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Comment by cstross | Hacker News Reader

The key word that's almost submerged in the article is molten.

Like previous sodium-sulphur batteries this one relies on a molten salt electrolyte, meaning you won't see it in your phone or laptop any time soon!

However, as it's being developed with the idea of grid-scale smoothing/backup, that's much less of a problem. (The square-cube law means that as you increase the volume of your molten salt cell, the surface area grows more slowly -- and thermal losses scale with surface area, so really big cells are cheaper to maintain at operating temperature.)

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No, these are room-temperature NaS batteries. They use some special electrolyte, but I have no idea how this really works. Their main drawback so far was longevity, but this battery has a capacity fade of 0.05% per cycle, which is on par at least with a poor Li-Ion battery. LiFePo4 is still superior in that regard, but the much higher capacity and hopefully lower cost (if they can be manufactured efficiently) might make up for that, hard to tell.

> but this battery has a capacity fade of 0.05% per cycle, which is on par at least with a poor Li-Ion battery.

20% lost at 400 cycles. This isn't so bad if it really offers 4x the capacity. In terms of usage it will last 1600 cycles comparatively speaking. Which is still far better than Li-Ion.

No, Li-Ion batteries can be twice as good:

"In 2003 it was reported the typical range of capacity loss in lithium-ion batteries after 500 charging and discharging cycles varied from 12.4% to 24.1%, giving an average capacity loss per cycle range of 0.025–0.048% per cycle."

(https://en.wikipedia.org/wiki/Capacity_loss)

And that was twenty years ago, things probably have improved. I think you have a wrong impression what is meant with "a battery lasts X cycles". That does not mean that it will be at zero capacity after 'X' cycles, but usually that it is down to ~70% of the initial capacity.

EDIT: Sorry, I missed the "comparatively speaking", so you mean when including the 4x capacity. You are right, of course.

I'd happily trade 2x capacity for 0.5x life in my cell phone battery, provided that the cell phone manufacturer just makes it easy to swap batteries.

Something that baffles me is how hard it's become to replace the battery. I had the original generation Galaxy S -- I loved that thing, because there was a little latch mechanism on the back-side. With a firm tug, the rear cover popped right off, allowing you to pop the battery out. It took less than 10 seconds to do a battery swap, which I used to great advantage while traveling (carried a second battery with me). Of course, back in those days, the typical battery capacity was not nearly as good.

In any event, I wish I could still do that with my current phone. It would be super slick if there was a tiny auxillary battery or 60-second hold-up capacitor too, so you wouldn't even have to shut the phone off.

>Something that baffles me is how hard it's become to replace the battery.

Why is this baffling? It makes perfect sense for batteries to be non-replaceable: you can make the phone slightly thinner, and you can charge owners a small fortune to replace them, which will usually result in them simply throwing the device away after a while and buying a new one. Just look at Apple: they pushed non-replaceable batteries (and also removed headphone jacks in favor of expensive airPods), and people love iPhones and can't wait to get the next version, even if it costs $1399 and they have to sell their kidney to buy it.

This is such a cynical take. By ditching removable bits they save on internal room which allows bigger batteries. I would take 25% better main battery life over removable any day. If you don’t mind carrying an extra item (because that’s what swappable batteries means — by the way how do you keep the spare charged?) then get an external. Even easier to swap and use, often supports pass-through charging, and doesn’t create yet another aperture that needs waterproofing.

I'm using a Fairphone 3. It's one of those repairable phones where you can replace faulty parts. The battery costs €30 bucks. For me it's not about carrying a spare battery, it's about throwing the old one away when it can't hold charge for a whole day, and installing a new one. So far I've done this twice with the FP3. I have no intention of replacing this phone any time soon. If I do, it'll be like the last time: I'll get another repairable phone (FP4? FP5?) Before that happens I might have to replace the lower assembly because the USB port is getting loose, but that's only €20.

You're missing the real reason for replaceable batteries: they need replacement after a few years because their capacity decreases with age.

Can they be recycled to get back close to 100% capacity?

My LifePo4 battery has a 6000 cycle guarantee at 60% capacity.

So its not even close yet

> So its not even close yet

Yes, if you compare just capacity fade, that's true. But the longevity of LiFePo4 comes with a lower charge density than Li-Ion, about 170 mAh/g. This NaS battery currently has 1017 mAh/g, so almost a factor of 6. If the capacity is higher, you don't have to cycle as often, but of course, mileage depends on the use case.

That lower capacity comes at a cost cut and a huge materials advantage. LFPs are made of highly available materials. (Lithium, iron and phosphate).

The higher capacity NMC batteries are constrained on nickel production.

