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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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

6

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

15

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

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

17

application.

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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

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

23

from Figure 8b.

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

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structure before and after 100 charging-discharging cycles respectively.

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

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

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

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

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

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

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

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

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

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

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

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

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

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Page 18 of 29

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

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

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

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very useful in practical applications.

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

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

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

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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.

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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

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

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

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

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

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

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

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

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

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

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battery can improve stability.

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CONCLUSIONS

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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.

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

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

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

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anode materials by compounding natural organic materials into metal oxides.

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SUPPORTING INFORMATION

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

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

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

13

charge on the ACS Publications website.

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AUTHOR INFORMATION

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Corresponding Authors

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

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Author Contributions

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

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

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

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manuscript.

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Notes

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The authors declare no competing financial interest.

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ACS Applied Nano Materials

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ACKNOWLEDGMENTS

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

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

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

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

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2682015QM04).

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