Carbon Nanocomposite with Dual-Carbon

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Energy, Environmental, and Catalysis Applications

A Hierarchical GeP5/Carbon Nanocomposite with Dual-Carbon Conductive Network as Promising Anode Material for Sodium Ion Batteries Qiu-Li Ning, Bao-Hua Hou, Ying-Ying Wang, Dao-Sheng Liu, ZhongZhen Luo, Wen-Hao Li, Yang Yang, Jin-Zhi Guo, and Xing-Long Wu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b11103 • Publication Date (Web): 02 Oct 2018 Downloaded from http://pubs.acs.org on October 3, 2018

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ACS Applied Materials & Interfaces

A Hierarchical GeP5/Carbon Nanocomposite with Dual-Carbon Conductive Network as Promising Anode Material for Sodium Ion Batteries †

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Qiu-Li Ning , Bao-Hua Hou , Ying-Ying Wang , Dao-Sheng Liu , Zhong-Zhen Luo* , WenHao Li†, Yang Yang†, Jin-Zhi Guo†, Xing-Long Wu*†‡ǁ †

National & Local United Engineering Laboratory for Power Batteries, Faculty of Chemistry, Northeast Normal University, Changchun, Jilin 130024, P. R. China ‡

Key Laboratory for UV Light-Emitting Materials and Technology, Northeast Normal University, Ministry of Education, Changchun, Jilin 130024, P. R. China §

School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798, Singapore ǁ

Institute of Advanced Electrochemical Energy, Xi'an University of Technology, Xi'an 710048, P. R. China Corresponding Authors * E-mail: [email protected] * E-mail: [email protected]

KEYWORDS: sodium ion batteries, anode material, GeP5, carbon conductive network, composite

ACS Paragon Plus Environment

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ABSTRACT：Due to the Earth’s scarcity of lithium, replacing lithium with earth-abundant and low-cost Sodium for Sodium ion batteries (SIBs) have recently become a promising substitute for lithium ion batteries (LIBs). However, the shortage of appropriate anode materials limits the development of SIBs. Here, a dual-carbon conductive network enhanced GeP5 (GeP5/acetylene black/partially reduced graphene oxide sheets (GeP5/AB/p-rGO)) composite is successfully prepared by a facile ball milling method. The dual-carbon network not only provides more transport pathways of electron, but also relaxes the huge volume change of the electrode material during the charge/discharge progress. Compared only AB or GO modified GeP5 (GeP5/AB or GeP5/GO) composite, the GeP5/AB/p-rGO composite shows a superior sodium storage performance with excellent rate and cycle performance. It delivers a high reversible capacity of 597.5 and 175 mAh/g at the current density of 0.1 and 5.0 A/g, respectively. Furthermore, at the current density of 0.5 A/g, the GeP5/AB/p-rGO composite shows the reversible capacity of 400 mAh/g after 50 cycles with a little capacity attenuation. All above results prove that the GeP5/AB/p-rGO composite has a good prospect of application as an anode material for SIBs.

1. INTRODUCTION In the last decade, lithium ion batteries (LIBs) as the main power sources for portable electronic devices, are gradually applied in large-scale products, such as hybrid vehicles (HEVs), electric vehicles (EVs), and energy storage systems (ESSs). However, ever-increasing demand of LIBs results in the shortage and fancy price of lithium resources.1-6 On the contrary, with the similar chemical properties as lithium, sodium is cheaper and more earth-abundant. Therefore, sodium ion batteries (SIBs) are considered as the promising alternative to LIBs.1, 7-11 However, SIBs show a relative low specific capacity, poor rate capability and cycling stability than LIBs.7,


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The larger ion radius (1.02 Å for Na+ vs 0.76 Å for Li+) results in the sluggish

electrochemical reaction kinetics and huge volume change of the electrode materials during the sodiation/desodiation progress.15-16 Meanwhile the graphite anode, which is well-developed in LIBs is not suitable for SIBs.17-19 Therefore, it is highly desired to develop new anode materials for SIBs with high specific capacity and excellent cycling performance. In recent years, alloy-type materials (e.g. Sn-based materials,20-23 Sb-based materials,24-26 Si-based materials,27-28 Ge-based materials,29-31 P-based materials32-34) have attracted wide attention because of their high theoretical specific capacity. However, these electrode materials suffer from the huge volume expansion during the alloying reaction, which causes the serious electrode pulverization and rapid capacity fade.1 So far, two available strategies, designing nanostructures and introducing conductive carbon (e.g. acetylene black, graphene) are used to accelerate the kinetics of the reaction and achieve stability of the alloy-type anode materials.1, 20, 28-29, 35-36

