Featured Toyota’s Redesigned Aqua uses a new Bipolar Nickel-Hydrogen Battery

Thanks ... fixed

 

Looks like there's still one lurking ... I think the battery specs might be around 27 kW, but around 1.3 kWh.

 

Toyota is not calling it one pedal driving. They are only talking about less switching your foot to the brake pedal. From the driver's seat, it will seem like having the car in B or a lower gear.

That would be an added complication, and likely reduce efficiency, as driving in a lower gear does with a traditional transmission.

Regenerative braking was out before hybrids, and some BEV prototypes had one pedal driving early on. They came about because electric motors can also work as generators, but the idea wasn't new. Locomotives have been using it for decades before; called dynamic braking. The train has a hand control that controls throttle and the dynamic braking. The only difference is from regen braking on one pedal driving is that there is a resistor bank instead of a battery.

 

Yes looks like its 27kW for Gen 3 and Gen 2 is only 20kW limited by DC-DC converter. It would be interesting to see specs for the new Aqua.

 

Metal hydrides can be made with less, or no, rare earth elements. Such batteries using them are still NiMH. Stainless steel can contain those metals. Toyota likely kept what the exact nickel alloy is out of the patent.

Nickel-hydrogen batteries have a pressure vessel because the reaction releases and takes up hydrogen gas, which is a low density state for the element. It is very unlikely that a porous nickel alloy structure has the volume to contain the gaseous hydrogen produced during the batteries use without a pressure vessel. Without the means of withstanding the pressure build up, the hydrogen will find a way out of the battery. More likely the nickel sponge is a metal hydride.

 

The patent illustrates the battery being held together by bolted metal plates or sealed in a metal case .. so presumably the new physical structure can contain some level of pressure.

 

That patent provides great information ... and gives you an insight into their long term plannings as the patent process started in 2016 and finished in 2020. So they have been working on this battery for at least 5 years but probably much longer ... but you never hear about it until the product is released.

There is also paper from 2007 "Transportation Bipolar Ni-MH Battery" ... where they say;

"The reduced current path leads to a design that has lower internal resistance, with the capability of supplying much higher power levels. However, most attempts at designing bipolar secondary batteries have suffered from the problems of electrolyte leakage and management of gas pressure within the cells."

So it looks like the patent shows how Toyota has address the leakage and gas pressure issues, in a battery that can be mass produced.

The paper also indicates production costs could by 25% less than Toyota's current Gen 2 Prius battery. They then go on to detail test results done with a Gen 2 Prius turned into a PHEV with a 6 kWh Bipolar NiMH battery.

 

All batteries have to deal with pressure build to some degree, and some even make use of venting to prevent catastrophic failure of the case.

Nickel-hydrogen batteries have cases to contain high pressure gases. They look like gas tanks with curved ends, or have thick walls.


There is a void around the cell stack for the hydrogen to occupy. A porous metal will have a reduced volume for the gas to inhabit, and thus result in higher pressures. Unless the metal is a hydride, and takes up the gas chemically.

Note what Toyota calls the battery in that 2007 paper.

 

Nickel-Hydrogen batteries are famous for insane cycle lifetimes. I can't remember the exact numbers but the ones on Hubble went through something like 120,000 cycles before replacement.

 

44,000 at 85% DOD is definitely in the "insane" category too!

 

They cycle the lithium batteries very shallow. 55%-75% or less, I think, to get the needed lifetime.

Nickel hydrogen batteries don't have to be expensive. Everything that's space-qualified is expensive. I remember in school a team I worked with had to buy 4 space-qualified 1/4x20 bolts for an experiment to ride on the Shuttle, and they were like $500 for the set.

 

According to that 2007 paper, the layer arrangement reduces electrolyte leakage. Likely through the pressure exerted through those bolted plates. The patent also states this is the keep the layers in contact with one another.

"Further, the negative active material layer contains a hydrogen storage alloy as a negative electrode active material."
https://patentimages.storage.googleapis.com/93/98/7a/b0d2923094bce2/US10693175.pdf

Isn't hydrogen storage alloy just another way of saying metal hydride?

Toyota has come up with uses different densities of porous material in the active area to deal with pressure generation from the oxygen produced by overcharging. Presumably, all the hydrogen goes into that storage alloy. Is there another chemical storage mechanism besides the standard hydride one, that would allow gaseous or pure hydrogen to be released?

 

OK the new Toyota ones don't have tanks ... here are the description & diagrams from the patent filing.

100 - The bipolar electrode plate 100 includes a current collector plate 10, a positive electrode active material layer 20 and a negative electrode active material layer 30. The current collector plate 10 has a first surface 11 and a second surface 12. The second surface 12 is the surface opposite to the first surface 11. The positive electrode active material layer 20 is arranged on the first surface 11. The negative electrode active material layer 30 is arranged on the second surface 12.

200 - A separator 200 is arranged between the bipolar electrode plates 100. The separator 200 may be, for example, a non-woven fabric made of polyolefin. The separator 200 holds the electrolytic solution. The electrolytic solution may be, for example, an aqueous potassium hydroxide (KOH) solution or the like. A gel electrolyte may be used instead of the electrolytic solution.

300 - The seal portion 300 is composed of, for example, a gasket 301, a seal ring 302, a sealant 303 and the like. The gasket 301 and the seal ring 302 may be made of polypropylene (PP), crosslinked polyethylene (PE), ethylene-propylene-diene rubber (EPDM), PTFE, or the like. The sealant 303 may be, for example, epoxy resin, silicone rubber, or the like.

400 - Part of the bipolar electrode plate 100 is connected in parallel by the lead tab 400

500 - The outer casing 500 may be, for example, a bag made of an aluminum laminated film. A part of the lead tab 400 is exposed from the exterior body 500 and functions as an external terminal. The gap between the outer package 500 and the lead tab 400 is sealed with resin 304 or the like, for example

 

One of the active layers is porous with varying porosity; more on the outside edge, and less in the center. Any oxygen produced during overcharging flows into those pores, which reduces the pressure increase from the introduction gas.

The question is where exactly does the hydrogen go. The patent mentions a porous hydrogen storage alloy in a short intro section. This could be an adsorption system, where the hydrogen just sticks to material's surface that is greatly increased by being porous. Then hydrogen storage alloy is used in the literature to also cover metal hydrides which have the hydrogen chemically bond to the material.

Perhaps the patent clarifies it at some point, but after reading about the active material in which oxygen is trapped, and how its density varies, three to five different ways, my eyes were starting to glaze over.