Elsevier

Solid State Ionics

Volume 338, 1 October 2019, Pages 121-126
Solid State Ionics

Hydrothermal synthesis of core-shell Mn3O4@C microspheres as superior anode materials for high-performance lithium-ion storage

https://doi.org/10.1016/j.ssi.2019.05.021Get rights and content

Highlights

  • Mn3O4@C microspheres constructed with aggregated nanoparticles are fabricated.

  • The carbon-shell structure Mn3O4@C microspheres enhance electrical conductivity.

  • Compared to pure Mn3O4, Mn3O4@C microspheres have superior rate stability.

  • Even after 800 cycles at 1 A/g, the discharge capacity can retain 992 mAh/g.

Abstract

The Mn3O4@C microspheres were prepared by combining a low temperature coating method of one-step hydrothermal process and subsequently annealing treatment. In this method, the resorcinol and formaldehyde (RF) were applied as carbon source to enhance the electrical conductivity of Mn3O4 microspheres. The resulting core-shell Mn3O4@C microspheres comprised of irregular aggregated nanoparticles with an average diameter of approximately 2 μm. The Mn3O4 microspheres were homogeneously coated by the carbon layers with a thickness of 50 nm. The Mn3O4@C microspheres exhibit dramatically excellent reversible discharge capacity of 913.8 mAh/g at 0.5 A/g after 300 cycles with an outstanding rate capability. The discharge capacity of Mn3O4@C microspheres could maintain up to 992 mAh/g even after 800 cycles at 1 A/g. The improved electrochemical performance of the synthesized Mn3O4@C microspheres is attributed to the fact that the carbon-shell structure can effectively buffer volume change, maintain structure integrity and improve electrical conductivity. The Mn3O4@C microspheres could be utilized as a promising candidate as the anode material for lithium-ion batteries.

Graphical abstract

The core-shell Mn3O4@C microspheres with ultra-long cycling life and outstanding rate performance are synthesized successfully through a facile hydrothermal process.

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Introduction

The rational design and development of high capacity and long lifespan electrode materials for rechargeable lithium-ion batteries (LIBs) are of great importance to meet the surging demands of energy devices [[1], [2], [3]]. Mn3O4 has exhibited promising applications for advanced LIBs in virtue of its high theoretical capacity (937 mAh/g), abundant resources, low cost and excellent safety performance [4,5]. However, Mn3O4 displays an extremely low electronic conductivity (10−7 to 10−8 S/cm) and drastic volume change during the charge/discharge processes, which severely hinders its practical applications [6,7].

Up to now, a large number of practical measures have been taken to improve these problems, such as morphology control [8,9], metal ion doping [10], and carbon composites [[11], [12], [13]]. Among them, carbon composite materials are a robust strategy to improve the electronic conductivity, effectively release the stress from the volume change during Li+ insertion/extraction and reduce unwanted side reactions between the electrode and the electrolyte [14,15]. Park et al. have synthesized carbon nanofiber/Mn3O4 by an electrophoretic deposition method, which exhibits a discharge capacity of 760 mAh/g after 50 cycles at 0.1 A/g [12]. Wang et al. have developed a solvothermal method for the synthesis of graphene/Mn3O4 nanocomposite membrane that delivers a high capacity of 308 mAh/g at 2 A/g [13]. Recently, RF has been employed as carbon source, which possesses high yield, low cost, stable chemical properties, good adsorption and catalytic performance of the prepared carbon spheres [[16], [17], [18]]. Zhang et al. have synthesized Fe3O4@C nanospheres by a Stöber method with RF as carbon sources, which exhibits a high adsorption capacity of 31.5 mg/g in water and 2 mg/g in cyclohexane solution [17]. Yang et al. have developed noble metal@RF core-shell nanostructures to promote research into catalytic applications [18]. Nonetheless, seldom research has been explored utilizing RF carbonization to improve the electrochemical properties of Mn3O4 for LIBs.

In this paper, we successfully designed the Mn3O4@C microspheres by a facile solvothermal synthesis method to take advantage of RF as carbon sources. Comparing to traditional strategies, our strategy can more easily implement and synthesize the Mn3O4@C microspheres with a homogeneous thin carbon layer, which can effectively raise the electrical conductivity and alleviate the volume change during Li+ insertion/extraction process. Furthermore, the Mn3O4@C microspheres exhibit superior electrochemical performance compared with Mn3O4.

Section snippets

Preparation of MnO2 microspheres

The MnO2 microspheres were synthesized by precipitation reaction. MnSO4 (0.012 mol) and NH4HCO3 (0.12 mol) were dissolved in distilled water (840 mL), respectively, to obtain A and B solutions. Then, the alcohol solution (168 mL) as dispersants were added to A solution under magnetic stirring for 20 min to gain C solution. The B solution was added to C solution under stirring for 2 h. The obtained precipitates were washed with distilled water and alcohol several times, subsequently dried at

Results and discussion

Based on extensive literature review, with the increase of temperature, hexagonal phase of MnO2 (PDF no. 30-0820) (Fig. S1) can be transformed into Mn2O3 and Mn3O4 gradually, and it is beneficial to form the oxide of low valence states at high temperature environment. In this experiment, because of the inert atmosphere and the presence of carbon, it is more conducive to the transformation of manganese to the low valence states [[19], [20], [21]]. For pure Mn3O4, all of the diffraction peaks can

Conclusions

In this paper, we strategically constructed Mn3O4@C microspheres via a low-temperature hydrothermal method and subsequently annealing treatment. The Mn3O4@C microsphere delivers a superior high-rate capacity of 372.3 mAh/g at 3.2 A/g and a stable long-term life span remaining a reversible capacity of 992 mAh/g after 800 cycles at 1 A/g. The RF plays an essential role in forming the core-shell structure and heightening the electronic conductivity of Mn3O4. This method provides a straightforward

Acknowledgments

This work is supported by the National Natural Science Foundation of China (Nos. 51479019 and 21476035) and Fundamental Research Funds for the Central Universities (3132016341).

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