Precise electrochemical calorimetry of LiCoO2/graphite lithium-ion cell -: Understanding thermal behavior and estimation of degradation mechanism

The thermal behavior of a lithium-ion cell during charge and discharge was determined using an isothermal calorimeter. In order to assign the thermal characteristics of the lithium-ion cell to the cathode (LiCoO2) and the anode (graphite) material, a LiCoO2/Li cell and a graphite/Li cell were prepared. The thermal behaviors were compared with that of a lithium-ion (LiCoO2/graphite) cell. The notable thermal characteristics could be attributed to the individual electrode materials. In particular, the discontinuous thermal profiles showed good agreement with the phase change of the host structure of each electrode material. The degradation factor of commercially available lithium-ion cells was determined using these discontinuous thermal profiles as an indicator of the electrode reactions. We found that the decrease in the effective active material of the graphite is the main cause of capacity fading after cycling. (C) 2002 The Electrochemical Society.