Dynamic Changes of Ni-Al LDH Nanosheets under Potential Cycling Investigated by In Situ Electrochemical Atomic Force Microscopy

Abstract

Nickel-aluminum layered double hydroxides (Ni-Al LDHs) are widely used in energy storage and conversion devices, and the impact of the Ni/Al molar ratio on the structural evolution and kinetic process is of great significance for improving reaction kinetics and efficiency. In this paper, the morphological evolutions and nanomechanical property changes of Ni-Al-n LDH (n is the Ni/Al molar ratio) nanosheets during potential cycling were explored by in situ electrochemical atomic force microscopy. The conversion of Ni2+ into Ni3+ and the amphoteric properties of Al3+ during potential cycling resulted in the dissolution of Ni-Al-n LDH nanosheets. The dissolution rate of Ni-Al-2 LDH nanosheets was slower than those of Ni-Al-2.5 LDH and Ni-Al-3 LDH nanosheets. Meanwhile, the Young’s modulus value of the dissolved area was much larger than that of the undissolved area, and the dissolved area exhibited a harder property. It was attributed to the different microcrystalline structures of Ni-Al LDH nanosheets affected by the Ni/Al molar ratio and the rearrangement of Ni2+ and Al3+ during the reaction. The slow dissolution of Ni-Al-2 LDH nanosheets was beneficial to improving the electrochemical performance, while the fast dissolution of Ni-Al-2.5 LDH and Ni-Al-3 LDH nanosheets was not conducive to the electrochemical performance. Understanding the effect of the Ni/Al molar ratio on the morphological evolutions and nanomechanical property changes of Ni-Al LDH nanosheets during potential cycling has important guiding significance for the subtle compositional modification and structural design of Ni-Al LDHs as an electrode material.