Bacterial-Derived, Compressible and Hierarchical Porous Carbon for

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Bacterial-Derived, Compressible and Hierarchical Porous Carbon for High Performance Potassium-ion Batteries Hongyan Li, Zheng Cheng, Qing Zhang, Avi Natan, Yang Yang, Daxian Cao, and Hongli Zhu Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.8b03845 • Publication Date (Web): 29 Oct 2018 Downloaded from http://pubs.acs.org on October 30, 2018

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Bacterial-Derived, Compressible and Hierarchical Porous Carbon for High

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Performance Potassium-ion Batteries

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Hongyan Li1, Zheng Cheng1, Qing Zhang1, Avi Natan1, Yang Yang1, Daxian Cao1, Hongli Zhu*,1

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1Department

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Massachusetts 02115, United States.

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*Corresponding author: Dr. Hongli Zhu

of Mechanical and Industrial Engineering, Northeastern University, Boston, E-mail: [email protected]

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Abstract

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Hierarchical-structure electrodes which are integrated with the merits of superior cycling

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stability and high rate performance are highly desired for energy storage in next-generation

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portable electronics. For the first time, we reported a compressible and hierarchical porous

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carbon nanofiber foam (CNFF) derived from sustainable and abundant biomaterial resources-

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bacterial cellulose for boosting the electrochemical performance of potassium ion batteries (PIB).

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The CNFF free-standing electrode with a hierarchical porous three-dimensional (3D) structure

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demonstrated excellent rate performance and good cyclic stability in the extended cycling test.

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Specifically, in the long-term cycling stability test, the CNFF electrode maintained a stable

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capacity of 158 mA h g-1 after 2000 cycles at a high current density of 1000 mA g-1, which has

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an average capacity decay of 0.006 % per cycle. After that, the CNFF electrode maintained a

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capacity of 141 mA h g-1 at a current density of 2000 mA g-1 for another 1500 cycles and a

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capacity of 122 mA h g-1 at a current density of 5000 mA g-1 for an additional 1000 cycles. The

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mechanism for the outstanding performance is that the hierarchical porous and stable CNFF with

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high surface area and good electronic conductivity provide sufficient sites for potassium ion

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storage. Furthermore, quantitative kinetics analysis has validated the capacitive- and diffusion-

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controlled charge storage contributions in the carbon foam electrode. This work will inspire the 1 ACS Paragon Plus Environment

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search for cost-effective and sustainable materials for potassium electrochemical energy storage.

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Key words: Potassium-ion batteries, bacterial cellulose, carbon nanofiber, hierarchical porous

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structure, compressible carbon foam

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Lithium based batteries are attractive energy sources because of the high energy density and low

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standard reduction potential of lithium metal. However, the application of lithium batteries is

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limited by the scarcity of lithium in the Earth’s crust, only 20 ppm.1, 2 In comparison, potassium,

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at 17,000 ppm, is much more abundant, therefore potassium based batteries are more affordable

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than their lithium counterparts. Extensive research efforts on the development of potassium-ion

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batteries for large-scale energy storage have been carried out since 2015.3, 4 In the past two years,

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several potassium-ion batteries (PIBs) anode materials such as graphite,5,

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microspheres,7 Prussian blue,8 MXene,9 Sn-C composite,10 chitin-based hard carbon,11 and

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transition metal compound12 have been studied. The main challenge facing PIBs is the low

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intrinsic kinetic of intercalation reaction caused by the large size of potassium ions (1.38 Ǻ),

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compared to lithium ions (0.76 Ǻ), and sodium ions (1.02 Ǻ). This larger ion size results in low

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reversible capacity and poor cycling stability.13 For this reason, pursuing highly ion-accessible

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PIBs anode materials with good structural stability is the key to improve the overall

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electrochemical performance of these batteries.

