Which chemistry is best for electrifying your vehicle?
Let's discover the different types of batteries
Composition and characteristics of lithium batteries with LCO chemistry:
Lithium-Cobalt-Oxide (LiCoO 2 )
Lithium batteries with LCO chemistry are the least recent, mainly used for electronic devices and mobile applications, and consist of a cobalt oxide cathode (positive electrode) and a graphite carbon anode (negative electrode).
The advantage of this chemistry is that it has a high specific energy and is perfect for medium-small batteries, that are able to perform well, so that they can be charged very quickly.
LCO batteries are in fact the most widely used for smartphones, digital cameras and portable laptops.
On the other hand, their use is mainly limited to applications that are not too large due to their safety limitations. They furthermore feature a rather low discharge current and this can lead them to overheat quickly under high loads.
They also contain a high proportion of cobalt, an expensive element that is difficult to find and associated with major ethical problems in extraction, and this is why an increasing number of manufacturers are now trying to do without it or limit its use as much as possible.
Composition and characteristics of lithium batteries with LMO chemistry:
Lithium-Manganese-Oxide (LiMn 2 O 4 )
Lithium batteries with LMO chemistry perform very similarly to those using LCO technology. They are widely used in small devices such as power tools.
The main characteristic of LMO batteries is their ability to provide much energy in a short time. LMN batteries consist of a manganese oxide cathode and a graphite anode.
They are often used for electric bikes, in gardening, medical equipment and power tools such as drills and screwdrivers.
LMO batteries have a higher thermal stability than batteries with LCO chemistry, but are limited by their capacity, which is lower than cobalt-based systems.
Composition and characteristics of lithium batteries with LFP chemistry:
Lithium – Iron – Phosphate (LiFePO4)
LFP chemistry responds best of all to the specific needs of the industrial sector, where excessive specific energy is not required, but where there is a need for very high safety and long life cycles. So we are talking about a very wide world, ranging from automation, robotics, logistics, construction, agriculture, boating, electric vehicles, to airport vehicles, aerial platforms and special vehicle In fact, batteries with LFP chemistry are the safest and most stable on the market today, and are available in large-capacity formats, as required by industrial systems, without the need to connect many small cells in parallel, which would lower their stability and compromise the safety of the vehicle. The life cycles in a battery with LFP chemistry today exceed 3,500 cycles and, if equipped with a good BMS system, can easily exceed 4,000, and in the future even more than 6,000 cycles may be expected.But we must be careful, when we talk about “life cycles” we must not think that after 3,500 cycles a battery is completely exhausted. In fact, it is important to remember that the end-of-life of a battery on a vehicle is always considered to be 80% capacity remaining, but there will still be plenty of possibilities for use in other areas, such as energy storage. Another advantage of LFP chemistry, besides its inherent safety and high life cycles, is that it has a flat discharge curve. In the image below, the curve tends to rise. This is the so-called charging curve, while the descending curves refer to the battery voltage during discharge. The voltage range from 100 % to 0 % is therefore very similar, and this is a fundamental fact, as it allows machines and industrial vehicles to guarantee the same performance from the beginning to the end of the discharge.
Lithium LFP Chemistry Discharg Curve
On the other hand, this advantage can also turn into a disadvantage, as, due to the flat curve, reading only the voltages will make it more complicated to determine a correct SOC (state of charge).
To avoid this limitation, the BMS system managing the battery will have to be designed in a smart way to provide the correct State of Charge and perform the balancing functions in the best possible way.
One of the many advantages of this chemistry is the total absence of cobalt, a material which, as we have already mentioned, is toxic, one of the most impactful for the environment.
Many lithium battery manufacturers are currently trying to reduce the percentage of cobalt in their batteries, so the LFP chemistry, being cobalt-free, starts with a big advantage.
Although only a few years ago, LFP batteries seemed to have been destined to be forgotten, as their energy density was very low, at around 100 Wh/Kg, today this technology
has literally re-emerged from the ashes with a very significant increase in energy density, reaching 170 Wh/Kg in a short time, prompting strong interest from the automotive world.
Further increases in gravimetric density to 220/230 Wh/Kg are already expected in the coming years.This is exactly why many car manufacturers have decided to reintroduce LFP chemistry for the electrification of their vehicles, first and foremost Tesla, which is currently using it in its “standard range”
vehicles as it guarantees a better level of safety, at a slightly lower cost than the NMC chemistry used for high-performance vehicles. Like Tesla, also BYD, Volkswagen and many other major automotive manufacturers now see great potential in LFP chemistry.
