What limits the energy density of Li-ion batteries?

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Comparing to other rechargeable batteries, Li-ion battery could reach the highest energy density today. Many scientists still keep researching to achieve higher energy density of Li-ion batteries. So what exactly limits the batteries' energy density? It seems there are many factors affecting it, such as, the materials of positive electrode and negative electrode, the electrolyte, and the diaphragm...

Some people think improving Li-ion batteries' energy density may involve many things. It won't be so simple with only changing the materials, because the balance of internal material composition even if a little wrong can cause serious problems. The real breakthrough in battery technology seems to be very difficult. When will the next breakthrough comes out in the battery industry? Welcome to share your kind comments.

 

[DaveTheDude]

I suspect a solid state battery will be the next usable development for flashlight-sized power cells. Something with a capacitor for fast reloading would be nice, too.

 

[jtr1962]

My money is on ultracapacitors. Right now they're only about one tenth the energy density of chemical batteries, but unlike chemical batteries they don't seem to have as many inherent limits. From my reading on the subject, the upper potential limit for chemical batteries seems to be in the 1000 Wh/kg area, give or take. Right now we're about one third of the way there with commercial batteries.

With ultracaps it's simply a matter of surface area, dielectric constant, and working voltage. Increase any one of them, you increase the energy density. There are certainly physical limits, but it's likely they're well above those for chemical batteries.

A good analogy here is comparing LEDs to incandescent light sources. With the latter, you're inherently limited by blackbody spectra. At low filament temperatures you get mostly IR, not visible light. At high temperatures (well above tungsten's melting point) you get mostly UV. Even if we had materials which remain solid at much higher temperatures than tungsten, as I understand it the highest efficiency possible would be about 95 lumens per watt at a filament temperature of about 6500K:

Most of the energy in the spectrum falls outside visible wavelengths.

On the other hand, LEDs generate light due to electrons losing energy when crossing a P-N junction. There's no inherent limit on their efficiency converting electrical power into light, beyond the fact that energy can't be created or destroyed. LEDs can theoretically be 100% efficient. For deep red and blue emitters we're already at ~80% efficiency commercially, perhaps 90% in the lab. LEDs are analogous to supercaps, while chemical batteries are closer to incandescent light sources. The latter simply has inherent limits due to the physics of chemical reactions.

 

[alpg88]

I think soon we'll realize storing energy is neither safe nor cheap. and will look for ways to make it right on the spot, actually we already did kinda, we invented fuel cells, but complexity and required infrastructure kinda limits it for now, but it is just 1 way, i'm sure as we look farther we'll find other ways, or revisit old discoveries and inventions. We actually have the tech that would eliminate the need for most batteries, we have it for over 100 years, it was tested and it works, Nikola Tesla's radiant energy. i strongly believe the reason it was abandoned was a political, not technological.

 

[JustAnOldFashionedLEDGuy]

Lithium-Sulfur batteries have a theoretical energy density of 2600wh/kg. It is thought that a practical version could be easily 3-4x the energy density of today's Lithium batteries. That is game changing.

Under the radar, but probably the biggest potential "thing" in batteries in the last year was production of a form of sulfur that makes long life lithium sulfur (and potentially sodium sulfur) batteries viable. https://drexel.edu/news/archive/2022/February/lithium-sulfur-cathode-carbonate-electrolyte Even bigger than CATL being ready or close for commercial sodium-ion car batteries.