Which substances store the most energy?

December 28, 2025 •

4 min read

In physics, the mass-energy equivalence principle, $E=mc^2$, reveals that matter itself is the ultimate energy store. Understanding which substances store the most energy is crucial for everything from developing new fuels to advancing battery technology. While most people think of fossil fuels or batteries, the answer spans a far wider and more astonishing spectrum of materials.

Quick Summary

This article examines various substances with high energy density, distinguishing between chemical, nuclear, and theoretical sources. It covers practical fuels like hydrogen and gasoline, advanced technologies like lithium-ion batteries, and the extreme theoretical limits of antimatter to answer which materials hold the most energy.

Key Points

Gravimetric vs. Volumetric Density: The 'most energy' can mean either energy per unit of mass (gravimetric) or per unit of volume (volumetric), which are key considerations for different applications like aerospace versus consumer electronics.
Antimatter has the highest energy density: Theoretically, antimatter offers the highest energy density possible, converting 100% of its mass to energy upon annihilation, though it is not a practical energy source for now.
Nuclear fuel is millions of times more energy-dense: Uranium-235 stores millions of times more energy per kilogram than fossil fuels, leveraging the power of nuclear fission.
Hydrogen has the highest chemical energy density by mass: By weight, hydrogen is the most energy-dense chemical fuel, but it has a very low volumetric density, complicating storage.
Fats are the most energy-dense biological molecule: For living organisms, lipids (fats) serve as the most efficient long-term energy storage, containing over twice the energy per gram as carbohydrates.
High energy density can pose safety risks: Packing more energy into a smaller space, particularly in batteries, increases the risk of thermal events if not managed carefully.
Batteries offer usable electrical energy: Modern lithium-ion batteries provide a relatively high energy density for direct electrical use, making them a cornerstone of portable electronics and electric vehicles.

Defining Energy Density: Mass vs. Volume

When asking which substances store the most energy, the answer depends on whether you are considering energy per unit of mass (gravimetric energy density) or energy per unit of volume (volumetric energy density). A substance might be lightweight and energy-rich, making its mass-based density high, but it may take up a lot of space, giving it a low volume-based density. Both metrics are critical in real-world applications, such as for aircraft (where weight is key) versus portable electronics (where size is paramount).

The Top Contenders: Nuclear and Antimatter

Beyond everyday chemical reactions, the true high-energy substances reside in the realms of nuclear physics and theoretical science. These materials dwarf the energy potential of even the most potent chemical fuels.

Nuclear Fuels

Nuclear fuels, such as uranium-235, store vast quantities of energy in their atomic nuclei. This energy is released through the process of nuclear fission, where the atom is split. One kilogram of uranium-235 can produce millions of times more energy than one kilogram of gasoline through fission. This is because nuclear reactions tap into the strong nuclear force, which is far more powerful than the electromagnetic forces governing chemical bonds.

Antimatter

For the highest possible energy storage, science points to antimatter. When matter and antimatter collide, they annihilate completely, converting 100% of their mass into energy according to $E=mc^2$. This yields an energy density orders of magnitude higher than any other known source. However, producing and storing antimatter is incredibly difficult and expensive, and remains largely in the realm of theoretical physics and advanced research, with practical applications still a long way off.

High-Energy Chemical Substances

While nuclear and antimatter energy are on another level, many chemical substances are notable for their high energy density, particularly in practical applications like transport and power generation.

Hydrogen

Hydrogen is celebrated for having the highest energy density of any chemical fuel by mass. At 142 megajoules per kilogram (MJ/kg), it is nearly three times more energy-dense by weight than gasoline. However, its volumetric energy density is very low under normal conditions, requiring compression or liquefaction for efficient storage, which is a major engineering challenge.

Hydrocarbon Fuels (Gasoline and Diesel)

As the foundation of modern transport, liquid hydrocarbons offer an excellent balance of energy density by both mass and volume. While their gravimetric density is lower than hydrogen, their liquid state makes them far easier to store and transport than gaseous hydrogen, as reflected in their high volumetric energy density.

