In Situ Carbonized Cellulose-Based Hybrid Film as Flexible Paper

Subscriber access provided by NEW MEXICO STATE UNIV

Letter

In-Situ Carbonized Cellulose-Based Hybrid Film as Flexible Paper-Anode for Lithium-Ion Batteries Shaomei Cao, Xin Feng, Yuanyuan Song, Hongjiang Liu, Miao Miao, Jianhui Fang, and Liyi Shi ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b10648 • Publication Date (Web): 03 Jan 2016 Downloaded from http://pubs.acs.org on January 4, 2016

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 free 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 accessible to all readers and 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.

ACS Applied Materials & Interfaces 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 23

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

ACS Applied Materials & Interfaces

In-Situ Carbonized Cellulose-Based Hybrid Film as Flexible Paper-Anode for Lithium-Ion Batteries Shaomei Cao†, Xin Feng*,†,Yuanyuan Song║, Hongjiang Liu‡, Miao Miao†, Jianhui Fang‡, Liyi Shi†

†

Research Center of Nano Science and Technology, Shanghai University, Shanghai 200444, P. R.

China

‡

Department of Chemistry, College of Science, Shanghai University, Shanghai 200444, P. R.

China

║

School of Materials Sciences and Engineering, Shanghai University, Shanghai 200444, P. R.

China.

KEYWORDS: Paper-anode; Cellulose nanofiber; In-situ Carbonization; Super rate performance; Lithium-ion batteries

ABSTRACT: Flexible free-standing carbonized cellulose-based hybrid film is integrately designed and served both as paper-anode and as lightweight current collector for lithium-ion batteries. The well-supported heterogeneous nano-architecture is constructed from Li4Ti5O12 (LTO), carbonized cellulose nanofiber (C-CNF) and carbon nanotubes (CNTs) using by a pressured extrusion papermaking method followed by in-situ carbonization under argon atmospheres. The in-situ carbonization of CNF/CNT hybrid film immobilized with 1

ACS Paragon Plus Environment


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

uniform-dispersed LTO results in a dramatic improvement in the electrical conductivity and specific surface area, so that the carbonized paper-anode exhibits extraordinary rate and cycling performance compared to the paper-anode without carbonization. The flexible, lightweight, single-layer cellulose-based hybrid films after carbonization can be utilized as promising electrode materials for high performance, low cost, and environmentally friendly lithium-ion batteries.

2


Page 2 of 23

Page 3 of 23

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


With the excessive consumption of non-renewable resources in consumer electronics, the accumulation of discarded electronic waste has already caused serious environmental concerns.1 Recently, flexible lithium ion batteries (LIBs) have received considerable attention as a promising power source in the next-generation lightweight and wearable electronic devices, such as soft portable electronic products, roll-up displays, implantable biomedical devices, and conformable health-monitoring electronic skin.2 Hence, there exists a need to develop an up-scalable, low cost, environmentally friendly process for the sustainable mass production of flexible LIBs with high product recyclability. Within this context, the metal current collector (e.g. Cu and Al foil), fluorine-based binder and toxic organic solvent in typical LIBs should be progressively substituted for the integrated construction of green-type lightweight paper-electrodes. Carbon nanotubes (CNTs) with excellent chemical stability, low density, high electrical conductivity and mechanical flexibility were successfully utilized to assemble conductive thin films as current collectors to replace heavy metals in the fabrication of lightweight LIBs or supercapacitors (SCs)3,4. Due to its biodegradability, lightweight, high elastic modulus and low thermal expansion,5 cellulose nanofiber (CNF) extracted from abundant renewable native biomass has shown a significant promise as binders,6,7 separators,8,9 dispersants10,11 for electrochemical applications in LIBs. By incorporating of CNTs into the non-conductive CNF fibrous networks, the hybrid cellulose-based paper with excellent mechanical flexibility and enhanced electrochemically active can be used as flexible supports for loading active materials by various coating methods.12 In fairly recent works, self-standing CNF/CNT hybrid paper-electrodes or complete cells embedded electrochemical active materials, such as Si,13 Li4Ti5O1214 or LiFePO4,9 were successfully elaborated using a

