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What is the energy density in a battery?

Specific energy density explained by wiki battery on wikibattery. Org
Specific Energy Density explained by Wiki Battery on wikibattery.org

Energy Density Definition

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 (Wh/kg) or the amount of energy per liter (Wh/L).

There is a “volumetric energy density“, short “energy density” and a specific energy density also known as gravimetric energy density

Some people call the energy density in short as “Energy” like the “specific energy”. However, this can be confusing as the energy in physics is a “state” and not a density.

What are the different types of energy densities?

The volumetric energy density

  • Energy density, or volumetric energy density, reflects the amount of energy stored per volume in liters (Wh/L). 

Specific energy density and gravimetric energy density,

  • Specific energy density, or gravimetric energy density, defines the amount of energy contained in the battery in per weight (Wh/kg)

When and where is energy density important?

Products that require long run times at moderate loads are optimized for high-energy density; the ability to deliver high current loads can be rather neglected. Electric cars require lithium-ion batteries with a high-energy density, since a passenger car usually wants to drive for a long time at a constant rate.

For electric cars, volumetric energy density is more important than specific energy density because battery space is limited. For electric aviation and aviation in general, the specific energy density is relevant because gravity has to be overcome constantly.

Volumetric energy density explained by wikibattery on www. Wikibattery. Org
Volumetric Energy Density explained by WikiBattery on www.Wikibattery.org

Energy density in a Battery-Pack

The energy density of a battery pack often is specified in e-car marketing.This figure takes into account all the components of a battery pack. This energy density of the “battery pack” is useful for the end user because this energy density is also effectively used in an electric car or other device. The high-energy density in LIB battery packs is responsible, among other things, for the good environmental balance in passenger cars.

Energy density in the "bare" battery cell

In development and in the trade, the energy density of the “bare cell” is often specified. This is higher than the energy density of the battery pack because “inactive battery components”(components which do not hold energy) such as a BMS, metal components, sealing materials, adhesives, thermal pastes and insulation materials that do not store energy are not included in the energy density. 

The following components are included here: active electrode materials, conductor films, electrolytes, separator, and a simple cell envelope.

Energy density in the "electrode material"

The highest energy density is usually given by researchers who investigate and develop a specific material. Here, for the most part, only the mass of the ACTIVE electrode material under investigation is considered (without additives, electrolytes, separator, and active counter-electrode).

This is justified, since in science one wants to investigate and compare individual materials.

However, for the researchers and readers of the research results, it is necessary to always describe exactly which cell components were considered in calculations for energy density, power, and capacity.

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