title: Visualization of electrochemically driven solid-state phase transformations using operando hard X-ray spectro-imaging.
abstract: In situ techniques with high temporal, spatial and chemical resolution are key to understand ubiquitous solid-state phase transformations, which are crucial to many technological applications. Hard X-ray spectro-imaging can visualize electrochemically driven phase transformations but demands considerably large samples with strong absorption signal so far. Here we show a conceptually new data analysis method to enable operando visualization of mechanistically relevant weakly absorbing samples at the nanoscale and study electrochemical reaction dynamics of iron fluoride, a promising high-capacity conversion cathode material. In two specially designed samples with distinctive microstructure and porosity, we observe homogeneous phase transformations during both discharge and charge, faster and more complete Li-storage occurring in porous polycrystalline iron fluoride, and further, incomplete charge reaction following a pathway different from conventional belief. These mechanistic insights provide guidelines for designing better conversion cathode materials to realize the promise of high-capacity lithium-ion batteries.
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors.forename: Linsen
authors.initials: L
authors.lastname: Li
authors.affiliation: Photon Sciences Directorate, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: Yu-chen Karen
authors.initials: YC
authors.lastname: Chen-Wiegart
authors.affiliation: Photon Sciences Directorate, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: Jiajun
authors.initials: J
authors.lastname: Wang
authors.affiliation: Department of Sustainable Energy Technologies, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: Peng
authors.initials: P
authors.lastname: Gao
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors.forename: Qi
authors.initials: Q
authors.lastname: Ding
authors.affiliation: 1] Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA [2] Department of Chemistry, University of Illinois at Chicago, Chicago, Illinois 60607, USA.
authors.forename: Young-Sang
authors.initials: YS
authors.lastname: Yu
authors.affiliation: Department of Sustainable Energy Technologies, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: Feng
authors.initials: F
authors.lastname: Wang
authors.affiliation: Department of Chemistry, University of Illinois at Chicago, Chicago, Illinois 60607, USA.
authors.forename: Jordi
authors.initials: J
authors.lastname: Cabana
authors.affiliation: Photon Sciences Directorate, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Wang
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors.forename: Song
authors.initials: S
authors.lastname: Jin