Design of new electrode materials for Li-ion and Na-ion batteries from the bloedite mineral Na2Mg(SO4)2·4H2O

Abstract

Mineralogy offers a large database to search for Li- or Na-based compounds having suitable structural features for acting as electrode materials, LiFePO₄ being one example. Here we further explore this avenue and report on the electrochemical properties of the bloedite type compounds Na₂M(SO₄)₂·4H₂O (M = Mg, Fe, Co, Ni, Zn) and their dehydrated phases Na₂M(SO₄)₂ (M = Fe, Co), whose structures have been solved via complementary synchrotron X-ray diffraction, neutron powder diffraction and transmission electron microscopy. Among these compounds, the hydrated and anhydrous iron-based phases show electrochemical activity with the reversible release/uptake of 1 Na⁺ or 1 Li⁺ at high voltages of ∼3.3 V vs. Na⁺/Na⁰ and ∼3.6 V vs. Li⁺/Li⁰, respectively. Although the reversible capacities remain lower than 100 mA h g⁻¹, we hope this work will stress further the importance of mineralogy as a source of inspiration for designing eco-efficient electrode materials.