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hard carbon

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Carbonaceous materials are very attractive for PIB anodes due to their high conductivity and

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chemical stability. For instance, Ci et al. reported FeCl3-intercalated graphite as an anode of

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PIBs.14 Yang et al. reported sulfur and oxygen co-doped porous hard carbon microspheres for

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PIBs.15 Du et al. also used spheroid-like KTi2(PO4)3@C nanocomposites as anode material for

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PIBs.16 However, considering the small-scale synthesis procedures for these works, the large-

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scale application of carbon-based anodes in PIBs remains challenging. Therefore, biomaterial 2 ACS Paragon Plus Environment

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resources are being researched as alternatives because they are sustainable and abundant.

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Bacterial cellulose (BC) nanofibers can be sustainably synthesized by bacteria culture on a large

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scale. The BC contain ultrafine nanofibrillar reticulated structures.17 BC possesses high purity

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(70-90%),18, 19 high crystallinity (84-89%),19, 20 excellent mechanical properties (490 MPa tensile

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strength and 17.6 GPa Young’s modulus),19,

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which render BC an appealing material for a wide range of applications such as food industry,

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textile industry, biomedical fields, etc.22, 23

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good biodegradability, and biocompatibility,

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Herein, carbon nanofiber foam (CNFF) was obtained through pyrolysis of the BC. The

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resulting CNFF has a three-dimensional (3D) network with hierarchical micro and mesopores

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structures and a high Brunauer-Emmett-Teller (BET) surface area (778.75 m2 g-1). Meanwhile,

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for the first time, such compressible CNFF has been used as freestanding anode for PIBs and it

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exhibits excellent rate performance and ultra-long cycling stability. The prepared CNFF was

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tested in a PIBs half-cell with the potassium metal as the counter electrode (Scheme 1a and b).

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As illustrated in Scheme 1c and d, the CNFF electrode presents high compressibility. The 3D

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networking structure is beneficial for ion transportation during the charge/discharge processes of

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the battery (Scheme 1e). Additionally, the highly reversible capacity and ultra-long cycle life of

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PIB are attributed to the unique structure of CNFF (Scheme 1e). The first aspect of the structure

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is the hierarchical porous structure which contains micropores on the carbon nanofiber as well as

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micro- and mesopores between the fibers, which provides plenty of effective sites for potassium

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ion storage. Another important feature of the CNFF is that the 3D carbon foam is highly

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conductive allowing electron transportation and the free space in the 3D network provides

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sufficient pathways for electrolyte infiltration into the structure. Lastly, the quasi-amorphous

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carbon possesses large interlayer spacing within a short range, which has the capability to

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accommodate a large amount of potassium ions during charge and discharge.15 Based on the

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above advantages, in the rate performance test, the CNFF electrode delivers high initial

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reversible capacities of 240 and 214 mA h g-1 at 50 and 100 mA g-1, respectively. In the long-

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term cycling stability test, at a high current density of 1000 mA g-1, the CNFF electrode

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maintains a stable capacity of 158 mA h g-1 for 2000 cycles, which translates into an average

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capacity decay of 0.006 % per cycle. After cycling at 1000 mA g-1 for 2000 cycles, the CNFF

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electrode is able to maintain a capacity of 141 mA h g-1 at a current density of 2000 mA g-1 for

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another 1500 cycles and a capacity of 122 mA h g-1 at a current density of 5000 mA g-1 for an

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additional 1000 cycles. Through the electrode reaction kinetic analysis, a surface induced

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capacitive process and diffusion controlled process were proposed to be the mechanism for the

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charge storage. The 3D porous carbon foam derived from BC is beneficial to enhancing the

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surface area, electrolyte transport, and charge storage.24 This work will open new opportunities

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for developing high-performance and cost-effective energy storage materials from sustainable

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biomaterials.

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Scheme 1. a) Schematic diagram of assembling CNFF freestanding electrode into potassium ion

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half-cell with a potassium metal counter electrode. b) Schematic diagram of potassium ion

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storage in CNFF surface structure. c-d) Schematic of the CNFF electrode’s high compressibility.

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e) Schematic of electron transfer and potassium ions storage in CNFF electrode.

