Improved Rate and Cycling Performances of Electrodes Based on

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Improved rate and cycling performances of electrodes based on BiFeO3 nanoflakes by compositing with organic pectin for advanced rechargeable Na-ion batteries Bai Sun, Shuang Suo Mao, Shou Hui Zhu, Guang Dong Zhou, Yu Dong Xia, and Yong Zhao ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.8b00011 • Publication Date (Web): 07 Feb 2018 Downloaded from http://pubs.acs.org on February 15, 2018

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ACS Applied Nano Materials

Improved Rate and Cycling Performances of Electrodes Based on BiFeO3 Nanoflakes by Compositing with Organic Pectin for Advanced Rechargeable Na-Ion Batteries Bai Sun,*,†,‡ Shuangsuo Mao,†,‡ Shouhui Zhu,†,‡ Guangdong Zhou,§ Yudong Xia,†,‡ and Yong Zhao*,†,‡ †

School of Physical Science and Technology, Southwest Jiaotong University, Chengdu, Sichuan 610031, China ‡ Key Laboratory of Magnetic Levitation Technologies and Maglev Trains, Ministry of Education of China, and Superconductivity and New Energy R&D Center, Southwest Jiaotong University, Chengdu, Sichuan 610031, China § Institute for Clean Energy & Advanced Materials (ICEAM), Southwest University, Chongqing 400715, China

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ABSTRACT: Advanced rechargeable Na-ion battery is favored by researchers owing to its

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relatively low-priced and earth-abundant resource. In this work, BiFeO3 nanoflakes by

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compositing with organic pectin as an outstanding anode material for rechargeable Na-ion

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batteries were fabricated by an improved hydrothermal process for the first time. We found that

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the BiFeO3/pectin nanoflakes as anode hold long-life and excellent charge-discharge

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performance with reversible capacity of 450 mAh g−1 which can retain 100% capacity after 100

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charge-discharge cycles. It is infered that the excellent performance of Na-ion batteries is

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contributed to viscoelastic pectin among BiFeO3 crystal lattices. The organic pectin can play a

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buffer role in the process of BiFeO3 crystal lattices expansion when Na ions inserted, indicating

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the BiFeO3/pectin nanoflakes are not easily degenerated as anode in Na-ion battery. This work

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provides great potential for fabricating low-priced and high power density Na-ion batteries for

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electronic equipment applications.

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Keywords: BiFeO3 nanoflakes; Organic pectin; Na-ion batteries; Viscoelastic; Hydrothermal

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INTRODUCTION

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Recently, Li-ion batteries, which is one of the most common rechargeable batteries, are

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being used widely in a variety of electronic devices.1,2 The potential application prospect for

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electrical vehicles, laptop, mobile phone and smart grids greatly accelerate the requirement on

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Li-ion battery, thus serious concerns on sustainable development of Li-ion batteries because the

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metal Li reserves are limited on the earth.3-5

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Na-ion batteries is considered the most likely candidates to take the place of conventional

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Li-ion batteries because of non-toxicity, low-priced sodium element and abundant resources.6

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Of course, it is important to exploit superior performance electrode materials to fabricating of

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Na-ion batteries.7 Similarly as Li-ion batteries, carbon based materials as electrode are feasible

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to store sodium reversibly.8–11 Up to date, there is many materials as anode of Na-ion battery

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have been investigated.12-19 Unfortunately, a lot of work reported Na-storage capacities are

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below and not meet the application requirements. However, theoretical calculation certifies that

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many materials could satisfy high capacities as electrode materials in Na-ion batteries.20

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Therefore, many researchers are trying to find out more suitable electrode materials for

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practical application of Na-ion rechargeable battery.

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BiFeO3, which is firstly found single phase multiferroic materials at room temperature,

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have attracted a lot of researchers' interest in many interdiscipline.21,22 BiFeO3 possess a lot of

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special properties, such as simultaneous ferroelectricity, magnetism and photovoltaic

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property.23-25 Specially, ternary metal oxide BiFeO3, which is a perovskite ABO3 (A: alkaline

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earth element; B: transition metal element) structure,26 has recently been studied as room-

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temperature multiferroic material.27,28 At the same time, the electrochemical properties based

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ABO3 materials have also been reported in previous works.29,30 Because the perovskite ABO3

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has excellent electrochemical and thermoelectric properties,30,31 and because of the BiFeO3 2


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crystal has octahedral structure, the Li ions or Na ions are relatively easy to insert. Therefore, it

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has high theoretical capacity and long cycle life.

