Defect modulation of ZnMn2O4 nanotube arrays as high-rate and durable cathode for flexible quasi-solid-state zinc ion battery
Graphical abstract
Introduction
With the booming of wearable, portable and implantable electronics, it is very urgent to exploit novel energy storage devices (ESDs) that have eminent energy and power densities, good cycling durability, high safety, and super flexibility.[1], [2], [3] Lithium-ion batteries (LIBs) have achieved great success in recent decades because of remarkable energy density and outstanding rechargeability. However, the high cost and shortage of lithium resources, toxic and flammable electrolytes, and unsatisfactory power density severely restrict its further development.[4], [5] As an alternative energy storage device, rechargeable Zn ion batteries (ZIBs) have recently attracted great interest of scientists due to the inherent advantages, such as good safety, abundant resources, cost-effective, environmental friendliness, large theoretical capacity, and low redox potential of Zn/Zn2+.[6], [7], [8] Up to the present, Prussian blue analogs[9] and MnO2 polymorphs[10] ZIBs have been exploited and made a good result. Unfortunately, compared with the large theoretical specific capacity (820 mAh g−1) of the zinc negative electrode, the reported capacity of positive electrode materials is still low, and the cycling stability also needs to be further improved.[11], [12], [13] To address this limitation, scientists have been committed to developing large-capacity cathode materials in past years.[14], [15], [16], [17], [18] So far, a wide range of materials have been designed as cathode materials for ZIBs and exhibit excellent electrochemical performance, such as molybdenum trioxide,[19], [20], [21] vanadium pentoxide,[22], [23], [24] metal vanadate,[25], [26], [27] vanadium disulfide,[28], [29] VNxOy,[30], [31] transition metal dichalcogenides,[32], [33], [34] and organic redox-active compounds[35], [36], [37], [38], [39]. In particular, Niu and his collaborators have successfully assembled a CaVO//Zn battery with CaVO cathode, which deliver a high capacity (300 mA h g−1 at 0.1 A g−1), superior rate capability (62 mA h g−1 at 30 A g−1) as well as admirable durability with almost no attenuation after 10 000 cycles.[40] Peng and coworkers employed oxygen-deficient vanadium oxide, which was prepared on the flexible carbon cloth as a robust cathode, and the assembled Od-VO//Zn device showed a high energy density of 298 Wh kg−1 with an ultralong lifespan.[41] Despite these considerable achievements, the great majority of cathode materials have so far been plagued by low capacity, poor rate performance, and short lifespan.[42] Yet, it is a challenging and urgent mission to develop novel cathode materials that have a large capacity, high-rate, and long cycling stability.
Spinel-structured oxides materials have shown great promise as desirable cathodes for ZIBs owing to their abundant oxidation states, enhanced redox couples, and reversible Zn2+ intercalation.[43], [44], [45], [46], [47], [48] To date, a variety of nanostructured spinel oxides materials, including Mn3O4,[43] LiMn2O4,[44], [47] ZnMn2O4 (ZMO),[45], [49] ZnCo2O4,[46] MgMn2O4,[48] have been explored and showed an impressive performance. Notably, ZMO with bivalent Zn at tetrahedral sites and trivalent Mn occupying octahedral sites has been extensively studied as a positive material for ZIBs given the large theoretical capacity, abundance, high redox potential, cost-effectiveness, and eco- friendliness. More importantly, ZMO exhibits enhanced redox couples and accessible active sites due to the unique diatomic synergistic effect.[50], [51] Recently, Chen Jun's group prepared a cation-deficient ZMO cathode nanomaterial and successfully assembled an aqueous ZMO/C//Zn device with 3 M Zn(CF3SO3)2 electrolyte, and this device could reach a decent specific capacity of 150 mA h g−1 at 50 mA g−1.[45] Based on a hollow porous ZMO cathode, the ZMO//Zn battery exhibited an appreciable specific capacity of 106.5 mA h g−1 when the current density was 100 mA g−1.[52] Despite these achievements, due to the intrinsically weak conductivity, insufficient active sites, and large volume change of ZMO, the rate performance and long-term durability of these current ZMO//Zn batteries are still not satisfactory. Exploring new ZMO based cathode materials with high intrinsic conductivity and structural stability is urgently desirable.
In this work, an effective and facile surface engineering strategy is demonstrated to ameliorate the intrinsic electronic structure of ZMO nanotube arrays (NTAs) (N-ZMO NTAs) using oxygen anion extraction and N modulation, which are supported on flexible carbon fiber cloth (CFC) as robust cathode for ZIBs. The NTAs support on interconnected CFC can endow with higher specific surface area, better permeability, faster electron, and ion transfer rate.[53], [54] Moreover, the stable hollow structure could efficaciously buffer the mechanical stress in the electrochemical process, thereby greatly enhance the cycle stability.[55] What is more, the introduced Ndoping and oxygen vacancies could promote electron density, provide active sites, lower bandgap, and enhance Zn2+ diffusion kinetics, thus improving intrinsic electronic conductivity and surface capacitive contribution.[4], [56] As a consequence, the as-fabricated ZIBs based on the N-ZMO NTAs cathode delivers an admirable specific capacity (223 mA h g−1 at 0.1 A g−1), impressive rate capability (133.3 mA h g−1 at 4 A g−1) as well as desirable long-term durability (92.1% after 1500 cycles). Encouragingly, this flexible quasi-solid-state ZIBs also presented a satisfactory energy density (214.6 W h kg−1), large power density (4 kW kg−1) as well as ultralong cycle life with 88.6% capacity retention after 1500 cycle, outperforming most of the current ZIBs devices.
Section snippets
Experimental section
Synthesize of N-ZMO NTAs cathode: All chemical reagents were purchased from Aladdin with analytically pure (AR), which could be used directly without any purification treatment. Electrodeposition was conducted by galvanostatic electrolysis method in a typical two-electrode cell system, consisting of a graphite counter electrode and a commercial carbon cloth working electrode. The specific synthesis steps were as follows:
- (1)
ZnO nanorod arrays (NRAs) were prepared on the CFC by a simple
Results and discussion
Fig. 1a presents the fabrication procedures of N-ZMO NTAs. Firstly, the ZnO NRAs were uniformly grown over the surface of CFC (Figure S1a) by electrochemical deposition, and the vertically aligned ZnO NRAs have a 3 mm length and 300 nm diameter (Figure S1b). After that, the ZMO nanoparticles were deposited onto the surface of ZnO NRAs and form a core–shell structure, in which the ZnO NRAs were coated with ZMO nanoparticles (Figure S1c). Notably, the ZMO nanoparticles are perfectly coated onto
Conclusion
In summary, a novel high-performance N-ZMO NTAs cathode was fabricated for flexible quasi-solid-state ZIBs through an efficient defect engineering strategy. Benefiting from the Ndoping coupled oxygen vacancies modulation, the N-ZMO NTAs cathode may be provided with good conductivity, efficient ion transport, rich active sites, and enhanced surface capacitive contribution. Furthermore, the 1D hollow NTAs nanoarchitecture can not only endow with a fast channel for zinc ion diffusion, but also
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
We acknowledge the Hainan Provincial Science and Technology Project (ZDYF2019160), Basic and Applied Basic Research Project of Guangdong Province (2019A1515110827), Science and Technology Planning Project of Guangzhou (201804010196, 2021), Education Commission of Guangdong Province (2019GKTSCX015), Advanced Functional Materials Scientific Research and Technical Service Team (X20190197) and Natural Science Project of Guangdong Industry Polytechnic (KJ2020-006).
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