3



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

conventional well-established papermaking route. Among the potential anode materials for LIBs, the cubic spinel Li4Ti5O12 (LTO) has attracted much attention for the evident advantages. LTO known as the “zero strain” material undergoes extremely small volumetric change (ca. 0.2%) during charge/discharge cycling15 and has a stable voltage plateau at approximately 1.56 V versus Li+/Li, which is free of the reductive electrolyte decomposition. However, LTO in the unlithiated state is electronically insulating because of the presence of Ti4+ with empty 3d orbitals and a large band gap of about 2 eV.16 So far, research efforts have been devoted to address the conductivity deficiency of pristine LTO according to component doping, morphology and structure modifications.17-19 Especially, the introduction of conducting materials (CNTs, carbon nanofiber, graphene, etc.) into LTO compositions is an effective strategy to improve the charge transfer kinetics in LTO electrodes.20-22 Jia et al.20combined nanostructured LTO with CNTs as flexible anodes for LIBs with superior rate performance and ultrastable cycling performance. The LTO-CNT composite anodes had a discharge capacity of 108 mAh·g−1 when discharged at super-high rates of 100 C, which was much higher than the corresponding capacity of 74 mAh· g−1 for the traditional LTO due to the improved conductivity. Zhang et al.22 developed LTO-carbon nanofiber composite anodes with significantly improved conductivity and Li ion diffusion coefficient. The LIBs electrodes delivered a remarkable capacity of 123 mAh· g−1 when charged/discharged at 15 C, which was much higher than 91 mAh· g−1 for those made from the neat LTO powders. As above mentioned, one-dimensional (1D) CNTs and carbon nanofiber have been proven to establish an efficient electron transfer and extensive conductive 3D networks in electrodes of LIBs at a much lower percolation threshold. At present, there is a trend of producing carbon nanofiber from natural substances for their abundant, easily attainable and nontoxic to

4


Page 4 of 23

Page 5 of 23

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


human.23 Herein, we developed a free-standing carbonized CNF-based hybrid film by using a pressured extrusion paper-making process and the subsequent low temperature carbonization. The conductive carbon nanofiber was obtained according to the in-situ carbonization of the previously formed LTO/CNF/CNT hybrid film using the CNF component as a carbon source. The single-layer paper-anode based on carbonized cellulose nanofiber (C-CNF), LTO and CNTs composites has a sufficiently electrical conductivity and enlarged specific surface area without destroying the mechanical integrity, which can distinctly improve the rate and cycle performance for the LIBs. The hybrid C-CNF and CNTs with interpenetrating fibrous structure synergistically served as an enhanced 3D porous conductive network and flexible building block for embedding LTO particles. In comparison with the previously reported dual-layer paper-electrodes using the CNF/CNT layer as a lightweight replacement for heavy metallic current collector,14 the single-layer LTO/C-CNF/CNT hybrid film with enhanced conductivity was rationally designed as both active material and current collector for LIBs paper-anode. Neither extra current collector nor fluorine-based binder is necessary in the single-layer paper-anode, so that the cost and overall weight of a LIB cell can be minimized. The flexible, lightweight, single-layer and free-standing LTO/C-CNF/CNT hybrid film with high conductivity, robust mechanical flexibility and high electrochemical performance will provide new feasibility for the eco-friendly production of flexible electrodes or complete LIBs for various applications including portable and wearable electronics. As is illustrated in Scheme 1, the LTO/CNF/CNT hybrid film with single-layer structure was fabricated by using a pressured extrusion papermaking method according to our previously

5



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

reported procedures14. The heterogeneous nano-architecture was constructed using LTO powders19 with particle size of 100-200 nm as active material, CNF24,25 with fiber diameter of 20-30 nm and aspect ratios of 20-200 as both building skeleton and bioresourced binder, and CNT with diameter of 30-50 nm and length of 5-12 µm as conductive enhancer, respectively. Subsequently, the LTO/CNF/CNT hybrid film was carbonized in a tube furnace under high purity argon flow at 400 °C for 2 h, and the flexible single-layer LTO/C-CNF/CNT paper-anode with high conductivity was ultimately obtained (see the Experimental section in ESI). The LTO/C-CNF/CNT paper-anode and the comparative LTO/CNF/CNT paper-anode without carbonization were denoted as LCC-A and LCC-U, respectively.

Scheme 1 Schematic illustration of preparation process of the flexible single-layer paper-electrode.