The question is more how many kWh can you store and extract over a lifetime at a given cost rather than how many cycles can it take.

If the 5999th charge is only holding appropriately 60% of a LifePo4 battery you don’t get 6,000 cycles * full battery capacity.

True, but you probably will get more before the battery becomes unusable in total.

It would be very nice if batteries were super predictable as in 'perfect until the 6 thousandth cycle and then dead', instead you get this gradual drop-off to the point where a battery is no longer usable for its intended purpose. Whether or not that is at 60% of the original capacity or not is moot if it doesn't make it to the 60% in the first place (lots of batteries get murdered well before the end of their design life), on the other hand if that means that the drop-off itself slows down then you might be able to get much more life out of them when treated carefully.

The big ones - in my experience, which is obviously not the final word on this - is to ensure that you don't charge batteries when they're very cold, that you don't use currents in excess of what they're made for (and preferably a bit below that) and that you don't subject them to mechanical stress. If you live by those rules you can make them stretch for a very long time, enough for technology itself, rather than that battery, to make your battery obsolete.

Witness the old lead-acid batteries used in cars, telephone switch boards and submarines. In cars they would last a couple of years at best, in telephone switch boards and submarines they would routinely outlast the rest of the installation.

The faster battery life deterioration might even be desirable for those manufacturers with planned obsolescence in mind, especially phone manufacturers

A somewhat shorter lifespan might be a decent trade if the materials are much more recyclable and if mining is produces less pollution.

also if the batteries are cheap enough they can be considered "partially rechargeable" and swapped out when the capacity fades too much

I suppose partially worn out batteries can also find new uses, such as stationary power reserves, where they're not being cycled a lot.

Is it 0.05% of the remaining capacity, or of the initial capacity?

The work describes a room temperature battery that uses an electrolyte of Na (sodium) in a propylene carbonate liquid carrier with electrodes made of graphene flakes with Mo and S embedded in the graphene framework. I don't know what the author of the article posted was trying to say when referring to molton Na-S, since it is not part of the battery described in the research, nor part of the manufacturing process. Probably the author did a search on Na-S for background, and not understanding how this differed, stuck it in.

That also jumped out at me when I read it. However, later on they state that this reaction works at room temperature:

> Using a simple pyrolysis process and carbon-based electrodes to improve the reactivity of sulphur and the reversibility of reactions between sulphur and sodium, the researchers’ battery has shaken off its formerly sluggish reputation, exhibiting super-high capacity and ultra-long life at room temperature.

This is confusing. Can someone make some sense of this?

> exhibiting super-high capacity and ultra-long life at room temperature.

Maybe this is just bad writing? The battery (at operating temp) has high capacity, and (at room temp) can be stored for a long time? The wikipedia page indicates that it is normal to store charged molten salt batteries at room temp when not being used.

https://en.wikipedia.org/wiki/Molten-salt_battery

I think it might literally mean "operates at room temperature" as in 25-35 degrees C. Not really sure how it works but there seems to be a distinction between high, intermediate, and room temperature for the Na-S battery's operating conditions.

Quote from: https://www.tandfonline.com/doi/full/10.1080/21663831.2022.2...

    1.1. History of Na-S batteries

    Research on Na-S batteries originated in the 1960s, with the first research focused on High-Temperature Sodium-Sulfur (HT-Na/S) batteries, which operate around 300–350 °C. A molten Na anode (melting point=98 °C), a molten sulfur cathode (melting point = 118 °C) and ceramic β'-Al2O3 as solid electrolyte are assembled into the HT-Na/S batteries [11]. HT-Na/S batteries avoid the dendrite problem and have high electrical conductivity. However, it also has the defects of high working temperature, high risk, low energy density and high operation cost. And then, the Intermediate-Temperature Sodium-Sulfur (IMT-Na/S) batteries were innovated in the 1970s and operate between 120–300 °C. The IMT-Na/S batteries also eliminated the dendrite problem, but the electronic conductivity and the utilization of sulfur also decreased. Researchers have been intensively investigating Room-Temperature Sodium-Sulfur (RT-Na/S) batteries, which operate around 25 °C-35 °C. RT-Na/S batteries can completely convert S8 to Na2S, so they have a high theoretical energy density (1274 Wh kg−1)

Maybe they found a way to mix it into an eutectic mixture? The article doesnt say much on the specific chemistry of the liquid salt. https://en.m.wikipedia.org/wiki/Eutectic_system

The title of their article[1] is "Atomically Dispersed Dual-Site Cathode with a Record High Sulfur Mass Loading for High-Performance Room-Temperature Sodium–Sulfur Batteries".

