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The holy grail of battery energy storage is a high-energy density. Why is this?
This is a matter of size and cost !
We want the battery to be small. This can be achieved with a high-energy density.
More importantly, we want the energy storage cost to be affordable and low. That means the stored kWh per unit should cost as low as possible.
The energy density describes the amount of energy that can be stored in a battery per mass or per volume.
Thus, the amount of energy per kg in Wh/kg or the amount of energy per liter in Wh/L.
Some people call the energy density in short as “Energy” like the “specific energy”. However, this can be confusing as the therm energy in physics has a different meaning.
An energy density number does not provide information on how quickly this energy can be used!
This knowledge is contained in a batteries’ power density, which describes the rate at which its energy can be put out.
This knowledge is contained in a batteries’ power density, which describes the rate at which its energy can be put out.
Typically, having a high-energy density goes along with a low-power density.
Energy density and power density differ in one important way – while battery energy density measures the watt-hours (wh) per kilogram mass (kg), power density measures the watt output per kilogram mass.
This is where power vs. energy comes into play. Power density measures how fast energy can be delivered, while energy density measures how much energy a battery holds.
If a battery contains more energy, it can also release more energy. In a controlled or uncontrolled way!
The liquid electrolytes in lithium-ion batteries are flammable and can ignite, posing a safety hazard.
That’s why batteries are designed with safety features that have, however, a negative impact on energy-density and cost.
When it comes to high-energy density, lithium-ion accumulators are the undisputed leader. They have changed our world with advances in energy consumption and portability.
The energy density of the best commercial high-end lithium-ion battery (bare cell density) is between 250 Wh/kg and 265 Wh/kg (2023).
The lithium-ion battery with currently the highest energy density is the lithium-ion NMC battery. It uses NMC 811 as the cathode and graphite carbon enriched with silicon as the anode.
The energy density of batteries is crucial because the higher the energy density, the longer the battery can deliver charge relative to its size.
Therefore, batteries with a high-energy density are smaller; lithium-ions in smartphones are an illustrative example.
The concept of commercial electric cars was possible only because the lithium-ions batteries do have a sufficiently high-energy density.
We call the energy density per mass the “specific energy density” with the Unit Wh/kg.
The “gravimetric energy density” is equivalent to the “specific energy density“. Therefore, we call the energy density per mass also the “gravimetric energy density” with the Unit Wh/kg.
We call the energy density per Volume the “volumetric energy density“, or short “energy density“. The Units are Wh/L.
Power density measures how fast energy can be delivered, while energy density measures how much energy a battery holds.
If a battery contains more energy, it can also release more energy, which potentially can dangerous. However, high-energy density batteries have multiple safety features to prevent an uncontrolled release of energy.
The energy density of the best commercial high-end lithium-ion battery (bare cell density) is between 250 Wh/kg and 265 Wh/kg (2023)
