Thermophysical properties of oxide cathode materials for lithium-ion batteries

Lithium-ion batteries are presently used as power sources in energy storage applications due to the adapted functionality and chemistry for a long cycle life-time, high energy density, high power density and relatively simple reaction mechanisms. The main challenge not only for electric vehicles but also for smaller portable devices as well as high capacity stationary storage facilities is related to safety behaviour under normal and abusive operation conditions. Understanding the heat generation and propagation in lithium-ion batteries and avoiding thermal runaway at high temperature is a critical issue. In an attempt to improve the battery safety, battery management systems (BMS) were introduced for thermal controlling batteries of high power and energy density. Therefore the thermal transport properties such as thermal conductivity, thermal diffusivity and specific heat capacities are required for a well optimization of the BMS. This study is focused on the investigation of the thermophysical properties of cathode materials typically used in the production of lithium-ion batteries. The cathode materials under investigation are self-made (LiCoO2, Li(NiMnCo)O2) and commercially prepared (blends of LiCoO2 and LiMn2O4) composite thick films containing active material mixed with additives (binder and carbon black) deposited on aluminum current collector foils. ... mehrThermal conductivity data were determined from thermal diffusivity measured by laser flash analysis, specific heat capacity measurements by calorimetric methods and density estimations. Furthermore, the transport properties were studied as a function of lithiation state of the cathodes. Delithiation process was performed using galvanostatic techniques on half cells with Swagelok® geometry. Scanning electron microscopy (Fig. 1a) and metallographic methods (light microscopy, Fig. 1b) were also used for structural investigations. The results presented in this work are the first experimental data of this kind which combine application oriented and fundamental research. Such data are highly relevant for simulation studies of thermal behavior including thermal runaway of lithium-ion batteries, in which the bulk properties are assumed, as a common approach, temperature independent.