Marinite Li₂Ni(SO₄)₂ as a New Member of the Bisulfate Family of High-Voltage Lithium Battery Cathodes

Development of sustainable, economic, and high-voltage cathode materials forms the cornerstone of cathode design for Li-ion batteries. Sulfate chemistry offers a fertile ground to discover high-voltage cathode materials stemming from a high electronegativity-based inductive effect. Herein, we have discovered a new polymorph of high-voltage m-Li2NiII(SO4)2 bisulfate using a scalable spray drying route. Neutron and synchrotron diffraction analysis revealed a monoclinic structure (s.g. P21/c, #14) built from corner-shared NiO6 octahedra and SO4 tetrahedra locating all Li+ in a distinct site. Low-temperature magnetic susceptibility and neutron diffraction measurements confirmed long-range A-type antiferromagnetic ordering in m-Li2NiII(SO4)2 below 15.2 K following the Goodenough–Kanamori–Anderson rule. In situ X-ray powder diffraction displayed an irreversible (monoclinic → orthorhombic) phase transformation at ∼400 °C. The m-Li2NiII(SO4)2 framework offers two-dimensional Li+ migration pathways as revealed by the bond valence site energy (BVSE) approach. The electronic structure obtained using first-principles (DFT) calculation shows a large electronic band gap (Eg ∼ 3.8 eV) with a trapped state near the Fermi energy level triggering polaronic conductivity. As per the DFT study, m-Li2NiII(SO4)2 can work as a 5.5 V (vs Li+/Li0) cathode for Li-ion batteries, with suitable electrolytes, coupling both cationic (NiII/III) and anionic (O–) redox activity.