Materials Today Chemistry
Layered silicate magadiite–derived three-dimensional honeycomb-like cobalt–nickel silicates as excellent cathode for hybrid supercapacitors
Graphical abstract
Introduction
Magadiite, a ubiquitous naturally occurring silicate, has been extensively studied because of its low cost, non-toxic, eco-friendly, mechanical strength, thermal stability, and easy to prepare. The appropriate layered structure and cation exchange properties features make magadiite a superior raw material and widely used as adsorbent or as the carrier of various active substances [[1], [2], [3], [4], [5], [6]], such as removing heavy metal species [7] or organic pollutants [8], adsorption and catalysis of toxic gases [9] or as a support for antibacterial agents [10]. However, most of these studies are stuck in the theoretical research or laboratory stage, and only a few studies are of practical use. So that, a large number of magadiite now is half-abandoned and half-forgotten, and it is extremely valuable for the development of useful materials [11]. Therefore, magadiite is still ‘a potential stock’ to be developed, and if it can be applied to the preparation of electrode materials, waste can be turned into treasure.
In the past decades, transition metal silicates (TMSs) have drawn great attention among multitudinous novel electrode materials because of their abundance, environmentally friendly, and high theoretical capacity (such as Co2SiO4 for about 1,500 mAh/g) [[12], [13], [14], [15]]. Numerous attempts have been made to apply TMSs as the anodes for lithium ion batteries (LIBs), and the result shows that the high initial capacity makes them a kind of great potential electrode materials [[16], [17], [18], [19]]. Just recently, many researchers try to use TMSs as electrode material for supercapacitors (SCs) [[20], [21], [22], [23], [24], [25], [26], [27], [28]]. For example, Cheng et al. synthesized Co2SiO4 nanobelts and some composites based on Co2SiO4, and all those materials exhibited excellent electrochemical properties as the SCs’ electrode materials [[29], [30], [31]]. Although some achievements have been made for the synthesis of TMSs, some problems have been exposed at the same time. Existing synthesis methods frequently use the SiO2 sphere (or TEOS), which is prepared by the Stöber method, as a silica source [32]. The complex preparation technology and high cost make it difficult to achieve industrial production [21,[33], [34], [35]]. It is worth noting that the laminates of magadiite are composed of silicon-oxygen tetrahedrons and the interlayer sodium ions only to neutral the electronegative layer board [36]. Therefore, in terms of the nature, magadiite is well qualified as a silicon source [37]. If magadiite can be used as a silicon source to synthesize TMSs, it does not only simplify the preparation process and reduce the production cost but also promote the large-scale production of TMSs as electrode materials. Furthermore, the poor ionic diffusion and low electronic conductivity cause poor electrochemical performance, including low capacity, poor cycling stability, and low rate stability, which seriously hinders their development in the field of electrochemistry [[38], [39], [40], [41]]. Therefore, it is crucial for TMSs to reduce their resistance and accelerate ion diffusion. The most used strategy is complex the TMSs with C-based materials [[42], [43], [44], [45], [46]], such as graphene or CNTs [47,48]. However, this method can complicate the preparation process and use more expensive materials, increasing the cost. Recently, in similar fields such as metal oxides or hydroxides, it has been reported that the synergistic effect of polymetals can improve the reactivity of materials [[49], [50], [51], [52], [53]], and we wonder whether the synergistic effect can also improve the intrinsic resistance of TMSs, such as other works [44,54].
Established on the previously mentioned assumption, herein, we designed and prepared the CoxNi2-xSiO4 with three-dimensional (3D) honeycomb-like morphology using magadiite as a silicon source, such as our recent work on the synthesis of manganese silicate nanosheets [55]. The cobalt–nickel silicates derived from magadiite are pure and well defined. The bimetallic synergistic effect can improve the reactivity and further enhance the electrochemical performance. Meanwhile, the 3D honeycomb-like architecture effectively promotes the ion diffusion and alleviates structural changes during the charge/discharge process. Consequently, at 0.5 A/g, the CoxNi2-xSiO4 exhibits an excellent electrochemical performance for a specific capacitance of 1,097 F/g (548 C/g) and cycle stability with 101% after 10,000 cycles. Moreover, the CoxNi2-xSiO4//AC HSC device delivers an energy density of 15.5 Wh/m2 at 1.34 W/m2 and 77.5 Wh/m2 at 0.57 W/m2 with 100% retention after 10,000 cycles. Our finding not only proves that the CoxNi2-xSiO4 can be successfully synthesized using the magadiite as a silicon source with enhanced electrochemical capabilities but also opens up a new way to prepare TMSs.
Section snippets
Pretreatment of mag
All chemicals were of analytical grade and used without any purification. The original magadiite (mag) was prepared by the hydrothermal method based on the works with some improvement [8,37], as represented in Supplementary Information. CTAB was adopted to pretreat the magadiite using a typical ion-exchange reaction. An amount of 1 g initial magadiite was added to 100 mL deionized water. The cation exchange capacity of magadiite is 2 meg/g [56]. Ten millimoles of cetyltriethylammnonium bromide
Characterization of CoxNi2-xSiO4
Fig. 1a schematically illustrates the formation process of the honeycomb-like CoxNi2-xSiO4, which mainly contains two steps: (1) pretreatment of mag and (2) hydrothermal synthesis of CoxNi2-xSiO4. The mag was synthesized based on our previous work [56], confirmed by the XRD pattern (Fig. S1b). The morphology of mag is rose-like shapes comprising nanosheets (Fig. S1a and Fig. 1b). After the exfoliation by CTAB, the XRD pattern in Fig. S1b confirms that the phase of CTA-mag is basically
Conclusion
In summary, 3D honeycomb-like architecture cobalt–nickel silicate is successfully designed and synthesized using magadiite as silicon source. The as-prepared CoxNi2-xSiO4 exhibits an outstanding electrochemical performance with 1,097 F/g (548 C/g) at 0.5 A/g and 101% retention after 10,000 cycles. The as-assembled CoxNi2-xSiO4//AC HSC device achieves the energy density of 77.5 Wh/m2 at 0.57 W/m2 with 100% capacitance retention after 10,000 cycles. Furthermore, the electrochemical performances
Authors’ contributions
X.J. contributed to methodology, validation, visualization, investigation, and writing the article. Y.Z. contributed to conceptualization; methodology; writing, reviewing, and editing the article; and supervision. X.D. and Y.M. contributed to visualization and investigation. X.L. contributed to supervision. C.M. contributed to supervision and 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 partially supported by National Natural Science Foundation of China (Grantgrant No. 21771030), the Fundamental Research Funds for the Cornell University (DUT21LK34) and Natural Science Foundation of Liaoning Province (2020-MS-113).
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