Tesla recently revealed that it intends to use lithium iron phosphate (LFP) batteries in its standard range vehicles. What are the functions of LFP batteries on lithium-ion batteries?
While lithium iron phosphate (LFP) batteries have been put on hold to support lithium-ion batteries before, this may be changing for electric vehicle manufacturers. Tesla's third quarter 2021 report announced that the company plans to transition to LFP batteries in all its standard range vehicles. The news of
reflects a larger trend of lithium iron phosphate batteries becoming increasingly popular in next-generation electric vehicles (EVs).
What is LFP battery?
LFP batteries use lithium iron phosphate (LiFePO4) as the cathode material, and graphite carbon electrode and metal backing are used as the anode. Unlike many positive electrode materials, LFP is a polyanionic compound composed of more than one negatively charged element. Compared with the two-dimensional plates of nickel manganese and cobalt, its atoms are arranged in crystal structures to form a 3D network of lithium ions.
LFP battery architecture. Image provided by Rebel Batteries
LFP batteries work similarly to other lithium-ion (Li-ion) batteries, moving between the positive and negative electrodes for charging and discharging. However, phosphate is a non-toxic material compared to cobalt oxide or manganese oxide. More importantly, LFP batteries are able to provide a constant voltage over a higher charge cycle of 2,000–3,000 times. What is the role of
battery management system in LFP batteries?
LFP batteries are not just made up of connected batteries; they include a system that ensures that the battery remains within a safe range. Battery Management System (BMS) protects, controls and monitors batteries under all operating conditions to ensure safety and extends battery life.
chart illustrates how charging indicators affect the life of the battery. Image from Illogicdictates and Wikimedia Commons[CC BY-SA 4.0]
Although lithium iron phosphate batteries are more tolerant than alternatives, they are still affected by overvoltage during charging, which reduces performance. The cathode material can also oxidize and become less stable. BMS is used to limit each battery and ensure that the battery itself remains at maximum voltage.
As the electrode material decomposes, undervoltage is a problem. If any battery power drops too low, the BMS can disconnect the battery from the circuit. It will also serve as a backup for overcurrent conditions and shut down the operation when a short circuit occurs.
Why is LFP batteries an ideal alternative to lithium-ion batteries?
lithium iron phosphate batteries have lower energy density than alternatives to lithium cobalt oxide (LiCoO2) and have a lower operating voltage. Despite these challenges, there is no denying the advantages of LFP batteries in electric vehicles.
Low cost and low impact
LFP is well known for its low cost and is estimated to be 70% lower per kilogram than nickel-rich NMC. The cost advantage comes from its chemical composition. Iron and phosphorus are exploited on a large scale worldwide and are widely used in many industries.
In 2020, the minimum reported battery price for LFP batteries reached below USD 100/kWh for the first time. LFP batteries also have less environmental impact; they contain no nickel or cobalt, and they are limited in supply, expensive and have a greater impact on the environment.
well-defined performance
LFP The life cycle of a battery is longer than that of other lithium-ion batteries because the battery's capacity loss is slower. Their lower operating voltage also means that the battery is less prone to capacity-affecting reactions.
several LFP batteries are connected in series and parallel. Image from Yo-Co-Man and Wikimedia Commons[CC BY-SA 4.0]
With consistent discharge voltage and lower internal resistance, LFP-driven vehicles can deliver power faster and achieve higher charging/discharge efficiency.
improves safety and stability
LFP has thermal stability and chemical stability, so it is not easy to explode or fire due to misuse or structural damage. In lithium cobalt oxide batteries, thermal runaway may be caused by the lack of cobalt with a negative temperature coefficient.
It is said that LFP has one-sixth of the heat that is nickel-rich NMC.The Co-O bonds in LFP cells are also stronger, so if short-circuit or overheat, the oxygen atoms will be released more slowly. More importantly, there is no lithium residue in fully charged batteries, and they are highly resistant to oxygen loss compared to the typical exothermic reactions of other lithium batteries.
Notes on large-scale adoption of LFP
Although lithium iron phosphate batteries are cheaper and more stable than alternatives, a key factor hindering large-scale adoption is energy density. The energy density of LFP batteries is much lower than that of alternatives, between 15% and 25%. However, with thicker electrodes, such as those used in Model 3 made in Shanghai, this situation begins to change, providing an energy density of 359Wh/L.
Because of the long life cycle of LFP batteries, after about a year of ownership, they actually have a larger capacity than lithium-ion batteries with similar weight. This means that over time, the energy density of these batteries becomes more comparable. Another obstacle to large-scale adoption of
is that a series of LFP patents have allowed China to dominate the market. With these patents expiration, it was suggested that LFP production would be localized along with vehicle manufacturing.
Major automakers such as Ford, Volkswagen and Tesla are increasingly leveraging the technology and replacing nickel or cobalt formulas. Tesla's recent announcement in its quarterly update is just the beginning. Tesla also briefly updated its 4680 battery pack, which will be able to provide greater energy density and range. Some speculate that Tesla will use a "battery-to-battery pack" structure to stuff more batteries and compensate for lower energy density.
Tesla recently said it will convert Model 3 EV to LFP battery. Image courtesy of Tesla
Although it is an outdated technology, LFP and its associated battery cost reduction may be the basis for accelerating the adoption of large-scale EVs. By 2023, the price of lithium-ion batteries is expected to be close to $100/kWh. LFP may make automakers pay more attention to factors such as convenience or charging time than just price.
