Comparing Lithium iron phosphate vs lithium ion battery is a very smart thing to do prior to deciding which of these battery chemistries to use.
They have some major differences.
One of them is way safer. The other way more energy dense.
That’s just the sneak peek.
In this article, you are going to learn in-depth differences between LiFePO4 and Li-ion cells. We will take a look at everything from current discharge rate to different chemistry compositions, use case scenarios, energy densities and a bunch of other battery features.
There is no perfect battery. However, knowing the features of the battery chemistry helps you make a way better decision when picking the cell for your device or a DIY project.
Now let’s first see a quick overview and then proceed to see an in-depth analysis with graphs that I drew up for you.
LiFePO4 vs Li-ion Comparison
Let’s first start off by defining the Li-ion in this case.
When we normally talk about a lithium ion battery what we are referring to is a battery with a graphite anode and a lithium manganese oxide or lithium cobalt oxide cathode or a combination between these elements with the addition of nickel and silicon. Your typical li-ions like 18650 cells or phone batteries and etc.
However, there are many Li-ion batteries. The LiFePO4 is also a Li-ion battery because it is a type of lithium-ion battery. So keep in mind that while we are comparing a Li-ion in a general sense as described above, we can’t talk about other lithium-ion battery types like Lithium Nickel Cobalt Aluminum Oxide or any other specialized type.
LiFePO4 also has a graphite anode but the cathode consists of iron phosphate. Now let’s have that quick overview shall we?
A quick overview of the differences
- Higher energy density
- Higher voltage – 3.6-3.7 nominal voltage and 4.2V maximum voltage
- Can have a high discharge rate
- 500-1000 life cycle
- 0.7-1C Typical charge rate
- Lower self-discharge
- Doesn’t tolerate 100% depth of discharge
- Contains Cobalt, Nickel, Manganese, Silicon this doesn’t make it very environmentally friendly
- Can combust, explode and catch fire
- Lower energy density
- Lower voltage – 3.2v nominal voltage and 3.65V maximum voltage
- Can have a high discharge rate
- 2000-10000+ life cycle depending on circumstances
- 1C Typical charge rate
- A bit higher self-discharge
- Tolerates well 100% depth of discharge
- Doesn’t contain expensive or environmentally dangerous metals
- Almost completely safe and free of combustion
There is a lot more to be said. These were just some general differences for a short overview.
Now let’s proceed to in depth Li-ion vs LiFePO4 battery comparison.
The Li-ion battery has an exceptionally good energy density. It is one of the most energy dense batteries in use today and it beats the LiFePO4s significantly.
Since there are a couple of types of lithium ions available today it is worth noting that the Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2) batteries achieve the best results when it comes to energy density and a lot of other factors as well.
If we take a look at a Sony VTC6 18650 cell that utilizes the NMC or LiNiMnCoO2 we will see a high energy capacity of 3000mAh coupled with a very good discharge rate of 15A. More on this soon.
LiFePO4 batteries have lower energy density than li-ion which means that you would need a physically bigger battery in order to have the same energy amount as with the Li-ions.
CDR – Continuous discharge rate
The LiFePO4 battery takes the lead in the continuous discharge rate race but this is not necessarily the case.
However, if we are comparing maximum capabilities when it comes to the high current drain then the lithium iron phosphate cells can be made to achieve better results. It is just that you should be diligent when buying batteries if you need to discharge them at a high current rate. Not all Lithium iron batteries are better than Lithium ions at this metric.
The Li-ion batteries have the best result with the lithium nickel manganese cobalt oxide cells. They are the most capable of outputting high current drains. Producing a cell that has a higher CDR rating will in turn reduce its capacity but that has also been improved. Using a silicon-based anode the lithium ion battery can significantly improve its capacity but at a cost of a lower life cycle. That is because the silicon influences the anode to be affected with shrinkage which causes the battery to die sooner in a long run.
But there is a better solution. Using a mixture of nickel, manganese and cobalt to produce high capacity and retain the ability of high discharge. Manganese has a special feature that allows forming of something called spinel structure. This structure is responsible for low resistance in the cell which allows for a higher discharge rate but reduces the overall capacity. The nickel on the other hand can contain higher energy which makes a combination of the two a win-win scenario.
