Entropy control and surface analysis of energy storage systems for advanced vehicles

The entropy control to maximize energy efficiency should be carried out by the development and introduction of functional materials in the advanced batteries. This procedure can be investigated by the calculations of thermal generation derived by each parameter. These approaches were done for the advanced Li-ion batteries for hybrid electric vehicle and electric vehicle applications. The thermal generation of Qp that is exothermic during both charge and discharge processes corresponds to the energy loss due to a polarization, and the thermal generation of Qj due to an electrical resistance of batteries will be produced. The thermal generation of Qr implies battery reactions. As a result, the total thermal generation: Qt will be expressed as below. Qt=Qr+Qp+Qj=nFT(δEe/δT)+Qp+Qj. Another topic is surface and bulk controls of electrode materials in any type of battery. A battery life will be determined by several factors like material designing, battery temperature or charge–discharge stress etc. Particularly, the stress of high temperature over 40 °C accelerated the degrading velocity of Li-ion batteries. Electron spin resonance data indicated the existence of Mn(II) instead of the original Mn(III) of a positive electrode in Li-ion batteries. This fact will support the decomposition of Mn(III) in LiMn2O4 to Mn(II) and Mn(IV) by the action of electrolyte. X-ray photoelectron spectroscopy data for the surface profiles on the negative electrode materials showed the existence of ether and phosphate compound on the surface of graphite carbon. It is thought that the decomposition of LiPF6 in the electrolyte took place.