Carbon Nanofiber Composites for

Jun 13, 2017 - LiOH was used to suppress oxygen evolution by increasing the oxygen overvoltage.(36-39) Galvanostatic charge and discharge tests were t...
3 downloads 17 Views 7MB Size
Download PDF
This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes.

Research Article pubs.acs.org/journal/ascecg

Facile Synthesis of Ni(OH)2/Carbon Nanofiber Composites for Improving NiZn Battery Cycling Life Yan Jian,# Dongming Wang,# Maozhan Huang, Hai-Lang Jia, Jianhua Sun, Xiaokai Song, and Mingyun Guan* Jiangsu Key Laboratory of Precious Metals Chemistry, School of Chemistry and Environmental Engineering, Jiangsu University of Technology, Changzhou, 213001, P. R. China S Supporting Information *

ABSTRACT: Carbon nanofibers (CNFs) were successfully functionalized by the hydrothermal treatment of wet CNFs containing concentrated HNO3. The method of synthesis was facile and eco-friendly. With the use of oxidized CNFs as substance, Ni(OH)2/oxidized CNFs hybrid materials were prepared by taking a two-step solution phase reaction. The XRD pattern and TEM image suggested a well crystalline Ni(OH)2 nanoplate with β-phase structure growth on the surface of CNFs. Electrochemistry test results displayed high specific capacitances and long cycle life of the composites. With the use of Ni(OH)2/ CNFs as cathode and Zn foil as anode, assembled NiZn pouch cells could achieve ∼1.75 V discharge voltage plateau, with a specific capacity ranging from 184 mAh·g−1 at a discharging current density of 5 mA·cm−2 to 91 mAh·g−1 at a discharging current density of 50 mA·cm−2. Its cycle stability was up to 1200 cycles with a capacity retention of >96% at attaining an energy density of 150 Wh·kg−1. Compared with a 6 mol·L−1 KOH solution electrolyte battery, the sodium polyacrylate gel electrolyte battery displayed better cycle performance. The function of the gel electrolyte was discussed. The facile method could be extended to the oxidization of the other carbon materials and synthesis of the others carbon composites. KEYWORDS: NiZn battery, Nickle hydroxide, Carbon nanofiber, Composite material, Gel electrolyte

■

INTRODUCTION Renewable energy, such as solar, wind, hydropower, geothermal, and wave energy, provides a solution to the shortage of energy originating from the rapid consumption of fossil fuels from the global community. However, these energy sources are intermittent in space and time, making it difficult for energy production to match the pattern of energy demand.1−4 Battery technologies played important roles in solving the storage of intermittent renewable energy.5,6 Among the kinds of batteries (lithium ion battery, Pb-acid battery, nickel-based battery, etc.), the NiZn battery has been attracting attention from the research and industry community since it was invented by Thomas Edison and is a promising secondary battery because of its high specific energy density, high specific power density, high open-circuit voltage, and low toxicity.7−12 But practical NiZn battery delivers up to ∼70 Wh·kg−1, which is only a ∼20% theoretical value of ∼372 Wh·kg−1 and lacks sufficient stability in alkaline solutions. In conventional NiZn batteries, the cathode usually consists of a mixture of β-Ni(OH)2, conductive additive, polymeric binder, and suitable current collectors. The physical mixture of active materials and conductive additive leads to inefficient charge transport from the active materials to the current collectors, which often causes the low performance of the battery.13−16 Recently researchers have discovered that the direct growth of Ni(OH)2 nanocrystal on nanocarbon materials afforded the © 2017 American Chemical Society

solutions owing to the facilitated electron transport from the strong chemical coupling between active materials and nanocarbon materials.17,18 Among nanocarbon materials, carbon nanotube and graphene have been commonly used as the support for inorganic/ nanocarbon hybrid materials.19,20 Dai and co-workers21−25 prepared Ni(OH)2/oxidized carbon nanotube (CNT) or graphene hybrid material by hydrolysis of nickel acetate in a N,N-dimethylformamide (DMF)-H2O mixed solvent. Zhang and co-workers26 synthesized nanoporous Ni(OH)2 thin film over three-dimensional ultrathin-graphite foam by hydrothermal reaction. In addition, there have been a variety of synthesis methods to synthesize Ni(OH)2 on top of CNT and graphene materials, such as the microwave irradiation approach, the precipitation method, and a solid-state reaction route, etc.27−30 However, CNT and graphene sheet usually are usually expensive and are not suitable for large-scale production of the electrode materials. In addition, with the use of an oxidized carbon nanotube as support, Ni(OH)2/CNT easily aggregates if dried in an oven, which could be detrimental to the performance of the resulting electrode, especially at a very large scale. In contrast, Received: April 6, 2017 Revised: May 27, 2017 Published: June 13, 2017 6827

