High-performance aqueous asymmetric supercapacitor based on hierarchical wheatear-like LiNi0.5Mn1.5O4 cathode and porous Fe2O3 anode

doi:10.1016/j.mtphys.2020.100337

Materials Today Physics

Volume 17, March 2021, 100337

https://doi.org/10.1016/j.mtphys.2020.100337 Get rights and content

Highlights

•
Develop a low-temperature lithiation method to synthesis wheatear-like LiNi_0.5Mn_1.5O₄ anchored on active carbon cloth (LNMO@ACC).
•
The LNMO@ACC electrode exhibits excellent electrochemical performance compared with almost reported Ni-based/Mn-based electrodes.
•
The Li⁺ adsorbs and diffuses more easily on (111) than (400) facet of LiNi_0.5Mn_1.5O₄ by DFT calculation.
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The aqueous ASC based on LNMO@ACC cathode and porous Fe₂O₃@ACC anode achieves a high energy density of 5.87 mWh cm^-3.

Abstract

The cobalt-free spinel LiNi_0.5Mn_1.5O₄ is actively explored as a cost-effective energy storage material. Herein, we report a low-temperature lithiation method to synthesize hierarchical wheatear-like LiNi_0.5Mn_1.5O₄ anchored on active carbon cloth (LNMO@ACC). The LNMO@ACC electrode exhibits a high areal capacitance (1468 mF cm⁻² at 1 mA cm⁻²), superior rate performance (1000 mF cm⁻² at 10 mA cm⁻²), and outstanding cycling stability (82.5% retention after 4000 cycles). The mechanism of Li ions adsorption and diffusion on (111) and (400) lattice planes of LiNi_0.5Mn_1.5O₄ is explained by density functional theory (DFT) calculations. The asymmetric supercapacitor (ASC) assembled by LNMO@ACC cathode and porous Fe₂O₃@ACC anode in 1 M LiNO₃ electrolyte achieves a wide potential window of 1.8 V, superior areal capacitance of 851 mF cm⁻², high energy density of 5.87 mWh cm⁻³ at a power density of 14.17 mW cm⁻³ and excellent cycle stability (retention of 88.6% after 8000 cycles at 20 mA cm⁻²). This work contributes a new method for preparing high-performance electrode materials and an effective strategy for high energy and power density supercapacitors by matching cathode and anode materials.

Graphical abstract

Introduction

The extensive energy demand of portable electronic products and electric vehicles has promoted the rapid development of high-efficiency energy storage technologies [[1], [2], [3]]. Among various energy storage systems, supercapacitors (SCs) have attracted much attention due to their high power density, fast charge-discharge capability and long cycle life. However, the relatively low energy density limits its practical applications [4,5]. Therefore, improving the energy density of SCs is a key factor for the future energy storage requirements. The improvement in energy density (E) can be achieved by maximizing the specific capacitance (C) and the operation voltage (V) according to E = 1/2 CV². Assembling asymmetric supercapacitors (ASCs) is a promising method to enhance specific capacitance, extend operating voltage and improve energy density by matching two different electrodes of respective potential windows [6]. Various ASCs have been reported, such as activated carbon (AC)//3D-Ni/Ni–Mn–O [7], Ni_0.25Mn_0.75O@C//AC [8], carbon nanotube (CNTs)//Li₄Ti₅O₁₂ [9], CNTs//Fe₃O₄@C [10], graphene//Ni₆MnO₈ [11], GrMnO₂//GrMoO₃ [12], N-GC//LiMn₂O₄ [13].

At present, the fabrication and appropriate matching of proper cathode and anode to achieve the wide voltage window for ASCs is promising research direction [6]. Various materials such as transition metal oxides, metal hydroxides, metal sulfides and metal-organic frameworks (MOFs) have been investigated extensively [[14], [15], [16], [17]]. Transition metal oxides have been reported and exhibited excellent specific capacitance because of faradaic charge-transfer reactions [2]. Especially, the manganese based transition metal oxides attract much attention due to its fast redox reaction rate, environment friendliness, low cost and abundant reserves in the earth [18,19]. The Mn based Li-ion insertion compound LiMn₂O₄ is a prominent cathode material for asymmetric supercapacitors because of its abundant channels for Li-ion diffusion and high theoretical capacity [20,21]. Recently, high voltage spinel cathode by substituting manganese with nickel (LiNi_0.5Mn_1.5O₄) has received much attention due to its higher energy density than LiMn₂O₄ [[22], [23], [24]]. However, the low conductivity for electrons and sluggish kinetic for lithium ions, the poor cycling stability caused by the dissolution of Mn³⁺ and structural degradation limit its applications [25].

To solve these problems, there are various synthetic methods to prepare the LiNi_0.5Mn_1.5O₄ (LNMO). One effective way is the wet chemistry synthesis, which is used to fabricate nanostructure LNMO for shorter Li⁺ diffusion pathways. Therefore, LNMO nanostructures with different morphologies appear, such as hierarchical LNMO micro-rods consisting of primary nanoparticles [26], truncated octahedron [27], core-shell structure [28], porous peanut-like [29], hierarchical desert-waves-like [25], hierarchical urchin-like [30]. Although treated by similar heat treatment, the different morphologies of those nanostructures show different crystal structure characteristics.

