There are many types of cells coming available from the EV Market space and there is quite a mix / variety. Many can be used for Energy Storage Systems but not all, some are better suited to larger scale systems due to the voltages & curves. Depending on pack type and how it can be broken down, the Voltages may not necessarily work with regular (average) equipment and often require Inverters / Chargers and even Solar Controllers which are highly programmable which allow for a broader voltage range.
The Chemistries Vary a lot. EV's have been and will be produced with LFP as well as several other chemistries. LFP is presently one of the safest chemistries with a profile that is "close to" Lead Acid battery profiles and therefore easier to mix in energy storage systems with little effort. Other chemistries CAN be dangerous & even volatile if not handled / managed properly. BTW: Avoid Used Nissan Cells ! lots of used & craptastic ones out there... they are generally junk. Some folks will hate that but it is true. Tesla Packs are popular but they have voltage curves that require a better grades of gear.
Pros & Cons... well there is many... but a few toppers on the list.
EV Batteries and the cells used within are ALL Matched, Batched & Binned to be identical for performance, charge & discharge, prior to assembly into packs. (main reason they cost so much more). Generally, they use Higher Energy Dense cells which are more volatile and potentially dangerous. EV batteries that have Failed Cells within a pack are decommissioned, sometimes they are repaired with defective cells being replaced but others go off to the 2nd life market if it's too costly or technically difficult (some packs cannot be repaired due to how they are assembled).
Keep in mind a very true adage: If it sounds too good to be true, it likely is false. If ANY vendor pressures you to buy something, PAUSE ! red flag !! There are always great deals to be had and they do come up often, one must be ready to act when it happens and when you "know" it is a good deal, patience is important and never ever impulse buy anything, 99% guarantee you will regret it.
There are some reputable vendors in Europe who sell new & Used cells and battery packs. Some actually use testing & evaluation centres ad class / catagorize cells for reselling or for mineral recovery. Such programs exist in France, Germany, Netherlands and I believe Belgium is putting up a faciltiy & sponsoring such as well. I also hear in the Rumour Mill (EV Side) that Norway was also working on some form of used Lithium Battery Recycling & Upcycling facility to test, evaluate and process used cells. I do not know if this is operational as yet or how soon it will be. Europe is far ahead in this area compared to North America who is just realizing this need.
In closing, I suggest you may have a look at some of our Known Good Suppliers for battery cell pricing so you have a baseline of what costs are for New LFP Cells for X capacites. That will let you compare the used EV cells costs to new LFP. As well you have to factor in equipment costs (if you have to buy higher grade configurable gear to handle the higher capacity cells) which adds up fast. At present the most popular cells are the 280AH format but due to high demand, the prices are now climbing due to supply... More is coming so not to worry.
Hope it helps, Good Luck.
Steve