[1] https://onlinelibrary.wiley.com/doi/10.1002/adma.202206828?u...

Just to add, yes, that paper is about solid state batteries.

The paper’s title is “Atomically Dispersed Dual-Site Cathode with a Record High Sulfur Mass Loading for High-Performance Room-Temperature Sodium–Sulfur Batteries” (https://onlinelibrary.wiley.com/doi/10.1002/adma.202206828?u...), so I guess you misread that.

The Wikipedia article mentions two types, molten and room temperature, each with their own pros and cons.

https://en.wikipedia.org/wiki/Sodium%E2%80%93sulfur_battery

The paper mentions making the battery at 300c (oven temperature) but the text talks about "room temperature" or "RT":

https://onlinelibrary.wiley.com/doi/10.1002/adma.202206828

"...thermally treated at 300 °C for 12 h. The Mo mass loading of S@MoS2-Mo1/SGF was ≈1.2 wt.%, measured by ICP-OES. The synthesis procedure of S@MoS2/SGF was the same as S@MoS2-Mo1/SGF but the thermal treatment was extended to 24 h. To prepare the S@SGF, pure SGF was used to replace Mo1/SGF. S@Mo1/SGF was prepared by pyrolyzing the mixture of Mo1/SGF and S at 155 °C for 12 h."

The only mentions of higher temperatures are for thermogravimetric analysis where they heat it to 800c and measure the amount of S as it varies with temperature.

Nope, the PR was poorly written (maybe the Department is experimenting with chatGPT ?).

Surprisingly the publication is freely available, and yes it's all room temp:

https://onlinelibrary.wiley.com/doi/10.1002/adma.202206828

My supervisor's wife was working at a pharma company back in the 2000s. Her job was to reproduce promising publications related to any conditions they were involved in. The reproducibility rate was something like 25%, which is higher than some other estimates I've seen looking across many fields, but still....

Incentives matter and right now they're the wrong ones

>Nope, the PR was poorly written (maybe the Department is experimenting with chatGPT ?).

ChatGPT probably would have done a much better job with access to the publication. Pretty soon, these lousy science journalists are all going to be out of a job when they can't even get basic facts correct, and the real scientists don't have time to write or review PR articles themselves, so an AI will fill that role instead.

That is not and never was the point -- sodium is in the same column as lithium on the periodic table, but it is significantly heavier than that, so mobile applications (cars, phones) are out of scope. Sodium is promising for stationary, community- or grid-level storage.

There are many good reasons to expect sodium batteries to beat li-ion batteries in specific energy. Yes, a sodium charge carrier is ~3.2 times heavier than a lithium ion, and yes, it holds a bit less charge, but none of this has to be relevant because in a normal li-ion battery less than 1% of the total mass is active charge carriers.

If you went by the simple properties of charge carriers alone, you'd expect lead-acid batteries to be at least 15 times worse than li-ion ones. However, the best lead-acid batteries are only ~8 times worse than the best li-ion batteries. Because even though the charge carriers are so much worse at doing their job, the chemistry is otherwise much more simple and easy to work with that it lets you pack a lot more charge carrier and lot less support infrastructure into the same battery.

Sodium is similar, in that if you have a viable electrolyte, you can expect to utilize a lot more than 1% of the mass of your battery for usable charge carriers. This is why it's absolutely possible for molten salt batteries to have specific energies much higher than the best lithium-ion ones. As far back as 2014 there was a lab-scale prototype that beat every li-ion battery then in existence. The big downside of course is the molten part -- these are stationary batteries not due to low specific energy, but the fact that they have to be heated above ~110C to operate, and it is much more economical to make such batteries as large as possible. And in that segment, the chase is not for the highest specific energy but the lowest cost per Wh.

The paper, that red_trumpet posted down on the replies is about solid state NaS batteries.

Very important detail. Thanks for highlighting.

Not only does this limit practicality for phones, cars, but it limits practicality at all. Some of the larger utility scale solar-collector designs ended up failing because of the challenges of maintaining elements that involve molten salt.

I (incorrectly it seems) assumed that “molten” was just part of the manufacturing process. This take makes more sense.

you won't see it in your phone or laptop any time soon

I know it's (probably) a compound and doesn't have the same properties as the individual constituents, but still I wouldn't feel entirely comfortable carrying around sodium and sulphur in my pocket all day. Maybe I'll let other people prove its safety over a few years first.

Is there any particular reason? Seems pretty naive to make any assumptions about the properties based on its elemental composition. Lithium is incredibly reactive and toxic in its pure form but you surely carry that around. Do you ever consume table salt, a compound of reactive sodium and toxic chlorine?

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