In this work, we develop a low-temperature lithiation method by directly converting the nickel-manganese precursor anchored on active carbon cloth (NMO@ACC) into hierarchical wheatear LiNi_0.5Mn_1.5O₄ (LNMO@ACC), which avoids the high temperature calcination near 800 °C comparing with the previous preparation methods of LiNi_0.5Mn_1.5O₄ [22,24,29] and greatly simplifies the production steps of electrode [23,25]. In the low temperature (200 °C), LiNi_0.5Mn_1.5O₄ is grown on carbon cloth in situ to form a self-supported electrode without binder, which greatly improves the conductivity and cycle stability. And the hierarchical wheatear LiNi_0.5Mn_1.5O₄ also improves the capacitance of the electrode because it is helpful to insertion and extraction of Li⁺ in the process of discharge and charge. The areal capacitance of LNMO@ACC reaches 1468 mF cm⁻², which is twice as NMO@ACC at a current density of 1 mA cm⁻² and retains 82.5% after 4000 cycles. Besides, we find that Li ions adsorb more easily and have a smaller diffusion barrier on (111) than (400) surface of LiNi_0.5Mn_1.5O₄ according to density functional theory (DFT) calculations. For assembling ASCs, the LNMO@ACC is as a cathode and the porous Fe₂O₃@ACC fabricated by simple hydrothermal and annealing processes is as anode in 1 M LiNO₃, which achieves excellent stability and rate performance in a large potential window of 1.8 V and obtains a high energy density of 5.87 mWh cm⁻³.

Section snippets

Synthesis of NMO@ACC precursor

The precursor of nickel manganese oxide on ACC was synthesized by the hydrothermal method and annealing treatment. The active carbon cloth (ACC) was prepared by treating the original carbon cloth with concentrated acid, which was reported in our previous work [31]. Typically, 2 mmol MnCl₂·4H₂O, 1 mmol NiCl₂·6H₂O, 3 mmol CO(NH₂)₂, 4 mmol NH₄F and 10 mmol CH₄N₂S were dissolved into a mixture solution with 30 mL deionized water and 10 mL ethylene glycol (EG). After that, a Teflon vessel autoclave

Results and discussion

Fig. 1 show the schematic illustration of the preparation process of LNMO@ACC cathode and Fe₂O₃@ACC anode. After acid treatment, the ACC possesses a graphitized structure and has many oxidation functional groups on its surface, which is beneficial to the growth of nanostructured materials on it [31]. The nickel-manganese precursor grows on active carbon cloth (NMO@ACC) by the hydrothermal method and annealing treatment. During hydrothermal process, the ethylene glycol (EG) serves as the

Conclusion

In summary, the hierarchical wheatear structural LiNi_0.5Mn_1.5O₄ and the porous Fe₂O₃ anchored on ACC are obtained by a simple low-temperature lithiation method and a hydrothermal-annealing process, respectively. We find that Li ions are more easily adsorbed on the (111) facets of LiNi_0.5Mn_1.5O₄, resulting in the good surface capacitive properties according to DFT calculations. Additionally, the assembled LNMO//Fe₂O₃ aqueous ASC demonstrates excellent stability in a large potential window of

Credit author statement

Shuang Luo: Design and complete experiments, Process experiment data, Draw figures, Write and revised manuscript; Jien Li: Assist in experimentation, such as synthetic materials and test performance, Complete the theoretical calculation; Junlin Lu, Feng Tao, Jing Wan: Participate in the discussion of the experimental plan and assiste in the experiment; Bin Zhang: Conduct TEM characterization of materials; Xiaoyuan Zhou: Thesis revision, Supervision; Chenguo Hu: Experimental design, Thesis

Declaration of competing interest

There are no conflicts to declare.

Acknowledgments

This work was supported by National Natural Science Foundation of China (52073037, 51772036), the Fundamental Research Funds for the Central University (2019CDXZWL001, 2020CDCGJ005) and Chongqing graduate tutor team construction project (ydstd1832).

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High-performance aqueous asymmetric supercapacitor based on hierarchical wheatear-like LiNi0.5Mn1.5O4 cathode and porous Fe2O3 anode

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Synthesis of NMO@ACC precursor

Results and discussion

Conclusion

Credit author statement

Declaration of competing interest

Acknowledgments

Chin. Chem. Lett.

Ceram. Int.

Mater.Today Energy

J. Power Sources

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Nanomater. Energy

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Chem. Eur J.

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High-performance aqueous asymmetric supercapacitor based on hierarchical wheatear-like LiNi_0.5Mn_1.5O₄ cathode and porous Fe₂O₃ anode

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Asymmetric supercapacitors based on graphene/MnO₂ nanospheres and graphene/MoO₃ nanosheets with high energy density

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The perfect matching between the low-cost Fe₂O₃ nanowire anode and the NiO nanoflake cathode significantly enhances the energy density of asymmetric supercapacitors

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