On the Ni0.75Ti1.5Fe0.5(PO4)3/C NASICON-type electrode material

Abstract

The effect of titanium chemical substitution with iron, coupled with introducing additional Ni2+ ions in the M1 site, on the electrochemical and structural properties of the previously studied Ni0.5Ti2(PO4)3 ([email protected]) material is investigated in this manuscript. The new Ni0.75Fe0.5Ti1.5(PO4)3/C ([email protected]) composition is prepared via the conventional sol-gel method and tested as new electrode material for lithium-ion batteries. In the voltage range of 1.85–3.0 V, the [email protected] electrode delivered a first discharge capacity around 118 mAh.g−1 at a slow current rate of 0.1C (6.25 mA g−1). unlike the [email protected], when the new [email protected] electrode is cycled at faster current rates such as 5C (312.56 mA g−1), the capacity dropped to about 65 mAh.g−1 which represents only 55% of the capacity obtained at 0.1C (6.25 mA g−1) but with a columbic efficiency of more than 99%. When long-term cycling performance stability was investigated, a remarkable stability was achieved revealing the positive influence of iron together with the extra Ni2+ ions in the M1 site, preserving the structural stability during the intercalation process of Li+ ions. A capacity retention of about 95% was obtained after 500 cycles at the current rate of 0.5C (31.26 mA g−1). When [email protected] was cycled in the voltage window 0.5–3.0 V, an average specific capacity of around 350 mAh.g−1 was achieved at the current rate of 0.1C resulted out of the decomposed NASICON structure.