Polytriphenylamine Derivative and Carbon Nanotubes as Cathode

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C: Energy Conversion and Storage; Energy and Charge Transport

Polytriphenylamine Derivative and Carbon Nanotubes as Cathode Materials for High-Performance Polymer-Based Batteries Tao Xu, Jiaqi Xiong, Xiaolong Du, Yang Zhang, Shaokun Song, Chuanxi Xiong, and Lijie Dong J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b03769 • Publication Date (Web): 16 Aug 2018 Downloaded from http://pubs.acs.org on August 17, 2018

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The Journal of Physical Chemistry

Polytriphenylamine Derivative and Carbon Nanotubes as Cathode Materials for HighPerformance Polymer-Based Batteries Tao Xu,a Jiaqi Xiong,a Xiaolong Du,a Yang Zhang,a Shaokun Song,a Chuanxi Xiong,a and Lijie Dong*a a

Center for Smart Materials and Devices, State Key Laboratory of Advanced

Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China.

Corresponding Author *Email: [email protected]. Tel.: (86) 27-87651775; Fax: (86) 27-87651779

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ACS Paragon Plus Environment

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ABSTRACT

Composites of polytriphenylamine (PTPA), its novel derivative poly(4carbamoyl-N,N-diphenylaniline-2,2,5,5-tetramethyl-pyr-rolin-1-oxyl) (PTPA-PO) and multiwalled carbon nanotubes (MWNTs) were synthesized by in situ polymerization. The characterization results showed that the CNTs were homogeneously distributed in the polymer matrix and formed a cross-linked conductive network. The electrical properties of PTPA/CNT composites were better than those of traditional acetylene black as conductive agents. Electrochemical tests showed that the initial specific discharge capacity of the PTPA/CNT composites was 107.6 mAh g-1 (theoretical capacity of PTPA is 109 mAh g -1). Furthermore, further research to increase the specific capacity demonstrated that the as-synthesized polytriphenylamine derivative, PTPAPO, with a CNT cathode presented two well-defined plateaus and an enhanced discharge capacity of 139.3 mAh g-1. Additionally, the PTPA-PO/CNT electrode showed superior cycling performance and remained above 90% of the initial capacity after 100 cycles. The enhanced electrochemical performance of PTPA-PO was due to its combination of the conducting polymer PTPA and free radical active site pendant PO, which increased its electrochemical reaction rate, and this composite is a promising material for high-performance polymer-based organic batteries.

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Introduction Rechargeable secondary batteries are closely linked to our daily lives and are widely used in power grid storage, laptop computers, mobile phones, and various wearable electronic devices.1-3 Among these batteries, lithium-ion batteries are the most commonly used because of their high operating voltage, low self-discharge and high energy storage density.4-6 These merits result in the broad application of lithium-ion batteries in society. However, the active materials of current commercialized Li-ion batteries are usually inorganic transition metals (Co, Mn, Ni, and Fe), and disposal of these metals may lead to severe health and environmental issues.7-9 Specifically, these disadvantages can be overcome by using organic materials as active substances due to their inherent safety, environmental benignity and flexibility.10-14 Research on Li-organic batteries has continued since they were originally developed in 1969.15 The transition from inorganic to organic active materials is accomplished by using different kinds of organic groups as redox reaction active sites to realize electron transport. Among the classes of batteries based on organic materials, organic radical batteries (ORBs) are the most interesting candidates for replacing inorganic Li-ion batteries due to their stable organic radicals.16-18 During the charge and discharge process of ORBs, the unpaired electrons on the organic radicals enable simple redox reactions in which electron transfer occurs per active unit.19-21 Thus, ORBs possess superior redox kinetics and allow excellent electrochemical properties with 3



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high specific capacity, high potential and long cycle life.22-24 In recent years, various conducting polymers have been investigated as energy storage active materials, such as poly (2,2,6,6-tetramethyl-1-piperidinyloxy-4-yl methacrylate) (PTMA),25 polypyrrole (PPY),26 and polyaniline (PAn)27. Introducing free radicals into a polymer chain is also beneficial for improving the performance of ORBs. For instance, Cheng Zhang and coworkers proved that the introduction of the 2,2,6,6-tetramethylpiperidinyl-N-oxy (TEMPO) radical improved the performance of an electrode and designed polypyrrole derivatives with TEMPO attached to the polymer backbone of PPY.28-29 Among various polymers, PTPA is an ideal material for organic batteries due to its attractive properties, such as excellent charge transport and high thermal and morphological stability.30 Researchers have reported that electrochemical oxidation of TPA in nonpolar electrolytes yields electrically conducting films of PTPA on the electrode surface,31 and PTPA showed an excellent electrochemical performance. The superior electrochemical performance of PTPA can be attributed to its framework, which is similar to that of high-electronic-conductivity poly-p-phenylene (PPP), and high-energy density, which is similar to that of polyaniline (PAn) units.32 The charging and discharging process of the PTPA electrode is accomplished by electrolyte anion doping and dedoping, and the oxidation-reduction response is shown in Fig. 1a. During the charge and discharge process of a traditional lithium-ion battery, only 4