DOI: 10.1021/acssuschemeng.7b01048 ACS Sustainable Chem. Eng. 2017, 5, 6827−6834

Research Article

ACS Sustainable Chemistry & Engineering

Figure 1. (a) XRD pattern including Ni(OH)2/CNFs, Ni(OH)2/CNFs precursor, and oxidized CNFs. (b) TEM image of Ni(OH)2/CNFs. (c) HRTEM image of Ni(OH)2/CNFs. (d) SAED pattern of Ni(OH)2/CNFs.

capacity ranging from 184 mAh·g−1 at a discharging current density of 5 mA·cm−2 to 91 mAh·g−1 at a discharging current density of 50 mA·cm−2 (based on the mass of active materials). The NiZn pouch cell displayed excellent cycle stability up to 1200 cycles with capacity retention of >96% at attaining an energy density of 150 Wh·kg−1. In addition, the possible reasons of polymer gel electrolyte improving the cycling stability of NiZn battery were discussed.

carbon nanofibers (CNFs) with relative big diameters (∼100 nm) and good conductivity could provide a solution to the aggregation problem, which would be a promising candidate replacing the carbon nanotube. Because of the lack of active sites, direct functionalization of carbon nanomaterials was needed before preparing inorganic/ nanocarbon hybrid nanomaterials. The most frequently used method is treatment of nanocarbon materials in strong oxidizing acid (like HNO3, HNO3−HCl, or HNO3−H2SO4) by the heat reflux method or the modified Hummer’s method to impart oxygen functional groups on the surface of carbon nanomaterials.24,31,32 These oxygen functional groups could serve as nucleation and anchored sites for nanocrystal growth to prepare inorganic hybrid nanomaterials. However, scaling up the production of functionalized carbon materials using such methods could produce large quantity of waste acid and could be unsafe while handling large amounts of acids. To relieve this limitation and get a low-cost inorganic/nanocarbon hybrid, here we reported a simplified oxidation procedure by hydrothermal treatment of wet CNFs containing concentrated HNO3. The scale can be potentially further improved to the kilogram scale. After functionalization, Ni(OH)2 nanoplates were grown on oxidized CNF surfaces by a two-step solution phase reaction. The hybrid materials can be easily redispersed in the water after being dried in an oven at 60 °C. Using Ni(OH)2/CNFs as cathode and Zn foil as anode, we assembled the NiZn pouch cells that could achieve an ∼1.75 V discharge voltage plateau, specific

■

EXPERIMENTAL SECTION

Surface Treatment of Carbon Nanofibers. The surface of carbon nanofibers does not own functional groups, so we oxidized the carbon nanofibers by a strong oxidizing acid treatment. Oxidized CNFs were synthesized using concentrated nitric acid by a hydrothermal method. Ten grams of CNFs (Beijing Dk Nano technology Co., LTD) and 180 mL of concentrated HNO3 were added to a 250 mL glass beaker and stirred. The glass beaker was sealed and laid aside for 3 h. The mixture was transferred into a suction flask and filtrated under vacuum. The wet CNFs were transferred into a 100 mL Teflon-line autoclave. The autoclave was sealed and maintained at 180 °C for 1 h, then allowed to cool to room temperature. Oxidized CNFs were dispersed into distilled water and washed with amounts of water until a pH of 7. The final product was dried in an electric oven at 80 °C. The recycled concentrated HNO3 after filtration can be reused to treat the CNFs. Preparation of β-Ni(OH)2/CNFs Composite Materials. The composite materials were prepared by a facile two-step method.24 Typically, ∼150 mg of oxidized CNFs were sonicated in 200 mL of DMF solvent to form stable dispersions, and 30 mL of Ni(OAc)2 (0.2 mol·L−1) aqueous solution was added into these dispersions. The 6828