Thermogravimetry analysis (TGA) was performed to investigate thermal pyrolysis of the cellulose-based hybrid films. Fig. 1 demonstrates the thermal decomposition of LCC-U and LCC-A hybrid films under nitrogen and oxygen atmospheres, respectively. The TGA profile of LCC-U exhibits three stages of weight loss under nitrogen atmosphere (Fig. 1a). The first stage from room temperature to 220 °C with small weight loss of about 2 wt% is due to desorption of 6


Page 6 of 23

Page 7 of 23

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


adsorbed water. At the second stage from 220 °C to 370 °C with main weight loss of 18 wt%, CNF undergoes the carbonization process by dehydration depolymerisation and decomposition.44 The third stage with small weight loss of about 4 wt% from 370 °C to 800 °C is attributed to the degradation of the carbon residues and CNTs. The result indicates that cellulose pyrolysis almost completed at 400 °C. On the other hand, it is obvious from the TGA curve of LCC-A hybrid film under nitrogen atmosphere (Fig. 1a), only a slowly weight loss less than 4 wt% is detected from 20 °C to 800 °C, indicating the completely carbonization of cellulose. For comparative purposes, the TGA curves of the hybrid films under oxygen atmosphere were also presented (Fig. 1b), LCC-U hybrid film displays a significant weight loss owing to the decomposition of organic and carbonaceous materials between 200 °C and 800 °C with 65 wt% residual weights. For LCC-A, a larger weight loss of about 30% happens from 500 °C to 620 °C corresponding to the oxidation and vaporization of the carbonized products and CNTs, and the residual 70 wt% of the total mass can be inferred as LTO content in LCC-A.

Figure 1 TGA profiles of LCC-U and LCC-A under (a) nitrogen atmosphere and (b) oxygen atmosphere. X-ray diffraction (XRD) patterns and Raman spectra were investigated to determine the phase components in the hybrid films as shown in Fig. 2a and 2b, respectively. Figure 2a compares XRD patterns of LCC-U and LCC-A hybrid film. It is obviously observed that all the characteristic 7



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

peaks marked by asterisk in both LCC-U and LCC-A XRD patterns are indexed to the typical spinel structure of LTO (JCPDS Card 49-0207, green line). The spinel LTO with “zero-strain” characteristic is beneficial for staining stable structure during charge and discharge reactions15. In addition, more remarkable, the typical (101) and (002) characteristic peaks of cellulose I in LCC-U XRD patterns disappeared after carbonization, while a characteristic peak of carbon was clearly observed for LCC-A, revealing the occurrence of thermal pyrolysis of CNF and the achievement of resulting derivatives of carbon nanofiber. Furthermore, the Raman spectra of LCC-U and LCC-A were utilized to verify the structure characteristics of carbon nanomaterials (Fig. 2b). Besides the typical peaks of LTO, corresponding to the characteristic of the spinel structure,26 three distinctive peaks at 1350 cm−1 (D-band), 1580 cm−1 (G-band), and 2700 cm−1 (2D-band) for both LCC-U and LCC-A are attributed to the presence of CNTs and graphite. The G-band is the primary phonon arising from lattice stretching in C-C bonding in the graphitic plane, and D-band corresponds to the disorder and defects in the graphitic lattice. The LCC-A hybrid film shows a lower ID/IG ratio (0.915) than that of LCC-U (0.936), indicative of that a less amount of defect in the graphitic materials.27

Figure 2 (a) XRD patterns of LCC-U and LCC-A hybrid films; (b) Raman spectra of LCC-U and LCC-A hybrid films. The Brunauer-Emmett-Teller (BET) specific surface area and pore structure of LCC-U and 8


Page 8 of 23

Page 9 of 23

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


LCC-A hybrid films were measured with nitrogen isothermal adsorption-desorption analysis (Fig. 3a). The BET surface area of LCC-A is 69.9 m2·g-1 larger than that of 43.1 m2·g-1 for LCC-U. The corresponding Barrett-Joyner-Halenda (BJH) pore diameter is 3.42 nm and pore volume is 1.116 cm3·g-1 for LCC-A, which are larger than that of 2.19 nm and 0.684 cm3· g-1 for LCC-U. The enlarged surface area and pore volume can be ascribed to the removal of water from the cellulose during thermal carbonization.28 The porous network structure of LCC-A hybrid film with uniform mesopores provides more efficient transport channels for Li ion to their interior voids and increases electrode-electrolyte interfacial contact area, which is beneficial for high rate LIBs applications. The electronic conductivity of the hybrid films was investigated as shown in Fig. 3b. Commonly, LTO in unlithiated state is electronically insulating with the conductivity less than 10-13 S·cm-1.16 By embedding LTO particles into the interpenetrated CNF and CNTs fibrous network, self-standing hybrid film with high conductivity for flexible electrodes was ultimately achieved14, in which CNF provides interconnected channels for effective ion transport and CNTs provides the required electron transport pathways. The conductivity of LCC-U hybrid film is gradually decreased from 18.0 to 4.4 S·cm-1 as the LTO content increased to 80%. It should be noted that the conductivity of the LCC-A hybrid film is dramatically improved after in-situ carbonization, implying that carbon nanofiber derived from CNF intertwines with CNTs together to form a continuous carbonized conductive network. Consequently, the electrical conductivity of LCC-U improves from 4.38 to 8.42 S·cm-1 for LCC-A even the LTO additives increased to 80%. It was deduced that the interpenetrating carbonized conductive network combined with LTO to form a self-standing paper-anode suitable for high rate performance flexible electronic applications.