Several studies have corroborated that nanosized Si shows sodium storage performance,

but Si was not suitable as an anode material for SIBs due to low electrochemical activity.27-28, 3739

On the contrary, Sn and Sb, showing a high theoretical specific capacity of 847 (Na15Sn4) and

660 mAh/g (Na3Sb), are extensively studied for SIBs. But the huge volume change leads to the electrode pulverization during sodiation/desodiation progress, consequently losing electrical contact with the current collector, capacity decay and hindering the application as a SIBs anode material.13, 40 Recently, Phosphorus (P) has attracted much attention due to its high theoretical specific capacity (w≈2600 mAh/g) and low cost. Zhou et al. reported hollow nanospheres with porous shells, which revealed great rate and cycle performance.33 Liu et al. developed a method to deposit red phosphorus nanodots densely and uniformly onto reduced graphene oxide sheets


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(P@RGO). The P@RGO flexible anode delivered a capacity of 914 mAh/g after 300 cycles at the current density of 1593.9 mA/g. Although some studies have carried out about the P-based materials for SIBs, the poor conductivity and huge volume expansion limit its practical application. Meanwhile, Ge is also regard as a promising anode material for SIBs. Its electrical conductivity and ion diffusivity are ~100 times and 400 times than those of Si.31 Thus, we hypothesized that a promising approach to enhance the conductivity of P could be via Ge alloying. Although it is an expensive material, we can availably ameliorate the low conductivity problem of P as small amount of active metal components. In GeP5 material, the content of Ge is little. Moreover, the GeP5 has been proved to have excellent lithium storage properties. Li et al. reported that GeP5/C anode for LIBs delivered excellent rate performance and a high initial coulombic efficiency.41 However, there are few works that had been previously explored of GeP5 as an anode material for SIBs.42-43 The AB shows the good electrical conductivity. With the particle size of about dozens of nanometers, it can contribute to mixing homogeneous with GeP5 nanoparticles. Moreover, GO has large specific surface area where AB and GeP5 nanoparticles uniformly disperse, mitigating volume expansion during the sodiation/desodiation. Therefore, a dual-carbon network of AB/GO is a good choice to enhance the electrochemical performance of GeP5 as an anode material for SIBs. In this work, the GeP5/AB/p-rGO composite is successfully prepared via a simple technique of ball milling. The ultra-small GeP5 and AB nanoparticles are uniformly dispersed on the layers of graphene oxide, forming the dual-carbon conductive network structure. The electrochemical tests corroborate that the GeP5/AB/p-rGO composite exhibits greatly improved sodium storage performance. Moreover, it has the best performance compared with the AB modified GeP5 (GeP5/AB) and GO modified GeP5 (GeP5/GO) composite. In detail, the GeP5/AB/p-rGO


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composite delivers a high reversible capacity of 597.5 and 175 mAh/g at the current density of 0.1 A/g and 5.0 A/g, respectively. The excellent sodium storage performance is benefit from the small particle size and the special dual-carbon conductive network structure. The former can short the transport path of the Na+. The latter can improve the conductivity of the electrode and effectively alleviate the volume expansion during discharging/charging process.

2. EXPERIMENTAL SECTION Preparation of the GeP5 and GeP5 composites All reagents were used without any treatment after purchase. Red phosphorus (P, SigmaAldrich) and Germanium powder (Ge, Sigma-Aldrich) were weighed according to the composition of GeP5. The total mass is ~4 g. The elements were loaded into a stainless-steel ball milling jar in a glove box under an argon atmosphere with an oxygen and water level below 0.1 ppm. The materials were ball-milled for 2 h by using the 8000D Mixer/Mill-dual high-energy ball mill. The GeP5/AB/p-rGO composite was synthetized in two steps. Firstly, 10 mg GO and 20 mg AB nanoparticles were ball milling for 12 hours at the protection of an argon atmosphere. And then 60 mg the pure GeP5 was milled to the above mixture for 2 hours. In addition, the GeP5 was mixed with GO and AB nanoparticles using the same weight ratios to prepare the GeP5/AB and GeP5/GO composites, respectively, with the same process as the preparation for the GeP5/AB/p-rGO composite. Material characterization


