Pointing at the BRCA and its list is like saying you won't buy a Subaru homologated (listed) rally car because McRae crashed one!
Puffing of LiPos is inevitable - there is nothing you can do to stop it. The process of manufacturing guarantees that because of variations in the chemistry of the LiPo that cannot be controlled perfectly dendrites will grow, they will penetrate the insulators, there will be local gassing and the LiPo will puff.
It doesn't matter who makes it, who puts a case and label around it or who puts it on what list, puffing of LiPos happens all the time and cannot be stopped. That is especially likely in our LiPo construction where everything is at its limits because of the discharge rates we want for racing. Consider what making a LiPo involves in terms of process control in manufacturing...
Lithium-ion cell separators most commonly are porous polyethylene, polypropylene, or composite polyethylene / polypropylene films. These films are typically on the order of 20 um (0.0007”) thick, although thinner (approximately 10 um or 0.0004”) and thicker films can be found (approximately
40 um). That’s 1/3 the thickness of a human hair!
If you'll forgive the technical novel...
Any number of minor defects on a cell anode can cause very localized lithium plating. A few examples include a scratch in the anode, a point of anode delamination, a point of anode over-compression, a thin spot in the anode, or a point where a metallic contaminant has plated. Such lithium plating results in the formation of lithium dendrites (hard crystals) and a mat of “dead lithium” composed of detached lithium dendrites.
Individual dendrite shorting is usually not significant, as resistive heating quickly breaks the dendrite. Resistive heating melts the separator locally which quickly heals over and prevents a dead short. That's one source of the gas that causes the puffing. However, if such shorting and heating occurs in the midst of a mat of dead lithium, it may be possible to ignite sufficient material to initiate an internal short of sufficient size to cause cell thermal runaway.
The amount of plated lithium needed for these situations is tiny - in the microgram region - and will have negligible effect on the behavior of the cell once thermal runaway is initiated. One important aspect of this lithium plating failure mechanism is that lithium dendrite growth only occurs during cell charging, since charging is accomplished by moving lithium ions (Li+) and electrons from the cathode to the anode.
Puffing is a sign that the cell is now not in the best of health and it is really good to see people taking this seriously and replacing their cells.
There's no point in blaming the list or the manufacturers - it is the technology we demand and the inability of the manufacturing process to be perfect all the time that leads to puffing.
Look back to the NiMh cells and ask yourself how many you and to buy in one season to be competitive and (at the end of the development cycle) how many just died on you. You couldn't buy competitive NiMh cells for less than £60 a pack and you'd be lucky if they stayed competitive for half a season and you didn't have the capacity to run flat out for any race length in any class. And as for the maintenance regime...!
Now you have competitive cells that cost around £50 to be competitive, last up to two seasons and take no complex maintenance. In order that they are made to a standard that gives the greatest amount of protection and standardisation to the user through limits on size, enclosure and price, there is a (BRCA) list.
The price you pay for that value, simplicity and standardisation is that some will puff and you have to replace them. Complain all we like, the answer is to suck it up as that is the price we have to pay for this technology.
I hope that helps understand why cells puff and why the list helps us. It seems our inventive people are finding lower-cost competitive alternatives that might not be at the cutting edge of the technology, but as a result are more robust in use. Go for it!!