9



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

Figure 3 (a) Nitrogen adsorption-desorption isotherm (inset) and BJH pore size distribution of LCC-U and LCC-A hybrid films; (b) Electrical conductivity of the LCC-U and LCC-A hybrid films with different LTO contents. The surface morphologies and macroscopic homogeneity of the LCC-U and LCC-A hybrid films were observed by field emission scanning electron microscope (FESEM) images as shown in Fig. 4. Both LCC-U and LCC-A hybrid films with diameter of ca. 49 mm have smooth and highly glossy surfaces (inset), while the surface of LCC-A becomes more uniform and compact than that of LCC-U (Fig. 4a, 4d). It can be demonstrated that well-consolidated network structure consisting of LTO, C-CNF and CNT was heterogeneously constructed after in-situ carbonization. The different sizes of CNF and CNTs tangled together to form a stable nano-architecture for paper-electrodes with high porosity and integrity as shown in Fig. 4b, 4c and 4e, 4f. Irregular particulate-shaped LTO with a particle size ranging from 100 nm to 200 nm was anchored into the CNTs/CNF and CNTs/C-CNF intertwined network matrixes, respectively. So the aggregation of LTO particles was substantially decreased. CNTs can be obviously observed in FESEM images (Fig. 4b~4f). On the other hand, individual CNF or C-CNF is difficult to be identified for their lower crystalline degree than that of LTO and CNT29. The phenomenon is also verified from TEM image of LTO/CNF/CNT (see Supporting Information, Fig. S1). The uniform dispersibility of LTO particles and the 3D interfibre voids was ascribed to the effects of CNF as a structure controlling

10


Page 10 of 23

Page 11 of 23

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


dispersant. The expanded interfibre spacing will facilitate ion diffusivity and therefore provide large reaction sites for electrochemical process.

Figure 4 (a-c) FESEM images of LCC-U at different magnifications, inset is the digital photos of LCC-U hybrid film; (d-f) FESEM images of LCC-A at different magnifications, inset is the digital photos of LCC-A hybrid film. Fig. 5 compares the cross-sectional micro-topographies of LCC-U and LCC-A hybrid films. The thicknesses of LCC-U and LCC-A with single layer were measured to be as 26.8 and 25.2 µm (Fig 5a, 5c), respectively. The slight contraction of LCC-A hybrid film in thickness might be caused by the thermal carbonization process. The flat surface of the hybrid films was due to the tight entanglement of highly flexible CNF and CNT during pressured extrusion. It is further seen from the zoomed-in images (Fig. 5b, 5d) that the cross section of LCC-A hybrid film after carbonization still reserves regular configuration of fibrous network and particulate LTO, implying that single-layer LCC-A hybrid film is suitable for the flexible self-standing paper-anode with sufficiently electrical conductivity and excellent mechanical robustness. The physically compact hybrid film with CNTs junctions soldered by carbon nanofiber is beneficial to reduce inter-nanotubes/nanofibers contact resistance and greatly improve the electrical conductivity,29 thus the single-layer LCC-A hybrid film was rationally designed as both active material and 11



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

current collector for LIBs anode, compared to the previously reported dual-layer paper-electrodes with CNT/CNF as a lightweight current collector.13,14

