Benefits of Lithium Iron Phosphate batteries (LiFePO4)
iron phosphate battery advantages
lithium iron phosphate batteries (LiFePO4 or LFP) offer lots of benefits compared to lead-acid batteries and other lithium batteries. Longer life span, no maintenance, extremely safe, lightweight, improved discharge and charge efficiency, just to name a few. LiFePO4 batteries are not the cheapest in the market, but due to a long life span and zero maintenance, it’s the best investment you can make over time.
New Tests Prove: LFP Lithium Batteries Live Longer than NMC
Recent independent degradation tests of commercial lithium batteries reveal a big surprise! Contrary to the claims of many NMC-based lithium battery manufacturers, LFP chemistry is superior compared to NMC – it is safer, offers a longer lifespan, and is generally less expensive than NMC, NCA.
The Two Main Types of Lithium-ion Battery Chemistries Used
Of all the various types of lithium-ion batteries, two emerge as the best choices for forklifts and other lift trucks: Lithium Ferrum Phosphate, or Lithium Iron Phosphate (LFP) and Lithium Nickel Manganese Cobalt Oxide (NMC).
The LFP battery chemistry has been around the longest. NMC is a relatively new technology. However, that doesn’t always translate into being a universally better technology. In electric vehicles (EVs), such as cars and trucks, it’s often the preferred choice due to overall less weight and higher energy density per kilogram. However, in the warehousing environment, where ambient temperature extremes are possible and weight is not the issue, the LFP battery is widespread and conversely may be a more favorable choice.
As a default, both NMC and LFP chemistries’ useful life can range between 3,000 to 5,000 cycles. However, with opportunity charging, that can be increased significantly, anywhere up to 7,000 cycle count. Whereas lead-acid shouldn’t be charged until it’s depleted to 20% battery capacity, Lithium-ion batteries thrive on what it calls opportunity charging. While the two types—LFP and NMC—operate similarly, there are some differences.
Degradation of Commercial Lithium-Ion Cells: Test Results
According to a 2020 paper from the Journal of the Electrochemical Society (Degradation of Commercial Lithium-Ion Cells as a Function of Chemistry and Cycling Conditions), LFP batteries have a longer lifespan than NMCs. This data contradicts the wide-spread notion that NMC cells are more durable and have a longer life span. These tests were first published in September 2020 but reached the news sections of material handing publications only recently. The authors of the article give one possible explanation – the data on real commercially available cells may vary with the change of manufacturing process, however subtle.
Under strict test conditions, commercially available lithium cells of both types were repeatedly discharged and charged from 0% to 100%. The result? According to the paper, “The LFP cells exhibit substantially longer cycle life spans under the examined conditions.”
The tests were performed at the Sandia National Laboratories as “part of a broader effort to determine and characterize the safety and reliability of commercial Li-ion cells.” The study examined the influence of temperature, depth of discharge (DOD), and discharge current on the long-term degradation of the commercial cells.
All cells were charged and discharged at a 0.5 C rate or the amount of discharge that will deplete the full capacity of a battery in two hours.
In the graphical representation shown (taken from the Journal’s 2020 technical paper), you can easily see that the discharge capacity retention for the LFP lithium battery (blue data points) far exceeded the NMC battery retention (indicated by the black data points) for each round of charge/discharge cycling. The graph indicates that the NMC degrades almost twice as quickly as the LFP, showing the superior overall performance of the LFP cells.
The testing showed LFPs had a better RTE (round trip efficiency) than NMCs, calculated by dividing the discharge energy by the charge energy. This calculation shows that the LFP is the more efficient, economical choice.
Lithium nickel cobalt aluminum oxide battery, or NCA, was also a part of this experiment and performed similar or worse than NMC. We do not focus on NCA in this article as it is not mainstream in the commercial use of lithium batteries for Material Handling, mainly due to safety and cost issues.
Both NMC and NCA cells demonstrated strong dependence on the depth of discharge, with greater sensitivity to full SOC range cycling compared to LFP cells.
LFP cells had the highest cycle lifetime across all conditions, but this performance gap was reduced when cells were compared according to the discharge energy throughput.
LFP and NMC Lithium Cells Chemistry: Charging Speed
There is one other major difference between LFP and NMC often used as a selling point in material handling. NMC lithium ion batteries are sometimes charged at a higher, faster rate, often compared to LFP using a 0 to 100% charge cycle. However, there is a tradeoff. To do this, the cables and connectors must be beefed up as the temperature generated by the process is higher. Additionally, the individual cells must be insulated from each other to contain and dissipate the heat. This is usually done using ceramic shields, increasing the cost of the battery unit.
LFP Lithium ion batteries normally charge at a lower rate, often up to 1.5 C rate. They can be fitted with dual plugs, however, that doubles the charge rate, while still maintaining a lower charging temperature. The current draw during the charging process is lower overall, potentially translating into a safer charge.