Cycle life of lithium iron phosphate (LiFePO4s) and lithium ion cells
The Lithium iron phosphate battery has a significantly better life cycle than other lithium ion battery chemistries.
Lithium ferro phosphate is one of the best battery chemistries when it comes to the cycle life duration. The LiFePO4 battery can last for 2000 life cycles at minimum if used in proper conditions.
The cycle life is one of the biggest advantages the LiFePO4 batteries have and one of the reasons they are replacing the good old lead acid battery. The quality of the cycle life will largely depend on the manufacturing conditions. The manufacturing process must be as clean as possible and without any moisture. It is important to select a quality LiFePO4 battery manufacturer for their longevity.
LiFePO4 and Li-ion Voltage
LiFePO4 battery has a nominal voltage of 3.30V and its typical voltage range is 2.5-3.65V.
The Li-ion battery has a nominal voltage of 3.6-3.7V depending on the chemistry and its typical operating range is 3.0V-4.2 volts.
The LiFePO4 battery disadvantage is its lower nominal voltage. This reduces the amount of specific energy they can contain. You will also need more cells connected in series with lithium-iron if you want to achieve higher voltage.
But on another hand, the advantage of LiFePO4 cell is that its voltage is close to the number 3 which means that you can easily make battery packs with multiples of 12 which are very standard in the battery industry. This is one of the reasons why lead-acid batteries can be easily replaced with lithium-iron phosphates.
A typical 12V lead acid battery can easily be replaced with a LiFePO4 battery that is composed of four cells in parallel.
Voltage discharge curve
LiFePO4 battery has a very flat voltage discharge curve which is an advantage over the li-ion batteries that have not as stable discharge curve.
Usually a lithium iron battery will keep its nominal voltage until near end of its capacity.
Li-ions on another hand have more expressed voltage drop over the course of the discharge cycle. But this has also improved over the years and today there are many li-ion cells that have very good discharge curves. These batteries are also known as heavy hitters as they can provide high voltage deep in their discharge cycle.
Charging Li-ion batteries is very similar to charging LiFePO4s. There are a few differences because the lithium iron phosphate battery has some different characteristics.
The conventional charge process for all lithium ion batteries can be separated in four stages. This applies to lithium ferro phosphate battery as well.
- The battery is charged with constant current
- Switch from constant current to constant voltage
- Charge termination
- Stand by with occasional topping charge
When an empty lithium-ion (and LiFePO4) cell is put on charge a charger will use a high constant current mode which charges the cell rapidly. This is the fast step of the charging process.
Once the cell/battery reaches a certain voltage the second stage commences. During the second step, the charging current begins to taper off but the charging voltage is kept at a constant rate which is why this step is called constant voltage. The second step saturates the battery properly and charges it to its maximum capacity.
Charge termination occurs once the maximum capacity and voltage of the battery are achieved.
Stand by phase tops off the battery after it has lost some of its capacity. This needs to be done with a quality charger and especially with li-ion batteries other than the lithium iron phosphates. Let’s see now what the specific differences these two chemistries have during these four charging steps.
The lithium iron phosphate battery is much more tolerant of high charge rates and overvoltage charge than other li-ions. This means that charging this battery can be done with a higher constant current and for a longer time.
In other words, the LiFePO4 batteries have a better tolerance for fast “forced” charging because their electrolyte doesn’t decompose as easily. Li-ion on another hand needs a more careful approach with the four-step process.
The LiFePO4 battery is also much more tolerant of overvoltage. Unlike with li-ions that can tolerate just about 0.1V overvoltage, the lithium iron can tolerate about 0.7V. This makes them much more acceptant of the stand by phase when a charger tops the battery.
The charge current that is applied during the constant current phase can be higher with LiFePO4 but it is not necessarily the case in real world applications. Sometimes this advantage of lithium iron phosphates is utilized and sometimes it is not.