Figure 5 (a,b) FESEM images of the cross section of LCC-U at different magnifications; (c,d) FESEM images of the cross section of LCC-A at different magnifications. The electrochemical performance of the LCC-U and LCC-A hybrid films as paper-anodes was investigated in the coin half-cells used Li-foil as counter electrode. Fig. 6a and 6b compare the galvanostatic charge/discharge curves of LCC-U and LCC-A at various current rates from 0.5 C to 10 C. For LCC-U, with the current rate increases from 0.5 C to 10 C, the charge/discharge capacity decreases rapidly from about 166 to 78 mAh· g-1, and the charge/discharge voltage plateau deviates from 1.60/1.55V for the electrode polarization at the large current. Whereas for LCC-A, all the galvanostatic charge/discharge curves show a long flat platform at a stable potential plateau, and the specific capacity decreases from about 160 to 140 mAh·g-1 when current rate increases from 0.5 C to 10 C, remaining 87.5% of the initial capacity of 0.5 C. The rate capability of LCC-U and LCC-A as a function of the cycle number at current rate of 0.5 C, 1 C, 2 C, 5 C and 10 C was further compared in Fig. 6c. At low current rate of 0.5 C and 1 C, the 12


Page 12 of 23

Page 13 of 23

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


capacity of LCC-U is slightly higher than that of LCC-A. But with the current rate gradually increasing to 2 C, 5 C and 10 C, the capacity of LCC-A is markedly higher than that of LCC-U. This indicates that the LCC-A paper-anode with better reaction kinetics is more suitable for high rate LIB applications after carbonization. Cycling performance of LCC-U and LCC-A at current rate of 5 C was further shown in Fig. 6d. It is obviously observed that the specific capacity for LCC-A remains 143 mAh·g-1 with negligible decay even after 1000 cycles, showing stable cycling performance and higher capacity retention ratio than those of LCC-U. On the other hand, the specific capacity for LCC-U decreases from 120 to 55 mAh·g-1 at the same conditions, with a capacity retention of 45.8%. The coulombic efficiency for both the paper-anodes is nearly 100%. It can be clearly concluded that the LCC-A paper-anode has the extraordinary rate and cycling performance superior to LCC-U paper-anode.

Figure 6 (a) Galvanostatic charge/discharge curves of LCC-U paper-anode; (b) Galvanostatic charge/discharge curves of LCC-A paper-anode; (c) Rate performance of LCC-U and LCC-A at

13



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

different current rates; (d) Cycling performance of the LCC-U and LCC-A at current rate of 5 C (The left shows the specific capacity and the right shows the coulombic efficiency). Cyclic voltammetry (CV) technique was employed to test the electrochemical process of the LCC-U and LCC-A paper-anodes as shown in Fig. 7. The shapes of redox peaks in a CV curve reflected the electrochemical reaction kinetics of lithium ion insertion and deinsertion. It can be found from Fig. 7a that the CV curves for LCC-U and LCC-A paper-anodes at various scanning rates appear a couple of redox peaks corresponding to the deinsertion/insertion of lithium ion into/out of LTO. With the increasing scan rates, the peaks gradually become broader and the peak current linearly increases. The LCC-A exhibits sharper peaks and higher slope than that of LCC-U, indicating that better transport behaviour of lithium ion and faster lithium diffusion coefficient.20 It was further verified that LCC-A paper-anode had better high rate performance. The electrochemical impedance spectra (EIS) of LCC-U and LCC-A paper-anodes were compared in Fig. 7b over the frequency range of 10 mHz to 100 kHz. Both the EIS composed of a semicircle at higher frequency range followed by linear part at lower frequency region, which was respectively related to the charge transfer resistance and associated with the lithium ion diffusion in the electrode. The charge transfer resistance for LCC-A is 17.0 ohm, smaller than that of 24.0 ohm for LCC-U, and much lower than most reported 100~200 ohm for LTO-based traditional and paper electrodes. As a result, LCC-A paper-anode with higher electrical conductivity and lower ion transport resistance greatly improved the rate capability of LIBs.

14


Page 14 of 23

Page 15 of 23

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


Figure 7 (a) Cyclic voltammogram of the LCC-U and LCC-A paper-anode at a scanning rate from 0.2 to 5.0 mV·s-1 in a voltage window of 0.8~2.5V; (b) Electrochemical impedance spectra of LCC-U and LCC-A, inside is the enlargement spectra of that in green box. The cycled electrodes were examined by FESEM to determine the microstructure changes as shown in Fig. 8. The integrity of the LCC-U and LCC-A paper-anodes maintain intact without any slightly microcracks after the cycling (Fig. 8a, 8d). But in the magnified images (Fig. 8c, 8f), LCC-U has an obvious agglomeration after cycling 1000 times, meanwhile LCC-A maintains well-supported network structure without any agglomeration, ensuring high interfacial contact with electrolyte. The results also indicate that the carbon nanofiber carbonized from CNF can efficiently strengthen the immobilization of LTO into the interpenetrating C-CNF/CNT conductive network for preventing agglomeration of LTO, as well as improving chemical stability of the conductive network against electrolyte during the cycling process.

