Simple Physical Mixing of Graphitic Wood-Derived Carbon For High-Performance Ni(OH)2 Electrodes: A Sustainable Strategy Beyond Metal Additives

Abstract

The replacement of expensive metal powders in Ni-(OH)₂-based cathodes is essential for reducing cost and environmental impact in aqueous Ni-Zn batteries. This work investigates graphitic wood-derived carbon (GWC) as a sustainable conductive additive to boost the performance of Ni-(OH)₂ pasted electrodes prepared by a simple physical mixing process. A number of graphitic wood-derived carbon qualities are explored as functional additives replacing expensive cobalt and nickel powder additives while maintaining the electrochemical performance of Ni-(OH)₂ electrodes in aqueous rechargeable Ni-Zn batteries. The GWC offers high electrical conductivity and a unique microsized particulate morphology. Optimizing the GWC content to 25 wt % yields a specific capacity of 284.2 mAh g^-1 at 0.2C, which is better than that of electrodes containing only Ni-(OH)₂, with Ni/Co powders, or commercial carbon black. Furthermore, the open-circuit voltage hysteresis and state of charge are studied to understand the charge/discharge process, suggesting that GWC is an effective alternative to expensive metal powders, providing a low-cost and sustainable strategy for improving Ni-(OH)₂-based electrodes through a straightforward manufacturing process.

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Characterizations of GWC: (a and b) SEM images of top-view, (c and d) SEM images of cross-view, (e and f) TEM images, (g) XRD pattern, (h) Raman spectrum, and (i) N₂ sorption isotherm, the inset is the pore size distribution curve.

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(a-c) SEM images of Ni­(OH)₂ powders, and (d) XRD patterns of the materials and pasted electrodes.

3

Compared electrochemical performance of electrodes with/without GWC additives: (a) the cycling curves, (b) the compared charge/discharge curves of the 10th cycle, (c) compared Nyquist plots, and the inset is a partial enlargement, and (d) the cycling stability at different current densities.

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(a) charge/discharge curves of different electrodes with different carbon contents at 0.2C, (b) discharge specific capacities of electrodes with/without different contents of GWC at 0.2C for 10 cycles, (c) Nyquist plots of different cells with different carbon, and (d) XRD patterns of the Ni­(OH)₂ electrode without carbon addition before and after electrochemical testing.

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(a–c) The open-circuit voltage hysteresis and 100% state of charge of different cells with different Ni-electrodes containing different GWC contents at 0.2C and different rest time, and (d) the compared open-circuit voltage hysteresis of different cells at 0.2C at a rest time of 4 min.

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Open-circuit voltage hysteresis and state of charge of different cells with different carbon additives at 0.2C with a rest time of 4 min, and the corresponding SEM images of the carbons: GWC (a), S,N-codoped wood carbon (b), commercial carbon black (c), graphitic carbon black 2 (d), graphene-1 (e), and graphene-2 (f), respectively.

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Electrochemical performance of different electrodes in a three-electrode system: (a) CV curves at 0.2 mV s^–1, and (b) the relationship between the peak current and the square root of scan rate.