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In addition, pectin, which can be extracted from most plants, is a water-soluble

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polysaccharide with the most complex structurally and functionally polysaccharide,32,33 and it

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is a class of galacturonic acid-rich polysaccharides.34 At the same time, pectin has a resistivity

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for protease and amylase. This makes pectin an ideal drug carrier for colon specific drug

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delivery.35,36 Therefore, the pectin is one of the valuable organic biomaterials in biological and

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medical applications.

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As far as we know, carbon-based materials is a kind of negative material with excellent

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electrochemistry performance in many applications.37,38 However, organic pectin doped

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metallic oxide based composite nanomaterial for preparing rechargeable battery have not been

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reported yet, and the hydrothermal method has a lot of advantages in the preparation of

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nanomaterials.39 In this study, BiFeO3/pectin nanoflakes were prepared by an improved

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hydrothermal process as anode material for fabricating Na-ion batteries, and further

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investigated the electrochemical behaviors of the BiFeO3/pectin nanoflakes anode associated

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with its physical and chemical properties. It is discovered that the pectin played a buffer role

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for BiFeO3 crystal lattice expansion to greatly enhance the insertion-desertion process,

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furthermore, the stability and cycle life is prominently improved. It can be achieved a higher

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capacity, longer cycle life and excellent reversibility when as-prepared product is used as

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anode material. This above excellent battery performance should be attributed to the promoting

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ions transport efficiency among the BiFeO3/pectin nanoflakes. This work provide an approach

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for massively-manufacturing BiFeO3/pectin nanoflakes for potential rechargeable batteries.

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EXPERIMENTAL SECTION

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Fabrication of BiFeO3/pectin nanoflakes. BiFeO3/pectin nanoflakes were prepared using

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a hydrothermal method through improved the preparation method reported in the literature.40,41

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Detailed preparation process is shown in Figure 1. The corresponding experiment flowchart is

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presented in Figure S1 (Figure S1 can be found in the Supporting Information). The detailed

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experimental process is as follows: 4.95 g of Bi(NO3)3·5H2O and 2.704 g of FeCl3·6H2O were

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firstly dissolved in 100 ml acetone (99.8%) under continuously stirring until adequately

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dissolved. Secondly, we slowly added appropriate amount of distilled water into above solution.

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Subsequently concentrated ammonia was added drop by drop until the pH value of solution is

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increased to 11~12. After stirring continuously for 2 hour, the sediment is washed a number of

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times using distilled water until the pH value is decreased to 6.5~7.5. Thirdly, the co-

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precipitate is re-dispersed in 80 ml of distilled water dissolved with 6.0 g of NaOH, then the

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solution was divided into two duplicate equably, with different proportions of pectin was added

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to above a part solution. Finally, We got the final product through the solution was heated at

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120 oC for 150 h in teflon-lined steel autoclave.

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Figure 1. The preparation process of the BiFeO3/pectin nanoflakes by hydrothermal method. 4


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Material characterizations. Microstructure of BiFeO3/pectin nanoflakes was checked by

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X-ray diffraction (XRD, Shimadzu XRD-7000). Surface morphology of BiFeO3/pectin

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nanoflakes was observed by scanning electron microscopy (SEM, JSM-6510). The elemental

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conditions were determined by energy dispersive X-ray spectroscopy (EDX, JSM-6700). The

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nanoscale size and morphology of BiFeO3/pectin nanoflakes were tested by transmission

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electron microscopy (TEM, JEM-2100).

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Na-ion battery construction and measurements. To prepare Na-ion battery anodes,

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BiFeO3-based materials (BiFeO3/pectin and BiFeO3), Super-P carbon and polyvinyldifluoride

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(Aldrich) with weight ratio of 8:1:1 were mixed in N-Methylpyrrolidone (NMP) solvent. The

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mixed slurry was evenly coated onto Cu foils. The as-prepared electrodes were dried at 80 oC

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under vacuum for 12 h in order to ensure that no water molecules are contained, then as-dried

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electrodes were directly transferred into Ar-protected glove box. The half-cells were made

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using as-prepared anodes, Celgard 2250 as separator, and Na metal foil with a purity of 99.9%

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acts counter electrode, in which the used electrolyte was 1.0 M NaClO4 in tetra ethylene glycol

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dimethyl ether. The charge/discharge,

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were carried out using a LAND cell test system and CHI-660E electrochemical workstation.