Safety is a big factor when we are talking about lithium ion batteries. The Lithium iron phosphate battery is the safest li-ion battery. Unlike all the other lithium-ions, the LiFePO4 is not going to explode or catch fire thanks to its chemical and thermal stability.
Li-ion batteries can easily combust and catch fire if they are physically damaged, short-circuited or overloaded beyond their continuous discharge rating. The li-ions also heat up way more during the charging process because they experience thermal runaway.
The lithium iron is much less likely to experience any issues in these scenarios and if it does it will in most cases vent without any combustion.
You should always practice battery safety. While lithium iron batteries are much safer this doesn’t mean that anyone should be careless with them.
Toxicity and environmental impact
Many li-ion chemistries contain toxic and expensive metals that need special care and recycling after the battery is no longer usable. Disposing li-ions is more difficult due to their nickel, cobalt, manganese and other metal contents.
The lithium iron phosphate battery is nontoxic and allows for much easier disposal. This makes it a better choice for manufacturers that want the simpler end of the battery life process.
LifePO4 cost compared to Li-ions
There are many different manufacturers, distributors and sellers of lithium ion and lithium phosphate cells and battery packs. Their prices can vary significantly due to battery features, quality of manufacturing, quality of storage, their business models and etc.
Precisely measuring the difference in price is difficult. Especially if we are talking price vs quality ratio for each of these battery chemistries and then comparing these with each other.
A Li-ion can have a very low CDR rating and capacity and be significantly cheaper than a similar LiFePO4. Or a LiFePO4 cell can be cheaper if it is manufactured with less care and quality control.
However, generally speaking when observing the market the LiFePO4 cells and battery packs are more expensive than Li-ions. This doesn’t include the long term cost. If we are thinking long term then the lithium iron phosphate batteries are cheaper than li-ions and sometimes significantly.
That is because the li-ion batteries have a significantly shorter life thanks to their relatively low life cycle number.
If you add the advantage of LiFePO4 safety, then you can see that this chemistry is even less expensive even if it has a higher initial price. Depending on the industry and use case, the added safety of lithium iron batteries can reduce overall project cost.
It is necessary to apply multidimensional thinking when determining which of these cells is worth your while depending on your use case.
Li-ion and LiFePO4 battery chemistries share a lot of application use cases. So they can both be used for the same devices and purposes but with different results.
An E-bike manufacturer may use li-ion like Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2) and get a very high energy density and mileage from the battery. On another hand, the manufacturer can use a LiFePO4 battery pack and get lower mileage but way longer battery lifespan.
While these batteries share the use cases there are certain uses where each of them excels the best. This is because these specific use cases utilize the battery characteristics to their fullest.
Lithium phosphate batteries are used most commonly for solar energy storage, generally for energy storage, industrial use, robotics and as a replacement for lead-acid batteries. That is thanks to their longevity, high discharge rate (meaning they can supply high current needs instantaneously and continuously), high temperature performance and safety. These batteries are also used for electric vehicles where it is not necessary to get as much energy density as possible in as smallest battery pack possible. Such use cases are industrial vehicles like forklifts, garbage trucks, electric grass mowers, golf caddies, e-bikes or electric cars made for battery longevity rather than mileage.
Li-ions are mostly used in everyday electronics like laptops and smartphones, electric vehicles, e-bikes, medical devices, power tools and similar. The Li-ion is in most cases the preferred choice due to higher energy density but it may not be a better choice because of a shorter lifespan, safety risks and more complex recycling.
If lithium iron phosphate battery ever becomes as energy dense as regular lithium ions it would totally dominate the market for sure.
But since that is not realistic we have to use li-ion batteries for almost all uses in everyday scenarios like electronic devices and electric vehicles. The energy density of li-ion is still such a major factor that in most applications overshadows the safety and longevity of LiFePO4 battery.
However, where possible the LiFePO4 have become an exceptional battery choice. Safe, reliable, robust and with an incredible lifespan the LiFePO4s are almost a perfect.
If you can either increase the size of your battery or lower the energy capacity for your use case, then the LiFePO4 will definitely be a better choice. But if you must prioritize capacity and battery size reduction then the li-ion like LiNiMnCoO2 will be your choice.