title: Rate-dependent phase transitions in Li2FeSiO4 cathode nanocrystals.
abstract: Nanostructured lithium metal orthosilicate materials hold a lot of promise as next generation cathodes but their full potential realization is hampered by complex crystal and electrochemical behavior. In this work Li2FeSiO4 crystals are synthesized using organic-assisted precipitation method. By varying the annealing temperature different structures are obtained, namely the monoclinic phase at 400°C, the orthorhombic phase at 900°C, and a mixed phase at 700°C. The three Li2FeSiO4 crystal phases exhibit totally different charge/discharge profiles upon delithiation/lithiation. Thus the 400°C monoclinic nanocrystals exhibit initially one Li extraction via typical solid solution reaction, while the 900°C orthorhombic crystals are characterized by unacceptably high cell polarization. In the meantime the mixed phase Li2FeSiO4 crystals reveal a mixed cycling profile. We have found that the monoclinic nanocrystals undergo phase transition to orthorhombic structure resulting in significant progressive deterioration of the material's Li storage capability. By contrast, we discovered when the monoclinic nanocrystals are cycled initially at higher rate (C/20) and subsequently subjected to low rate (C/50) cycling the material's intercalation performance is stabilized. The discovered rate-dependent electrochemically-induced phase transition and stabilization of lithium metal silicate structure provides a novel and potentially rewarding avenue towards the development of high capacity Li-ion cathodes.
authors.affiliation: 1] Materials Engineering, McGill University, Montréal, Québec H3A 0C5, Canada [2] Institut de recherché d' Hydro-Québec (IREQ), Varennes, Québec J3X 1S1, Canada.
authors.forename: Xia
authors.initials: X
authors.lastname: Lu
authors.affiliation: Materials Engineering, McGill University, Montréal, Québec H3A 0C5, Canada.
authors.forename: Huijing
authors.initials: H
authors.lastname: Wei
authors.affiliation: Materials Engineering, McGill University, Montréal, Québec H3A 0C5, Canada.
authors.forename: Hsien-Chieh
authors.initials: HC
authors.lastname: Chiu
authors.affiliation: Materials Engineering, McGill University, Montréal, Québec H3A 0C5, Canada.
authors.forename: Raynald
authors.initials: R
authors.lastname: Gauvin
authors.affiliation: Institut de recherché d' Hydro-Québec (IREQ), Varennes, Québec J3X 1S1, Canada.
authors.forename: Pierre
authors.initials: P
authors.lastname: Hovington
authors.affiliation: Institut de recherché d' Hydro-Québec (IREQ), Varennes, Québec J3X 1S1, Canada.
authors.forename: Abdelbast
authors.initials: A
authors.lastname: Guerfi
authors.affiliation: Institut de recherché d' Hydro-Québec (IREQ), Varennes, Québec J3X 1S1, Canada.
authors.forename: Karim
authors.initials: K
authors.lastname: Zaghib
authors.affiliation: Materials Engineering, McGill University, Montréal, Québec H3A 0C5, Canada.
authors.forename: George P
authors.initials: GP
authors.lastname: Demopoulos