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Comment by aetherspawn | Hacker News Reader

It's unclear, but if this is Toyota's proven NiMH technology from the Prius, rather than Lithium technology (i.e. in the Tesla Powerwall), I'd personally opt for this.

It will last longer, and is a lot safer. Unlike Lithium, NiMH is not particularly unstable at high temperatures or flammable. And Prius batteries have been proven to last more than 20 years (at reduced capacity) without any safety problems -- we don't ever see Prius' catching fire.

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This would be an interesting choice.

a) it will not necessarily last longer, li-ion in the right conditions (particularly more stable chemistries) have superior cycle life experience in practice

b) yes, newest batteries decay slowly over time and don’t ‘just die’ - but this is the same as li-ion

c) safety is mitigated in the modern setting by utilizing the same charge controllers used to keep EV car batteries safe. Remember most North American homes with a natural gas furnace literally is a controlled blast of explosive gas without a smell that people just have and don’t think about - as the tech goes on the learning curve the management issues (I.e. disconnecting faulty cels individually) seems like a plausible end solution, even if that is necessary.

Lastly, while NiMH does not use soon to be very scare processed lithium, NiMH uses very large amounts of nickel, cobalt and comparatively exotic ‘rare earth metals’ who’s production should be expected to be even more challenging to scale.

All that said - I am all for us scaling up all of these technologies so that each can fit within a particular market niche based on inherent pros and cons.

> natural gas furnace literally is a controlled blast of explosive gas without a smell

OT: in Europe, a thiol is added to natural gas to give it a distinctive smell. Isn't the same done in the US?

Yes. I think parent referring to normal operation of furnace not smelling since a furnace is considered safe.

> safety is mitigated in the modern setting by utilizing the same charge controllers used to keep EV car batteries safe

The problem is fire safety, if the house is on fire the lithium battery is going to make it much worse. Controller ofcourse does not help there

> we don't ever see Prius' catching fire.

I mean, definitely not in the news as much as Tesla...

2018 https://money.cnn.com/2018/09/05/news/companies/toyota-prius...

2019 https://www.yahoo.com/entertainment/toyota-prius-catches-fir...

The headline of the first article is "Toyota is recalling 1 million hybrids at risk of catching fire", did Tesla ever do any similar recall, because of potential fire risks?

You don't get a car recalled if customers don't report issues.

Customers don't report issues if you force them to sign NDAs to get their cars fixed under warranty.

That wasn't a battery issue though, it was a wiring harness issue. That's a relatively common problem even in gas cars. Cars have a lot of wiring.

Nothing to do with batteries or chemistry, it is some insulation on the wiring harness that can wear away.

> we don't ever see Prius' catching fire.

You've probably never seen an old Prius. Here in Fiji, our roads are filled with second-hand Priuses (from Japan), and we have a Prius fire every two months at least.

I suppose its hard to tell if any Prius fire is due to electrical or ICE; kinda the worst of both worlds (and I note that as a happy Prius owner).

Perhaps look at the BYD batteries, they are LiFePO₄, which is a lot safer than the Tesla Powerwall (I believe that is NMC?). It should also last longer under the same cycle conditions. The only downside is it is more temperature sensitive in terms of capacity and life, but that could be mitigated by for instance installing it indoors.

I was under the impression this chemistry is a lot more unstable but denser and lighter. Isn’t it what is used in drones and you have to charge them inside a firebox because they’re more prone to thermal runaway?

Eh, people have to charge drone batteries carefully not because of chemistry, but because of sketchy industry norms.

Almost every other industry making lithium-battery-powered products insists on 'genuine' batteries and tells people buying third-party replacements is taking your life into your own hands. Drone enthusiasts, on the other hand? Ordering batteries from unknown suppliers on ebay or aliexpress isn't unusual.

And even reputable drone battery brands face the temptation to advertise a spec without any safety margin, to stay competitive. If all your competitors advertise '90C discharge' on the assumption they get the cooling of the drone's fans, you gotta follow suit to stay competitive.

At the same time, can you think of any other application that takes a battery from full to empty in 15 minutes? Or an application that runs its batteries without a BMS, fuse, or battery temperature monitoring?

(Of course, in a sense that's a reasonable state of affairs - shutting down because the battery's overheated isn't exactly a safety feature for a drone, unlike for a battery drill or vacuum cleaner)

LiFePO₄? Drones probably use LiCoO2. It has a much higher energy density and higher C-rate than LiFePO₄. LiFePO₄ has a much higher thermal runaway temperature than NMC (and other chemistries). I found this article with a short summation: https://www.newcastlesys.com/blog/lithium-ion-vs-lithium-iro...

