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The O‐type layered nickel oxides suffer from undesired cooperative Jahn–Teller distortion stemming from Ni3+ ions and undergo multiple biphasic structural transformations during the insertion/extraction of large Na+ ions, posing a significant challenge to stabilize the structural integrity. We present here a systematic investigation of the impact of substituting 5 % divalent (Mg2+) or trivalent (Al3+ or Co3+) ions for Ni3+ to alleviate Na+ion ordering and perturb the Jahn–Teller effect to enhance structural stability. We gauge a fundamental understanding of the Mg−O and Na−O or Mg−O−Na bonding interactions, noting that the ionicity of the Mg−O bond deshields the electronic cloud of oxygen from Na+ ions. Furthermore, calculations of the Van Vleck distortion modes reveal a relaxation of NiO6 octahedra from Jahn–Teller distortion and a reduced electron density at the interlayer with Mg2+ substitution. Long‐range (operando X‐ray diffraction) and short‐range (magic angle spinning nuclear magnetic resonance) structural analyses provide insights into reduced ordering, allowing a stable continuous solid solution. Overall, Mg‐substitution results in a high‐capacity retention of ~96 % even after 100 cycles, showcasing the potential of this strategy for overcoming the structural instabilities and enhancing the performance of sodium‐ion batteries. [ABSTRACT FROM AUTHOR]

P3-type layered K0.48Mn0.4Co0.6O2 was synthesized using a solid-state method. By stabilising into a rhombohedral structure [s.g. R3m (#160)], it delivers a reversible capacity of 64 mA h g−1 with a nominal voltage of ∼3.0 V (vs. K/K+) and it has good cycling stability. It involves a solid-solution redox mechanism, and forms an economical and stable oxide insertion material for potassium-ion batteries. [ABSTRACT FROM AUTHOR]

Aqueous rechargeable zinc-ion batteries have immense commercial potential in the primary battery market, which is largely occupied by alkaline zinc/manganese oxide batteries. These storage systems are desirable for large-scale applications due to their superior safety, high capacity, fast ionic conductivity and low cost. Pursuing new Mn-based cathodes for Zn-ion batteries, cryptomelane with a specific chemical composition of K1.33Mn8O16 was synthesized using a simple sonochemical technique. The formation of phase pure tetragonal K1.33Mn8O16 with I4/m symmetry was confirmed by X-ray diffraction. When tested as a cathode for Zn-ion batteries, cryptomelane K1.33Mn8O16 demonstrated a high reversible capacity of 312 mA h g−1 at a rate of C/10. Robust cycling stability was observed retaining more than 80% of initial capacity after 650 cycles with ∼99% coulombic efficiency. The intercalation chemistry of Zn–MnO2 systems is very rich involving polymorphism and phase transformations during charge/discharge cycles. Synergizing ex situ X-ray diffraction and spectroscopy with the electrochemical titration technique, we have examined the detailed mechanism of (de)intercalation of Zn2+ into cryptomelane K1.33Mn8O16, which is proposed as a potential cathode for Zn-ion batteries. [ABSTRACT FROM AUTHOR]

Noble-metal-free, bifunctional catalysts are essential to develop high-performance, cost-effective water-splitting systems. The current work explores the bifunctional electrocatalytic behavior of two sodium cobalt phosphate systems, namely, NaCoPO4 and Na2CoP2O7, prepared by solution combustion synthesis (SCS) for the first time. Formation of phase-pure orthorhombic maricite NaCoPO4 (space group: Pnma) and orthorhombic Na2CoP2O7 (space group: Pna21) was confirmed by Rietveld refinement. The electrocatalytic activity of maricite NaCoPO4 and Na2CoP2O7 was investigated by using linear sweep voltammetry with a rotating disk electrode (RDE). The oxygen reduction reaction (ORR) activities of these sodium cobalt phosphates are comparable to Vulcan carbon black and Pt/C. Oxygen evolution reaction (OER) activity of Na2CoP2O7 is dominant compared to NaCoPO4 and Pt/C. The Tafel slope, electron-transfer number, and stability of the sodium-metal phosphates were calculated in different concentrations of Na+-containing aqueous electrolyte. The bifunctional activity and good stability of the sodium cobalt phosphates stem from cobalt ions and stabilization of the catalytic centers by the phosphate frameworks. The present work demonstrates sodium cobalt phosphates as alternate cost-effective, novel electrocatalysts for efficient OER/ORR activity in alkaline solution. [ABSTRACT FROM AUTHOR]

Reversible electrochemical potassium-ion intercalation in P2-type NaxCoO2 was examined for the first time. Hexagonal Na0.84CoO2 platelets prepared by a solution combustion synthesis technique were found to work as an efficient host for K+ intercalation. They deliver a high reversible capacity of 82 mA h g−1, good rate capability and excellent cycling performance up to 50 cycles. [ABSTRACT FROM AUTHOR]

The O-type layered nickel oxides suffer from undesired cooperative Jahn-Teller distortion stemming from Ni 3+ ions and undergo multiple biphasic structural transformations during the insertion/extraction of large Na + ions, posing a significant challenge to stabilize the structural integrity. We present here a systematic investigation of the impact of substituting 5 % divalent (Mg 2+ ) or trivalent (Al 3+ or Co 3+ ) ions for Ni 3+ to alleviate Na + ion ordering and perturb the Jahn-Teller effect to enhance structural stability. We gauge a fundamental understanding of the Mg-O and Na-O or Mg-O-Na bonding interactions, noting that the ionicity of the Mg-O bond deshields the electronic cloud of oxygen from Na + ions. Furthermore, calculations of the Van Vleck distortion modes reveal a relaxation of NiO 6 octahedra from Jahn-Teller distortion and a reduced electron density at the interlayer with Mg 2+ substitution. Long-range (operando X-ray diffraction) and short-range (magic angle spinning nuclear magnetic resonance) structural analyses provide insights into reduced ordering, allowing a stable continuous solid solution. Overall, Mg-substitution results in a high-capacity retention of ~96 % even after 100 cycles, showcasing the potential of this strategy for overcoming the structural instabilities and enhancing the performance of sodium-ion batteries., (© 2024 Wiley-VCH GmbH.)

P3-type layered K 0.48 Mn 0.4 Co 0.6 O 2 was synthesized using a solid-state method. By stabilising into a rhombohedral structure [s.g. R3m (#160)], it delivers a reversible capacity of 64 mA h g -1 with a nominal voltage of ∼3.0 V (vs. K/K + ) and it has good cycling stability. It involves a solid-solution redox mechanism, and forms an economical and stable oxide insertion material for potassium-ion batteries.

Reversible electrochemical potassium-ion intercalation in P2-type Na x CoO 2 was examined for the first time. Hexagonal Na 0.84 CoO 2 platelets prepared by a solution combustion synthesis technique were found to work as an efficient host for K + intercalation. They deliver a high reversible capacity of 82 mA h g -1 , good rate capability and excellent cycling performance up to 50 cycles.