Enlarged Interlayer Spacing in Cobalt–Manganese Layered Double Hydroxide Guiding Transformation to Layered Structure for High Supercapacitance

Abstract

Cobalt–manganese layered double hydroxide (CoMn-LDH) has been known as a highly desired cathode material used with an alkaline electrolyte. However, the layered double hydroxide structure is unstable and changes almost instantly in alkaline solution due to the instability of a manganese­(III) ion. Thus, it is important to investigate the true active phase for designing efficient electrode materials. In this work, the metal–organic framework is used as a templating precursor to derive CoMn-LDH from three different manganese solutions, namely, MnSO4, Mn­(NO3)2, and MnCl2. Anions in the solutions participate in the derivation process and strongly affect the layer structure, phase transformation process, and charge storage properties of the resulting materials. CoMn-LDH synthesized from manganese sulfate solution exhibits the largest interlayer spacing of 1.08 nm, and more interestingly, the layered structure can well be retained in KOH solution, while the other two synthesized from manganese chloride and nitrate solutions transform into the spinel structure. As a cathode material, it delivers a high areal capacity of 582.07 mC/cm2 at 2 mA/cm2 , which is about 100% higher than those of the other two samples. The present work explores the active phase of CoMn-LDH in the alkaline electrolyte and proposes a potential mechanism of the phase transformation, which provides insights into understanding and designing of the active electrode materials for stable and high-performing supercapacitors in an alkaline environment.

Chemical Modifications of Layered Double Hydroxides in the Supercapacitor

“…This architecture can effectively prevent the restacking of rGO and the aggregation of NiCo 2 O 4 and has fast reversible redox reactions and long-term stability for supercapacitors. Liu et al [70] synthesized ultrathin NiCoAl-LDH (m-LDH) nanosheets and N-doped reduced graphene oxide (NRG) nanohybrids by alkaline etching of pre-synthesized ultrathin NiCoAl-LDH nanosheets and electrostatic assembly. The chemical states of the active Ni/Co elements were modulated by the alkaline etching, and more oxygen vacancies were created in the m-LDH nanosheets.…”

“…Some other anions such as OH − , NO 3 − , SO 4 2− , and Cl − are promising candidate anions and have been widely researched. Wang et al [ 61 ] reported the effect of NO 3 − , SO 4 2− , and Cl − anions on the structure and capacitive performance of MnCo‐LDHs, as shown in Figure a. In detail, the different interlayer anions dramatically affect the phase transformation, structure, and charge storage properties of the MnCo‐LDH materials.…”

Recent Progress in Two‐Dimensional Layered Double Hydroxides and Their Derivatives for Supercapacitors

“…Second, the interlayer anions can tailor the microporous structure and provide more active sites, leading to an enhanced capacitive performance. [9,18] Positive chargesi nt he host layers and weak interactions of interlayer anions with the host-layer cations enablet he LDH to adsorb various types of anionic species in the interlayer spacing by directi ntercalation or by anion exchange. Several molecules (such as dodecyl sulfate ions, [52] glucose, [22] ethylene glycol, [19] and acetate [53] )h ave been intercalated into the interlayers of LDHs to constructS Ce lectrode materials.…”

“…[52] Our group investigated the effect of NO 3 À ,C l À ,a nd SO 4 2À anions on the structure and capacitive performances of CoMn LDH. [18] The intercalationa nionss trongly affect the layer structure, phase transformationp rocess, and charge-storage properties of the CoMn LDH electrode materials. In particular,S O 4 2Àintercalated CoMn LDH shows the largesti nterlayer spacing of 1.08 nm, and the most stable layered structure in KOH electrolyte compared with those of NO 3 À -a nd Cl À -intercalated CoMn LDHs.…”

“…[14] There are several processing techniques that have been developed to synthesize LDHs for applications in SCs, such as hydrothermal, [15] electrodeposition, [16] chemical exfoliation and self-assembly, [17] and templating methods. [18] The LDHs thus-developedh aveb een studied for their performance as electrode materials in energy storage, in which they can offer the following advantages:1 )LDHs with al amellar structure and grown High-performance supercapacitors have attracted great attention due to their high power, fast charging/discharging, long lifetime, and high safety.H owever,t he generally low energy density and overall device performance of supercapacitors limit their applications.I nr ecent years, the design of rational electrode materials has provent ob ea ne ffective pathway to improvet he capacitive performances of supercapacitors. Layered double hydroxides (LDHs), have shown great potential in new-generation supercapacitors, due to their unique two-dimensional layered structures with ah igh surfacea rea and tun-able composition of the host layers and intercalation species.…”