Lithium iron phosphate (LFP) batteries are cheaper to produce and more stable than traditional nickel-based chemistries. New research from a Tesla-funded lab has found that LFP batteries degrade faster when fully charged, and repeated charging at a high state of charge increases negative reactions within the pack.
Electric vehicles with lithium iron phosphate (LFP) batteries are becoming more popular around the world. Compared to traditional nickel manganese cobalt (NMC) batteries, LFP packs have the advantages of being cheaper to manufacture, lower fire risk, and longer lifespan. However, due to their lower energy density, automakers typically use LFP batteries in entry-level models such as the rear-wheel drive Tesla Model 3, the base Ford Mustang Mach-E, and the Dual Standard's second-generation Rivian R1S.
According to the automakers, it's best to charge your vehicle's LFP battery to 100% regularly — at least once a week for Tesla and once a month for Ford. This helps calibrate the pack so you can get a more accurate range reading in the gauge cluster every time you drive. They also recommend doing this to maintain the health of your battery and prevent degradation of performance.
CATL's new Shenxing Plus LFP battery claims to be able to add 372 miles of driving range in just 10 minutes.
This is the exact opposite of what happens with NMC packs found in most EVs, including long-range Teslas, where manufacturers recommend limiting daily charging to 80-90%. Charging to 100% can reduce the pack's energy retention capacity over time. This occurs primarily because battery life is negatively correlated with heat and voltage: the higher the state of charge, the higher the voltage and heat in the pack, accelerating degradation.
But a new study published this week in the Journal Of Electrochemical Society contradicts what automakers have said about LFP charging patterns. The study says that repeated charging cycles at high states of charge can damage LFP cells over time. The study identifies how this happens at the most detailed level, but kudos to YouTuber Jason Fenske of Engineering Explained for breaking it down for us.
The researchers found that when LFP batteries are kept fully charged, high voltage and heat can lead to the formation of harmful compounds within the pack. When the pack is cycled frequently — that is, repeatedly discharged and fully charged — these harmful compounds build up on the anode, consuming lithium and causing degradation. “Higher SoC leads to higher voltages, which accelerate the repeated negative reactions in the electrolyte and consume lithium reserves,” the authors wrote.
Ford and CATL are partnering to produce LFP battery cells in Michigan.
If you won't be driving your EV for long periods, it's helpful to leave the battery at a low state of charge; voltage decay won't do any harm in the long run. “Cycling near the upper charge limit (75-100% SoC) has a detrimental effect on LFP/graphite cells. Our results show that there is a correlation between the average SoC at which the battery operates and the rate of capacity fade, implying that a lower average SoC translates into a longer lifetime…,” the study states. “It is therefore important to minimize the time spent cycling at a high state of charge.”
One of the authors of the study is Dr. Jeff Dern, an award-winning battery researcher who runs the Tesla-funded Jeff Dern Research Group. Dern's lab is one of Tesla's lesser-known weapons that helped the brand master NMC chemistry. Electric Autonomy Canada toured the Tesla-funded lab at Canada's Dalhousie University last year. The media described the relationship between Tesla and the Dern Research Group as “a yin-yang dynamic: one side is a fast-moving, always-greedy business; the other is a slow-moving but hard-working academic lab.”
The entry-level 2024 Rivian R1S gets an LFP battery pack for the first time.
Still, there are some drawbacks. The study claims that 0-25% charging cycles will extend battery life, which seems meaningless in terms of everyday user convenience, especially if you don't have a charger at home or in the office and rely on public charging. The study focuses only on battery life, not the best overall charging method. It doesn't take into account specific use cases, convenience, charging times, or anything else that might be best for the broader range of EV buyers. So it's still wise to follow the car manufacturer's recommendations.
Having a larger charging capacity is an advantage in most cases, such as on road trips, when you need to charge your vehicle from home during a power outage, during winter when range loss accelerates, or if you just want peace of mind. What's more, modern batteries can last hundreds of thousands of miles even if you charge them incorrectly. This is one of the reasons why brands offer long warranties on their batteries. This does not make this research any less valuable, as it still accomplishes the very important task of discovering further aspects of a relatively new technology.
Best of all, the authors don't recommend changing charging habits: “How realistic is it to cycle battery cells only in the low SoC range? Clearly there is a trade-off between usable capacity and capacity retention… It is not realistic to recommend cycling LFP cells only between 0%-25% SoC, as it would be a waste of capacity.”
