Binder-free NiCoFe layered double hydroxide nanosheets for flexible energy storage devices with high-rate-retention characteristics

In this study, NiCoFe layered double hydroxide (LDH) nanosheets with various composition ratios are synthesized via a simple electrodeposition method. The NiCoFe LDH prepared with a precursor molar ratio of Ni:Co:Fe = 1:2:0.1 shows the best performance with a specific capacity of 727 C g(-1) at 1 A g(-1), a high rate retention of 77% at 50 A g(-1), and a capacity retention of 87% after 10,00 0 cycles. The quick in-operando X-ray absorption study shows that the electrochemical activity of the various LDHs mainly originates from the change in the valence state of Ni ions, and the Fe ions improve the rate capability as well as the cycling stability. Furthermore, a solid-state energy storage device is fabricated using the NiCoFe-(1:2:0.1) LDH as the positive electrode, commercial activated carbon as the negative electrode, and PVA-KOH as the electrolyte. The device exhibits an energy density of 8.7 Wh kg(-1) at 62.8 W kg(-1) and 6.8 Wh kg(-1) at 3139.2 W kg(-1). The cycling stabilities of the device under folding and unfolding conditions are also evaluated, and the performances are found about the same, revealing great potential for flexible energy storage applications. (C) 2021 Published by Elsevier Ltd.

Automated summary

NiCoFe layered double hydroxide (LDH) nanosheets were synthesized with different composition ratios, with Ni:Co:Fe = 1:2:0.1 showing the best performance in terms of specific capacity, rate retention, and cycling stability. In-operando X-ray absorption study revealed that the electrochemical activity of LDHs is mainly influenced by the valence state of Ni ions, with Fe ions enhancing rate capability and cycling stability. A solid-state energy storage device utilizing NiCoFe-(1:2:0.1) LDH as the positive electrode exhibited high energy density and cycling stability, showing potential for flexible energy storage applications.