Composition and characteristics of lithium batteries with NMC chemistry:
Nickel – Manganese – Cobalt (LiNixMnyCozO2)
To date, batteries with NMC chemistry remain the most frequently used in the automotive sector.
With this chemistry, a very high specific energy of up to 220 – 240 Wh/kg can be achieved. This is clearly a decisive competitive advantage for a car, as it allows a large amount of energy to be stored with a low weight and volume,
allowing more energy to be installed in the vehicle than other lithium-based technologies.
There are various types of NMC chemistry:
NMC 111 (Nickel 33.3% – Manganese 33.3% – Cobalt 33.3%)
NMC 622 (Nickel 60% – Manganese 20% – Cobalt 20%)
NMC 811 (Nickel 80% – Manganese 10% – Cobalt 10%)
Composition and characteristics of lithium batteries with NCA chemistry:
Nickel – Cobalt – Aluminum (LiNiCoAIO2)
Batteries with NCA chemistry are also used in the automotive sector alongside with NMC batteries. Their safety rating is slightly lower than that of NMCs, but at the same time they have a very high energy density, reaching 250-300 Wh/Kg. The NCA The cell structure is very similar to that of the NMC 811, with a high nickel content and a low cobalt and aluminum content. Due to their high energy storage capacity, NCA lithium batteries are often used in blends with NMC chemistries to achieve a compromise between energy density, safety and stability.
Composition and characteristics of lithium batteries with LTO chemistry
Lithium titanate (Li4Ti5O12)
It is a chemistry that is still little mentioned, but it appears to be very promising in terms of life cycles, as its low internal voltages and lack of mechanical stress allow it to degrade very little, easily reaching 15,000 to 20,000 use of this cycles. Particular advantage, it could be used for the electrification of cars and vehicles subject to very heavy use, but at present it still carries some problems that limit its use and diffusion.
Its weak points are 2:
The low energy density (177Wh/l) and gravimetric density (60-70 Wh/Kg) as well as a lower nominal voltage of 2.4 V or 2.8 V: this means that more cells will be needed in series to achieve the desired battery voltage .
Its currently very high cost which is reflected in a low number of global LTO cell manufacturers, this probably due to the current low volumes demanded by the market
Its advantages, on the other hand, include not only its long service life, but also its wide temperature range, and its excellent susceptibility to high-power charging and discharging, i.e. high C-Rate (ratio of current to rated capacity).
The ideal use of LTO technology are heavy-duty applications such as AGVs (automated guided vehicles): imagine fleets of self-driving forklift trucks working 24/7, which also take advantage of fast charging to reduce downtime and consequently increase plant efficiency.
From Theory to Practice: Using the Right Lithium Chemistry for Every Application
We have outlined the 6 main types of lithium-based chemistry that are currently most widely used in the various electrification areas. But we must not think that these chemistries are in competition with each other, quite the contrary! They are all valuable and high-performing, but each lithium chemical works best in different areas of use.
This diagram shows a comparison of the various characteristics of the chemistries in terms of:
● Specific Energy or Gravimetric Density [Wh/Kg]: is the ratio of the amount of energy contained (Wh = V x Ah) to the weight of the battery.
● Safety: which is closely related to thermal stability because intrinsic safety depends very much on how thermally stable the components are
● C- Rate: charge/discharge rate, i.e. the ratio between the charge or discharge current (A) and the nominal capacity of the cell (Ah). This is a parameter closely linked to the cell’s ability to generate power.
● Life cycle: Number of times the cell can be discharged and charged until the end of life is reached, normally considered when 80% residual capacity is reached.
LFP and LTO batteries for the industrial sector
In industry, agriculture, or even for the electrification of special vehicles, especially if it is about highly cyclic applications that put stress on the battery, it is better to use chemistries such as LFP and LTO, where service life, reliability and safety are the most important requirements.
In the industrial world, therefore, the issue of space is less of a constraint, just as it is not essential to have excessive performance or energy density. When evaluating the choice of the right chemistry, the more important factor of safety therefore comes into play, an aspect that few people want to, and can, compromise on.
It is better to have a battery that is slightly bulkier, but provides optimum safety and has a significantly longer service life. There are vehicles, such as LGVs and AGVs which are required to be used intensively and work incessantly around the clock, as a result, their batteries will even do 3 or 4 charging cycles in a single day. The LFP chemistry will therefore easily support them with its more than 4,000 recharge cycles. If batteries for stationary storage are necessary, then energy density would mean almost nothing, and, on the contrary, battery cost and life cycles would be the elements behind the choice of the chemistry. LFP chemistry would then find its place.