Australia first to test new lithium-sulphur batteries(newscientist.com) |
Australia first to test new lithium-sulphur batteries(newscientist.com) |
Publication link: https://advances.sciencemag.org/content/6/1/eaay2757
“In order to have much cheaper energy and more ethical batteries, we need a radically new energy storage system,” says Shaibani. The researchers will further test battery prototypes with a view to manufacturing them commercially in Australia in coming years.
It appears that Shaibani is saying that their new battery chemistry is an example of a radically improved battery that removes ethical problems while it improves energy density. The way the New Scientist article is written, that preceding paragraph makes it sound like Shaibani's new chemistry still needs improvements to remove cobalt.
There is already no nickel, manganese, or cobalt in this new lithium-sulfur cathode (nor in most lithium-sulfur cathodes). See Table S1 in the supplementary table for elemental analysis:
https://advances.sciencemag.org/content/advances/suppl/2019/...
A few papers about the electrolyte problem are e.g.:
https://pubs.acs.org/doi/abs/10.1021/acscentsci.7b00123
https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.2017059...
Meanwhile Li-ion batteries were invented in seventies, it took 20 years to commercialization. First cells had 100W h/kg, and 30 years later we are slowly approaching 300W h/kg.
It still only lasts a couple of hundred charge cycles before wearing out:
https://advances.sciencemag.org/content/6/1/eaay2757
"The cells are stable for more than 200 cycles..."
A twofold improvement in capacity would kill gasoline cars dead. That's 300 miles of range out of a 600lb battery. Adding up the weights of various components the electric car would weight about the same as a gasoline one.
While the failure modes of metal lithium anode batteries are terrifying that's probably okay for grid applications. Difference between a cell phone stuffed under a pillow and a battery in a concrete vault at at substation.
Many companies are on the fore-front of batteries...if this chemistry is legit and available, you will know when Tesla or LG chem or one of the big players buys this groups' IP.
Until subsidies are increased...
Pet peeve of mine is how big business like to champion capitalism, but when they start failing they no longer like those rules and want government help to stay relevant and afloat.
At the nominal rate of 750 amp hours per kilogram for lithium-Sulphur is well above normal lithium-ion batteries. But compared to gasoline, it raises the bar from 1% vs gas, to 2%. Do I have that right?
Second, it's based on use submissions. You think we should know something interesting about the AU fires? Submit a good article about it I guess. If I and others learn something interesting, it'll get voted up. That's how it works.
This naturally makes battery improvements a huge win. If you double power density you can cut the weight of the battery by more than half for the same range, since not only do you get the same power from a lighter battery, now the car is lighter and requires less energy to accelerate.
new weight for energy density calculation = (total battery weight) - (ICE component weight) + (electric motor weight)
And battery packs have cooling systems too. So no savings there.
Specific energy (watts-hours per kilogram) is the entire ballgame with batteries and transportation.
The problem is with degradation - it seems the new batteries only last 200 cycles.
Don't fool yourself - there's a transmission element in an electric car too. The power has to get to the wheels, regardless of the power plant.
https://en.wikipedia.org/wiki/Gasoline_gallon_equivalent
Unfortunately, internal combustion engines have a pathetic fuel economy since they run at low temperatures (around the boiling point of water). All heat engines are limited by the Carnot efficiency, which improves with higher temperature differential. In practice, other cycles like Otto, Diesel, Rankine and Brayton are lower than Carnot and improve with things like higher compression ratio:
Carnot efficiency = (T.hot - T.cold)/T.hot
where T is in Kelvin
A low compression, naturally aspirated engine running at room temperature with nothing done to improve fuel economy runs at (373.15 - 298)/373.15 = 20% efficiency. I've heard figures as low as 8% for rubber meets the road efficiency in older passenger cars, which I believe, since we drove a ’68 Cadillac that got 5 mpg back in the 90s when gas was under $1 per gallon.
The best modern high compression engines typically achieve 25-30% efficiency at best. So I figure there are about 8-10 kWh/kg (28.8-36 MJ/kg) available in gasoline with modern vehicles. Cars built before ‘70s efficiency standards would be more like 2.5-3 kWh/kg (9-10.8 MJ/kg).
Unfortunately, it's not just that people don't care how ridiculously inefficient their vehicles are, it's that politicians corrupted by the fossil fuel industry and vehicle manufacturing lobbies never stop conspiring to lower efficiency standards:
https://www.vox.com/2019/4/6/18295544/epa-california-fuel-ec...
But I digress.
Electric motors typically run at about 95% efficiency, so we can probably assume 90% efficiency to the road. That’s over 10 times more efficient than classic cars!
Looks like Tesla lithium ion batteries are 0.254 kWh/kg (0.914 MJ/kg):
http://theconversation.com/teslas-batteries-have-reached-the...
Which is very close to the theoretical ideal for lithium ion of 0.294 kWh/kg (1.058 MJ/kg):
https://en.wikipedia.org/wiki/Energy_density#Tables_of_energ...
I'm having trouble finding energy densities for the new lithium sulfur batteries:
https://advances.sciencemag.org/content/6/1/eaay2757
https://advances.sciencemag.org/content/advances/6/1/eaay275...
