title: Current-induced transition from particle-by-particle to concurrent intercalation in phase-separating battery electrodes.
abstract: Many battery electrodes contain ensembles of nanoparticles that phase-separate on (de)intercalation. In such electrodes, the fraction of actively intercalating particles directly impacts cycle life: a vanishing population concentrates the current in a small number of particles, leading to current hotspots. Reports of the active particle population in the phase-separating electrode lithium iron phosphate (LiFePO4; LFP) vary widely, ranging from near 0% (particle-by-particle) to 100% (concurrent intercalation). Using synchrotron-based X-ray microscopy, we probed the individual state-of-charge for over 3,000 LFP particles. We observed that the active population depends strongly on the cycling current, exhibiting particle-by-particle-like behaviour at low rates and increasingly concurrent behaviour at high rates, consistent with our phase-field porous electrode simulations. Contrary to intuition, the current density, or current per active internal surface area, is nearly invariant with the global electrode cycling rate. Rather, the electrode accommodates higher current by increasing the active particle population. This behaviour results from thermodynamic transformation barriers in LFP, and such a phenomenon probably extends to other phase-separating battery materials. We propose that modifying the transformation barrier and exchange current density can increase the active population and thus the current homogeneity. This could introduce new paradigms to enhance the cycle life of phase-separating battery electrodes.
authors.affiliation: Department of Materials Science &Engineering, Stanford University, Stanford, California 94305, USA.
authors.forename: Yiyang
authors.initials: Y
authors.lastname: Li
authors.affiliation: Sandia National Laboratories, Livermore, California 94551, USA.
authors.forename: Farid
authors.initials: F
authors.lastname: El Gabaly
authors.affiliation: Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Todd R
authors.initials: TR
authors.lastname: Ferguson
authors.affiliation: Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Raymond B
authors.initials: RB
authors.lastname: Smith
authors.affiliation: Sandia National Laboratories, Livermore, California 94551, USA.
authors.forename: Norman C
authors.initials: NC
authors.lastname: Bartelt
authors.affiliation: Sandia National Laboratories, Livermore, California 94551, USA.
authors.forename: Joshua D
authors.initials: JD
authors.lastname: Sugar
authors.affiliation: Sandia National Laboratories, Albuquerque, New Mexico 87185, USA.
authors.forename: Kyle R
authors.initials: KR
authors.lastname: Fenton
authors.affiliation: Samsung Advanced Institute of Technology America, Cambridge, Massachusetts 02142, USA.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Cogswell
authors.affiliation: Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: A L David
authors.initials: AL
authors.lastname: Kilcoyne
authors.affiliation: Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Tolek
authors.initials: T
authors.lastname: Tyliszczak
authors.affiliation: 1] Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA [2] Department of Mathematics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Martin Z
authors.initials: MZ
authors.lastname: Bazant
authors.affiliation: 1] Department of Materials Science &Engineering, Stanford University, Stanford, California 94305, USA [2] Stanford Institute of Materials and Energy Science, Menlo Park, California 94025, USA.
authors.forename: William C
authors.initials: WC
authors.lastname: Chueh