In reality, the higher charge rate of the NMC is a non-issue. With the use of opportunity charging (which benefits lithium batteries), the battery should never become fully discharged. Therefore, charging from a fully discharged battery to a fully charged battery will rarely, if ever, be encountered.
The takeaway is simple. Even though it may be promoted that the higher charge rate for NMC is possible, there is no measurable time savings increase nor downtime decrease to validate the necessity of charge rates over 1 C rate.
LFP vs NMC
While NMC cells are often promoted as a newer, more advanced technology, they carry some other significant pitfalls. The flashpoint (the temperature at which a chemical will ignite) is significantly lower than LFP. The flashpoint for NMC is 419 degrees Fahrenheit, while LFP’s flashpoint is as high as 518 degrees. In other words, the NMC is more likely to ignite and burn under the right conditions. For example, a high charge rate contributes to thermal runaway, potential heat damage and is more prevalent in NMC battery pack than in LFP.
Both the technology and chemistry of the NMC cause it to run hotter during both use and charging, requiring more heat dissipation measures. Ceramic tiles are used to separate the cells in an NMC battery for heat control. This is a measure not needed in LFP chemistry technology.
While the NMC is a technology with potentially faster-charging rates and a slightly higher nominal voltage per cell (3.7V compared to LFP’s 3.2V), there are no distinct advantages to justify the higher purchase price. While exact pricing fluctuates with the market, an NMC battery costs somewhere between 30% to 50% more. The LFP chemistry is actually a safer technology and will perform well, and even outperform, the more expensive NMC.
The LFP battery outperforms the old, less safe, and less efficient lead-acid battery. So does the NMC. But, when the total cost of ownership of forklift batteries is a driving factor, LFP may be the better choice.
Lead-Acid Forklift Batteries
We cannot skip the inevitable comparison to the lead-acid chemistry in this article, as this is still a prevalent technology in the forklift world. Lead-acid cells are wet cells. Electrical power is generated by liquid chemicals, interacting with the lead. The lead is converted into lead sulfate by a chemical reaction with the acid. When connected to a load (the forklift), the electrons move through it, balancing the electrons. Simply put, the battery is “discharged.” Recharging the battery reverses the process.
While lead-acid batteries have been around the longest, there are some inherent pitfalls. For example, they do have a limited number of charge cycles, somewhere around 1,500. However, that also means that a cycle is used up every time you charge the battery.
Ideally, the battery should be charged when it’s depleted to between 20 and 30 percent remaining charge to avoid capacity loss. Charging when the capacity is less than 20% can damage both the battery and the lift. Charging more often, say above 60%, and you’re wasting charges. The battery’s life will be shortened.
The charging/discharging processes also give off toxic and flammable gases. This makes lead-acid hazardous, both during operation and charging. Lead-acid batteries are also maintenance intensive. If water levels are not monitored and maintained properly—both high and low levels—battery life is shortened, and dangerous conditions can arise.
Finally, to properly maintain these batteries, you need to follow the 8-8-8 rule: eight hours of use, eight hours of charging, eight hours of the cool-down period, again, to avoid battery capacity loss due to the degradation mechanism of this technology. That means the battery can only be used during one full shift in 24 hours. And that means that you must have an additional backup battery to swap out for each work shift.
Compared to lead-acid batteries, both NMC and LFP Li ion batteries have a longer overall lifespan and a significantly higher number of charge discharge cycles. Unlike lead-acid, lithium-ion chemistry thrives with frequent charges. Their usable life is increased by opportunity charging during breaks and lunches.
Additionally, battery maintenance is minimal compared to the lead-acid battery. You don’t need to monitor the electrolyte levels because they’re non-existent. And battery room ventilation isn’t required since there is no dangerous gassing during the charging process. Most of the condition monitoring is done by the battery itself using advanced electronics of its battery management system.
Final Thoughts On Battery Chemistry Choice
In choosing the correct battery for your operation, don’t go by initial cost alone. Consider the overall cost of ownership during the life of the battery. The safer operation and longevity of lithium-ion chemistry should be factored in.
A battery with lithium-ion chemistry makes better sense, from both an operational efficiency standpoint, and the increased safety factor afforded.
Even so, don’t make the decision quickly, without weighing the pros and cons of both NMC and LFP battery chemistries.
NMC is an excellent choice for electric vehicles. But the price tag may not be worth it for forklift and PIT (powered industrial truck) use. Overall, there is no significant performance increase, and LFP technology demonstrates a slower battery degradation and a longer cycle life when handled properly.
While some NMC batteries may offer a faster charging rate (possibly up to 3 C rate), that isn’t necessarily a requirement due to opportunity charging. You rarely charge a battery from 0 to 100 percent.
LFP batteries charge at a lower rate, but the rate can be increased easily if it is a requirement.