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one kind of ion migrates back and forth between the two poles. However, when a lithium-PTPA battery is charged and discharged, lithium ions only migrate between the negative electrode and the electrolyte, and anions only migrate between the positive electrode and the electrolyte, resulting in a simultaneous migration of two ions. This property makes PTPA a promising material for Li-organic batteries. However, the low conductivity of a polymer is a major obstacle to improving its electrochemical performance. The role of the conductive additive in an electrode is often ignored by researchers. Currently, carbon nanotubes (CNTs) are attracting increasing attention because of their excellent physical and chemical properties, especially their excellent electronic conductivity.33-36 Numerous studies have shown that CNTs can be a promising candidate for lithium-ion batteries due to their special electrochemical and mechanical properties.37-39 Compared with traditional carbon conductive additives, such as acetylene black, Super P and graphite, CNTs require relatively low loading in a composite electrode to establish an effective conductive network, improving the electrochemical performance of a secondary battery.40-41 On the other hand, evidence indicates electron transfer when polymer molecules interact with CNTs. Therefore, we synthesized PTPA/CNT composites by in situ polymerization to obtain materials with enhanced performance that can form porous electrodes and facilitate transport of ions in an electrolyte. CNTs provide a path for electron transport from the redox active units of an organic radical polymer to the 5



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current collector. Herein, a PTPA/CNT composite was prepared via in situ polymerization. As expected, electrochemical tests showed that the PTPA/CNT composite has an excellent performance. However, further improving the performance is difficult because the composites has almost reached the theoretical capacity value of PTPA. Therefore, we designed a polymer structure and synthesized polytriphenylamine derivative (PTPA-PO), as reported in our previous work.42 The electrode reaction mechanism is shown in Fig. 1b. Herein, we also synthesized a unique PTPA-PO/CNT composite by in situ polymerization and used it as a cathode material in organic radical batteries. CNTs were coated with the active polymer to form a highly active PTPAPO/CNT electrode. The CNTs provide an efficient electron conducting path in the polymer matrix and form a stable network-like structure that enhances the transmission of electrons between polymer particles. Compared with that of PTPA/CNT, the specific capacity of PTPA-PO/CNT increased by approximately 30%. The main reason for this increase is that the nitroxide radical attached to the amidation reaction is involved in the electrode reaction during charging and discharging based on the increased redox capacity of the material. Therefore, the organic electrode material PTPA-PO/CNT synthesized by in situ polymerization shows an outstanding electrochemical performance and has a wide range of application prospects on polymer-based organic radical batteries. 6


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(a)

(b)

Figure 1. Schematic representation of the electrochemical mechanism for (a) PTPA and (b) PTPA-PO. Experimental Section Chemicals:

N-Methyl-2-pyrrolidone

phenylbenzenamine,

5%

palladium

(NMP, on

AR),

carbon

N-(4-nitrophenyl)-N(Pd/C,

5%),

N,N’,

dicyclohexylcarbodiimide (DCC, 99%), and 4-dimethylaminopyridine (DMAP, 99%) were purchased from Aladdin. 3-Carbamoyl-2,2,5,5-tetramethyl-3-pyrrolin-1-yloxy (nitroxide radical, 99%) was purchased from Sigma-Aldrich. Ferric chloride anhydrous (FeCl3, AR), trichloromethane (CHCl3), methanol, triphenylamine (TPA), acetone and ether were purchased from Sinopharm Chemical Reagent Co., Ltd. MWNTs (diameter 20-30 nm; length 10-30 μm) were purchased from Timesnano. Poly (vinylidene fluoride) (PVDF) was used as the binder for electrode materials. The liquid electrolyte (1 M LiPF6 in ethylene carbonate (EC)/dimethyl carbonate (DMC) (1:1, v/v)) was supplied by Guotai-Huarong New Chemical Materials Co., Ltd. 7



