As lithium-ion batteries are now found everywhere, from your mobile phone to your electric car, we will show in this article 10 key differences between the two technologies, and demonstrate how lithium-ion batteries are taking over the century old lead-acid technology.
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1- Lead-Acid Vs Lithium-Ion: How do they work?
Lead-acid and lithium-ion batteries share the same working principle based on electrochemistry. They store (charge) and release (discharge) electrons (electricity) through electrochemical reactions.
Both of them feature the following parts:
- Two electrodes: Anode (-), Cathode (+)
- Membrane separator
They differ in the material used for each component:
|Cathode||PbO2||Lithium Oxide (LiFePO4, LiCoO2, LiMn2O4 etc…)|
|Electrolyte||H2SO4 (liquid, gel)||Lithium salt (liquid, solid, gel)|
Below is a schematic representation of the working principle of a lithium battery during discharging and charging, the same also apply to lead-acid:
While discharging, Lithium ions (Li+) are exchanged between the negative electrode (anode) and the positive electrode (cathode). To balance the reaction, electrons are released from the negative electrode to the positive electrode.
While charging, the opposite reaction occurs, and electrons are flowing from the positive electrode to the negative.
For Lead-Acid, similar reactions happen but this is the acid electrolyte (H2SO4) which participates to the reaction with 2H+ (aqueous protons).
2- Lead-Acid Vs Lithium-Ion: Which one has the best capacity?
From a microscopic point of view, the capacity of a battery is related to the global charge of the transferred ions (Li+ or H+), multiplied by the working voltage of the electrochemical reaction.
Here we have a main difference between Lead-Acid and Lithium-Ion: lithium is the lightest metal on earth, one kg of lithium contains 29 times more atoms than lead. In addition, the working voltage of Lithium-Ion is 3.2V vs 2V for lead-acid. Consequently, you can store much more energy in 1kg of lithium battery than in lead-acid.
In the chart below, we have summarized the energy storage capacity of both technologies. The theoretical density does not take into account the mass of the electrolyte and other components (battery casing, safety equipment…).
|Storage capacity theory||167 Wh/kg||11’600 Wh/kg|
|Storage capacity practice||30 – 40 Wh/kg||110 – 250 Wh/kg|
Two other interesting figures are the battery compacity, also called energy density in Wh/l and the specific power of the battery in W/kg.
|Energy density||80-90 Wh/l||250 – 670 Wh/l|
|Specific power||180 W/kg||250 – 340 W/kg|
In the end, Lithium-Ion batteries are lighter (up to 6 times for the same capacity) than lead acid, more compact, and up to two times more powerful.
3- Lead-Acid Vs Lithium-Ion: Can you fully discharge?
Maximum depth of discharge
If you had already purchased a lead-acid battery, you might have noticed that the manufacturer advises not to discharge the battery below 50% of its full capacity to improve its life duration. Indeed, in lead-acid batteries, over discharging creates parasite reactions (sulfatation) at the electrodes, slowly damaging the system.
Researchers and engineers worked hard on this matter and introduced the GEL and AGM batteries. Both of them offer better depth of discharge (DOD) than the traditional flooded lead-acid battery but are still affected if fully discharged.
On the other side, degradations in lithium batteries only start when the depth of discharge reaches 60%, therefore manufacturers recommend 80% DOD to improve their total life duration. Recent improvement, enables 100% DOD without extra damage to the battery.
Self discharge rate
Both technologies, when stored, will slowly loose their initial capacity. The discharge rate is affected by the initial charging state of the battery. It is recommended to fully charge your battery before storing it. For Lead-acid, the self-discharge rate is 3-20% a month, and for Lithium-Ion: 0.35-2.5% per month.
The charge efficiency reflects the actual quantity of energy effectively stored in the battery. For example, when charging a 1 kWh battery you might use more than 1 kWh, due to internal loose.
For lead-acid technologies, you’ll get around 90% efficiency and for lithium batteries 95% to 99%.
4- Lead-Acid Vs Lithium-Ion: What is the most durable?
Durability is one of the most important parameters to consider when buying a product.
The same applies to batteries, and unfortunately this is clearly not the strength of Lead-Acid batteries. Over the years some improvements were made: lead-acid batteries became maintenance-free and AGM and GEL technologies were introduced that slightly improve their performances.
However, in my opinion, with only 2 years of good services (when discharged at 50% of its maximum capacity) the life duration is extremely low, specially for a century old technology. If deeply discharged at each cycle (80% or more), your lead-acid battery will only work well for 350 cycles or one year.
On the other side, lithium batteries have increased their life duration over the last 5 years, and manufacturers are now offering warranty as high as 10’000 cycles or 10 years (70% of initial capacity).
5- Lead-Acid Vs Lithium-Ion: Do they support quick charge/discharge?
