Research PaperAreca-inspired core-shell structured MnO@C composite towards enhanced lithium-ion storage
Graphical abstract
Inspired by the structure of areca, unique areca-like core-shell structured MnO@C composites containing of the MnO core and N-doped porous carbon shell are prepared via a biomass-assisted strategy. As a result, the as-prepared MnO@C-800 composite presents remarkable electrochemical performance as LIBs anodes.
Introduction
Recently, lithium-ion batteries (LIBs) have received unprecedented attention in the energy field, due to their high energy density and stably cycling lifetime [[1], [2], [3]]. However, the graphite anode with a low theoretical capacity of only ∼372 mA h g−1 based on traditional intercalation mechanism cannot match the requirements of high energy density storage devices [[4], [5], [6]]. On the contrary, conversion-type anode materials are gradually occupying a leading position derived from their special conversion mechanism, which produces a higher specific capacity [7,8]. Among them, MnO, which has the advantages of both low cost and high theoretical capacity (∼756 mA h g−1), is one of the most eye-catching conversion-type anode materials for LIBs [9,10]. Nevertheless, the low conductivity and huge volume expansion during the discharge/charge process of MnO materials lead to the unsatisfied cycle performance and rate capacity.
To alleviate those intrinsic demerits, two strategies including building nanostructures and compositing with carbonaceous material have been implemented to enhance the Li storage [[11], [12], [13]]. Nanostructured MnO materials can significantly shorten the Li+ transmission path to achieve fast reaction kinetics, while the introduced carbonaceous matrix improves the conductivity of whole composite and relieves the volume changes. Even though the strengthened rate and cycle performance has been realization by one or a combination of the above methods, the poor structural stability during lithiation/de-lithiation process still restricts the cycle lifespan of the electrode material. To figure these issues out, for instance, Li's group [14] developed the core-shell structured MnO@C nanopeapods with excellent performance in LIBs. Hu et al. [15] reported the core–shell MnO@C nanospheres, which exhibited a superior rate capacity of 463 mA h g−1 at high current density of 5.0 A g−1. In addition, heteroatom (N/O/S) doping is also an effective strategy by virtue of its ability to improve the conductivity of materials and provide abundant Li+ active sites. Lin and his co-workers [16] designed the porous N-doped MnO/C microspheres, and showed enhanced cycling performance of 786 mA h g−1 at 0.5 A g−1 over 200 cycles. Thus, it is an effective and feasible strategy that developing MnO@C composites with proper built-in space and robust porous carbon framework structure to adjust the volume variation, and promote the electrochemical reaction kinetics.
Herein, inspired by the structure of areca, unique areca-like core-shell MnO@C composites consisting of the MnO core and N-doped porous carbon shell are prepared via an agaric-assisted strategy, as shown in Fig. 1. Firstly, agaric has an easily degradable and strong water absorption function, showing a huge potential for diversified applications [17,18]. Secondly, the abundant heteroatoms (N/O) contained in the organic matter of agaric can enhance the Li+ active sites [19]. In addition, such core-shell structure can alleviate the rigid stress caused by volume expansion during the cycling process, while the N-doped porous carbon shell ensures fast electrochemical reaction kinetics, resulting in excellent rate capacity and remarkable cycling stability. As a result, the MnO@C composite shows the superior specific capacities of 915.9 and 218.1 mA h g−1 at 0.1 and 5.0 A g−1, respectively, and maintains an outstanding cycling performance over 900 cycles at 1.0 A g−1, revealing a huge application prospect as LIBs anode materials.
Section snippets
Materials synthesis
Firstly, the agaric-based solution as carbon source was prepared by the modified hydrothermal and ultrasonic-assisted method. In brief, the dried agaric (8.0 g) was added in deionized water (DI, 100 mL) within an autoclave (120 mL) and maintained at 120 °C for 18 h. After cooling down, the brown agaric-based solution was obtained by further sonicated for 20 min (Fig. S1a). Next, KMnO4 (0.79 g) was dissolved in the agaric-based solution (100 mL) with mechanical stirring for 10 min to form
Results and discussion
The morphologies of MnCO3@C and MnO@C-800 composites were first characterized by SEM and TEM (Fig. 2). As shown in Figs. 2a, b and S2a, the MnCO3@C composite exhibits a regular areca-like core-shell structure with smooth surfaces. After annealing process, the areca-like shape is inherited by MnO@C-800 composite with a uniform size of about ∼2 μm (Figs. 2c and S2b). It is also observed that the surface of the MnO@C-800 becomes rougher after calcination, indicating that abundant pore structures
Conclusions
In summary, inspired by the structure of areca, we have successful prepared areca-like MnO@C composite with core-shell structure. The effect of temperature on the formation of core-shell structured MnO@C samples are systematically studied. Benefiting from the multiple merits including areca-like core-shell structure and fast electrochemical reaction kinetics, the preferred MnO@C-800 composite presents high lithium storage performance (915.9 mA h g−1 at 0.1 A g−1), superior rate capacity
CRediT authorship contribution statement
Lingfeng Zhu: Experiments, Data curation, Writing – original draft. Yun Wang: Experiments, Data curation. Minji Wang: Experiments, Data curation. Yaping Xiong: Experiments, Data curation. Ze Zhang: Writing – original draft, Writing – review & editing. Ji Yu: Writing – review & editing. Yaohui Qu: Writing – review & editing. Jianxin Cai: Supervision, Funding acquisition. Zhenyu Yang: Writing – review & editing, Supervision, 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.
Acknowledgments
This work was supported by National Natural Science Foundation of China (Grant No. 21863006 and 51704134), Science Foundation of Jiangxi Province (Grant No. 20192ACB21010 and 20202ACB202004) and Guangdong Innovation Research Team for High Education (2017KCKTD030), High-level Talents Project of Dongguan University of Technology (KCYKYQD2017017).
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