Ni nanofoams composites for lithium ion battery anodes

Journal Pre-proof Facile fabrication of core-shell Ni3 Se2 /Ni nanofoams composites for lithium ion battery anodes Zhongren Wang, Quanbin Gao, Peng Lv, Xiuwan Li, Xinhui Wang, Baihua Qu

PII:

S1005-0302(19)30342-1

DOI:

https://doi.org/10.1016/j.jmst.2019.08.021

Reference:

JMST 1745

To appear in:

Journal of Materials Science & Technology

Received Date:

10 May 2019

Revised Date:

28 August 2019

Accepted Date:

30 August 2019

Please cite this article as: { doi: https://doi.org/ This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier.

Research Article

Facile fabrication of core-shell Ni3Se2/Ni nanofoams composites for lithium ion battery anodes Zhongren Wang 1, Quanbin Gao 1, Peng Lv 1, Xiuwan Li 1,*, Xinhui Wang 2,*, Baihua Qu 3

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Fujian Provincial Key Laboratory of Light Propagation and Transformation, College of Information Science and Engineering, Huaqiao University, Xiamen 361000, China College of Physics and Information Engineering, Institute of Micro-Nano Devices and Solar

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2

Cells, Fuzhou University, Fuzhou 350108, China 3

Pen-Tung Sah Institute of Micro-Nano Science and Technology, Xiamen University, Xiamen

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361000, China

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[Received 10 May 2019; Received in revised form 28 August 2019; Accepted 30 August 2019]

* Corresponding author. Ph.D.; Tel.: +86 592 6162380. E-mail address: [email protected]

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Abstract

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(X.W. Li).

Due to the highly porous structure, large specific surface area, and 3D interconnected metal conductive network, nanoporous metal foams have attracted a lot of attention in the field of energy conversion and storage, especially lithium-ion batteries, which are ideal for current collectors. In this work, we develop a facile approach to fabricate core-shell Ni3Se2/Ni nanofoams

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composites. The Ni3Se2/Ni composites make full use of both the advantages of metal conductive network and core-shell structure, resulting in a high capacity and superior rate performance. In addition, the composites can be directly converted into electrode by a simple mechanical compression, which is more convenient than traditional casting method. What’s more, this material and its structure can be extended to other devices in the field of energy conversion and storage.

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Keywords: Metal foams, Ni3Se2, core-shell structure, composites, Lithium ion battery

1. Introduction Thanks to porous structure, large specific surface area, and excellent electrical conductivity, nanoporous metal foams are increasingly favored by researchers in the field of energy storage and conversion[1-5]. Especially in metal-air batteries, solar cells, supercapacitors, and lithium/sodium ion batteries, nanoporous metal foams with metal ductility and 3D interconnected metal conductive network are ideal as an electrode current collector[6-8]. Due to

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these promising applications, much research has focused on developing synthetic methods. For example, Lang et al. prepared nanoporous gold substrate by the chemical de-alloying method, then plated MnO2 into the nanopores used as electrode for supercapacitor [9]. Owing to the high conductivity and fast ion diffusion of nanoprous gold substrate, the specific capacitance of the

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MnO2 is close to the theoretical value. Hoang et al. exploited electrodeposition method to

synthesize Cu films with high surface area and tunable morphology, and this nanoporous copper

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films exhibit high activity for CO2 reduction[10]. Wang et al. have fabricated a continuous mesoporous PtRu film on macroporous Ni foam (mPtRu–NF) by an in situ fabrication method,

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which shows a highly active bi-functional catalyst for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER)[11].

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However, those methods are too complicated and inefficient to meet the industrial production of low cost nanoporous metal foams electrodes. More importantly, the nanoporous metal foam and the active materials are synthesized by multi-steps in the above mentioned methods[12, 13].

In this work, we prepare core-shell Ni3Se2/Ni nanofoams composites by a facile combustion

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method. Ni3Se2 is a recently-recognized semiconductor material with great potential in energy storage and conversion, such as lithium/sodium ion batteries, supercapacitors, dye-sensitized solar cells, electrocatalytic hydrogen evolution and oxygenation, and wastewater treatment [14-19]. Especially in the field of energy storage, Ni3Se2 material has a greater advantage than elemental Se (lithium-selenium batteries)[20, 21]. This can be attributed to the following two points: First, the presence of Ni in the compound can greatly reduce the volume expansion of materials during discharge process; Second, metal Ni after reduction by Li after discharge can improve the electrical conductivity of materials [22, 23]. Compared to Ni3Se2 materials with different 2

morphology, core-shell Ni3Se2/Ni nanofoams composites make full use of the advantages of nano- and microporous metal foam as current collector. At the same time, the core-shell structure allows the Ni3Se2 materials to quickly acquire enough lithium ions from electrolyte. Combining the advantages of nano- and microporous metal foam and core-shell structure, Ni 3Se2/Ni nanofoams composites exhibit superior cycling and rate performance, which are suitable for lithium ion battery electrodes. 2. Experiment details 2.1 Synthesis of core-shell Ni3Se2/Ni nanofoams composites:

