Surface morphology, elastic modulus and hardness of thin film cathodes for Li-ion rechargeable batteries

In this study, surface morphology, elastic modulus and hardness of two thin film cathode materials, namely layered structured LiNi 1/3 Co 1/3 Mn 1/3 O 2 and spinel structured LiMn 2 O 4 , during the charge/discharge cycles, are measured by using Scanning Electron Microscopy, Atomic Force Microscopy and nanoindentation experiments. Furthermore, the effects of depth of discharge (DOD) and charging rate (current density) on the changes of elastic modulus and hardness of the spinel structured LiMn 2 O 4 are also investigated. The results have shown that both elastic modulus and hardness of the thin film cathodes have been significantly affected by the charge/discharge cycles as well as the condition of the charge/discharge processes. These results suggest the importance of the mechanical properties of the cathode materials to the reliability and integrity of the cathode materials to be used for the Li-ion batteries. The possible mechanisms of the changes in mechanical properties are also discussed.