Compare: Primary risk of overdischarge of a cell is SoH degradation.
When all intercalated Lithium ions from the cathode are depleted during charge, the oxides of the cathode material start to disassociate and form oxygen gas which is flammable.
During charge, lithium atoms move out of the cathode material, e. g. Lithium-Cobalt Oxide (including NMC variant), the layers can collapse if we charge more than half of the theoretical capacity:
Part of Battery safety.
Related:
‣