Patent 6,936,371 - Recycling Battery Pack

I would recommend using Google patent search to get a copy. The overall process is well defined. It is not a trivial process since it required a vacuum, plastic welding, and handling KOH while not absorbing CO_{2}. Still, it means it should be possible to refurbish our NHW11 and NHW20 batteries and keep them rolling until 'the wheels fall off.'

Bob Wilson

 

Not to trivialize the risks and technical challenges, it also makes sense to share what is known so we can conduct informed investigation. Trying to replicate this process is not trivial and anyone wishing to commercialize this process will have to deal with royalties. Worse, I think this patent is a dead-end approach and reveals a major problem with current traction battery design.

Personally, I think the idea of plastic welding is nuts. It requires using the same plastic forming method used to manufacture the battery. This can be done but it is not trivial and quality control of each plastic weld becomes a major challenge. After the first time, it becomes less and less likely to succeed (ever try to re-weld an existing weld?)

It makes more sense to modify the battery once so water replacement is both practical and safe. This is an engineering challenge but no worse than many other engineering problems. There is data that Prius traction batteries at 'like new' Ahr capacities improves Prius performance. IMHO, the loss of traction battery capacity should be treated like any other operating fluid loss or wear.

I have one NHW20 battery module and 79 test NHW11 battery modules not counting the 38 in my 2003 Prius. I'm measuring the capacity of the weakest modules and finding:

Ahr
0.5 - from failed, replaced traction battery
2.0
2.2
2.2
2.2
2.3

4.4 - from salvage
5.0
5.5
​

I am looking at how to refurbish the cell assemblies with the lowest Ahr capacity and return them to 'like new' capacity. This patent shows one of several approaches.

Bob Wilson

 

Patents are a funny thing. If you use it for your personal use, an experiment, no problem. But if you try to sell something based on the patent, then there comes the risk of patent infringement. The solution is to apply for royalties and come to terms with the patent holder.

The key is to do it for your own benefit and don't offer someone else's hard work as your own. Of course, if you come up with a different process that accomplishes the same goal, electrolyte replacement, so much the better.

Now if someone comes up with a kit that might be used for some alternate approach, well again, no harm done. If this kit avoids dealing with a saturated KOH solution, I know some folks would be relieved.

Bob Wilson

 

Thanks Tom,

I've been pretty much following standard practice and realized that like speeding 5 mph over the limit, in the USA there is a separate problem of enforcement. But first, I need experimental data that shows an alternate or better approach and that is what I'm working on.

Bob Wilson

 

Hi folks,

I bought a worn out battery pack from an NHW11 because I knew it had at least one failed cell. The following shows the voltage as function of time as my MRC 989 battery charger tried to go through a refurbishment cycle after adding distilled water:

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The proof is how quickly the voltage jumps up during the charge and later drops as soon as the discharge cycle begins. But worse, during discharge the dead cell began working like an electrolysis cell, generating hydrogen and oxygen gas that bubbled out of a small leak in one of access holes that failed to seal with JB Weld epoxy:

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One problem with the epoxy sealed hole is the original hole is covered up preventing drill-out and resealing. So instead, I decided to try using stainless steel tee nuts, stainless steel screws and rubber gaskets. This will allow easy electrolyte replacement in the future:

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The tee nuts were installed using a soldering iron and pre-drilled, access hole. These are test samples that I'll use for stress testing as well as 'blue printing' the battery module.

The epoxy-hole method failed because when I tried to close the hole, the cell assembly was still out-gassing. This meant the epoxy at one end failed to flow into the hole and set:

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You'll notice the hole on the right, next to the B+ terminal is not filled with epoxy.

Going from left to right, the first cell has a fully closed epoxy hole; the over pressure valve, the temperature probe cup, the first tee nut, second tee nut, and the last cell with the incompletely sealed, epoxy hole:

​

There are dimension and process issues to test as well as pressure testing. But if the system works as expected, we may be able to return used NHW11 cells (and possibly NHW20) to like new.

BTW, the electrolyte, KOH, is a very powerful, caustic lye solution that will dissolve organic material like skin, eyes and clothing. It is risky to take a battery apart and requires: (1) eye protection, (2) face and breathing protection, and (3) skin protection. Treat the guts as if they are burning hot, lava and you'll have the right attitude:

​

I don't recommend repeating this experiment but I figured posting some of the results is better than ignorance. Toyota has a patent on how to refurbish a Prius battery and my experiments are aimed at understanding how well it works. But I also realize how dangerous this is and would recommend those who have some interest understand what has been accomplished and what remains.

So far, I have yet to 'recover' a cell. These initial experiments are aimed at the mechanical aspects of the problem. Soon enough, I'll get a chance to test the rest and then environmental regression testing. This means I need to make sure it works from below freezing to nearly boiling.

Toyota has a battery refurbishment patent but the method I'm following differs in these aspects:

• plastic welding vs. permanent, stainless steel ports
• KOH electrolyte vs degassed distilled water
• weight electrolyte vs. level measurement

Otherwise, we are after the same end result, returning a battery module to a significant part of the initial capacity.

Bob Wilson

 

The first recovered battery:

I'm running another series to see how high the efficiency will go. But as far as capacity is concerned, this one is just a little over 6.5 Ahr.

Bob Wilson

 

Lessons learned:

• plastic welding is more difficult than my skills
• failed to figure out how to seal terminals
• water replacement and charge-discharge cycles brought battery modules to more than new spec

Bob Wilson