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Powder X-ray diffraction (XRD) patterns were collected from the Rigaku D/Smartlab (Cu Ka radiation). The morphology of the prepared materials was characterized by Transmission electron microscopy (TEM, JEOL-2100 F, 200 kV), the scanning electron microscopy (SEM) (HITACHI-SU8010, 10 kV). The element mappings were performed by using the energy dispersive X-ray spectroscopy (EDX). Electrochemical measurements Electrochemical performance was tested in 2032 coin cells. The GeP5/AB/p-rGO electrode was prepared by coating the slurry of the GeP5/AB/p-rGO (90 wt %) and CMC (10 wt %) onto the copper foil (no extra conductive additives). For comparison, the GeP5, GeP5/AB and GeP5/GO electrodes were also consisted of 70 wt % pure GeP5, GeP5/AB and GeP5/GO, respectively, 20 wt % conductive additives (AB) and 10 wt % CMC. And then the prepared electrode was dried at 60 ℃ in vacuum for one night. The mass loading of the electrode material is about 1.5 mg cm-3.The electrolyte was 1.0 mol L-1 NaClO4 in a mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) in a 1:1 volume ratio with 5% fluoroethylene carbonate (FEC). The coin cell was assembled in the glove box filled with argon and the oxygen and moisture content of below 0.1 ppm. The constant current charge-discharge measurements were carried on a LAND (Wuhan Kingnuo Electronics, China) cycler. The cyclic voltammetry (CV) curves were carried on the CHI 750 system (Chenhua Instruments, China).

3. RESULTS AND DISCUSSION


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The GeP5/AB/p-rGO composite was prepared as an anode material for SIBs by ball milling. As shown in Figure 1, the GeP5 nanoparticles are surrounded by AB nanoparticles formed carbon conductive network. Then, there are uniformly dispersed on the layers of graphene oxide, forming the structure of the dual-carbon conductive network. The dual-carbon network will not only shorten the transport distance of the Na+ and electron, but also relax the huge volume change during the charge/discharge progress, which greatly improve the rate and cycle performance of the electrode material.1, 34 Figure 2a shows the X-ray diffraction (XRD) patterns for the GeP5 nanoparticles and GeP5/AB/p-rGO composite. The diffraction peaks of the high energy mechanical milling (HEMM) prepared GeP5 nanoparticles can be clearly detected. However, for GeP5/AB/p-rGO composite, the intensity of GeP5 phase’s diffraction peaks is sharply decreased. That is caused by the decadence of the GeP5 crystallization, the reduced particle size and carbon coating, which can be proved by the scanning electron microscopy (SEM).34, 44 And as shown in Figure S1, the intensity ratio of D band and G band (ID/IG) of the GO, AB/p-rGO and GeP5/AB/p-rGO is 0.91, 1.04 and 1.05 respectively. The result indicates that the GO is partially reduced to rGO during ball milling.45 As shown in the SEM images of GeP5/AB/p-rGO composite (Figure 2b and 2c) and GeP5 nanoparticles (Figure 2d), the GeP5 and AB nanoparticles are uniformly dispersed on the layers of GO. Moreover, the GeP5 nanoparticles are surrounded by the AB nanoparticles formed carbon conductive network, forming the structure of the dual-carbon conductive network. This dual-carbon conductive network provides more pathways of electron and will effectively alleviate the stress of volume expansion during sodiation/desodiation reactions. Furthermore, the size of the GeP5 is greatly reduced from hundreds of nanometers to dozens of nanometers, which efficaciously shortens the path for Na+ diffusion and mitigates the strain during the


