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Comment by unwind | Hacker News Reader

So ... As the battery is used, bonds are formed between oxygen molecules in the air, and the lithium ions on the battery's electrodes. Weight is saved by "borrowing" those O2s from the air, as compared to carrying them around fixed in an oxide. Fine.

Does that mean that as the battery charge is depleted (=it runs out of free lithium ions, I guess), it's mass increases due to all the newly bound oxygen being stored in there? That's counter-intuitive enough to just be awesome!

Also, a large-scale battery whose charge level is directly related to its mass (albeit inversely so, from my intuition) and supports recharging is almost a bit like magic. I hope they pull this off, so I can learn to weigh my car before going on long trips, in the future. :)

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Imagine NASCAR with these batteries - Cars covered in solar panels. Drivers carefully timing their recharge pitstops to keep their weight down. Every fan in the stands has a big reflector to reflect sunlight at their favorite car.

I saw sunburned people blinding drivers and causing crashes.

NASCAR fans are not very happy with "fuel mileage" races, and I would imagine what you describe would be far worse.

// also not very fond of people who say we watch for the wrecks

But wouldn't it catch on if they actually thought they could help their favorite driver win? Seems like an idea like that could be revolutionary.

As organic_code pointed out, blinding the drivers is a real possibility. Also, races are fairly long and holding a mirror up for two or three hours doesn't sound like a lot of fun. New drivers in the sport have no chance of winning (see last years Daytona 500). Never mind the problem track owners will have selling concessions to a group of people who cannot eat / drink for most of the race.

I want to watch a driver's skill, not the energy output of his / her fans.

Why recharge when you can just replace the batteries in such a situation? It would make for a better show, anyways.

It reminds me of planting a tree in a pot, and then realizing in a few years the tree is a lot bigger and weighs a lot more than the pot when you started.

That's because the carbon mass of the tree comes entirely from the air (CO2). For 1kg of carbon mass your tree has to process 2000m^3 of air.

Weight is also saved by using Oxygen instead of heavy metals to donate electrons. Using oxygen (Mr 16) over lead (Mr ~207) will be the main source of weight save.

Li-ion batteries don't use lead.

I'd imagine that more weight is saved because all of the oxidant in the reaction is actively used, and you're not carrying plenty of it around hidden behind surfaces that prevent it from being part of the reaction.

Cool. that would actually be a useful UI feedback property: to check if your phone needs recharging, just pick it up. If it feels heavy it needs to be charged.

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