Figure 8 (a-c) FESEM images of LCC-U after cycling at 5 C for 1000 times, inset is the photograph of the cycled LCC-U paper-anode; (d-f) FESEM images of LCC-A after cycling at 5C 15



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

for 1000 times, inset is the photograph of the cycled LCC-A paper-anode. Notably, the cellulose-based paper-electrode is a promising key component for constructing a flexible LIB. Herein, an ingenious protocol was designed to integrate LCC-A hybrid film as paper-anode and Li-foil as counter electrode for flexible LIB. Fig. 9 shows the schematic of the hierarchical flexible LIB and the prototype LIB encapsulated by a plastic shell. The flexible LIB shows excellent mechanical strength under bending for hundreds of cycles. The LIB still works well in lighting an LED device at different bending angles (Fig. 9c and d), revealing significant potential applications in flexible electronics, such as bendable displays and other irregularly shaped energy storage devices.12,13,20,30

Figure 9 (a) Schematic illustration of a flexible LIB assembled using LCC-A paper-anode; (b-d) Digital pictures showing a lighted red LED connected to a flexible LIB being bent. In summary, we have developed a flexible, single-layer and free-standing carbonized cellulose-based hybrid film as LIBs paper-anode without the additional current collector by a simple two-step fabrication process. The single-layer hybrid film comprising of LTO, CNF and CNTs was rapidly fabricated by a pressured extrusion papermaking method and subsequently in-situ carbonized under argon atmospheres to construct a well-supported heterogeneous 16


Page 16 of 23

Page 17 of 23

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-architecture with high specific area and enhanced electrical conductivity. Owing to the uniform distribution and immobilization of LTO into the interpenetrating C-CNF/CNT conductive network, the carbonized paper-anode (LCC-A) exhibits extraordinary rate and cycling performance compared to the paper-anode without carbonization (LCC-U). The LCC-A paper-anode has favourable transport behaviour of lithium ion, and delivers a high reversible discharge capacity of 160 mAh·g-1 and remains to 140 mAh·g-1 even after 10 C with coulombic efficiency nearly 100%. Moreover, the proposed water-based method developed here may be extended to fabricate high performance LIBs paper-electrodes with high throughput. The incorporating of biodegradable cellulose components into LIBs would provide ways for many types of eco-friendly flexible electronics that could help reduce the consumption of non-renewable resources.

ASSOCIATED CONTENT * Supporting Information Experimental details of the flexible free-standing cellulose based paper-anode; TEM image of LTO/CNF/CNT. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION *Corresponding Author: *E-mail: [email protected] (X. Feng).

ACKNOWLEDGMENTS

17



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 18 of 23

This work was financially sponsored by Natural Science Foundation of Shanghai (13ZR1415100, 15ZR1415100). We are also grateful to Instrumental Analysis & Research Center of Shanghai University.

REFERENCES (1) Jung, Y. H.; Chang, T.-H.; Zhang, H.; Yao, C.; Zheng, Q.; Yang, V. W.; Mi, H.; Kim, M.; Cho, S. J.; Park, D.-W.; Jiang, H.; Lee, J.; Qiu, Y.; Zhou, W.; Cai, Z.; Gong, S.; Ma, Z. High-Performance Green Flexible Electronics Based on Biodegradable Cellulose Nanofibril Paper. Nat. Commun. 2015, 6, 7170. (2) Hu, Y.; Sun, X. Flexible Rechargeable Lithium Ion Batteries: Advances and Challenges in Materials and Process Technologies. J. Mater. Chem. A 2014, 2, 10712–10738. (3) Gao, H.; Hou, F.; Wana, Z.; Zhao, S.; Yang, D.; Liu, J.; Guo, A.; Gong, Y. One-Step Synthesis Films

of

Continuous

Free-Standing

Carbon Nanotubes-Titanium

Oxide

Composite

as Anodes for Lithium-Ion Batteries. Electrochim. Acta 2015, 154, 321–328.