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sodiation/desodiation progress. This structure is also confirmed from the transmission electron microscope (TEM) tests. As shown in Figure 2e-f, AB nanoparticles are distributed on the GO sheets with a particle size of about 50 nm. The HRTEM shows the lattice spacing of 0.257 nm, which corresponds to that of the (012) crystal planes of the GeP5 (Figure S2).34 Moreover, it is clearly shows that the GeP5 nanoparticles with a diameter of about 10 nm are embedded in the AB conductive network. As shown in Figure S3, the elemental mapping of the GeP5/AB/p-rGO composite corroborates the homogeneous distribution of Ge (green), P (red), C (blue), and oxygen (red). This proves that the GeP5, AB and GO are uniform distribution in the GeP5/AB/prGO composite by the method of ball milling. The electrochemical properties of the GeP5/AB/p-rGO composite are evaluated in half cells. Figure 3a shows the cyclic voltammetry curves (CVs) of the GeP5/AB/p-rGO composite electrode at a scan rate of 0.1 mV/s for the first five cycles. During the first discharge progress, the irreversible cathodic peak at about 0.7 V can be assigned to the side reaction of the solid electrolyte interface (SEI) film formation.42 The big broad cathodic peak of 0.22 V could be vested in the Na+ insertion reaction with the GeP5 to form the NaGe and Na3P. In the subsequent cathodic scans, the peak of 0.22 V splits into two peaks of 0.22 and 0.84 V.42 And the anodic peaks of 0.51 and 1.56 V can be corresponded to a stepwise desodiation process from the Na3P phase to form intermediates of NaP, Na3P11 and NaP7, and P, respectively, which indicates a multi-step redox reaction.46-48 Furthermore, the broad peak at 0.76 V belongs to the desodiation process from the Na3P and NaGe phases.42 The other three materials show the similar peaks in the first cycles (Figure S4). The well-overlapped curves in the following four cycles, indicating superior sodiation/desodiation reversibility of the GeP5/AB/p-rGO composite electrode. This process can be attributed to the following reaction (1)-(3). It can be calculated that the theoretical


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capacity of GeP5 is 1888 mAh/g. The Ge contributes 118 mAh/g and the 5 P contribute 1770 mAh/g. P + 16 + 10 → + 5

(1)

3 + 3 +

(2)

+ +

(3)

The discharge/charge curves of the GeP5/AB/p-rGO composite electrode are tested between the voltage of 0.01 and 2.8 V at the current of 0.1 A/g (Figure 3b). The discharge plateau of the first cycle at about 0.7 V is the side reaction of the solid electrolyte interface (SEI) film formation, which is consistent with the peak at 0.7 V of CV. And the plateau of 0.22 V belongs to the Na+ insertion reaction with the GeP5 to form the NaGe and Na3P. The charge plateaus at 0.36, 0.51 and 0.76 V are corresponded to a stepwise desodiation process from the Na3P phase, consistent with the results of the CV. But the plateau of 1.56 V is unconspicuous. The well overlapped curves suggest the good cycle stability for GeP5/AB/p-rGO composite as SIBs anode. Figure 4a shows the discharge and charge curves of the GeP5 nanoparticles and the other three carbon compounding composites (GeP5/AB, GeP5/GO and GeP5/AB/p-rGO) for the first several cycles. The test is carried out in the voltage of 0.01 to 2.8 V at the current of 0.1 A/g. The discharge curve of the GeP5 nanoparticles at the first cycle exhibits two flat voltage plateaus at 0.7 to 0.5 V and below 0.5 V, which belong to the formation of the SEI film and the Na+ insertion to the GeP5 respectively. And the charge voltage plateau can vest in the desodiation from Na3P. But it is different from the other three carbon compounding composites (GeP5/AB, GeP5/GO and GeP5/AB/p-rGO) that the voltage plateau is short at the second charge curve. Tt’s difficult to achieve de-alloying due to electrode pulverization during the sodiation/desodiation


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progress. Also, the quick capacity decay can be ascribed to large volume expansion during cycling, besides the electrode pulverization and formation of thick SEI layers. The main discharge voltage plateaus of carbon composites are similar to the pure GeP5 nanoparticles. The plateaus at 0.51 and 1.56 V can be corresponded to a stepwise desodiation process from the Na3P phase to intermediates of NaP, Na3P11 and NaP7, and P, respectively. Furthermore, the plateau at 0.76 V can belong to the desodiation process of Na3P and NaGe phase. After several cycles, the capacity of the GeP5, GeP5/AB, GeP5/GO, GeP5/AB/p-rGO is successively 124, 330, 302, and 564 mAh/g with the capacity retention ratio of 27.7%, 87.5%, 26.0%, and 94.5%, respectively. It suggests that dual-carbon composite has greatly enhanced the cycle performance than that of pure GeP5. The rate performances of the four materials with current densities of 0.1, 0.2, 0.5, 1.0, 2.0 and 5.0 A/g are shown in Figure 4b. The GeP5/AB/p-rGO composite not only exhibits the highest reversible capacity but also show the best rate performance than the other three materials. The reversible capacities of the GeP5/AB/p-rGO composite are 575, 477, 374, 311, 243 and 163 mAh/g at the current density of 0.1, 0.2, 0.5, 1.0, 2.0 and 5.0 A/g, respectively (Figure S5). More remarkable, the GeP5/AB/p-rGO composite still retain a high capacity of 163 mAh/g at the large current density of 5.0 A/g. When the current density reverts to 0.1 A/g, the capacity of the GeP5/AB/p-rGO composite can return to 555 mAh/g, indicating the excellent rate performance which benefits from the dual-carbon conductive network structure. The cycle performances of the GeP5/AB/p-rGO composite, GeP5, GeP5/AB, and GeP5/GO electrode materials at the current of 0.5 A/g are shown in Figure 4c. Obviously, the GeP5/AB/p-rGO composite shows the best cycle performance with the least capacity attenuation. All the carbon compounding composites exhibit higher capacity retention than the pristine GeP5 nanoparticles. The reversible capacities of the GeP5/AB/p-rGO, GeP5/AB and GeP5/GO composites are about 400, 200, and 50 mAh/g