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Synthesis of PTPA/CNT and PTPA-PO/CNT composite materials: Acidification of the CNTs was performed by oxidation of raw MWNTs with HNO3/H2SO4 (3:1) at 60 °C for 5 h with vigorous stirring. Polytriphenylamine/carbon nanotube (PTPA/CNT) composites were synthesized using triphenylamine monomers and CNTs by the following steps. First, triphenylamine was completely dissolved in chloroform. Then chemically purified CNTs were added to the solution, and the suspension was sonicated for 2 h to ensure the CNTs were evenly dispersed. Then, an appropriate amount of ferric chloride was added as a catalyst, and the mixture was stirred under nitrogen for 6 h at room temperature. After the polymerization reaction finished, the product was poured into methanol to precipitate the composite. The solution was then filtered, and the solid was washed with methanol several times. Finally, the composite was dried under vacuum at 60 °C for 12 h. The ratios of PTPA and CNT were 2:8, 4:6, 7:3, and 9:1 by weight. Pure PTPA was synthesized in a similar manner as mentioned above without the addition of CNTs. The synthesis of PTPA-PO was published in our previous work.42 The PTPA-PO/CNT composite was prepared according to the above method with TPAPO as a monomer in place of TPA. Fabrication of a Li-organic batterry coin cell: Cathode electrodes were obtained by separately mixing PTPA and CNT, PTPA and acetylene black, and PTPA/CNT and PTPA-PO/CNT with 10 wt% PVDF in NMP (AR) for approximately 40 min in an agate mortar. The mixture slurry was cast evenly over aluminum foil as a current collector to 8


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create the cathode. Then, the aluminum foil was dried in a vacuum oven at 60 oC for 12 h before further use. After this, the foil was cut into a small round piece with a diameter of approximately 14 mm. The obtained product served as a positive electrode versus a lithium metal counter electrode in a CR 2016 coin-type cell with a polypropylene separator (Celgard 2400). The electrolyte solution was 1 M LiPF6 dissolved in ethylene carbonate/dimethyl carbonate (EC/DMC, 1/1, v/v). The cell was assembled in an argonfilled glove box (water content < 0.1 ppm, oxygen content < 0.1 ppm). Characterization and electrochemical investigations of the composites: FT-IR spectra were obtained using Thermo Nicolet Nexus spectrometer with KBr pellets. The morphology of the composites was characterized by field emission scanning electron microscopy (FE-SEM, Zeiss Ultra Plus) to observe the microstructure of the particles. The charge-discharge tests were conducted with a LANDCT2001A instrument at a current density of 20 mA g-1. The cyclic voltammetry (CV) experiments on the polymer lithium-ion battery based on the prepared electrode were performed with a SZCL-ZA electrochemical working station at a scan rate of 0.1 mV s-1. The cycling stability and rate performance were obtained by repeating the charging-discharging process at different current densities. Results and Discussion

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PTPA PTPA-PO

PTPA-PO

3500

3000

2500

2000

1500

819 821

1645 1594 1594 1542 1490 1490 1365 1322 1328 1300 1274 1273

PTPA

3305

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

Transmittance(%)


1000

Wavenumbers(cm-1)

Figure 2. FT-IR spectra of PTPA and PTPA-PO The obtained PTPA and PTPA-PO were analyzed by an FT-IR spectrometer (Fig. 2). The absorption peaks of PTPA were observed in the FT-IR spectra and compared with those in the typical FT-IR spectrum of PTPA.32 The characteristic peaks at 1594 cm-1, 1322 cm-1, 1490 cm-1, 1274 cm-1, and 819 cm-1 correspond to the C=C ring stretching vibration, C-H bending vibration, C-C stretching vibration, C-N stretching vibration and C-H out-of-plane vibration, respectively. Furthermore, the peaks at 1274 cm-1, and 819 cm-1 are the vibrations of tertiary amines and 1,4-disubstituted benzene rings, respectively, and their presence showed that chemical polymerization occurred. In addition, PTPA-PO had many new characteristic peaks compared to those of PTPA. The characteristic peaks of an amide bond and PO radical also appeared in the spectrum: 3305 cm-1 is the characteristic absorption peak of N-H in an amide bond; 1645 cm-1 is the absorption of C=O in an amide bond peak; 1365 cm-1 is the characteristic absorption peak of nitroxide free radicals; and 1300 cm-1 is the deformation of CNH groups.43 The results demonstrated that PTPA-PO was formed during the polymerization reaction, and 10


