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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-Li 2 Ni II (SO 4 ) 2 bisulfate using a scalable spray drying route. Neutron and synchrotron diffraction analysis revealed a monoclinic structure (s.g. P2 1 / c, #14) built from corner-shared NiO 6 octahedra and SO 4 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-Li 2 Ni II (SO 4 ) 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-Li 2 Ni II (SO 4 ) 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 (E g ∼ 3.8 eV) with a trapped state near the Fermi energy level triggering polaronic conductivity. As per the DFT study, m-Li 2 Ni II (SO 4 ) 2 can work as a 5.5 V (vs Li + /Li 0 ) cathode for Li-ion batteries, with suitable electrolytes, coupling both cationic (Ni II/III ) and anionic (O − ) redox activity.

Developing earth-abundant low-cost bifunctional oxygen electrocatalysts is a key approach to realizing efficient energy storage and conversion. By exploring Co-based sodium battery materials, here we have unveiled nanostructured pyrophosphate Na2CoP2O7 polymorphs displaying efficient bifunctional electrocatalytic activity. While the orthorhombic polymorph (o-NCPy) has superior oxygen evolution reaction (OER) activity, the triclinic polymorph (t-NCPy) delivers better oxygen reduction reaction (ORR) activity. Simply by tuning the annealing condition, these pyrophosphate polymorphs can be easily prepared at temperatures as low as 500 °C. The electrocatalytic activity is rooted in the Co redox center with the (100) active surface and stable structural framework as per ab initio calculations. It marks the first case of phospho-anionic systems with both polymorphs showing stable bifunctional activity with low combined overpotential (ca. ∼0.7 V) comparable to that of reported state-of-the-art catalysts. These nanoscale cobalt pyrophosphates can be implemented in rechargeable zinc–air batteries.