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The battery performance test was performed at charge-discharge rates from 0.1 C to 20 C at

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voltage window of 0.05 to 2.5 V.

cycle measurements and electrochemical properties

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RESULTS AND DISCUSSION

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The SEM image of BiFeO3 and BiFeO3/pectin nanoflakes respectively are displayed in

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Figure S2 (the Figure S2 is shown in the Supporting Information). We can observe that the as-

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prepared product was consisted of nanoflakes with size of few hundreds of nanometers. The

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TEM image (Figure 2a,c) exhibits that the individual BiFeO3 and BiFeO3/pectin nanoflakes.

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Figure 2b,d represents a high-resolution TEM (HRTEM) image, displaying a crystallizing ideal

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structure. Moreover, the interplanar spacing of ~0.28 nm is the (110) crystal faces of BiFeO3

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according to the previous literature.42,43 Therefore, the HRTEM image (Figure 2b,d) and

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selected area electron diffraction (SAED) pattern (The inset of Figure 2b,d) indicate that the

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BiFeO3 and BiFeO3/pectin nanoflakes show an excellent single-crystalline structure. Moreover,

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it is very obvious that the pectin is adhered on BiFeO3 nanoflakes from Figure 2c, and the

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pectin nanoparticles are very evenly dispersed on the surface of the BiFeO3 nanoflakes.

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Figure 2. (a) TEM image of BiFeO3 nanoflakes. (b) HRTEM image of BiFeO3 nanoflakes. The

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inset show SAED pattern of BiFeO3 nanoflakes. (c) TEM image of BiFeO3/pectin nanoflakes.

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(d) HRTEM image of BiFeO3/pectin nanoflakes; The inset show SAED pattern of

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BiFeO3/pectin nanoflakes.

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Figure 3a exhibits the XRD patterns of the pectin, BiFeO3 nanoflakes and BiFeO3/pectin

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nanoflakes respectively. It is highly obvious that the pure phase of BiFeO3 were prepared by

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hydrothermal method (Figure 3a), indicating that these diffraction peaks can be distributed to

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BiFeO3 (JCPDS 20-0169),44,45 and the sharp peaks indicating that BiFeO3 nanosheets have

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good crystallinity. The BiFeO3/pectin nanoflakes possess only Bi, Fe, O and C from the EDX

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data, among the Al peak was induced by the substrate because of we dissolved BiFeO3/pectin

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nanoflakes powder in alcohol, then it was dispersed on a piece of Al for EDX characterization,

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thus the Al peak was induced by the substrate (Figure 3b). The BiFeO3:pectin ratio is 9:1 in the

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BiFeO3/pectin nanoflakes within instrumental errors.

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Figure 3. (a) The X-ray diffraction (XRD) results of pectin, BiFeO3 nanoflakes and

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BiFeO3/Pectin nanoflakes, respectively. (b) The EDX data of pectin, BiFeO3 nanoflakes and

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BiFeO3/Pectin nanoflakes, respectively; The inserted table shows the percentage of elements.

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The cyclic voltammetric (CV) curves, which is measured on the BiFeO3 and BiFeO3/pectin

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nanoflakes electrodes, show two obvious cathodic peaks at 0.32 V and near 0.62 V and one

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anodic peaks at 0.75 V for the as-prepared BiFeO3/pectin nanoflakes at a scan rate of 0.5 mV s-

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in Figure 4a. We can also deduce that these two peaks can be originated from the oxidation of

Fe0 to Fe3+ to re-form BiFeO3.46-49

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Figure 4a shows that a slight structural rearrangement of active substances leads to a

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superior contact between the collector and the electrolyte in the first few cycles. The process

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above should be analogous to what happens in Li-ion battery.28,47 At second cycle scanning, it

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can be observed a wide range of split peaks, which will further reduce a clear peak in the cycle.

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Reduplication of second and third cathodic scans showed reversibility and capacity stability.

