liveforphysics said:
The path forward for cells isn't a pouch or can, both of those are vessels attempting to contain a fluid in a limited volume in a situation where micro-gassing is continuous. The safety difference between various types of lithium ion cells doesn't begin to change much until the anode ceases to have an SEI layer (like LTO). The SEI layer is the first thing to go in most types of situations that cause a hazardous event with a battery, no matter what the cathode mixture may happen to be.
If they are not pouch or can then they are an idealistic solution that does not exist in the immediate or short term (possibly long term). I will believe it is a possibility when a proof of concept is delivered so funding can be secured.
The existence of a working proof of concept can inherently not precede something being a possibility. That mindset is a reason why folks predominately use ICE for daily transportation needs.
As far as the second part of the above argument - it obfuscates the simple truth with lower level details.
The real goal is to create a battery system that can be abused... and still be safe and viable.
Absolutely. Contrary to the BS delivered by marketing teams, Lithium iron hasn't proven to be that in real-world safety testing. This is because no matter how stable the cathode material, if the anode still has gnarly thermal decomposition when the cell is poked or overcharged (as seen with A123 cells etc), it still isn't at the level of safety needed.
It was thought that the "BMS" could serve this purpose... but to date I have yet to see an implementation of a system that utilizes a BMS where the addition of the BMS does not LOWER the overall reliability of the product.
Agreed, no BMS can reduce safety risks at intrinsic cell-level hazard levels. The best they can do is disable a battery from being used that has an issue before it becomes a safety concern. BMS budgets and design emphasis (i.e. weight at the Systems Negotiation Level) will have to double or triple for them to work as desired.
No amount of BMS budget makes the cells themselves safer, and further I don't know that at any level it can offer a safer function than simply shutting down a pack with an issue from being used. No amount of balance current shuttling corrects an issue with a cell that has abnormal internal self-discharge or corrosion etc.
A lead acid battery can be driven into the ground... then charged back up... and it is reasonably safe and "works".
Lead acid has caused some of the most spectacular battery explosions on this forum and in industry. Does not typically cause fires, just nasty explosions when abused in the right/wrong application. They also decay drastically when over-discharged contrary to popular belief. They are in a state of failure by design from the moment the plates are wetted with electrolyte.
For Lithium technology to be completely embraced it must have similar characteristics.
I would say it already has superior characteristics in all respects (including safety and durability), including cost over the life of the vehicle (if we're talking about EV batteries).
Case in Point:: NiCd memory issues hosed the Rechargeable Revolution for 2 decades.
IMHO, what hosed the revolution was people choosing to take the attitude of not creatively pushing to create superior battery options. The state of the art of today batteries were entirely possible to have in the 1960's or maybe sooner. Had development efforts been directed towards safe and higher energy density batteries as a priority above what efforts and resources were directed towards technology of mass-murder and people settling for getting by with what already was proven in batteries. The act of settling and making-do is the moment your progress ceases, or at best becomes incremental and therefore not paradigm shifting.
liveforphysics said:
The solution is solid electrolytes using no SEI layers and batteries made without the need for cell level interconnects, because without the limitations of the electrolyte voltage stress induced decomposition, you can make laminated flat stacks conducting through the Z-axis of the current collector foils, resulting in orders of magnitude lower conduction losses and heating in a battery. Anything less is nothing more than a temporary compromise to show people EV's can function.
Many solid electrolytes already are working, but at this moment the manufacturing processes/costs are outrageous. Fortunately, manufacturing processes can be solved, no matter how difficult they seem initially.
Yea - with enough money.
Or, no money and a single inspired genius. I believe huge money is what generates the minimally creative incremental steps. The real breakthroughs often come out of some impoverished tinkerers basement.
Sooo...... if we are going to debate (and be it known I swore off from arguing with Luke years ago)...
A wise decision if you make the illusion of 'winning' something your goal criteria, but one that misses both the benefits and joys of exchanging constructive thoughts. In my own life experience, it seems everytime honest discourse and disagreement occurs, there is an opportunity for all involved to walk away wiser than had they not participated.
The question to debate is this:
If you take two cell technologies:
Say...
A LiPo Pouch (or XYZ non-LiFe Pouch) and a LiFePO4 Can
I know you know this, but just to be clear for others, what is in a modern can or pouch cell is the same active material guts, one is rolled up and stuffed in a can while the other is laminated into a foil pouch.
You take them both and abuse the shit out of them... (in all the ways we do)
When the test is done
1) Which has a higher probability of creating a hazardous situation?
The can is a pressure vessel that bursts at a potentially dangerous to humans pressure and associated shrapnel velocities etc. The failure of a pouch cell to be capable of containing high pressures is an inherent safety feature against it becoming a pressure vessel (and if the vent on a can is done right, this is true for can's as well).
2) Which retains a greater ability to be useful after abuse
Depending on the type of abuse (over-discharge, over-charge, extreme over-temperature etc), the right answer would be to retire either of them from further use. My hunch is that the can would stay low impedance longer during abuse than a pouch cell that wasn't clamped and constrained effectively. That's because the can physically prevents the foil layers from separating and developing space from each other that prevents that active material from being usable.
3) Which one would be easier to "bin" for reuse?
If your primary concern is safety, then neither. If your primary concern is a garage project that gets baby-sat by some uncommonly knowledgeable and prudent DIY EV battery nerd with elaborate monitoring (I say monitoring only, because substantial corrective action like significant balancing is just inviting unsafe conditions), than I would say the best type of reuse is the type that indivdual has the most expertise in safely using. Can's don't show you when they are 'puffed'. You can bin it from a capacity and Ri value, and think it's good to go into a pack while it's 1psi away from exploding or venting, a pouch cell gives you a visual indication of pressure. The downside with re-using pouch cells is that handling them with human hands you are damaging them, and in many situations it becomes impossible to extract them from a pack without causing damage, even if being extremely careful.
Those are the kind of things I am thinking about
We will see after I do some testing.
To date... 99% of my testing has been with pouches.
Annnndddd.... those shit Emoli cells you encouraged me to explore. :x
Cells and battery topology are on a steep development curve. If you ever try using an original iPhone or HTC G1 you will wonder what anyone saw in them at the time of release, and yet without that release we wouldn't have the Note 4 Edge to enjoy today. All technology has the same fate, to become irrelevant.
-methods