Comparison of Cycle Life of LFP and NMC Lithium Batteries

Two Main Lithium-Ion Battery Chemistry 

Among the various types of lithium-ion batteries, two are the best choices for forklifts and other lift trucks: lithium iron phosphate (LFP) and lithium nickel manganese cobalt (NMC).

LFP battery chemistry has the longest history. NMC is a relatively new technology. However, that doesn't mean it's a universally better technology. In electric vehicles (EVs) such as cars and trucks, NMC is often preferred due to its lighter weight and higher energy density per kilogram. However, in warehousing environments, where ambient temperatures can reach extreme levels and weight is not an issue, LFP batteries are widely used.

By default, both NMC and LFP chemistry have a battery life of between 3000 and 5000 cycles. However, if given the opportunity to recharge, the service life can be greatly extended, up to 7,000 cycles. While lead-acid batteries cannot be recharged until they are 20% depleted, lithium-ion batteries thrive on what is called "opportunity charging". Although the two batteries - LFP and NMC - work similarly, there are some differences.

Decay test results for commercial lithium-ion batteries

According to a paper Degradation of Commercial Lithium-Ion Cells as a Function of Chemistry and Cycling Conditions published in 2020 in the Journal of the Electrochemical Society, LFP batteries have a longer life than NMC batteries. This data contradicts the common belief that NMC batteries are more durable and last longer. The tests were first published in September 2020, but only recently appeared in the news sections of materials handling publications. The author of the article gives a possible explanation-the data of actual commercially available batteries may change with changes in the manufacturing process, no matter how subtle the change is.

Under strict testing conditions, two types of commercially available lithium batteries were repeatedly discharged and charged from 0% to 100%. How is the result? The paper states: "Under the test conditions of this article, the cycle life of LFP batteries is greatly extended." The tests were conducted at Sandia National Laboratories "as part of a broader effort to determine and characterize the safety and reliability of commercial lithium-ion batteries." The study examined the effects of temperature, depth of discharge (DoD) and discharge current on the long-term degradation of commercial batteries.

LFP chemical properties are better than NMC

All batteries are charged and discharged at a rate of 0.5C, which means the entire battery capacity is consumed within two hours. It can be easily seen from the figure that in each charge and discharge cycle, the discharge capacity retention rate of the LFP lithium battery (blue data point) far exceeds the discharge capacity retention rate of the NMC battery (black data point). As can be seen from the figure, the decay rate of NMC batteries is almost twice that of LFP batteries, indicating that the overall performance of LFP batteries is superior.

Tests show that LFP's RTE (round trip efficiency) is better than NMC. The calculation method is to divide the discharge energy by the charging energy. This calculation method shows that LFP is the more efficient and economical choice. Nickel-cobalt-aluminum lithium batteries (or NCA) are also part of this experiment, and their performance is similar to or worse than NMC. We do not focus on NCA in this article because NCA is not a mainstream material for commercial applications of lithium batteries mainly due to safety and cost issues.

Both NMC and NCA cells are highly dependent on discharge depth and are more sensitive to full SoC range cycling than LFP cells. LFP cells had the highest cycle life under all conditions, but this performance gap narrowed when comparing cells based on discharge energy throughput.

LFP and NMC Lithium Battery Chemistry: Charging Speed

There is another major difference between LFP and NMC in the material handling world. NMC lithium-ion batteries sometimes charge at higher and faster rates, and NMC typically uses 0 to 100% charge cycles compared to LFP. However, this requires weighing the pros and cons. To do this, the strength of cables and connectors must be increased because the process generates higher temperatures. Additionally, individual cells must be insulated from each other to contain and dissipate heat. This often uses a ceramic shield, which increases the cost of the battery unit.

LFP lithium-ion batteries typically have a lower charging rate, typically 1.5C. However, they can be fitted with dual plugs, which will double the charging speed while still maintaining a lower charging temperature. Overall, the current draw during charging is lower, potentially leading to safer charging.

In fact, NMC's higher charging speed is not a problem. Take advantage of opportunities to recharge (good for lithium batteries) and the battery will never be fully discharged. Therefore, charging from a completely discharged battery to a fully charged battery rarely happens. The lesson this gives us is simple. Although there is publicity that NMC can adopt higher charging rates, there is no significant time saving or downtime reduction to justify charging rates beyond 1C.

LFP and NMC

While NMC batteries are often promoted as newer, more advanced technology, they also suffer from some other significant flaws. NMC batteries have a significantly lower flash point (the temperature at which chemicals ignite) than LFP batteries. NMC has a flash point of 419 degrees Fahrenheit, while LFP has a flash point of 518 degrees Fahrenheit. In other words, under the right conditions, NMC ignites and burns more easily. For example, high charge rates can lead to thermal runaway and potential thermal damage, which is more common in NMC battery packs than in LFPs.

The technical and chemical characteristics of NMC cause it to generate heat during use and charging, so more heat dissipation measures need to be taken. To control heat, ceramic baffles are used in NMC batteries to separate the cells. This is a measure not required by LFP chemistry technology.

While NMC technology may charge faster and have a slightly higher nominal voltage per cell (3.7V versus 3.2V for LFP), there are no clear advantages to justify the higher purchase price of. Although the specific price fluctuates with the market, the price of NMC batteries is about 30% to 50% higher. LFP chemistry batteries are actually a safer technology that performs well and even outperforms the more expensive NMC batteries. LFP batteries outperform older lead-acid batteries, which are less safe and efficient. The same goes for NMC. However, when the total cost of ownership of a forklift battery is a driving factor, LFP may be the better choice.

Warm Notes for Customers

When choosing the right battery, don't just consider the initial cost. Consider the total cost of ownership over the life of the battery. Lithium-ion chemistry batteries operate safer and last longer, which are all factors that should be considered. Whether from the perspective of operating efficiency or the improvement of safety factors, lithium-ion chemical batteries are more reasonable.

Even so, don’t make a decision without weighing the pros and cons of NMC and LFP battery chemistries.

Overall, the performance of NMC batteries has not been significantly improved, while LFP technology, when handled properly, results in slower battery decay and longer cycle life.

While some NMC batteries may offer faster charging (possibly up to 3C), this is not necessarily a requirement for opportunistic charging. Batteries rarely charge from 0 to 100%.

LFP batteries have a lower charge rate, but the charge rate can be easily increased if needed. The data shows that LFP batteries have the highest cycle life under all conditions.