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Results and Discussion

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Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were

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employed to inspect the morphology of BC aerogel and CNFF. BC is a homopolysaccharide with

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a high molecular weight, with each molecule consisting of β-1,4-anhydro-ᴅ-glucopyranose units

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(Figure S1a). BC can be generated by a cost-effective acetobacter xylinum large-scale

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fermentation process (Figure 1a and Figure S1b). Figure 1b and Figure S2 are SEM images of

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BC aerogel. The large piece of BC hydrogel was cut into rectangular shape pellicles (Figure 1c),

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followed by freeze-drying process to obtain the BC aerogel. The CNFF was then obtained by

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pyrolysis of BC aerogel at 1000 oC under N2 atmosphere. The CNFF product exhibits a

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hierarchical porous and ultrafine 3D nanofibrillar reticulated structure (Figure 1d). After the

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carbonization treatment, a high-magnification SEM image is used to indicate that the porous 3D

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network structure of the BC aerogel is maintained, along with large numbers of junctions and

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nanofibers with a diameter between 10-30 nm (Figure 1e). Hierarchical pores, necessary for

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trapping potassium ions, were generated between the fibers when the CNFF was compressed in

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the battery (Figure 1f). The TEM image of CNFF (Figure 1g) further confirms the fibrous

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structure which could enable fast electron and ion transport along 3D directions. The TEM image

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of higher magnification (Figure 1h and Figure S3) shows lots of nanopores on the surface of the

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carbonized nanofibers, which are beneficial for absorbing the potassium ions. The first level pore

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is micropores on the carbon nanofiber, Figure S3a-c. The second level pore is micro- and 5 ACS Paragon Plus Environment

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mesopores between the fibers, Figure S3 d-f. High resolution TEM (HRTEM) image reveals a

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disordered pattern with localized short-range order (Figure 1i and Figure S4). The interlayer

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spacing of (d002) was measured to be 0.38 ± 0.01 nm which is larger than that of graphite (0.34

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nm). The large interlayer spacing implies a potential to accommodate a certain amount of

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potassium ions during charge and discharge. The high angle annular dark field scanning TEM

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and elemental mapping images clearly reveal the distributions of C in the CNFF (Figures S5).

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Figure 1. a) A large piece of purified BC hydrogel with fiber content of ~ 0.5 wt% is generated

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by a cost-effective acetobacter xylinum fermentation process in large-scale. b) SEM images of

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original BC aerogel. c) Schematic diagram of preparation of CNFF. d) SEM image of CNFF,

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showing a porous and fine 3D network structure. e) High-magnification SEM image of CNFF. f)

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High-magnification SEM image of carbon nanofibers. g) TEM image of CNFF. h) High-

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magnification TEM image of CNFF with red dotted circle in (h) showing the porous structure. i)

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HR-TEM image of CNFF. (Northeastern University seal is reproduced with permission.)


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Stress-strain curves, x-ray diffraction (XRD), N2 adsorption-desorption isotherms and

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Raman spectra were used to further investigate the structure and composition of CNFF. A piece

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of CNFF with dimensions of 2.4 × 1.3 × 0.6 cm3 (length × width × height) weighs 9.96 mg

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(Figure S6a and S6b). Thus, it can stand on the top of a flower stably (Figure 2a). It is

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noteworthy that the CNFF is fire resistant when exposed to the flames from ethanol. No volume

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shrinkage of CNFF is observed after repeated exposures to flames, and its morphology and

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inherent 3D porous structure remain the same (Figure S7). Mechanically, CNFF is highly elastic

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and flexible. As shown in Figure 2b, CNFF can withstand a manual compression of up to 90 %

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volume reduction and still recover its original volume without any fractures, proving the material

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is elastic and robust. In the stress-strain curve, two characteristic regions can be recognized in the

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loading process (εmaxima = 90 %) a linear elastic region of ε < 70 % due to the bending of

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nanofibers and the elastic buckling of nanofibrous pores, and a densification region of ε > 70 %

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due to complete collapse. The stresses remain above zero until ε = 0 in the unloading process,

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suggesting complete volume recovery without deformations. When the CNFF is compressed to

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90 % volume reduction, it has a very low compressive stress of 13.8 KPa owing to highly porous

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and compressible structure. Figure 2c displays the Raman spectroscopy analysis for CNFF,

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which exhibits the two peaks at 1361 and 1591 cm-1 assigned to the D band and the G band of

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carbon, respectively. The degree of graphitic disordering ID/IG is 0.85 for CNFF. The obviously

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broadened diffraction (002) peak in the XRD pattern at 2θ = 23.59° is shown in Figure 2d.

