How Do Reactions at the Anode/Electrolyte Interface Determine the Cathode Performance in Lithium-Ion Batteries?

Today, it is common knowledge, that materials science in the field of electrochemical energy storage has to follow a system approach as the interactions between active materials, electrolyte, separator and various inactive materials (binder, current collector, conductive fillers, cell-housing, etc.) which are of similar or even higher importance than the properties and performance parameters of the individual materials only. In particular, for lithium-ion batteries, it is widely accepted that the electrolyte interacts and reacts with the electrodes. Here, we report how reactions at a graphite anode (involving electrolyte decomposition and solid electrolyte interphase (SEI) formation), affect the performance of a LiCoO2 (LCO) cathode and the full lithium-ion cell during cycling. We discuss effects of the SEI-forming electrolyte additive vinylene carbonate (VC) and the influence of graphite anodes with different surface areas on the cycling stability, end of charge (EOC) and end of discharge (EOD) potentials of the LCO cathode. We will thus elucidate the failure mechanism of LCO/graphite cells by showing that the formation and growth of SEI on the anode, resistance increase in the cathode, electrode and electrolyte degradation in general, as well as capacity and power fade of the lithium ion cell are in fact strongly interrelated processes.