An insight into crystal, electronic, and local structures of lithium iron silicate (Li(2)FeSiO(4)) materials upon lithium extraction

Recently, orthosilicate, Li(2)MSiO(4) (where M=transition metal) materials have been attracting considerable attention for potential use as a new generation cathode for Li-ion batteries due to their safety, low toxicity, and low cost characteristics. In addition, the presence of two Li(+) ions in the molecule offers a multiple electron-charge transfer (M(2+)/M(3+) and M(3+)/M(4+) redox couples), thus allowing a high achievable capacity of more than 320 mA h/g per M unit. Good electrochemical properties of Li(2)FeSiO(4) have been reported through several approaches such as downsizing of the particles, carbon-coating, etc. However, in addition to electrochemical performance, fundamental understanding regarding crystal, electronic and local structure changes during charge/discharge processes is also important and needs more rigorous investigation. In this work, lithium iron silicates (Li(2)FeSiO(4)/C) in space group of Pnma: a=10.6671(3) A, b=6.2689(2) A, and c=5.0042(2) A have been prepared by solid-state reaction. The synthesized as well as chemical delithiated samples have been characterized by XRD, HRTEM, AAS and XAS techniques. We will show the results focusing on Fe K-edge XANES, EXAFS, HRTEM and XRD of the Li(2-x)FeSiO(4) samples and discuss how the crystal, electronic, and local structure changes upon Li(+) de-intercalation.