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

Abstract

The Li_1+xTi_2−xFe_x(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 Li_1.2Ti_1.8Fe_0.2(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.