Nonequilibrium Structural Dynamics of Nanoparticlesin LiNi1/2Mn3/2O4Cathode under OperandoConditions.

Westudy nonequilibrium structural dynamics in LiNi1/2Mn3/2O4spinel cathode material during fastcharge/discharge under operando conditions using coherent X-rays.Our in situ measurements reveal a hysteretic behavior of the structureupon cycling and we directly observe the interplay between differenttransformation mechanisms: solid solution and two-phase reactionsat the single nanoparticle level. For high lithium concentrationssolid solution is observed upon both charge and discharge. For lowlithium concentration, we find concurrent solid solution and two-phasereactions upon charge, while a pure two-phase reaction is found upondischarge. A delithiation model based on an ionic blockade layer onthe particle surface is proposed to explain the distinct structuraltransformation mechanisms in nonequilibrium conditions. This studyaddresses the controversy of why two-phase materials show exemplarykinetics and opens new avenues to understand fundamental processesunderlying charge transfer, which will be invaluable for developingthe next generation battery materials. [ABSTRACT FROM AUTHOR]