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after 50 cycles. The capacity retention ratios are about 81.6%, 66.7% and 5.9%, respectively. However, the reversible capacity of the pristine GeP5 nanoparticles has almost attenuated to zero after 3 cycles. The improved cycle performance of the carbon compounding composite attributes to the carbon conductive network which can not only relieve the stress of volume expansion but provide fast electron transmission paths during the sodiation/desodiation progress. Thus, the GeP5/AB/p-rGO composite shows the best sodium storage performance with the benefits of the special dual-carbon conductive network structure. The results demonstrated that the carbon conductive network the GeP5/AB/p-rGO composite formed by the AB nanoparticles and GO network not only provides more the paths of electron and Na+ diffusion, but also is the good buffering of volume expansion of the materials, which result in the superior cycle performance of the GeP5/AB/p-rGO composite. To further study the sodium storage mechanism of the GeP5/AB/p-rGO composite, as shown in Figure 5a, the CV curves have been tested to investigate the kinetic process at different scan rates of 0.1, 0.2, 0.3, 0.5 and 1 mV/s. The result reveals that the peak current of the material is not proportional to the square root of scan rate, which indicates that both of non-faradaic process and faradaic are contained:49 =

(1)

log = × log + log

(2)

where a and b are adjustable parameters. For b = 0.5, the sodium storage procedure of the GeP5/AB/p-rGO composite is mainly controlled by the diffusion behaviors. For b ~ 1, the sodium storage procedure of the GeP5/AB/p-rGO composite is the main subject to the pseudocapacitive behaviors. Log (i) vs. log (v) plots of the sample at three redox peaks are


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present in Figure 5b.The slope of the plot is b-value. The results reveal that the b-values of the GeP5/AB/p-rGO composite are 0.79, 0.64 and 0.79 at peaks 1, 2 and 3, respectively. For the values of approach to 1, suggesting that the charge–discharge process of the GeP5/AB/p-rGO composite is related to both diffusion reaction and capacitive behavior. Furthermore, the capacitive contribution at various scan rates is calculated by the following equation (Figure 5c): = k +

!

".

(3)

where k1v and k2v0.5 represent the capacitive and the diffusion contributions, respectively. As shown in Figure 5d, the capacitive contributions of the GeP5/AB/p-rGO composite are 55.6%, 65.2%, 68.7%, 73.5% and 79.6% at different scan rates of 0.1, 0.2, 0.3, 0.5 and 1 mV/s, respectively. The results further indicate that the sodium storage procedure of the GeP5/AB/prGO composite is mainly controlled by the pseudocapacitive behaviors. That is the reason of GeP5/AB/p-rGO composite shows the fast reaction kinetic and best rate performance compared with GeP5, GeP5/AB, and GeP5/GO. The EIS measurements are conducted to further investigate the electrochemical performance of GeP5 via the dual-carbon conductive network modification. Figure S7 shows the comparison of the typical Nyquist plots (Zre vs. -Zim) between GeP5 and the other three GeP5/carbon composites in half cells before cycling. It is disclosed clearly that three GeP5/carbon composites show the smaller impedance (the smaller diameter of the semicircle in Nyquist plots) than that of GeP5 anode, demonstrating that the strategy of carbon compound can significantly improve their electrical conductivity. Moreover, the GeP5/AB/p-rGO composite has the smallest impedance in the three composites, which is consistent with the above Na+ storage performance.