DOI: 10.1021/acssuschemeng.7b01048 ACS Sustainable Chem. Eng. 2017, 5, 6827−6834

Research Article

ACS Sustainable Chemistry & Engineering

Figure 2. (a) CV curves of β-Ni(OH)2/CNFs composites (1.2 mg) at different scan rates in 6 M KOH solution. (b) Average specific capacity of Ni(OH)2/CNFs composites at different scan rates calculated from CV data in panel a. (c) CV curves of β-Ni(OH)2/CNFs precursor (1.1 mg) at different scan rates in 6 M KOH solution. (d) Cycling stability of the β-Ni(OH)2/CNFs and β-Ni(OH)2/CNFs precursors at scan rate 100 mV·S1− and loading of 1.2 mg·cm−2. suspension was heated to 85 °C and reacted for 8 h with magnetic stirring. After that, the precursor Ni(OH)2/CNFs composites were collected and washed with distill water. The obtained products were dispersed in ∼150 mL of distill water and then transferred into 250 mL Teflon-lined stainless steel autoclave. The precursor was treated at 200 °C for 56 h by hydrothermal conditions. The final products were collected by filtration, washed several times with distill water, and were air oven-dried at 60 °C. Materials Characterization. X-ray diffraction (XRD) patterns were recorded using a powder diffractometer (Rigaku D/max-2500, Cu Kα radiation). Transmission electron microscopy (TEM), high resolved TEM (HRTEM) images and selected-area electron-diffraction (SAED) pattern were obtained on a JEM 2100 instrument at an acceleration voltage of 200 kV. The Raman spectrum was recorded at ambient temperature on an inVia-Reflex Raman spectrometer with an argon ion laser at an excitation wavelength of 488 nm. Cyclic voltammetry (CV) measurement and chronopotentiometry were performed on a CHI 660E electrochemistry workstation (Shanghai Chenhua Instrument Co., China). Electro-performance of the NiZn pouch cell was carried out on Neware electrochemistry measurement system. Preparation of Working Electrodes and Electrochemical Measurements. The preparation process of the working electrode was as follows: First, β-Ni(OH)2/CNFs composite and polytetrafluoroethylene binder (PTFE, 60 wt % water suspension) mixed in a weight ratio of 100:2. Next, the mixture was dispersed in ethanol with the help of untrasonication for 20 min to form a homogeneous ink. Finally, the dispersion was drop-dried into a 1 cm × 1 cm nickel foam (100 ppi, 95% porosity, 1.6 mm thick) at 80 °C. Before electrochemical measurement, the thickness of the working electrode was compressed to about 0.5 mm. Electrochemical performance of the Ni(OH)2/CNFs single electrode was measured in a beaker cell by a typical three-electrode configuration with 6 M KOH aqueous solution as electrolyte, a graphite rod as counter

electrode, and standard calomel electrode (SCE) as reference electrode. Electrochemical performance of the NiZn battery was measured in a pouch cell by a two-electrode system setup. The electrolyte was 6 M KOH + 1 M lithium hydroxide (LiOH) + poly(acrylic acid) sodium (PAAS) (0.33 g per 10 mL of electrolyte) saturated with ZnO gel. The Zn foil with 1 cm × 1 cm was used as anode. The full battery was assembled by integrating both anode and cathode together with a piece of commercial separator (thickness of 0.22 mm, Changzhou Hengsheng Battery Materials Co., LTD) between the two electrodes. The cycling performance testing of NiZn battery was to charge at charge time 3 min, charge current density 2.35A·g−1 up to 2.2 V cutoff, and then discharge at discharge current density 2.54 A·g−1 down to 0.8 V cutoff.

■

RESULTS AND DISCUSSION

Oxidation of nanocarbon materials is highly important for synthesizing high quality Ni(OH)2/nanocarbon materials. Ideal oxidation of nanocarbon materials can open up the outer walls of nanocarbon materials to create many oxygen functional groups or defects without breaking the interior to maintain good conductivity. The oxygen functional groups can serve as the nucleation and growth sites of Ni(OH)2 via a covalent carbon− oxygen-metal bonding. After the oxidation procedure, the oxidized CNFs can be well dispersed in various solvent without crashing out at the bottom for hours. To synthesize Ni(OH)2/ CNFs hybrid, oxidized CNFs were first dispersed in DMF solution, followed by hydrolysis of nickel acetate at 85 °C with selective nucleation and growth of Ni(OH)2 nanoparticles on the oxidized CNFs support. Hydrothermal steps at 200 °C for 56 h 6829

DOI: 10.1021/acssuschemeng.7b01048 ACS Sustainable Chem. Eng. 2017, 5, 6827−6834

Research Article

ACS Sustainable Chemistry & Engineering

Figure 3. Three-electrode electrochemical measurements of the β-Ni(OH)2/CNFs composite in 6 M KOH aqueous solution. (a) Galvanostatic discharge curves at different current densities under loading of 10 mg·cm−2. (b) Mass-specific capacity of composites calculated from the corresponding discharge curve for various mass loadings and current densities. (c) Calculated area-specific capacity with various mass loadings at 10 mA·cm−2 of the discharge current density. (d) Cycle performance of the Ni(OH)2/CNFs hybrid at 100 mA·cm−2 under loading of 10 mg·cm−2.

