Preparation, structure and properties of Na2Mn3(SO4)4: a new potential candidate with high voltage for Na-ion batteries

Abstract

Recently, several excellent SO₄-based polyanion cathodes for Na-ion batteries (NIBs) were exploited, e.g. Na_2+2xM_2−x(SO₄)₃ (M = Fe and Mn), which can make NIBs competitive with state-of-the-art Li-ion batteries (LIBs). To search for more excellent SO₄-based materials for NIBs, we studied the Na₂SO₄–MnSO₄ system and isolated a new compound Na₂Mn₃(SO₄)₄, which crystallizes in the orthorhombic space group Cmc2₁ with a = 14.8307(18) Å, b = 9.9107(18) Å, c = 8.6845(12) Å, and Z = 4. The structure has tunnels for the migration of Na⁺ ions, which can be confirmed by using BVS maps. The impedance studies further demonstrated the mobility of Na⁺ ions. A high redox potential with a value of 4.48 V was obtained using the density functional theory (DFT) method based on ab initio calculations. Additionally, magnetic tests, infrared spectroscopy (IR), and differential scanning calorimetry (DSC) were also employed for the characterization of the material.