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The core-shell Ni3Se2/Ni nanofoams composites were fabricated by a facile combustion method which is a modification of that reported by previous works[12, 13, 24]. In a typical

synthesis, 1 mmol selenium urea (SeC(NH2)2) and 50 mmol nickel nitrate (Ni(NO 3)2•6H2O) were dissolved in 30 mL 2-methoxyethanol (C3H8O2) with stirring for 3 h at 80 °C to form suspended

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colloid. The obtained colloid was heated up to 120 °C without stirring. It burnt tempestuously in seconds in the atmosphere to form a Ni 3Se2/NiO/Ni nanofoams precursor. Then the precursor

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was reduced at 450 °C in hydrogen atmosphere for 3 h and the Ni 3Se2/Ni nanofoams composites were obtained. The composites were pressed at 6 MPa forming discs of 12 mm in diameter with

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the mass of 20-30 mg. The mass of active materials of Ni 3Se2 was calculated by the content of selenium and the mass ratio of active materials is about 1 mg/cm2.

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2.2 Structural and Electrochemical characterization: X-ray diffraction (XRD) pattern was collected on a Rigaku D/Max-2400 with Cu Kα radiation. X-ray photoelectron spectroscopy (XPS) was collected on Thermo ESCALAB 250XI. Field emission scan electron microscopy (FESEM) images were obtained on Nova Nano SEM

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450. Transmission electron microscopy (TEM) images, high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) images, energy dispersive X-ray (EDX) spectroscopy, EDX elemental mapping and EDX elemental line-scanning were performed on TECNAI F-30 transmission electron microscope operating at 300 kV. Electrochemical characterizations were carried out using CR-2032 type coin cell, which was assembled in a high-purity argon filled glove box (H 2O < 0.1 ppm, O2 < 0.1 ppm, Mikrouna Co., Ltd) by using the core-shell Ni3Se2/Ni nanofoams composites electrode as the working electrode and Li foil as the counter and reference electrode. Celgard 2320 was used as the separator 3

membrane. The electrolyte was prepared by 1 M lithium hexafluorophosphate (LiPF 6) dissolved in the solution of ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate in a 1:1:1 volume ratio. The galvanostatic discharge-charge cycling and cyclic voltammetry were carried out at room temperature by using a multichannel battery tester (Neware, BTS-610) and an electrochemical workstation (CHI, 660E), respectively. 3. Discussion and results The schematic illustration for the fabrication of core-shell Ni3Se2/Ni nanofoams composites is shown in Fig. 1. 3D porous nanofoams composites are prepared by the combustion method. As

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previously reported, the products without selenium urea are Ni nanofoams [24]. After adding selenium urea, Ni3Se2 materials are grown on the surface of Ni nanofoams to form a core-shell composite structure. In this structure, Ni 3Se2 materials can quickly obtain electrons from the 3D interconnected metal conductive network inside the core-shell structure and lithium ions from

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electrolyte outside the core-shell structure, which can greatly improve the specific capacity and rate performance.

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Fig. 2(a) shows the X-ray diffraction (XRD) patterns of the pure Ni nanofoams and assynthesized composites with selenium urea. Three strong diffraction peaks located at 44.4°,

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51.7°, and 76.2° appear in the patterns, and correspond to the (111), (200) and (220) faces of metallic nickel (JCPDS 04-0850), respectively. The other distinct diffraction peaks located at 20.9°, 29.5°, 30.0°, 37.1°, 42.6°, 47.7°, 48.2°, 52.7°, and 53.4° can be indexed to the (101),

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(110), (012), (003), (202), (211), (113), (122) and (104) planes of hexagonal Ni 3Se2 (JCPDS 850754), respectively. No other peaks can be observed, suggesting high purity of the sample. X -ray photoelectron spectroscopy (XPS) is employed to further analyze the sample. The typical survey spectrum of composties (Fig. S2) reveals the presence of nickel and selenium on the surface. In order to prove the valence of the element, Peak fitted for the Ni and Se elements are given in Fig.

