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Australia first to test new lithium-sulphur batteries

newscientist.com

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Re: Australia first to test new lithium-sulphur batteries

#51

Post by Gibbon1 »

audunw wrote: post #47
JoeAltmaier wrote: post #26

Earlier quoted context omitted.

Nowhere near. The Tesla battery pack is 1000 lbs. There are entire cars that don't weigh that. Race car engine is 200lbs. 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.

> And battery packs have cooling systems too. So no savings there. 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"…

You can look at actual numbers. Instead of a Model 3. Lets compare a Chevy Bolt with a Prius.

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.

Re: Australia first to test new lithium-sulphur batteries

#52

Post by credit_guy »

zackmorris wrote: post #49
JoeAltmaier wrote: post #10

Lithium-Sulphur has high energy per kilogram which makes it good for transportation. Also high energy per dollar to manufacture which makes it good for grid storage (where weight and size don't matter too much, but cost does). 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 th…

Gasoline has about 33 kWh/kg (118.8 MJ/kg): 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 ar…

Gas engines with 40-45% efficiency are possible [1].

[1] https://phys.org/news/2019-06-efficiency-gas.html

Re: Australia first to test new lithium-sulphur batteries

#53

Post by JoeAltmaier »

elil17 wrote: post #33
JoeAltmaier wrote: post #29

Earlier quoted context omitted.

Its all problems, so far. Weight, heat, size, charge cycles, range. Its only recently that its been even possible to make a practical electric car. 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.

An electric car transmission is a usually a simple reduction (two gears). An ICE transmission is usually a six speed shifter, often with hydraulic controls. A world of difference in terms of weight and maintainability.

That's just talking gearbox. Then there's casing, shafts, mounts, cooling. The difference in number of gears is the smaller part.

Re: Australia first to test new lithium-sulphur batteries

#54

Post by ajuc »

JoeAltmaier wrote: post #53
elil17 wrote: post #33

Earlier quoted context omitted.

An electric car transmission is a usually a simple reduction (two gears). An ICE transmission is usually a six speed shifter, often with hydraulic controls. A world of difference in terms of weight and maintainability.

That's just talking gearbox. Then there's casing, shafts, mounts, cooling. The difference in number of gears is the smaller part.

This is Tesla mechanically: https://qph.fs.quoracdn.net/main-qimg-fa63245953aaf5f393e851...

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.

Re: Australia first to test new lithium-sulphur batteries

#55

Post by zackmorris »

credit_guy wrote: post #52
zackmorris wrote: post #49

Earlier quoted context omitted.

Gasoline has about 33 kWh/kg (118.8 MJ/kg): 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 ar…

Gas engines with 40-45% efficiency are possible [1]. [1] https://phys.org/news/2019-06-efficiency-gas.html

Hey thanks for that! I didn't know that methane has low knock so could be thought of as a high-octane fuel (which allows for higher compression which translates to higher thermodynamic efficiency). That has promising ramifications for a future methane fuel economy, where hydrogen from high-temperature solar thermal electrolysis is combined with a carbon source (perhaps CO2 from the air) to create methane. Propane would be ideal due to its low pressure storage if its conversion from methane can be scaled up. But compressed natural gas (CNG) is fine as well with methane and the gasses have similar properties.

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.

Re: Australia first to test new lithium-sulphur batteries

#56

Post by credit_guy »

zackmorris wrote: post #55
credit_guy wrote: post #52

Earlier quoted context omitted.

Gas engines with 40-45% efficiency are possible [1]. [1] https://phys.org/news/2019-06-efficiency-gas.html

Hey thanks for that! I didn't know that methane has low knock so could be thought of as a high-octane fuel (which allows for higher compression which translates to higher thermodynamic efficiency). That has promising ramifications for a future methane fuel economy, where hydrogen from high-temperature solar thermal electrolysis is combined with a carbon source (perhaps CO2 from the air) to create methane. Propane wou…

Ceramics never made it into internal combustion engines, but they did make it into jet engines. In particular the whole 737-MAX debacle is because of the fabulous new engine built by GE, which Boeing simply thought they cannnot not install it on their 737 (unfortunately, they did a patch work at that).

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-...

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