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its structure was characterized by both the characteristic peak of PTPA and the PO radical group. Fig. 3 shows the TEM images of both the raw and acid-treated CNTs. Fig. 3 (a) is the image of pristine CNTs, and many entangled clusters of CNTs are observed with some small black dots, which may be residual catalyst from CNT preparation. To

Figure 3. TEM images of CNTs before (a) and after (b) treatment with acid enhance the dispersibility of CNTs in the polymerization process, they were treated with a mixed acid solution. As shown in Fig. 3 (b), the aggregates and black dots in the pristine CNTs disappeared, and the CNTs also showed a high degree of dispersion, which improves their conductivity. In the presence of mixed acid, some functional groups were added to the CNTs, which then became shorter. The microstructure of PTPA, a physical mixture of PTPA and acetylene black, and the PTPA/CNT and PTPA-PO composites were characterized (Fig. 4). Fig. 4a is the SEM image of PTPA. Dozens of micron-sized particles with irregular porous structures can be seen. The surface of PTPA is coral-like, and particles are connected through 11



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holes and interlaced into a mesh. This structure may be due to the distortion and folding

(a)

(b)

(c)

(d)

Figure 4. SEM images of (a) PTPA (scale bar: 20 μm); (b) physical mixture of PTPA and acetylene black (scale bar: 200 nm); (c) in-situ polymerization of PTPA/CNTs (scale bar: 200 nm); (d) in-situ polymerization of PTPA-PO/CNTs (scale bar: 300 nm) of the polymer chain. This structure can provide sufficient surface area and ion transport channels for the electrode reaction, which facilitates the redox reaction of PTPA. The physical mixture of PTPA with acetylene black can be seen in Fig. 4b. The mixture is not homogeneous, and some acetylene black aggregates in the polymer matrix. This structure may result in unstable charge transfer, which will not result in the best performance of PTPA. For PTPA/CNT (Fig. 4c), the composite particles are evenly distributed. Furthermore, the CNTs are equally coated with the polymer prepared by in situ 12


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polymerization. Comparatively, this form increases the contact between the CNTs and the polymer, enhancing the electrical conductivity. As shown in Fig. 4d, the synthesized polymer samples of PTPA-PO contain more than a dozen micron-sized, irregular particles, and the surface of these particles is rough and intertwined. Compared with PTPA, this structure of PTPA-PO has a large number of gaps. The purified MWNTs imbedded in the polymer matrix provide an effective electronic conduction path for the electrode, which is also homogeneously dispersed and forms a cross-linked conductive network in the polymer matrix. This porous structure facilitates sufficient contact between the polymer active material and the electrolyte, and forms a network structure after in situ polymerization of the CNTs to provide a sufficiently large surface area and ion transport path for the polymer electrode reaction.

Figure 5. (a) The charge-discharge curves of the Li-PTPA cell at a current of 20 mA g1

, (b) CV curve of PTPA in 1 mol/L LiPF6 EC/DMC (v/v, 1:1) measured at a scan rate

of 0.1 mv s-1, (c) rate performances and (d) electrochemical impedance spectroscopy of 13



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PTPA. The performances were derived from 2016 coin-type cells with an optimized mass ratio of PTPA: acetylene black: PVDF=5:4:1. Fig. 5 displays the electrochemical response of PTPA in the LiPF6 electrolyte. As shown in the charge-discharge curves in Fig. 5a, the Li/PTPA cell exhibits a reversible initial discharge capacity of 102.6 mAh g-1, which is approximately 94% of its theoretical redox capacity (theoretical capacity of 109 mAh g-1). Furthermore, the PTPA cathode shows a stable discharge capacity of 92.3 mAh g-1 after 100 cycles retaining 90% of its initial capacity. Fig. 5b shows the CV of PTPA. The CV curve shows two different redox peaks. A pair of peaks located at 3.9 V / 3.78 V and 3.74 V / 3.61 V correspond to the charge-discharge of the PTPA electrode. The voltage platform corresponds to the lithium-ion doping and dedoping process at the electrode. The peak current of the CV curve is almost equal and the potential difference is only approximately 0.12 V, indicating that the polarization reaction is minimal. The results indicate that the PTPA electrode has an outstanding oxidation-reduction reversibility. The cyclic performance of PTPA at different rates (Fig. 5c), also displays a high reversible capacity of 78 mAh g -1 and 65 mAh g-1 at current densities of 300 mA g-1 and 500 mA g-1, respectively. The detailed reaction kinetics of the PTPA electrode were investigated using electrochemical impedance spectroscopy (EIS). The semicircular depression at high frequencies is the interface impedance (i.e., solid-electrolyte interface (SEI) and charge-transfer impedance), while the low-frequency line 14