Due to technical limitations, lead-acid batteries don’t support quick charge. Their charging time range from 6 to 15 hours and is following a three steps process as explained below:
- Bulk charge: charging voltage increases steadily to its maximum value and charging current is kept at its maximum value. The battery will reach up to 80% of its full capacity in approximately 6 to 8 hours.
- Absorption charge: charging voltage is kept at its maximum value, while the current slowly decreases until the battery is charged at 90-95%.
- Float charge: charging voltage and current decreases to zero, while the battery reaches full charge.
On the other hand, lithium batteries are fit for quick charge. You can charge them to 80% of their full capacity in 1 to 2 hours (depending on the power output of your charger). The remaining 20% will take another 2 to 3 hours. Therefore, you can fully charge a lithium-ion battery in 3 to 5 hours.
Both type of batteries support quick discharge and can provide intense pulses of current (hundred of amps) if required.
6- Lead Acid Vs Lithium Ion: Which one is the best for solar energy?
Solar energy, like all renewables, is intermittent. Therefore, its power output varies depending on the time of the day, and the weather. Passing by clouds generate drastic power output modifications that strongly affect the battery charging current. Lead-acid batteries could be damaged by those variations, as mentioned before they have to follow a three steps process for proper charging.
In addition, their charging time could reach 15 hours, and in most countries days are shorter than 15 hours, full charge could never be reached.
On the other hand, intermittent charging does not affect lithium-ion batteries and it can take only few hours to full charge. Consequently, they are perfectly fit for solar energy storage.
7- Lead-Acid Vs Lithium-Ion: Are they safe?
Lead-acid and lithium-ion both contain hazardous material that could possibly harms the users and the environment.
To make their products safe, manufacturers have developed different strategies summarized in the chart below:
|Lead acid||Spilling of acidic electrolyte||Electrolyte as a Gel or absorbed on a glass mat (AGM)|
|Release of highly toxic H2S gas||Valve Regulation|
|Lithium-Ion||Fire/explosion||Air tight packaging|
|Battery Management System (BMS)|
Most of the lead-acid batteries available on the market are now Valve Regulated (VRLA) and maintenance-free, therefore safe to use.
Lithium when pure is highly flammable in contact with air, Battery Management Systems (BMS) were developed for safety purpose to monitor each battery cell and make sure that there is no overcharge/discharge.
In the end, both type of batteries are safe to use, but still need to be handle with precaution.
8- Lead Acid Vs Lithium Ion: Which one is the cheapest?
The Levelized Cost of Storage (LCOS) is the best way to compare the cost of different battery technologies. LCOS is expressed in USD/kWh and takes into account all the expenses related to energy storage over the lifespan of a battery.
As batteries are maintenance free, the only cost would be the price of the battery itself.
Let’s have a look at the example below:
|Lithium-ion 12V, 100Ah||Lead-acid 12V, 100Ah|
|Upfront cost||739.99 USD||174.99 USD|
|Depth of discharge||80%||50%|
|Total number of cycles||(10 years) – 3600 cycles||(2 years) – 700 cycles|
|Total kWh over life time||3’456 kWh||420 kWh|
|LCOS||0.214 USD/kWh||0.417 USD/kWh|
At first, the lithium-ion battery (LiFePO4) costs 4 times more than the lead-acid battery. However, it lasts much longer and in the end, has the lowest LCOS. Therefore, over its lifetime the lithium battery is two times cheaper than the lead-acid.
9- Lead Acid Vs Lithium Ion: Can you recycle?
As previously mentioned, both batteries contain hazardous and highly toxic material, and should be disposed properly.
Lead-acid batteries are the most recycled product in the world. The recycling rate reaches almost 100% in the US as nearly all parts (sulfuric acid electrolyte, ABS casing, lead plates) can be recycled. New lead acid batteries usually contain more than 80% recycled material.
On the other hand, lithium-ion is a new technology and recycling is still on a learning phase. However, recent studies show that lithium batteries could be recycled up to 96%. In 2018, 97’000 tons of lithium batteries were recycled and battery recycling is now seen as a source of material as demand rises.
10- Lead Acid Vs Lithium Ion: Can you DIY?
Lead Acid batteries are sealed and cannot be upgraded or modified.
On the contrary, lithium-ion batteries are modular and you could build your own battery pack at home.
When purchasing a lithium battery, you are actually buying multiple battery cells assemble together and all connected to the Battery Management System (BMS).
All elements constituting the lithium battery pack could be bought individually online.
Manufacturers are selling prismatic lithium battery cells of various capacity (from 10Ah to 300Ah), all rated at 3.2V.
This illustrates the great modularity of lithium batteries.
Finally, this is a KO victory for lithium-ion batteries over Lead-acid batteries.
Indeed, lithium-ion batteries offer larger capacities, are more durable, light weight, efficient and cheaper to use than lead-acid. Furthermore, they are modular and you can build your battery pack at home.
In the coming years, thanks to the fast development of electric vehicles, lithium battery prices will drop further down, making this technology even more attractive.