The influence of iron substitution on the electrochemical properties of Li1+xTi2−xFex(PO4)3/C composites as electrodes for lithium batteries

The Li1+xTi2−xFex(PO4)3/C series with 0 ≤ x ≤ 0.4 was prepared by a sol–gel method. XRD patterns showed a rhombohedral phase and minor contribution of an orthorhombic phase. The local environment of the phosphate structure was analyzed by 31P MAS NMR spectroscopy. The electrochemical lithium insertion revealed two reversible regions for Fe3+/Fe2+ and Ti4+/Ti3+ reactions as confirmed by 57Fe Mössbauer spectroscopy. Capacity values as large as 130 mA h g−1 were recorded for Li1.2Ti1.8Fe0.2(PO4)3/C after 40 cycles. The drastic decrease in capacity observed for LiTi2(PO4)3/C cycled at C/2 was explained in terms of a lower kinetic response at the electrode–electrolyte interphase.