Elsevier

Materials Letters

Volume 276, 1 October 2020, 128205
Materials Letters

Facile synthesis of Mo2N quantum dots embedded N-doped carbon nanosheets composite as advanced anode materials for lithium-ion batteries

https://doi.org/10.1016/j.matlet.2020.128205Get rights and content

Highlights

  • Mo2N embedded N-doped carbon nanosheets hybrid was prepared by a one-pot method.

  • The Mo2N nanoparticles with ultrasmall size can shorten the ions diffusion length.

  • Rich N doping and defects in NC create plenty of active sites for Li storage.

  • Mo2N@NC achieved good performance due to its unique embedded heterostructure.

Abstract

Mo2N quantum dots embedded N-doped carbon nanosheets (Mo2N@NC) composite are prepared by a facile one-pot approach and applied as anode material for lithium-ion batteries. In this unique embedded Mo2N@NC heterostructure, the ultrasmall Mo2N nanoparticles possess short paths for Li+ ion diffusion, while the NC can facilitate fast electron transportation, provide plenty of active sites for lithium storage, and buffer the volume change of Mo2N nanoparticles during charge/discharge process. As a result, the Mo2N@NC electrode achieves a large reversible capacity of 826 mAh g−1, good rate capability (378 mAh g−1 at 2 A g−1), and excellent cycling stability (up to 3000 cycles).

Introduction

Lithium-ion batteries (LIBs) are currently the most important power supply for convenient electronic products and electric vehicles (EVs) [1]. In recent years, transition metal nitrides (TMNs) with high theoretical capacity and high electrical conductivity are considered as attractive anode materials for LIBs to replace commercialized graphite anodes with low theoretical capacity (372 mAh g−1) [2], [3]. However, the intrinsic sluggish conversion reaction kinetics and large volume change during cycling of TMNs still hinder their practical applications. Designing nanostructured TMNs has been proved to be an effective way to improve the rate performance of TMNs electrodes by shortening ions diffusion route [4], [5]. Moreover, mixing or/and coating the TMNs with carbon materials is also possible to improve the electrochemical performance by buffering the volume change of TMNs and providing more lithium storage sites with hetero-elements doping [6], [7]. Nevertheless, most of nanostructured TMNs/carbon materials were synthesized through complex procedures, involving the first preparation of metal or metal oxide/carbon precursors, and subsequent nitridation process [5], [6], [7]. It is still a great challenge to develop a facile method to prepare high-performance TMNs/carbon composite.

Herein, we have developed a facile one-pot method to fabricate Mo2N quantum dots embedded N-doped carbon nanosheets (Mo2N@NC) composite by simply calcinating a gel in Ar atmosphere. As expected, the Mo2N@NC electrode exhibited a large specific capacity, excellent rate performance, and long cycle life, demonstrating great advantages of this unique embedded heterostructure design.

Section snippets

Experimental section

Urea (10 g), citric acid (0.7 g), and H24Mo7N6O24·4H2O (0.7 g) were dissolved in a solution composed of 90 mL ethanol and 30 mL distilled water under moderate agitation at 75 °C to get a sol. The sol was then dried at 100 °C overnight to form a gel. The obtained gel was preheated at 350 °C for 4 h and then heated at 700 °C for 6 h in Ar atmosphere to obtain the final Mo2N@NC. For comparison, NC was synthesized by using the same method without adding H24Mo7N6O24·4H2O in the precursor.

The samples

Results and discussion

The fabrication procedure of Mo2N@NC composite is schematically illustrated in Fig. 1a. Urea, citric acid, and H24Mo7N6O24·4H2O were homogeneously mixed in a beaker to get a gel precursor. The gel precursor was preheated at 350 °C and then heated at 700 °C in Ar atmosphere to obtain the Mo2N@NC product. Under the 350 °C treatment, urea may self-polymerize and condensate into g-C3N4 nanosheets [8], [9]. Meanwhile, the aromatic carbon intermediates originated from the decomposition of citric acid

Conclusions

In summary, Mo2N@NC composite with embedded heterostructure has been successfully prepared by a facile one pot method. With rational design, the Mo2N@NC electrode exhibits a high reversible capacity, good rate capability, and long cycle life. This work provides adaptable strategy for preparing high performance TMNs anode materials for LIBs.

CRediT authorship contribution statement

Hong Yi: Conceptualization, Methodology, Investigation, Data curation, Visualization. Yu Huang: Methodology, Validation. Zhoucheng Sha: Formal analysis. Xiaohui Zhu: Investigation, Resources. Qiuying Xia: Methodology, Formal analysis, Writing - review & editing. Hui Xia: Writing - review & editing, Supervision, Project administration, Funding acquisition.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by National Natural Science Foundation of China (No. 51772154, 51972174).

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