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The wide peak observed after second cycles is caused by the amorphous/crystal structural

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damage of the material. There is some similar wide peaks have been reported in the previous

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work.48 Our results can be used to further analyze the mechanism of chemical reaction for

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BiFeO3/pectin nanoflakes electrode. It is noteworthy that the peak of the near 0.3 V for the

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BiFeO3 nanoflakes sample becomes clearer in the second and third cycles. The potential

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polarization during cycles increases the affinity of the non-complex sample, the electrolyte can

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penetrate into the inner hole of the nano-hole with much larger reaction peak.48,49 We think the

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peak may be due to the large diffusion limiting current in the large porous surface. Anyway,

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the BiFeO3/pectin nanoflakes as anode material for Na-ion battery shows a good

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electrochemical properties, which display more obvious oxidation and reduction peaks.

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However, the BiFeO3 nanoflakes as anode materials for Na-ion battery, the stability of the

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redox properties are relatively poor with the charge-discharge cycle. Therefore, the

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BiFeO3/pectin nanoflakes is more suitable as anode material of Na-ion battery.

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Figure 4. (a) Cyclic voltammetric (CV) curves of BiFeO3 and BiFeO3/pectin as anode

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materials at the rate of 0.5 mV s-1. (b) First three charge–discharge curves of the BiFeO3 and

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BiFeO3/pectin as anode materials for Na-ion batteries under a current density of 100 mA g-1. (c)

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Profile of discharge capacity and cycle number of BiFeO3 nanoflakes and BiFeO3/pectin

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nanoflakes electrodes. (d) The curve of the discharge capacity and cycles number of BiFeO3

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nanoflakes and BiFeO3/pectin nanoflakes electrodes under a current rate of 500 mA g-1. 9



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During the first three charge-discharge cycles, the BiFeO3/pectin nanoflakes anode in the

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voltage range from 0.05 to 2.50 V at a current density of 100 mA g-1 is shown in Figure 4b, we

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can see that the discharge and charge capacities are 720 mA h g-1 and 280 mA h g-1

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respectively for BiFeO3/pectin nanoflakes but it is 420 mA h g-1 and 80 mA h g-1 respectively

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for the BiFeO3 nanoflakes in the first cycle. The specific power and specific energy can also be

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calculated according to the previous literature.50 We can see the initial capacity loss is very

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obvious from Figure 4b, it may be because that there is a part of a process to alloy incomplete

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is irreversible in the process of electrochemical reaction, especially the formed solid electrolyte

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interface (SEI), which could lead to apparent attenuation of capacity due to hinder the full

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contact of active material and electrolyte..51,52

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Figure 4c exhibits the variation curve of discharge capacity with the cycle number at

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various current rates for the BiFeO3/pectin nanoflakes electrodes, which represents that the

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discharge capacities at 50, 100, 200, 500, 1000 mA g-1 are 750, 500, 300, 200 and 150 mAh g-1,

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respectively. In particular, the first discharge capacity is 1550 mAh g-1 when the BiFeO3/pectin

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nanoflakes was used as electrode materials. Obviously, the discharge capacity can be increased

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to 700 mA h g-1 along with the discharge current density is decreased from 1000 mA g-1 to 50

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mA g-1, the capacity value is nearly as large as the initial corresponding discharge capacity at

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50 mA g-1. It is very obvious that these values are significantly higher than the corresponding

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capacity of BiFeO3 nanoflakes electrode materials. That is to say the cyclic stability of battery

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performance is really not ideal. not perfect for BiFeO3 nanoflakes. The results indicate that the

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BiFeO3/pectin nanoflakes has a perfect rate capacity at each current densities.

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Figure 4d shows the variation curve of discharge capacity with the cycle number for

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BiFeO3 nanoflakes and BiFeO3/pectin nanoflakes-based electrodes at the current rate of 500

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mA g-1. These curves were measured at voltage window between 0.05 and 2.5 V for continuity

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100 times. We can see from these data that the discharge capacity under a discharge current of

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500 mA g-1 for the BiFeO3/pectin nanoflakes has been not decayed and retained approximately

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100% of corresponding initial capacity after 100 times charge-discharge, while the BiFeO3

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nanoflakes electrode only retained 95% of its initial capacity. Indeed, for the electronically

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driven application by using battery, it is been more concerned about its cycle life. The BiFeO3

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nanoflakes based electrodes materials exhibits a relatively lower cycle life. From here we see

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that a long cycle life could only be achieved through compound pectin into BiFeO3 nanoflakes.

