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Lithium-ion batteries are not only valued for their durability and freedom from maintenance, but also for their comparatively high energy density. Find out what this means and what influence the material used in the batteries has on energy density in our guide.
The Importance of energy density in lithium-ion batteries
Energy density provides a battery with power over a longer period of time – even with a small battery size. It indicates how long, for example, an electric stacker truck can be used before you need to recharge it. A high energy density has the advantage that it stores a large amount of energy in a battery whose format is nevertheless compact. In other words:
Energy density refers to the distribution of energy over a certain size. The greater the energy density of a lithium-ion battery, the longer the electric stacker truck can be powered by it, for example, being usable even for extensive lifting tasks.
Volumetric and gravimetric energy density of Li-ion batteries
The quantity, to which lithium-ion energy density is distributed, can be defined as:
• Spatial:
The so-called volumetric energy density describes the energy measure in joules per unit volume in cubic metres. The following applies for the same amount of stored energy: the greater the volumetric energy density, the smaller the dimensions of the battery.
• Capacity per mass:
The gravimetric energy density indicates the energy measure in joules per mass in kilograms. The energy density of lithium-ion batteries is usually given gravimetrically, i.e., as capacity per mass. How high the energy density of these batteries is, depends on the cathode material used. Mostly, cobalt oxide is used here. This offers an energy density of up to 180 watt-hours per kilogram (Wh/kg). Although negative electrodes made of lithium cobalt nickel, for example, allow an energy density of up to 240 watt-hours per kilogram, lithium-ion batteries with around 170 watt-hours per kilogram are used more frequently. Because of the lower energy density, these batteries offer more than 500 charging cycles and are thus more durable overall.
Coulomb Efficiency
The Coulomb Efficiency (CE) describes the charge efficiency with which the energy stored in the battery can be extracted again, i.e., used. In addition to a high energy density, lithium-ion batteries have a Coulomb efficiency of almost 100 percent: almost all the current you charge into a lithium-ion battery can be withdrawn again. Accordingly, lithium batteries are far more efficient than lead-acid batteries, which only achieve an efficiency of 65 percent. The energy storage units remain particularly powerful if you not only charge lithium-ion batteries properly, but also correctly store your lithium-ion batteries when they are not in use.
Overview: Energy density of different lithium-ion batteries
Depending on the construction of lithium-ion batteries, they can achieve different energy densities:
| Lithium Battery Type | Energy Density |
|---|---|
| Lithium cobalt dioxide battery | 110–160 Wh/kg |
| Lithium polymer battery | 100–150 Wh/kg |
| Lithium iron phosphate battery | 80–140 Wh/kg |
| Lithium titanate battery | 90 Wh/kg |
Especially in the field of electromobility, research is currently being conducted on lithium battery energy density. Future rechargeable lithium batteries are expected to achieve an energy density of over 400 Wh/kg based on Li-sulphur or up to 800 Wh/l based on Li-Air.
FAQ on the power density of lithium-ion batteries
Energy density refers to the distribution of energy over a certain size.
Energy density is subdivided as follows:
1. Gravimetric energy density: indicates the measure of energy in joules per mass in kilograms.
2. Volumetric energy density: indicates the measure of energy in joules per volume of space in cubic metres.
Coulomb efficiency refers to how much energy per volume can be extracted from a battery.
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