Lithium-air batteries

[Serge]

The linked paper describes the same kind of power brick that you mention above.

Interesting concept - a primary battery that would take a Roadster 50,000 miles (or am I missing something?)

I got 27K "ideal EPA range" with cell voltage of 3V.
40,000 g * 50 Ah /g * 3V = 6 MWh (quite a pack)
6 mWh * 244 miles / 54kWh = 27,111 miles.

Numbers make sense, given that such a pack would contain a lot of pure lithium metal, a very energy dense material, as anode.

Lithium air sounds really nice, and it has HUGE potential ... but there are still many kinks to work out. For example, very low power

Indeed a discharge rate of .1 A/g at 3V equals power density of just 30 W/kg -- 10x weaker than lithium ion. The paper does not specifically mention whether tests were conducted at atmospheric pressure, but perhaps increasing pressure could result in higher current flow.

Now I'm sure these little issues can be resolved by keeping the batteries temperature-conditioned like the Roadster already does, and by paralleling with some Li-Ion batteries to supply the power while Li-Air batteries supply the energy.

Or trickle charge an ultra-capacitor, some of which have power density of 6KW/kg.

[dpeilow]

Why only 40kg?

[Serge]

Why only 40kg?

I originally wanted to compare to weight-equivalent of Roadster's ESS. Shame on me for forgetting how many grams are in a kilogram

On second thought, 40 Kg is about the right weight for a "power-brick"; could probably go even lower to 20 Kg for 12K miles. Gosh, I hope they can make this technology work soon ...

[bolosky]

Indeed a discharge rate of .1 A/g at 3V equals power density of just 30 W/kg -- 10x weaker than lithium ion. The paper does not specifically mention whether tests were conducted at atmospheric pressure, but perhaps increasing pressure could result in higher current flow.

Did you just invent an EV supercharger?

Seriously, though, to generate the ~190kW that the Roadster uses, you'd need over 6000 kg of batteries! You would, presumably, use some kind of power buffer (like an ultracap) to cover for bursts, but you'd still need the main battery to provide the long-haul average power. At 250Wh/mile and 60 m/h, you need 15kW sustained, which would still be 500kg of batteries at 30 W/kg. That's somewhat bigger than the Roadster's battery, and still kind of on the weak side.

That is, I think to be useful in cars, they need a big improvement in power density.

[Serge]

Did you just invent an EV supercharger?

Seriously, though, to generate the ~190kW that the Roadster uses, you'd need over 6000 kg of batteries! You would, presumably, use some kind of power buffer (like an ultracap) to cover for bursts, but you'd still need the main battery to provide the long-haul average power. At 250Wh/mile and 60 m/h, you need 15kW sustained, which would still be 500kg of batteries at 30 W/kg. That's somewhat bigger than the Roadster's battery, and still kind of on the weak side.

That is, I think to be useful in cars, they need a big improvement in power density.

Well, I goofed on the order of magnitude (1 kg = 10^3 g), which means that .1 A/g translates into 300 W/kg, not 30. This level is presumably comparable to power output of lithium-ion cells currently employed in Roadster's ESS, so make that "power-brick" a 50 kg (instead of 40) for 15 kW on the go recharge of high power [low energy density] main traction battery. This looks like the game changer many were looking for (or did I goof with numbers somewhere again?)

[dpeilow]

Another way to look at it is that to deliver 190kW you'd need 633kg of the things.

633kg leads to 95MWh, which even with 'real world' power use is over 300,000 miles...




EDIT - so this felt a little too good to be true and here is why:

Having had time to read the linked article (as opposed to relying on the quotes above) I've seen there is some 'cheating' going on with the numbers. The energy density they are quoting is for the cathode only.

Comparison of cathode discharging capacity with that of conventional lithium ion battery.
mAh per 1 gram of cathode.

Calculated based on mass of air electrode = (porous carbon + catalyst + binder) and mass of cathode of a lithium-ion battery = (active material + conduction assisting carbon + binder)

It felt slightly wrong given that the scaling up I did earlier based on this chart came out at ~50000 miles per charge, whereas the calculation from scratch came out at >300,000 miles.

Thinking about it, this can be verified by taking the 150mAh/g figure they have for Li-ion and working out Wh/kg, which comes out at 555Wh/kg. The alarm bells should be ringing, as the number for available batteries is under 200Wh/kg (2.775 times less).

So if you divide the 300,000 miles number by 2.775 (=108108) and then the ratio of the above pack to the Roadster's approximate mass of 18650 cells (633/320), you get 54,652 miles. Given some of the uncertainties in the information available, that's pretty close.

It's not clear, but that 2.775 divider also probably applies to the power density, so we are definitely back to the li-ion/capacitor based buffer to get peak power. But interestingly, it actually doesn't specify that 0.1A/g is the maximum discharge rate.

Still, this is an awesome achievement - I'd be interested to see the paper they presented in March for more details.

[dpeilow]

New lithium-air cell could make car recharging obsolete

[Tdave]

Does "air" in Lithium-Air means it actively uses atmospheric air during its operation?

[Serge]

Does "air" in Lithium-Air means it actively uses atmospheric air during its operation?

The oxygen component of it

[JRP3]

New lithium-air cell could make car recharging obsolete

More like "could make recharging impossible".

The plan from the Japanese researchers calls for an electric car driver to exchange one type of electrolyte in a battery cell for a new air electrode when the battery runs low.

I have no interest in a battery that I can't charge cheaply at home. It negates one of the great benefits of an EV, low cost overnight home charging and never having to stop at a "gas" station or being tied into a single "fuel" source or provider.