(Dr. Margret Wohlfahrt Mehrens, head of the Electrochemical Materials Research Department at ZSW, Ulm, Germany).
Long life, efficient and safe high energy storage systems are the key components for new car concepts (hybrid and full electric cars) as well as for intermediate storage of renewable energy sources. However, present lithium ion technology does not fulfill completely the requirements in terms of energy density, wide operation temperature, long life behavior and safety even under abuse conditions. A very promising approach for further improvement of lithium-ion batteries is realizing new high-potential cathodes materials able to operate close to 5 V vs. Li/Li+. The application of these cathodes leads to a higher cell voltage, which leads to higher energy density, lower costs and a lower complexity of the complete battery system. Furthermore, the use of high-voltage positive electrode materials allows replacing graphite by alternative more stable negative electrode materials like lithium titanates, leading to lithium ion batteries with improved safety and life time. In principle high voltage cathode materials are well known for many years but still need to be optimized for practical applications with respect to life time and safety in complete cells. The high charging potential of the cathode leads to increased electrolyte degradation and other side reactions with passive components like binder, current collector or separator that compromise the performance of the full cell. The SEI formation at the negative electrode is strongly influenced by electrolyte impurities formed by electrolyte oxidation on the cathode side. These side reactions can lead to capacity fading on the anode side and low cycling life in full cells. The presentation will give an overview about recent developments of high voltage cathode materials with respect to energy density, rate capability, cycling life and safety. Challenges for electrode and full cell development will be addressed. Dominant ageing mechanisms and various approaches to overcome these problems will be discussed.

Biography of Dr. Margret Wohlfahrt-Mehrens

Dr. Margret Wohlfahrt-Mehrens is the head of the Electrochemical Materials Research Department at ZSW (Center for Solar Energy and Hydrogen Research) in Ulm Germany. Margret Wohlfahrt-Mehrens studied chemistry at the University of Bonn, where she received her diploma in 1984. She made her doctoral thesis in the field of electro catalysis at the University of Witten-Herdecke. 1990 she joined ZSW in Ulm. There she worked in the field of new energy technologies and new materials for energy storage systems. Since 1995 she is leading the Department of Accumulators Materials Research at ZSW. In addition she is PI of the Material II group at the new tended new Helmholtz Institute in Ulm.