Lithium Ion Solar Battery
Lithium Ion Solar Battery

Lithium Ion Solar Battery

The lithium battery, also known as lithium ion solar battery, stands out among other types of batteries for storing more energy in less space and with less weight, as its main component is always lithium – a low-density mineral element with just three protons and three neutrons, which is capable of high performance even in small and light devices, such as cell phones.

With different types (which depend on the chemical composition of each battery and may involve other elements combined with lithium, such as iodine or oxygen), lithium batteries are today essential parts in electric vehicles, airplanes, drones, cell phones, notebooks, and electronics in general.

But this universe of applications continues to grow – and, increasingly, the lithium-ion battery has become more common in the solar energy sector as one of the most modern solutions for energy storage.

How does a lithium solar battery work?

The lithium-ion battery (used in solar energy systems) has lithium salts (LiClO4) as electrolytes, dissolved in organic solvents to enable the chemical reaction. The operation of this battery is possible thanks to the internal parts present in the device:

Cathodes: these are the positive poles of the battery, which store lithium ions and give up their electrons. They can be made from different materials. Learn more here about the different types of lithium batteries.

Anodes: these are the negative poles of the battery, which receive electrons. They are generally composed of carbon-based materials (such as synthetic graphite).

Lithium ion layer: is separated from the cathode, but provides the electrons that make the battery operate.

Separator and solvent material: The battery must have a semipermeable solvent material that separates the anodes and cathodes and allows only lithium ions to flow between one side of the device and the other. Generally, ether is used to provide these chemical reactions.

When the battery is charged (i.e., stores energy), lithium ions migrate from the cathodes to the anodes through the solvent material. The reverse process occurs when the battery is discharged (lithium ions migrate from the anodes to the cathode). During this process, the battery sends the previously stored energy to the system.

It is worth remembering that lithium batteries are rechargeable – therefore, these two processes (charging and discharging) can be repeated for several cycles, according to the useful life of each battery (generally stipulated in number of cycles).

The Types of Lithium Ion Batteries

There are several types of lithium-ion batteries, which vary depending on the material that makes up the cathode (positive pole) of each battery, their internal chemical reactions or other characteristics.

Below, I present the main types of lithium batteries:

LFP – Lithium Iron Phosphate Battery (LiFePO4)

Lithium iron phosphate (LFP) batteries are suitable for photovoltaic solar energy systems because they provide high energy density. The reaction between phosphate materials (present in the cathode) and lithium provides these batteries, in general, with high current capacity and longer useful life.

These batteries also stand out for their good thermal stability (they can operate between +60ºC and -30ºC), as phosphate has good tolerance to temperature variations.

In addition to being safe, LFP batteries are also more forgiving of being fully charged and do not experience as much stress as other types when exposed to deep discharges. They have an energy density (battery) of around 150 Wh/kg and a useful life of around 6,000 cycles.

LMO – Lithium manganese oxide battery (LiMn2O4)

The combination of manganese oxide with lithium provides advantages such as fast charging and high current discharge, which makes its use interesting, for example, in some components of electric cars.

On the other hand, this composition also results in a shorter lifespan and lower battery capacity, making it common to mix lithium-manganese batteries with lithium-manganese cobalt oxide (NMC) to achieve better cost-benefit.

The lithium manganese oxide (LMO) battery has an energy density of around 0.41 kWh/kg and a useful life of between 1,500 and 3,000 cycles.

LCO – Lithium cobalt oxide battery (LiCoO2)

LCO was the first type of lithium battery commercially explored and continues to this day as the main combination used in consumer electronic devices (such as cell phones, laptops, cameras and tablets). 

They have good energy density, long functional life and are easy to produce on a large scale (although there is limited access to cobalt). On the other hand, this lithium battery does not have the same charge and discharge capacity as the LFP (iron phosphate) lithium battery to meet larger applications, such as use in electric vehicles or solar and stationary systems.

The LCO lithium battery generally has an energy density of around 0.58 kWh/kg and a useful life of 1,500 and 2,000 cycles.

 NCA – Lithium Nickel Cobalt Aluminum Oxide Battery (LiNiCoAlO2)

These are batteries that are similar to NMC lithium batteries and bring some advantages such as long useful life, good power and energy density. They can, however, bring disadvantages in aspects such as safety and cost, and are only recommended for special applications. Tesla also uses this type of battery in its electric vehicles.

LiPO – Lithium Battery with Polymers 

There are batteries that are distinguished from others not by the material that makes up their positive electrolyte (cathode), but by their separator, which can be made with a polymer (similar to a plastic film) and not with the traditional porous separator. Generally, lithium polymer (LIPO) batteries are based on cobalt, but they can also include other types of materials.

As the polymer has low conductivity and needs very high temperatures (above 60ºC) to carry out the operation, it is also more common for this type of battery to have a wet micro porous separator that improves its functioning. As an advantage, they can be lighter and made in a greater variety of formats than batteries with traditional separators (which makes polymer devices more flexible).

