What are the technology improvements of the 4th generation of lithium iron phosphate (LFP) batteries, and what do they mean for battery energy storage system (BESS) applications?
What are the 4th generation LFP batteries?
LFP batteries have been gaining a larger share of BESS and EV markets because of their safety, longevity and low cost compared to nickel manganese cobalt (NMC) batteries. The trade-off is that they have a lower energy density compared to NMC batteries, but as the generations of LFP have evolved, their energy density has increased and continued to get closer to that of NMC. The energy density improvements over the generations have not come from changing the underlying LiFePO₄ crystal but rather from improving the compaction density of the electrodes.
The lower energy density of LFP over the years has been attributed to a lower material density and, therefore, a lower compaction density. That has continued to improve over the generations, with compaction density the defining factor separating different generations of LFP batteries.
The compaction density is the amount of material that can be packed within a given electrode volume. Increasing the compaction density, and packing the active material more tightly, is the main way to improve the gravimetric and volumetric energy density of a battery without changing the chemistry of the cell.
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The 4th generation of LFP is now starting to hit the market. A higher compaction density allows more material to be loaded in a given volume and gives the battery a higher capacity (due to having a higher volumetric energy density). Each generation is defined by a certain compaction density threshold, and for 4th generation LFP batteries it is a compaction density of 2.6g/cm3 and above.
How 4th generation LFP batteries differ to other generation LFP batteries
The main difference between the different generations is the powder compaction density of the electrodes and there are defined boundaries. These boundaries are:
- Generation 2: 2.4g/cm³
- Generation 3: 2.5g/cm³
- Generation 4: 2.6g/cm³
- Generation 5: 2.7g/cm³
This also translates to an electrode compaction density of 2.65g/cm³ and a cell energy density 180-200Wh/kg for 3rd generation LFP batteries. For 4th generation batteries, they have an electrode compaction density of 2.8g/cm³ and a cell energy density around 200-205Wh/kg. There are also some that reports of a transitional generation―and LFP 4.5 generation―with a powder compaction density of 2.65g/cm³.
Over the years, each new generation has brought different features to the battery. Generation 2 LFP focused on the commercialisation of the LiFePO₄ crystal for ensuring a high safety and cost. Generation 3 LFP focused on achieving a better particle distribution in the electrodes and was the first major step towards increasing the powder density, electrode density and cell energy density.
Generation 4 LFP is where there are bigger changes due to the reduced inactive space inside the cathode pushing the cell energy density closer to NMC. Generation 4 LFP batteries are also able to overcome the usual ion-transport penalties of high compaction and can fast charge up to 4C. One of the biggest practical changes between the 3rd and 4th generation is that they have gone from a simpler to a more complex production. The other market change is that 3rd generation batteries were more mass-market battery but 4th generation LFP batteries are currently higher-end products.
What has changed in the architecture of the batteries?
First off, there is a change in particle architecture within the cathode, not crystal structure. Particle grading technology is used to engineer the distribution of particle sizes so that smaller particles can fill in the gaps between the larger particles in the electrode. This increases the packing density without needing to break up particles or change their surface properties.
The second major change is the use of a different precursor synthesis route. Other generations use an iron phosphate route whereas the 4th generation favours a ferrous oxalate synthesis route as it produces a more uniform particle size distribution and greater compaction density. However, this synthesis route is more demanding and less robust than the iron phosphate route.
Achieving the higher compaction density in 4th generation LFP batteries does require higher purity lithium, iron and phosphate materials, as well as tighter process controls to ensure a precise particle-size control and uniform carbon coating. Increasing the compaction density also reduces the surface area between the electrode and electrolyte which slows ion transport, leading to a lower voltage and discharge energy. This is where some of the manufacturing complexity comes in because more electrode engineering takes place to ensure that the ionic pathways remain efficient when changing the pore architecture of the electrodes.
What 4th generation LFP batteries means for energy storage system (ESS) use cases
For EVs, LFP’s fast-charging capabilities had to be traded-off against energy density, but the high compaction density gives the best of both and pushes the energy density of LFP batteries into the mid-range of NMC batteries. But the benefit is not just limited to EVs. The extra energy density, particularly the volumetric energy density, is a benefit to BESS.
BESS are housed in shipping containers, and you can only put so many cells inside the containers. The added safety and long cycle life is already a benefit for BESS applications but by increasing the compaction density of the cathode, and in turn the volumetric energy density, a higher capacity can be stored within the same BESS footprint. A higher volumetric density is achieved because removing the inter-particle voids and replacing them with more active material particles increases the active material mass per unit volume.
As well as packing more energy into the same footprint, higher energy density reduces the relative amount of balance of plant (BOP) equipment and cabling needed, reducing cost.
While increasing the compaction density can reduce the internal cell resistance because the contact area between the particles increases (leading to an increase in conductive channels and impedance reduction), there are some downsides such as a lower ion movement and reduced discharge energy. However, unlike EVs which need a high discharge output, BESS are often discharged much slower, so slower discharge is not as big of an issue for BESS as it is other applications.
So, overall, the higher the compaction density, the higher the volumetric energy density, and therefore the higher capacity per unit area of BESS. It is a critical way to increase capacity without increasing the footprint, and this is where 4th-generation LFP cells and beyond could excel for BESS applications. By integrating more energy-dense cells, the number of required containers at GWh-scale utility sites can be reduced and/or more capacity can be installed in the same space, which could help with both higher capacities for installations that need them and overbuilding some BESS installations.
The reduced footprint also means that more BESS could be installed in commercial and urban areas where large-scale container installations wouldn’t fit due to space constraints or would face opposition due to their size.
Looking towards 5th generation LFP batteries
The manufacturing complexity associated with increasing the compaction density while simultaneously using tighter process controls to ensure a high performance and cell energy density means that there are fewer companies producing 4th generation LFP batteries.
However, while the supply chain is still limited for the 4th generation, companies are already looking towards the production and supply of 5th generation LFP batteries, with a few Chinese companies already moved towards commercial mass production of 5th generation batteries.
The generation 5 LFP batteries follow the same +0.05–0.10g/cm³ step pattern for each generation and require a compaction density of at least 2.70g/cm³. It should be no surprise to hear that CATL, BYD and Gotion High-Tech are the companies at the forefront of 5th generation LFP manufacturing. Currently the generation 5 batteries being developed have an energy density around 205Wh/kg. This has been confirmed by both Gotion and CATL (Shenxing PLUS battery).
The generation 5 LFP batteries will use the same practical gradation technology as the 4th generation but tuned to a higher compaction density target. So, unlike the generation 3 to 4 transition which was a marked difference in approach, fabricating generation 5 batteries are this time utilising the lessons learned from generation 4 batteries and pushing the capabilities further.
Even though generation 5 LFP batteries are starting to be made, they face even more difficult supply chain challenges than generation 4 LFP batteries. There are a lot fewer companies at the generation 5 stage, so the supply chain isn’t as robust. It’s been confirmed that a lot of the cathode materials in the generation 4 LFP batteries are going to be supplied by Fulin Precision but there has not been disclosure as of yet for the generation 5 LFP batteries.
