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Comment by craftyguy | Hacker News Reader

> U-M engineers created a ceramic layer that stabilizes the surface—keeping dendrites from forming and preventing fires

I'm curious how strong this ceramic layer is. When I hear 'ceramic' I think of 'brittle, fragile' materials, and I'm not sure having a battery that would explode if dropped or hit would be much of an improvement.

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I used to have the same intuition but also just recently started to learn about material sciences. They refer to 'ceramics' as a wide family of material that is comparable to "metal" and "crystals" and the likes. These families are usually categorized by the type of atomic bonds found in them. Example, Wikipedia starts the article on "Ceramic" with:

   A ceramic is a non-metallic solid material comprising an 
   inorganic compound of metal, non-metal or metalloid atoms 
   primarily held in ionic and covalent bonds.

At least, if your mental model was about ceramic vases and ornamental objects.

This reminds me of an article on Ars Technica a couple of years ago:

https://arstechnica.com/science/2016/02/dutch-researchers-ha...

Interesting, thank you for the explanation. I generally think of things like tiles (e.g. like the ones on the space shuttle that were fragile) when I hear ceramics.

The insulator in common aluminum electrolytic capacitors is also a ceramic -- aluminum oxide. The positive plate is aluminum, and the oxide grows on it because when the capacitor is charged, the positive plate attracts free oxygen atoms from the electrolyte (and hydrogen atoms are released at the cathode).

While it is brittle, it's also self-healing. When it cracks and exposes the aluminum underneath, a new layer of oxide is plated immediately, as long as the capacitor is charged.

Equipment that's been left powered off for a long time and then turned on can sometimes have caps explode because there's a lot of leakage current from holes in the ceramic until it heals (minutes to hours). Lithium batteries are usually completely ruined if they ever discharge down to zero.

> When I hear 'ceramic' I think of 'brittle, fragile' materials

You might be surprised to find out that the best body armor today - NIJ level IV (and similar standards in other countries), the kind that can stop armor-piercing bullets - is made either entirely of ceramic, or (lately) is a ceramic/polyethylene laminate.

Side note: you probably wouldn't expect polyethylene show up in this context either - the one used is ultra-high-molecular-weight polyethylene, and much like ceramics used, it's pretty different from our "common sense" perception of the material.

As far as fragility of such ceramics, this is a topic that comes up often enough to spawn an obligatory "will it ...?" genre on YouTube. So you can watch something like this, and judge for yourself:

https://www.youtube.com/watch?v=YSK4U2Poo0k

Ceramic has been used in electronic circuits for decades. Take a look at these ceramic capacitors: https://en.wikipedia.org/wiki/Ceramic_capacitor

Also, the raspberry pi uses a ceramic heat sink.

I think the strength of ceramics varies greatly depending on how they're made. For example, ceramics are used to make armor plates that are strong enough to stop assault rifle rounds https://en.wikipedia.org/wiki/Sapi_plate#Materials_and_capab...

They stop bullets but break in the process. This absorbs much of the energy.

"Military testing calls for survivability of three hits from the round marked on the plate."

When I hear ceramic, I tend to think kitchen knife or superconductor. There's a lot more to ceramics than pots and jars.

Not sure about this one, but GE is making engine components out of a ceramic composite: https://www.ge.com/reports/space-age-cmcs-aviations-new-cup-...

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