title: Engineering the Transformation Strain in LiMnyFe1-yPO4 Olivines for Ultrahigh Rate Battery Cathodes.
abstract: Alkali ion intercalation compounds used as battery electrodes often exhibit first-order phase transitions during electrochemical cycling, accompanied by significant transformation strains. Despite ∼30 years of research into the behavior of such compounds, the relationship between transformation strain and electrode performance, especially the rate at which working ions (e.g., Li) can be intercalated and deintercalated, is still absent. In this work, we use the LiMnyFe1-yPO4 system for a systematic study, and measure using operando synchrotron radiation powder X-ray diffraction (SR-PXD) the dynamic strain behavior as a function of the Mn content (y) in powders of ∼50 nm average diameter. The dynamically produced strain deviates significantly from what is expected from the equilibrium phase diagrams and demonstrates metastability but nonetheless spans a wide range from 0 to 8 vol % with y. For the first time, we show that the discharge capacity at high C-rates (20-50C rate) varies in inverse proportion to the transformation strain, implying that engineering electrode materials for reduced strain can be used to maximize the power capability of batteries.
authors.affiliation: Department of Material Science and Engineering, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.|Department of Physics, Chemistry, and Pharmacy, University of Southern Denmark , Campusvej 55, 5230, Odense M, Denmark.
authors.forename: Dorthe B
authors.initials: DB
authors.lastname: Ravnsbæk
authors.affiliation: Department of Material Science and Engineering, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
authors.forename: Kai
authors.initials: K
authors.lastname: Xiang
authors.affiliation: Department of Material Science and Engineering, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
authors.forename: Wenting
authors.initials: W
authors.lastname: Xing
authors.affiliation: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory , 9700 S. Cass Avenue, Argonne, Illinois 60439, United States.
authors.forename: Olaf J
authors.initials: OJ
authors.lastname: Borkiewicz
authors.affiliation: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory , 9700 S. Cass Avenue, Argonne, Illinois 60439, United States.
authors.forename: Kamila M
authors.initials: KM
authors.lastname: Wiaderek
authors.affiliation: A123-Systems , 200 West Street, Waltham, Massachusetts 02451, United States.
authors.forename: Paul
authors.initials: P
authors.lastname: Gionet
authors.affiliation: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory , 9700 S. Cass Avenue, Argonne, Illinois 60439, United States.
authors.forename: Karena W
authors.initials: KW
authors.lastname: Chapman
authors.affiliation: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory , 9700 S. Cass Avenue, Argonne, Illinois 60439, United States.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Chupas
authors.affiliation: Department of Materials Science and NanoEngineering (MSNE), Rice University , 6100 Main MS-325, Houston, Texas 77005-1827, United States.
authors.forename: Ming
authors.initials: M
authors.lastname: Tang
authors.affiliation: Department of Material Science and Engineering, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
authors.forename: Yet-Ming
authors.initials: YM
authors.lastname: Chiang
keywords: Li-ion batteries; X-ray diffraction; cathode; lithium manganese iron phosphate; misfit strain; operando; phase transformation; rate capability