Over the last twenty years, batteries based on Lithium-Ion (Li-ion) chemistries have become the leading choice for numerous rechargeable applications ranging from smartphones to electric vehicles. But not all Li-ion batteries are equal. And when it comes to an environmentally-friendly, green solution, the LiFePO (LFP) battery stands to be the clear winner.
Why Li-ion versus other rechargeable battery chemistries such as Nickel-Metal Hydride (NiMH) or the venerable lead-acid? With an atomic number of 3, lithium is the lightest metal. It offers the greatest electrochemical potential and provides the largest specific energy per weight—both huge advantages for a battery. Unfortunately, metallic lithium is also unstable, flammable, and potentially explosive when exposed to air or water. Consequently, researchers have concentrated for years on batteries based around more stable lithium compounds.
The primary components of a rechargeable Li-ion battery cell are a positive electrode (cathode), a negative electrode (anode), and an electrolyte. The cathode consists of an intercalated lithium compound –i.e., one with layered structure that allows for the reversible inclusion or insertion of a lithium ion during charging or discharging. There are several common cathode compounds with differing characteristics. The anode is commonly made of graphite.
The liquid electrolyte consists of lithium salts in an organic solvent such as ethylene carbonate or dimethyl carbonate. During operation, lithium ions move from the anode to the cathode during discharging, and in the reverse direction during charging. A lithium polymer (LiPo) battery uses a polymer gel as the electrolyte.
Lithium-ion has a nominal cell voltage of 3.6V, higher than NiMH (1.5 V) and lead-acid (2.0 V). As a result, fewer cells have to be stacked in series to produce high voltages for applications such as EV traction motors.
LFP – the best choice for the planet
As its name implies, the LFP battery uses a lithium-ion-derived chemistry and shares many advantages and disadvantages with other types of lithium-ion batteries. All Li-ion batteries use energy during manufacturing and require the mining of lithium and other key ingredients. However, when it comes to the health of the planet, there are significant differences between them.
Commonly used cathodes such as lithium nickel manganese cobalt oxide ("NMC") or lithium cobalt oxide LiCoO2 require materials, nickel, and cobalt, that are both supply-constrained and expensive. Human rights concerns persist around cobalt mining, such as mine safety and the use of child labor. Environmental issues associated with nickel mining include greenhouse gas emissions, habitat destruction, and contamination of air, water, and soil.
The LFP battery uses Lithium Iron Phosphate (LiFePO4) as the cathode, paired with an anode made from graphite with a metallic backing. The LFP cathode uses low-cost, non-toxic materials – iron and phosphate – that are abundant and low cost.
Green applications for LiFePO4 batteries
Applications for Li-ion batteries include backup power and UPS; consumer devices such as smartphones and laptops; electric vehicles; and energy storage.
In some applications - electric vehicles, for example – NMC batteries are preferred due to their higher energy density that translates into greater range for a given size, a key requirement in the space-constrained environment of an EV.
In energy storage, the fastest-growing need is for balancing supply and demand supply in green power applications such as wind or solar that generate electricity with minimal carbon emissions.
Solar and wind power adoption is growing rapidly. According to green energy researcher BNEF, the price of solar PV modules has dropped by 89% from 2010 to 2019 and should decline by another 34% by 2030. The result has been a large increase in both residential and utility-scale solar installations. Similarly, wind energy prices have fallen by 70% in the last decade. But the wind doesn’t always blow and the sun doesn’t always shine, so PV and wind installations rely on energy storage systems to provide a consistent source of electrical power.
Energy density isn’t the overwhelming concern for designers of energy storage systems. Instead, they focus on other factors, such as long-term battery degradation that depends on multiple factors including temperature, state-of-charge, and load profile. Other important factors include the need for periodic maintenance as many solar and wind installations are in remote locations and left unattended for extended periods.
LFP batteries have several advantages over lead-acid batteries or other lithium battery technologies for energy storage. Compared to lead-acid batteries, they are inherently stable and non-combustible, and free from outgassing, fumes, and leaks. Their life span is up to ten times that of lead-acid batteries, giving a lower total cost of ownership (TCO).
Fire risk is another key concern, especially in residential PV installations. Well-publicized incidents such as the Boeing Dreamliner fires and images of melted EVs have raised public awareness of Li-ion battery fires caused by thermal runaway. Compared to other Li-ion battery chemistries such as NMC, the LFP thermal runaway tolerance is increased by over 100°F, resulting in major safety differences between the two chemistries. An NMC battery is significantly more likely to catch fire compared to LFP. Likewise, under normal operating conditions, LFP will maintain a more stable internal temperature when constantly cycling. As a result, LFP chemistry is ideal for residential solar power storage.
Ease of recycling
The disposal or recycling of batteries remains a key environmental issue. More than 3 million tons of lead-acid batteries are discarded every year. While some are safely recycled to recover lead and other materials, many end up in landfills, especially in developing countries, and toxins can cause fires and explosions and poison food and water supplies for generations.
The long lifetimes of lithium batteries used for energy storage and transportation mean that many of these batteries are still in use, so recycling processes are still in their infancy. Only 50% of the 180,000 metric tons of Li-ion batteries available for recycling in 2019 were recycled, with the rest being discarded. As more Li-ion batteries reach end-of-life, recycling will become more efficient.
Regardless of type, Li-ion batteries can be recycled to recover the materials used in their electrodes, wiring, and casings. Recycled batteries will become more widely accessible as the industry matures. With electrodes made of non-toxic materials, LiFePO4 batteries pose far less risk to the environment than either lead-acid batteries or other Li-ion chemistries.
Conclusion: LFP is the green choice in batteries
Manufacturing batteries of any kind requires energy and resources, but lithium iron phosphate batteries have several advantages over other technologies in terms of resource consumption and safety. They have great potential to help reduce carbon emissions when used in wind and solar power systems.