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corresponds to ion diffusion. The resistance values of all parts of the electrode were relatively small, which is consistent with the charge-transfer reaction of the free radical polymer and the fast kinetics of the lithium-ion diffusion reaction. As shown in Fig. 6, different CNTs content influenced the electrochemical properties. A PTPA content of 90 wt% results in the best performance, and the first discharge capacity of the PTPA/CNT composite can reach up to 107.6 mA h g -1, as shown in Fig. 6a, which is 98.7% of the theoretical capacity of PTPA (theoretical capacity of 109 mA h g-1). In contrast, when the CNT content increases, the specific capacity decreases, which may be due to the uneven distribution of PTPA. Fig. 6b shows the cycle stability of the PTPA/CNT composite at a current density of 20 mA g1

. The cell exhibits a high initial discharge capacity and excellent cyclic behavior with

only a slight decay in performance, even after 100 cycles. To further explore the electrochemical properties of the composites, EIS measurements were carried out, as shown in Fig. 6c. The high-frequency semicircles correspond to the charge-transfer resistance (Rct) between the active polymer and the electrolyte, while the lowfrequency region corresponds to the diffusion of ions within the electrode materials. As seen in the figure, when the content of PTPA is 90%, the charge-transfer resistance (Rct) value is the smallest, which agrees with the previous performance. As comparison, physical mixture of PTPA and CNTs with different mass ratios were carried out (see Fig. S1 in the Supporting Information), which were 90% PTPA/CNT, 80% PTPA/CNT, 15



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70% PTPA/CNT by weight. The results show that the first discharge specific capacity of 80% PTPA with CNTs is the highest, and reaches 103.1 mAh g-1. Compared with physical mixing, in-situ polymerization can achieve a better performance with less conductive agent, which can improve the performance of the electrode.

Figure 6 (a) The specific capacity curves, (b) cycle performance and (c) EIS results of the PTPA/CNT lithium -ion battery at room temperature. Fig. 7 displays the electrochemical performance of the PTPA-PO/CNT electrode in 1 mol L-1 LiPF6 EC / DMC (v/v, 1: 1) electrolyte at a voltage in the range of 2.0 V4.2 V. From Fig.7a, we can see that there are three pairs of redox peaks in the CV curve of the PTPA-PO electrode at 3.82 V / 3.69 V, 3.60 V / 3.49 V, 3.12 V / 2.56 V. The redox peak corresponds to the doping/dedoping process of the PTPA-PO electrode. Among these peaks, the two pairs of redox peaks at 3.82 V / 3.69 V and 3.60 V / 3.49 V correspond to the triphenylamine structural unit of the electrode reaction, which is explained in Fig. 5. The remaining redox peaks at 3.12 V / 2.56 V are the electrode reaction of the PO radical. Accordingly, the first charge and discharge curve of the PTPA-PO/CNT electrode, as shown in Fig. 7b, exhibits a higher specific capacity than 16


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PTPA/CNT, and the reversible discharge capacity can reach 139 mAh g-1 due to its two electrons reduction process.

Figure 7. Electrochemical performance of 90 % PTPA-PO/CNT. (a) CV curve at a scan rate of 0.1 mV s-1; (b) the first charge and discharge curve at a constant current of 20 mA g-1; (c) Cycling performance of 90 % PTPA-PO/CNT at a constant current density of 20 mA g-1; (d) Cycling performance of 90 % PTPA-PO/CNT at different current densities. Fig. 7c shows the cycle performance of PTPA-PO/CNT at a current density of 20 mA g-1. The PTPA-PO/CNT electrode shows a stable reversible capacity of 128 mAh g-1 with 91.6% capacity retention of the first discharging capacity after 100 cycles. As displayed in Fig.7d, the PTPA-PO/CNT electrode delivers a high reversible capacity of 120 mAh g-1 and 105 mAh g-1 at high constant current densities of 100 mA g-1 and 300 17