The drones you're thinking of here (FPV stunt drones, racing drones) have the most demanding discharge profile of any use for lithium batteries.

The whole drone is built around draining current from the smallest possible battery, as fast as possible, right up to the limit of safety. Charging is also a faster-is-better thing, from a pilot's perspective.

This kind of maximum discharge raises the risk of dendrite shorts considerably, which are what pops a lithium battery usually. So a firebox is a good idea for this case, it's just inherently dangerous to be right at the limit of energy-per-gram and discharge capacity all the time.

The chemistry is also never LiFePo, which is too heavy.

Hybrids (so presumably Prius' too) are the most likely type of vehicle to catch on fire: https://www.autoinsuranceez.com/gas-vs-electric-car-fires/

That source mentions BMW and Chrysler hybrids as problematic. (go figure) Toyota's NiMH batteries have a very good record for reliability and safety going back two decades.

Hybrids on average have a greater fire risk because they have more opportunity for mistakes -- they have both the spicy components from an EV and the spicy components from a gas car.

Based on the list there Toyota isn’t even listed?

It weighs 142kg for 9kWh. It is almost certain that it is NiMH.

For stationary applications why not.

The good thing about grid storage is that you don't need the weight and density of lithium. That's especially good because it looks like we don't have enough lithium for electrification of transportation. Lithium supplies will improve in a few years, but right now I think we should incentivize using lithium in mobile applications. There are plenty of technologies for power storage that don't use lithium.

There's more lithium on Earth than lead. And it should be pretty easy to recycle once the market is there.

Right. But we aren't setup to extract all that much of it yet. 5 years from now? Maybe. Next year? No.

nickel metal hydride? is that really better. i never had good experience with those.

lifepo4 is where it's at.

NiMH is "better" for residential (in my opinion) in the sense that it is more inert than any Li-based battery. If you crush or set fire to LiFePo4, it will burn.

What's interesting is because Toyota has been developing the NiMH for so long, it has achieved densities of approx. 150Wh/kg, which actually makes it about as good as Lithium technology from 5 years ago, but without any of the stability problems.

NiMH were incredibly annoying back when I last messed with RC cars, which was when NiMH was the latest and greatest battery chemistry in use there. They rarely delivered in practice what was in writing quite promising capacities, and they were incredibly delicate when it came to heat.

The wikipedia page for NiMH also mentions things like venting hydrogen gas when overcharged...

Looking through the LiFePo4 pages on wikipedia the safety and durability profile seems superior to NiMH, but maybe the LiFePo4 pages there are just fixated on vs. other Li-Ion chemistries.

My impression ATM is if you've got LiFePo4 available it's preferable to NiMH. And my personal experience with a LiFePo4 portable battery booster for jumping cars and emergency charging stuff has been an incredibly positive one. The thing is like a tiny weightless magic box that tolerates incredible abuse without losing any charge even stored for a year in desert temps, and somehow manages to put out enough current to start large-displacement high-compression V8s.

What's interesting is because Toyota has been developing the NiMH for so long, it has achieved densities of approx. 150Wh/kg

This is an interesting point; why hasn't Toyota made longer-range plugin hybrids with these batteries, which would seem to be sensical? Looks like the largest battery in a plug-in Prius so far is just 8.8 kWh, according to Wikipedia.

I would guess that there is not much room for them to develop the battery technology further, as it seems they are close to the absolute limit of the materials' performance.

So to start a plug-in hybrid program using that battery technology, could be very bad (outpriced, outperformed) if there was suddenly a huge leap forward in Li density and safety.

> why hasn't Toyota made longer-range plugin hybrids with these batteries

Because even Toyota found the Lithium works better for that application.

NiMH's faults can be compensated for by managing recharge and discharge cycles - toyota has specialized in this for a long time, it's a few steps above your average AA battery

They just only use 40-80% SoC; it's nothing special to carry 2x+ the battery to try and make up for an inferior chemistry. That also doesn't compensate for the high self-discharge rate.

Does this also mean it's not subject to the increasing prices of lithium?

Nickel is also expensive. Usually it's quite a bit more expensive than lithium, but it seems that lithium prices are spiking at the moment.

(The amount needed is also relevant, I'm not sure exactly how much lithium is in lithium ion batteries and how much nickel is NiMH.)

Nickel prices have rocketed up lately too.

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