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3(a) and (b). For the Ni element (Fig. 3(a)), there are two spin-orbit doublets and two shakeup satellites. The fitted peaks at about 874.00 eV and 856.12 eV are attributed to the divalent Ni ion, which corresponds to Ni 2p 1/2 and Ni 2p3/2[25, 26]. The other pair of fitting peaks are located at about 870.05 eV and 852.95 eV, corresponding to Ni 2p 1/2 and Ni 2p3/2, derived from the trivalent Ni ion[25, 26]. Fig. 3(b) shows the Se 3d spectrum. Two fitting peaks located at about 55.40 eV and 54.58 eV are corresponding to the Se 3d3/2 and Se 3d5/2, which is from the typical of nickel selenides[25, 27]. These XPS results confirm the majority phase on the surface of composites is Ni3Se2. 4

The low magnification SEM morphology of Ni 3Se2/Ni nanofoams composites is shown in Fig. 2(b). Same as pure Ni nanofoams (as shown in Fig. S1), 3D interconnected network structure of Ni3Se2/Ni nanofoams composites is still retained. Fig. 2(c) and (d) shows the higher magnification SEM of composites. It can be seen that the surface of the materials probably has crystal morphology. Compared to pure Ni nanofoams, it can be determined that these structures are derived from Ni3Se2 materials. From the structure, a large number of hexagons can be found, proving hexagonal structure of Ni3Se2. TEM further confirms the core-shell structure of Ni 3Se2/Ni. As can be seen from Fig. 4(a), porous structrue can be observed clearly, which is consistent with the SEM results. Fig. 4(b)

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shows the high-resolution TEM image near the edge of nanofoams. It can be seen that the

materials show excellent lattice spacing strips. The measured lattice spacing of 0.30 nm in the inset is in good agreement with (110) interplanar distances of the hexagonal Ni3Se2 phase. The fast Fourier transform (FFT) pattern taken from Fig. 4(b) shows crystal lattice and

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polycrystalline rings with various orientations. The crystal lattice corresponds to the Ni 3Se2

while polycrystalline rings to Ni. Fig. S3(a) shows the large-scale lattice structure of composites.

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From the corresponding FFT pattern (as shown in Fig. 4(d)), it can be seen that the crystal structure of this region is mainly polycrystalline. Fig. S3(b) shows the high-resolution TEM

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image, which is a typical polycrystalline structure. The measured lattice spacing of 0.20 and 0.17 nm is in good agreement with (111) and (200) interplanar distances of the Ni metal.

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Subsequently, composites are characterized by energy-dispersive X-ray spectroscopy (EDS) attached to the TEM, as shown in Fig. 4(h). Compositional analysis reveals that the elements contained in composites are Ni, Cu, and Se. The elements of Ni and Se signal are derived from the Ni3Se2 and Ni nanofoams, and the Cu signal is from copper mesh, which can be negligible. Fig. 4(e-g) shows TEM elemental mapping images of the composites. The mapping images of Ni

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and Se elements are given in Fig. 4(f) and 4(g), respectively. From the element mapping, it can be known that Ni is the major element. This is evident that the structural framework of nanofoams is made of Ni metal, which illustrates that Ni 3Se2 materials are evently distributed on the surfaces of nanofoams. To further prove this core-shell structure, a line-scan TEM-EDS elemental analysis of composites is shown in Fig. 4(i). Analysis results show the Se element is consistent with the distribution of Ni element. According to the intensity ratio of Se and Ni elements, the core-shell structure of Ni 3Se2/Ni can be determined. The composite electrode obtained by mechanical compression was directly used as a 5

working electrode of CR-2032 coin cell. Fig. 5(a) shows cyclic voltammetric (CV) curves recorded in the potential window at the scan rate of 0.2 mV/s. A strong peak around 0.75 V can be seen in the first cathodic scan, which corresponds to the initial reduction of Ni 3Se2 to metallic Ni (Ni3Se2 + 4Li+ + 4e- → 3Ni + 2Li2Se)[28, 29]. Near the strong peak, a weak peak around 0.40 V can be found. This peak corresponds to reduction of NiO to metallic Ni (NiO + 2Li + + 2e- → Ni + Li2O), which is formed in the combustion process. During anodic scan, there are three peaks. One peak located at 1.40 V is due to the oxidation of Ni to Ni 2+ (Ni + Li2O → NiO + 2Li+ + 2e-). Two other peaks at 2.10 and 2.40 V are due to the formation of Ni 3Se2 (3Ni + 2Li2Se →Ni3Se2 + 4Li+ + 4e-). In the subsequent cycles, peak position has changed as the formation of stable

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lithium-ion embedding channel. Fig. S4 shows the representative discharge/charge voltage profiles of composites electrode at 1 C. During the first discharge, there are two obvious voltage platforms at 1.25 and 0.80 V. In contrast, three voltage platforms appeared in the charge process at 1.50, 2.00 and 2.30 V,