LTO – Lithium Titanate Battery

The main aspect that differentiates the types of lithium ion batteries is the materials that make up the positive pole (cathodes) of each device. However, there are also variations of negative poles (negative pole), which are not always made of graphite. An example are batteries with a lithium titanate electrode (Li4Ti5O12 – LTO), a material that contributes to aspects such as high safety and long useful life.

Lithium Battery Sizing in Solar Energy Systems

When we use batteries in photovoltaic solar energy systems, we must always know the system parameters to then calculate the number of batteries that will be used (sizing). In addition to daily energy consumption, we must also observe the application of the solar project and the necessary autonomy (i.e., how long the system needs to be able to operate at times without solar energy generation) 

Once the daily energy consumption and required autonomy are known, the quantity and capacity of batteries can be dimensioned so that they operate for a certain number of days until a new charge cycle.

The capacity to be determined for the battery bank will vary depending on the type of battery adopted – with lithium batteries being the most advantageous in this aspect, as they tend to withstand greater depths of discharge (DoD) without compromising their useful life (quantity of cycles).

Compared to common stationary batteries (lead-acid), lithium batteries can operate with a lower energy storage capacity (normally given in Wh). This way, optimizing the battery bank’s size (achieving better performance in smaller spaces) is possible.

To better understand how the lithium battery can match the performance of other models with a smaller installed capacity, check out a comparison between the sizing of different types of batteries.

What is the ideal Depth of Discharge (DoD) for a Lithium Battery?

The depth of discharge of a battery (also called DoD – Depth of Discharge) is the amount of energy stored in the battery that was used, compared to the device’s total capacity.

Most batteries have a curve that demonstrates their operational limits and that shows the influence of a high DoD in relation to the number of cycles it is capable of supporting (in other words, the battery’s useful life).

Lithium-ion solar batteries are deep-cycle batteries

This means that, with the lithium solar battery, it is possible to use more of the stored energy without having to charge it as often. Some lead-acid batteries can also reach maximum DoDs of up to 80%, but with a significant loss in cycling capacity.

How much space does a Lithium Battery occupy in a Photovoltaic Solar Energy system?

This is another advantage of lithium over other stationary battery models. Lithium has better energy density and is therefore capable of generating more energy in less space (that is, it offers the same performance in a smaller installed capacity).

Can the Lithium Battery last a long time without being discharged? 

The lithium-ion battery also differs from stationary lead-acid batteries due to its longer storage time (that is, the period that the battery can remain without being recharged without compromising its useful life).

In the case of lithium batteries, considering storage at 20ºC, it is possible to keep them stored for a year without recharging them. This is a big advantage over lead-acid batteries, which, under the same conditions, usually require recharging at least every 6 months to avoid being damaged.

This difference occurs because lead-acid batteries have much greater self-discharges than lithium batteries, in addition to a lower maximum DoD limit.

Lithium Battery Life

LFP lithium-ion iron phosphate batteries (most used in solar energy systems) have a useful life of between 4,000 and 10,000 cycles, depending on the depth of discharge (DoD), which can represent a duration of 10 to 20 years, while Lead-acid batteries last from 6 months to 10 years (depending on model and other usage factors).

In the case of lithium, even with high depths of discharge (such as 90% DoD – that is, using almost the full charge of the battery before charging it again), the device must withstand the number of cycles informed by the manufacturer, while Lead-acid batteries tend to suffer great damage to their useful life with discharges of this size

Lithium Battery Price

Although they have a higher initial investment than stationary lead-acid batteries, lithium batteries for solar energy have several advantages throughout their use (such as greater efficiency in charging and discharging, and longer useful life even in deep cycles), which end up making it the most cost-effective choice for energy storage systems (storage).

How much does the lithium battery for solar energy cost?

If we consider the cost per cycle (that is, we divide the initial price of the product by the number of times the battery can be charged and discharged throughout its useful life) and also if we consider that the cycles of a lithium battery can be more in depth, we will see that the lithium battery can be at least three times more economical compared to lead-acid models.

The fact that they last much longer and there is no need to buy another battery for at least a decade makes lithium batteries cheaper in the medium term and an excellent deal. After all, batteries must be purchased to last a long time and guarantee good storage.

Additionally, solar energy systems are often installed in remote locations. The cost of maintenance, service for battery changes, system reliability, and other factors bring additional advantages to lithium battery systems.

Lithium Battery Weight

Lithium is one of the known elements with the highest energy density: that is, it can concentrate a lot of energy in small spaces and, when used in the composition of a battery, it naturally tends to offer lighter solutions with high capacity.

The exact weight of each battery will depend on a number of factors, such as the size and capacity of each device, as well as the extra weight of its casing.

However, in a real comparison of existing products on the market, a lithium iron phosphate (LFP) battery delivers 5000Wh with a 40 kg device, while the same capacity would require a battery bank weighing more than 110 kg with solar batteries. lead-acid battery (i.e.: in the example, the lithium battery offers the same capacity with less than half the weight).

How the Lithium Battery reacts to high temperatures

The lithium-ion battery is very tolerant to variations in ambient temperatures, capable of operating in a range of -10ºC to 60ºC without losing useful life. 