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As shown in Figure S7, the initial Coulombic efficiency of the GeP5/AB/p-rGO composite is about 60%, and the next cycle is 95%, close to 100%, showing the best cycle performance than the other three materials. Furthermore ， the superior electrochemical performance of the GeP5/AB/p-rGO composite compared to GeP5/AB and GeP5/GO composite is benefit from the special structure of dual-carbon conductive network as shown in Figure 6. The dual-carbon conductive network provides more transport pathways for the electron and the small particle size can shorten the transport path of the Na+, both of which improve the electrochemical reaction kinetics and contribute to better electrochemical performance of the GeP5/AB/p-rGO composite as an anode for SIBs. Furthermore, the flexible dual-carbon conductive network can not only improve the conductivity of the electrode, but also effectively alleviate the volume expansion of the electrodes during discharging/charging process, improving the cycle performance of the anode material. To further testify the superior cycle performance of the GeP5/AB/p-rGO composite, the SEM images of the GeP5/AB/p-rGO composite anode before and after cycling are shown in Figure 7. Figure 7a is the SEM image of the pristine GeP5 anode before cycling, and Figure 7b-c show the morphology of the GeP5 anode after 10 cycles. It is clear shows that the pristine GeP5 anode has cracked and pulverized after 10 cycles. On the contrary, as shown in Figure 7d-e, the integrity of GeP5/AB/p-rGO anode is very well retained after 30 cycles. As shown in Figure 7f, the special dual-carbon structure keeps intact, powerfully proving that the structure of the prepared GeP5/AB/p-rGO composite is very stable. And it is expected to be used as an anode material for sodium ion batteries. And Table S1 shows the comparison of the cycle performance between the GeP5/AB/p-rGO and previous works. So far, only two works have reported GeP5 anode for SIBs. The GeP5/AB/p-rGO composite exhibits good cycle performance at larger


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current density of 0.5 A/g. Moreover, this work provides a novel design of a dual-carbon conductive network to improve the electrochemical performance of GeP5 anode for the first time.

4. CONCLUSIONS The GeP5/AB/p-rGO composite with dual-carbon conductive network is successfully prepared as an anode material for SIBs by a simple technique of ball milling. The dual-carbon conductive network structure is formed by GeP5 and AB nanoparticles uniformly dispersed on the GO layers. The GeP5/AB/p-rGO composite exhibits significantly improved Na-storage properties compared with GeP5/AB and GeP5/GO composites. As the anode material for SIBs, it exhibits excellent rate performance and deliver a large reversible capacity of 175 mAh/g at the current density of 5.0 A/g. Remarkably, the GeP5/AB/p-rGO composite shows the reversible capacity of 400 mAh/g after 50 cycles at the current density of 0.5 A/g. This excellent rate and cycle performance benefit from the small size of the GeP5 and the special dual-carbon conductive network structure. The former shortens the Na+ diffusion paths, and the latter provides more transport paths of electron.


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Figure 1. Illustration of the synthesis process for the GeP5/AB/p-rGO composite.

Figure 2. (a) XRD patterns of the GeP5 nanoparticles and GeP5/AB/p-rGO composite, (b, c) the SEM images of the GeP5/AB/p-rGO composite. (d) SEM image of the GeP5 nanoparticles. (e) TEM image of the GeP5/AB/p-rGO composite. (f) HRTEM image of the GeP5/AB/p-rGO composite.


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Figure 3. The sodium storage mechanism of the GeP5/AB/p-rGO composite. (a) CV curves of the initial five cycles at the scan rate of 0.1 mV/s; (b) Discharge/charge curves of the initial five cycles at the current density of 0.1 A/g.


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Figure 4. (a) The galvanostatic curves of the initial five cycles of the GeP5/GO, GeP5/AB/p-rGO, GeP5/AB and two cycles of GeP5 at the current density of 0.1 A/g. The comparison of (b) rate capabilities and (c) long-cycling stability among the GeP5, GeP5/GO, GeP5/AB/p-rGO, GeP5/AB.

