Energy Density of Batteries-Types and Formula

Energy density refers to the amount of energy a battery poses compared to its size. It has become a vital metric, especially in modern devices. Most gadgets nowadays require a lot of energy but from a small-sized battery. 

The higher the energy density of a battery, the longer it can emit charge. This means batteries with high energy density are in demand because they occupy less space. For instance, electronic devices such as smartphones, laptops, and tablets require high-density batteries to power them for a long period. In this article, I will take you through everything you need to know about energy density. 

The Energy Density of the Battery Formula

There are two ways to find the energy density of a battery. The first method is known as gravimetric energy density. This refers to how much energy a battery contains in proportion to its weight. The second method is referred to as volumetric energy density. In this method, you divide the energy of a battery by its volume.

Battery energy is usually measured in watt-hours. It represents using one watt in an hour. To get the energy density, we, therefore, need to divide watt hours which is its energy, by its weight (kg or g) or by its volume (liters).

Gravimetric Energy Density = Watt-hours / Weight 

Volumetric Energy Density = Watt-hours / Volume

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The first step is to determine the Wh of the battery. Next, you need to determine the weight or volume of the divide. You can provide the answer as Wh/Kg or Wh/L. Note that when calculating the energy density of other energy sources, it can be more than 1000 Wh/kg. Therefore you can represent the answer as KWh/kg or KWh/L. This is because 1000-watt hours makes 1 Kilo-watt hour. 

It is important to note that energy density is different from Power density. The former refers to the battery energy stored compared to its volume or weight. Contrary,  power density refers to the power output per kilogram. In simple terms, energy density measures the amount of energy a battery holds, while power density measure how much it produces.

Energy Density of Battery Types

Batteries hold different energy densities depending on their chemical composition. Let's take a look at the energy densities of the most used battery types.

Lithium Cobalt Oxide

Lithium Cobalt Oxide has one of the highest densities, which ranges from 150 -200 Wh/Kg. The cathode is made of cobalt. A layered structure lies in between the cathode and the anode to allow the movement of the lithium ions. Lithium cathode batteries are popular in electric vehicles, laptops, and cell phones.  

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Although they hold the most energy, lithium cobalt oxide batteries are very expensive. This is because they are short in supply, and there is an increased demand for electric cars. 

Lithium Nickel Manganese Cobalt Oxide Batteries

NMC batteries have a high energy density which ranges from 150 Wh/kg to 220Wh/kg. Nickel and Manganese are added to add stability. Its also used in electric vehicles, e-bikes, and medical devices. The chemistry in this battery determines its energy density. Nickel is unstable with a high energy density, while Manganese is stable with a low energy density. 

Lead Acid (SLA/VLRA

Lead-acid batteries hold the least energy density. They hold approximately 30 to 40 Wh/kg, which is equivalent to 60 to 75 Wh/L. Lead acid is one of the oldest battery types to be created. Despite having a low energy density, they are used for many applications, such as starting the car engine.

Nickel Metal Hydride

Nickel Metal Hydride, popularly known as NiMH, has an energy density of 100 Wh/Kg. These batteries hold more energy density compared to NiCd batteries. NiMH batteries are popular because they are less prone to explosion and leakage. For this reason, they are widely used as an alternative to alkaline batteries

Alkaline Battery

The alkaline battery energy density ranges from 85 to 190 Wh/kg. It obtains its energy from a chemical reaction between manganese dioxide and Zinc metal. Alkaline batteries are often preferred compared to Zinc Carbonate batteries because of their long shelf life and higher energy density. 

Energy Density of Battery vs Jet Fuel

The only thing standing in between the future of flying cars is energy density. This is also part of the reason why we still rely on gasoline and jet fuel for airplanes and space shuttles. In simple terms, most batteries are heavy with inadequate energy density for such advanced applications.

Even when you compare the most advanced and dense batteries, they are still nowhere close to jet fuel. For instance, a Tesla Model 3 battery has an energy density of 207 Wh/kg. From an electric car's point of view, these are good numbers but not enough for air navigation.

Jet fuel holds an energy density of 9.6 KWh/L which is about 50 times denser than lithium batteries. However, the density reduces to about 14 times more than batteries due to the inefficiency of the internal combustion. This takes into consideration 1000 pounds of batteries compared to the energy density of 1000 pounds of jet fuel. 

Researchers say that the energy density of batteries could match that of Jet fuel in 30 years based on the current development trends. A lot of companies are investing heavily in making batteries more energy-dense and more efficient. This means that flying cars are close to disrupting the urban transport system. 

The batteries that most manufacturers are betting on include Lithium-Oxygen, nickel-iron, and magnesium. Furthermore, some companies are also investing in solid-state batteries. These types of batteries could provide a higher density than those that rely on polymer or liquid-based electrolytes. 

Apart from flying car applications, future batteries will play a vital part in storing clean energy. Many institutions may adopt it as the fight against climate change heats up. The future of electric flights is just a few developments away. National governments and big companies are in the front runner to ensure batteries achieve a high energy density closer to or even more than jet fuel. The biggest challenge facing the industry is the availability of raw materials. It is expensive to mine Lithium as it requires a lot of water. On the other hand, cobalt deposits are shrinking.