Ni(OH)2/CNFs possess a good degree of crystallinity. The TEM image in Figure 1b revealed that β-Ni(OH)2 with well-defined hexagonal nanoplates grew on the oxidized carbon nanofibers. The Ni(OH)2 nanoplates have side lengths of hundreds of nanometers and the thickness of only a few nanometers. The HRTEM image in Figure 1c showed clear lattice strips throughout the crystal, suggesting the single crystal nature of β-Ni(OH)2. The SAED pattern in Figure 1d further evidenced the single-crystal nature of the nanoplates and the preferential [001] growth direction. The electrochemical properties of β-Ni(OH)2/CNFs composite were evaluated using a three-electrode system in 6 M KOH aqueous solution. Nickel foam support deposited with approximate 1.2 mg of β-Ni(OH)2/CNFs hybrid was compressed for electrochemical tests in a beaker cell with a Hg/ Hg2Cl2 (in saturated KCl solution) reference electrode. Figure 2a showed CV curves of the β-Ni(OH)2/CNFs at different scan rates ranging from 5 mV·s−1 to 40 mV·s−1. A pair of oxidation and reduction peaks corresponded to the reversible reactions of Ni(II)/Ni(III) (Figure 2a).21 It is noticed that the background signal of the nickel foam was negligible (Figure S3). The specific capacitances of β-Ni(OH)2/CNFs composites were calculated to be 208.4 mAh·g−1 (1250.6 F·g−1) (based on mass of Ni(OH)2, 0.945 mg in 1.2 mg Ni(OH)2/CNFs) at a scan rate of 5 mV·s−1 (Figure 2b) and 191.9 mAh·g−1 (1151.9 F·g−1) at a high scan rate of 40 mV·s−1, ∼92% of that at 5 mV·s−1 (Figure 2b). The CV curves of the Ni(OH)2/CNFs hybrid precursors were further measured at various scan rates (Figure 2c). Its average specific capacitances were calculated to be 214.6 mAh g−1 (1679.7 F·g−1)

were then applied to crystallization of intermediate products and transformation into a stable β-phase Ni(OH)2 structure. Oxidized carbon nanofibers were characterized by transmission electron microscopy. TEM image of CNFs (Supporting Information Figure S1-a) showed the range of CNF diameters to be about 60−150 nm. The HRTEM image in Figure S1b shows the clear lattice strips which evidenced the good crystalline nature of the interior. Raman spectra of CNFs and oxidized CNFs (Figure S2) showed that there were two strong peaks at 1579 (G-band) and 1334 cm−1 (D-band). ID/IG values of CNFs and oxidized CNFs were 0.12 and 0.20, respectively, which suggested oxidized CNFs had more defects. It was beneficial for the formation of Ni(OH)2/CNFs hybrid materials.33 The strong (111) peaks in the XRD pattern of the CNFs (JCPDS No 750444, Figure 1a) indicated the high crystalline structure of the nanofiber, owning good conductivity. Ni(OH)2/CNFs precursor was first synthesized by Ni(OAc)2 hydrolysis and then the Ni(OH)2/CNFs were obtained by hydrothermal treatment of the Ni(OH)2/CNFs precursor. To compare the difference between them, we took XRD measurement of Ni(OH)2/CNFs precursor and Ni(OH)2/CNFs. Most peaks in the XRD pattern of Ni(OH)2/CNFs precursor (Figure 1a) were indexed to βNi(OH)2/CNFs (JCPDS No 73-1520). Except for the main peaks, one weak peak from nickel acetate hydrate (JCPDS No 25-0901) was also detected, suggesting that some Ac− ions intercalate in the interlayer.34,35 After hydrothermal treatment, the intensity of index peaks increased and all index peaks except the C peak in the XRD pattern of Ni(OH)2/CNFs were indexed to β-Ni(OH)2 (JCPDS No 73-1520), which suggested that 6830

DOI: 10.1021/acssuschemeng.7b01048 ACS Sustainable Chem. Eng. 2017, 5, 6827−6834

Research Article

ACS Sustainable Chemistry & Engineering

Figure 4. (a) Schematic representation of the NiZn battery made from Ni(OH)2/CNFs composite materials. (b) Galvanostatic discharge curves at various current densities in solution of 6 M KOH, 1 M LiOH, and PAAS saturated with ZnO. (c) Ragone plot of the NiZn battery measure in panel b. (d) Charge/discharge curves of the NiZn battery at a charge current density 2.35A·g−1 and discharge current density of 2.54 A·g−1. (e) Energy density vs cycle number curves of the NiZn battery (we set charge time 3 min at a charge current density 2.35A·g−1 and discharge current density 2.54 A·g−1). (f) HRTEM image of Ni(OH)2/CNFs composite in NiZn battery after more than 1200 cycles.

improving the stability of β-Ni(OH)2/CNFs hybrids by increasing the crystallinity of the active materials. The electrochemical properties of the β-Ni(OH)2/CNFs loaded into 1 cm2 nickel foam (loading of ∼10 mg·cm−2, unless otherwise stated) were explored by galvanostatic charge/ discharge measurements using a standard three-electrode system in 6 M KOH solution. Figure 3a showed galvanostatic discharge curves of the hybrid material at current densities of 10, 20, 50, 100 mA·cm−2. Flat discharge plateaus, evidencing battery electrode behavior, were displayed in the voltage range of 0.15−0.25 V. We calculated the specific capacity at different discharge current densities. Excellent rate capability with almost no capacity loss at higher current density was obtained. We also prepared the Ni(OH)2/CNFs electrode at different loadings of

