Unveiling the migration behavior of lithium ions in NCM/Graphite full cell via in operando neutron diffraction

Abstract

The improvement of electrochemical performance of lithium-ion (Li-ion) batteries requires in-depth understanding on the structural evolution of electrodes during electrochemical cycling. By taking advantages of sensitive, penetrative and nondestructive properties of neutrons, we adopted in operando neutron diffraction technique to explore structural characteristics of electrodes in LiNi0.5Co0.2Mn0.3O2/Graphite full cell during cycling in real time. It is revealed that the concentration of Li/Ni antisite defects varies and presents regular volcano shape in layered cathode during cycling due to the competition effect between delithiation and magnetic frustration. Moreover, visualization of the Li-ion migration pathway in cathode by maximum entropy method indicates that lithium ions diffuse via tetrahedral site hopping path at the initial state of charge, but a newly-discovered indirect zigzag hopping path dominates afterwards. As for graphite anode counterpart, the intercalation of lithium ions into anode undergoes few distinct stages, including the formation of an intermediate phase with lithium gradient. All these observations concerning the simultaneous structural variation of both cathode and anode unveil the underlying migration behavior of lithium ions in NCM/Graphite full cell and enlighten us to devise an optimized pathway for Li-ion migration toward achieving high-performance Li-ion batteries.