Hierarchical NiMn Layered Double Hydroxide/Carbon Nanotubes Architecture with Superb Energy Density for Flexible Supercapacitors

Abstract

A hierarchical nanostructure composed of NiMn‐layered double hydroxide (NiMn‐LDH) microcrystals grafted on carbon nanotube (CNT) backbone is constructed by an in situ growth route, which exhibits superior supercapacitive performance. The resulting composite material (NiMn‐LDH/CNT) displays a three‐dimensional architecture with tunable Ni/Mn ratio, well‐defined core‐shell configuration, and enlarged surface area. An electrochemical investigation shows that the Ni3Mn1‐LDH/CNT electrode is rather active, which delivers a maximum specific capacitance of 2960 F g–1 (at 1.5 A g–1), excellent rate capability (79.5% retention at 30 A g–1), and cyclic stability. Moreover, an all‐solid‐state asymmetric supercapacitor (SC) with good flexibility is fabricated by using the NiMn‐LDH/CNT film and reduced graphene oxide (RGO)/CNT film as the positive and negative electrode, respectively, exhibiting a wide cell voltage of 1.7 V and largely enhanced energy density up to 88.3 Wh kg–1 (based on the total weight of the device). By virtue of the high‐capacity of pseudocapacitive hydroxides and desirable conductivity of carbon‐based materials, the monolithic design demonstrated in this work provides a promising approach for the development of flexible energy storage systems.

Ultra-small, size-controlled Ni(OH)2 nanoparticles: elucidating the relationship between particle size and electrochemical performance for advanced energy storage devices

“…In contrast, a reverse trend in R ct and D is observed as the size of the Ni(OH) 2 nanoparticles further decreases below 7.9 nm, and a decrease in the capacity occurs. It should be noted that this reverse trend in R ct and D is synchronized with the rapidly decreasing trend in σ caused by the quantum confinement effect, which is consistent with other reports 10,13,[30][31][32][33][34][35] and confirms the underlying relationship between σ, R ct and D. As a result, 3.3-nm Ni(OH) 2 nanoparticles have a minimum capacity value because of their low conductivity, large charge transfer resistance and small proton diffusion coefficient.…”

“…Moreover, many works have proven that the conductivity of electrode materials is closely related to the diffusion of protons through the nanoparticle and the redox reaction rate on the surface. 10,13,[30][31][32][33][34][35] This result leads us to hypothesize that the charge transfer resistance (R ct ) and proton diffusion coefficient (D) in the electrodes and electrolytes could change and differ from the traditional understanding because the particle size of Ni(OH) 2 is less than the critical size.…”

Two‐Dimensional Hybrid Materials: Transferring Technology from Biology to Society

“…For instance when graphene [48] or carbon nanotubes [49] are mixed with LDH nanosheets to yield a so-called molecular-scale heteroassembly, high performance supercapacitors are obtained combining both high capacity and high power rate. In the case of 2D/2D heterostructure, this is explained by the heterostacking of redoxable LDH nanosheets and conductive graphene into a genuine superlattice structure that, as a consequence, improves the charge transfer efficiency, while for the 1D/2D, a quasi-3D architecture is obtained, displaying well-defined core-shell configuration and enlarged surface area.…”

Transition metal oxides/hydroxides nanoarrays for aqueous electrochemical energy storage systems

“…Yuan et al [72] and Zhao et al [73] )), have attracted increasing interest from both academic and industrial angles due to their wide applications in various areas [74]. Recently, LDHs with vertically aligned structures have exhibited great potential in SCs [75][76][77][78]. Gu et al [79] prepared a NiTi-LDH nanosheet film by a two-step hydrothermal process, which showed a high areal capacitance of 10.37 F cm −2 at 5 mA cm −2 .…”