(based on mass of Ni(OH)2, 0.866 mg in 1.1 mg Ni(OH)2/ CNFs precursors) at a scan rate of 5 mV·s−1 (Figure 2c) and 162.3 mAh·g−1 (1007.5 F·g−1) at a high scan rate of 40 mV·s−1, 76% of that at 5 mV·s−1. The above results suggested the capacity of the Ni(OH)2/CNFs hybrid precursor showed more decay under higher scan rates probably due to the insufficient electron transport under low crystallinity. Cycle stability of the βNi(OH)2/CNFs hybrid and its precursor were tested under a scan rate of 100 mV·s−1. Figure 2d showed that the β-Ni(OH)2/ CNFs composite electrode displayed good cycling stability with little capacity decay after 1000 cycles; however, the β-Ni(OH)2/ CNFs composite precursor electrode exhibited bad cycling stability with more capacity decay at 400 cycles. Therefore, the hydrothermal treatment of precursors is highly important for 6831

DOI: 10.1021/acssuschemeng.7b01048 ACS Sustainable Chem. Eng. 2017, 5, 6827−6834

Research Article

ACS Sustainable Chemistry & Engineering

Figure 5. Surface observations of a Zn anode: (a) SEM images of the Zn foil and (b) SEM images of the Zn anode obtained from NiZn cells after 1200 cycles, indicating no dendrite formation over these cycles.

1200 cycles at attaining an energy density of 150 Wh·kg−1 and 96% of the initial capacity remained after 1200 cycles (Figure 4e). The excellent stability was attributed to a highly stable βNi(OH)2 phase and gel electrolyte. As compared to another NiZn battery recently fabricated, our work displayed better performance in the retention rate and cycle (Supporting Information-Table 1). The structure of Ni(OH)2/CNFs was investigated after cycling. A comparison of the TEM images of Ni(OH)2/CNFs composite before and after cycling shows that the morphology of Ni(OH)2 before cycling (Figure 1b) was nanoplates. After cycling, nanoplates transformed into irregular plate-like structures (Figure S4-a,b). The HRTEM image (Figure 4f) displayed Ni(OH)2 still bonded with the oxidized CNFs after more than 1200 cycles. It indicated that the coupling between Ni(OH)2 and oxidized CNFs was firm. We carried out similar electrochemical measurements for the NiZn battery in 6 M KOH electrolyte without PAAS with a constant charging time of 3 min at a charge current density of 2.35A g−1 and discharge current density of 2.54 A g−1. The result (Figure S5-a) showed that the battery was quite unstable and short-circuited after 150 cycles, indicating the important role of sodium polyacrylate in improving the electrochemical performance of the NiZn battery. We characterized the surface morphology of the Zn foil before and after charge and discharge (Figure 5). There existed granular zinc deposits on the surface of the electrode, and no dendrites were observed after 1200 cycles (Figure 5b). It indicated that the polymer PAAS gel electrolyte remarkably suppressed the formation of dendrites and enhanced electrochemical stability.40 We also carried out the measurement of the NiZn battery in 6 M KOH electrolyte with only small amount of PAAS (0.05 g per 10 mL of electrolyte) in the same test condition. The result (Figure S5-b) was that the battery short circuited after 250 cycles. These data indicate that the polymer hydrogel electrolyte can remarkably improve the stability of NiZn battery. The possible reasons are as follows: The first reason is possibly due to the high viscosity of the electrolyte, causing low preference of zinc growth at the tips. The second reason is that water loss can be minimized owing to gelling of the PAAS gel electrolyte.41 The third reason is that the dissolution and diffusion of the zincate ions might be restrained in the KOH aqueous solution owing to gelling, producing a high concentration of zincate ions around the neighboring electrode surface, which is advantageous to form the granular zinc deposits on the surface of the electrode during charging.40,42,43 The detailed reason requires investigation.

