(Invited) Predicting the Interfacial Reactions Between Cathodes and Liquid and Solid Electrolytes

Very few interfaces in lithium batteries are stable at the extreme electrochemical conditions imposed on them during operation of a lithium battery. When modern layered cathode materials are charged to high voltage in liquid electrolytes they tend to lose oxygen near the surface leading to a transformation to spinel and rocksalt phases. These phases significantly increase the cathode impedance, and lead to loss of capacity and rate performance. By presenting a detailed study of the surface phases in Ni-based layered materials I will show how first principles methods can be used to model this transformation and study the growth of impedance resulting from them. Similarly, interfacial stability is one of the most limiting issues in solid-state batteries where the liquid electrolyte has been replaced by a solid state Li-ion conductor. Most compounds that display very high Li mobility are not stable at the extreme anode and/or cathode potentials and require passivation or the use of buffer layers. I will show how these interfacial reactions can be predicted with first principles calculations. Our results confirm that very few conductors will be stable at the high voltage of the cathode material.