Contrary to existing perception, the data shows that LFP cells have the highest cycle lifetime across all conditions.
Both Lithium-ion types are much safer than older lead-acid technology. However, the lower flashpoint of the NMC (419 degrees Fahrenheit) increases the possibility of a fire hazard, particularly at the high charge rate.
How long does a LiFePO4 battery last?
Generally speaking, lithium iron phosphate has a life span of up to 10 years. This is because it can undergo more than 4000 deep cycles. One deep cycle means fully charging the battery, fully discharging it, and then fully charging it again. Assuming you cycle your battery once a day and no other factors come into play, your battery should last more than 10 years.
Proper use can also extend the life of your battery. So you should know more about battery maintenance tips than you should know about battery life. Of course, you also need to know the factors that affect the life of your battery.
What is LiFePO4?
LiFePO4 stands for Lithium Iron Phosphate (Li) Iron (Fe) (PO4). It is a type of lithium battery. Compared with lead-acid batteries and other lithium batteries, it has many advantages such as longer life, lighter weight and better safety performance, lithium iron phosphate batteries are becoming more and more popular in the industry. More and more people are buying lithium iron phosphate batteries.
There are different models of lithium iron phosphate batteries, more on the market are 12v 100ah LiFePO4 batteries, 48v 100ah LiFePO4 batteries, and 51.2v 100ah Server Rack Lithium LiFePO4 Battery. They are widely used in golf carts, RVs, fishing boats and other fields.
Why do LiFePO4 batteries last longer than lead-acid batteries?
It has to do with the material properties of lithium iron phosphate and lead acid. On average, LiFePO4 batteries can last between 2,000 and 5,000 charge and discharge cycles without compromising their performance. Lead-acid batteries, on the other hand, can only last 200 to 500 cycles.
Basically, LiFePO4 batteries last about 5 to 10 years compared to lead-acid batteries that need to be replaced every 1-3 years. A comparative analysis conducted by the researchers shows that LiFePO4 batteries have low losses and longer cycle life and lower storage depletion rates than lead-acid batteries for use in power microgrid systems.
Factors that affect LiFePO4 batteries life span
There are many factors that affect the life of a lithium iron phosphate battery, and you should read them carefully and memorize them.
Use the right battery charger. Poor quality chargers can shorten the life of LiFePO4 batteries.
Do not let the battery sit too long with a low charge. The life of the battery will be greatly reduced if it is discharged all the time.
Do not overcharge. Overcharging will shorten the life of the LiFePO4 battery.
Standby status. Is your battery always in a dormant state?
Device Maintenance. Are your connected devices kept neat and spotless? Cleaning all ports will help extend battery life.
Maintenance tips of LiFePO4 batteries
Clean the terminals before installation
The terminals on top of the battery are made of aluminum and copper, which over time can form an oxide layer when exposed to air. Before installing the battery interconnects and BMS module, thoroughly clean the battery terminals with a wire brush to remove oxidation. If bare copper battery interconnects are used, these should also be cleaned. Removing the oxide layer will greatly improve conduction and reduce heat buildup at the terminals. (In extreme cases, heat buildup on the terminals due to poor conduction has been known to melt the plastic around the terminals and damage the BMS module!)
Proper charging of LiFePO4 batteries
The most common causes of premature failure of LiFePO4 batteries are overcharging and overdischarging. To ensure optimal performance of LiFePO4 batteries throughout their lifetime, we need to charge them properly. One of the main causes of shortened battery life and poor performance is overcharging.
Overcharging can result in.
Lack of a proper battery protection system
Infection of battery protection system failure
Incorrect installation of the battery protection system
Heat inside the battery, overcharging may cause a fire
On 12v battery, by preventing the total battery voltage from falling below 11.5v and using low voltage cutoff instead of BMS, no battery damage will occur. On the other end, charge to no more than 14.2v and no battery should be overcharged.
On the other hand, over-discharging may also cause damage to LiFePO4 cells. If any battery is near empty (less than 2.5V), the BMS must be disconnected from the load. The battery may be slightly damaged below 2.0V, but is usually recoverable. However, a battery driven to a negative voltage will suffer unrecoverable damage.
Frequent charging and shallower cycles
For Li-ion batteries, battery life will be longer if deep discharge is avoided. The proper DoD range is 70-80% (depth of discharge), except in emergencies.
Store LiFePO4 batteries at the correct temperature
Proper storage is also important if you want to take good care of your LiFePO4 battery.
Batteries may self-discharge during storage (<3% per month for LiFePO4), and high temperatures can reduce the capacity and performance of LiFePO4 batteries. Therefore, storing the battery at the proper ambient temperature will extend its life. The following is the recommended storage temperature range.
1 month: -20°C to 60°C
Three months: -20 °C to 45 °C
Six months: -20 °C to 25 °C