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respectively. This phenomenon is well in agreement with the CV results. Fig. 5(b) shows the discharge-charge cycling for the Ni3Se2 electrode at 1 C. The initial discharge and charge

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capacities are 489.6 and 369.0 mA h/g, respectively, corresponding to the coulombic efficient of 75.5 %. The irreversible capacity may be caused by the decomposition of electrolyte and the

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formation of solid electrolyte interface (SEI) layer on surface of active materials [30-32]. After 100 cycles, the discharge and charge capacities are 460.8 and 453.6 mA h/g respectively, suggesting excellent capacity retention of the Ni 3Se2 electrode. The large increasing specific capacity could

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be attributed to the reversible growth of the polymeric gel-like film resulted from kinetically activated electrolyte degradation [33, 34].

Moreover, the rate performance of Ni 3Se2 electrode was investigated (Fig. 5(c)). The capacities are perfectly stable at the given current densities. The discharge capacities are 383.4

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(5th), 370.6 (15th), 358.3 (25th), and 345.9 (35th) at rates of 0.5, 1, 2, and 4 C, respectively. These capacities at different rate are almost the same, which shows excellent rate capability. More importantly, when the current rate is returned to 1 C, the electrode recovers its initial capacity and reaches to 447.1 mA h/g in the 60th cycle, indicating superior structural stability. Fig. 5(d) shows the representative discharge-charge voltage profiles at various rates ranging from 0.5 C to 4 C. It can be clearly seen that all the voltage profiles at different rates are nearly the same, indicating the similar overpotentials at different rates. This phenomenon originated from a unique nanofoams core-shell structure. Ni3Se2 material as active material uniformly grows on the

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surface of Ni nanofoams. The thin Ni3Se2 layer can ensure that all Ni 3Se2 materials are able to get enough electrons and Li-ions in time, which can effectively reduce the electrochemical polarization of the composite electrode. To further demonstrate the advantages of composite, the electrochemical impedance spectra (EIS) were measured at 1.4 V versus Li+ /Li after 3 CV cycles, and the impedance data were analyzed by fitting the equivalent electrical circuit shown in Fig. S5. Fitting data indicated that the electrolyte resistance (R0), surface film resistance (RSEI) and charge transfer resistance (Rct) are 6.21, 4.82, and 22.72 Ohms, respectively, which proves the structural advantages of core-shell Ni3Se2/Ni nanofoams composites.

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4. Conclusion In summary, we developed a facile combustion method to fabricate core-shell Ni3Se2/Ni nanofoams composites for high-power LIBs application. The Ni 3Se2/Ni nanofoams composites can deliver a high reversible capacity up to 460.8 mA h/g after 100 cycles at 1 C, and a capacity

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of 345.9 mA h/g at 4 C. The high reversible capacity and capacity retention in this work could be ascribed to two reasons. First, the 3D interconnect nanofoam structure can provide electrons quickly for the active material. Second, Ni 3Se2 materials as the shell for core-shell structure can

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get enough Li-ions from the electrolyte. More importantly, this unique core-shell structure for Ni3Se2 can be exploited to apply other field of energy storage and conversion, such as solar cell,

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Acknowledgements

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electrocatalysis, photocatalysis, and supercapacitor.

This project was financially supported by the Promotion Program for Young and Middleaged Teacher in Science and Technology Research of Huaqiao University (ZQN-PY608), the Fujian Provincial Natural Science Foundation of China (No. 2017J05008), and the National

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Natural Science Foundation of China (No. 11704071).

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Figure list:

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Fig. 1. Schematic showing the fabrication process for Ni nanofoams and Ni 3Se2/Ni nanofaoms composites by combustion method.

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Fig. 2. (a) XRD patterns of the composites and pure Ni nanofoams; (b), (c), and (d) differentmagnification SEM images of Ni 3Se2/Ni nanofoams composites.

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Fig. 3. XPS spectra of (a) Ni 2p and (b) Se 3d for Ni 3Se2/Ni nanofoams composites.

Fig. 4. (a) low- and (b) high-magnification TEM image of composites; (c) FFT pattern near the edge; (d) FFT pattern inside the nanaofoams; (e) HAADF-STEM images, (f) and (g) EDS mapping images, (h) EDS pattern, (i) line scan analysis (HAADF-STEM image in the inset) of Ni3Se2/Ni nanofoams composites.

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Fig. 5. Electrochemical performances of the Ni3Se2/Ni nanofoams composites electrodes: (a) Cyclic voltammograms for the initial 4 cycles; (b) cycling performance of composites at 1C; (c) Cycling at various current rates from 0.5 to 4C; (d) Representative discharge/charge curves at various rates.

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