Figure 5. (a) CV curves of the GeP5/AB/p-rGO at different scan rates from 0.1 to 1.0 mV/s, (b) log(i) vs. log(v) plots for the GeP5/AB/p-rGO, (c) CV curve with the pseudocapacitive fraction shown by the darkly cyan region of the GeP5/AB/p-rGO at a scan rate of 1 mV/s, (d) the pseudocapacitive contribution of the GeP5/AB/p-rGO at different scan rates.


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Figure 6. Illustration of the rational design for the (a) GeP5/AB/p-rGO, (b) GeP5/AB and (c) GeP5/GO anode.


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Figure 7. Morphologic changes of the surface on the electrodes upon cell test: (a) the fresh electrode and (b, c) the electrode after 10 cycles of the GeP5 anode, (d) the fresh electrode and (e, f) the electrode after 30 cycles of the GeP5/AB/p-rGO anode. ASSOCIATED CONTENT Supporting Information Raman spectra of the GO, AB/p-rGO and GeP5/AB/p-rGO composite; HRTEM image of the GeP5/AB/p-rGO composite; SEM image and elemental mapping of the GeP5/AB/p-rGO composite; comparison of CV curves, EIS spectra and the coulombic efficiency. AUTHOR INFORMATION Corresponding Author * E-mail: [email protected]


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* E-mail: [email protected] Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was financially supported by the National Natural Science Foundation of China (51602048), and the Fundamental Research Funds for the Central Universities (2412017FZ013). REFERENCES (1) Lao, M.; Zhang, Y.; Luo, W.; Yan, Q.; Sun, W.; Dou, S. X., Alloy-Based Anode Materials toward Advanced Sodium-Ion Batteries. Adv. Mater. 2017, 29, 1700622-1700645. (2) Yabuuchi, N.; Kubota, K.; Dahbi, M.; Komaba, S., Research Development on SodiumIon Batteries. chem. Rev. 2014, 14, 11636-11682. (3) Pan, H.; Hu, Y.-S.; Chen, L., Room-Temperature Stationary Sodium-Ion Batteries for Large-Scale Electric Energy Storage. Energy Environ. Sci. 2013, 6, 2338-2360. (4) Palomares, V.; Casas-Cabanas, M.; Castillo-Martinez, E.; Han, M. H.; Rojo, T., Update on Na-based Battery Materials. A Growing Research Path. Palomares 2013, 6, 2312-2337. (5) Cui, J.; Zhan, T.-G.; Zhang, K.-D.; Chen, D., The Recent Advances in Constructing Designed Electrode in Lithium Metal Batteries. Chin. Chem. Lett. 2017, 28, 2171-2179. (6) Xu, R.; Sun, Y.; Wang, Y.; Huang, J.; Zhang, Q., Two-Dimensional Vermiculite Separator for Lithium Sulfur Batteries. Chin. Chem. Lett. 2017, 28, 2235-2238. (7) Chen, W.; Chen, C.; Xiong, X.; Hu, P.; Hao, Z.; Huang, Y., Coordination of SurfaceInduced Reaction and Intercalation: Toward a High-Performance Carbon Anode for Sodium-Ion Batteries. Adv. Sci. 2017, 4, 1600500-1600507. (8) Datta, M. K.; Epur, R.; Saha, P.; Kadakia, K.; Park, S. K.; Kumta, P. N., Tin and Graphite Based Nanocomposites: Potential Anode for Sodium Ion Batteries. J. Power Sources 2013, 225, 316-322. (9) Dahbi, M.; Yabuuchi, N.; Fukunishi, M.; Kubota, K.; Chihara, K.; Tokiwa, K.; Yu, X.-f.; Ushiyama, H.; Yamashita, K.; Son, J.-Y.; Cui, Y.-T.; Oji, H.; Komaba, S., Black Phosphorus as a High-Capacity, High-Capability Negative Electrode for Sodium-Ion Batteries: Investigation of the Electrode/Electrolyte Interface. Chem. Mater. 2016, 28, 1625-1635. (10) Guo, J. Z.; Wan, F.; Wu, X. L.; Zhang, J. P., Sodium-Ion Batteries: Work Mechanism and the Research Progress of Key Electrode Materials. J. Mol. Sci. 2016, 32, 265-279. (11) You, Y.; Kim, S. O.; Manthiram, A., A Honeycomb‐Layered Oxide Cathode for Sodium‐Ion Batteries with Suppressed P3-O1 Phase Transition. Adv. Energy Mater. 2017, 7, 1601698-1601705.


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Carbon Nanocomposite with Dual-Carbon

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