The search to generate more energy from less material while preventing the combustion of more fossil fuels than the Earth can handle has continued to spawn creative ideas. Nuclear fusion records are smashed, even if only by the tiniest margins and seconds at a time. On the other hand, solar panels are becoming increasingly efficient, and their installation is becoming more strategic to reap bigger gains.

Still, it remains challenging to determine how the generated energy can be stored and relinquished on demand across the electricity grid. As battery storage and manufacturing capacity trend upwards, their prices plummet.

As batteries are increasingly used in electronic devices, cars, and even for solar power storage at home, energy density becomes crucial. The commercialization of lithium-ion batteries has led to significant advancements in energy density.

Currently, the most efficient lithium batteries contain about 954,000 joules of energy per kilogram (2.2 pounds) of mass. This is roughly 22 times the energy from burning one kilogram of oil. Modern lithium batteries can store energy at a high density, corresponding to 42,000,000 joules per cubic meter.

Batteries are expected to play a vital role in promoting green technologies. However, despite the significant breakthroughs, we are still likely in the very early stages of battery energy density development.

Theoretical scientists are particularly imaginative in projecting how innovations can take us years into the future. In a recent study, two physicists explored the limits of battery energy density based on Einstein's general theory of relativity.

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