The Solid Electrolyte Interphase – The Most Important and the Least Understood Solid Electrolyte in Rechargeable Li Batteries

In this chapter, the Solid Electrolyte Interphase (SEI) concept is introduced and the different requirements on the electrolyte and on the SEI formation process in the presence of various anode materials (metallic lithium, graphitic carbons, and lithium storage metals/alloys), in particular, similarities and differences, are highlighted. The difficulties to understand and analyze the SEI characteristics and composition are discussed by examples.