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

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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 3d 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 3d and O 2p orbitals. Hence, the electronic conductivity is significantly enhanced and the electrostatic repulsion between Mg2+ and host layers is greatly reduced, giving rise to the improved diffusion kinetics and storage‐capacity of Mg2+. 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.
Funding Information
  • National Natural Science Foundation of China (22379063)

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