Ni(OH)2/CNFs and measured the charge/discharge behaviors at different current densities (Figure 3b). Figure 3b displayed that no significant capacity drop could be observed and capacities of 178 mAh·g−1 and 150 mAh·g−1 were achieved with a loading of 2 mg·cm−2 and 20 mg·cm−2, respectively, at the current density of 50 mA·cm−2. The total area-specific capacity enhanced linearly with increased loading up to 20 mg·cm−2 (Figure 3c). When 20 mg·cm−2 was loaded, the Ni(OH)2/CNFs composite electrode could deliver a high area-specific capacity of 6.38 mAh·cm−2. Charge/discharge cycling stability is critical to battery electrode material especially at high loadings. We investigated the cycling stability of the Ni(OH)2/CNFs composite electrode with 10 mg· cm−2 at a high charge/discharge current density of 100 mA·cm−2, and negligible decay of discharge capacity was observed over 1000 cycles, maintaining the specific capacity of 150 mAh·g−1 (Figure 3d). To match practical application, a pouch cell was engineered out of β-Ni(OH)2/CNFs hybrid cathode and Zn foil anode. Figure 4a was schematic representation of the NiZn battery made from Ni(OH)2/CNFs composite materials and Zn foil. The electrolyte was 6 M KOH, 1 M LiOH, and PAAS (0.33 g per 10 mL of electrolyte) saturated with ZnO gel. LiOH was used to suppress oxygen evolution by increasing the oxygen overvoltage.36−39 Galvanostatic charge and discharge tests were then conducted at various current rates, as shown in Figure 4b. The discharge voltage profiles of the NiZn battery at different current densities demonstrated operating voltages of 1.7−1.8 V at current densities from 5 mA·cm−2 to 50 mA·cm−2. The NiZn cell was able to deliver high specific energy of 184 mAh·g−1 at a current density of 5 mA·cm−2. It still maintained a high capacity of 91 mAh·g−1 at a current density of 50 mA·cm−2 (based on the active mass of Ni(OH)2 and Zn involved in the reaction). It suggested excellent capacitance and high-rate capability. Figure 4c demonstrated a Ragone plot achieved by further calculating the energy and power density based on the data of Figure 4b. The NiZn battery could perform a peak energy density of 325 Wh· kg−1 at a power density of 1.23 kW·kg−1 and peak power density 11.4 kW·kg−1 at an energy density 166 Wh·kg−1. Importantly, the columbic efficiency was nearly 100% for each charge−discharge cycle (Figure 4d). Cycle life is one of the critical criterions to batteries that restrains the application of the NiZn battery. A conventional NiZn battery shows significant decay and degradation of electrode materials within 500 cycles. In contrast, with a constant charging time of 3 min at a charge current density of 2.35A·g−1 and discharge current density of 2.54 A·g−1, our NiZn pouch cell showed much improved cycling stability up to 6832

DOI: 10.1021/acssuschemeng.7b01048 ACS Sustainable Chem. Eng. 2017, 5, 6827−6834

Research Article

ACS Sustainable Chemistry & Engineering

■

(4) Dunn, B.; Kamath, H.; Tarascon, J. M. Electrical energy storage for the grid: a battery of choices. Science 2011, 334, 928−935. (5) Massé, R. C.; Uchaker, E.; Cao, G. Z. Beyond Li-ion: electrode materials for sodium- and magnesium-ion batteries. Sci. China Mater. 2015, 58, 715−766. (6) Armand, M.; Tarascon, J. M. Building better batteries. Nature 2008, 451, 652−657. (7) Edison, T. Reversible galvanic battery. US1901042514A [P]. (8) Yang, B.; Yang, Z. H.; Wang, R. J.; Wang, T. T. Layered double hydroxide/carbon nanotubes composite as a high performance anode material for Ni-Zn secondary batteries. Electrochim. Acta 2013, 111, 581−587. (9) Coates, D.; Ferreira, E.; Charkey, A. An improved nickel/zinc battery for ventricular assist systems. J. Power Sources 1997, 65, 109− 115. (10) Zhao, T. H.; Shangguan, E. B.; Lia, Y.; Lia, J.; Chang, Z. R.; Li, Q. M.; Yuan, X. Z.; Wang, H. J. Facile synthesis of high tap density ZnO microspheres as advanced anode material for alkaline nickel-zinc rechargeable batteries. Electrochim. Acta 2015, 182, 173−182. (11) Liu, J. P.; Guan, C.; Zhou, C.; Fan, Z.; Ke, Q. Q.; Zhang, G. Z.; Liu, C.; Wang, J. A flexible quasi-solid-state nickel−zinc battery with high energy and power densities based on 3D electrode design. Adv. Mater. 2016, 28, 8732−8739. (12) Geng, M.; Northwood, D. O. Development of advanced rechargeable Ni/MH and Ni/Zn batteries. Int. J. Hydrogen Energy 2003, 28, 633−636. (13) Jindra, J. Sealed Ni−Zn cells, 1996−1998. J. Power Sources 2000, 88, 202−205. (14) Li, H. B.; Yu, M. H.; Wang, F. X.; Liu, P.; Liang, Y.; Xiao, J.; Wang, C. X.; Tong, Y. X.; Yang, G. W. Amorphous nickel hydroxide nanospheres with ultrahigh capacitance and energy density as electrochemical pseudocapacitor materials. Nat. Commun. 2013, 4, 1894. (15) Kim, H.; Jeong, G.; Kim, Y.-U.; Kim, J.-H.; Park, C.-M.; Sohn, H.J. Metallic anodes for next generation secondary batteries. Chem. Soc. Rev. 2013, 42, 9011−9034. (16) Jindra, J. Progress in sealed Ni-Zn cells, 1991−1995. J. Power Sources 1997, 66, 15−25. (17) Wang, H. L.; Dai, H. J. Strongly coupled inorganic−nano-carbon hybrid materials for energy storage strongly coupled inorganic−nanocarbon hybrid materials for energy storage. Chem. Soc. Rev. 2013, 42, 3088−3113. (18) Liang, Y.; Wang, H.; Diao, P.; Chang, W.; Hong, G.; Li, Y.; Gong, M.; Xie, L.; Zhou, J.; Wang, J.; Regier, T. Z.; Wei, F.; Dai, H. Oxygen reduction electrocatalyst based on strongly coupled cobalt oxide nanocrystals and carbon nanotubes. J. Am. Chem. Soc. 2012, 134, 15849−15857. (19) Varadwaj, G. B. B; Nyamori, V. O. Layered double hydroxide- and graphene-based hierarchical nanocomposites: Synthetic strategies and promising applications in energy conversion and conservation. Nano Res. 2016, 9, 3598−3621. (20) Xu, Y. X.; Huang, X. Q.; Lin, Z. Y.; Zhong, X.; Huang, Y.; Duan, X. F. One-step strategy to graphene/Ni(OH)2 composite hydrogels as advanced three-dimensional supercapacitor electrode materials. Nano Res. 2013, 6, 65−76. (21) Wang, H. L.; Casalongue, H. S.; Liang, Y. Y.; Dai, H. J. Ni(OH)2 nanoplates grown on graphene as advanced electrochemical pseudocapacitor materials. J. Am. Chem. Soc. 2010, 132, 7472−7477. (22) Gong, M.; Li, Y. G.; Wang, H. L.; Liang, Y. Y.; Wu, J. Z.; Zhou, J. G.; Wang, J.; Regier, T.; Wei, F.; Dai, H. J. An advanced NiFe layered double hydroxide electrocatalyst for water oxidation. J. Am. Chem. Soc. 2013, 135, 8452−8455. (23) Wang, H. L.; Liang, Y. Y.; Mirfakhrai, T.; Chen, Z.; Casalongue, H. S.; Dai, H. J. Advanced asymmetrical supercapacitors based on graphene hybrid materials. Nano Res. 2011, 4, 729−736. (24) Wang, H.; Liang, Y.; Gong, M.; Li, Y.; Chang, W.; Mefford, T.; Zhou, J.; Wang, J.; Regier, T.; Wei, F.; Dai, H. J. An ultrafast nickel−iron battery from strongly coupled inorganic nanoparticle/nanocarbon hybrid materials. Nat. Commun. 2012, 3, 917.