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This may be because the BiFeO3/pectin nanoflakes composite obtained by hydrothermal

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reaction process, which could serve as a buffer role in the process of BiFeO3 crystal lattices

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expansion, thus the pectin can enhance the availability of BiFeO3/pectin nanoflakes in the

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process of electrochemical reaction.53,54 Furthermore, pectin is a kind of organic material, in

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the hydrothermal reaction process with high temperature and high pressure, it may occur

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hydrolysis reaction, then closely attached to the surface of BiFeO3 nanoflakes, thereby

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reducing the reunion of BiFeO3 nanostructures, thus it can generate a lot of micropores, and

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these micropores can increase the electrolyte into, thus can increase the discharge capacity.

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More importantly, we can find in Figure S3 and Figure S4 that the relatively increase of

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discharge capacity become more obvious at higher rates and the Coulombic efficiencies at

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large rates can be approached 100% for each charing-discharing cycle, implying sufficient fast

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sodium diffusion and sufficient reversibility for the Na-ion intercalation/intercalation in the

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BiFO3/pectin nanoflakes electrode, which can lead to excellent rate capability,55 suggesting the

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BiFeO3/pectin nanoflakes electrode can provide more sodium storage sites than BiFeO3

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nanoflakes electrode.56 (Figure S3 and Figure S4 are shown in Supporting Information).

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Further, we analyzed the effect of different pectin doping amount on the capacity of

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BiFeO3/pectin nanoflakes based on Na-ion battery. We can found that the battery capacity

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showed a significant enlarge with the increase of the doping amount of pectin from 0.1% to 1%

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(Figure 5a). However, the capacity of the battery began to decline when the doping amount of

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pectin beyond 10%. It should be noted that the capacity-cycle curves show the same change

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trend (Figure 5b). This may be because it is not enough to play a buffer role when the Na ions

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inserted into the BiFeO3 for the too few pectin doped into the BiFeO3 nanoflakes. However, the

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excess pectin will hinder the battery because the conductivity of organic pectin is relatively

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poor. Therefore, the amount control of the doped pectin is very important in our work.

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Figure 5. (a) The variation curve of discharge capacity with the cycle number of BiFeO3/pectin

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nanoflakes electrodes with different pectin doping amount. (b) The variation curve of discharge

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capacity with the cycle number of BiFeO3/pectin nanoflakes electrodes with different pectin

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doping amount.

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Figure 6. The surface SEM morphology image of the as-prepared electrode material, BiFeO3

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nanoflakes (a, b) and BiFeO3/pectin nanoflakes (c, d), after 100 cycles charge-discharge.

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Figure 6 shows the surface SEM morphology image of the BiFeO3 nanoflakes and

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BiFeO3/pectin nanoflakes after 100 cycles charge-discharge. It is very obvious that the

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nanostructure of BiFeO3 nanoflakes is almost absolutely destroyed after 100 charge-discharge

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cycles (Figure 6a,b). However, we found that nanostructure of BiFeO3/pectin nanoflakes are

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still preserved (Figure 6c,d). Therefore, it can be judged from the above results that pectin

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plays a very significant function, which can enhance the availability of BiFeO3/pectin

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nanoflakes in the process of electrochemical reaction during charging and discharging in Na-

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ion battery. With the continuously increasing of charge-discharge cycles, the surface of

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BiFeO3/pectin nanoflakes appears much micro-pores, which can provide larger contact area

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Page 14 of 29

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between electrolyte and BiFeO3/pectin nanoflakes, thus more Na ions can enter BiFeO3/pectin

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nanoflakes, thereby, it can effectively increase the discharge capacity after 80 cycles, as shown

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in Figure 6b. These results are absolutely consistent with the that of Figure 6b. Further, the

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SEM morphology image of the electrode material, BiFeO3 nanoflakes and BiFeO3/pectin

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nanoflakes, after 200 charge-discharge cycles is also present the same evolution from Figure

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S5 (Figure S5 is shown in Supporting Information).

