Lead-acid vs Lithium-ion battery: Which is better?

Both Lead-acid and Lithium-ion have the same function of providing electricity.

When you are considering storing energy in your house or office.

The battery is one of the best energy storage options.

Batteries can power your cell phones, Electric Vehicles, laptops, pocket calculators, electric wheelchairs, refrigerators, fans, radios, and many more electrical and electronic gadgets.

We see different types of batteries.

But in this post, we’ll limit our discussion to two types of batteries that you can pair with solar installations.

These are Lead-acid batteries and Lithium-ion batteries.

Although both do the same function of providing electricity.

The main difference lies in their internal chemistry, cost, and performance.

Energy conversion in a battery

Any battery is a power pack that stores chemical energy.

When you connect the load (bulb) to it through wires.

It starts converting that chemical energy slowly into flowing electrons (electricity).

These electrons reach the bulb through the wire and it starts glowing.

This energy is limited and often lasts a few days, weeks, months, or years.

Parts of the battery

The basic unit of a battery is a cell.

A battery consists of 2 or more cells joined together.

Each cell has 3 main sub-parts

2 electrodes (one is called a positive terminal and another is a negative terminal) are separated and immersed in an electrolyte.

(The electrolyte facilitates the transport mechanism of ions between the two electrodes).

The electrodes are made of different types of material.

Why electrodes are made of different materials?

Let us understand the basics of electron flow.

Every element has the capacity of pulling electrons in its vicinity.

This ability is defined as the electronegativity of an element.

And the value of electronegativity depends on the atomic structure of an element.

Two different metals have different values of electronegativity (tendency to pull electrons).

When placed close to each other in an electrolyte.

The metal with a higher value of electronegativity will pull the electrons towards itself.

Hence the flow of electrons starts.

And

This movement is absent when two electrodes of the same material are placed close to each other.

Types of Batteries

We see batteries of different shapes, sizes, and capacities.

The electrolytes might be different, the electrodes may be of a different material.

But the basic function of the battery remains the same to provide the current to run the load.

We see two types of batteries:

1. Primary Battery

These batteries can’t be recharged once they are depleted. Hence are also called disposable batteries.

2. Secondary batteries

They can be recharged again and again hundreds of times.

The battery in your smartphone is an example of a secondary battery.

When you are charging your smartphone, you’re actually feeding the current to the battery in the reverse direction which provides current to run the cell phone.

The lithium-ion batteries and the lead acid batteries are both examples of secondary batteries.

Both can be recharged again and again.

Let me discuss the lead acid battery first.

Lead-acid battery

It was in 1859 when these batteries were first discovered by French Physicist Gaston Plante.

I can say that it is the oldest, most trusted, and the matured technology in the market.

In a lead-acid battery, the 2 electrodes are made of lead (Pb) and lead-peroxide (PbO₂) which are immersed in an aqueous solution of sulphuric acid (H₂SO₄).

The whole chemistry is packed in a thick plastic case to avoid the spilling of corrosive sulphuric acid.

The load is connected externally outside the battery between the 2 electrodes.

Working

The sulphuric acid inside the battery splits into H+ (Hydrogen ions) and SO₄² (sulfate ions).

The H+ ions travel towards PbO₂. They react with a lead peroxide plate and make Lead Sulphate (PbSO₄) and water (H₂O).

While on the other hand, SO₄² ions move towards the lead plate and also make PbSO₄.

In this process, the electrons start accumulating over the lead plate.

And

When we connect the two plates externally through a wire, these accumulated electrons find a way to move out and reach the other plate.

And

If you have connected a load in between this path, the electrons also pass through it and it starts glowing. When the battery is completely discharged, both plates become PbSO₄ and aqueous H₂SO₄ becomes dilute.

The voltage of the battery drops and it no longer provides current to the load.

Yes, we can recharge the battery by providing current from an external source.

And

This could be my favorite solar electricity.

When we charge the battery, in reverse polarity, the electrodes regain their original composition, and dilute H₂SO₄ becomes aqueous.

Again, the battery is ready to provide the current to the load.

Lithium-ion Battery

It was GN Lewis who discovered the concept of Lithium-ion batteries in 1912.

And in 1970, the first non-rechargeable lithium battery was rolled out into the market for commercial use.

Initially, the lithium electrode was used in the battery.

Lithium with atomic number 3 is a very light, soft, and silvery-white alkali metal.

It has a very high energy density.

And

This intrinsic property makes it store more energy in less volume.

And

You get a very high current.

But the problem was that it becomes unstable during charging and as the temperature rises.

And

We saw instances where the lithium batteries exploded during charging.

Since it is highly unstable.

We use lithium ions for more stability and almost the same performance as lithium provides.

Later, Sony introduced advanced Li-ion batteries.

The 2 electrodes used in Li-ion batteries are Graphite and lithium-cobalt-oxide.

