What is lithium iron phosphate battery?

Lithium iron phosphate batteries are different from lithium-ion batteries, which is a common misunderstanding. In reality, there are many types of lithium-ion batteries, and lithium phosphate battery is just one of them.

Let’s take a look at what is lithium iron phosphate, why it is ideal for certain types of batteries, and how it compares with other lithium-ion battery options.

Lithium iron phosphate is a compound LiFePO4 or “LFP” for short. LFP has good electrochemical performance and low resistance and is one of the safest and most stable cathode materials that can be used in lithium-ion batteries.

Lithium iron phosphate battery is a kind of lithium-ion battery that uses lithium iron phosphate as cathode material to store lithium ions. LFP batteries usually use graphite as the negative electrode material. The chemical composition of LFP batteries gives them a high-rated current, good thermal stability, and a long life cycle.

Most lithium-iron phosphate batteries have four battery cells connected in series. The nominal voltage of the LFP battery is 3.2 volts. Connecting four LFP batteries in series produces a 12-volt battery, which is an excellent alternative to many 12-volt lead-acid batteries.

Lithium Iron Phosphate VS. Alternative lithium ion type

Lithium iron phosphate is just one of many lithium-ion batteries. Changing the compound of the cathode can produce different kinds of lithium-ion batteries. Some of the most common choices are lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium nickel cobalt aluminum oxide (NCA), lithium nickel manganese cobalt oxide (NMC), and lithium titanate (LTO).

Each of these battery types has different advantages and disadvantages, making them very suitable for different applications. Looking at the main characteristics of these battery types, we can see the location of lithium phosphate batteries and which applications they are most suitable for.

Energy Density

Among other lithium-ion types, LFP batteries have one of the highest specific power ratings. In other words, the high specific power means that the LFP battery can provide a lot of current and power without overheating.

On the other hand, it is important to remember that LFP batteries have the lowest specific energy rating. Low specific energy means that the energy storage capacity per unit weight of LFP batteries is lower than other lithium-ion batteries. This is usually not a big problem, because the capacity of the battery pack can be increased by connecting multiple batteries in parallel. The applications require extremely high energy density in a very light space (such as pure electric vehicles), and this may not be ideal.

Battery life cycle

The life of a lithium iron phosphate battery starts from approximately 2,000 full discharge cycles and increases according to the depth of discharge. The battery cells and internal battery management system (BMS) used by Dragonfly Energy have been tested over 5,000 full discharge cycles while retaining 80% of the original battery capacity.

The life span of LFP is second only to lithium titanate. However, LTO batteries have historically been the most expensive lithium-ion battery option, which makes them too expensive for most applications.

Discharge rate

The discharge rate is measured by the multiple of the battery capacity, which means that the 1C discharge rate of a 100Ah battery is 100A continuous. Commercially available LFP batteries traditionally have a continuous discharge rating of 1C, but depending on the battery management system, this rating may be exceeded in a short time.

The LFP battery itself can usually safely provide a short 25C discharge. The ability to exceed 1C allows you to use LFP batteries in high-power applications that may have startup spikes in current consumption.

Operating temperature

The LFP battery will not enter a thermal runaway state until about 270 degrees Celsius. Compared with other common lithium-ion battery options, LFP batteries have the second-highest operating temperature limit.

Exceeding the temperature limit of the lithium-ion battery can cause damage, and may cause thermal runaway, which may cause a fire. The high operating limit of LFP significantly reduces the possibility of thermal runaway events. The combination of LFP and high-quality BMS can turn off the battery before these conditions (approximately 57 degrees Celsius), which has significant safety advantages.

Safety Advantage

The LFP battery is one of the stable chemical components in all lithium-ion options. This stability makes them one of the safest choices for consumer and industrial applications.

The only other relatively safe option is lithium titanate, which is usually too costly and cannot operate at the correct voltage to replace 12V in most cases.

Lithium Iron Phosphate vs. Lead-acid batteries

Compared with traditional lead-acid batteries, lithium phosphate batteries have many advantages. Most notably, the energy density of LFP batteries is approximately four times that of lead-acid batteries. You can deep cycle LFP batteries repeatedly without damaging them. They also charge faster than lead-acid batteries 5.

This high energy density can extend the operating time while reducing the weight of the battery system.

The chemical reaction inside the lead-acid battery will cause outgassing, which requires the user to exhaust the battery and add water regularly. If the battery is not stored upright, the acid solution may leak, which can damage the battery and cause confusion. Alternatively, LFP batteries will not vent, nor do they need to be vented or refilled. Even better, you can install them in any orientation.

LFP batteries were initially more expensive than lead-acid batteries. However, the long life of the LFP battery offsets its high upfront cost. In most cases, the service life of LFP batteries is 5-10 times longer than that of lead-acid batteries, resulting in significant overall cost savings.

The best lithium iron phosphate battery used to replace lead-acid battery applications

There are many different lithium-ion batteries to choose from, and some even exceed lithium-iron phosphate in certain performance categories. However, when replacing a 12-volt lead-acid battery, LFP is the best option available.

The main reason for this is that the nominal battery voltage of lithium iron phosphate is 3.2 volts. The nominal voltage of a 12-volt lead-acid battery is approximately 12.7 volts. Therefore, connecting four batteries in series inside the battery will produce 12.8 volts (4 x 3.2 = 12.8)-an almost perfect match! This is not possible with any other lithium-ion battery type.

In addition to almost perfect voltage matching, LFP also has other advantages as a lead-acid replacement. As mentioned above, LFP batteries have the characteristics of long-lasting, stable, safe, durable, lightweight, and high energy density. This makes them very suitable for many applications! Applications such as trolling motors, RVs, and golf carts have traditionally relied on lead-acid batteries.

Conclusion

In short, a lithium iron phosphate battery is just one of many different types of lithium-ion batteries. However, the unique characteristics that make up the LFP battery make it an excellent alternative to the 12-volt lead-acid battery in the past.