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According to the Bragg’s law, the interlayer spacing of CNFF is ≈ 0.38 nm, which is larger than

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the d-spacing value of the (002) plane of graphite (0.33 nm). The specific surface area and pore

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size distribution of the CNFF were further investigated by nitrogen adsorption-desorption

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isotherms. The isotherm curve exhibits an obvious volume jump at very low relative pressure due


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to micropores filling, and the pronounced hysteresis loop reveals the majority of mesopores

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(Figure 2e). Based on the BET test, the CNFF possesses a high specific surface area of 778.75

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m2 g-1. The peaks for the micropores and mesopores dominate the chart of pore size distribution,

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with the micropores accounting for 53.32 % of the total surface area, as shown in Figure 2f. The

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percolated 3D network structures and the large amount of the micropores inside CNFF facilitate

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the rapid transport of electrons and ions, which is significant for the storage of potassium ions in

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the PIBs. Meanwhile, the cost analysis of the CNFF electrode with commercial carbon foam and

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graphene foam are presented in Table S1.


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Figure 2. a) Photograph of the CNFF standing on a flower, indicating its foam-like property. b)

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Compressive stress-strain curves of loading-unloading cycle at a strain of 90 % of the CNFF.

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The insets in b) are the sequential photographs of the CNFF during the compression process. c)


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Raman spectroscopy of CNFF. d) XRD pattern of CNFF. e) Representative nitrogen adsorption-

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desorption isotherm curve of CNFF. f) Pore size distribution of the CNFF electrode.

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In Figure 3, the detailed electrochemical characteristics of the CNFF were presented.

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Typically, cyclic voltammetry (CV) analysis is applied to get the deep understanding into unique

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surface-driven dominated potassium ion storage behavior. Figure 3a shows the CV curves of the

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CNFF/potassium half cells in the voltage range of 0.01 V - 2.80 V (vs. K+/K) at a scan rate of 0.1

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mV s-1. The broad reduction peak below 1.0 V on the 1st cycle is due to the formation of solid

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electrolyte interphase (SEI) film on the CNFF electrode.25 Furthermore, the CV curves from the

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2nd cycle to the 5th cycle are very comparable, indicating excellent reversibility.

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Moreover, according to the following Equation (1), two kinds of charge storage mechanism

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of the capacitive effects (k1v) and diffusion controlled (k2v1/2) contributions can be identified by

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CV curves analysis (Figure 3b):3, 26

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𝒊(𝑽) = 𝒌𝟏𝒗 + 𝒌𝟐𝒗𝟏/𝟐

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or

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𝒊(𝑽) 𝒗𝟏/𝟐 = 𝒌𝟏𝒗𝟏/𝟐 + 𝒌𝟐

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where k1 and k2 are constants, i is the current (A) at a fixed potential and ν is the sweep rate (mV

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s-1). According to the Equation (2), as shown in Figure S8, the slope obtained by fitting the line

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represents k1, and the resulting intercept represents k2. Figure 3c and Figure S9 show the CV

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curves analysis at various sweep rates from 0.2 mV s-1 to 1.0 mV s-1. Among the CV curves, the

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capacitive-controlled region marked as blue and the diffusion-controlled region marked as red.

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The capacitive-controlled contribution is 51% at a low scan rate of 0.2 mV s-1. The proportions

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of capacitive contribution increased gradually with the sweep rate and reach up to 68% at a high

(1)

(2)


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scan rate of 1.0 mV s-1 (Figure 3d). This phenomenon further confirmed that the capacitive- and

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diffusion-controlled are two potassium ion storage mechanisms in CNFF.27 The adsorption of the

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potassium ions on the CNFF electrode, caused by the large specific area and rich ion trapping

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pores. Meanwhile the steady contribution of the adsorptive mechanism (double-layer capacitance

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effect) significantly enhances the overall capacity of CNFF based PIBs.

