Bacterial-Derived, Compressible, and Hierarchical Porous Carbon for

Subscriber access provided by The University of Texas at El Paso (UTEP)

Communication

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

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 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

1

Bacterial-Derived, Compressible and Hierarchical Porous Carbon for High

2

Performance Potassium-ion Batteries

3

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

4 5

1Department

6

Massachusetts 02115, United States.

7

*Corresponding author: Dr. Hongli Zhu

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

8 9

Abstract

10

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

11

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

12

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

13

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

14

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

15

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

16

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

17

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

18

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

19

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

20

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

21

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

22

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

23

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

24

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

25

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

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

Page 2 of 20

26

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

27

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

28

structure, compressible carbon foam

29 30

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

31

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

32

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

33

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

34

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

35

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

36

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

37

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

38

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

39

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

40

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

41

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

42

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

43

electrochemical performance of these batteries.

6

hard carbon

44

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

45

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

46

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

47

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

48

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

49

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

Page 3 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

50

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

51

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

52

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

53

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

54

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

55

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

56

textile industry, biomedical fields, etc.22, 23

21

good biodegradability, and biocompatibility,

57

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

58

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

59

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

60

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

61

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

62

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

63

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

64

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

65

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

66

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

67

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

68

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

69

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

70

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

71

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

72

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

3 ACS Paragon Plus Environment

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

73

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

74

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

75

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

76

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

77

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

78

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

79

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

80

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

81

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

82

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

83

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

84

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

85

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

86

biomaterials.

87


Page 4 of 20

Page 5 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

88

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

89

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

90

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

91

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

92

Results and Discussion

93

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

94

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

95

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

96

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

97

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

98

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

99

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

100

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

101

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

102

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

103

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

104

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

105

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

106

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

107

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

108

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

109

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

110

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

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

111

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

112

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

113

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

114

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

115

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

116

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

117 118

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

119

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

120

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

121

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

122

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

123

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

124

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


Page 6 of 20

Page 7 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

125

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

126

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

127

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

128

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

129

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

130

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

131

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

132

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

133

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

134

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

135

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

136

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

137

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

138

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

139

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

140

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

141

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

142

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

143

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

144

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

145

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

146

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

147

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


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

148

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

149

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

150

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

151

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

152

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

153

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

154

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

155

graphene foam are presented in Table S1.


Page 8 of 20

Page 9 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

156 157

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

158

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

159

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


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

160

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

161

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

162

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

163

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

164

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

165

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

166

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

167

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

168

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

169

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

170

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

171

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

172

𝒊(𝑽) = 𝒌𝟏𝒗 + 𝒌𝟐𝒗𝟏/𝟐

173

or

174

𝒊(𝑽) 𝒗𝟏/𝟐 = 𝒌𝟏𝒗𝟏/𝟐 + 𝒌𝟐

175

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

176

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

177

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

178

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

179

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

180

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

181

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

(1)

(2)


Page 10 of 20

Page 11 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

182

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

183

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

184

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

185

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

186

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

187

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

188

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

189

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

190

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

191

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

192

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

193

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

194

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

195

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

196

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

197

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

198

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

199

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

200

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

201


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

202 203

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

204

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

205

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)

206

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

207

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

208

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

209

S10. f) Bode plot of CNFF anode.

210

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

211

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

212

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

213

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

214

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

215

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

216

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

Page 12 of 20

Page 13 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

217

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

218

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

219

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

220

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

221

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

222

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

223

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

224

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

225

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

226

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

227

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

228

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

229

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

230

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

231

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

232

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

233

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

234

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

235

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

236

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

237

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

238

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

239

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


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

240

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

241

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

242

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

243

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

244

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

245

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

246

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

247

respectively.

248

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

249

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

250

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

251

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

252

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

253

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

254

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

255

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

256

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

257

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

258

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

259

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

260

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

261

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


Page 14 of 20

Page 15 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

262 263

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

264

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

265

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

266

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

267

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

268

battery rested for 10 days before changing current density.

269


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

270 271

Conclusions

272

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

273

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

274

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

275

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

276

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

277

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

278

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

279

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

280

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

281

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

282

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

283

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

284

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

285

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

286

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

287

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

288

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

289

ASSOCIATED CONTENT

290

Supporting Information


Page 16 of 20

Page 17 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

291

Additional experimental and figures including SEM results, cycling performance and

292

comparison table.

293

AUTHOR INFORMATION

294

Corresponding Author

295

*E-mail: [email protected]

296

ORCID:

297

Hongli Zhu: 0000-0003-1733-4333

298

Hongyan Li: 0000-0002-7073-5198

299

Author Contributions

300

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

301

Notes

302

The authors declare no competing financial interest.

303

ACKNOWLEDGMENTS

304

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

305

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

306

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

307

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

308

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


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

309

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

310

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

311

References

312

(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.

362 363


Page 20 of 20

Bacterial-Derived, Compressible, and Hierarchical Porous Carbon for

Recommend Documents