Exploiting Na2MnPO4F as a high-capacity and well-reversible cathode material for Na-ion batteries

Abstract

A Na₂MnPO₄F/C nanocomposite material is successfully synthesized via spray drying, followed by a high-temperature sintering method. It is shown that the highly phase-pure Na₂MnPO₄F with symmetry of the P2₁/n space group is uniformly embedded in the carbon networks, which play a key role in building up a highly efficient, electron-flow channel and elevating the electronic conductivity of the nanocomposites. The electrochemical measurements show that the initial discharge capacity of Na₂MnPO₄F reaches up to 140 and 178 mA h g⁻¹ at 30 °C and 55 °C, respectively. Furthermore, the capacity still maintains 135 mA h g⁻¹ after 20 cycles at 55 °C. The Na⁺ diffusion coefficient in Na₂MnPO₄F is calculated at about 10⁻¹⁷ cm² s⁻¹ by the GITT method. The impressive cycling performance of the material is ascribed to the good structural reversibility and stability of Na₂MnPO₄F, which are confirmed by the ex situ XRD measurements during the first cycle and after 30 cycles.