Valence Engineering Boosts Kinetics and Storage Capacity of Layered Double Hydroxides for Aqueous Magnesium‐Ion Batteries

Abstract The kinetics and storage‐capacity of NiCoMg‐ternary layered double hydroxide (NiCoMg‐LDH) are successfully boosted by valence engineering. As the cathode for aqueous magnesium‐ion batteries (AMIBs), the assembled NiCoMg‐LDH//active carbon (AC) delivers a high specific discharge capacity (121.0 mAh·g −1 at 0.2 A·g −1 ), long‐term cycling stability (85% capacity retention after 2000 cycles at 1.0 A·g −1 ) and an excellent performance at −30 °C. Moreover, NiCoMg‐LDH//perylenediimide (PTCDI) is assembled, achieving a high specific discharge capacity and long‐term cycling stability. X‐ray absorption spectra (XAS)/X‐ray photoelectron spectroscopy (XPS) analyses and Density functional theory (DFT) calculations disclose that the electrons are redistributed due to the 3 d orbital overlap of Co/Ni atoms in NiCoMg‐LDH, which obviously reduces the valence states of Co/Ni atoms, enhances Mg─O bond strength and degree of hybridization of Co/Ni 3 d and O 2 p orbitals. Hence, the electronic conductivity is significantly enhanced and the electrostatic repulsion between Mg 2+ and host layers is greatly reduced, giving rise to the improved diffusion kinetics and storage‐capacity of Mg 2+ . Furthermore, in situ Raman/X‐ray diffraction (XRD) and ex situ XPS reveal corresponding energy‐storage mechanism. This paper not only demonstrates the feasibility of LDHs as cathode for AMIBs, but also offers a new modification method of valence engineering for high‐performance electrode materials.