Synthesis, characterization and electrochemical properties of a novel triphosphate LiFe2P3O10

A novel lithium iron phosphate has been synthesized by a solution route at moderate temperature. The structure was determined from powder by XRD, HRTEM and SAED experiments. LiFe₂P₃O₁₀ tripolyphosphate crystallizes in the monoclinic system, space group P2₁/m, with lattice constants a = 4.597(7) Å, b = 8.566(4) Å, c = 9.051(4) Å, β = 97.47° and Z = 2. Internal and external vibrational modes (Raman and FTIR) show that the dominant spectral features come from the (P₃O₁₀)⁵⁻ oxo-anions displaying internal and external modes along with the P-O-P bridging modes. Magnetic measurements are consistent with the high-spin configuration of Fe²⁺ cation with an effective magnetic moment 5.51 μ_B. A weak antiferromagnetic ordering is observed below the Néel temperature at T_N = 19 K. Electron paramagnetic resonance spectroscopy confirms this electronic configuration and provides evidence of the presence of a carbonaceous layer onto the particle surface. Electrochemical measurements were carried out in lithium cells with LiPF₆-EC-DEC electrolyte at 25 °C. The material delivered a capacity 70 mAh/g in the voltage range 2.7-3.9 V, close to the theoretical value (72 mAh/g). The resulting cyclic voltammogram indicates a stable structure with a good reversibility with the redox peaks at 3.26 and 3.13 V vs. Li⁰/Li⁺.