CONCLUSION We demonstrated successful synthesis of oxidized CNFs by a simplified oxidization procedure. With the use of oxidized CNFs as substrate, β-Ni(OH)2 /CNFs composite material was synthesized and used as a novel electrode material. The Ni(OH)2/CNFs cathode showed a high specific capacity of 220 mAh·g−1 and superior cycling stability. By pairing the Ni(OH)2/CNFs cathode at high loading with the Zn anode, we were capable of engineering a promising pouch cell with high energy density, high power density, and long cycle life in a gel electrolyte. Further studies on improving the cycle life of a higher loading Ni(OH)2/CNFs electrode as well as suppressing the formation of zinc dendrite over a longer term would greatly promote the NiZn battery assembled with Ni(OH)2/carbon composites forward into practical application. In addition, an established facile oxidation method of CNFs could extend to functionalizing the other carbon nanomaterials, which were used to synthesize carbon composites.

■

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.7b01048. TEM image and Ranan spectrum of CNFs, CV curve of nickel foam, TEM image of Ni(OH)2/CNFs composites after >1200 cycles, energy density vs cycle number curves of the NiZn battery without PAAS and with 0.05 g PAAS per 10 mL electrolyte, and table of comparison studies for various NiZn battery performances (PDF)

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Mingyun Guan: 0000-0002-7130-5085 Author Contributions #

Y.J. and D.W. contributed equally to this work

Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors thank Dr. Ming Gong from Stanford University for the article revision and experiments guidance. This work was supported by the National Natural Science Foundation of China (No. 21373103, 21401083), Jiangsu Province Natural Science Foundation (No. BK2011260), International Science and Technology Cooperation Program of Changzhou (No. CZ20160014), Postgraduate Research & Practice Innovation Program of Jiangsu Province (No. 20820111614) for the financial support.

■

REFERENCES

(1) Aricò, A.; Bruce, P.; Scrosati, B.; Tarascon, J.-M.; van Schalkwijk, W. Nanostructured materials for advanced energy conversion and storage devices. Nat. Mater. 2005, 4, 366−377. (2) Guo, Y. G.; Hu, J. S.; Wan, L. J. Nanostructured materials for electrochemical energy conversion and storage devices. Adv. Mater. 2008, 20, 2878−2887. (3) Manthiram, A.; Murugan, A. V.; Sarkar, A.; Muraliganth, T. Nanostructured electrode materials for electrochemical energy storage and conversion. Energy Environ. Sci. 2008, 1, 621−638. 6833

