Abstract
AbstractTransition metal oxides have a great potential in sodium‐ion capacitors (SICs) due to their pronouncedly higher capacity and low cost. However, their poor conductivity and fragile structure hinder their development. Herein, core‐shell‐like nickel‐cobalt oxysulfide (NCOS) nanowires are synthesized and demonstrated as an advanced SICs anode. The bimetallic oxysulfide with multiple cation valence can promote the sodium ion adsorption and redox reaction, massive defects enable accommodation of the volume change in the sodiation/desodiation process, meanwhile the core‐shell‐like structure provides abundant channels for fast transfer of sodium ions, thereby synergistically making the NCOS electrode exhibit a high reversible sodium ion storage capacity (1468.5 mAh g−1 at 0.1 A g−1) and an excellent cyclability (90.5% capacity retention after 1000 cycles). The in‐situ X‐ray diffraction analysis unravels the insertion and conversion mechanism for sodium storage in NCOS, and the enhanced capability of NCOS is further verified by the kinetic analysis and theoretical calculations. Finally, SICs consisting of the NCOS anode and a boron‐nitrogen co‐doped carbon nanotubes cathode deliver an energy density of 205.7 Wh kg−1, a power density of 22.5 kW kg−1, and an outstanding cycling lifespan. These results indicate an efficient strategy in designing a high‐performance anode for sodium storage based on bimetallic dianion compounds.
Highlights
Wang, Shouzhi; Zhao, Huaping; Lv, Songyang; Jiang, Hehe; Shao, Yongliang; Wu, Yongzhong; Hao, Xiaopeng; Lei, Yong: Insight into nickel-cobalt oxysulfide nanowires as advanced anode for sodiumion capacitors
sodium-ion batteries (SIBs), state-of-the-art sodium-ion capacitors (SICs) have emerged, which the motivation is to combine the advantages of both SIBs and supercapacitors to insertion and conversion mechanism for sodium storage in nickel-cobalt oxysulfide (NCOS), and the enhanced capability of NCOS is further verified by the kinetic analysis and theoretical calculations
According to the high-resolution transmission electron microscopy (TEM) (HRTEM) image (Figure 1f), the nanoparticles dispersed in the inner region of NCOS nanowire are highly crystalline with the size of about 10 nm, while the outer shell is an obvious layer with a thickness of ≈30 nm
Summary
The initial Columbic efficiency is 73.2%, and this capacity loss can be ascribed to irreversible processes in the first charge–discharge cycle, such as side reactions and SEI film formation.[34] For comparison, CV curves and charge/discharge profiles of NCO and NCS electrodes indicate the low capacity and rate capability of NCO and NCS electrodes (Figure S7, Supporting Information). Electrochemical performance of NCOS//BCN SICs. a) Schematic of the assembled SIC device (inset shows diagram of the operation potential range for configuration); b) CV curves at various current densities; c) GCD curves at increasing current densities; d) capacitances as a function of scan rate and current density; e) cycling performance, insert shows GCD curves before and after cycle; f) Ragone plots in comparison with other SICs reported in literature; and g) shows the image of commercial LEDs powered by the fabricated SICs. 205.7 Wh kg−1 at a power density of 125 W kg−1 based on the total mass of both electrodes. These merits of the NCOS//BCN SIC device with high-voltage output, excellent energy and power density, as well as cycling life, show great potential for future electrochemical energy storage applications
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