(4) Du, L.; Yang, P.; Yu, X.; Liu, P.; Song, J.; Mai, W. Flexible Supercapacitors Based on Carbon Nanotube/MnO2 Nanotube Hybrid Porousfilms for Wearable Electronic Devices. J. Mater. Chem. A 2014, 2, 17561–17567. (5) Jabbour, L.; Destro, M.; Chaussy, D.; Gerbaldi, C.; Penazzi, N.; Bodoardo, S.; Beneventi, D. Flexible Cellulose/LiFePO4 Paper-Cathodes: Toward Eco-Friendly All-Paper Li-Ion Batteries. Cellulose 2013, 20, 571–582. (6) Kim, G. T.; Jeong, S. S.; Joost, M.; Rocca, E.; Winter, M.; Passerini, S.; Balducci, A. Use of Natural Binders and Ionic Liquid Electrolytes for Greener and Safer Lithium-ion Batteries. J.

18


Page 19 of 23

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


Power Sources 2011, 196, 2187–2194. (7) Sen, U. K.; Mitra, S. High-Rate and High-Energy-Density Lithium-Ion Battery Anode Containing 2D MoS2 Nanowall and Cellulose Binder. ACS Appl. Mater. Interfaces 2013, 5, 1240−1247. (8) Chun, S. J.; Choi, E. S.; Lee, E. H.; Kim, J. H.; Lee, S. Y. Eco-Friendly Cellulose Nanofiber Paper-Derived Separator Membranes Featuring Tunable Nanoporous Network Channels for Lithium-Ion Batteries. J. Mater. Chem. 2012, 22, 16618–16626. (9) Leijonmarck, S.; Cornell, A.; Lindbergh, G.; Wågberg, L. Single-Paper Flexible Li-Ion Battery Cells Through a Paper-Making Process Based on Nano-Fibrillated Cellulose. J. Mater. Chem. A 2013, 1, 4671–4677. (10) Li, Y.; Zhu, H.; Shen, F.; Wan, J.; Lacey, S.; Fang, Z.; Dai, H.; Hu, L. Nanocellulose as Green Dispersant for Two-Dimensional Energy Materials. Nano Energy 2015, 13, 346–354. (11) Hamedi, M. M.; Hajian, A.; Fall, A. B.; Håkansson, K.; Salajkova, M.; Lundell, F.; Wågberg L.; Berglund, L. A. Highly Conducting, Strong Nanocomposites Based on Nanocellulose-Assisted Aqueous Dispersions of Single-Wall Carbon Nanotubes. ACS Nano 2014, 8, 2467–2476. (12) Zhou, G. M.; Li F.; Cheng, H. M. Progress in Flexible Lithium Batteries and Future Prospects. Energy Environ. Sci. 2014, 7, 1307–1338. (13) Wang, Z.; Xu, C.; Tammela, P.; Huo, J.; Strømme, M.; Edström, K.; Gustafsson, T.; Nyholm, L. Flexible Freestanding Cladophora Nanocellulose Paper based Si Anodes for Lithium-Ion Batteries. J. Mater. Chem. A 2015, 3, 14109–14115. (14) Cao, S. M.; Feng, X.; Song, Y. Y.; Xue, X.; Liu, H. J.; Miao, M.; Fang, J. H.; Shi, L. Y.