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In order to evaluate the charge transfer resistance and ion diffusion of CNFF electrode after

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1st, 50th, 500th, 1000th cycles, the electrochemical impedance spectroscopy (EIS) analysis was

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employed. As shown in Figure 3e, two regions are defined at the Nyquist plots: 1) the semicircle

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in high frequency to medium frequency region; and 2) the Warburg line in low frequency region.

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The semicircle represents the charge transfer resistance (Rct) and the sloping line corresponds to

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the ion diffusion.28 It can be found that the Rct continuously decreases from 2037 Ω for initial

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cycle to 1531 Ω for the 50th cycle and continues to decrease to 55 Ω and 46 Ω for the 500th and

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1000th cycle, respectively (Table S2). It suggests that both the charge transfer resistance and the

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ion diffusion resistance of CNFF anode are reduced after cycling. This unique behavior can be

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explained as the “self-activating” process.28 The bode plot between the phase angles and the

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frequencies of PIBs are shown in Figure 3f. The characteristic frequency ƒ0 (- 45° phase angle)

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increases from 5.8 Hz (1st cycle) to 25 Hz (1000th cycle). Therefore, the corresponding relaxation

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time constant τ0, which was derived from reciprocal of frequency, is largely shortened from 0.17

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s (1st cycle) to 0.04 s (1000th cycle), suggesting the accelerating electrochemical response.

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Figure 3. Electrochemical kinetic analysis of potassium ions storage behavior of CNFF

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electrodes. a) CV curves (1st to 5th cycles) obtained at the scan rate of 0.1 mV s-1. b) CV curves

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obtained at the scan rates of 0.2 mV s-1, 0.4 mV s-1, 0.6 mV s-1, 0.8 mV s-1 and 1.0 mV s-1. c)

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Capacitive charge storage contributions at scan rates of 0.2 mV s-1. d) Contribution ratios of

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capacitive and diffusion capacities at various scan rates. e) Nyquist plots of CNFF anode after

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different cycles. Solid line is simulation data. The equivalent circuit model is shown in Figure

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S10. f) Bode plot of CNFF anode.

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The CNFF was tested as an anode material in half cells to illustrate its potential for PIBs.

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Due to its unique structure and good electronic conductivity, foam was used directly as the

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working anode without a current collector, conductive additive, and binder. The rate capability of

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the CNFF electrode is described in Figure 4a-b. The reversible capacity of the electrode was 240,

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236, 214, 202, 181, and 164 mAh g-1 at the current density of 50, 80, 100, 200, 500, and 1000

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mA g-1, respectively. More importantly, after cycling at high current densities, the electrode was

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able to maintain a reversible capacity of 230 mAh g-1 at a lower current density of 80 mA g-1. 12 ACS Paragon Plus Environment

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The initial charge and discharge curves are displayed separately in Figure S11, from which we

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can see CNFF with high initial capacity shows a large irreversible capacity associated with SEI

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formation in the first cycle, indicating that the electrochemical behavior of CNFF is strongly

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related to electrode’s high surface area.25 In the future, we will use different approaches to

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further improve the first Columbic efficiency, including conducting pre-potassiation of electrode,

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constructing composite electrode, and reducing the specific surface area of the electrode. After

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the first cycle, no obvious plateau is observed during the charge/discharge cycle. The loss of

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reaction plateau can be explained by two possible reasons. One reason is that a large number of

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potassium ions experience adsorption/desorption on the micro/mesopores of CNFF, leading to

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the inconspicuous voltage plateau. The other reason is that the larger size of potassium ions

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could cause sluggish kinetics of the chemical reaction.27 When compared to the rate performance

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of freestanding graphene film (FGF) based PIB anodes, the rate capability of CNFF based PIBs

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has a much higher at various current densities. Although a capacity of 148 mAh g-1 is achieved

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for FGF based PIB under the current density of 50 mA g-1, the capacity decays rapidly with the

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increase of current density. There is no capacity contribution from FGF after current density of

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200 mA g-1 (Figure 4b). This means that the very limited interlayer spacing and very limited

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pore structure of FGF cannot potassiate or de-potassiate.29 Upon the various current density, the

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outstanding cycling capability of CNFF further proves its remarkable reversibility and stability.