And electrolyte is the salt of lithium like Lithium hexafluorophosphate (LiPF₆).

Just like a lead-acid battery, a li-ion battery can recharge again and again.

Let us know how the different internal chemistry of the batteries affect their cost and performance.

Nominal Voltage

We know that a battery is a collection of cells.

And each cell in a lead-acid battery has a nominal voltage of 2.2 volts.

And

a battery with 6 cells connected has a nominal voltage of 13.2 volts (6 x 2.2 volts).

And

when the battery discharges, each cell’s voltage drops to 1.8 volts, making the battery voltage come down to 10.8 volts (6 x 1.8 volts).

Thereafter, it needs charging from an external source.

The nominal voltage of a Li-ion cell is 3.6 volts which are higher than the nominal voltage of a single lead-acid cell.

This higher voltage gives an advantage to the li-ion battery to provide more energy in a given time.

Battery Capacity

It defines how much energy a battery can store per litre.

A lead-acid battery stores energy between 80 to 90 W-h per liter.

{Watt-Hour (W-h) is the unit of energy}.

Whereas a Li-ion battery has a capacity of 200 to 600 W-h per liter.

Giving me an average of 400 W-h/L {(200 + 600)/2}.

In simple words, when I take a Lead-acid battery on one hand and Li-ion on another having the same energy capacity.

The Li-ion battery will occupy near to 1/5^th volume of the Lead-acid battery.

In the market, you see that the battery capacity is defined in terms of Ampere-hours.

We see 12 volts batteries coming in 100 Ah to 350 Ah.

It generally takes near to 8 hours for charging and discharging the lead acid battery of the above capacities.

For example, a 12 volts battery with 200 Ah capacity can provide a 25-ampere current in 1 hour and in this way lasts for 8 hours.

It is not that you cannot withdraw more than 25 amperes.

You can but it impacts the useful life of the battery.

Similarly, for charging the battery, it should get 25 amperes current so that it gets charged in 8 hours.

More than 25 amperes, can charge it faster.

But it can overheat the battery and increase the gas formation inside the battery.

Therefore, the ideal charging and discharging current for 12 volts/200 Ah battery is 25 amperes.

Depth-of-Discharge (DOD)

This metric tells the extent of charge that can be withdrawn safely from the battery.

This is defined in terms of the percentage of the total charge in the battery.

For example, an 1800 W-h battery with 50% DOD means that 900 W-h (50% of 1800 W-h) can be taken out safely from the battery.

It is not that you cannot withdraw beyond this limit.

You can but doing so affects the useful life of the battery.

A battery with a higher DOD is preferred over the lower one.

It is normal to see li-ion batteries with DOD over 85%.

(You can withdraw 85% of the total capacity in a single cycle).

While Lead-acid batteries have a DOD of around 50%.

The improved DOD of Li-ion batteries is credited to the high energy density of Li-ions.

The efficiency of Lead-acid and Lithium-ion

What percentage of chemical energy in the battery is converted into useful electrical energy defines the efficiency of the battery.

Lead-acid batteries have efficiencies of around 80% – 85%.

While it is normal to see Li-ion batteries coming with 95% efficiency.

Charging time

The average charging time for a Lead-acid battery is 8 hours.

Whereas the li-ion batteries take much less time.

The li-ion chemistry makes it possible to completely charge the battery in 3 hours or even in less time.

Lifespan

Li-ion batteries have many numbers of useful cycles.

One discharge and one charge make 1 complete cycle of a battery.

Lead-acid batteries have 500 cycles while Li-ion batteries have over 3000 cycles.

Cost

You saw that the Li-ion batteries have an upper edge almost in all aspects.

Still, we see the widespread popularity of Lead-acid batteries.

The reason is that these were discovered first and were less expensive than Li-ion batteries.

This is the key driver in the wide-scale acceptability of these batteries. Also, these batteries are available in large quantities and in different sizes.

Which is the right option Lead-acid or Lithium-ion?

Both lead-acid and li-ion batteries store energy which can be used later when required.

However, each battery type has its own advantages under different situations.

If your system size is small then choosing a lead-acid battery over the Li-ion would be the wise decision.

This will keep the overall system more affordable.

Also, if your system is operating at a higher ambient temperature then again Lead-acid batteries would be the right choice.

As the li-ion batteries tend to become unstable at higher temperatures.

The lead acid batteries are also suitable in conditions when backup needed is less frequent.

For example, you have a grid-tied solar power system and you use electrical appliances mostly in the daytime.

The solar panels can easily meet the daytime requirement.

Your energy needs at the night are minimum.

Then, in this case, a lead-acid battery can easily meet your energy needs.

However, when your system size is large and you need frequent battery backup. Then li-ion batteries are the ideal solution to meet your energy needs for a longer time.

• For most solar power systems, Li-ion batteries are more efficient, reliable, and have longer lifespans.
• Lead acid batteries are cheaper than Li-ion batteries.

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