Calcium-ion batteries (CIBs) are under investigation as next-generation energy storage devices due to their theoretically high operating potentials and lower costs tied to the high natural abundance of calcium. However, the development of CIBs has been limited by the lack of available positive electrode materials. Here, for the first time, we report two functional polyanionic phosphate materials as high-voltage cathodes for CIBs at room temperature. NaV2(PO4)3 electrodes were found to reversibly intercalate 0.6 mol of Ca2+ (81 mA h g–1) near 3.2 V (vs Ca2+/Ca) with stable cycling performance at a current density of 3.5 mA g–1. The olivine framework material FePO4 reversibly intercalates 0.2 mol of Ca2+ (72 mA h g–1) near 2.9 V (vs Ca2+/Ca) at a current density of 7.5 mA g–1 in the first cycle. Structural, electronic, and compositional changes are consistent with reversible Ca2+ intercalation into these two materials.

Lattice Mg2+ in a tailored solid solution spinel, MgCrMnO4, is electrochemically utilized at high Mn-redox potentials in a nonaqueous electrolyte. Complementary evidence from experimental and theoretical analyses supports bulk Mg2+ (de)­intercalation throughout the designed oxide frame where strong electrostatic interaction between Mg2+ and O2– exists. Mg/Mn antisite inversion in the spinel is lowered to ∼10% via postannealing at 350 °C to further improve Mg2+ mobility. Spinel lattice is preserved upon removal of Mg2+ without any phase transformations, denoting structural stability at the charged state at a high potential ∼3.0 V (vs Mg/Mg2+). Clear remagnesiation upon first discharge, harvesting up to ∼180 Wh/kg at 60 °C is shown. In the remagnesiated state, insertion of Mg2+ into interstitial sites in the spinel is detected, possibly resulting in partial reversibility which needs to be addressed for structural stability. The observations constitute a first clear path to the development of a practical high voltage Mg-ion cathode using a spinel oxide.

Transition metal dichalcogenide (TMDCs) alloys could provide a wide range of physical and chemical properties, ranging from charge density waves to superconductivity and electrochemical activities. While many exciting behaviors of unary TMDCs have been predicted, the vast compositional space of TMDC alloys has remained largely unexplored due to our lack in understanding of their stability when accommodating different cations or chalcogens in a single-phase. Here, we report a theory-guided synthesis approach to achieve unexplored quasi-binary TMDC alloys through computationally predicted stability maps. We have generated equilibrium temperature-composition phase diagrams using first-principles calculations to identify the stability for 25 quasi-binary TMDC alloys, including those involving non-isovalent cations and verify them experimentally by synthesizing a subset of 12 predicted alloys using a scalable chemical vapor transport method. We demonstrate that the synthesized alloys can be exfoliated into 2D structures, and some of them exhibit: (i) outstanding thermal stability tested up to 1230 K, (ii) exceptionally high electrochemical activity for CO 2 reduction reaction in a kinetically limited regime with near zero overpotential for CO formation, (iii) excellent energy efficiency in a high rate Li-air battery, and (iv) high break-down current density for interconnect applications. This framework can be extended to accelerate the discovery of other TMDC alloys for various applications.As a class of 2D materials, transition metal dichalcogenides (TMDCs) display diverse physical properties, including topological insulator properties, [1,2] superconductivity, [3][4][5][6] valley polarization, [7][8][9][10] and enhanced electrocatalytic activity for various chemical reactions. [11][12][13][14][15][16][17][18] This diversity arises due to the ability of TMDCs to accommodate different transition-metal elements, such as Mo, W, V, Nb, Ta, Re and others, with the three chalcogens (S, Se, and Te) in stable layered structures -that can be exfoliated to a desired number of 2D layers to control quantum confinement. Their properties can be further tuned