Investigation of the failure mechanisms of Li-ion batteries and the consequences of their failure is of vital importance to the design of durable batteries. In this work, we examined the electrochemical performance of half and full Li-ion battery cells with several cathode materials including LiMn0.8Fe0.2PO4 (LMFP), LiMi0.5Mn1.5O 4 (LMNO), and Li[LixNiyCozMn1?x?y?z]O2 Li-rich layered oxides (HC-MNC). In contrast to half cells which demonstrated good cycling performance with more than 90% of their initial capacities retained after 100 cycles, the full cells exhibited severe capacity loss. Based on postmortem analyzes of electrodes from cells cycled at 30 and 60°C, using electrochemical, spectroscopic, and microscopic techniques, we conclude that the loss of active lithium ions due to parasitic side reactions is a main reason for capacity fading of Li-ion battery full cells. Structural degradation of the electrodes during cycling is at best a second order effect.