Lithium ion batteries ... why do they spoil?

Factual Questions
1

Why do lithium-ion batteries spoil? I’ve had a laptop for a couple years and just had to replace the battery. I heard that LiIon batteries last about 2 years, and that’s just what mine lasted.

More importantly, in general terms, why do they fail? And more important than that, do all of them die 2 years after they are manufactured? If I buy 10 now, will they all be dead in a couple years, or is it because they are [ not charged | charged | periodically discharged | periodically charged ] that they go bad?

2

See this page. The corrosiveness of the Lithium compound, the strict limits of what can be in the electrolyte, etc., all contribute to a fairly fragile cell that is at the limits of our current tech to control.