@JandJ,
I have not done anywhere near enough research into Niobium metallurgy to give my opinion on separation techniques or its proposed use case for batteries but what I can comment on from firsthand experience is failure of our current lithium battery technology due do the swelling of the cathode within the cell as you mentioned in point 4 of your above post - which is a huge improvement if the Niobium tech works as intended and takes off.
My trade is as an Auto-electrician, and consequently have spent some time over the years repairing small electronics as well. From handheld radios, computers and mobile phones through to camping appliances and torches, so many things have rechargeable lithium batteries in them now. Normally when something is presented to me for repair due to it not working or not charging I find (depending on what i'm working with) one or more of the battery cells swollen. This swelling is what leads to the fires - due to the swelling physically pushing the other cells into something they shouldn't be touching or rupturing entirely. Once a fire starts its all over - The heat damage causes a domino effect of further damage to otherwise undamaged components causing further fires and further energy discharge, potentially causing further damage. The thing is, with a handheld device, you're probably looking at a battery rated to 2100mAh @ 5v or 3700mAh @ 7.3v, something like that, with the batteries comprised of 1-3 cells. (in kWh that's 0.0105kWh - 0.0270kWh respectively)
I have had a swollen lithium battery from a Samsung mobile phone go nuclear on the bench once removed from the phone, and I was lucky as I could drop a container straight over it and starve it of oxygen pretty well immediately before it got completely out of control.
This is a vastly different circumstance for an electric vehicle battery, however. The very idea of a cell swelling within a battery unit in one of those gives me nightmares, and unfortunately by the time one of them goes up in flames its too late to dissect the battery unit to investigate what went wrong.
A short list I grabbed from ev-database.org - I do not know if this information is 100% correct.
Tesla Model S - 100kWh Battery comprised of 7920 400v cells.
BYD Han - 88kWh Battery comprised of 178 800v cells.
Hyundai IONIQ 5 - 84kWh Battery comprised of 384 400v cells.
Nissan Leaf - 62kWh Battery comprised of 288 400v cells.
The above list isn't comprehensive and may not be 100% correct but demonstrates the point of these EV Battery units being immensely power dense and comprised of MANY cell units. It only takes one cell to fail due to the swelling issue to bring one of these units unstuck...good luck dropping a container over the top of a car if it goes up in flames...
So IMO, if this use of Niobium in the batteries takes off, its game on for EVs again. Kills two birds with one stone. I havn't had much exposure to EVs or Hybids yet but the usual response I get when I ask owners is that they like them, but wouldn't have another one. Charging time is the issue they all mention. I have yet to find someone who is worried about the fire risk however...
(20min delay)