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After 100 cycles at a current density of 200 mA g-1, the potassiation capacity remains 168 mA h

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g-1 (Figure 4c). When the current density is further increased to 500 mA g-1, the capacity

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retention is 156 mA h g-1 after 500 cycles (Figure 4d). After the above cycling, the battery was

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left alone for 10 days and then was tested at a current density of 500 mA g-1. It can be seen that

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the performance of same battery still achieves a capacity of 143 mA h g-1 after another 500


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cycles (Figure S12). In addition, the batteries were also worked at the current density of 1000

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mA g-1 for 2000 cycles to test the long term cycling stability. From the Figure 4e, it can be

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clearly seen that a reversible capacity of 158 mA h g-1 is obtained upon cycling, which has an

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average capacity decay of 0.006 % per cycle. After finishing the first 2000 cycles at 1000 mA g-1,

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the battery was tested under the high current densities of 2000 mA g-1 for 1500 cycles and 5000

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mA g-1 for 1000 cycles, respectively. The capacity of CNFF electrode reachs to 141 mA h g-1 at

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2000 mA g-1 after 1500 cycles and 122 mA h g-1 after another 1000 cycles at 5000 mA g-1,

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respectively.

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The electrochemical performance of CNFF based PIBs is more attractive than most of the

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state-of-art of carbon and metal material-based PIB anodes (compared in Table S3). From the

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above experimental results, a large number of pore structures and the fibrous structure present

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the synergistic effect for boosting the electrochemical performance. The superior performance is

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attributed to the following reasons. First, the micropores which account for more than 50% of the

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total surface area on the carbon nanofiber can act as reservoirs for storage of potassium ions.

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Second, under the compression of 1D nanofibers, the large amount of micro/mesopores between

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the nanofibers can also store potassium ions. The PIB half-cell is able to lighten a red light-

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emitting diode (working voltage 1.9-2.2 V, Figure S13) after fully charged. Figure S14 are SEM

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images (side view and top view) after the battery was cycled 1000 times at a current density of

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500 mA g-1, from which we can see the structure of carbon nanofiber is preserved and contains a

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large number of pore structures. These images evidence that the structure of carbon electrode is

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well maintained under compression, which is crucial for electron transport and battery cycling

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stability. Hence, the compressibility of CNFF is a critical factor for cycling stability.


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Figure 4. a) The charge-discharge profiles of CNFF at various current densities. b) Rate

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capability of CNFF and free-standing graphene film at current densities from 50 to 1000 mA g-1

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for PIB. c) Cycling performances of CNFF at current density of 200 mA g-1. d) Cycling

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performances of CNFF at current density of 500 mA g-1. e) Long term cycling performances of

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CNFF anode at different current density of 1000 mA g-1, 2000 mA g-1 and 5000 mA g-1. The

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battery rested for 10 days before changing current density.

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Conclusions

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In conclusion, a compressible, hierarchical porous, and high-performance BC derived CNFF was

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developed in an economical and eco-friendly way for the freestanding anode of PIBs.

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Electrochemical tests showed that the CNFF based PIBs exhibit high stable capacity of 240 mAh

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g-1 at current density of 50 mA g-1, and a capacity of 122 mAh g-1 at high current density of 5000

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mA g-1. Meanwhile, for the cycling performances, the battery at current density of 1000 mA g-1

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maintains a highly reversible capacity of 158 mA h g-1 for more than 2000 cycles with only

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0.006 % capacity decay per cycle. This performance is superior to most carbon-based electrodes

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currently in PIBs. The high reversible capacity and excellent cycle capability can be attributed to

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three main reasons. The first is the hierarchical pores of the structure. The micropores on carbon

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nanofiber and the micro/mesopores between the fibers provide an abundance of effective sites

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for potassium ion storage. The second reason is that the 3D carbon foam not only provides a

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highly conductive reticulated network for electron transport, but also supplies sufficient space for

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the transportation of electrolyte through the porous structure. The third and final reason is that

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the quasi-amorphous carbon possesses larger interlayer spacing in a shorter range compared to

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graphite, indicating the potential to accommodate a certain amount of potassium ions during

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charge and discharge. This work will hopefully encourage further research for cost-effective and

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eco-friendly materials used for potassium ion batteries and other battery energy storage systems.

