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Nickel Iron (NiFe) Lithium Iron (LiFePO4)

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Advantages of Lithium-ion Batteries

Advantages of Lithium-ion Batteries

 

Lead acid batteries are made from a mixture of lead plates and sulfuric acid. This was the first type of rechargeable battery invented back in 1859.

On the other hand, lithium-ion batteries are a much newer invention, and have only been around here, commercially speaking, since the 1980s. 

Lithium technology has become well proven in small power electronics such as laptops or wireless tools, and has become progressively common in these applications - coming out of the older chemical composition of the NiCad rechargeable battery (nickel-cadmium) due to the many advantages of lithium.

But as you can recall the many stories from a few years ago about the batteries of defective laptops bursting into flames - the lithium-ion batteries also gained a reputation for catching fire in a dramatic fashion. The formulation of the commonly used lithium-ion battery had been LiCoO2 (lithium-cobalt-oxide), and this battery chemical composition is prone to thermal leakage if the battery is accidentally overcharged. This could lead the battery to jump on call by itself - and a lithium fire burns hot and fast.

This is one of the reasons why lithium is rarely used to create large battery banks.

But in 1966 a new formula of lithium-ion batteries was developed - lithium-ion-phosphate. Known as LiFePO4 or LFP, these batteries have a slightly lower energy density but are intrinsically incombustible, and much safer than those of lithium-cobalt-oxide and once you consider the advantages, lithium-ion batteries become extremely tempting.

1.- Superior "usable" capacity:

Unlike lead acid batteries, it is considered practical to regularly use 90% of the nominal capacity of a lithium battery bank, and occasionally more. Consider a 100 A hour battery - if it were lead acid it could only be used 30 to 50 A hour capacity, but with the LFP lithium you could take 90 A hour or even 100 A hour (100% DoD or depth of discharge) .

2.- Superior Life Cycles:

The experimental results indicate that it could expect from 3,000 to 10,000 life cycles for a bank of lithium-iron phosphate batteries. Both, the C ratio and the depth of discharge (DoD) affect the expected useful life. Some recent measure shows that a LFP battery will deliver more than 80% of its capacity after 3,000 cycles at 100% DoD (depth of discharge) or even 8,000 cycles at 65% DoD (depth of discharge). All these tests are made with cycles of 1C ratio, that is, with rates of charges - 1 hour downloads; If this rhythm or time is higher, the cycles increase markedly, reaching 20,000 cycles.

In contrast, even the best deep cycle lead acid batteries provide 250-1,200 cycles.

The drawing below shows the expected number of cycles for the lily-ion-phosphate batteries in different DoD at 1C ratio, ie, charges and discharges in 1h.

3.- Advantages of size and weight

To highlight the only feature in terms of weight and size of lithium-ion batteries, let's take a concrete example of two commercial batteries: acid lead vs lithium battery.

4.- Fast and efficient loading

Lithium-ion batteries can be charged "quickly" at 100% capacity. Unlike lead acid, there is no need for the final phase of absorption to obtain 20% final storage, if your charger is powerful enough, lithium batteries can also be charged incredibly fast. If you can supply enough charging amps - you can actually fully charge a lithium-ion battery in just 30 minutes!

But even if you can not completely fill it to 100%, do not worry - unlike acid lead, this phenomenon does not damage the batteries.

This gives us a lot of flexibility when it comes to selecting energy sources without the need to worry about periodically making a full charge. Several days partially cloudy with your solar system? No problem. With lithium, charge what you can and do not worry about leaving the battery bank perpetually undercharged.

5.- Very little energy wasted:

Lead acid batteries are less efficient at storing energy than lithium-ion batteries. Lithium batteries charge at almost 100% efficiency, compared to the 85% efficiency of most lead acid batteries.

This can be especially important when you are charging via solar, when you are trying to get the maximum possible efficiency out of all the amps before the sun goes down or gets covered in clouds. With a limited roof this becomes very important when optimizing any power surface you can mount.

6.- Climatic resistance:

Lead acid and lithium batteries lose capacity in cold environments. Lithium-ion batteries are much more efficient at low temperatures. In addition, the discharge ratio affects the performance of lead acid batteries. At -20ºC, a lithium battery that delivers a current 1C, can deliver more than 80% of its energy when the lead acid battery will deliver 30% of its capacity. For harsh environments (heat or cold), lithium-ion is the appropriate technological solution.

7.- Versatility in its location mode:

Lithium-ion batteries do not need to be stored vertically, or in a ventilated battery compartment.

8.- Zero maintenance requirements:

The lithium-ion batteries have a free maintenance in a relatively long period. A "rolling" process to be sure that the cells in a battery bank are charged equally is automatically provided by the BMS. Just charge the battery and you're done.