DOI: 10.1021/acssuschemeng.7b01048 ACS Sustainable Chem. Eng. 2017, 5, 6827−6834

Research Article

ACS Sustainable Chemistry & Engineering (25) Gong, M.; Li, Y. G.; Zhang, H. B.; Zhang, B.; Zhou, W.; Feng, J. H.; Wang, L.; Liang, Y. Y.; Fan, Z. J.; Liu, J.; Dai, H. J. Ultrafast highcapacity NiZn battery with NiAlCo layered double hydroxide. Energy Environ. Sci. 2014, 7, 2025−2032. (26) Ji, J. Y.; Zhang, L. L.; Ji, H. X.; Li, Y.; Zhao, X.; Bai, X.; Fan, X. B.; Zhang, F. B.; Ruoff, R. S. Nanoporous Ni(OH)2 thin film on 3D ultrathin-graphite foam for asymmetric supercapacitor. ACS Nano 2013, 7, 6237−6243. (27) Farjami, E.; Rottmayerb, M. A.; Deinera, L. J. Evidence for oxygen reduction reaction activity of a Ni(OH)2/graphene oxide catalyst. J. Mater. Chem. A 2013, 1, 15501−15508. (28) Zhou, X. M.; Xia, Z. M.; Zhang, Z. Y.; Ma, Y. Y.; Qu, Y. Q. Onestep synthesis of multi-walled carbon nanotubes/ultra-thin Ni(OH)2 nanoplate composite as efficient catalysts for water oxidation. J. Mater. Chem. A 2014, 2, 11799−11806. (29) Sun, Z. P.; Lu, X. M. A solid-state reaction route to anchoring Ni(OH)2 nanoparticles on reduced graphene oxide sheets for supercapacitors. Ind. Eng. Chem. Res. 2012, 51, 9973−9979. (30) Zhang, L. S.; Ding, Q. W.; Huang, Y. P.; Gu, H. H.; Miao, Y. E.; Liu, T. X. Flexible hybrid membranes with Ni(OH)2 nanoplatelets vertically grown on electrospun carbon nanofibers for high-performance supercapacitors. ACS Appl. Mater. Interfaces 2015, 7, 22669−22677. (31) Gao, S. Y.; He, S. Y.; Zang, P. Y.; Dang, L. Q.; Shi, F.; Xu, H.; Liu, Z. H.; Lei, Z. B. Polyaniline nanorods grown on hollow carbon fibers as high-performance supercapacitor electrodes. ChemElectroChem 2016, 3, 1142−1149. (32) Surisetty, V. R.; Dalai, A. K.; Kozinski, J. Alkali-promoted trimetallic Co-Rh-Mo sulfide catalysts for higher alcohols synthesis from synthesis gas: comparison of MWCNT and activated carbon supports. Ind. Eng. Chem. Res. 2010, 49, 6956−6963. (33) Lou, Z. S.; Chen, Q. W.; Wang, W.; Zhang, Y. F. Synthesis of carbon nanotubes by reduction of carbon dioxide with metallic lithium. Carbon 2003, 41, 3063−3074. (34) Zhang, L. J.; Hui, K. N.; Hui, K. S.; Lee, H. High-performance hybrid supercapacitor with 3D hierarchical porous flower-like layered double hydroxide grown on nickel foam as binder free electrode. J. Power Sources 2016, 318, 76−85. (35) Zha, D. S.; Sun, H. H.; Fu, Y. S.; Ouyang, X. P.; Wang, X. Acetate anion-intercalated nickel-cobalt layered double hydroxide nanosheets supported on Ni foam for high-performance supercapacitors with excellent long-term cycling stability. Electrochim. Acta 2017, 236, 18−27. (36) Tuomi, D. The forming process in nickel positive electrodes. J. Electrochem. Soc. 1965, 112 (1), 1−12. (37) Thirsk, H. R.; Briggs, G. W. D. The nickel hydroxide and related electrodes. Electrochemistry 1974, 4, 33−54. (38) Rubin, E. J.; Baboian, R. A. Correlation of the solution properties and the electrochemical behavior of the nickel hydroxide electrode in binary aqueous alkali hydroxides. J. Electrochem. Soc. 1971, 118, 428− 533. (39) Shukla, A. K.; Venugopalan, S.; Hariprakash, B. Nickel-based rechargeable batteries. J. Power Sources 2001, 100, 125−148. (40) Iwakura, C.; Murakami, H.; Nohara, S.; Furukawa, N.; Inoue, H. Charge−discharge characteristics of nickel/zinc battery with polymer hydrogel electrolyte. J. Power Sources 2005, 152, 291−294. (41) Li, Y. G.; Dai, H. J. Recent advances in zinc-air batteries. Chem. Soc. Rev. 2014, 43, 5257−5275. (42) Lee, S. H.; Kim, K.; Yi, C. W. Poly(acrylamide-co-acrylic acid) gel electrolytes for Ni-Zn secondary batteries. Bull. Korean Chem. Soc. 2013, 34, 717−718. (43) Choudhury, N. A.; Sampath, S.; Shukla, A. K. Hydrogel-polymer electrolytes for electrochemical capacitors: an overview. Energy Environ. Sci. 2009, 2, 55−67.

6834

DOI: 10.1021/acssuschemeng.7b01048 ACS Sustainable Chem. Eng. 2017, 5, 6827−6834