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Table 1 The interplanar spacing from SAED, HRTEM and simulation calculation for as-

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prepared sample. d(211)/nm

d(110)/nm

d(212)/nm

d(210)/nm

SAED

0.28

0.31

0.24

0.26

HRTEM

0.26

0.28

0.23

0.25

Simulation calculation

0.28

0.29

0.24

0.24

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Table 2 The interplanar spacing from SAED, HRTEM and simulation calculation after 100

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charge-discharge cycles. d(211)/nm

d(110)/nm

d(212)/nm

d(210)/nm

SAED

0.28

0.37

0.24

0.26

HRTEM

0.26

0.35

0.23

0.25

Simulation calculation

0.28

0.38

0.24

0.24

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The HRTEM image of BiFeO3/pectin nanoflakes exhibits the fringes with a spacing of 0.28

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nm, corresponding to (110) planes of BiFeO3, for as-prepared sample but it change into 0.35

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nm after 100 charge-discharge cycles, (Figure S6a,c). The corresponding SAED pattern in the

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Figure S6b,d displays a single-crystalline structure for BiFeO3/pectin nanoflakes. We can

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observe that spacing of (211), (212) and (210) planes is not changed after 100 cycles charge-

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discharge from Table 1,2, and these values of SAED and HRTEM is coincident with

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simulation calculation. However, it is highly obvious that the spacing of (110) plane is

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tempestuously increased after 100 charge-discharge cycles whether it comes from the

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observation of the SAED and HRTEM or from the simulation calculation (Table 1,2).

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Figure 7. The XRD of BiFeO3 nanoflakes and BiFeO3/pectin nanoflakes as anode materials

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charged to 2.5 V and then discharged to 0.05 V respectively for the first cycle (a, b), after 100

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cycles charge-discharge (c, d) and after 200 cycles charge-discharge (e, f).

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Figure 7 displays the XRD of BiFeO3 nanoflakes and BiFeO3/pectin nanoflakes as anode

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materials charged to 2.5 V and then discharged to 0.05 V respectively for the first cycle (Figure

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7a, b), after 100 charge-discharge cycles (Figure 7c, d) and after 200 charge-discharge cycles

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(Figure 7e, f). We found that the peak shift of BiFeO3/pectin nanoflakes is smaller than BiFeO3

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nanoflakes, which indicate pectin can reduce the expansion of BiFeO3 crystals. According to

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Scherrer’s formula:

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d = kλ/Bcosθ

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we can calculate to get the value of d(110) is 0.29 nm but it is increased to 0.37 nm for BiFeO3

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nanoflakes. However, the value of d(110) is only increased to 0.35 nm for BiFeO3/pectin

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nanoflakes, these values are consistent with Table 1,2. The above results fully demonstrate that

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the stability of BiFeO3/pectin nanoflakes is relatively better than that of BiFeO3 nanoflakes. As

16

a result, BiFeO3/pectin nanoflakes is a more potential anode material for Na-ion batteries in

17

application.

18

Actually, BiFeO3 is a multiferroic material, which can synchronously display the

19

spontaneous ferroelectric polarization and antiferromagnetism at room temperature. The

20

direction of polarization is usually along the perovskite structure [111] axis,57,58 its crystal

21

structure is shown in Figure 8a. It can be seen that the crystal shape of BiFeO3 is changed after

22

100 charging-discharging cycles because Na ions are inserted into the lattice of BiFeO3 crystals

23

from Figure 8b.

24

16


Page 17 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

2

Figure 8. (a) Schematic diagram of BiFeO3 crystal. (b) and (c) The SAED for BiFeO3 crystal

3

structure before and after 100 charging-discharging cycles respectively.

4

5

The impedance analysis of the BiFeO3 nanoflakes and BiFeO3/pectin nanoflakes for Na-ion

6

battery is shown in Figure 9. The Nyquist plots consist of two partly overlapped semicircle is

7

located at the middle and high frequency zone and an inclined line in the low frequency

8

area.59,60 We can see that the nyquist plots exhibit a charge transfer resistance at higher

9

frequency region while a capacitive behavior at lower frequency region,61 indicating the

10

impedance becomes larger with the increasing of charge-discharge cycles. Before charging-

11

discharging cycles, after first charging-discharging cycles and after 100 discharging-charging

12

cycles, the impedance of BiFeO3 nanoflakes anode is smaller than impedance of BiFeO3/pectin