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ASSOCIATED CONTENT

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Supporting Information


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Additional experimental and figures including SEM results, cycling performance and

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comparison table.

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AUTHOR INFORMATION

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Corresponding Author

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*E-mail: [email protected]

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ORCID:

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Hongli Zhu: 0000-0003-1733-4333

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Hongyan Li: 0000-0002-7073-5198

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Author Contributions

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H. Li and Z. Cheng contributed equally to this work.

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Notes

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The authors declare no competing financial interest.

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ACKNOWLEDGMENTS

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H. Zhu acknowledges the Tier 1 support from Northeastern University and Financial Start-up

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support. The authors thank the Kostas Research Institute at Northeastern University for the use

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of facilities. The authors acknowledge the use of XRD facilities under the auspices of the

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Northeastern University Center for Renewable Energy Technology (NUCRET). The authors

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thank Dr. Xiulei Ji and Heng Jiang from Oregon State University for the BET surface area test.


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We acknowledge Dr. Sandra Shefelbine in Mechanical and Industrial Engineering for sharing the

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Instron 5565A testing machine and Dr. Lei Zhang for helping with the compression test.

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References

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(1) Zhao, J.; Zhou, G.; Yan, K.; Xie, J.; Li, Y.; Liao, L.; Jin, Y.; Liu, K.; Hsu, P. C.; Wang, J.

313

Nat. Nanotechnol. 2017, 12, 10, 993-999.

314

(2) Olivetti, E. A.; Ceder, G.; Gaustad, G. G.; Fu, X. Joule 2017, 1, 229-243.

315

(3) Xu, Y.; Zhang, C.; Zhou, M.; Fu, Q.; Zhao, C.; Wu, M.; Lei, Y. Nat. Commun. 2018, 9,

316

1720-1730.

317

(4) Chen, Y.; Luo, W.; Carter, M.; Zhou, L.; Dai, J.; Fu, K.; Lacey, S.; Li, T.; Wan, J.; Han, X.

318

Nano Energy 2015, 18, 205-211.

319

(5) Luo, W.; Wan, J.; Ozdemir, B.; Bao, W.; Chen, Y.; Dai, J.; Lin, H.; Xu, Y.; Gu, F.; Barone,

320

V.; Hu, L. Nano Lett. 2015, 15, 7671-7677.

321

(6) Jian, Z.; Luo, W.; Ji, X. J. Am. Chem. Soc. 2015, 137, 11566-11569.

322

(7) Jian, Z.; Xing, Z.; Bommier, C.; Li, Z.; Ji, X. Adv. Energy Mater. 2016, 6, 1501874.

323

(8) Lee, J. H.; Ali, G.; Kim, D. H.; Chung, K. Y. Adv. Energy Mater. 2017, 7, 1601491.

324

(9) Zeng, C.; Xie, F.; Yang, X.; Jaroniec, M.; Zhang, L.; Qiao, S. Z. Angew. Chem., Int. Ed.

325

2018, 57, 8540-8544.

326

(10) Zhang, W.; Mao, J.; Li, S.; Chen, Z.; Guo, Z. J. Am. Chem. Soc. 2017, 139, 3316-3319.

327

(11) Chen, C.; Wang, Z.; Zhang, B.; Miao, L.; Cai, J.; Peng, L.; Huang, Y.; Jiang, J.; Huang, Y.;

328

Zhang, L. Energy Storage Materials 2017, 8, 161-168.

