Chutchamon Sirisopanaporn

Silicate cathodes for lithium batteries: alternatives to phosphates?

Polyoxyanion compounds, particularly the olivine-phosphate LiFePO4, are receiving considerable attention as alternative cathodes for rechargeable lithium batteries. More recently, an entirely new class of polyoxyanion cathodes based on the orthosilicates, Li2MSiO4 (where M = Mn, Fe, and Co), has been attracting growing interest. In the case of Li2FeSiO4, iron and silicon are among the most abundant and lowest cost elements, and hence offer the tantalising prospect of preparing cheap and safe cathodes from rust and sand! This Highlight presents an overview of recent developments and future challenges of silicate cathode materials focusing on their structural polymorphs, electrochemical behaviour and nanomaterials chemistry.

Dependence of Li2FeSiO4 Electrochemistry on Structure

Small differences in the FeO(4) arrangements (orientation, size, and distortion) do influence the equilibrium potential measured during the first oxidation of Fe(2+) to Fe(3+) in all polymorphs of Li(2)FeSiO(4).

Crystal Structure of a New Polymorph of Li2FeSiO4

We report on the crystal structure of a new polymorph of Li(2)FeSiO(4) (prepared by annealing under argon at 900 degrees C and quenching to 25 degrees C) characterized by electron microscopy and powder X-ray and neutron diffraction. The crystal structure of Li(2)FeSiO(4) quenched from 900 degrees C is isostructural with Li(2)CdSiO(4), described in the space group Pmnb with lattice parameters a = 6.2836(1) A, b = 10.6572(1) A, and c = 5.0386(1) A. A close comparison is made with the structure of Li(2)FeSiO(4) quenched from 700 degrees C, published recently by Nishimura et al. (J. Am. Chem. Soc. 2008, 130, 13212). The two polymorphs differ mainly on the respective orientations and alternate sequences of corner-sharing FeO(4) and SiO(4) tetrahedra.

On the Origin of the Electrochemical Capacity of Li2Fe0.8Mn0.2SiO4

On the Origin of the Electrochemical Capacity of Li2Fe0.8Mn0.2SiO4 Robert Dominko, Chutchamon Sirisopanaporn,* Christian Masquelier, Darko Hanzel, Iztok Arcon, and Miran Gaberscek** National Institute of Chemistry, SI-1001 Ljubljana, Slovenia ALISTORE-European Research Institute, 80039 Amiens Cedex, France Universite de Picardie Jules Verne, 80039 Amiens, France Jozef Stefan Institute, SI-1000 Ljubljana, Slovenia University of Nova Gorica, SI-5000 Nova Gorica, Slovenia Faculty for Chemistry and Chemical Technology, University of Ljubljana, 1000 Ljubljana, Slovenia

Polymorphism in Li2(Fe,Mn)SiO4: A combined diffraction and NMR study

Li2MSiO4 compounds have been attracting significant attention as lithium intercalation compounds for the next generation of rechargeable lithium batteries. Their structures consist of slightly distorted close packed oxygen slabs between which cations occupy half the tetrahedral sites, leading to a range of polymorphs. In this paper we describe the rich polymorphism observed across the Li2FezMn(1−z)SiO4 solid solution, characterized by detailed powder neutron and X-ray diffraction studies, combined with solid state NMR. This polymorphism reflects that seen in the end-members, with a gradual transition from Fe-like behaviour for iron-rich compositions, to Mn-like behaviour with increasing manganese content.

Understanding 6Li MAS NMR spectra of Li2MSiO4 materials (M=Mn, Fe, Zn)

Analysis of (6)Li MAS NMR spectra of several lithium transition-metal orthosilicates (Li(2)MSiO(4), M = Mn, Fe, Zn) improved the understanding of the relation between the spectral parameters and the structural characteristics of the materials. It was shown that for manganese- and iron-containing materials the width of the (6)Li spinning-sideband powder patterns can be roughly related to the arrangement of the transition-metal cations within the first cation coordination sphere around lithium. In mixed zinc-manganese lithium orthosilicates the (6)Li isotropic shift depends on the number of Li-O-Mn bonds, in which a particular lithium site is involved. Each bond contributes a small negative Fermi-contact hyperfine shift of about -20 to -40 ppm. The precise values of the contributions cannot be easily related to the geometry of the bonds. In iron-containing materials the isotropic shifts are composed of two contributions, the hyperfine shift and the pseudo-contact shift. The latter depends on the anisotropy of the magnetic susceptibility of the material. The magnetic properties of the iron-containing lithium orthosilicates are responsible also for very broad lines within their (6)Li MAS NMR spectra. Pure zinc-lithium orthosilicate exhibits a narrow (6)Li MAS NMR isotropic signal and no spinning-sideband powder pattern.