When considering a new battery for your home energy storage system, naturally you want the best value for your money, the best performing solution, and the most sustainable one. LFP batteries seem to gather all these points. Here I explore these topics so that you can make an informed choice.
What makes LFP batteries so special?
LFP stands for Lithium-Iron-Phosphate, a type of active material that cedes and takes Li-ions during the battery charging/discharging process. This material is made from widely abundant minerals, which significantly lowers the cost of the system compared to other battery chemistries. But that is not the only advantage of LFP. This material is also non-toxic and quite stable compared to other Li-ion counterparts, making it inherently safer.
To me, it all comes from the LFP crystalline structure. This is the way atoms are arranged within the material, with channels that allow for the Li-ions to move without a significant distortion of the structure. Similar to when you are trying to move through a tunnel; if you occupy a volume smaller than the tunnel opening, you can move freely through it. The ionic size of Li+ is ~76 pm, and that of Fe2+ is ~78 pm (which sets the available size of the intercalation spaces within the crystalline structure, or the tunnel size in our analogy). In this case, the channels are just big enough for the Li-ions to move (the driving mechanism being of electro-chemical nature), yet continuous advances in the understanding of the Li migration mechanisms coupled with improvements in manufacturing technologies and engineering of the materials allow its good performance. At the same time, the Li intercalation channels within the structure are somewhat fixed, meaning that the process of extraction and insertion of Li-ions will not result in the collapse of the structure or in significant volumetric distortions, or in additional chemical reactions (other than Li migration). While that is a bit too physics focused, it is fundamentally what differentiates LFPs from other Li-ion batteries (LIBs).
Let’s now discuss performance
LIBs are widely used because of their great energy density properties (~200-270 Wh/kg). For comparison, lead-acid batteries exhibit less than 100 Wh/kg; and nickel metal hydride reach slightly over 100 Wh/kg. The higher the energy density the longer the batteries would perform (runtime), and the higher the capacity of the battery. Higher energy density is desirable not only in terms of available energy, but also because it implies a smaller footprint in terms of volume and weight. Hence systems can be designed to be smaller and lighter, without compromising their power performance. Another commonly used metric is the power density, which is the power the battery can deliver with respect to its mass. High power density is desirable for fast-charging applications; and when a large power demand exists over a small period of time, such as for powering critical systems during grid-power outages. LFPs in particular exhibit an energy density ranging from around 135 to 190 Wh/kg; and a power density between 200 to 450 W/kg, and while the former is certainly mid-range within LIB technologies, LFP batteries have the longest lifespan offered by LIBs, with around 6500 to 8000 cycles. This is certainly a trade-off to consider because replacements will not be necessary for around 17-21 years (considering an “ideal” operation of 1 cycle/day, typical of systems charging during the day using solar panels and discharging during the evening/night), giving the best value for the investment in the long term. Notice the highlight of “ideal” operation. In reality, this operation may change, and also environmental conditions and battery use will impact the battery calendar life. So, strictly speaking that time is reduced, and it is a phenomenon common to all batteries.
Back to my thoughts on the LFP crystalline structure; while other LIB cathode materials also exhibit intercalation spaces for the Li-ions to move through, unlike other cathode chemistries LFP has a bridged ordered 3-dimensional (3D) structure. That is, the tunnels are actually stable (not changing) within the 3D framework. Cathode materials used in other battery chemistries have either a layered structure or a 3D framework prone to significant distortions with the charging and discharging cycles (similar to a sponge that swells when moistened and shrinks when dried, but to a smaller extent), resulting in degradation of the materials and a limited lifespan. Nevertheless, advances in materials engineering and processing help mitigate this degradation, and better performance can be expected in future developments for all Li-ion chemistries as it is an area of active research.
The follow up question would be, why are other Li-ion chemistries used then? – The reason is, they exhibit the highest energy density available today, and depending on the application a smaller footprint becomes critical. For example, the energy density of NMC is roughly 30% higher than that of LFP. While this may not be a concern when accommodating an energy storage system in traditionally ample single-family homes; a smaller footprint may be preferred for apartments in densely populated cities, or multiple-storey buildings. Similarly, data centers (with hundreds of backup battery systems), generally prefer chemistries that take less space. It should also be noted that aside from controlling the properties at the materials level; all LIBs incorporate a battery management system (BMS), engineered to ensure a safe operation and maximize the battery performance and lifespan.