Lithium-Ion Batteries

Representing electrochemical storage, modern lithium-ion batteries have a high energy density compared to older battery types, though they pale in comparison to chemical fuels. Their appeal lies in their ability to provide electricity directly without combustion, making them critical for electronics and electric vehicles.

Biological Storage

In the biological world, organisms have evolved to store energy efficiently to survive.

Lipids (Fats)

In humans and animals, lipids (fats) are the primary source of long-term energy storage. They offer approximately 9 calories per gram, more than double the energy density of carbohydrates or proteins. This high concentration allows organisms to store large amounts of energy in a compact form.

Carbohydrates (Glycogen)

For quick energy, organisms use carbohydrates. While less energy-dense than fats (around 4 calories per gram), they can be broken down rapidly for immediate use. Glycogen is the primary carbohydrate storage form in animals.

Comparison of Energy Storage Methods

To put these differences into perspective, the table below compares the energy densities of various substances and technologies.


Substance/Technology	Type of Energy	Gravimetric Energy Density (MJ/kg)	Volumetric Energy Density (MJ/L)	Primary Application
Antimatter	Annihilation	~1.8 x $10^{17}$	N/A	Theoretical
Uranium-235	Nuclear Fission	~7.9 x $10^7$	~1.5 x $10^9$	Nuclear Power
Hydrogen	Chemical (Combustion)	142	8 (liquid)	Rocketry, Fuel Cells
Gasoline	Chemical (Combustion)	44	32	Transportation
Lipids (Fats)	Biological	37	N/A	Animal Energy Storage
NMC Battery	Electrochemical	0.54-0.79	1.1-2.4	EVs, Electronics
Carbohydrates	Biological	17	N/A	Quick Energy

Conclusion: The Final Word on Energy Storage

The search for which substances store the most energy reveals a hierarchy of energy storage, from biological lipids used for long-term reserves to the staggering power contained within atomic nuclei and antimatter. While practical applications currently rely on a trade-off between energy density and manageability, the potential of nuclear fuel and, someday, antimatter shows the immense power latent in the fundamental properties of matter. Hydrogen offers a compelling combination of high gravimetric density for transportation, while chemical hydrocarbons remain vital for their volumetric efficiency and existing infrastructure. Ultimately, the 'best' substance depends entirely on the specific application's requirements.

The Future of High-Density Energy Storage

Ongoing research in areas like next-generation battery technology (solid-state batteries), advanced nuclear reactors (breeder reactors), and hydrogen storage methods (cryo-compression) aims to push the boundaries of energy density further. These innovations will be crucial for a sustainable future, enabling more efficient and powerful solutions across various sectors, from powering homes to long-distance travel. The development of fuels that can be created from excess renewable electricity, like synthetic methane or ammonia, represents another promising avenue for chemical energy storage.

The information provided in this article is for general knowledge and informational purposes only. It is not intended as a substitute for professional advice from a qualified expert in physics, chemistry, or engineering.

Frequently Asked Questions

Fats store more than twice as much energy per gram as carbohydrates. While carbohydrates provide quick, accessible energy, fats are used by the body for long-term, compact energy storage.

Yes, but it depends on the measurement. Hydrogen has a much higher energy density by mass (per kg), but gasoline has a significantly higher energy density by volume (per liter). This is why hydrogen vehicles require pressurized or liquid fuel tanks.

Nuclear energy is the most concentrated practical form of energy. One kilogram of nuclear fuel can yield millions of times more energy than a kilogram of any chemical fuel, although antimatter holds an even higher theoretical energy density.

Lithium-ion batteries generally have the highest energy density among commercial battery technologies. However, different lithium-ion chemistries exist, with lithium cobalt oxide (LCO) having particularly high energy density, though some risk is involved.

Energy density is typically measured in two ways: gravimetric energy density (energy per unit of mass, e.g., MJ/kg or Wh/kg) and volumetric energy density (energy per unit of volume, e.g., MJ/L or Wh/L).

Theoretically, antimatter is the most energy-dense substance in the universe, as the annihilation of matter and antimatter converts their entire mass into pure energy.

The technology to produce and safely store antimatter is currently far too complex, expensive, and energy-intensive for practical use. Scientists can only create and contain tiny, short-lived amounts for research purposes.