Honeycomb ZnO/N/C obtained from cornsilk and ZIF-8 dual induced method for long-life aqueous zinc-ion batteries
Introduction
As the issues of energy shortages and environmental pollution, the demand for low-priced, high safety and eco-friendly superior energy storage devices become increasingly urgent [[1], [2], [3]]. Lithium ion batteries (LIBs) features with high-up operation voltage and high energy density are regarded as most promising choice. However, a number of shortcomings such as high cost, electrolyte toxicity, and large safety risk and limited lithium resources seriously hinder their practical application for large-scale energy storage [4,5]. Recently, many rechargeable aqueous ion batteries (e.g. K+, Zn2+ and Al3+) are proposed owing to their perfect safety, lower cost and eco-friendliness [[6], [7], [8]]. Among the various options, aqueous zinc ion batteries (ZIBs) display enormous potentials owing to the following unique merits: Firstly, the earth’s abundance of Zn reduces the cost of next generation battery anode. Secondly, the neutral mild aqueous electrolyte achieves safe and environmental friendly energy devices. Thirdly, the appropriate Zn2+/Zn redox potential (−0.76 V vs. SHE) avoids the water decomposition. Finally, it possesses high theoretical capacity of 820 mAh g−1 [[9], [10], [11]]. Aqueous ZIBs are first reported in 2012 by Kang et al., which composes of tunnel-type MnO2 cathode, zinc metal anode and 1 M ZnSO4 aqueous electrolyte [12]. After this pioneering demonstration, Mn-based materials [13,14], Prussian blue analogs [15,16] and V-based materials [17,18] have been deeply explored as potential Zn2+ ion host materials. Up to now, the further development of aqueous ZIBs cathodes is mainly hampered by the large steric hindrance effects of divalent hydrated Zn2+ ions. Ample ion storage space, unimpeded ion transfer tunnel, fast and reversible Zn2+ intercalation and deintercalation and stable host structure are the necessary conditions to achieve large capacity and superior rate and cycling performance.
Carbons derived from biomass possess superior properties: (a) natural abundance, low price of original materials, facile accessibility; (b) excellent chemical and thermal stability; (c) large specific surface area; (d) excellent electrical conductivity; (e) tunable porosity allows fast ions transfer as well as favorable Zn2+ ion adsorption [[19], [20], [21], [22]]. But they suffer from the low specific capacities.
Metal-organic framework (MOF) is a wonderful structural material that was first proposed in 1995 by Yaghi [23], the interactions of H-bonding, p–p stacking as well as Van der Waals forces make the MOF forming a three-dimensional tunnel structure [24]. Much of transitional metal oxide porous structure has been obtained by the thermal treated of MOFs [25,26]. As the ZIF-8 is zinc basis MOF containing nitrogen element. Using ZIF-8 to obtain ZnO/N/C composite will be an efficacious method [[27], [28], [29]]. But simple derivatives of MOFs are usually unstable and fragile, which brings difficulties to their further applications in energy storage.
This paper proposes a dual induction method of MOF and biomass using ZIF-8 and corn silk as precursors to synthesize honeycomb ZnO/N/C. Benefit from excellent mechanical stability of the biochar, the honeycomb ZnO/N/C exhibits super cycle performance. Due to the porous nature of ZIF-8, the ZnO/N/C performs impressive specific capacity and rate performance. The obtained honeycomb ZnO/N/C delivers the specific capacity of 172.2 mAh g−1 at 0.3 A g−1 (with energy density 112.8 Wh kg−1), outstanding longtime stability (97.0% of capacity retain over 8000 cycles at 1.0 A g−1) and superior rate performance. The remarkable electrochemical properties render the honeycomb ZnO/N/C is an extremely promising cathode for the ZIBs devices.
Section snippets
Preparation of the cornsilk derived porous biochar (BC)
The cornsilks were cut into small pieces, washed thoroughly with distilled water to get rid of the impurity, and then were dried in an oven under 60 °C for 12 h. Then, the cornsilk was mixed with KOH in the weight ratio of 5:4 under magnetic stirred for 3 h, after that the mixtures were put into vacuum oven at 80 °C for 3 h. Next, the products were carbonized at 700 °C for 1 h with the heating rate of 5 °C min−1 at the argon gas atmosphere. After it naturally cooled down to environmental
Results and discussion
The way used to fabricate honeycomb ZnO/N/C is displayed in Fig. 1. Starting from one step activation and carbonation of cornsilk, the porous biochar (BC) is first obtained. On this basis, ZnO are introduced into BC by hydrothermal method, and then the coordination reaction of Zn2+ and 2-methylimidazole takes place on the lattice node of ZnO to form ZIF-8 MOF on the surface of porous BC. Finally, the ZIF-8/BC is directly pyrolyzed at 500 °C under N2 flow to obtain honeycomb ZnO/N/C.
The detailed
Conclusion
In summary, a unique honeycomb ZnO/N/C is obtained from ZIF-8 and cornsilk dual derived method. It is obviously that the biochar heightens the structure stability and cycle performance, and the ZIF-8 derived ZnO/N/C improves the specific capacity and rate performance of the cathode. This unique honeycomb ZnO/N/C, reduces the internal resistance, enhances the structure stability, and enriches the ion diffusion channels, so as to improve the capacity, rate performance and cycle life of the
CRediT authorship contribution statement
Yuqiu Huo: Conceptualization, Methodology, Supervision, Writing - review & editing. Ying Teng: Data curation, Writing - original draft. Kuizhe Cai: Visualization, Software. Huiya Chen: Visualization, Software.
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 is financially supported by the National Natural Science Foundation of China (51574062).
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