13

nanoflakes anode. However, it is interesting that the impedance of BiFeO3/pectin nanoflakes

14

anode is smaller than the impedance of BiFeO3 nanoflakes anode after 100 discharging-

15

charging cycles. The lower resistance for the BiFeO3/pectin nanoflakes anode after 200

16

discharging-charging cycles mainly owing to maintenance of BiFeO3 crystal lattice by doped

17

pectin, resulting in quick Na-ion diffusion and small volume change of BiFeO3/pectin

17



Page 18 of 29

1

nanoflakes anode. Therefore, the BiFeO3/pectin composite material as anode of Na-ion battery

2

can improve conductivity and reduce internal resistance of battery, that is to say, it can reduce

3

the energy consumption of the battery and increase the output power of the battery, which is

4

very useful in practical applications.

5

6

7

Figure 9. The impedance analysis of the BiFeO3 nanoflakes and BiFeO3/pectin nanoflakes for

8

Na-ion battery before charging-discharging cycles (a), after first charging-discharging cycles

9

(b), after 100 discharging-charging cycles (c), after 100 discharging-charging cycles (d).

10

18


Page 19 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

The mechanisms for BiFeO3/pectin nanoflakes as anode materials can increase the capacity

2

and improve stability of charging-discharging cycles for Na-ion battery is shown in Figure 10.

3

In this work, for BiFeO3 nanoflakes, the crystal of BiFeO3 is easily distorted when Na ions are

4

inserted into the BiFeO3 lattice. However, the crystal of BiFeO3/pectin nanoflakes as anode

5

material in Na-ion battery is not easily distorted when Na ions are inserted into the BiFeO3

6

lattice due to the pectin serve an important function in the automatic recovery process of

7

BiFeO3 lattice, as shown in Figure 10. Our results indicate that BiFeO3/pectin nanostructures

8

can not only effectively buffer volume changes during charging and discharging cycles, but

9

pectin also provides an excellent ion transport pathway, leading to excellent cycle performance

10

and stable rate performance. Therefore, excellent BiFeO3/pectin nanoflakes can achieve

11

excellent performance, high power density and cycle stability in storage performance, which

12

provides a potential candidate for low cost anode materials for Na-ion batteries.

13

14

15

Figure 10. A schematic diagram of the BiFeO3/pectin nanoflakes as anode material in Na-ion

16

battery can improve stability.

17

19



1

Page 20 of 29

CONCLUSIONS

2

In brief, BiFeO3/pectin nanoflakes were prepared by a co-precipitation associated

3

hydrothermal method, and were made into an anode material for preparing Na-ion batteries.

4

Out results indicate that the BiFeO3/pectin nanoflakes doped by 1% pectin remarkably retains

5

nearly 100% of its reversible capacity after 100 charge-discharge cycles. Our work provides a

6

very effective way to prepare high capacity, high power density and long life Na-ion battery

7

anode materials by compounding natural organic materials into metal oxides.

8

9

SUPPORTING INFORMATION

10

The detail synthesis process of BiFeO3/pectin nanoflakes, SEM image, TEM image, SAED

11

pattern, capacity performance of BiFeO3/pectin nanoflakes electrodes at various current rates

12

are shown in the Supporting Information. The Supporting Information is available free of

13

charge on the ACS Publications website.

14

15

AUTHOR INFORMATION

16

Corresponding Authors

17

*E-mail: [email protected]; [email protected]

18

Author Contributions

19

B. Sun, S. Mao, and S. Zhu contributed equally for this work. The manuscript was written

20

through contributions of all authors. G. Zhou make a detailed and useful discussions and TEM

21

test. All authors have discussed related results and approval to the final version of the

22

manuscript.

23

Notes

24

The authors declare no competing financial interest.

20


Page 21 of 29 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

2

ACKNOWLEDGMENTS

3

The authors are grateful for the National Natural Science Foundation of China (No. 51377138,

4

11504303, 51702265), The 863 Program (No. 2014AA032701), the Sichuan Province Science

5

Foundation (No. 2017JY0057), the Applied Science and Technology Project of Sichuan

6

Province (No. 2017JY0056), the Fundamental Research Funds for the Central Universities (No.

7

2682015QM04).

8

9

10

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