329

(12) Ren, X.; Zhao, Q.; McCulloch, W. D.; Wu, Y. Nano Res. 2017, 10, 1313-1321.

330

(13) Yang, C.; Feng, J.; Lv, F.; Zhou, J.; Lin, C.; Wang, K.; Zhang, Y.; Yang, Y.; Wang, W.; Li,

331

J. Adv.Mater. 2018, 30, 1800036. 18 ACS Paragon Plus Environment

Page 18 of 20

Page 19 of 20 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

Nano Letters

332

(14) Li, D.; Zhu, M.; Chen, L.; Chen, L.; Zhai, W.; Ai, Q.; Hou, G.; Sun, Q.; Liu, Y.; Liang, Z.

333

Adv. Mater. Interfaces 2018, 5, 1800606.

334

(15) Chen, M.; Wang, W.; Liang, X.; Gong, S.; Liu, J.; Wang, Q.; Guo, S.; Yang, H. Adv.

335

Energy Mater. 2018, 8, 1800171.

336

(16) Wei, Z.; Wang, D.; Li, M.; Gao, Y.; Wang, C.; Chen, G.; Du, F. Adv. Energy Mater.2018,

337

10, 1801102.

338

(17) Wu, Z. Y.; Liang, H. W.; Chen, L. F.; Hu, B. C.; Yu, S. H. Acc. Chem. Res. 2015, 49, 96-

339

105.

340

(18) Vasconcelos, N. F.; Feitosa, J. P. A.; da Gama, F. M. P.; Morais, J. P. S.; Andrade, F. K.; de

341

Souza, M. d. S. M.; de Freitas Rosa, M. Carbohyd. Polym. 2017, 155, 425-431.

342

(19) Shen, X.; Shamshina, J. L.; Berton, P.; Gurau, G.; Rogers, R. D. Green Chem. 2016, 18, 53-

343

75.

344

(20) Cheng, Z.; Yang, R.; Liu, X.; Liu, X.; Chen, H. Bioresource Technol. 2017, 234, 8-14.

345

(21) Håkansson, K. M.; Fall, A. B.; Lundell, F.; Yu, S.; Krywka, C.; Roth, S. V.; Santoro, G.;

346

Kvick, M.; Wittberg, L. P.; Wågberg, L. Nat. Commun. 2014, 5, 4018.

347

(22) Wang, S.; Jiang, F.; Xu, X.; Kuang, Y.; Fu, K.; Hitz, E.; Hu, L. Adv. Mater. 2017, 29,

348

1702498.

349

(23) Liang, H. W.; Guan, Q. F.; Song, L. T.; Yao, H. B.; Lei, X.; Yu, S. H. NPG Asia Mater.

350

2012, 4, (6), e19.

351

(24) Wu, Z. Y.; Liang, H. W.; Hu, B. C.; Yu, S. H. Angew. Chem., Int. Ed. 2018,

352

DOI.org/10.1002/ange.201802663.

353

(25) Wang, Y.; Wang, Z.; Chen, Y.; Zhang, H.; Yousaf, M.; Wu, H.; Zou, M.; Cao, A.; Han, R.

354

P. Adv. Mater. 2018, 30, 1802074.


Nano Letters 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

355

(26) Brezesinski, T.; Wang, J.; Tolbert, S. H.; Dunn, B. Nat. Mater. 2010, 9, (2), 146-151.

356

(27) Wang, W.; Zhou, J.; Wang, Z.; Zhao, L.; Li, P.; Yang, Y.; Yang, C.; Huang, H.; Guo, S.

357

Adv. Energy Mater. 2018, 8, 1701648.

358

(28) Wang, G.; Yu, M.; Wang, J.; Li, D.; Tan, D.; Löffler, M.; Zhuang, X.; Müllen, K.; Feng, X.

359

Adv. Mater. 2018, 30, 1800533.

360

(29) Bin, D. S.; Lin, X. J.; Sun, Y. G.; Xu, Y. S.; Zhang, K.; Cao, A. M.; Wan, L. J. Am. Chem.

361

Soc. 2018, 140, 7127-7134.

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