I'm going to use their low number of 1200 mAh/kg, working between 1.7 and 2.5 V, so averaging 2.1 V (which is very inaccurate without integration), we can call it about 2.520 kWh/kg (9.072 MJ/kg). That would be about 10 times denser than Tesla batteries. Maybe they are estimating half the density in the real world due to packaging or something, in order to arrive at their "5 times longer battery life" headline.
So anyway, the real numbers are:
Gasoline 33 kWh/kg 118.8 MJ/kg (ideal)
Gasoline 8-10 kWh/kg 28.8-36 MJ/kg (actual for modern vehicle)
Gasoline 2.5-3 kWh/kg 9-10.8 MJ/kg (actual for pre-70s vehicle
Lithium sulfur 2.520 kWh/kg 9.072 MJ/kg (ideal)
Lithium sulfur 1.260 kWh/kg 4.536 MJ/kg (actual)
Lithium ion 0.294 kWh/kg 1.058 MJ/kg (ideal)
Lithium ion 0.254 kWh/kg 0.914 MJ/kg (actual for Tesla)
I was thinking about what I said about the Carnot cycle and maybe it wasn't quite accurate. I tend to think about the world through a first-order effects lens. So the easiest way to explain why a turbine is usually more efficient than an internal combustion engine is that the turbine runs at a much higher temperate.
But the gasses in an internal combustion engine can reach a fairly high temperature as long as it's beneath the sag temperature of the metal block (otherwise you get warped valves). There was a lot of nonsense in engines before fuel injection attempting to prevent preignition when the mixture passed by the valves (in order to run as lean as possible, which caused excess heat) that I always thought was pretty silly.
Also there was a lot of work in the 80s and 90s to make ceramic engines in order to run at a higher temperature that never went anywhere as far as I can tell. They would have been lubricated by graphite and basically last forever. I think they were abandoned due to brittleness, but they would be great today with a continuously variable transmission or as a generator running at constant RPM like with locomotives.
Here's a quote from [1].
"These “super ceramics” are as tough as metals, but they are also one-third as heavy and can operate at 2,400 degrees Fahrenheit—500 degrees higher than the most advanced alloys. This combination allows engineers to design lighter components for engines that don’t need as much cooling air, generate more power and burn less fuel."
2400F is about 1600K. If you plug this into the Carnot efficiency formula and use a T_cold of about 220, you get something like 86%. If they ever find a way to replace the silicon carbide they currently use with hafnium carbide, they can reach 90%
[1] https://www.ge.com/reports/space-age-cmcs-aviations-new-cup-...
The curb weight of a Model 3 is in the same ballpark as a BMW 3 Series or Ford Taurus. Lighter cars exist but mostly because they're significantly smaller or slower or both.
That's not quite true. At the very least, EVs require a much smaller radiator, if it has one at all. Some EVs don't have cooling at all (Nissan Leaf), although that increases degradation in hotter climates.
I think his point stands.. An ICE engine weight at least 200lb. With transmission it could be up to 600lb. The Model S engine is 70lbs.
You "only" need to halve the weight of a Model S battery for the drivetrain+battery to be in the same ballpark as an ICE drivetrain as far as I can tell.
Chevy Bolt is about 3500lbs Prius is about 3000lbs.
Chevy Bolts battery weighs 440 kg or about 968lbs.
Reduce the battery weight by 1/2 and save 484 lbs. So the weight drops to 3016.
So point stands if the battery power density improves 2X then the weight penalty disappears.
Please don't pretend it's anywhere close in complexity and weight to the ICE. Of course if you include batteries then it's heavier. But that's why people are excited for any small change in battery energy density.
uBlock Origin is very reliable on my Firefox on Android.
You know, Safari and Chrome are not your only options on mobile.
You seem to carry a misconception from an older battery chemistry (I don't remember which, but it was common in early cell phones), where it was supposedly better to discharge the battery completely before charging again.
Most chemistries are not like that, as far as I know. In fact, with li-ion it's better to charge every night, if your EV battery has a good buffer, or you can configure it to charge to 80% except for days where you'll actually need 100%.
Maintaining 99% for 200 cycles seem pretty good to me. Possibly better than Li-ion? It depends on how fast the battery degrades after that. But I'm pretty sure my EV lost its first 1% way before 200 cycles.
https://batteryuniversity.com/learn/article/how_to_prolong_l...
To distill it down to a single figure: If you drain the battery down to 40% capacity between recharges, you can expect it to take ~600 charge cycles for total capacity to drop by 30%. If you only drain it down to 90% between recharges, the number of cycles increases to ~6,000.
The article doesn't specify, but I assume that's using a slow charge. I am guessing that with a fast charge, which is what is implemented in most consumer electronics, the difference would be even more stark.
But, assuming it’s an issue a hybrid design with say 150 miles of daily driving lithium ion and 150 x4 = 600 miles of extended range is another option.
But increased battery degradation starts way before you hit that limit. At least with cell phones, that tend to push battery cells pretty hard, you'll have pretty bad degradation when discharging to 0%. I think most EVs have a higher cut-off, and most people don't discharge EVs to near 0% anyway.