Bashing cheap Chinese no-name junk is quite cheap but unfortunately the name brand battery manufacturers aren't immune to this issue and the resulting battery fires either. The issue is much more complex than just "cheap people buying cheap low quality junk."
I have worked the last half a year on a product designed to non-destructively analyze and check Li-ion batteries, the kind you would find in anything from power tools to cars (even from the largest names in the EV market). The cheap appliance batteries aren't checked/inspected at all during production, only visual checks for damage are done and spot checks on selected cells from a batch are done with more comprehensive testing for QA and process control purposes. So you can easily get a lemon battery for your phone, laptop or e-bike where the internal layers/electrodes are kinked or touching, causing a short and a fire even from major names like Samsung.
Batteries for cars are inspected more rigorously but still, pretty much nobody does 100% inspection of assembled batteries. It is not possible to do non-destructively except by x-raying and inspecting every single cell. Even normal x-ray is not enough, one has to use computer tomography to look at the cell from multiple angles. This is a very costly and time consuming process, so it isn't done systematically on 100% of cells either. There are some battery vendors heavily investing in this equipment but given that a single CT scan takes minutes (in the best case!) and we are talking about production lines spitting out thousands of cells every hour, you can imagine how much would 100% inspection cost in terms of CT hardware, operating costs, etc.
And this covers only sorting out cells that are defective during manufacture already due to some process failure (assembly issues, delaminations, etc). Cells can and do fail later as well, for various reasons, the electronics could fail, the cells could overheat because of poor cooling or ambient temperature triggering a runaway, etc.
The worst issue is that even the manufacturers themselves don't really know what will make the battery fail later in its life. There is some empirical knowledge, such as if the anodes are not overhanging the cathodes inside the battery sufficiently or the anodes are too deformed it is likely a short will occur and such battery should be recycled but beyond that it is mostly guesswork. There isn't really anything like a DIN or ISO norm for Li-ion batteries and when there is an EV fire it is very rare that the battery gets taken apart to investigate what caused it (or that you even have anything to take apart after the fire).
Even worse - each manufacturer has their own, completely proprietary, processes and criteria. We had huge problems even getting examples of how a good and a bad battery looks like from them in order to be able to actually make that tool - it is all considered proprietary information, trade secret because the market is so competitive.
I really do hope we get some less "explosive" chemistry soon and Li-ion will put out to pasture.
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