Beyond Li-ion chemistries, as more demanding applications are being considered, novel battery materials and combinations emerge, evincing a fast-evolving space with continuous improvement. Some of these include nickel-zinc, sodium-ion and solid-state batteries, that optimize for specific performance parameters. Nickel-zinc is known for its outstanding safety properties and high power density; while Na-ion for its high availability and low cost. Solid-state batteries, on the other hand belong to a different category, where the electrolyte is a solid (as opposed to all other mentioned examples); and although still at the research stage, have the potential to revolutionize the battery field.
Speaking about battery sustainability
There are many sustainability angles to consider for LIBs. As with any commercial product, resources are involved in the manufacturing of LIBs as well as in their use. During the fabrication process, minerals, metals, water, and energy are invested and waste products generated. In the use phase, resources are needed for the correct operation of the system, including maintenance and/or replacement of parts. End-of-life is the final stage where the component is removed from operation and refurbished, recycled, or disposed of. The good news with LIBs is that increasingly there are more efforts in these areas, with an emphasis in a circular economy. I.e. the refurbishment and recycling aspects are now part of the battery design stage, maximizing the utilization of the materials and lowering the environmental impact.
The main environmental impact categories applicable to batteries are: global warming potential (measured in kgCO2 equivalent and commonly known as carbon footprint); mineral and fossil resource depletion; water use; and freshwater ecotoxicity. The quantification of the impact in these categories is determined using life cycle analysis (LCA) standards and protocols; yet, particular conditions of the supply chain, manufacturing processes, and practices can make significant variations to the environmental impact of similar/equivalent batteries. Leading vendors and battery manufacturers understand the importance of sustainability and are starting to incorporate environmental product declarations (EPDs) in their products specifications. At a minimum, EPDs cover acidification, eutrophication, global warming, ozone depletion, and smog formation categories.
Comparatively speaking, considering the CO2 emissions from battery production, LFP batteries have lower CO2 emissions than any nickel containing Li-ion chemistry, stemming from LFPs lower energy use for production and a longer battery lifespan. Additionally, the global distribution of iron and phosphorous is somewhat homogeneous, favoring local supply chains and reducing the emissions associated with precursors transportation. Also regarding metal depletion, particulate matter formation, and terrestrial acidification, LFP batteries have lower environmental impact than NMC and NCA based Li-ion batteries.
Regarding recycling, globally, increasing efforts to establish robust and circular recycling systems are being sought, mainly from the great volume of expected discarded EV batteries from the transportation sector, and the need to secure supply chains for critical materials such as those used in batteries. Up to today recycling of LIB focused on high nickel and cobalt chemistries, mainly due to the high value of recovered materials and incentives. This however is expected to change to include LFPs, since the massive adoption of this type of battery for EVs will result in a significant number of retiring batteries in the next decade or two. Stay tuned, as we are preparing a white paper on Recycling and Circularity of LIBs, where we discuss more in depth the current and future trends, as well as the business opportunities in this field.
In addition to these, social impact is a perspective receiving increasingly more attention from consumers and regulatory bodies. Examples of this are the recently adopted European Battery Directive and the German Supply Chain Act, holding companies accountable for protecting the human rights in their supply chains. Regarding social impact, LFP has the advantage of not using cobalt (considered as conflict mineral); nevertheless, almost all LIBs share a similar score, underlying the importance of careful supplier selection and on-site investigations.
Li-ion batteries are by now a mature technology, yet it is an area of continuous research and improvement making the technology even more promising. The current performance of LFP batteries is superior compared to other battery technologies (lead-acid and nickel metal hydride) and even to alternative Li-ion chemistries if we consider the lifespan, non-toxicity, and overall safety aspects. Moreover, from a sustainability perspective, these factors lower the environmental impact of LFPs. Altogether, these are good reasons to welcome LFP batteries into your home.