This means, in practical terms, that it is possible to work with lithium-ion batteries in hot and cold regions without affecting the product’s durability, while lead-acid batteries, in general, begin to lose their useful life when they are exposed to environments above 25ºC.

Furthermore, for safety reasons, lithium batteries are also usually protected in metallic casings that increase their resistance to high temperatures – in some cases even preventing the equipment from being damaged at external temperatures that can reach up to 600ºC, which is the melting point of lithium.

Another protection device in most lithium batteries is the BMS function – which monitors several parameters of the battery and its cells (such as voltage, current, and temperature), in addition to controlling the input and output current of the battery and its cells with the rest of the system.

Thus, it is possible to prevent, for example, the battery from exceeding a temperature of 60ºC (causing the equipment itself to stop operating if there is a risk of overheating).

Is the Lithium Battery safe?

Yes. All lithium batteries – including those used in notebooks, tools, cell phones, stationary systems and electric vehicles – have evolved a lot in terms of safety in recent years/decades.

The lithium battery generally used in solar energy systems (the lithium-ion iron phosphate battery – LFP) stands out for its superior safety compared to other types of lithium ions, as iron and phosphate are metals that significantly reduce the risk of accidents with lithium and increase the thermal tolerance of the cells. As an additional safety, LFP lithium batteries also have robust protective casings to ward off accidents further.

Is it true that the Lithium Battery expands and can explode or catch fire?

There are cases of explosions with lithium batteries, in addition to the recall of some batteries by companies that did not consider their equipment safe enough. This generally occurs when there are protection failures in the batteries and lithium comes into contact with oxygen, which can cause the metal to expand or in some cases the cells can reach the flash point and start a fire.

These incidents, however, generally occur with lithium batteries composed of cobalt and manganese, in electronics or transportation applications. In the case of solar energy systems, lithium iron phosphate (LFP) greatly reduces these risks, as it has a safer chemical composition. Furthermore, these batteries have a BMS management system, which causes the battery to stop working automatically in cases where there is a risk of overheating.

Is the Lithium Battery radioactive?

There is no risk of a lithium battery emitting radiation or radioactive gases. This type of confusion occurs because some lithium batteries can emit toxic gases – but again, this type of incident is extremely rare in lithium ion iron phosphate (LFP) battery applications in solar power systems, as the equipment is manufactured with one of the safest lithium compositions and are protected by robust casings, which prevent contact and direct handling of lithium.

Does a lithium battery deteriorate if it comes into contact with water?

Like oxygen, water is another element that, combined with lithium, can generate a spontaneous combustion process capable of causing accidents or damaging equipment. However, this should not be a problem in the case of iron phosphate ion (LFP) batteries used in solar energy systems, which are protected by casings that can come into contact with water without problem and protect the battery well.

What is the BMS for in the Lithium Battery?

The BMS is an electronic management system that monitors the condition of the battery and its cells, always maintaining its operation within safe and efficient parameters for the battery. battery, thus extending its useful life. This system does not exist in lead-acid batteries (which can be monitored by the charge controller in many cases), but is mandatory in lithium batteries. 

In general, the BMS monitors parameters such as voltage, currents and temperature of the cells and the battery as a whole, controlling the input and output current between it and the rest of the system. Thus, it is possible to prevent, for example, the battery from exceeding a temperature of 60º C (causing the equipment itself to stop operating if there is a risk of overheating). This monitoring and control can be done for individual cells, sets of cells, packs or for the battery as a whole.

Does the Lithium Battery need maintenance?

Unlike some solar batteries that require routine maintenance – especially so-called “flooded” lead-acid batteries, which require electrolyte replenishment, lithium-ion batteries are generally maintenance-free and should function smoothly. throughout its useful life, as informed by the manufacturer.

How is the Lithium Battery disposed of and recycled?

Before thinking about disposing of a lithium battery, it is important to consider second-life options for these devices. When they reach approximately 80% of their useful life and may lose some performance, lithium ion batteries can be removed from solar energy systems and used for backup or UPS systems, where they are able to last even longer for approximately 5 to 10 years (since these applications will not demand the maximum of your capacity). Therefore, it is common to say that lithium batteries “have two or even three lives”.

Important: this second battery life is optional and represents a chance to make the equipment last longer, with another function. However, lithium batteries can also be used until the end of their useful life in their original photovoltaic systems – what may occur is a loss of performance in recent years (as manufacturers specify in their technical manuals).

After the lithium battery ends its useful life, it is necessary to transform the lithium into a salt that does not harm the environment to dispose of it, as lithium equipment in its raw state is a non-reusable product and cannot be returned to nature.

For this complex process to be guaranteed, a law may require all lithium battery manufacturers in the country to offer a disposal service to their consumers, offering adequate information and specific disposal points for these materials.

Although each country’s regulations are different, there are global practices to ensure the correct disposal of lithium and all manufactured batteries must be identified so that they can be recognized at any time during the product’s useful life and even after its end.

In other words, at the end of the lithium battery’s useful life, you should contact the manufacturer to be informed on how to dispose of it – and it is expected that the company will partner with a recycler to dispose of the already unused battery.

You cannot copy content of this page