title: Nonequilibrium structural dynamics of nanoparticles in LiNi(1/2)Mn(3/2)O4 cathode under operando conditions.
abstract: We study nonequilibrium structural dynamics in LiNi1/2Mn3/2O4 spinel cathode material during fast charge/discharge under operando conditions using coherent X-rays. Our in situ measurements reveal a hysteretic behavior of the structure upon cycling and we directly observe the interplay between different transformation mechanisms: solid solution and two-phase reactions at the single nanoparticle level. For high lithium concentrations solid solution is observed upon both charge and discharge. For low lithium concentration, we find concurrent solid solution and two-phase reactions upon charge, while a pure two-phase reaction is found upon discharge. A delithiation model based on an ionic blockade layer on the particle surface is proposed to explain the distinct structural transformation mechanisms in nonequilibrium conditions. This study addresses the controversy of why two-phase materials show exemplary kinetics and opens new avenues to understand fundamental processes underlying charge transfer, which will be invaluable for developing the next generation battery materials.
authors.affiliation: Department of Physics, University of California-San Diego , La Jolla, California 92093-0319, United States.
authors.forename: Andrej
authors.initials: A
authors.lastname: Singer
authors.forename: Andrew
authors.initials: A
authors.lastname: Ulvestad
authors.forename: Hyung-Man
authors.initials: HM
authors.lastname: Cho
authors.forename: Jong Woo
authors.initials: JW
authors.lastname: Kim
authors.forename: Jörg
authors.initials: J
authors.lastname: Maser
authors.forename: Ross
authors.initials: R
authors.lastname: Harder
authors.forename: Ying Shirley
authors.initials: YS
authors.lastname: Meng
authors.forename: Oleg G
authors.initials: OG
authors.lastname: Shpyrko
keywords: Lithium ion batteries; coherent X-rays; in situ; metastable solid solution; operando; phase transformation