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mA g-1, respectively. Even at a higher current density of 500 mA g -1, the electrode displays a relatively high specific capacity of 96 mAh g -1. Such excellent cyclability is attributed to the rapid reaction kinetics of the two free radical groups and the structural stability of the PTPA-PO backbone. The electrochemical performances of PTPAPO/CNT are better than acetylene black as a conductive agent, reported in our previous work.42 This is because acetylene black is small in granular form and easily falls into the void formed by the active material particles, which cannot achieve good electrical conductivity. However, CNTs can easily build conductive network in the electrode due to its unique structure and provide facile channel for the transport of electrons, thereby improving the conductivity of the batteries. Conclusions We have successfully prepared polymer composite materials of PTPA/CNT and PTPA-PO/CNT. Moreover, 10 wt% CNTs and 90 wt% PTPA or PTPA-PO resulted in the best performance. The PTPA and PTPA-PO with CNT composites are promising materials that can be used in organic radical batteries and serve as electrodes with a 10 wt% PVDF binder. Through in-situ polymerization, CNTs can be uniformly dispersed, and the contact between the CNTs and the polymer matrix can be enhanced. Composites with CNTs as electrode have fast electron transport because of the good conductivity of CNTs and the formation of a cross-linked conductive network through a well-connected CNT network. 18


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Therefore, in situ polymerization improves the discharge capacity and cyclability more than physical mixing of the conducting agents. The fabricated composite electrode of PTPA/CNT has a 2.5 V-4.2 V voltage platform versus Li+/Li, and its initial specific discharge capacity is 107.6 mAh g-1. For the structural design of the polymer, we used PTPA as the backbone, introduced a free radical PO into its side chain, and synthesized a novel polytriphenylamine derivative PTPA-PO with a high electrochemical performance and wide voltage range of 2.0 V- 4.2V. This derivative has one more radical active site that improves its performance relative to that of PTPA. Furthermore, the assembled polymer-based lithium-ion battery with the PTPA-PO/CNT electrode showed a stable reversible capacity of 128 mAh g -1 with 91.6% capacity retention of the first discharging capacity after 100 cycles, reflecting favorable redox reversibility. The results show that the PTPA-PO/CNT composite has good electrochemical properties and is a very suitable electrode material candidate for polymer based organic radical batteries. Acknowledgments This work is financially supported by the National Nature Science Foundation of China (No. 51773163 and No.51706166), the Key Program of Natural Science Foundation of Hubei Province of China (2016CFA008), and the Excellent Dissertation Cultivation Funds of Wuhan University of Technology (2017-YS-008).

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TOC Graphics

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Figure 1. Schematic representation of the electrochemical mechanism for (a) PTPA and (b) PTPA-PO.


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Figure 2. FT-IR spectra of PTPA and PTPA-PO 49x38mm (300 x 300 DPI)



Figure 3. TEM images of CNTs before (a) and after (b) treatment with acid 60x35mm (300 x 300 DPI)


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Figure 4. SEM images of (a) PTPA ( scale bar: 20 µm); (b) physical mixture of PTPA and acetylene black (scale bar: 200 nm); (c) in-situ polymerization of PTPA/CNTs (scale bar: 200 nm); (d) in-situ polymerization of PTPA-PO/CNTs (scale bar: 300 nm) 70x57mm (300 x 300 DPI)



Figure 5. (a) The charge-discharge curves of the Li-PTPA cell at a current of 20 mA g-1, (b) CV curve of PTPA in 1 mol/L LiPF6 EC/DMC (v/v, 1:1) measured at a scan rate of 0.1 mv s-1, (c) rate performances and (d) electrochemical impedance spectroscopy of PTPA. The performances were derived from 2016 coin-type cells with an optimized mass ratio of PTPA: acetylene black: PVDF=5:4:1.


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Figure 6 (a) The specific capacity curves, (b) cycle performance and (c) EIS results of the PTPA/CNT lithium -ion battery at room temperature. 70x21mm (300 x 300 DPI)



Figure 7. Electrochemical performance of 90 % PTPA-PO/CNT. (a) CV curve at a scan rate of 0.1 mV s-1; (b) the first charge and discharge curve at a constant current of 20 mA g-1; (c) Cycling performance of 90 % PTPA-PO/CNT at a constant current density of 20 mA g-1; (d) Cycling performance of 90 % PTPA-PO/CNT at different current densities. 80x60mm (300 x 300 DPI)


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Figure S1. Initial charge–discharge profiles of physical mixing of PTPA and CNTs with different mass ratios 49x38mm (300 x 300 DPI)



80x33mm (300 x 300 DPI)


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Polytriphenylamine Derivative and Carbon Nanotubes as Cathode

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