P75 pouch-shaped cells that Farasis Energy decided to test to demonstrate their durability. The target was a million miles, about 1.6 million kilometers, translated by the Chinese cell manufacturer into 5,000 charge/discharge cycles. The company estimated it could reproduce this scenario in an accelerated manner over a period of 24 to 36 months.
Considering that various parameters can cause premature wear, the recharge operations were carried out in different conditions, sometimes intensively. This included discharging to over 90% and recharging from 10 to 80% in 20 or 30 minutes.
Farasis Energy engineers also manipulated temperature to replicate conditions experienced in the main automotive markets such as the United States, Western Europe, and China. To simulate what cells endure in electric vehicle packs, pressure also varied during laboratory tests.
Results
With an energy density of 270 Wh/kg, the P75 cells still showed an energy capacity of nearly 85% after 5,000 cycles compared to the beginning of their life. The P73 cells (285 Wh/kg) performed slightly lower at 82.5%. Farasis Energy translates these results as confidently stating that batteries using these cells can last a million miles over 15 years while retaining over 70% of their capacity.
The manufacturer attributes this durability to choices made at its level. Firstly, the use of a semi-solid material to cover the separators in the cells. This recipe reduces the amount of electrolyte while ensuring excellent ionic conductivity and chemical stability.
For the cathode and anode, the materials in them are said to have high stability. Farasis Energy also mentions an electrolyte/electrode interface optimized for improved performance.
Also in Trucks and eVToL
To justify the use of NMC chemistry (Nickel Manganese Cobalt), the company claims that it can gain about 300 km of range on trucks compared to the LFP (Lithium Iron Phosphate) blend.
These P75 and P73 cells from Farasis Energy have been independently tested by eVToL manufacturers, these vertical take-off and landing devices envisioned as the next taxis for dense urban areas.
It is reported that these cells can withstand more than 10,000 flights, leading the involved industries to prefer these pouch cells over cylindrical or prismatic models.
Author’s Opinion
While not taking internally conducted tests by a lithium-ion cell manufacturer at face value, they are hardly surprising when electric vehicles manage to exceed 500,000 km with their original batteries without major degradation.
There are two small concerns, however, without questioning the results or the durability of plugged-in vehicles. Firstly, the temperature range used during the tests, between 25 and 35°C. This does not cover the known temperature ranges in China, Western Europe, and the United States, rather falling within an ideal range. Unless the first value is negative (-25°C), but poorly transcribed.
The second point is the estimated 15-year durability. Where does this figure come from? Farasis Energy does not explain. If we observe that with 5,000 cycles in 2 to 3 years, we still retain between 80 and 85% of the original capacity, then why not over 70% after 15 years? A few more years are needed to be sure in real operating cases.