19



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

Integrated Fast Assembly of Free-Standing Lithium Titanate/Carbon Nanotube/Cellulose Nanofiber Hybrid Network Film as Flexible Paper-Electrode for Lithium-ion Batteries. ACS Appl. Mater. Interfaces 2015, 7, 10695–10701. (15) Ronci, F.; Reale, P.; Scrosati, B.; Panero, S.; Albertini, V. R.; di Michiel, M.; Perfetti, P.; Merino, J. M. High-Resolution In-Situ Structural Measurements of the Li4/3Ti5/3O4 “Zero-Strain” Insertion Material. J. Phys. Chem. B 2002, 106, 3082–3086. (16) Ouyang, C. Y.; Zhong, Z. Y.; Lei, M. S. Ab Initio Studies of Structural and Electronic Properties of Li4Ti5O12 Spinel. Electrochem. Commun. 2007, 9, 1107–1112. (17) Li, B.; Han, C.; He, Y.; Yang, C.; Du, H.; Yang, Q.; Kang, F. Facile Synthesis of Li4Ti5O12/C Composite with Super Rate Performance. Energy Environ. Sci. 2012, 5, 9595–9602. (18) Cheng, C.; Liu, H.; Li, J.; Xue, X.; Cao, H.; Wang, D.; Shi, L. Fabrication of Spinel Li4−xTi5O12 via Ion Exchange for High-Rate Lithium-Ion Batteries. J. Power Sources 2015, 283, 237–242. (19) Cheng, C.; Liu, H.; Xue, X.; Cao, H.; Shi, L. Highly Dispersed Copper Nanoparticle Modified Nano Li4Ti5O12 with High Rate Performance for Lithium Ion Battery. Electrochim. Acta 2014, 120, 226–230. (20) Jia, X.; Kan, Y.; Zhu, X.; Ning, G.; Lu, Y.; Wei, F. Building Flexible Li4Ti5O12/CNT Lithium-Ion Battery Anodes with Superior Rate Performance and Ultralong Cycling Stability. Nano Energy 2014, 10, 344–352. (21) Shen, L.; Yuan, C.; Luo, H.; Zhang, X.; Yang, S.; Lu, X. In situ Synthesis of High-Loading Li4Ti5O12-Graphene Hybrid Nanostructures for High Rate Lithium Ion Batteries. Nanoscale 2011, 3, 572–574.

20


Page 20 of 23

Page 21 of 23

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


(22) Zhang, B.; Liu, Y.; Huang, Z.; Oh, S.; Yu, Y.; Mai, Y.-W.; Kim, J.-K. Urchin-Like Li4Ti5O12-Carbon Nanofiber Composites for High Rate Performance Anodes in Li-Ion Batteries. J. Mater. Chem. 2012, 22, 12133–12140. (23) Huang, Y.; Zheng, M.; Lin, Z.; Zhao, B.; Zhang, S.; Yang, J.; Zhu, C.; Zhang, H.; Sun, D.; Shi, Y. Flexible Cathodes and Multifunctional Interlayers based on Carbonized Bacterial Cellulose for High-Performance Lithium–Sulfur Batteries. J. Mater. Chem. A 2015, 3, 10910–10918. (24) Feng, X.; Meng, X. H.; Zhao, J. P.; Miao, M.; Shi, L. Y.; Zhang, S. P.; Fang, J. H. Extraction and Preparation of Cellulose Nanocrystals from Dealginate Kelp Residue: Structures and Morphological Characterization. Cellulose 2015, 22, 1763–1772. (25) Cao, Y.; Jiang, Y. Q.; Song, Y. Y.; Cao, S. M.; Miao, M.; Feng, X.; Fang, J. H.; Shi, L. Y. Combined Bleaching and Hhydrolysis for Isolation of Cellulose Nanofibrils from Waste Sackcloth. Carbohydr. Polym. 2015, 131, 152–158. (26) Zhu, Z.; Cheng, F.; Chen, J. Investigation of Effects of Carbon Coating on the Electrochemical Performance of Li4Ti5O12/C Nanocomposites. J. Mater. Chem. A 2013, 1, 9484– 9490. (27) Rahimi, R.; Ochoa, M.; Yu, W.; Ziaie, B. Highly Stretchable and Sensitive Unidirectional Strain Sensor via Laser Carbonization. ACS Appl. Mater. Interfaces 2015, 7, 4463–4470. (28) Wang, L.; Schütz, C.; Salazar-Alvarez G.; Titirici, M. M. Carbon Aerogels from Bacterial Nanocellulose as Anodes for Lithium Ion Batteries. RSC Adv. 2014, 4, 17549–17554. (29) Song, Y. Y.; Jiang, Y. Q.; Shi, L. Y.; Cao, S. M.; Feng, X.; Miao, M.; Fang, J. H. Solution-Processed Assembly of Ultrathin Transparent Conductive Cellulose Nanopaper Embedding AgNWs. Nanoscale 2015, 7, 13694–13701.

21



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

(30) Chen, S.; Xin, Y.; Zhou, Y.; Ma, Y.; Zhou, H.; Qi, L. Self-Supported Li4Ti5O12 Nanosheet Arrays for Lithium Ion Batteries with Excellent Rate Capability and Ultralong Cycle Life. Energy Environ. Sci. 2014, 7, 1924–1930.

22


Page 22 of 23

Page 23 of 23

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


Table of Contents

23


In Situ Carbonized Cellulose-Based Hybrid Film as Flexible Paper

Recommend Documents